CN118511299A

CN118511299A - Preparation method of anode active material, secondary battery and electric device

Info

Publication number: CN118511299A
Application number: CN202280088115.3A
Authority: CN
Inventors: 邓柏炟; 康蒙; 曾晨; 何立兵
Original assignee: Contemporary Amperex Technology Co Ltd
Current assignee: Contemporary Amperex Technology Co Ltd
Priority date: 2022-10-12
Filing date: 2022-10-12
Publication date: 2024-08-16
Also published as: WO2024077522A1

Abstract

The application relates to a preparation method of a negative electrode active material, which comprises the following steps: carrying out first negative pressure roasting on natural graphite; coating a first liquid hard carbon coating precursor on the natural graphite subjected to the first negative pressure roasting, presintering, and forming a primary coating layer; and coating a second liquid hard carbon coating precursor on the surface of the primary coating layer, and carbonizing to form a secondary coating layer. And to a corresponding anode active material, secondary battery, and electric device. The coating layer of the anode active material has lower coating quantity and better coating uniformity, and can improve the storage performance, the dynamic performance and the cycle performance of the battery.

Description

Preparation method of anode active material, secondary battery and electric device

Technical Field

The application relates to the technical field of secondary batteries, in particular to a preparation method of a negative electrode active material, the negative electrode active material, a secondary battery and an electric device.

Background

In recent years, with the increasing range of applications of secondary ion batteries, secondary batteries are widely used in energy storage power systems such as hydraulic power, firepower, wind power and solar power stations, and in various fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment, aerospace and the like. As secondary batteries have been greatly developed, higher demands are also being made on their dynamic properties, storage properties, cycle properties, and the like.

The negative electrode is an important component in the secondary battery, and the negative electrode active material has an important influence on the kinetic performance, storage performance, cycle performance, and the like of the secondary battery. With the rapid development of secondary batteries, higher demands are also being made on the performance of the anode active material. Therefore, the search for a negative electrode active material having more excellent performance is one of the research directions that the skilled person is focusing on.

Disclosure of Invention

The present application has been made in view of the above problems, and an object of the present application is to provide a method for producing a negative electrode active material, which can improve the storage performance, the dynamic performance, and the cycle performance of a battery by providing a negative electrode active material having a low coating amount and a good coating uniformity.

In order to achieve the above object, a first aspect of the present application provides a method for preparing a negative electrode active material, comprising the steps of:

Carrying out first negative pressure roasting on natural graphite;

Coating a first liquid hard carbon coating precursor on the natural graphite subjected to the first negative pressure roasting, presintering, and forming a primary coating layer; and

And coating a second liquid hard carbon coating precursor on the surface of the primary coating layer, and carbonizing to form a secondary coating layer.

The method comprises the steps of carrying out first negative pressure roasting treatment on natural graphite before the first liquid hard carbon coating precursor is coated on the natural graphite to form a primary coating layer; the water and gas absorbed in the pores inside the natural graphite can be discharged through the first negative pressure roasting, so that the liquid hard carbon coating precursor can be uniformly attached to the natural graphite in the subsequent coating step, the coating amount is reduced, the effect of uniform coating under the condition of low coating amount is achieved, and the battery adopting the negative electrode active material has good storage performance and dynamic performance; in addition, the hard carbon coating layer can be better filled into the pores of the natural graphite to play a role of a dimensionally stable skeleton, so that the cyclic expansion of the natural graphite is effectively inhibited, and the battery has good cycle performance.

In any embodiment of the present application, the vacuum degree of the first negative pressure roasting is 0 to 0.5 atm, the roasting temperature is 120 to 300 ℃ and the roasting time is 2 to 8 hours. Therefore, the moisture and gas adsorbed in the natural graphite pores can be fully removed, the dynamic performance is not affected, and the energy consumption is not increased.

In any embodiment of the present application, the coating of the first liquid hard carbon coated precursor on the natural graphite after the first negative pressure roasting includes the following steps: transferring the natural graphite subjected to the first negative pressure roasting into vacuum coating equipment filled with the first liquid hard carbon coating precursor under the vacuum condition, and vacuumizing and stirring for 4-7 h at 120-200 ℃. Therefore, moisture and gas can be prevented from reentering the pores in the natural graphite transferring and coating process, and uniform coating is facilitated.

In any embodiment of the present application, the pre-sintering temperature is 400 to 600 ℃, and the pre-sintering time is 0.5 to 2 hours. Thus, the first liquid hard carbon coating precursor can be better induced to form a uniform and thin primary coating layer on the natural graphite, and the primary coating layer can be well filled into the pores of the natural graphite.

In any embodiment of the present application, after forming the primary coating layer and before coating the surface of the primary coating layer with the second liquid hard carbon coated precursor, the preparation method further includes a step of performing a second negative pressure calcination on the natural graphite. Therefore, the water and gas adsorbed in the natural graphite pores can be discharged, and the subsequent formation of a secondary coating layer with lower and uniform coating amount is facilitated.

In any embodiment of the present application, the vacuum degree of the second negative pressure roasting is 0.1-0.3 atm, the roasting temperature is 100-150 ℃ and the roasting time is 1-3 h. Therefore, the moisture and gas adsorbed in the natural graphite pores can be fully removed, the uniformity of the secondary coating layer is improved, the dynamic performance is not affected, and the energy consumption is not increased.

In any embodiment of the present application, the coating of the surface of the primary coating layer with the second liquid hard carbon coating precursor includes the following steps: transferring the natural graphite subjected to the second negative pressure roasting into vacuum coating equipment filled with the second liquid hard carbon coating precursor under the vacuum condition, and vacuumizing and stirring for 2-4 h at 120-200 ℃. Therefore, moisture and gas can be prevented from entering the pore again in the natural graphite transferring and secondary coating process, and uniform coating is facilitated.

In any embodiment of the application, the carbonization temperature is 800-1300 ℃, the carbonization time is 4-8 hours, and the carbonization is performed under inert gas atmosphere. Therefore, the secondary coating layer can be well filled into the pores of the natural graphite, the effect of coating and reinforcing is better achieved, and the coating effect is improved.

