CN112421020B - Cathode material and electrochemical device and electronic device using the same - Google Patents

Abstract

The present application relates to the technical field of energy storage, and in particular, to a positive electrode material and an electrochemical device and electronic device using the same. The positive electrode material includes: a substrate; and a surface layer covering at least part of the surface of the substrate, the surface layer including a rock-salt phase layer; the oxygen element mass percentage of the rock-salt phase layer is W1, and the oxygen element of the substrate is The mass percentage content is W2, and the ratio W1/W2 of the W1 to the W2 is 0.15-0.65. The positive electrode material of the present application has good structural stability and is helpful to improve the cycle performance of the electrochemical device under high voltage working conditions.

Description

Positive electrode material, and electrochemical device and electronic device using same

Technical Field

The application relates to the technical field of energy storage, in particular to a positive electrode material, an electrochemical device using the same and electronic equipment.

Background

Electrochemical devices (e.g., lithium ion batteries) are widely used in the fields of mobile phones, computers, wearable devices, unmanned planes, electric vehicles, large-scale energy storage devices, and the like due to their advantages of high energy density, long cycle life, no memory effect, and the like. As the technology advances and the demand for such devices increases, the demand for electrochemical devices has increased significantly. The development of lithium ion batteries having better characteristics such as cycle stability and storage performance under high voltage is one of the important research directions in the field of lithium ion batteries.

Among them, the positive electrode material as an important component of the lithium ion battery has a significant influence on the performance thereof, and thus continuous optimization and improvement of the positive electrode material are very important. Under the high-voltage working condition, byproducts are easily generated on the surface of the anode of the lithium ion battery, so that the cycle performance of the lithium ion battery is influenced. For example, when a traditional lithium cobaltate positive electrode material works under a high voltage condition, the structural stability and the electrochemical stability of the traditional lithium cobaltate positive electrode material are poor, the electrochemical performance and the safety performance of a battery can be obviously reduced, and the use requirement of people on a lithium ion battery is difficult to meet.

In view of the above, there is a real need to provide an improved cathode material having excellent high voltage stability and an electrochemical device comprising the same.

Disclosure of Invention

An object of the present invention is to provide a positive electrode material having a specific surface structure, having good structural stability and thus high voltage stability, and capable of solving at least one of the problems existing in the related art to at least some extent, and an electrochemical device and an electronic apparatus using the same.

According to a first aspect of the present application, there is provided a positive electrode material comprising: a substrate; and a surface layer portion covering at least a part of a surface of the base body, the surface layer portion including a rock salt phase layer; the rock salt phase layer comprises W1 oxygen element by mass, the matrix comprises W2 oxygen element by mass, and the ratio W1/W2 of W1 to W2 is 0.15-0.65.

According to some embodiments of the application, the rock salt looks layer includes rock salt looks and hole to observation direction orthographic projection, the projected area of hole with the projected area's of rock salt looks ratio is 0.01 ~ 0.7.

According to some embodiments of the application, a ratio of a projected area of the hole to a projected area of the rock salt phase is 0.2-0.7.

According to some embodiments of the present application, the rock salt phase layer and the matrix both comprise the element TM; the mass percentage of the TM element of the rock salt phase layer is T1, the mass percentage of the TM element of the matrix is T2, the ratio of T1 to T2 is 0.15-0.5, and the TM element comprises at least one of Co, Mn or Ni.

According to some embodiments of the application, the thickness of the rock salt phase layer is 20nm to 200 nm.

According to some embodiments of the present application, the overburden portion further includes a transition layer between the rock-salt phase layer and the matrix, wherein the transition layer is derived from interdiffusion of elements in the rock-salt phase layer and the matrix.

According to some embodiments of the present application, the rock salt phase layer comprises element a, the a comprising at least one of F, N or Na.

According to some embodiments of the application, the rock salt phase comprises M_xA_yO_mWherein M comprises at least one of Co, Mn, Ni, Ti, Al, Mg, Fe, Cu, V, Mo, Zn or Cr, A comprises at least one of F, N or Na, x is more than or equal to 1 and less than or equal to 6, y is more than or equal to 1 and less than or equal to 6M is more than or equal to 4, 0.5x and less than or equal to 2x + y. Preferably, according to some embodiments of the present application, the M comprises at least one of Co, Mn, Ni, Ti, Al, Mg.

According to some embodiments of the present application, the matrix comprises a lithium transition metal composite oxide having a composition of Li_aMe_bCo_cO_d-eT_eWherein Me comprises at least one of Mn, Ni, Ti, Al, Mg, Fe, Cu, V, Mo, Zn, Zr or Cr, T is halogen, a is more than or equal to 0.2 and less than or equal to 1.2, b is more than or equal to 0 and less than or equal to 1, 0<c is less than or equal to 1, d is less than or equal to 2 and e is more than or equal to 0 and less than or equal to 1. Preferably, according to some embodiments of the present application, the Me comprises at least one of Mn, Ni, Ti, Al, Mg.

Preferably, according to some embodiments of the present application, the composition of the lithium transition metal composite oxide is Li_aNi_b1Mn_b2Co_cO_d-eT_eWherein a is more than or equal to 0.8 and less than or equal to 1.2, b is more than or equal to 0 and is 1+ b2 and less than or equal to 1, 0<c is less than or equal to 1. Preferably, according to some embodiments of the present application, the composition of the lithium transition metal composite oxide includes LiCoO₂、LiNi_1/3Mn_1/3Co_1/3O₂、LiNi_0.5Mn_0.3Co_0.2O₂、LiNi_0.8Mn_0.1Co_0.1O₂、LiNi_0.6Mn_0.2Co_0.2O₂At least one of (1).

Preferably, according to some embodiments of the present application, the composition of the lithium transition metal composite oxide is Li_aAl_b3Mg_b4Ti_b5Co_cO_d-eT_eWherein a is more than or equal to 0.8 and less than or equal to 1.2, b is more than or equal to 0 and less than or equal to 1 and 3+ b4+ b5, and<c is less than or equal to 1. Preferably, according to some embodiments of the present application, the composition of the lithium transition metal composite oxide includes LiAl_0.01Co_0.99O₂、LiAl_0.01Mg_0.01Ti_0.01Co_0.97O₂、LiMg_0.05Co_0.95O₂At least one of (1).

According to a second aspect of the present application, there is provided an electrochemical device comprising a cathode, an anode and an electrolyte, the cathode comprising the cathode material according to the above-described embodiments of the present application.

According to some embodiments of the application, the rock salt phase layer comprises element a and the electrolyte comprises the element a, the a comprising at least one of F, N or Na, the mass percent content of element a in the rock salt phase layer differing from the mass percent content of element a in the electrolyte by no more than 10%.

According to some embodiments of the present application, the electrochemical device is a lithium ion battery.

According to a third aspect of the present application, there is provided an electronic device comprising the electrochemical device according to the above-described embodiments of the present application.

The technical scheme of the application has at least the following beneficial effects:

the application provides a positive pole material and including this positive pole material's electrochemical device and electronic equipment, wherein positive pole material's characteristics lie in that the surface cladding has the rock salt phase layer, all contain elemental oxygen in this rock salt phase layer and the base member, and the oxygen content of rock salt phase layer and the oxygen content of base member's ratio is in suitable range, this kind of rock salt phase layer structure has the ion conduction ability, have very strong restriction oxygen and dissolve out the ability, can block electrolyte invasion simultaneously, positive pole material's structural stability has been increased, have improved cycle performance under high voltage.

Drawings

Drawings necessary for describing embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application. It is to be understood that the drawings in the following description are only some of the embodiments of the present application. It will be apparent to those skilled in the art that other embodiments of the figures can be obtained from the structures illustrated in these figures.

Fig. 1 is a STEM diagram of a rock salt phase-pore of a positive electrode material provided in an exemplary embodiment of the present application;

fig. 2 is a rock salt phase-pore grayscale distribution diagram of a positive electrode material according to an exemplary embodiment of the present disclosure;

FIG. 3 is a diagram illustrating elemental distribution of a positive electrode material provided in an exemplary embodiment of the present disclosure; wherein, fig. 3(a) is a schematic diagram of the distribution of oxygen element, and fig. 3(b) is a schematic diagram of the distribution of cobalt element;

fig. 4 is a schematic diagram of cycle performance of the lithium ion batteries provided in example 1 and comparative example 1 of the present application.

Detailed Description

Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application. Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the present application.

The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.

In the detailed description and claims, a list of items linked by the term "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if item A, B is listed, the phrase "at least one of A, B" means only a; only B; or A and B. In another example, if item A, B, C is listed, the phrase "at least one of A, B, C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity, and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

An electrode (positive electrode or negative electrode) of an electrochemical device (e.g., a lithium ion battery) is generally prepared by the following method: mixing an active material, a conductive agent, a thickening agent, a binder and a solvent, and then coating the mixed slurry on a current collector. The active material is of critical importance for the performance of the electrochemical device, since the total amount of cell voltage, capacity and cyclability, as well as free energy changes, is generally determined by the electrode material, which is based on the electrochemical reaction at the two electrodes depending on the material chosen at the two electrodes. In addition, the cycle performance of the electrochemical device may vary depending on the kind of the active material.

