CN118016978A

CN118016978A - Electrochemical device and preparation method of positive electrode material

Info

Publication number: CN118016978A
Application number: CN202410351193.9A
Authority: CN
Inventors: 刘小浪
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-09-18
Filing date: 2021-09-18
Publication date: 2024-05-10
Also published as: CN114788051B; CN114788051A; WO2023039877A1

Abstract

The present application relates to an electrochemical device comprising a positive electrode material comprising composite particles comprising lithium fluoride and a transition metal fluoride, wherein the molar ratio x of the lithium fluoride and the transition metal fluoride satisfies: x is more than 0 and less than or equal to 0.135. The positive electrode material has the advantages of simple preparation process, low requirement on equipment, high yield and easy realization of large-scale production; and when used in the electrochemical device, the charge-discharge performance and the cycle stability of the electrochemical device can be effectively improved. The application also relates to a preparation method of the anode material.

Description

Electrochemical device and preparation method of positive electrode material

Technical Field

The application relates to the field of energy storage, in particular to an electrochemical device and a preparation method of a positive electrode material.

Background

Compared with the traditional rechargeable battery, the lithium ion battery has the characteristics of high energy density, long service life and the like, and is an ideal energy storage device. Since commercialization, lithium ion batteries have been widely used in portable electronic products such as smart phones, notebook computers, charger, etc., and gradually occupy the market in new energy automobiles and large-scale power grid energy storage fields. However, the current commercial lithium ion battery anode material is limited by an electrochemical reaction mechanism and a crystal structure, and the improvement of specific capacity of the lithium ion battery anode material encounters a bottleneck, so that the requirements of the fields of 5G, new energy automobiles, smart grid energy storage and the like on batteries with higher energy density are difficult to meet. In order to develop a lithium ion battery with higher energy density, development of a new generation of positive electrode material different from the conventional intercalation material has become a research hotspot in the new energy field.

As an alternative to conventional intercalation chemicals, metal fluorides are a very promising positive electrode material for lithium secondary batteries. Metal fluorides have a typical multiple electron conversion reaction mechanism, and 1mol of the compound can react with more than 2mol of lithium ions, so that the capacity of the substance is multiple times that of the intercalation compound, and the substance has higher specific capacity. In addition, because fluorine element has strong electronegativity and large free energy, and forms a compound with metal element, a strong ionic bond can be formed between the metal and fluorine, so the material also has higher working voltage generally. Taking FeF ₃ as an example, when three-electron conversion reaction occurs, the theoretical specific capacity is up to 712mAh/g, the voltage platform is about 2.7V, and the theoretical energy density is far higher than LiFePO₄(LFP)、LiNi_xMn_yCo_zO₂(NMC)、LiNi_xCo_yAl_zO₂(NCA)、LiCoO₂(LCO) and other traditional anode materials.

However, the existing metal fluoride as a positive electrode material has the problems of low gram capacity exertion, rapid cycle decay and the like. First, metal fluorides are relatively ionic, typically having a relatively large energy band width, which results in extremely low conductivity, low ion mobility and slow conversion kinetics, and large cell polarization during charge and discharge. Secondly, nano metal simple substance particles are continuously agglomerated and continuously coarsened in repeated conversion reaction circulation, and side reactions are extremely easy to occur with electrolyte, so that not only is active material loss caused, but also an original stable solid electrolyte membrane is possibly damaged. In view of the above problems, a great deal of modification research work has been carried out by researchers. For example, kim et al (Kim T,Jae W J,Kim H,et al.A cathode material for lithium-ion batteries based on graphitized carbon-wrapped FeF₃nanoparticles prepared by facile polymerization[J].Journal of Materials Chemistry A,2016,4(38):14857-14864.) used FeCl ₃ as the iron source, citric acid (C ₆H₈O₇) as the carbon source and chelating agent, ethylene glycol as the crosslinking agent, and then heat treated with HF gas to encapsulate FeF ₃ in graphite particles to obtain a carbon coated FeF ₃ composite. Compared with pure FeF ₃, the prepared carbon-coated FeF ₃ composite material has higher capacity and more stable cycle performance. Fan et al (Fan X,Hu E,Ji X,et al.High energy-density and reversibility of iron fluoride cathode enabled via an intercalation extrusion reaction[J].Nature Communications,2018,9:2324) prepared Co-O Co-doped FeOF nanomaterial by hydrothermal reaction using FeF ₃·3H₂ O and CoF ₃ as solutes and n-propanol as solvent. Compared with FeF ₃, the Fe-O covalent bond in FeOF replaces part of Fe-F ionic bond, improves the intrinsic conductivity of the material, and simultaneously realizes the stable cycle performance of the material under high multiplying power and high specific capacity due to the catalysis of Co. Fu et al (Fu W,Zhao E,Sun Z,et al.Iron Fluoride-Carbon Nanocomposite Nanofibers as Free-Standing Cathodes for High-Energy Lithium Batteries[J].Advanced Functional Materials,2018,28(32):1801711) encapsulated FeF ₃ in carbon nanofibers by an electrospinning process to produce FeF ₃/C composite fiber materials. The composite fiber material not only can maintain FeF ₃ particles at the nano level, but also can protect the structure of FeF ₃ from being damaged. Meanwhile, the carbon nanofiber provides a good channel for rapid transfer of ions and electrons, and can reduce unnecessary reaction between electrolyte and the surface of FeF ₃. After 400 weeks of cycling, the FeF ₃/C composite fiber material still has a reversible capacity of 500mAh/g through a charge-discharge test.

These studies have improved the electrochemical properties of metal fluorides to some extent, but have disadvantages in that high-risk HF gas is required, or the yield of materials is low, the cost is high, and the difficulty of mass production is great.

Disclosure of Invention

In order to solve the problems of the prior art, the present application provides an electrochemical device including a positive electrode material. The positive electrode material has the advantages of simple preparation process, low equipment requirement, high yield and easy realization of large-scale production, and can effectively improve the charge and discharge performance and the cycle stability of an electrochemical device when being used for the electrochemical device.

In a first aspect, the present application provides an electrochemical device comprising a positive electrode material comprising composite particles comprising lithium fluoride and a transition metal fluoride, wherein the molar ratio x of lithium fluoride to transition metal fluoride is such that: x is more than 0 and less than or equal to 0.135. According to the application, the transition metal fluoride and a certain proportion of lithium fluoride are compounded, so that the fluoride ions are always excessive in the charging process, and the metal ions can be ensured to be completely converted into stable metal fluoride, so that a large amount of metal ions in the positive electrode are prevented from being dissolved out, and the high discharge specific capacity and high cycle stability of the material are realized. In addition, by compounding lithium fluoride, other impurity elements are not introduced, other performances of the electrochemical device are not affected, and the introduced lithium can also provide part of active lithium, so that the electrochemical stability of the electrochemical device can be further improved.

According to some embodiments of the application, the positive electrode material comprises LiF and MF _y after full charge of the electrochemical device, wherein 2.ltoreq.y.ltoreq.3, and m comprises at least one of transition metals.