In any embodiment of the present application, the first liquid hard carbon coating precursor includes one or more of phenolic resin, epoxy resin and petroleum resin, and the mass fraction of the resin in the first liquid hard carbon coating precursor is 30-70%.

In any embodiment of the present application, the second liquid hard carbon coating precursor includes one or more of phenolic resin, epoxy resin and petroleum resin, and the mass fraction of the resin in the second liquid hard carbon coating precursor is 10-30%. Thus, the mass fraction of resin in the second liquid hard carbon coated precursor is less than the mass fraction of resin in the first liquid hard carbon coated precursor.

In any embodiment of the present application, the primary coating layer is coated with the natural graphite at a mass ratio of 2 to 5%. Is a lower coating amount.

In any embodiment of the present application, the secondary coating layer is coated on the natural graphite in a mass ratio of 1 to 3%. Therefore, the preparation method of the application can adopt lower coating amount and realize uniform coating of each coating layer.

In any embodiment of the present application, the natural graphite satisfies at least one of the following conditions a to c before the first negative pressure firing:

a. the volume average particle diameter Dv ₅₀ is 6-15 mu m;

optionally, the volume average particle diameter Dv ₅₀ is 8-12 μm;

b. Volume average particle diameter (Dv ₉₀-Dv ₁₀)/Dv ₅₀ is 1.0 to 1.4;

alternatively, the volume average particle diameter (Dv ₉₀-Dv ₁₀)/Dv ₅₀ is 1.0 to 1.2;

c. The tap density TD is 0.7-1.1 g/cm ³;

Optionally, the tap density TD is 0.8-1.0 g/cm ³.

In any embodiment of the present application, the anode active material satisfies at least one of the following conditions d to g:

d. The volume average particle diameter Dv ₅₀ is 7-17 mu m;

Optionally, the volume average particle diameter Dv ₅₀ is 9-13 μm;

e. Volume average particle diameter (Dv ₉₀-Dv ₁₀)/Dv ₅₀ is 1.0 to 1.3;

f. the tap density TD is 0.7-1.1 g/cm ³;

Optionally, the tap density TD is 0.85-0.95 g/cm ³;

g. BET specific surface area is 1.0-5.0 m ²/g;

Alternatively, the BET specific surface area is 1.5 to 3.5m ²/g.

The second aspect of the present application also provides a negative electrode active material prepared by the preparation method of the negative electrode active material according to the first aspect of the present application.

Therefore, the negative electrode active material has lower coating amount and better coating uniformity, and a battery adopting the negative electrode active material has good storage performance, dynamic performance and cycle performance.

The third aspect of the application also provides a secondary battery comprising the anode active material according to the second aspect of the application.

The fourth aspect of the application also provides an electric device comprising the secondary battery selected from the third aspect of the application.

According to the preparation method of the negative electrode material, the first negative pressure roasting treatment is carried out on the natural graphite before the first liquid hard carbon coating precursor is coated, so that the water and gas adsorbed in the pores of the natural graphite can be discharged, the liquid hard carbon coating precursor can be uniformly attached to the natural graphite in the subsequent coating step, the coating amount is reduced, the effect of uniform coating under the condition of low coating amount is achieved, and the battery adopting the negative electrode active material has good storage performance and dynamic performance; in addition, the hard carbon coating layer can be better filled into the pores of the natural graphite to play a role of a dimensionally stable skeleton, so that the cyclic expansion of the natural graphite is effectively inhibited, and the battery has good cycle performance.

Drawings

Fig. 1 is a scanning electron microscope image of a negative electrode active material according to an embodiment of the present application.

Fig. 2 is a schematic view of a secondary battery according to an embodiment of the present application.

Fig. 3 is an exploded view of the secondary battery according to an embodiment of the present application shown in fig. 2.

Fig. 4 is a schematic view of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.

Reference numerals illustrate:

5. A secondary battery; 51. a housing; 52. an electrode assembly; 53. a cover plate; 6. and (5) an electric device.

Detailed Description

Hereinafter, embodiments of a method for producing a negative electrode active material, a secondary battery, a battery module, a battery pack, and an electric device according to the present application are specifically disclosed with reference to the accompanying drawings as appropriate. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of the actual same structure may be omitted. This is to avoid that the following description becomes unnecessarily lengthy, facilitating the understanding of those skilled in the art. Furthermore, the drawings and the following description are provided for a full understanding of the present application by those skilled in the art, and are not intended to limit the subject matter recited in the claims.

The "range" disclosed herein is defined in terms of lower and upper limits, with the given range being defined by the selection of a lower and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges that are defined in this way can be inclusive or exclusive of the endpoints, and any combination can be made, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, it is understood that ranges of 60 to 110 and 80 to 120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4 and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise indicated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is only a shorthand representation of a combination of these values. When a certain parameter is expressed as an integer of 2 or more, it is disclosed that the parameter is, for example, an integer of 2,3,4,5,6,7, 8, 9, 10,11, 12 or the like.

All embodiments of the application and alternative embodiments may be combined with each other to form new solutions, unless otherwise specified.

All technical features and optional technical features of the application may be combined with each other to form new technical solutions, unless specified otherwise.

All the steps of the present application may be performed sequentially or randomly, preferably sequentially, unless otherwise specified. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), and the like.

The terms "comprising" and "including" as used herein mean open ended or closed ended, unless otherwise noted. For example, the terms "comprising" and "comprises" may mean that other components not listed may be included or included, or that only listed components may be included or included.

The term "or" is inclusive in this application, unless otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or absent); a is false (or absent) and B is true (or present); or both A and B are true (or present).