In order to meet the demand of people for high energy density of electrochemical devices such as lithium ion batteries, the voltage platform of the lithium ion batteries needs to be increased again and again. However, as the voltage is increased, side reactions between the positive electrode material and the electrolyte become more severe, and the surface layer of the particles of the positive electrode material is inactivated by phase transition, thereby causing an increase in resistance and a loss in capacity. In addition, the electrolyte is oxidized on the surface of the positive electrode material to form a by-product and adheres to the surface of the positive electrode material, further resulting in an increase in resistance and a rapid decrease in capacity of the positive electrode material. Therefore, it is important to improve the stability of the positive electrode material or the surface of the positive electrode material.

In the prior art, in order to improve the cycle performance and safety performance of the cathode material under high voltage, the surface of the cathode material is usually coated or doped to improve the stability of the surface of the cathode material. For example, when a common positive electrode material lithium cobaltate in the prior art is modified, other metal elements are usually introduced to replace cobalt elements in the lithium cobaltate or other non-metal elements are usually introduced to replace oxygen elements in the lithium cobaltate to stabilize the bulk structure of the lithium cobaltate. For another example, in the prior art, a stable coating layer is formed on the surface of the resynthesized lithium cobaltate to reduce or isolate side reactions between the lithium cobaltate and the electrolyte, and the cycle life of the material is prolonged. However, the above improvement means has some disadvantages, such as requiring more complicated process operation, increasing process cost, and being not suitable for industrial production.

At least in order to overcome the defects in the prior art, the application of the invention is used for further research on the surface structure of the cathode material, and the application ensures the cycle performance of the electrochemical device under the high-voltage condition by using the cathode material with a specific surface structure, and alleviates the problems of poor structural stability and poor electrochemical stability caused under the high-voltage working condition, thereby improving the cycle performance of the electrochemical device. The positive electrode material with the special surface structure can be realized by adopting a rock salt phase layer which is generated in situ and has a rock salt phase-hole specific proportion and structure, so that the positive electrode material cannot lose effectiveness in the high-voltage application process.

In some embodiments of the present application, an electrochemical device is provided that includes a positive electrode, a negative electrode, and an electrolyte as described below.

[ Positive electrode ]

According to some embodiments of the present application, there is provided a positive electrode including: a positive electrode current collector and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer may be one or more layers, and each of the plurality of positive electrode active material layers may contain the same or different positive electrode materials. Wherein the positive electrode material includes a positive electrode active material. Taking an electrochemical device as an example of a lithium ion battery, the positive electrode active material is any material capable of reversibly intercalating and deintercalating metal ions such as lithium ions.

According to some embodiments of the present application, there is no particular limitation on the kind of the positive electrode current collector, and a known current collector may be used. Examples of the positive electrode current collector include, but are not limited to, metal materials such as aluminum, nickel-plated steel, and the like. In some embodiments, the positive current collector is aluminum.

In some embodiments, the positive electrode material of the present application is characterized in that it comprises: a substrate; and a surface layer portion covering at least a part of a surface of the base body, the surface layer portion including a rock-salt phase layer; wherein the mass percent of oxygen element in the rock salt phase layer is W1, the mass percent of oxygen element in the matrix is W2, and the ratio W1/W2 of W1 to W2 is 0.15-0.65.

According to some embodiments of the present application, oxygen is introduced into the matrix and the rock salt phase layer of the cathode material simultaneously, and the ratio of the mass percentage of oxygen in the rock salt phase layer to the mass percentage of oxygen in the matrix is in the range of 0.15 to 0.65, and any point value in the range or any subinterval in the range falls within the protection scope of the present application. Preferably, in some embodiments, the ratio of the mass percent of the oxygen element in the rock salt phase layer to the mass percent of the oxygen element in the matrix is in the range of 0.19 to 0.60. Typically, but not by way of limitation, the ratio of the mass percent of elemental oxygen of the rock salt phase layer to the mass percent of elemental oxygen of the matrix is, for example, about 0.15, about 0.16, about 0.19, about 0.2, about 0.3, about 0.35, about 0.4, about 0.45, about 0.5, about 0.55, about 0.6, about 0.65, and any two of these values in a range and any value in a range.

The adjustment and optimization of the ratio of W1 to W2 can help to improve the electrochemical performance of the cathode material, especially the cycle performance. Specifically, the rock salt phase salt layer mainly contains anions such as elemental oxygen and fluorine, and the anions inside the matrix are mainly oxygen. When oxygen and transition metal are connected by covalent bonds to form a framework structure, the oxygen can fix the transition metal to form a channel to ensure lithium ion transmission. When the ratio of W1 to W2 is less than 0.15, the oxygen content of the rock salt phase layer is too low, the oxygen defect concentration is too high, the oxygen structure is easy to destabilize, oxygen in the structure can assist lithium ion transmission, and too little oxygen element is not beneficial to ion transmission, thus deteriorating the cycle performance. When the ratio of W1 to W2 is greater than 0.65, the rock salt layer has more oxygen-rich structures, and is easy to form a large amount of side reactions with electrolyte, so that the instability of the rock salt phase layer and the interface layer is caused, and the cycle performance is also deteriorated.

In some embodiments, the rock-salt phase layer comprises rock-salt phases and holes, orthographic projection is performed in the observation direction, and the ratio of the projection area of the holes to the projection area of the rock-salt phases is 0.01-0.7.

The term "projected area of the hole relative to the projected area of the rock salt phase" refers to the value of the projected area of the hole compared to the projected area of the rock salt phase, projected in the forward direction of observation. In some embodiments, the observation area of the rock salt phase layer contains both rock salt phase and holes, and the observation direction orthographically projects, the proportion of the projection area of the rock salt phase in the observation area is greater than the proportion of the projection area of the holes, and especially the value obtained by comparing the projection area of the holes with the projection area of the rock salt phase is in the range of 0.01-0.7.

The surface of the anode material is at least partially covered with a rock salt phase layer which is formed by rock salt phases and holes, and the rock salt phase-hole structure has strong capability of limiting oxygen dissolution, can block electrolyte invasion, increases the structural stability of the anode material and has improved cycle performance under high voltage. In detail, the rock salt phase structure is generated in situ during the high voltage cycle and thus is more tightly combined with the material, and the pore structure is formed by a plurality of oxygen vacancies formed by oxygen precipitated in the early stage of the cycle after rearrangement. Generally, the rock-salt phase structure is compact without conducting ions, and the compact rock-salt phase layer can cause the electrical conductivity of the material to be rapidly reduced and the material to be ineffective. The rock salt phase-pore structure obtained by the rearrangement is an incompact layer, so that the ion conducting capability exists. In addition, the hole is a softer structure in the structure, and the rock salt phase is a stiffer structure, so that the soft and stiff composite structure is beneficial to releasing stress, and the stability of the structure is kept during the circulation process.

In addition, it is also worth noting that the surface rock salt phase of the rock salt phase layer and the hole coexist, and orthographic projection is performed in the observation direction, the ratio of the projection area of the hole to the projection area of the rock salt phase is 0.01-0.7, and any point value in the range or any sub-interval in the range belongs to the protection range of the application. Preferably, in some embodiments, the ratio of the projected area of the aperture to the projected area of the rock salt phase is from about 0.2 to about 0.7. More preferably, in some embodiments, the ratio of the projected area of the aperture to the projected area of the rock salt phase is from about 0.3 to about 0.6. Typically, but not by way of limitation, the ratio of the projected area of the aperture to the projected area of the rock salt phase is, for example, about 0.01, about 0.1, about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, and any of these ranges and ranges between any two of these points.

The projection area ratio of the holes to the rock salt phase is suitable, so that the compactness of the rock salt phase layer is suitable, the ion conduction capability of the rock salt phase layer is improved, the conduction capability of the anode material to lithium ions can be effectively improved by improving the ion conduction capability of the anode material, and the impedance of the anode material is reduced. In addition, the rock salt phase layer with appropriate compactness is beneficial to stress release and can effectively resist corrosion of electrolyte, so that the cathode material disclosed by the application presents excellent structural stability and cycle performance under high-voltage charge and discharge conditions in the cycle process.

In some embodiments, both the rock salt phase layer and the matrix comprise the element TM; the mass percentage of the TM element of the rock salt phase layer is T1, the mass percentage of the TM element of the matrix is T2, and the ratio of T1 to T2 is 0.15-0.5, wherein the TM element comprises at least one of Co, Mn or Ni.

According to some embodiments of the present application, an element TM is introduced into both the matrix and the rock salt phase of the cathode material, for example, the element TM may be Co, may be Mn, may be Ni, may be Co and Mn, may be Co and Ni, may be Ni and Mn, may be Co, Mn and Ni, and particularly, the element TM may be a Co element. Thus, by introducing the element TM into the matrix and the rock salt phase, the matrix and the rock salt phase can have better compatibility, solid solution between the matrix and the rock salt phase is promoted, the association between the matrix and the rock salt phase can be strengthened, the rock salt phase can be more strongly attached to the surface of the matrix, the surface structure of the anode material can be stabilized, and the interface characteristic of the anode material can be improved. In addition, the lithium ion composite material also contributes to constructing an effective lithium ion channel and promoting the transmission and diffusion of lithium ions.