According to some embodiments of the application, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particles satisfies: x is more than or equal to 0.025 and less than or equal to 0.11. When the content of lithium fluoride in the composite particles is too low, the improvement of the performance of the electrochemical device is not obvious; when the content of lithium fluoride is too high, since lithium fluoride does not provide a discharge gram capacity, and at the same time, the intrinsic conductivity is extremely low, the content is too high, which may reduce the discharge gram capacity of the cathode material.

According to some embodiments of the application, the composite particles have peaks in the X-ray spectrum between 23 ° and 24 ° in 2θ, the half-width of the peaks being 0.15 ° to 0.3 °. The half-width of the above peak of the composite particles within the above range indicates that the lattice order of the composite particles is reduced and that mixing between LiF and transition metal fluoride is more uniform. According to some embodiments of the application, the composite particle has a grain size of 30nm to 100nm, wherein the grain size is calculated by Scherrer formula.

According to some embodiments of the application, in the transition metal fluoride, the molar ratio y of fluorine element and transition metal element satisfies: y is more than or equal to 2 and less than or equal to 3.

According to some embodiments of the application, the positive electrode material satisfies at least one of the following conditions (a) to (b): (a) The transition metal comprises at least one of Fe, co, ni, mn or Cu; (b) The transition metal fluoride includes at least one of FeF₃、CoF₃、Fe_0.9Co_0.1F₃、NiF₃、MnF₃、FeF₂、CoF₂、NiF₂ or CuF ₂. According to some embodiments of the application, the transition metal comprises at least one of Fe, co, ni, mn or Cu in the positive electrode material. According to some embodiments of the application, the transition metal fluoride comprises at least one of FeF₃、CoF₃、Fe_0.9Co_0.1F₃、NiF₃、MnF₃、FeF₂、CoF₂、NiF₂ or CuF ₂ in the positive electrode material.

In a second aspect, the present application provides a method for preparing a positive electrode material, comprising the steps of: mixing lithium fluoride and a transition metal fluoride to obtain a first mixture, wherein the molar ratio z of lithium fluoride and transition metal fluoride satisfies: z is more than 0 and less than or equal to 0.13; and subjecting the first mixture to a heat treatment.

According to some embodiments of the application, the preparation method satisfies at least one of the following conditions (a) to (d): (a) The transition metal comprises at least one of Fe, co, ni, mn or Cu; (b) The transition metal fluoride includes at least one of FeF₃、CoF₃、Fe_0.9Co_0.1F₃、NiF₃、MnF₃、FeF₂、CoF₂、NiF₂ or CuF ₂; (c) The molar ratio z of lithium fluoride to transition metal fluoride is such that: z is more than or equal to 0.03 and less than or equal to 0.1; (d) The temperature of the heat treatment is 200 ℃ to 400 ℃, and the time of the heat treatment is 6 hours to 24 hours. According to some embodiments of the application, the transition metal comprises at least one of Fe, co, ni, mn or Cu; the molar ratio z of lithium fluoride to transition metal fluoride is such that: z is more than or equal to 0.03 and less than or equal to 0.1; the temperature of the heat treatment is 200 ℃ to 400 ℃, and the time of the heat treatment is 6 hours to 24 hours. According to some embodiments of the application, the transition metal fluoride comprises at least one of FeF₃、CoF₃、Fe_0.9Co_0.1F₃、NiF₃、MnF₃、FeF₂、CoF₂、NiF₂ or CuF ₂; the molar ratio z of lithium fluoride to transition metal fluoride is such that: z is more than or equal to 0.03 and less than or equal to 0.1; the temperature of the heat treatment is 200 ℃ to 400 ℃, and the time of the heat treatment is 6 hours to 24 hours.

According to some embodiments of the application, the molar ratio z of lithium fluoride to transition metal fluoride satisfies: z is more than or equal to 0.03 and less than or equal to 0.1. When the content of lithium fluoride is too low, the prepared positive electrode material has no obvious improvement on the performance of an electrochemical device; when the content of lithium fluoride is too high, since lithium fluoride does not provide a discharge gram capacity, and the intrinsic conductivity thereof is extremely low, the content is too high, which may reduce the discharge gram capacity of the prepared positive electrode material.

According to some embodiments of the application, the temperature of the heat treatment is 200 ℃ to 400 ℃. According to some embodiments of the application, the time of the heat treatment is from 6 hours to 24 hours. When the heat treatment temperature is too low, atoms cannot overcome the diffusion barrier, and diffusion is difficult to carry out, so that the prepared anode material has poor electrochemical performance. When the heat treatment temperature is too high, on one hand, the transition metal fluoride may react with oxygen adsorbed on the surface of the transition metal fluoride or air introduced by a tube furnace due to poor sealing, so that inert impurity phases are generated, and on the other hand, the transition metal fluoride is extremely easy to decompose at high temperature to generate low-valence metal fluoride, and the electrochemical performance of the obtained anode material is reduced.

In a third aspect, the present application provides an electrochemical device comprising a positive electrode comprising the positive electrode material according to the first aspect of the present application or the positive electrode material prepared by the method according to the second aspect.

According to some embodiments of the application, the positive electrode material comprises LiF and MF _y after full charge of the electrochemical device, wherein 2.ltoreq.y.ltoreq.3, M comprising at least one of the transition metals. According to some embodiments of the application, M comprises at least one of Fe, co, ni, mn or Cu.

In a fourth aspect, the present application provides an electronic device comprising the electrochemical device according to the third aspect of the present application.

The application provides a positive electrode material, which comprises lithium fluoride and transition metal fluoride composite particles. Compared with the conventional metal fluoride, the cathode material enables dissolution of metal ions in the charge and discharge process of the electrochemical device to be inhibited, and higher specific discharge capacity and cycle stability are realized. In addition, the preparation process of the positive electrode material provided by the application is simple, the equipment requirement is low, and the large-scale production is easy to realize.

Drawings

Fig. 1 is an XRD pattern of the positive electrode material in comparative example 1 and examples 1 to 5 of the present application.

Fig. 2 is an SEM image of the positive electrode material in example 2 of the present application.

Fig. 3 shows the comparison of the discharge curves of the 2 nd turn of the positive electrode materials in examples 6 to 10 of the present application and comparative example 3.

Fig. 4 shows cyclic voltammograms of an electrochemical device in example 10 of the present application.

Detailed Description

For the purpose of making the objects, technical solutions and advantages of the present application more apparent, the technical solutions of the present application will be clearly and completely described below with reference to the embodiments, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. The related embodiments described herein are of illustrative nature and are intended to provide a basic understanding of the application. The embodiments of the present application should not be construed as limiting the application.

For simplicity, only a few numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form a range not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each separately disclosed point or individual value may itself be combined as a lower limit or upper limit with any other point or individual value or with other lower limit or upper limit to form a range not explicitly recited.

In the description herein, unless otherwise indicated, "above", "below" includes this number.