At present, as secondary batteries have been greatly developed, higher demands are also being made on the dynamic performance, storage performance and cycle performance of the secondary batteries. Secondary batteries having excellent performance have high demands on negative electrode active materials. Therefore, the search for a negative electrode active material having more excellent performance is one of the research directions that the skilled person is focusing on. In the traditional method for coating soft carbon on the surface of graphite, the coating layer is easily converted into graphite in the graphitization process, and the dynamic performance of the battery can be possibly deteriorated; the traditional method adopting solid phase coating can not ensure the uniformity of coating, and is easy to bond to form extremely high active reaction sites, so that the storage performance is deteriorated. The inventor researches and discovers a preparation method of a cathode active material, which adopts natural graphite as a base material, wherein the natural graphite is subjected to first negative pressure roasting, and then a primary coating layer and a secondary coating layer are sequentially formed on the natural graphite. The preparation method can obtain the coating layer with low coating amount and uniform coating, and can improve the dynamic performance, the storage performance and the cycle performance of the battery.

In some embodiments, a first aspect of the present application provides a method for preparing a negative active material, comprising the steps of:

Carrying out first negative pressure roasting on natural graphite;

According to the preparation method of the negative electrode active material, before the first liquid hard carbon coating precursor is coated on the natural graphite to form the primary coating layer, the first negative pressure roasting treatment is carried out on the natural graphite, and moisture and gas adsorbed in the internal pores of the natural graphite are discharged, so that the liquid hard carbon coating precursor can be uniformly attached to the natural graphite in the subsequent coating step, the coating amount is reduced, the effect of uniform coating under the condition of low coating amount is achieved, and a battery adopting the negative electrode active material has good storage performance and dynamic performance.

In addition, the hard carbon coating layer can be better filled into the pores of the natural graphite through the first negative pressure roasting treatment, so that the natural graphite has a dimensionally stable skeleton function, the cyclic expansion of the natural graphite can be effectively inhibited, and the battery adopting the negative electrode active material has good cyclic performance. Compared with artificial graphite, natural graphite has higher compaction density and capacity, and can improve the energy density of the battery.

In some embodiments, the first negative pressure firing has a vacuum of 0 to 0.5 atmospheres, a firing temperature of 120 to 300 ℃, and a firing time of 2 to 8 hours. Thereby, it is ensured that moisture and gas adsorbed in the pores of the natural graphite are sufficiently removed. When the vacuum degree is insufficient, the roasting temperature is too low or the roasting time is too short, the moisture and gas in the natural graphite pores can be not removed cleanly; when the roasting temperature is too high or the roasting time is too long, the functional groups on the surface of the natural graphite can react, the dynamic performance is affected, and the energy consumption can be increased.

It will be understood that, in the above "vacuum degree is 0 to 0.5 atmospheres", values include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the point values and the embodiments: 0 atmosphere, 0.1 atmosphere, 0.15 atmosphere, 0.2 atmosphere, 0.25 atmosphere, 0.3 atmosphere, 0.35 atmosphere, 0.4 atmosphere, 0.45 atmosphere, 0.5 atmosphere. Similarly, in the above "firing temperature of 120 to 300 ℃, values include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the point values and the following in the examples: 120 ℃,150 ℃, 180 ℃,200 ℃, 220 ℃, 240 ℃, 260 ℃, 280 ℃, 300 ℃. In the above "firing time is 2h to 8h", the values include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the point values and the following in the examples: 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h.

In any embodiment of the present application, coating a first liquid hard carbon coated precursor on the first negative pressure calcined natural graphite comprises the steps of: transferring the natural graphite subjected to the first negative pressure roasting to vacuum coating equipment filled with the first liquid hard carbon coating precursor through a sealing channel under the vacuum condition, and vacuumizing and stirring for 4-7 h at 120-200 ℃. Therefore, after the first negative pressure roasting, the natural graphite is transferred to the vacuum coating equipment containing the first liquid hard carbon coating precursor for coating through the sealing channel, so that moisture and gas can not reenter the pores in the transfer and coating processes of the natural graphite, and uniform coating is facilitated.

It will be appreciated that one end of the sealed passageway is in communication with the firing furnace in which the first negative pressure firing is performed, and the other end thereof is in communication with the vacuum envelope vessel. In the process of transferring the baked natural graphite into the vacuum coating container, the vacuum state is kept, and external moisture and gas are prevented from entering the sealing channel, so that the moisture and the gas are prevented from being re-adsorbed in the pores of the natural graphite. It will be understood that in the above "stirring under vacuum at 120 to 200 ℃ for 4 to 7 hours", the values of the temperature and the stirring time include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the temperature point value and the temperature point value in the examples: 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃, 200 ℃; including but not limited to the agitation time point values in the examples: 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h.

It will be understood that, in the foregoing "the temperature of burn-in is 400 to 600 ℃, the values include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the point values and the following examples: 400 ℃, 420 ℃, 440 ℃, 460 ℃, 480 ℃, 500 ℃, 520 ℃, 540 ℃, 560 ℃, 580 ℃, 600 ℃. In the foregoing "burn-in time is 0.5 to 2h", the values include the minimum value and the maximum value of the range, and each value between the minimum value and the maximum value, and specific examples include, but are not limited to, the dot values and the following in the embodiments: 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h.

In any embodiment of the present application, after forming the primary coating layer and before coating the surface of the primary coating layer with the second liquid hard carbon coated precursor, the preparation method further includes a step of performing a second negative pressure calcination on the natural graphite. Therefore, the water and gas adsorbed in the natural graphite pores can be discharged before the second liquid hard carbon coating precursor is coated, and the subsequent formation of a secondary coating layer with lower and uniform coating amount is facilitated.

In any embodiment of the present application, the vacuum degree of the second negative pressure roasting is 0.1-0.3 atm, the roasting temperature is 100-150 ℃ and the roasting time is 1-3 h. Therefore, the moisture and gas adsorbed in the natural graphite pores can be fully removed, and the uniformity of the secondary coating layer can be improved. When the vacuum degree is insufficient, the roasting temperature is too low or the roasting time is too short, the moisture and gas in the natural graphite pores can be not removed cleanly; when the roasting temperature is too high or the roasting time is too long, the functional groups on the surface of the natural graphite can react, the kinetic performance is affected, and the energy consumption can be increased.