Wherein the mass percentage ratio of the element TM in the rock salt phase layer to the element TM in the matrix is in the range of 0.15-0.5, and further may be in the range of 0.19-0.49. Typically, but not by way of limitation, the ratio of the mass percent of elemental TM of the rock salt phase layer to the mass percent of elemental TM of the matrix is, for example, about 0.15, about 0.16, about 0.19, about 0.2, about 0.3, about 0.35, about 0.4, about 0.45, about 0.48, about 0.49, about 0.5, and any two of these points form a range and any value in the range.

The electrochemical performance of the cathode material is improved by adjusting and optimizing the ratio of T1 to T2. In particular, the element TM in the rock salt phase layer may originate from synthesis introduction or internal migration during circulation. And the rock salt phase layer can isolate the contact of the electrolyte and the matrix, thereby reducing the migration of the element TM. The element TM in the rock-salt phase layer can ensure electron transport in the rock-salt phase layer. When the ratio of T1 to T2 is less than 0.15, the content of the element TM in the rock salt phase layer is made low, electron transport properties are reduced, and cycle performance is lowered. And when the ratio of T1 to T2 is greater than 0.5, the content of the element TM in the rock salt phase layer is higher, the TM in the rock salt phase layer continuously reacts with the electrolyte to overflow, and the effect of the TM as a protective layer is reduced.

In some embodiments, the thickness of the rock salt phase layer is between 20nm and 200 nm. In some embodiments, the thickness of the rock salt phase layer is between 30nm and 180 nm. In some embodiments, the thickness of the rock salt phase layer is between 40nm and 150 nm. Typically, but not by way of limitation, the thickness of the rock salt phase layer may be, for example, about 20nm, about 30nm, about 40nm, about 50nm, about 60nm, about 80nm, about 100nm, about 120nm, about 150nm, about 180nm, about 200nm, and any of the ranges and ranges formed by any two of these points.

In some embodiments, the rock salt phase layer comprises element a, including but not limited to at least one of F, N or Na, and the electrolyte comprises element a.

According to some embodiments of the present application, element a is introduced into both the rock salt phase of the positive electrode material and the electrolyte, for example, element a may be F, may be N, may be Na, may be F and N, may be F and Na, may be N and Na, may be F, N and Na. Therefore, in the electrochemical application process, the rock salt phase layer has stronger affinity with the electrolyte, and the further transformation of the surface rock salt layer structure and the generation of interface by-products caused by side reactions are reduced. And the element A can be dynamically transmitted in a rock salt phase layer and electrolyte, so that the surface layer structure is better adapted to the ion transmission of a system.

Wherein, the difference between the mass percentage of the element A in the rock salt phase layer and the mass percentage of the element A in the electrolyte is not more than 10 percent, namely, | the mass percentage of the element A in the rock salt phase layer-the mass percentage of the element A in the electrolyte is less than or equal to 10 percent. The mass percentage of the element A in the rock salt phase layer can be obtained by EDS test.

In some embodiments, the rock salt phase comprises M_xA_yO_mWherein M comprises at least one of Co, Mn, Ni, Ti, Al, Mg, Fe, Cu, V, Mo, Zn or Cr, A comprises at least one of F, N or Na, x is more than or equal to 1 and less than or equal to 6, y is more than or equal to 1 and less than or equal to 4, and M is more than or equal to 0.5x and less than or equal to 2x + y. Preferably, according to some embodiments of the present application, M comprises at least one of Co, Mn, Ni, Ti, Al, Mg. It is to be understood that the element M in the rock salt phase comprises at least the same type of element TM as the matrix material contains, i.e. the element M comprises at least one of Co, Mn or Ni.

In some embodiments, the rock salt phase may be Al in composition_x1Co_x2F_yO_mWherein x1+ x2 is not less than 1 and not more than 6, y is not less than 1 and not more than 4, m is not less than 0.5(x1+ x2) and not more than 2(x1+ x2) + y.

In some embodiments, the rock salt phase may be Al in composition_x1Co_x2Ti_x3F_yO_mOr Al_x1Co_x2Ni_x3F_yO_mOr Ni_x1Mn_x2Co_x3F_yO_mWherein x1+ x2+ x3 is not less than 1 and not more than 6, y is not less than 1 and not more than 4, m is not less than 0.5(x1+ x2+ x3) and not more than 2(x1+ x2+ x3) + y.

In some embodiments, the rock salt phase may be Al in composition_x1Mg_x2Ti_x3Co_x4F_yO_mWherein, x1+ x2+ x3+ x4 is not less than 1 and not more than 6, y is not less than 1 and not more than 4, m is not less than 0.5(x1+ x2+ x3+ x4) and not more than 2(x1+ x2+ x3+ x4) + y.

In some embodiments, the rock salt phase may be Al in composition_x1Co_x2Na_y1F_y2O_mWherein x1+ x2 is not less than 1 and not more than 6, y1+ y2 is not less than 1 and not more than 4, and m is not less than 0.5(x1+ x2) and not more than 2(x1+ x2) + (y1+ y 2).

The specific type of the matrix is not particularly limited, and any positive electrode active material that can exhibit electrochemical activity (e.g., can reversibly intercalate or deintercalate lithium ions) is within the scope of the present invention. For example, the matrix may include, but is not limited to, a lithium-containing transition metal composite oxide. For example, the lithium-containing transition metal composite oxide may be a lithium-containing transition metal composite oxide containing a cobalt (Co) element.

In some embodiments, the matrix comprises a ternary material. Preferably, according to some embodiments of the present application, the ternary material comprises one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, doped modified lithium nickel cobalt manganese oxide or doped modified lithium nickel cobalt aluminate.

In some embodiments, the matrix comprises a lithium transition metal composite oxide, which may be, for example, lithium cobaltate or a doping-modified lithium cobaltate.

In some embodiments, the composition of the lithium transition metal composite oxide may be represented as Li_aMe_bCo_cO_d-eT_eWherein Me comprises at least one of Mn, Ni, Ti, Al, Mg, Fe, Cu, V, Mo, Zn, Zr or Cr, T is halogen, a is more than or equal to 0.2 and less than or equal to 1.2, b is more than or equal to 0 and less than or equal to 1, 0<c is less than or equal to 1, d is less than or equal to 2 and e is more than or equal to 0 and less than or equal to 1. Preferably, according to some embodiments of the present application, Me comprises at least one of Mn, Ni, Ti, Al, Mg.

In some embodiments, the composition of the lithium transition metal composite oxide is Li_aNi_b1Mn_b2Co_cO_d-eT_eWherein a is more than or equal to 0.8 and less than or equal to 1.2, b is more than or equal to 0 and is 1+ b2 and less than or equal to 1, 0<c is less than or equal to 1, and the specific value ranges of b1 and b2 are not particularly limited, such as 0 less than or equal to b1 less than 1 and 0 less than or equal to b2 less than 1. Preferably, according to some embodiments of the present application, the composition of the lithium metal composite oxide includes LiCoO₂、LiNi_1/3Mn_1/3Co_1/3O₂、LiNi_0.5Mn_0.3Co_0.2O₂、LiNi_0.8Mn_0.1Co_0.1O₂、LiNi_0.6Mn_0.2Co_0.2O₂At least one of (1).

In some embodiments, the composition of the lithium metal composite oxide is Li_aAl_b3Mg_b4Ti_b5Co_cO_d-eT_eWherein, 0 is not less than b3+ b4+ b5 is not more than 1, and the specific value ranges of b3, b4 and b5 are not specially limited, such as 0 is not less than b3 < 1, 0 is not less than b4 < 1, and 0 is not less than b5 < 1. Preferably, according to some embodiments of the present application, the composition of the lithium metal composite oxide includes LiAl_0.01Co_0.99O₂、LiAl_0.01Mg_0.01Ti_0.01Co_0.97O₂、LiMg_0.05Co_0.95O₂At least one of (1).

In some embodiments, the positive electrode material further comprises a binder, and optionally further comprises a positive electrode conductive material.

The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding of the positive electrode active material to the current collector. Non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.

In some embodiments, the positive electrode material further comprises a positive electrode conductive material, thereby imparting conductivity to the electrode. The positive electrode conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the positive electrode conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

Based on the characteristics of the positive electrode material, the positive electrode material has excellent structural stability. When the cathode material described herein is applied to an electrochemical device (e.g., a lithium ion battery), the electrochemical device can exhibit excellent electrochemical properties, particularly good cycle properties.

Embodiments of the present application also provide methods for preparing the cathode materials to which the above embodiments relate. The preparation method is simple and easy to implement, wide in raw material source, easy to control reaction conditions and suitable for industrial production.

In some embodiments, the positive electrode material is prepared by a solid phase sintering coating method. In other embodiments, the cathode material is prepared by a method jointly constructed by solid-phase sintering and electrochemical reaction.