Unless otherwise indicated, terms used in the present application have well-known meanings commonly understood by those skilled in the art. Unless otherwise indicated, the numerical values of the parameters set forth in the present application may be measured by various measurement methods commonly used in the art (e.g., may be tested according to the methods set forth in the examples of the present application).

The list of items to which the term "at least one of," "at least one of," or other similar terms are connected may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means only a; 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 component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.

1. Positive electrode material

In a first aspect, the present application provides a positive electrode material comprising composite particles comprising lithium fluoride and a transition metal fluoride, wherein the molar ratio x of lithium fluoride to transition metal fluoride satisfies: x is more than 0 and less than or equal to 0.135.

The conventional single metal fluoride anode material firstly generates nano metal simple substance particles and LiF in the discharging process; in the subsequent charging process, the nano-metal simple substance is oxidized into metal ions and recombined with fluorine ions to generate metal fluoride. Since the nano material is easy to generate segregation or agglomeration, the periphery of metal ions which are possibly generated by oxidation in the charging process does not have enough fluoride ions to combine with the metal ions to generate stable metal fluoride. The surplus metal ions are easily dissolved into the electrolyte and undergo side reactions with the electrolyte, or shuttle to the negative electrode and are reduced to metal elemental dendrites. The irreversible reaction process not only can cause the loss of the positive electrode active material to quickly attenuate the gram capacity of the electrochemical device, but also can cause the short circuit inside the electrochemical device to generate circulating water jump and even safety accidents because the metal simple substance dendrites pierce through the separator.

According to the application, the transition metal fluoride and a certain proportion of lithium fluoride are compounded, so that the fluoride ions are always excessive in the charging process, and the metal ions can be ensured to be completely converted into stable metal fluoride, so that a large amount of metal ions in the positive electrode are prevented from being dissolved out, and the high discharge specific capacity and high cycle stability of the material are realized. In addition, by compounding lithium fluoride, other impurity elements are not introduced, other performances of the electrochemical device are not affected, and the introduced lithium can also provide part of active lithium, so that the electrochemical stability of the electrochemical device can be further improved.

According to some embodiments of the application, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particles is 0.01, 0.02, 0.035, 0.04, 0.045, 0.055, 0.065, 0.07, 0.075, 0.085, 0.09, 0.095, 0.11, 0.12, or a range of any two of these values. When the content of lithium fluoride in the composite particles is too low, the improvement of the performance of the electrochemical device is not obvious; when the content of lithium fluoride is too high, since lithium fluoride does not provide a discharge gram capacity and its intrinsic conductivity is extremely low, the content is too high, which may lower the discharge gram capacity of the positive electrode material.

In some embodiments, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particle satisfies: x is more than or equal to 0.025 and less than or equal to 0.11. In some embodiments, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particle satisfies: x is more than or equal to 0.03 and less than or equal to 0.1. In some embodiments, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particle satisfies: x is more than or equal to 0.05 and less than or equal to 0.08.

According to some embodiments of the application, the composite particles have peaks in the X-ray spectrum between 23 ° and 24 ° in 2θ, the half-width of the peaks being 0.15 ° to 0.3 °. In some embodiments, the half-peak width is 0.16 °, 0.18 °, 0.20 °, 0.22 °, 0.24 °, 0.27 °, or a range of any two of these values. In some embodiments, the half-peak width is 0.15 ° to 0.25 °. The half-width of the above peak of the composite particles within the above range indicates that the lattice order of the composite particles is reduced and that mixing between LiF and transition metal fluoride is more uniform.

According to some embodiments of the application, the composite particle has a grain size of 30nm to 100nm, wherein the grain size is calculated by Scherrer formula. In some embodiments, the composite particle has a grain size of 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, or a range of any two of these values.

According to some embodiments of the application, the transition metal comprises at least one of Fe, co, ni, mn or Cu. In some embodiments, the transition metal is Fe. In some embodiments, the transition metal is Co. In some embodiments, the transition metals are Fe and Co.

According to some embodiments of the application, the transition metal fluoride is represented by the composition MF _y, wherein M is selected from one of the transition metals, preferably from one of Fe, co, ni, mn or Cu, and 2.ltoreq.y.ltoreq.3.

According to some embodiments of the application, the transition metal fluoride is represented by the composition M1 _y1M2_y2F_y3, wherein M1 and M2 are different and are each independently selected from one of the transition metals, preferably from one of Fe, co, ni, mn or Cu, 2.ltoreq.y ₃/(y₁+y₂). Ltoreq.3.

According to some embodiments of the application, the transition metal fluoride comprises at least one of FeF₃、CoF₃、Fe_0.9Co_0.1F₃、NiF₃、MnF₃、FeF₂、CoF₂、NiF₂ or CuF ₂.

2. Preparation method of positive electrode material

In a second aspect, the present application provides a method for preparing a positive electrode material, comprising the steps of: mixing lithium fluoride and a transition metal fluoride to obtain a first mixture, wherein the molar ratio z of lithium fluoride and transition metal fluoride satisfies: z is more than 0 and less than or equal to 0.13; and heat treating the first mixture.

According to some embodiments of the application, the molar ratio z of lithium fluoride to transition metal fluoride is 0.01, 0.02, 0.035, 0.04, 0.045, 0.055, 0.065, 0.07, 0.075, 0.085, 0.09, 0.095, 0.11, 0.12, or a range of any two of these values. When the content of lithium fluoride is too low, the improvement of the performance of the electrochemical device is not obvious; when the content of lithium fluoride is too high, since lithium fluoride does not provide a discharge gram capacity, and at the same time, the intrinsic conductivity is extremely low, the content is too high, which may reduce the discharge gram capacity of the cathode material.

In some embodiments, the molar ratio z of lithium fluoride to transition metal fluoride satisfies: z is more than or equal to 0.03 and less than or equal to 0.1. In some embodiments, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particle satisfies: z is more than or equal to 0.05 and less than or equal to 0.08.

According to some embodiments of the application, the time of mixing is from 1h to 5h, such as 2h, 3h, or 4h, etc. In some embodiments, the lithium fluoride and the transition metal fluoride may be mixed using a mechanical mixing method such as ball milling. In some embodiments, the rotational speed of the ball mill is 300r/min to 1000r/min, such as 400r/min, 500r/min, 600r/min, 800r/min, or the like.

According to some embodiments of the application, the temperature of the heat treatment is 200 ℃ to 400 ℃. When the heat treatment temperature is too low, atoms cannot overcome the diffusion barrier, and diffusion is difficult to carry out, so that the prepared anode material has poor electrochemical performance. When the heat treatment temperature is too high, on one hand, the transition metal fluoride may react with oxygen adsorbed on the surface of the transition metal fluoride or air introduced by a tube furnace due to poor sealing, so that inert impurity phases are generated, and on the other hand, the transition metal fluoride is extremely easy to decompose at high temperature to generate low-valence metal fluoride, and the electrochemical performance of the obtained anode material is reduced.