It will be understood that, in the above "vacuum degree is 0.1 to 0.3 atmospheres", values include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the point values and the embodiments: 0.1 atmosphere, 0.15 atmosphere, 0.2 atmosphere, 0.25 atmosphere, 0.3 atmosphere. Similarly, in the above "firing temperature is 100 to 150 ℃, the values include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the point values and the following in the examples: 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃. In the above "firing time of 1 to 3 hours", the values include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the point values and the following in the examples: 1h, 1.2h, 1.5h, 1.8h, 2.0h, 2.2h, 2.5h, 2.8h, 3h.

In any embodiment of the present application, the coating of the surface of the primary coating layer with the second liquid hard carbon coating precursor includes the steps of: transferring the natural graphite subjected to the second negative pressure roasting to vacuum coating equipment filled with the second liquid hard carbon coating precursor through a sealing channel under the vacuum condition, and vacuumizing and stirring for 2-4 hours at 120-200 ℃. Therefore, after the second negative pressure roasting, the natural graphite is transferred to the vacuum coating equipment containing the second liquid hard carbon coating precursor for coating through the sealing channel, so that the moisture and gas can not reenter the pores in the natural graphite transferring and secondary coating process, and uniform coating is more facilitated.

Similarly, one end of the sealing passage is communicated with a roasting furnace for carrying out the second negative pressure roasting, and the other end of the sealing passage is communicated with a vacuum coating container for carrying out the secondary coating. In the process of transferring the baked natural graphite into the vacuum coating container, the vacuum state is kept, and external moisture and gas are prevented from entering the sealing channel, so that the moisture and the gas are prevented from being re-adsorbed in the pores of the natural graphite. It will be understood that in the above "stirring under vacuum at 120 to 200 ℃ for 2 to 4 hours", the values of the temperature and the stirring time include the minimum value and the maximum value of the range, and each value between such minimum value and maximum value, and specific examples include, but are not limited to, the temperature point value and the temperature point value in the examples: 120 ℃, 130 ℃, 140 ℃, 150 ℃, 160 ℃, 170 ℃, 180 ℃, 190 ℃, 200 ℃; including but not limited to the agitation time point values in the examples: 2h, 2.5h, 3h, 3.5h, 4h.

In any embodiment of the application, the carbonization temperature is 800-1300 ℃, the carbonization time is 4-8 hours, and the carbonization is performed under inert gas atmosphere. Therefore, the second liquid hard carbon coating precursor can be better induced to form a uniform and thin secondary coating layer on the natural graphite, so that the secondary coating layer can be well filled into the pores of the natural graphite, the effect of coating and reinforcing is better achieved, and the coating effect is improved.

It is understood that carbonization temperatures include, but are not limited to, the following specific values: 800 ℃, 850 ℃, 900 ℃, 950 ℃,1000 ℃, 1050 ℃, 1100 ℃, 1150 ℃, 1200 ℃, 1250 ℃, 1300 ℃. Carbonization times include, but are not limited to, the following specific values: 4h, 4.4h, 4.8h, 5h, 5.4h, 5.8h, 6h, 6.4h, 6.8h, 7h, 7.4h, 7.8h, 8h.

In any embodiment of the present application, the first liquid hard carbon coating precursor includes one or more of phenolic resin, epoxy resin and petroleum resin, and the mass fraction of the resin in the first liquid hard carbon coating precursor is 30-70%. That is, the first liquid hard carbon-coated precursor may contain only any one of a phenolic resin, an epoxy resin, and a petroleum resin, or may contain a combination of any two or three of the above three resins. The mass fraction of resin in the first liquid hard carbon coating precursor may be, but is not limited to, the following specific values: 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%.

In any embodiment of the present application, the second liquid hard carbon coating precursor includes one or more of phenolic resin, epoxy resin and petroleum resin, and the mass fraction of the resin in the second liquid hard carbon coating precursor is 10-30%. Typically, the mass fraction of resin in the second liquid hard carbon coated precursor is less than the mass fraction of resin in the first liquid hard carbon coated precursor.

In any embodiment of the present application, the primary coating layer is coated with the natural graphite at a mass ratio of 2 to 5%. Because the preparation method adopts negative pressure roasting, the water and gas in the natural graphite pores are removed, so that the liquid hard carbon coating precursor can easily enter the pores; therefore, the primary coating layer of the present application can achieve uniform coating at a low coating amount of 2 to 5%.

In any embodiment of the present application, the secondary coating layer is coated on the natural graphite in a mass ratio of 1 to 3%. The secondary coating layer mainly plays a role in coating and reinforcing the primary coating layer, and improves the coating effect. Similarly, the preparation method of the application can adopt lower secondary coating amount to achieve good coating effect.

a. the volume average particle diameter Dv ₅₀ is 6-15 mu m;

optionally, the volume average particle diameter Dv ₅₀ is 8-12 μm;

c. The tap density TD is 0.7-1.1 g/cm ³;

Optionally, the tap density TD is 0.8-1.0 g/cm ³.

It is understood that the volume average particle diameter Dv ₅₀ of natural graphite may be, but is not limited to: 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm. The volume average particle size (Dv ₉₀-Dv ₁₀)/Dv ₅₀ may be, but is not limited to, 1.0, 1.1, 1.2, 1.3, 1.4. Tap density TD may be, but is not limited to, 0.7g/cm ³、0.8g/cm ³、0.9g/cm ³、1.0g/cm ³、1.1g/cm ³.

d. The volume average particle diameter Dv ₅₀ is 7-17 mu m;

Optionally, the volume average particle diameter Dv ₅₀ is 9-13 μm;

f. the tap density TD is 0.7-1.1 g/cm ³;

Optionally, the tap density TD is 0.85-0.95 g/cm ³;

g. BET specific surface area is 1.0-5.0 m ²/g;

Alternatively, the BET specific surface area is 1.5 to 3.5m ²/g.

It can be appreciated that the volume average particle diameter Dv ₅₀ of the anode active material may be, but is not limited to: 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm. Volume average particle size (Dv ₉₀-Dv ₁₀)/Dv ₅₀ may be, but is not limited to, 1.0, 1.1, 1.2, 1.3. Tap density TD may be, but is not limited to, 0.7g/cm ³、0.8g/cm ³、0.9g/cm ³、1.0g/cm ³、1.1g/cm ³. BET specific surface area may be, but is not limited to ：1.0m ²/g、1.4m ²/g、1.8m ²/g、2.0m ²/g、2.4m ²/g、2.8m ²/g、3.0m ²/g、3.4m ²/g、3.8m ²/g、4.0m ²/g、4.4m ²/g、4.8m ²/g、5.0m ²/g.