Illustratively, taking the base material as lithium cobaltate as an example, a rock salt phase layer is formed on the surface of the lithium cobaltate by a solid-phase sintering coating method, so as to obtain the rock salt phase layer coated lithium cobaltate cathode material with a rock salt phase-hole structure. However, it should be understood that the matrix material is not limited to lithium cobaltate, and when other types of matrix materials are used, the same or similar method may be used to prepare the positive electrode material. Specifically, the solid-phase sintering coating may include the steps of:

(1) mixing lithium carbonate and cobaltosic oxide according to a certain proportion.

(2) And (2) stirring the mixture obtained in the step (1) for about 6 to about 24 hours until the mixture is uniformly mixed.

(3) And (3) carrying out high-temperature treatment on the powder obtained in the step (2), grinding and sieving to obtain the lithium cobaltate.

(4) Sequentially adding the following substances into the lithium cobaltate obtained in the step (3): compounds containing the element M, e.g. Co-containing compounds, e.g. CoO, CoCl₂、Co₂O₃Etc.; compounds containing element A, e.g. F, e.g. NH₄F, etc.; additives such as KClO₃Oxalic acid, NH₄HCO₃And the like. Preferably, CoCl2, NH4F and NH are added in sequence to the lithium cobaltate obtained in step (3)₄HCO₃Which is (CoCl)₂、NH₄F and NH₄HCO₃) The total mass is from about 0.3% to about 5% of the mass of the lithium cobaltate, and wherein the mass of cobalt is less than about 40% and the mass of the additive is no less than about 5%.

(5) Stirring the mixture of the step (4) for about 6 hours to about 12 hours until the mixture is uniform.

(6) And (5) carrying out high-temperature treatment on the mixture obtained in the step (5), grinding and sieving to obtain the lithium cobaltate cathode material with a rock salt phase layer with a rock salt phase-hole structure.

In some embodiments, the molar ratio of lithium carbonate to cobaltosic oxide in step (1) is in the range of about 0.9 to about 1.1.

In some embodiments, the criterion for uniform mixing of the powders in steps (1), (2) and (5) is the lack of significant agglomeration and segregation. The specific manner of mixing is not particularly limited, and for example, the mixing may be performed using, but not limited to, any of a ball mill mixer, a V-blender, a three-dimensional blender, a gas flow blender, and a horizontal blender.

In some embodiments, in step (3), the sintering temperature ranges from about 500 ℃ to about 1100 ℃ and the sintering time ranges from about 12 hours to about 72 hours.

In some embodiments, the atmosphere of sintering is an air atmosphere or an inert atmosphere.

In some embodiments, the standard of screening in steps (3) and (6) is about 100 to about 500 mesh.

In some embodiments, the temperature of the treatment is related to the substance added in (4), the temperature ranges from about 300 to about 1000 deg.C, preferably about 500 deg.C, and the reaction time is from about 4 to about 24 hours, preferably about 8 hours.

In some embodiments, in step (4), the added compound containing the element M may be a Co-containing compound, but is not limited to a Co-containing compound, and for example, may also be substituted with Ni, Mn, or other suitable precursor, or a mixture thereof. The added compound containing element a may be a F-containing compound, but is not limited to a F-containing compound, and may also be, for example, Na, N, or other suitable compound or mixture.

In other embodiments, taking the substrate material as lithium cobaltate as an example, a rock salt phase layer is formed on the surface of the lithium cobaltate by a solid-phase sintering combined electrochemical reaction method, so as to obtain the rock salt phase layer-coated lithium cobaltate positive electrode material with a rock salt phase-pore structure. However, it should be understood that the matrix material is not limited to lithium cobaltate, and when other types of matrix materials are used, the same or similar method may be used to prepare the positive electrode material. Specifically, the solid-phase sintering combined electrochemical reaction method can comprise the following steps:

(a) the solid-phase sintering reaction is utilized to obtain a base material such as a lithium cobaltate material.

(b) And (b) performing secondary sintering reaction on the lithium cobaltate material obtained in the step (a) to modify the surface.

(c) Assembling the lithium cobaltate material from step (b) to form a battery in which the electrolyte contains element a, a comprising at least one of F, N or Na, and the content of element a in the rock salt phase differs from the content of element a in the electrolyte by no more than about 10%. For example, the electrolyte comprises EC + DMC + PC + VC ═ 1:1:1:1, and 1molLiPF₆And adding LiPF₆NaPF of about 0.1% by mass₆. And charging was performed at a current density of 10mA/g, charging was performed to X1V as a cut-off voltage, and constant voltage charging was maintained at X1 until the current was less than s uA. Standing for about 5min after charge, discharging with about 5mA/g current, changing to about 50mA/g discharge current after 1h discharge, discharging to X2V, and standing for about 5 min.

And (c) circulating for 2-5 circles by using the method in the step (c) to obtain the cathode material.

In some embodiments, in step (c), X1 is not less than about 4.6V and not more than about 4.8V; preferably about 4.7V. X2 is not higher than about 3.5V, not lower than about 2.8V, preferably about 3.0V. S is between about 10 and about 70uA, preferably about 50 uA.

According to an embodiment of the present application, the surface of the positive electrode material needs to form a rock salt phase coating layer with dense and sparse phases, that is, the positive electrode material of the rock salt phase layer with a rock salt phase-pore structure. The formation of the rock salt phase layer can be modified by common metal oxides and the like, and additives with decomposition capability are added into the modified substances, and the additives are decomposed after high-temperature reaction, so that the surface coating layer of the material forms a structure with alternate density. The addition of the decomposable substance is related to the proportion of the loose structure to a certain extent, but is not an absolute mathematical direct proportion relation. In addition, the method of solid phase sintering combined with electrochemical reaction is just one example of the method, and is not necessarily applicable to all systems. The principle is that the original coating layer, the material near surface layer and the like react and recombine by controlling the conditions of charging cut-off voltage, current density and the like, so that a structure with density and density is formed.

[ negative electrode ]

A negative electrode in some embodiments of the present application, comprising: a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

According to some embodiments of the present application, the anode active material layer includes an anode active material, and a specific kind of the anode active material is not particularly limited and may be selected as needed.

In some embodiments, the negative active material may be a negative active material capable of absorbing/releasing lithium (Li), including, but not limited to, carbon materials, silicon-based materials, metal compounds, oxides, sulfides, nitrides of lithium such as LiN₃Lithium metal, metals that form alloys with lithium, and polymeric materials.

In some embodiments, carbon materials may include, but are not limited to: low graphitizable carbon, artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, pyrolytic carbon, coke, glassy carbon, organic polymer compound sintered body, carbon fibers, and activated carbon. The coke may include pitch coke, needle coke, and petroleum coke, among others. The organic polymer compound sintered body refers to a material obtained by calcining a polymer material (for example, phenol plastic or furan resin) at an appropriate temperature to carbonize it, which may be classified as low-graphitizable carbon or graphitizable carbon. Polymeric materials may include, but are not limited to, polyacetylene and polypyrrole.

Among these anode materials capable of absorbing/releasing lithium (Li), further, a material having a charge and discharge voltage close to that of lithium metal is selected. This is because the lower the charge and discharge voltage of the negative electrode material, the easier the lithium ion battery has a higher energy density. Among them, the negative electrode material may be selected from carbon materials because their crystal structures are only slightly changed upon charge and discharge, and therefore, good cycle characteristics and large charge and discharge capacities can be obtained. Graphite is particularly preferred because it gives a large electrochemical equivalent and a high energy density.

In addition, the anode material capable of absorbing/releasing lithium (Li) may include elemental lithium metal, metal elements and semimetal elements capable of forming an alloy with lithium (Li), alloys and compounds including such elements, and the like. In particular, they are used together with a carbon material because in this case, good cycle characteristics and high energy density can be obtained. Alloys as used herein include, in addition to alloys comprising two or more metallic elements, alloys comprising one or more metallic elements and one or more semi-metallic elements. The alloy may be in the following state solid solution, eutectic crystal (eutectic mixture), intermetallic compound and mixture thereof. Examples of the metallic element and the semi-metallic element may include tin (Sn), lead (Pb), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium (Y), and hafnium (Hf).

In some embodiments, the negative active material may also be selected from silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO₂Spinel-structured lithiated TiO₂-Li₄Ti₅O₁₂And one or more of Li-Al alloy.

In addition, an inorganic compound excluding lithium (Li), such as MnO, may be used in the negative electrode₂、V₂O₅、V₆O₁₃NiS, and MoS.

In some embodiments, the negative active material layer may include a binder and optionally further include a conductive material.

The binder improves the binding of the negative active material particles to each other and the binding of the negative active material to the current collector. Non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, and the like.

The negative active material layer includes a conductive material, thereby imparting conductivity to the electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

As the negative electrode current collector holding the negative electrode active material, any known current collector may be used. Examples of the negative electrode current collector include, but are not limited to, metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, and the like. In some embodiments, the negative current collector is copper.