In some embodiments, the temperature of the heat treatment is 220 ℃, 240 ℃, 260 ℃, 280 ℃, 310 ℃, 330 ℃, 350 ℃, 370 ℃, 390 ℃, or a range of any two of these values. In some embodiments, the temperature of the above heat treatment is 200 ℃ to 350 ℃. In some embodiments, the temperature of the above heat treatment is 250 ℃ to 300 ℃.

According to some embodiments of the application, the first mixture is heat treated in an inert atmosphere. In some embodiments, the inert atmosphere is an argon atmosphere or a nitrogen atmosphere.

According to some embodiments of the application, the time of the heat treatment is 6h to 24h, e.g. 7h, 10h, 15h or 20h, etc.

According to some embodiments of the application, the transition metal is selected from at least one of Fe, co, ni, mn or Cu. In some embodiments, the transition metal is Fe and/or Co.

According to some embodiments of the application, the transition metal fluoride is represented by the composition MF _y, where M is selected from one of the transition metals, preferably from one of Fe, co, ni, mn or Cu, and 2.ltoreq.y.ltoreq.3.

The application also provides the positive electrode material prepared by the method, wherein the positive electrode material comprises composite particles, the composite particles comprise lithium fluoride and transition metal fluoride, and the molar ratio x of the lithium fluoride to the transition metal fluoride satisfies the following conditions: x is more than 0 and less than or equal to 0.135.

According to some embodiments of the application, the molar ratio x of lithium fluoride to transition metal fluoride in the composite particles is 0.01, 0.02, 0.035, 0.04, 0.045, 0.055, 0.065, 0.07, 0.075, 0.085, 0.09, 0.095, 0.11, 0.12, or a range of any two of these values.

According to some embodiments of the application, the composite particles have peaks in the X-ray spectrum between 23 ° and 24 ° in 2θ, the half-width of the peaks being 0.15 ° to 0.3 °. According to some embodiments of the application, the composite particle has a grain size of 30nm to 100nm, wherein the grain size is calculated by Scherrer formula.

According to some embodiments of the present application, in the transition metal fluoride of the positive electrode material, the molar ratio y of the fluorine element and the transition metal element satisfies: y is more than or equal to 2 and less than or equal to 3.

According to some embodiments of the application, the transition metal of the positive electrode material is selected from at least one of Fe, co, ni, mn or Cu. In some embodiments, the transition metal is Fe. In some embodiments, the transition metal is Co. In some embodiments, the transition metals are Fe and Co.

According to some embodiments of the application, the transition metal fluoride of the positive electrode material is represented by the composition MF _y, wherein M is selected from one of the transition metals, preferably from one of Fe, co, ni, mn or Cu, and 2.ltoreq.y.ltoreq.3.

According to some embodiments of the application, the transition metal fluoride of the positive electrode material is represented by the composition M1 _y1M2_y2F_y3, wherein M1 and M2 are different and are each independently selected from one of the transition metals, preferably from one of Fe, co, ni, mn or Cu, and 2.ltoreq.y ₃/(y₁+y₂). Ltoreq.3.

According to some embodiments of the application, the transition metal fluoride of the positive electrode material comprises at least one of FeF₃、CoF₃、Fe_0.9Co_0.1F₃、NiF₃、MnF₃、FeF₂、CoF₂、NiF₂ or CuF ₂.

3. Electrochemical device

The electrochemical device provided by the application comprises a positive electrode, wherein the positive electrode comprises the positive electrode material disclosed by the first aspect of the application or the positive electrode material prepared by the preparation method disclosed by the second aspect of the application.

According to some embodiments of the application, the positive electrode material comprises LiF and MF _y after full charge of the electrochemical device, wherein 2.ltoreq.y.ltoreq.3, M comprising at least one of the transition metals. In some embodiments, the transition metal is selected from at least one of Fe, co, ni, mn or Cu. In some embodiments, the transition metal is Fe. In some embodiments, the transition metal is Co. In some embodiments, the transition metals are Fe and Co. In some embodiments, the molar ratio X 'of LiF and MF _y in the positive electrode material satisfies 0 < X'. Ltoreq.0.135 after full charge of the electrochemical device.

According to some embodiments of the application, the positive electrode further comprises a conductive agent and a binder. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethyleneoxy-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or the like. In some embodiments, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, synthetic graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

According to some embodiments of the application, the positive electrode further comprises a positive electrode current collector. In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, or the like) on a polymer substrate.

The positive electrode of the present application may be prepared by methods well known in the art. In general, materials such as a positive electrode material, an optional conductive agent (such as carbon materials such as carbon black and metal particles, etc.), a binder (such as SBR), other optional additives (such as PTC thermistor materials, etc.) are mixed together and dispersed in a solvent (such as deionized water), uniformly stirred and uniformly coated on a positive electrode current collector, and dried to obtain a positive electrode containing a positive electrode membrane.

According to some embodiments of the application, the electrochemical device further comprises a negative electrode.

According to some embodiments of the present application, a negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on a surface of the negative electrode current collector. In some embodiments, the anode active material layer includes an anode active material, which may include a material that reversibly intercalates/deintercalates lithium ions, lithium metal alloy, or transition metal oxide. In some embodiments, the negative active material includes at least one of a carbon material or a silicon material. The carbon material comprises at least one of graphite, hard carbon, and the silicon material comprises at least one of silicon, a silicon oxygen compound, a silicon carbon compound, or a silicon alloy. In some embodiments, the anode active material layer includes a binder, and the binder may include various binder polymers. In some embodiments, the binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, or styrene butadiene rubber. In some embodiments, the anode active material layer further includes a conductive material to improve electrode conductivity. Any conductive material may be used as the conductive material as long as it does not cause chemical change. In some embodiments, the conductive material comprises at least one of conductive carbon black, acetylene black, carbon nanotubes, ketjen black, conductive graphite, or graphene.

According to some embodiments of the application, the negative electrode is lithium metal or a lithium-containing alloy. In some embodiments, the negative electrode is a lithium sheet.

According to some embodiments of the application, the electrochemical device further comprises an electrolyte or a solid state electrolyte.

According to some embodiments of the present application, the electrolyte that may be used in embodiments of the present application may be an electrolyte known in the art.

In some embodiments, the electrolyte includes an organic solvent, a lithium salt, and an additive. The organic solvent of the electrolyte according to the present application may be any organic solvent known in the art as a solvent of the electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and may be any electrolyte known in the art. The additive of the electrolyte according to the present application may be any additive known in the art as an electrolyte additive. In some embodiments, the organic solvent includes, but is not limited to: ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent comprises an ether-type solvent, for example, comprising at least one of 1, 3-Dioxapentacyclic (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF ₆), lithium tetrafluoroborate (LiBF ₄), lithium difluorophosphate (LiPO ₂F₂), lithium bis (trifluoromethanesulfonyl) imide LiN (CF ₃SO₂)₂ (LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO ₂F)₂) (LiFSI), lithium bis (oxalato) borate LiB (C ₂O₄)₂ (LiBOB), or lithium difluorooxalato borate LiBF ₂(C₂O₄) (lidaob).