The secondary battery and the power consumption device according to the present application will be described below with reference to the drawings.

Unless otherwise specified, the components, material types, or contents of the mentioned batteries are applicable to both lithium ion secondary batteries and sodium ion secondary batteries.

In one embodiment of the present application, a secondary battery is provided.

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. During the charge and discharge of the battery, active ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The isolating film is arranged between the positive pole piece and the negative pole piece, and mainly plays a role in preventing the positive pole piece and the negative pole piece from being short-circuited, and meanwhile ions can pass through the isolating film.

Positive electrode plate

The positive electrode plate comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode film layer comprises the positive electrode active material of the first aspect of the application.

As an example, the positive electrode current collector has two surfaces opposing in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two surfaces opposing the positive electrode current collector.

In some embodiments, the positive current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base layer. The composite current collector may be formed by forming a metal material on a polymeric material substrate. Wherein the metal material includes, but is not limited to, aluminum alloy, nickel alloy, titanium alloy, silver alloy, and the like. Polymeric substrates (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.)

In some embodiments, the positive electrode active material may comprise a positive electrode active material for a battery as known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more. Wherein, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (e.g., liCoO ₂), lithium nickel oxide (e.g., liNiO ₂), lithium manganese oxide (e.g., liMnO ₂、LiMn ₂O ₄), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi _1/3Co _1/3Mn _1/3O ₂ (which may also be abbreviated as NCM ₃₃₃)、LiNi _0.5Co _0.2Mn _0.3O ₂ (which may also be abbreviated as NCM ₅₂₃)、LiNi _0.5Co _0.25Mn _0.25O ₂ (which may also be abbreviated as NCM ₂₁₁)、LiNi _0.6Co _0.2Mn _0.2O ₂ (which may also be abbreviated as NCM ₆₂₂)、LiNi _0.8Co _0.1Mn _0.1O ₂ (which may also be abbreviated as NCM ₈₁₁)), lithium nickel manganese oxide (which may also be abbreviated as NCM ₃₃₃)、LiNi _0.5Co _0.2Mn _0.3O ₂ (which may also be abbreviated as NCM 42 examples of the olivine structured lithium-containing phosphate may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (which may also be abbreviated as LFP)), a composite of lithium iron phosphate and carbon, a composite of lithium manganese phosphate (such as LiMnPO ₄), a composite of lithium manganese phosphate and carbon, a composite of lithium manganese phosphate, lithium iron phosphate, and a composite of lithium manganese phosphate and carbon.

As an example, the positive electrode active material of the sodium ion secondary battery may include at least one of the following materials: at least one of sodium transition metal oxide, polyanion compound and Prussian blue compound. However, the present application is not limited to these materials, and other conventionally known materials that can be used as a positive electrode active material of a sodium ion battery may be used.

As an alternative embodiment of the present application, the transition metal in the sodium transition metal oxide may be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce. The sodium transition metal oxide is Na _xMO ₂, wherein M is one or more of Ti, V, mn, co, ni, fe, cr and Cu, and x is more than 0 and less than or equal to 1.

As an alternative embodiment of the present application, the polyanion compound may be a compound having sodium ion, transition metal ion and tetrahedral type (YO ₄) ^n- anion unit, the transition metal may be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce, Y may be at least one of P, S and Si, and n represents (YO ₄) ^n- valence state).

The polyanionic compound may be a compound having a sodium ion, a transition metal ion, a tetrahedral type (YO ₄) ^n- anion unit and a halogen anion), wherein the transition metal may be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce, Y may be at least one of P, S and Si, and n represents (YO ₄) ^n- valence state, and the halogen may be at least one of F, cl and Br.

The polyanionic compound may also be a compound of the type having sodium ions, tetrahedral (YO ₄) ^n- anion units, polyhedral units (ZO _y) ^m+ and optionally halogen anions. Y may be at least one of P, S and Si, n represents (YO ₄) ^n- valence; Z represents transition metal, at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce), m represents (ZO _y) ^m+ valence; halogen may be at least one of F, cl and Br).

The polyanion compound is at least one of NaFePO ₄、Na ₃V ₂(PO4) ₃ (sodium vanadium phosphate, NVP for short), na ₄Fe ₃(PO ₄) ₂(P ₂O ₇), naM 'PO4F (M' is one or more of V, fe, mn and Ni) and Na ₃(VO _y) ₂(PO ₄) ₂F _3-2y (y is more than or equal to 0 and less than or equal to 1).

Prussian blue compounds may be a class of compounds having sodium ions, transition metal ions, and cyanide ions (CN ^-). The transition metal may be at least one of Mn, fe, ni, co, cr, cu, ti, zn, V, zr and Ce. Prussian blue compounds are, for example, na _aMe _bMe' _c(CN) ₆, where Me and Me' are each independently at least one of Ni, cu, fe, mn, co and Zn, 0< a.ltoreq.2, 0< b < 1, 0< c < 1.

The weight ratio of the positive electrode active material in the positive electrode film layer is 80-100 wt%, based on the total weight of the positive electrode film layer.

In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluoroacrylate resin. The weight ratio of the binder in the positive electrode film layer is 0-20% by weight based on the total weight of the positive electrode film layer.

In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The weight ratio of the conductive agent in the positive electrode film layer is 0-20% by weight based on the total weight of the positive electrode film layer.

In some embodiments, the positive electrode sheet may be prepared by: dispersing the components for preparing the positive electrode plate, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (such as N-methyl pyrrolidone) to form positive electrode slurry, wherein the solid content of the positive electrode slurry is 40-80 wt%, the viscosity of the positive electrode slurry at room temperature is adjusted to 5000-25000 mPa.s, the positive electrode slurry is coated on the surface of a positive electrode current collector, and the positive electrode slurry is formed after being dried and cold-pressed by a cold rolling mill; the unit surface density of the positive electrode powder coating is 150-350 mg/m ², the compacted density of the positive electrode plate is 3.0-3.6 g/cm ³, and the compacted density of the positive electrode plate is 3.3-3.5 g/cm ³.