In the case where the negative electrode current collector is a metal material, the form of the negative electrode current collector may include, but is not limited to, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal film, a metal lath, a stamped metal, a foamed metal, and the like. In some embodiments, the negative electrode current collector is a metal thin film. In some embodiments, the negative current collector is a copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil based on a rolling process or an electrolytic copper foil based on an electrolytic process.

In some embodiments, the thickness of the negative electrode current collector is greater than 1 μm or greater than 5 μm. In some embodiments, the thickness of the negative electrode current collector is less than 100 μm or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within a range consisting of any two of the above values.

[ electrolyte ]

The electrolyte used in the electrochemical device of the present application includes an electrolyte and a solvent dissolving the electrolyte. In some embodiments, the electrolyte used in the electrochemical device of the present application further comprises an additive.

In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can act as a solvent for the electrolyte.

In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonate, chain carbonate, cyclic carboxylate, chain carboxylate, cyclic ether, chain ether, phosphorus-containing organic solvent, sulfur-containing organic solvent, and aromatic fluorine-containing solvent.

In some embodiments, examples of cyclic carbonates can include, but are not limited to, one or more of the following: ethylene Carbonate (EC), Propylene Carbonate (PC) and butylene carbonate. In some embodiments, the cyclic carbonate has 3 to 6 carbon atoms.

In some embodiments, examples of chain carbonates can include, but are not limited to, one or more of the following: and chain carbonates such as dimethyl carbonate, methylethyl carbonate, diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate. Examples of chain carbonates substituted with fluorine may include, but are not limited to, one or more of the following: bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) carbonate, bis (2-fluoroethyl) carbonate, bis (2, 2-difluoroethyl) carbonate, bis (2,2, 2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2, 2-difluoroethyl methyl carbonate, and 2,2, 2-trifluoroethyl methyl carbonate, and the like.

In some embodiments, examples of cyclic carboxylic acid esters may include, but are not limited to, one or more of the following: one or more of gamma-butyrolactone and gamma-valerolactone. In some embodiments, a portion of the hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

In some embodiments, examples of chain carboxylic acid esters can include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate, and the like. In some embodiments, a part of hydrogen atoms of the chain carboxylic acid ester may be substituted with fluorine. In some embodiments, examples of the fluorine-substituted chain carboxylic acid ester may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, 2,2, 2-trifluoroethyl trifluoroacetate, and the like.

In some embodiments, examples of cyclic ethers may include, but are not limited to, one or more of the following: tetrahydrofuran, 2-methyltetrahydrofuran, 1, 3-dioxolane, 2-methyl-1, 3-dioxolane, 4-methyl-1, 3-dioxolane, 1, 3-dioxane, 1, 4-dioxane and dimethoxypropane.

In some embodiments, examples of chain ethers may include, but are not limited to, one or more of the following: dimethoxymethane, 1-dimethoxyethane, 1, 2-dimethoxyethane, diethoxymethane, 1-diethoxyethane, 1, 2-diethoxyethane, ethoxymethoxymethane, 1-ethoxymethoxyethane, 1, 2-ethoxymethoxyethane, and the like.

In some embodiments, examples of the phosphorus-containing organic solvent may include, but are not limited to, one or more of the following: trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphate, tris (2,2, 2-trifluoroethyl) phosphate, tris (2,2,3, 3-pentafluoropropyl) phosphate, and the like.

In some embodiments, examples of sulfur-containing organic solvents may include, but are not limited to, one or more of the following: sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, ethylmethylsulfone, methylpropylsulfone, dimethylsulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate and dibutyl sulfate. In some embodiments, a portion of the hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

In some embodiments, the aromatic fluorine-containing solvent includes, but is not limited to, one or more of the following: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene and trifluoromethylbenzene.

In some embodiments, the solvent used in the electrolyte of the present application includes cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application includes at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, or ethyl acetate. In some embodiments, the solvent used in the electrolyte of the present application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, gamma-butyrolactone, and combinations thereof.

After the chain carboxylate and/or the cyclic carboxylate are added into the electrolyte, the chain carboxylate and/or the cyclic carboxylate can form a passivation film on the surface of an electrode, so that the capacity retention rate of the electrochemical device after intermittent charging cycle is improved. In some embodiments, the electrolyte contains 1% to 60% of chain carboxylic acid ester, cyclic carboxylic acid ester, and combinations thereof. In some embodiments, the electrolyte comprises ethyl propionate, propyl propionate, γ -butyrolactone, and combinations thereof in an amount of 1% to 60%, 10% to 50%, 20% to 50%, based on the total weight of the electrolyte. In some embodiments, the electrolyte contains 1% to 60%, 10% to 60%, 20% to 50%, 20% to 40%, or 30% propyl propionate, based on the total weight of the electrolyte.

In some embodiments, additives are included in the electrolyte, examples of which may include, but are not limited to, one or more of the following: fluoro carbonate, ethylene carbonate containing carbon-carbon double bond, compound containing sulfur-oxygen double bond and acid anhydride.

In some embodiments, the additive is present in an amount of 0.01% to 15%, 0.1% to 10%, or 1% to 5%, based on the total weight of the electrolyte.

In some embodiments, the additive comprises one or more fluoro carbonates. The fluoro carbonate may cooperate with the propionate to form a stable protective film on the surface of the negative electrode at the time of charge/discharge of the lithium ion battery, thereby inhibiting the decomposition reaction of the electrolyte.

In some embodiments, the fluoro carbonate has the formula C ═ O (OR)₁)(OR₂) Wherein R is₁And R₂Each selected from alkyl or haloalkyl groups having 1 to 6 carbon atoms, wherein R is₁And R₂At least one of which is selected from fluoroalkyl groups having 1-6 carbon atoms, and R₁And R₂Optionally together with the atoms to which they are attached form a 5-to 7-membered ring.

In some embodiments, examples of the fluoro-carbonates may include, but are not limited to, one or more of the following: fluoroethylene carbonate, cis-4, 4-difluoroethylene carbonate, trans-4, 4-difluoroethylene carbonate, 4, 5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, trifluoromethyl methyl carbonate, trifluoroethylmethyl carbonate, and ethyl trifluoroethyl carbonate, and the like.

In some embodiments, the additive comprises one or more ethylene carbonates containing carbon-carbon double bonds. Examples of ethylene carbonates containing carbon-carbon double bonds may include, but are not limited to, one or more of the following: vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1, 2-dimethyl vinylene carbonate, 1, 2-diethyl vinylene carbonate, fluoroethylene carbonate and trifluoromethyl vinylene carbonate; vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-2-vinyl ethylene carbonate, 1-n-propyl-2-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-divinyl ethylene carbonate, 1, 2-divinyl ethylene carbonate, 1-dimethyl-2-methylene ethylene carbonate, 1-diethyl-2-methylene ethylene carbonate, and the like. In some embodiments, the ethylene carbonate containing a carbon-carbon double bond includes vinylene carbonate, which is easily available and can achieve more excellent effects.

In some embodiments, the additive comprises one or more compounds containing a sulfur-oxygen double bond. Examples of the compound containing an oxy-sulfur double bond may include, but are not limited to, one or more of the following: cyclic sulfuric acid esters, chain sulfonic acid esters, cyclic sulfonic acid esters, chain sulfurous acid esters, cyclic sulfurous acid esters, and the like.

In some embodiments, the additive is a combination of a fluoro carbonate and ethylene carbonate containing carbon-carbon double bonds. In some embodiments, the additive is a combination of a fluoro carbonate and a compound containing a thiooxy double bond. In some embodiments, the additive is a combination of a fluoro carbonate and a compound having 2-4 cyano groups. In some embodiments, the additive is a combination of a fluoro carbonate and a cyclic carboxylic acid ester. In some embodiments, the additive is a combination of a fluoro carbonate and a cyclic phosphoric anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a sulfonic anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid sulfonic anhydride.