According to some embodiments of the application, the solid state electrolyte comprises at least one of Li_2+xAl_2+xSi_1-xS₆(0≤x<1)、Li₃YCl₆,Li₃YBr₆,Li₃OCl,LiPON,Li_0.5La_0.5TiO₃、Li_1+xAl_xTi_2-x(PO₄)₃、Li₇La₃Zr₂O₁₂、Li₁₀GeP₂S₁₂(LGPS)、Li_9.54Si_1.74P_1.44S_11.7Cl_0.3、Li_3.25Ge_0.25P_0.75S₄、Li₁₁AlP₂S₁₂ and Li ₇P₃S₁₁.

According to some embodiments of the application, a separator is provided between the positive electrode and the negative electrode to prevent short circuit. The material and shape of the separator used in the embodiments of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic, etc., formed from a material that is stable to the electrolyte of the present application. For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer comprises at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected. The surface treatment layer is provided on at least one surface of the base material layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer formed by mixing a polymer and an inorganic substance. The inorganic layer includes inorganic particles including at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate, and a binder. The binder comprises at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylic polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

According to some embodiments of the application, the electrochemical device of the application includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, lithium secondary batteries include, but are not limited to: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.

4. Electronic device

The electronic device of the present application may be any device using the electrochemical device according to the third aspect of the present application.

In some embodiments, the electronic device includes, but is not limited to: notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, headsets, video recorders, liquid crystal televisions, hand-held cleaners, portable CD-players, mini-compact discs, transceivers, electronic notebooks, calculators, memory cards, portable audio recorders, radios, stand-by power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game machines, watches, electric tools, flash lamps, cameras, household large-sized batteries or lithium-ion capacitors, and the like.

Examples and comparative examples

Example 1

2.966G (26.25 mmol) of FeF ₃ raw material and 0.034g (1.31 mmol) of LiF raw material are weighed respectively, stirred uniformly, then put into a 50mL agate tank, and ball-milled for 2h at a rotation speed of 500 r/min. And then placing the obtained mixture material in a tubular furnace protected by argon atmosphere, and heating to 180 ℃ at a heating rate of 5 ℃/min for heat treatment, wherein the heat treatment time is 12h. After the heat treatment is finished, the material is naturally cooled to room temperature, and the positive electrode material with the nominal composition of 0.05LiF.FeF ₃ is obtained after crushing and sieving treatment.

Manufacturing a lithium secondary battery: firstly, the positive electrode material of 0.05LiF.FeF ₃, a conductive agent (SP) and a bonding agent PVDF are mixed according to the mass ratio of 60:30:10 is added into N-methyl pyrrolidone (NMP) and stirred to be homogenized to prepare the anode slurry. And uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil by using a scraper, and drying, cold pressing and punching to prepare the positive electrode plate. And finally, taking the positive pole piece as a positive pole, taking a lithium piece as a negative pole, taking Cellgard 2400 as a diaphragm, taking 4.6mol/L LiFSI and DME as electrolyte, and assembling the CR2430 button cell in a glove box in an argon atmosphere.

Examples 2 to 5

Preparation of cathode material and fabrication of button cell referring to example 1, except that in examples 2 to 5, the heat treatment temperatures in the preparation of cathode material were 200 ℃,300 ℃, 400 ℃ and 430 ℃, respectively.

Example 6

2.979G (26.36 mmol) of FeF ₃ raw material and 0.021g (0.81 mmol) of LiF raw material are weighed respectively, stirred uniformly, then put into a 50mL agate tank, and ball-milled for 2h at a rotation speed of 500 r/min. And then placing the obtained mixture material in a tubular furnace protected by argon atmosphere, and heating to 250 ℃ at a heating rate of 5 ℃/min for heat treatment, wherein the heat treatment time is 12h. After the heat treatment is finished, the material is naturally cooled to room temperature, and the anode material with the nominal composition of 0.03LiF.FeF ₃ is obtained after crushing and sieving treatment.

Reference example 1 was made to a lithium secondary battery based on the above-described 0.03lif. Fef ₃ positive electrode material.

Example 7

Separately, 2.959g (26.19 mmol) of FeF ₃ raw material and 0.041g (1.58 mmol) of LiF raw material were weighed out, and the rest was subjected to the same experimental preparation procedure as in example 1 to obtain a positive electrode material having a nominal composition of 0.06LiF.FeF ₃.

Reference example 1 was made to a lithium secondary battery based on the above-described 0.06lif. Fef ₃ positive electrode material.

Example 8

Separately, 2.946g (26.07 mmol) of FeF ₃ raw material and 0.054g (2.08 mmol) of LiF raw material were weighed out, and the rest was subjected to the same experimental preparation procedure as in example 1 to obtain a positive electrode material having a nominal composition of 0.08LiF. FeF ₃.

Reference example 1 was made to a lithium secondary battery based on the above-described 0.08lif. Fef ₃ positive electrode material.

Example 9

Separately, 2.933g (25.96 mmol) of FeF ₃ raw material and 0.067g (2.59 mmol) of LiF raw material were weighed out, and the rest was subjected to the same experimental preparation procedure as in example 1 to obtain a positive electrode material having a nominal composition of 0.1LiF.FeF ₃.

Reference example 1 was made to a lithium secondary battery based on the above 0.1lif. Fef ₃ positive electrode material.

Example 10

2.913G (25.78 mmol) of FeF ₃ raw material and 0.087g (3.36 mmol) of LiF raw material were weighed out separately, and the rest was prepared by the same experimental procedure as in example 1 to obtain a positive electrode material having a nominal composition of 0.13LiF. FeF ₃.

Reference example 1 was made to a lithium secondary battery based on the above 0.13lif. Fef ₃ positive electrode material.

Example 11

2.662G (23.56 mmol) of FeF ₃ raw material, 0.304g (2.62 mmol) of CoF ₃ raw material and 0.034g (1.31 mmol) of LiF raw material are respectively weighed, stirred uniformly, then put into a 50mL agate tank, and ball-milled for 2h at a rotation speed of 500 r/min. And then placing the obtained mixture material in a tubular furnace protected by argon atmosphere, and heating to 300 ℃ at a heating rate of 5 ℃/min for heat treatment, wherein the heat treatment time is 12h. After the heat treatment is finished, the material is naturally cooled to room temperature, and the anode material with the nominal composition of 0.05LiF.Fe _0.9Co_0.1F₃ is obtained after crushing and sieving treatment.