The calculation formula of the compaction density is as follows:

compacted density = coated area density/(post-extrusion pole piece thickness-current collector thickness).

Negative pole piece

The negative electrode plate comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises a negative electrode active material.

As an example, the anode current collector has two surfaces opposing in its own thickness direction, and the anode film layer is provided on either one or both of the two surfaces opposing the anode current collector.

In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base material. The composite current collector may be formed by forming a metal material on a polymeric material substrate. The metal material includes, but is not limited to, copper alloy, nickel alloy, titanium alloy, silver alloy, etc., and the polymer material substrate includes, but is not limited to, polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

In some embodiments, the negative electrode active material is a negative electrode active material according to the present application described above, or a negative electrode active material prepared by the above-described preparation method according to the present application.

In some embodiments, the negative electrode film layer further optionally includes a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The weight ratio of the binder in the negative electrode film layer is 0 to 30% by weight based on the total weight of the negative electrode film layer.

In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent is at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. The weight ratio of the conductive agent in the negative electrode film layer is 0-20% by weight based on the total weight of the negative electrode film layer.

In some embodiments, the negative electrode film layer may optionally further include other adjuvants, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like. The weight ratio of the other auxiliary agents in the negative electrode film layer is 0-15% by weight based on the total weight of the negative electrode film layer.

In some embodiments, the negative electrode sheet may be prepared by: dispersing the components for preparing the negative electrode plate, such as the negative electrode active material, the conductive agent, the binder and any other components, in a solvent (such as deionized water) to form a negative electrode slurry, wherein the solid content of the negative electrode slurry is 30-70wt%, and the viscosity of the negative electrode slurry at room temperature is adjusted to 2000-10000 mPa.s; and (3) coating the obtained negative electrode slurry on a negative electrode current collector, and performing a drying procedure, cold pressing, such as a pair roller, to obtain a negative electrode plate. The unit area density of the negative electrode powder coating is 75-220mg/m ², and the compacted density of the negative electrode plate is 1.2-2.0g/m ³.

Electrolyte composition

The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The application is not particularly limited in the kind of electrolyte, and may be selected according to the need. For example, the electrolyte may be liquid, gel, or all solid.

In some embodiments, the electrolyte is an electrolyte. The electrolyte includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF ₆), lithium tetrafluoroborate (LiBF ₄), lithium perchlorate (LiClO ₄), lithium hexafluoroarsenate (LiAsF ₆), lithium bis-fluorosulfonimide (LiFSI), lithium bis-trifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalato borate (lipfob), lithium dioxaato borate (LiBOB), lithium difluorophosphate (LiPO ₂F ₂), lithium difluorodioxaato phosphate (LiDFOP), and lithium tetrafluorooxalato phosphate (LiTFOP). The concentration of the electrolyte salt is usually 0.5 to 5mol/L.

In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene Carbonate (EC), propylene Carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethylene Propyl Carbonate (EPC), butylene Carbonate (BC), methyl Formate (MF), methyl Acetate (MA), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), 1, 4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, and the like.

Isolation film

In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known porous separator having good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolating film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some embodiments, the thickness of the separator is 6 to 40 μm, optionally 12 to 20 μm.

In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte described above.

In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The exterior package of the secondary battery may also be a pouch type pouch, for example. The material of the flexible bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The shape of the secondary battery is not particularly limited in the present application, and may be cylindrical, square, or any other shape. For example, fig. 2 is a secondary battery 5 of a square structure as one example.

In some embodiments, referring to fig. 3, the outer package may include a housing 51 and a cover 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate enclose a receiving chamber. The housing 51 has an opening communicating with the accommodation chamber, and the cover plate 53 can be provided to cover the opening to close the accommodation chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is enclosed in the accommodating chamber. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art may select according to specific practical requirements.

In some embodiments, the secondary batteries 5 may be assembled into a battery module, and the number of the secondary batteries 5 included in the battery module may be one or more, and a specific number may be selected by one skilled in the art according to the application and capacity of the battery module.

In the battery module, the plurality of secondary batteries 5 may be arranged in order along the longitudinal direction of the battery module. Of course, the arrangement may be performed in any other way. The plurality of secondary batteries 5 may be further fixed by fasteners.

Alternatively, the battery module may further include a case having an accommodating space in which the plurality of secondary batteries 5 are accommodated.

In some embodiments, the above battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and a specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

A battery case and a plurality of battery modules disposed in the battery case may be included in the battery pack. The battery box comprises an upper box body and a lower box body, wherein the upper box body can be covered on the lower box body, and a closed space for accommodating the battery module is formed. The plurality of battery modules may be arranged in the battery case in any manner.

In addition, the application also provides an electric device which comprises at least one of the secondary battery, the battery module or the battery pack. The secondary battery, the battery module, or the battery pack may be used as a power source of the power consumption device, and may also be used as an energy storage unit of the power consumption device. The power utilization device may include mobile devices (e.g., cell phones, notebook computers, etc.), electric vehicles (e.g., electric-only vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

As the electricity consumption device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirements thereof.

Fig. 4 is an electrical device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or the like. In order to meet the high power and high energy density requirements of the secondary battery by the power consumption device, a battery pack or a battery module may be employed.

As another example, the device may be a cell phone, tablet computer, notebook computer, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.

Examples

In order to make the technical problems, technical schemes and beneficial effects solved by the application more clear, the application will be further described in detail below with reference to the embodiments and the accompanying drawings. It will be apparent that the described embodiments are only some, but not all, embodiments of the application. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the application, its application, or uses. All other embodiments, which can be made by a person skilled in the art based on the embodiments of the application without any inventive effort, are intended to fall within the scope of the application.