According to some embodiments of the present application, the electrolyte is not particularly limited, and a substance known as an electrolyte may be arbitrarily used. In the case of a lithium secondary battery, a lithium salt is generally used. Examples of the electrolyte may include, but are not limited to, LiPF₆、LiBF₄、LiClO₄、LiAlF₄、LiSbF₆、LiTaF₆、LiWF₇Inorganic lithium salts; LiWOF₅Lithium tungstate species; HCO₂Li、CH₃CO₂Li、CH₂FCO₂Li、CHF₂CO₂Li、CF₃CO₂Li、CF₃CH₂CO₂Li、CF₃CF₂CO₂Li、CF₃CF₂CF₂CO₂Li、CF₃CF₂CF₂CF₂CO₂Lithium carboxylates such as Li; FSO₃Li、CH₃SO₃Li、CH₂FSO₃Li、CHF₂SO₃Li、CF₃SO₃Li、CF₃CF₂SO₃Li、CF₃CF₂CF₂SO₃Li、CF₃CF₂CF₂CF₂SO₃Lithium sulfonate salt of Li or the likeClass; LiN (FCO)₂、LiN(FCO)(FSO₂)、LiN(FSO₂)₂、LiN(FSO₂)(CF₃SO₂)、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂Cyclic 1, 2-perfluoroethane bis-sulfonyl imide lithium, cyclic 1, 3-perfluoropropane bis-sulfonyl imide lithium, LiN (CF)₃SO₂)(C₄F₉SO₂) Lithium imide salts; LiC (FSO)₂)₃、LiC(CF₃SO₂)₃、LiC(C₂F₅SO₂)₃Lithium methide salts; lithium (malonate) borate salts such as lithium bis (malonate) borate salt and lithium difluoro (malonate) borate salt; lithium (malonate) phosphates such as lithium tris (malonate) phosphate, lithium difluorobis (malonate) phosphate, and lithium tetrafluoro (malonate) phosphate; and LiPF₄(CF₃)₂、LiPF₄(C₂F₅)₂、LiPF₄(CF₃SO₂)₂、LiPF₄(C₂F₅SO₂)₂、LiBF₃CF₃、LiBF₃C₂F₅、LiBF₃C₃F₇、LiBF₂(CF₃)₂、LiBF₂(C₂F₅)₂、LiBF₂(CF₃SO₂)₂、LiBF₂(C₂F₅SO₂)₂Fluorine-containing organic lithium salts; lithium oxalato borate salts such as lithium difluorooxalato borate and lithium bis (oxalato) borate; lithium oxalato phosphate salts such as lithium tetrafluorooxalato phosphate, lithium difluorobis (oxalato) phosphate, and lithium tris (oxalato) phosphate.

In some embodiments, the electrolyte is selected from LiPF₆、LiSbF₆、LiTaF₆、FSO₃Li、CF₃SO₃Li、LiN(FSO₂)₂、LiN(FSO₂)(CF₃SO₂)、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, and LiC (FSO)₂)₃、LiC(CF₃SO₂)₃、LiC(C₂F₅SO₂)₃、LiBF₃CF₃、LiBF₃C₂F₅、LiPF₃(CF₃)₃、LiPF₃(C₂F₅)₃Lithium difluorooxalato borate, lithium bis (oxalato) borate, or lithium difluorobis (oxalato) phosphate, which contribute to improvement in output characteristics, high-rate charge-discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like of an electrochemical device.

The content of the electrolyte is not particularly limited as long as the effects of the present application are not impaired. Illustratively, in some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3mol/L or greater than 0.4mol/L or greater than 0.5 mol/L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3mol/L, less than 2.5mol/L, or less than 2.0 mol/L. In some embodiments, the total molar concentration of lithium in the electrolyte is within a range consisting of any two of the above values. When the electrolyte concentration is within the above range, lithium as charged particles is not excessively small, and the viscosity can be made to be in an appropriate range, so that good conductivity is easily ensured.

In the case where two or more electrolytes are used, the electrolyte includes at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate. In some embodiments, the electrolyte comprises a salt selected from the group consisting of a monofluorophosphate, an oxalate, and a fluorosulfonate. In some embodiments, the electrolyte comprises a lithium salt. In some embodiments, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is more than 0.01% or more than 0.1% based on the total weight of the electrolyte. In some embodiments, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is less than 20% or less than 10% based on the total weight of the electrolyte. In some embodiments, the amount of a salt selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates is within a range consisting of any two of the foregoing values.

In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates, and one or more salts in addition thereto. As other salts, there may be mentioned the lithium salts exemplified hereinabove, and LiPF in some examples₆、LiN(FSO₂)(CF₃SO₂)、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, and LiC (FSO)₂)₃、LiC(CF₃SO₂)₃、LiC(C₂F₅SO₂)₃、LiBF₃CF₃、LiBF₃C₂F₅、LiPF₃(CF₃)₃、LiPF₃(C₂F₅)₃. In some embodiments, the additional salt is LiPF₆。

In some embodiments, the amount of the additional salt is greater than 0.01% or greater than 0.1% based on the total weight of the electrolyte. In some embodiments, the amount of the other salt is less than 20%, less than 15%, or less than 10% based on the total weight of the electrolyte. In some embodiments, the amount of other salts is within a range consisting of any two of the above values. The other salts having the above contents help to balance the conductivity and viscosity of the electrolyte.

The electrolyte solution may contain, in addition to the above-mentioned solvent, additive and electrolyte salt, additional additives such as a negative electrode coating film forming agent, a positive electrode protecting agent, and an overcharge preventing agent, as required. As the additive, additives generally used in nonaqueous electrolyte secondary batteries may be used, and examples thereof may include, but are not limited to, vinylene carbonate, succinic anhydride, biphenyl, cyclohexylbenzene, 2, 4-difluoroanisole, propane sultone, propene sultone, and the like. These additives may be used alone or in any combination thereof. The content of these additives in the electrolyte solution is not particularly limited, and may be appropriately set according to the kind of the additives. In some embodiments, the additive is present in an amount less than 5%, in the range of 0.01% to 5%, or in the range of 0.2% to 5%, based on the total weight of the electrolyte.

[ isolation film ]

In order to prevent short-circuiting, a separator is generally provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is generally used by penetrating the separator.

The material and shape of the separator are not particularly limited as long as the effects of the present application are not significantly impaired. The separator may be a resin, glass fiber, inorganic substance, or the like formed of a material stable to the electrolyte solution of the present application. In some embodiments, the barrier film includes a porous sheet having excellent liquid retention properties, a nonwoven fabric-like material, or the like. Examples of materials for the resin or glass fiber separator film may include, but are not limited to, polyolefins, aramids, polytetrafluoroethylene, polyethersulfone, glass filters, and the like. In some embodiments, the material of the separation membrane is a glass filter. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned separator may be used alone or in any combination.

The separator may also be a material in which the above materials are laminated, and examples thereof include, but are not limited to, a three-layer separator in which polypropylene, polyethylene, polypropylene are laminated in this order, and the like.

Examples of the material of the inorganic substance may include, but are not limited to, oxides such as alumina, silica, nitrides such as aluminum nitride, silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, and the like). Forms of inorganic matter may include, but are not limited to, particulate or fibrous.

The form of the separator may be a film form, and examples thereof include, but are not limited to, nonwoven fabric, woven fabric, microporous film, and the like. In the film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned separate film-like separator, the following separators may be used: the separator is formed by forming a composite porous layer containing the inorganic particles on the surface of the positive electrode and/or the negative electrode using a resin-based binder, and is formed by forming porous layers on both surfaces of the positive electrode using, for example, a fluororesin as a binder and alumina particles having a particle size of 90% less than 1 μm.

The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the isolation film is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the barrier film is within a range consisting of any two of the above values. When the thickness of the separator is within the above range, the insulating property and mechanical strength can be ensured, and the rate characteristics and energy density of the electrochemical device can be ensured.

When a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is arbitrary. In some embodiments, the porosity of the separator is greater than 20%, greater than 35%, or greater than 45%. In some embodiments, the porosity of the separator is less than 90%, less than 85%, or less than 75%. In some embodiments, the porosity of the separator is within a range consisting of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and the membrane resistance can be suppressed, so that the electrochemical device has good rate characteristics.

The average pore diameter of the separator is also arbitrary. In some embodiments, the mean pore size of the separator is less than 0.5 μm or less than 0.2 μm. In some embodiments, the mean pore size of the separator is greater than 0.05 μm. In some embodiments, the mean pore diameter of the separator is within a range consisting of any two of the above values. If the average pore diameter of the separator exceeds the above range, short circuits are likely to occur. When the average pore diameter of the separation membrane is within the above range, the membrane resistance can be suppressed while preventing short-circuiting, so that the electrochemical device has good rate characteristics.

[ electrochemical device ]

The electrochemical device includes an electrode group, a current collecting structure, an outer case, and a protective member.

Electrode group

The electrode group may have any of a laminated structure in which the positive electrode and the negative electrode are laminated with the separator interposed therebetween, and a structure in which the positive electrode and the negative electrode are spirally wound with the separator interposed therebetween. In some embodiments, the electrode group has a mass occupying ratio (electrode group occupying ratio) of more than 40% or more than 50% in the battery internal volume. In some embodiments, the electrode set occupancy is less than 90% or less than 80%. In some embodiments, the electrode set occupancy is within a range consisting of any two of the above values. When the electrode group occupancy is within the above range, the capacity of the electrochemical device can be secured, and the deterioration of the characteristics such as repeated charge/discharge performance and high-temperature storage due to the increase in internal pressure can be suppressed, and the operation of the gas release valve can be prevented.

Current collecting structure

The current collecting structure is not particularly limited. In some embodiments, the current collecting structure is a structure that reduces the resistance of the wiring portion and the bonding portion. When the electrode group has the above-described laminated structure, a structure in which the metal core portions of the respective electrode layers are bundled and welded to the terminals is suitably used. Since the internal resistance increases when the electrode area increases, it is also preferable to provide 2 or more terminals in the electrode to reduce the resistance. When the electrode group has the above-described wound structure, 2 or more lead structures are provided for the positive electrode and the negative electrode, respectively, and the terminals are bundled together, whereby the internal resistance can be reduced.