Manufacturing an all-solid-state lithium secondary battery: the positive electrode material of 0.05lif.fe0.9co0.1f ₃, the solid electrolyte Li10GeP ₂S₁₂ (LGPS) and conductive carbon (SP) were mixed according to a mass ratio of 4:5:1, grinding for more than 30 minutes by an agate mortar to obtain the mixed powder of the positive electrode materials. Next, 100mg of Li ₁₀GeP₂S₁₂ (LGPS) and 50mg of Li ₇P₃S₁₁ (LPS) were weighed respectively, placed in a cold press mold, and a double-layer solid electrolyte membrane sheet was obtained under a pressure of 240 MPa. Then, placing the mixed powder of the anode material and the double-layer solid electrolyte into a stainless steel cold-pressing mold, wherein the mixed powder of the anode material is placed into an LGPS layer, and cold-pressing and molding are carried out under the pressure of 250MPa, so as to obtain a sheet of the anode and the solid electrolyte; and finally, placing a metal lithium sheet at one side of the LPS layer, placing the metal lithium sheet and the sheet in a cold pressing mold together, further applying 150MPa pressure to enable the interfaces of the positive electrode, the solid electrolyte and the metal lithium sheet to be fully contacted, and fastening by using screws to obtain a solid battery sample.

Example 12

2.632G (23.29 mmol) of FeF ₃ raw material, 0.300g (2.59 mmol) of CoF ₃ raw material and 0.067g (2.59 mmol) of LiF raw material were weighed out respectively, and the rest was prepared by the same experimental procedure as in example 11 to obtain a positive electrode material with a nominal composition of 0.1LiF.Fe _0.9Co_0.1F₃.

Reference example 11 was made on the basis of the above-described 0.1lif.fe _0.9Co_0.1F₃ positive electrode material.

Example 13

2.603G (23.04 mmol) of FeF ₃ raw material, 0.297g (2.56 mmol) of CoF ₃ raw material and 0.100g (3.86 mmol) of LiF raw material were weighed out respectively, and the rest was prepared by the same experimental procedure as in example 11 to obtain a positive electrode material having a nominal composition of 0.15LiF.Fe _0.9Co_0.1F₃.

Reference example 11 was made on the basis of the above-described 0.15lif.fe _0.9Co_0.1F₃ positive electrode material.

Comparative example 1

2.966G (26.25 mmol) of FeF ₃ raw material and 0.034g (1.31 mmol) of LiF raw material are respectively weighed, put into a 50mL agate tank, ball-milled for 12h at 500r/min and sieved to obtain the anode material with the nominal composition of 0.05LiF.FeF ₃. Reference example 1 was made to a lithium secondary battery based on the above-described 0.05lif. Fef ₃ material.

Comparative example 2

3G of commercial FeF ₃ raw material is weighed, filled into a 50mL agate tank, and ball-milled for 2 hours at 500r/min to obtain a small-particle FeF ₃ material.

Reference example 1 was made to a lithium secondary battery based on the above-described FeF ₃ material.

Comparative example 3

3G of commercial FeF ₃ raw material is weighed, put into a 50ml agate tank and ball-milled for 2 hours at 500 r/min. And then placing the obtained mixture material in a tubular furnace protected by argon atmosphere, and heating to 250 ℃ at a heating rate of 5 ℃/min for heat treatment, wherein the heat treatment temperature is 12h. After the heat treatment is finished, the material is naturally cooled to room temperature, and the small-particle FeF ₃ material after the heat treatment is obtained after crushing and sieving treatment.

Comparative example 4

Firstly, weighing 3g of commercial FeF ₃ raw materials, filling the raw materials into a 50mL agate tank, and ball milling for 12 hours at 500r/min to obtain a small-particle FeF ₃ material. Then, mixing the small-particle FeF ₃ material with LiF raw materials, a conductive agent (SP) and a binder PVDF according to a mass ratio of 58.9:1.1:30:10, adding the mixture into N-methyl pyrrolidone (NMP), stirring and homogenizing to prepare anode slurry, uniformly coating the anode slurry on an anode current collector aluminum foil by using a scraper, and finally drying, cold pressing and punching to prepare the anode plate. The amount of LiF relative to FeF ₃ in the prepared positive electrode sheet was 0.08. Reference example 1 was produced for a lithium secondary battery using the positive electrode sheet as a positive electrode.

Comparative example 5

2.69G (23.80 mmol) of commercial FeF ₃ and 0.31g (2.68 mmol) of CoF ₃ were weighed into a 50mL agate jar and ball-milled at 500r/min for 2h. And then placing the obtained mixture material in a tubular furnace protected by argon atmosphere, and heating to 300 ℃ at a heating rate of 5 ℃/min for heat treatment, wherein the heat treatment temperature is 12h. After the heat treatment is finished, the material is naturally cooled to room temperature, and the anode material with the nominal composition of Fe _0.9Co_0.1F₃ is obtained after crushing and sieving treatment.

Reference example 11 was made for an all-solid-state lithium secondary battery based on the above-described Fe _0.9Co_0.1F₃ material.

Test method

1. Discharge gram Capacity and cycle Capacity Retention test

(1) CR2430 button cell

After the CR2430 button cell is aged for 24 hours in a constant temperature room (25 ℃), the initial activation is carried out on the 1 st turn at the charge-discharge current density of 25mA/g, and the charge-discharge current density of the 2 nd and subsequent turns is changed to 50mA/g. The 2 nd turn discharge gram capacity is taken as a reference standard of cyclic gram capacity decay, namely, the n th turn capacity retention rate=n th turn discharge capacity/2 nd turn discharge capacity×100%. In the charge and discharge process, the lower limit of the discharge cut-off voltage is 1V, and the upper limit of the charge cut-off voltage is 4V.

(2) All-solid-state lithium secondary battery

After the all-solid-state lithium secondary battery is aged for 24 hours in a constant temperature room (25 ℃), the 1 st turn is activated at the charge-discharge current density of 10mA/g, and the charge-discharge current density of the 2 nd and subsequent turns is changed to 25mA/g. The 2 nd turn discharge gram capacity is taken as a reference standard of cyclic gram capacity decay, namely, the n th turn capacity retention rate=n th turn discharge capacity/2 nd turn discharge capacity×100%. In the charge and discharge process, the lower limit of the discharge cut-off voltage is 1V, and the upper limit of the charge cut-off voltage is 4V.

2. XRD testing

Testing the anode material by adopting an X-ray powder diffractometer (XRD, instrument model: bruker D8 ADVANCE), wherein the target material is Cu K alpha; the voltage and current are 40KV/35mA, the scanning angle range is 10 DEG to 60 DEG, and the scanning speed is 5 DEG/min.

3. Grain size calculation

The grain size of the material is calculated by Scherrer formula d=kλ/βcos θ. Where D is the grain size, K is the Scherrer constant (k=0.94), λ is the wavelength of Cu kα rays, β is the half-width value (radian units), and θ is the bragg angle of the X-ray diffraction peak.

4. SEM test

The scanning electron microscope characterization was recorded by PhilipsXL-30 type field emission scanning electron microscope and detected at 10kV,10 mA.

5. Positive electrode material element composition test

And (3) testing the element composition of the positive electrode material, wherein the content of Li, fe and Co is measured by an Inductively Coupled Plasma (ICP) tester of Optima 7000DV of PE company in the United states, and the content of F is measured by a Siemens ion chromatography tester. Before F element test, a certain amount of dilute nitric acid solution is needed to dissolve the positive electrode material to be tested, so that an aqueous solution of F ^- is completely formed, and then the test is carried out.