The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

1. Preparation example

1. Preparation of negative electrode active material

Preparation example 1

(1) Roasting natural graphite green pellets with the volume average particle diameter Dv ₅₀ of 10 mu m for 3 hours at the temperature of 200 ℃ under the vacuum degree of 0.1 atmosphere;

(2) Transferring the roasted natural graphite from the roasting device to a vacuum coating kettle with a first liquid hard carbon coating precursor inside through a sealing pipeline, and vacuumizing at 180 ℃ for continuous stirring for 4 hours; wherein the mass fraction of the resin in the first liquid hard carbon coating precursor is 50%;

(3) Collecting natural graphite coated with a first liquid hard carbon coating precursor, presintering for 1h in a nitrogen atmosphere at 500 ℃ to form a primary coating layer filling the pores of the natural graphite; the coating mass ratio of the primary coating layer is 3%;

(4) Roasting the natural graphite with the primary coating layer for 1h at 200 ℃ under the vacuum degree of 0.1 atmosphere;

(5) Transferring the roasted natural graphite from the roasting device to a vacuum coating kettle with a second liquid hard carbon coating precursor (20%) inside through a sealing pipeline, and continuously stirring for 2 hours at 120 ℃ in a vacuumizing mode; wherein the mass fraction of the resin in the second liquid hard carbon coating precursor is 20%;

(6) Collecting natural graphite coated with a second liquid hard carbon coating precursor, and carbonizing for 6 hours in a nitrogen atmosphere at 1100 ℃ to form a thin and uniform secondary coating layer; the coating mass ratio of the secondary coating layer is 2%; a negative electrode active material having a primary coating layer and a secondary coating layer was obtained, and a scanning electron microscope image of the negative electrode active material was shown in fig. 1.

Preparation example 2:

This preparation example was substantially the same as preparation example 1 except that the temperature of carbonization in step (6) was 1200 ℃.

Preparation example 3:

This preparation example was substantially the same as preparation example 1 except that the carbonization temperature in step (6) was 1300 ℃.

Preparation example 4:

This production example was substantially the same as production example 1 except that the time of the carbonization treatment in step (6) was 7 hours.

Preparation example 5:

This production example was substantially the same as production example 1 except that the time of the carbonization treatment in step (6) was 5 hours.

Preparation example 6:

this production example was substantially the same as production example 1 except that the volume average particle diameter Dv ₅₀ of the natural graphite green pellets in step (1) was 12 μm.

Preparation example 7:

This production example was substantially the same as production example 1 except that the vacuum degree was adjusted to 0.15 atm in step (1).

Preparation example 8:

This production example was substantially the same as production example 1 except that the baking treatment temperature was adjusted to 250℃in step (1).

Preparation example 9:

This production example was substantially the same as production example 1 except that the calcination treatment time was adjusted to 5 hours in step (1).

Preparation example 10:

This preparation example was substantially the same as preparation example 1 except that the vacuum-drawn continuous stirring temperature was adjusted to 200℃in step (2).

Preparation example 11:

This preparation example is substantially the same as preparation example 1 except that the duration of the stirring under vacuum in step (2) was adjusted to 6 hours.

Preparation example 12:

This preparation example is substantially the same as preparation example 1 except that the mass fraction of the resin in the first liquid hard carbon-coated precursor selected in step (2) is adjusted to 70%.

Preparation example 13:

This preparation example is substantially the same as preparation example 1 except that the burn-in treatment temperature is adjusted to 600 c in step (3).

Preparation example 14:

this preparation example is substantially the same as preparation example 1 except that the burn-in treatment time is adjusted to 2 hours in step (3).

Preparation example 15:

This production example was substantially the same as production example 1 except that the coating mass ratio of the primary coating layer in step (3) was 4%.

Preparation example 16:

this production example is substantially the same as production example 1 except that the degree of vacuum of the natural graphite firing having the primary coating layer is adjusted to 0.15 atm in step (4).

Preparation example 17:

This production example is substantially the same as production example 1 except that the natural graphite having a primary coating layer is calcined for 1.5 hours in step (4).

Preparation example 18:

This production example is substantially the same as production example 1 except that the natural graphite having a primary coating layer is calcined for 2 hours in step (4).

Preparation example 19:

This preparation example was substantially the same as preparation example 1 except that the temperature of the vacuum-drawn continuous agitation in step (5) was adjusted to 150 ℃.

Preparation example 20:

This preparation example was substantially the same as preparation example 1 except that the time of the evacuation and continuous stirring in step (5) was adjusted to 2.5 hours.

Preparation example 21:

This preparation example is substantially the same as preparation example 1 except that the mass fraction of the resin in the second liquid hard carbon-coated precursor selected in step (5) is adjusted to 10%.

Preparation example 22:

This production example was substantially the same as production example 1 except that the conditions of the negative pressure firing in step (1) were a firing temperature of 300℃and a firing time of 8 hours.

Comparative example 1 was prepared:

This comparative preparation example is substantially the same as that of preparation example 1 except that the volume average particle diameter Dv ₅₀ of the natural graphite in step (1) is 18 μm.

Comparative example 2 was prepared:

This comparative preparation example is substantially the same as preparation example 1 except that the natural graphite green pellets are not subjected to the negative pressure calcination treatment in step (1), but are directly coated with the first liquid hard carbon-coated precursor.

2. Negative electrode active material Performance test

2.1 Gram Capacity test of Material

Uniformly mixing the prepared anode active material, a conductive agent Super P and a binder (PVDF) with a solvent NMP (N-methylpyrrolidone) according to a mass ratio of 91.6:1.8:6.6 to prepare slurry; coating the prepared slurry on a copper foil current collector, drying in an oven, and cold pressing for standby, wherein the compacting range is as follows: 1.4-1.6 g/cm ³; taking a metal lithium sheet as a counter electrode; polyethylene (PE) film is used as the isolating film; ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed according to a volume ratio of 1:1:1, and then LiPF ₆ is uniformly dissolved in the solution to obtain an electrolyte.