External casing

The material of the outer case is not particularly limited as long as it is stable to the electrolyte used. The outer case may be made of, but not limited to, a metal such as nickel-plated steel plate, stainless steel, aluminum, an aluminum alloy, or a magnesium alloy, or a laminated film of a resin and an aluminum foil. In some embodiments, the outer case is a metal or laminated film of aluminum or aluminum alloy.

The metal-based outer case includes, but is not limited to, a hermetically sealed structure formed by welding metals to each other by laser welding, resistance welding, or ultrasonic welding; or a caulking structure formed by using the metal through a resin spacer. The outer case using the laminated film includes, but is not limited to, a sealed structure formed by thermally bonding resin layers to each other. In order to improve the sealing property, a resin different from the resin used for the laminate film may be interposed between the resin layers. When the resin layer is thermally adhered to the current collecting terminal to form a sealed structure, a resin having a polar group or a modified resin into which a polar group has been introduced may be used as the resin to be interposed, because of the bonding between the metal and the resin. The shape of the outer package is also arbitrary, and may be any of a cylindrical shape, a square shape, a laminated shape, a button shape, a large size, and the like.

Protective element

The protection element may be a Positive Temperature Coefficient (PTC) element whose resistance increases when abnormal heat radiation or an excessive current flows, a temperature fuse, a thermistor, a valve (current cutoff valve) that cuts off a current flowing through a circuit by rapidly increasing the internal pressure or internal temperature of the battery when abnormal heat radiation occurs, or the like. The protective element may be selected from elements that do not operate under normal use of high current, and may be designed so that abnormal heat release or thermal runaway does not occur even if the protective element is not present.

The electrochemical device of the present application includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

In some embodiments of the present application, taking a lithium ion secondary battery as an example, a positive electrode, a separator, and a negative electrode are sequentially wound or stacked to form an electrode member, and then packaged in, for example, an aluminum plastic film, and then injected with an electrolyte, formed, and packaged to form the lithium ion secondary battery. Then, the prepared lithium ion secondary battery was subjected to a performance test and a cycle test. Those skilled in the art will appreciate that the above-described methods of making electrochemical devices (e.g., lithium ion batteries) are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure herein.

[ electronic apparatus ]

The present application further provides an electronic device comprising an electrochemical device according to the present application.

The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic apparatus known in the art. In some embodiments, the electrochemical device of the present application can be used in, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular phones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large batteries, lithium ion capacitors, and the like.

Taking a lithium ion battery as an example and describing the preparation of the lithium ion battery with reference to specific examples, those skilled in the art will understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

Examples

The following describes performance evaluation according to examples and comparative examples of lithium ion batteries of the present application.

Preparation of lithium ion battery

1. Preparation of the Positive electrode

The positive electrode material, the conductive material (Super-P) and polyvinylidene fluoride (PVDF) prepared in the following examples and comparative examples were mixed in 95%: 2%: 3 percent of the mixture is mixed with N-methyl pyrrolidone (NMP) and stirred evenly to obtain the anode slurry. And coating the anode slurry on an aluminum foil with the thickness of 12 mu m, drying, cold pressing, cutting into pieces, and welding a tab to obtain the anode.

2. Preparation of the negative electrode

Graphite, sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) are fully stirred and mixed in a proper amount of deionized water solvent according to the weight ratio of 97.5: 1.5: 1 to form uniform negative electrode slurry. The negative electrode slurry was coated on a negative current collector copper foil and dried at 85 ℃. And then, cutting edges, cutting pieces, slitting and drying to obtain a negative active material layer, and then cutting pieces and welding lugs to obtain the negative electrode.

3. Preparation of the electrolyte

Mixing EC, DMC, PC and VC (weight ratio is 1:1:1: 0.01) under the dry argon atmosphere, and adding LiPF₆Mixing uniformly to form a basic electrolyte, wherein LiPF₆The concentration of (2) is 1 mol/L.

4. Preparation of the separator

Polyethylene (PE) porous polymer films were used as separators.

5. Preparation of lithium ion battery

The obtained positive electrode, separator and negative electrode were wound in order and placed in an outer packaging foil, leaving a liquid inlet. And (4) pouring electrolyte from the electrolyte injection port, packaging, and performing formation, capacity and other processes to obtain the lithium ion battery.

Specific embodiments of the cathode material provided in the present application will be described in detail below.

The preparation method of the cathode material in example 1 is as follows: and mixing lithium carbonate and cobaltosic oxide according to the molar ratio of lithium to cobalt being 1.05, reacting for 12 hours at 1000 ℃ after uniformly mixing, and grinding and sieving to obtain the matrix material lithium cobaltate. Then, a coating material AlF which is not more than 1 percent of the mass of the lithium cobaltate is added into the base material lithium cobaltate₃、CoF₂And TiO₂And satisfies the molar ratio Al: co: ti is 4: 1:1, adding NH with the mass of 30 percent of the coating material₄F and oxalic acid, NH₄F and oxalic acid are equal in mass. Fully mixing, reacting at 500 ℃ for 12h, grinding and sieving to obtain the cathode material.

The preparation method of the cathode material in example 2 is as follows: lithium carbonate and cobaltosic oxide were mixed in a ratio of the molar ratio of lithium to cobalt of 1.05, and a molar ratio of Al: alumina with Co being 0.01:0.99, reacting at 1000 ℃ for 12h after being uniformly mixed, grinding and sieving to obtain the matrix material. Then, a coating CoCl of 0.6% by mass of the base material was added to the base material₂、Al₂O₃And sodium oxalate, and satisfies the molar ratio Al: co: na is 1:1:1, adding a mixture of ammonium oxalate and ammonium fluoride with the same mass ratio, wherein the mass of the mixture is 30 percent of that of the coating. Fully mixing, reacting for 8h at 500 ℃, grinding and sieving to obtain the cathode material.

The preparation method of the cathode material in the embodiment 3 comprises the following steps: mixing lithium carbonate and cobaltosic oxide according to the molar ratio of the lithium to the cobalt being 1.06, and adding oxide Al of three elements of aluminum, magnesium and titanium₂O₃MgO and TiO₂The molar ratio of Co: al: mg: ti is 0.97:0.01:0.01:0.01, the mixture is reacted for 18 hours at 950 ℃ after being evenly mixed, and the matrix material is obtained after grinding and sieving. Then, a coating material AlF which does not exceed 1 percent of the mass of the base material is added into the base material₃、MgF₂、TiO₂And CoF₂And satisfies the molar ratio Al: mg: ti: co 2: 1:1: 10, adding a mixture of ammonium fluoride and ammonium oxalate with the mass ratio of 45 percent of the coating material. Fully mixing, reacting for 6h at 600 ℃, grinding and sieving to obtain the cathode material.

The preparation method of the cathode material in the embodiment 4 comprises the following steps: and mixing lithium carbonate and cobaltosic oxide according to the molar ratio of the lithium to the cobaltosic oxide of 1.045, reacting at 1000 ℃ for 12 hours after uniformly mixing, and grinding and sieving to obtain the matrix material. Assembling the obtained base material to obtain a battery, wherein the electrolyte is EC + DMC + PC + VC: 1:1: 0.01% by mass of 1mol/L LiPF with 2% by mass of EC of sodium 2-Cl-benzenesulfonate and 1% by mass of succinonitrile₆(ii) a The anode is graphite. And charged to 4.7V at a current density of 10mA/g, and charged at a constant voltage to a current of less than 50 uA. Then standing for 5min, discharging at 5mA/g current density for 1h, discharging at 50mA/g current density to 3.0V, and standing for 5 min. And circulating for 3 circles to obtain the cathode material.

The preparation method of the cathode material in the embodiment 5 comprises the following steps: mixing Ni_0.5Mn_0.3Co_0.2(OH)₂And lithium carbonate according to the molar ratio of (Ni + Mn + Co) to Li elements of 1: 1.05, reacting at 600 ℃ for 24 hours in an oxygen atmosphere, grinding and sieving to obtain a base material. Then adding Ni: mn: co 1.5: 1: 0.1 NiF₂、MnF₂And Co₂O₃And adding a mixed salt of ammonium bicarbonate and ammonium fluoride with an equal mass ratio of 40% of the mass ratio of the mixture A. Fully and uniformly stirring, reacting for 8 hours at 450 ℃, and then grinding and sieving to obtain the anode material.

Example 6 differs from example 5 in that: adding a coating Al which is not more than 1 percent of the mass of lithium cobaltate into a base material lithium cobaltate₂O₃And CoF₂And satisfies the molar ratio Al: co 2: 1, adding NaF with the coating quality of 40%. The rest is the same as in example 1.

Example 7 differs from example 1 in that: adding a coating AlF not more than 1% of the mass of lithium cobaltate into a base material lithium cobaltate₃、CoF₂And Ni (OH)₂And satisfies the molar ratio Al: co: ni ═ 1: 2:5, adding NaF and sodium bicarbonate with the mass ratio of 50 percent of the coating material. The rest is the same as in example 1.

Example 8 differs from example 1 in that: adding NaF and sodium oxalate with the coating mass of 30 percent, wherein the NaF and the sodium oxalate are equal in mass.