Test results

Table 1 shows the effect of heat treatment temperature on the performance of the resulting cathode material and lithium ion batteries comprising the same.

Among them, the cathode materials of comparative example 1 and examples 1 to 5 were mixed with FeF ₃ and LiF using ball milling during the preparation process. The electrolytes in the lithium ion batteries of comparative example 1 and examples 1 to 5 were both lifsi+dme, and the nominal composition of the initial cathode material was 0.05lif.fef ₃.

TABLE 1

The effect of heat treatment temperature on gram capacity and cycle stability of the metal fluoride composite positive electrode material (i.e., the positive electrode material of the present application) is given in table 1 for comparative example 1 and examples 1 to 5. When only a simple ball milling compounding treatment was performed, the discharge gram capacity at the 2 nd turn and the capacity retention rate at the 20 th turn of the positive electrode material in comparative example 1 were both lowest, namely 429.8mAh/g and 72.2%, respectively. When the heat treatment temperature was 180 ℃, the capacity retention rate at the 2 nd turn of discharge gram and the 20 th turn of the positive electrode material in example 1 was slightly improved as compared with comparative example 1, but was not significant. As the heat treatment temperature was increased to 300 ℃, the discharge gram capacity and the capacity retention rate of the positive electrode material in example 3 both reached the maximum values, which were increased by 40.4mAh/g and 15.0% respectively, as compared with comparative example 1. The heat treatment temperature was further increased to 400 ℃ and above, and both the discharge gram capacity and the cycle stability of the positive electrode materials in examples 4 and 5 showed a decrease trend. When the heat treatment temperature was 430 ℃, the discharge gram capacity and the capacity retention rate of the positive electrode material in example 5 were already at the same level as those of the positive electrode material in comparative example 1.

The above results show that the preferable heat treatment temperature in the preparation process of the positive electrode material of the present application is 200 to 400 ℃. When the heat treatment temperature is too low, atoms cannot overcome the barrier of diffusion, and diffusion is difficult to carry out, so that the material exhibits poor electrochemical performance. When the heat treatment temperature is too high, on one hand, the transition metal fluoride may react with oxygen adsorbed on the surface of the material or air introduced by the tube furnace due to poor sealing, so that inert impurity phases are generated, and on the other hand, the transition metal fluoride is extremely easy to decompose at high temperature to generate low-valence transition metal fluoride, and the electrochemical performance of the material is reduced.

The XRD test results of the positive electrode materials in comparative example 1 and examples 1 to 5 are shown in fig. 1. When the heat treatment temperature is less than 200 ℃, the XRD spectra of the positive electrode material in example 1 and the XRD spectrum of the positive electrode material in comparative example 1 are very similar, and the main phases are FeF ₃, and contain very little LiF. Since LiF is less compounded and the crystallinity is reduced by ball milling, the XRD diffraction peak is not significant, which is consistent with the electrochemical performance exhibited by the positive electrode material.

When the heat treatment temperature is 200 to 400 ℃, XRD of the positive electrode material in the corresponding example shows a more remarkable difference than that of the positive electrode material in comparative example 1. First, the half-width of the diffraction peak at around 23.8 ° corresponding to the (101) crystal plane of FeF ₃ appears to be significantly broader, which may be related to the interdiffusion reactions of LiF and FeF ₃ materials. Wherein the corresponding half-width in comparative example 1 was 0.09 °, the grain size of the positive electrode material was calculated to be large, about 117nm according to the Scherrer formula, whereas the half-widths in examples 1 to 5 were respectively 0.12 °, 0.2 °, 0.22 °, 0.25 ° and 0.26 °, and the grain sizes of the materials were calculated to be 88nm, 53nm, 48nm, 42nm and 40nm according to the Scherrer formula, respectively. The reaction kinetics of the converted metal fluoride positive electrode material is poor, and the smaller the grain size is, the more favorable the reaction kinetics is improved, and the electrochemical performance is further improved. Next, the intensity of the characteristic diffraction peak of LiF ((the diffraction peak of about 38.7 ° corresponding to the (111) crystal plane and about 45.0 ° corresponding to the (200) crystal plane) gradually decreases with an increase in the heat treatment temperature. The broadened diffraction peaks mean that the lattice order of the material is reduced, and the intensity of the LiF characteristic diffraction peaks is reduced, which indicates that LiF and FeF ₃ are subjected to diffusion reaction in the heat treatment process. Further, when the temperature is raised to 400 ℃ or higher, the XRD spectrum of the positive electrode material of example 5 also shows a diffraction peak of FeF ₂ (which may correspond to pyrolysis of FeF ₃: feF ₃→FeF₂+F₂), and is accompanied by other unknown weak hetero-phase diffraction peaks.

Table 1 also gives the elemental composition and phase composition in different states of the positive electrode materials in comparative example 1 and examples 1 to 5. As can be seen from table 1, for the initial positive electrode material, the actual measured elemental composition of the material is very close to the nominal composition of the material. The relative content of F element slightly decreases with increasing heat treatment temperature, which is consistent with XRD test results. During the high temperature heat treatment, a very small portion of the FeF ₃ is decomposed to form FeF ₂, resulting in a small amount of F element loss. Too high a heat treatment temperature will result in more loss of F element and may affect the electrical properties of the material. After the battery is formed, the active substances in the positive electrode plate are mainly LiF and Fe after the battery is fully placed to 1V for the first time, and the active substances originate from the reaction process of FeF ₃ +Li- & gtFe+LiF. Since the initial LiF is excessive, the ratio of Li to F element molar content in the fully-discharged positive electrode material is measured to be slightly greater than 1, in line with the expectation. Further, the molar ratio of the LiF to Fe in the positive electrode plate after full discharge is more than 3, so that the nano Fe simple substance can be completely converted into metal fluoride in the subsequent charging process, and the capacity of the battery can be more favorably exerted.

Table 2 shows the effect of the molar ratio of LiF to transition metal fluoride in the positive electrode material on the performance of the lithium ion battery of the positive electrode material.

Among them, the electrolyte in the lithium ion batteries of comparative examples 2 to 4 and examples 6 to 10 was lifsi+dme.

TABLE 2

The relative content of LiF in the positive electrode material as a function of gram-to-discharge capacity and capacity retention rate are given in table 2 for comparative examples 2 to 4 and examples 6 to 10. First, by comparing comparative example 2 and comparative example 3, it can be derived that: for a transition metal fluoride positive electrode material that does not contain lithium fluoride, whether heat treatment is performed has a substantially negligible effect on the electrochemical properties of the material, and therefore the effect of heat treatment on the electrochemical properties of the transition metal fluoride positive electrode material that does not contain lithium fluoride can be eliminated. Secondly, compared with comparative example 2, in comparative example 4, 0.08mol of LiF is directly added in the preparation process of the positive electrode slurry, the electrochemical performance of the material after the material is made into a battery is not obviously changed, and the electrochemical performance of the material cannot be improved by simply adopting a simple mechanical mixing and adding manner. Therefore, the key to the improvement of electrochemical properties of the positive electrode material is lithium fluoride, and proper temperature is required for heat treatment. The effect of the heat treatment as described above is to promote a more uniform composition of the material.