Example 9 differs from example 5 in that: then adding 5% by mass of NaSCN and 10% by mass of NH into the base material₄Cl。

Comparative example 1

Mixing lithium carbonate and cobaltosic oxide according to the molar ratio of lithium to cobalt being 1.03, adding magnesium element which is 0.05 percent of the mass of the cobalt element, reacting the mixture at 900 ℃ for 24 hours, grinding and sieving the mixture to obtain the cathode material.

Comparative example 2

Mixing lithium carbonate and cobaltosic oxide according to the molar ratio of lithium to cobalt of 1.05, reacting the mixture at 950 ℃ for 18 hours, grinding and sieving the mixture. And then adding titanium oxide accounting for 0.02% of the mass of the lithium cobaltate and ammonium fluoride accounting for 0.005% of the mass of the lithium cobaltate, fully and uniformly stirring, reacting at 750 ℃ for 8 hours, grinding and sieving to obtain the cathode material.

Comparative example 3

Mixing lithium carbonate and cobaltosic oxide according to the molar ratio of lithium to cobalt of 1.00, reacting the mixture at 950 ℃ for 18 hours, grinding and sieving the mixture. And then adding alumina and ammonium oxalate with the mass of 0.02 percent of that of the lithium cobaltate, fully and uniformly stirring, reacting at 750 ℃ for 8 hours, grinding and sieving to obtain the anode material.

Comparative example 4

Mixing Ni_0.5Mn_0.3Co_0.2(OH)₂And lithium carbonate according to a molar ratio of (Ni + Mn + Co) to Li element of 1: 1.05, reacting at 600 ℃ for 24 hours in an oxygen atmosphere, grinding and sieving to obtain the cathode material.

Comparative example 5

Mixing lithium carbonate and cobaltosic oxide according to the molar ratio of lithium to cobalt of 1.05, reacting for 12h at 1000 ℃ after uniformly mixing the lithium carbonate and the cobaltosic oxide, grinding and sieving. Then adding a mixture AlF not more than 1% of the weight of lithium cobaltate₃And Co₂O₃And satisfies the molar ratio Al: co 1:1, fully mixing, reacting at 500 ℃ for 12h, grinding and sieving to obtain the cathode material.

The specific positive electrode material compositions of examples 1 to 9 and comparative examples 1 to 5 are shown in table 1 below.

The measurement methods of the performance parameters of examples and comparative examples are as follows.

Second, testing method

1. Elemental analysis of positive electrode material

The soft package battery cell is arranged at 10-30mA/cm²Fully discharging the cathode plate to be below 3.5V under the current density, standing for 10min, and then disassembling the cathode plate in a glove box to obtain a cathode plate; if the material is powder material, the material is directly used.

Transferring the positive plate into an FEI Vion Plasma FIB (focused ion beam) cavity, and processing to obtain a sample for STEM analysis, wherein the surface of the sample is required to be protected by Pt and processed by a Ga ion beam, and the thickness of the sample is not more than 100 nm; and cleaning in a low voltage mode to remove the machined residual surface of the sample.

Observing a sample under an FEI Titan 3G 260-300 transmission electron microscope or the like, and collecting data by using EDS (electron-beam spectroscopy) at a proper multiplying power; obtaining the element content in the range of the surface, the near surface and the like of the material.

At least 3 different positions were collected and averaged.

2. Rock salt-pore analysis

In the process of analyzing the element of the positive electrode material in the method 1, the surface of the material is photographed in a STEM microscope to obtain a structural image with a proper magnification. The mode requiring photographing is HAADF.

The photographed picture is imported into image J, and a three-dimensional grayscale distribution map is obtained by grayscale analysis. In the gray distribution diagram, the area which is greater than 50% of the maximum gray is marked as the projection area of the rock salt phase, and the part which is lower than 50% is marked as the projection area of the hole.

3. Electrochemical cycling test

Charging the lithium ion battery to 4.6V at a constant current of 0.5C at 25 ℃, then charging to 0.05C at a constant voltage of 4.6V, then discharging to 3.0V at a constant current of 0.5C, and recording the discharge capacity as D0; and (3) carrying out a cycle flow of '0.5C charging-0.5C discharging' for multiple times according to the conditions, carrying out 50 cycles in a cycle, and testing the discharge capacity D of the 50 th cycle.

The capacity retention after normal temperature cycling was calculated as follows:

capacity retention (%) after 50 cycles at 25 ℃ was D/D0 × 100%.

Third, test results

The performance tests of the positive electrode materials and the lithium ion batteries in examples 1 to 9 and comparative examples 1 to 5 were performed, and the test results are shown in tables 1 and 2 below.

TABLE 1

As can be seen from the data in table 1, in examples 1 to 7 of the positive electrode material having the rock salt phase layer, the capacity retention rate at high voltage was greatly improved and the positive electrode material had good high-voltage cycle performance, as compared to comparative example 1 containing no rock salt phase layer. Examples 1 to 7 in which the ratio of the oxygen content in the rock salt phase to the oxygen content in the matrix (W1/W2) was 0.15 to 0.65 had more excellent cycle stability than comparative examples 2 and 3 in which W1/W2 was 0.79 and 0.78. Examples 1 to 7 in which the ratio of the TM content in the rock salt phase to the matrix (T1/T2) was 0.15 to 0.5 had more excellent cycle stability than comparative example 2 in which T1/T2 was 0.61.

In addition, examples 1-5 and 7, in which the projected area ratio of the hole to the rock salt phase is 0.01 to 0.7, have more excellent cycle stability than example 6, in which the projected area ratio of the hole to the rock salt phase is 0. This is due to the fact that the composite structure of the pores and the rock salt phase facilitates the release of stresses, thereby maintaining structural stability during cycling.

TABLE 2

As can be seen from the data in Table 2, examples 1, 5, 8-9 in which the difference between the mass% of the element A in the rock salt phase and the mass% of the element A in the electrolyte was not more than 10% had more excellent cycle stability than comparative examples 4-5 in which the difference in the contents was more than 10%.

Reference throughout this specification to "an embodiment," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that at least one embodiment or example in this application includes a particular feature, structure, material, or characteristic described in the embodiment or example. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims (11)

1. a positive electrode material, is characterized in that, described positive electrode material comprises: matrix; and a surface layer covering at least part of the surface of the substrate, the surface layer including a rock-salt phase layer; The mass percentage of oxygen elements in the rock-salt phase layer is W1, the mass percentage of oxygen elements in the matrix is W2, and the ratio W1/W2 of the W1 to the W2 is 0.15-0.65; the rock-salt phase layer is The mass percent content of oxygen element W1 and the mass percent content of oxygen element W2 of the matrix are obtained by using an energy dispersive spectrometer test under a transmission electron microscope. 2. The positive electrode material according to claim 1, wherein the rock-salt phase layer comprises a rock-salt phase and a hole, and is orthographically projected in the observation direction, and the ratio of the projected area of the hole to the projected area of the rock-salt phase is 0.01 to 0.7. 3 . The cathode material according to claim 2 , wherein the ratio of the projected area of the pores to the projected area of the rock salt phase is 0.2 to 0.7. 4 . 4. The cathode material according to claim 1, wherein the rock-salt phase layer and the matrix both contain element TM; The mass percentage content of TM elements in the rock-salt phase layer is T1, the mass percentage content of TM elements in the matrix is T2, and the ratio of T1 to T2 is 0.15-0.5, wherein the element TM includes Co, Mn or at least one of Ni. 5 . The cathode material according to claim 1 , wherein the rock-salt phase layer has a thickness of 20 nm to 200 nm. 6 . 6 . The cathode material according to claim 1 , wherein the rock-salt phase layer contains element A, and the A includes at least one of F, N or Na. 7 . 7 . The cathode material according to claim 1 , wherein the rock-salt phase layer comprises M _× A _y O _m , wherein the M comprises Co, Mn, Ni, Ti, Al, Mg, Fe, Cu , at least one of V, Mo, Zn or Cr, the A includes at least one of F, N or Na, 1≤x≤6, 1≤y≤4, 0.5x≤m≤2x+y. 8 . The cathode material according to claim 1 , wherein the matrix comprises a lithium transition metal composite oxide, and the lithium transition metal composite oxide is composed of Li _a Me _b Co _c O _{de Te} , wherein , the Me includes at least one of Mn, Ni, Ti, Al, Mg, Fe, Cu, V, Mo, Zn, Zr or Cr, T is halogen, 0.2≤a≤1.2, 0≤b≤1, 0<c≤1, 1≤d≤2, 0≤e≤1. 9. An electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the positive electrode material according to any one of claims 1-8. 10 . The electrochemical device according to claim 9 , wherein the rock-salt phase layer comprises element A, and the electrolyte comprises the element A, and the A comprises at least one of F, N or Na. 11 . The difference between the mass percentage content of element A in the rock-salt phase layer and the mass percentage content of element A in the electrolyte solution is not more than 10%. 11. An electronic device, characterized by comprising the electrochemical device according to any one of claims 9-10.

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