As shown in fig. 3, as the LiF content increases, the discharge gram capacity of the cathode materials in comparative example 2 and examples 6 to 10 shows a trend of increasing and then decreasing. When the amount of LiF relative to the substance of FeF ₃ was 0.08, the discharge gram capacity of the positive electrode material in example 8 reached a maximum of 540.2mAh/g, and the improvement ratio reached 25% as compared to comparative example 2. When the amount of LiF relative to the mass of FeF ₃ was 0.13, the discharge gram capacity of the material in example 10 had been reduced to 465.1mAh/g. Since LiF does not provide the gram discharge capacity and its intrinsic conductivity is extremely low, too high an addition ratio can sacrifice the gram discharge capacity of the cathode material. In addition, it can be seen from the comparison of example 6 and comparative example 2 that: by compounding LiF in the transition metal fluoride material, the material cycle stability is significantly improved. Specifically, when the compounding ratio of LiF was only 0.03mol, the discharge capacity retention rate of the positive electrode material of example 6 at the 20 th turn was increased from 70.4% to 85.7% in comparative example 2. With the increase of the relative content of LiF in the positive electrode material, the cycling stability of the positive electrode material is further improved. The material of example 10 had a cycle retention of up to 92.1% when the amount of LiF relative to the mass of FeF ₃ was 0.13.

FIG. 4 shows the comparison of cyclic voltammograms of the battery at the 2 nd and 5 th turns of example 10, the test voltage interval is 1V to 4.2V, the sweep rate is 0.1mV/s, and the two curves can be seen to be basically coincident, further illustrating that the positive electrode material of the application has extremely high cyclic stability.

The mechanism by which the electrochemical performance of the positive electrode material is remarkably improved by the composite LiF is presumed to be: the traditional conversion reaction type metal fluoride positive electrode material firstly generates nano metal simple substance particles and LiF in the discharging process. In the subsequent charging process, the nano-metal simple substance is oxidized into metal ions and recombined with fluorine ions to generate metal fluoride. Since the nano material is easy to generate segregation or agglomeration, the periphery of metal ions which are possibly generated by oxidation in the charging process does not have enough fluoride ions to combine with the metal ions to generate stable metal fluoride. The metal ions which are not converted into metal fluoride are easy to dissolve into electrolyte and shuttle to the negative electrode to be reduced into metal simple substance dendrites, so that the loss of the positive electrode active material is caused, the gram capacity of the battery is rapidly attenuated, and the short circuit occurs in the battery due to the fact that the metal simple substance dendrites penetrate through the separator, so that circulating water jump occurs. However, after the positive electrode material is compounded with a certain proportion of lithium fluoride, fluoride ions are always excessive in the charging process, so that the metal ions can be ensured to be completely converted into stable metal fluoride, a large amount of metal ions in the positive electrode are prevented from being dissolved out, and the high discharge specific capacity and high cycle stability of the material are further realized. Finally, by compounding LiF, other impurity elements are not introduced, other performances of the battery are not affected, and the introduced Li can also provide partial active lithium, so that the electrochemical stability can be further improved.

Table 3 shows the test results of the positive electrode material of the present application in an all-solid battery.

Wherein, the electrolyte in the lithium ion batteries of comparative example 5 and examples 11 to 13 is lgps+lps, the pretreatment mode is ball milling, and the heat treatment temperature is 300 ℃.

TABLE 3 Table 3

The test results of the positive electrode materials in the all solid-state batteries are given in table 3 for comparative example 5 and examples 11 to 13. As is clear from comparison with comparative example 5, when the proportion of composite LiF in the Fe _0.9Co_0.1F₃ cathode material is 0.1 or less, both the discharge gram capacity and the cycle stability of the materials in examples are improved to different extents. However, when the compounding amount of LiF was further increased to about 0.15, the initial discharge gram capacity was lost too much in spite of its better cycle stability. Specifically, the positive electrode material of example 13 had a capacity retention rate of approximately 93% after 20 cycles, but had an initial discharge gram capacity reduced to around 420mAh/g, which was lower than 443mAh/g of the material of comparative example 5. Similar to the previous results, it is shown that LiF itself does not provide gram capacity, but that excess would instead reduce the overall gram capacity of the material. In general, the electrochemical performance of the conversion type metal fluoride positive electrode material is improved by compounding LiF with a certain proportion, and the conversion type metal fluoride positive electrode material has certain universal applicability.

While certain exemplary embodiments of the application have been illustrated and described, the application is not limited to the disclosed embodiments. Rather, one of ordinary skill in the art will recognize that certain modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. An electrochemical device comprising a positive electrode material comprising composite particles comprising lithium fluoride and a transition metal fluoride, wherein the molar ratio x of lithium fluoride and transition metal fluoride satisfies: x is more than 0 and less than or equal to 0.135.

2. The electrochemical device of claim 1, wherein after the electrochemical device is fully charged, the positive electrode material comprises LiF and MF _y, wherein 2.ltoreq.y.ltoreq.3, and m comprises at least one of transition metals.

3. The electrochemical device of claim 1, wherein 0.025 +.x +.0.11.

4. The electrochemical device according to claim 1, wherein the composite particles have a peak between 23 ° and 24 ° in an X-ray spectrum, the peak having a half-width of 0.15 ° to 0.3 °;

And/or the composite particles have a grain size of 30nm to 100nm, wherein the grain size is calculated by the Scherrer formula.

5. The electrochemical device according to claim 1, wherein in the transition metal fluoride, a molar ratio y of fluorine element and transition metal element satisfies: y is more than or equal to 2 and less than or equal to 3.

6. The electrochemical device of claim 1, the transition metal comprising at least one of Fe, co, ni, mn or Cu.

7. The electrochemical device of claim 1, the transition metal fluoride comprising at least one of FeF₃、CoF₃、Fe_0.9Co_0.1F₃、NiF₃、MnF₃、FeF₂、CoF₂、NiF₂ or CuF ₂.

8. The preparation method of the positive electrode material comprises the following steps:

Mixing lithium fluoride and a transition metal fluoride to obtain a first mixture, wherein the molar ratio z of lithium fluoride and transition metal fluoride satisfies: z is more than 0 and less than or equal to 0.13; and

The first mixture is heat treated.

9. The production method according to claim 8, wherein at least one of the following conditions (a) to (d) is satisfied:

(a) The transition metal comprises at least one of Fe, co, ni, mn or Cu;

(b) The transition metal fluoride includes at least one of FeF₃、CoF₃、Fe_0.9Co_0.1F₃、NiF₃、MnF₃、FeF₂、CoF₂、NiF₂ or CuF ₂;

(c) The molar ratio z of lithium fluoride to transition metal fluoride satisfies: z is more than or equal to 0.03 and less than or equal to 0.1;

(d) The temperature of the heat treatment is 200-400 ℃, and the time of the heat treatment is 6-24 hours.