Wherein, the concentration of LiPF ₆ is 1mol/L; the above parts were assembled into CR 2430-type button cells in an argon-protected glove box. After the obtained button cell is stood for 12 hours, constant current discharge is carried out to 0.005V at the current of 0.05C, the button cell is stood for 10 minutes, constant current discharge is carried out to 0.005V at the current of 50 mu A, the button cell is stood for 10 minutes, constant current discharge is carried out to 0.005V at the current of 10 mu A, and the sum of three discharge capacities is the discharge capacity; then, constant current charging was performed to 2.000V at a current of 0.1C, and the charging capacity was recorded. The ratio of the charge capacity to the mass of the negative electrode active material is the gram capacity of the prepared negative electrode active material, and the ratio of the charge capacity to the discharge capacity is the first coulombic efficiency.

2.2 Volume average particle diameter Dv ₅₀ test

And adding 0.1g of the prepared negative electrode active material into a clean beaker filled with 20mL of water, carrying out ultrasonic treatment for 5min, testing the background after the parameters of a Markov 3000 laser particle sizer device are adjusted, and then adding a sample preparation sample into the device. After the shading degree ranges from 8% to 12%, the test is started. The particle size distribution is tested according to diffraction or scattering phenomena generated when laser irradiates particles, the scattering light angle caused by large particles is small, the smaller particles are larger, light rings with different radiuses are formed on a focal plane through a rich lens, the light rings with large radiuses correspond to smaller particle sizes, the small light rings correspond to large particle sizes, the quantity information of the particle size particles can be analyzed through signing of light of the light rings, and the particle size distribution is obtained through computer processing after the information is converted into an electric signal through a photoelectric receiver.

Meaning of Dv ₅₀ data: the particle diameter of 50% of the total volume is larger than this value, and the particle diameter of 50% of the total volume is smaller than this value. Dv ₅₀ represents the median particle size of the powder.

2.3 Particle size distribution Width test

The particle size distribution width= (Dv ₉₀-Dv ₁₀)/Dv ₅₀; volume distribution data obtained by laser particle size test is obtained by calculation through a formula.

The different product parameters of the negative electrode active materials of preparation examples 1 to 22 and the negative electrode active materials of preparation comparative examples 1 to 2 are detailed in table 1.

TABLE 1 preparation of the negative electrode active materials of examples 1 to 22 and preparation of different product parameters of the negative electrode active materials of comparative examples 1 to 2

2. Application examples

Example 1

(1) Preparation of positive electrode plate

Dispersing an anode active material, conductive carbon black SP and a binder PVDF into a solvent NMP according to a weight ratio of 98:1:1, and uniformly mixing to obtain anode slurry; and uniformly coating the anode slurry on an anode current collector aluminum foil, and drying and cold pressing to obtain an anode plate, wherein the coating amount of the anode plate per unit area is 0.27g/1540.25mm ².

(2) Preparation of negative electrode plate

Mixing the anode active material prepared in the preparation example 1, sodium carboxymethyl cellulose serving as a thickener, styrene-butadiene rubber serving as an adhesive and acetylene black serving as a conductive agent according to a mass ratio of 97:1:1:1, adding deionized water, and obtaining anode slurry under the action of a vacuum stirrer; uniformly coating the negative electrode slurry on a copper foil; and (3) airing the copper foil at room temperature, transferring to a baking oven at 120 ℃ for drying for 1h, and then carrying out cold pressing and slitting to obtain the negative plate, wherein the coating amount per unit area is 0.17g/1540.25mm ².

(3) Isolation film

A polypropylene separator film of 12 μm thickness was selected.

(4) Preparation of electrolyte

The organic solvent is a mixed solution containing Ethylene Carbonate (EC), ethylmethyl carbonate (EMC) and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC and DEC is 20:20:60. In an argon atmosphere glove box with a water content of <10ppm, the fully dried lithium salt LiPF ₆ was dissolved in an organic solvent and mixed uniformly to obtain an electrolyte. Wherein the concentration of the lithium salt is 1mol/L.

(5) Preparation of a Battery

And sequentially stacking the positive plate, the isolating film and the negative plate, enabling the isolating film to be positioned between the positive plate and the negative plate to play a role of isolation, winding the isolating film into a square bare cell, then loading the bare cell into an aluminum plastic film, baking at 80 ℃ to remove water, injecting 10g of corresponding nonaqueous electrolyte, sealing, and obtaining a finished battery with the capacity of 4000mAh after the working procedures of standing, hot and cold pressing, formation, clamping, capacity division and the like.

The secondary batteries of examples 2 to 22 and the secondary batteries of comparative examples 1 to 2 were similar to the secondary battery preparation method of example 1, but the negative electrode active materials of the corresponding preparation examples were used.

3. Battery performance test

1. Days of storage test

And standing the soft package batteries prepared in the examples and the comparative examples for 12h at 25 ℃, then performing constant current discharge to 2.8V at a current of 1C, standing for 5min, performing constant current charge to 4.2V at a current of 0.33C, performing constant voltage charge to 0.05C, standing for 5min, and performing constant current discharge to 2.8V at a current of 1C to obtain the measured initial capacity C0 of the battery. After 10min of standing, the battery was charged again to 100% SOC (State of Charge) according to the above charging procedure, and then stored in a 60℃incubator until the capacity retention rate (Cn/C0.times.100%) was less than or equal to 80%, and the number of days of storage was recorded. The more days of storage represents the better storage life of the battery.

2. Quick charge performance test

The secondary batteries prepared in the examples and the comparative examples are charged to 4.25V at constant current of 1C (namely, the current value of the theoretical capacity is completely discharged in1 h), then charged to 0.05C at constant voltage, kept stand for 5min, then charged to 4.25V at constant current of 0.5C, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, 4.5C0 or 0V negative electrode cut-off potential (based on the previous arrival), after each charge is completed, the corresponding negative electrode potential is required to be discharged to 2.8V by 1C0, the charging to 10%, 20%, 30% … …% SOC and the charging state under different charging rates is recorded, a rate-negative electrode potential curve under different SOC states is drawn, the charging window under different SOC states is drawn, the corresponding critical rate C20% SOC, C30% SOC, C40% SOC, C50% SOC, C60% SOC, C70% SOC and C80% SOC are recorded, and the charging time of the following equation (60/C20% SOC is 60+C 60+30% SOC) is calculated to obtain the charging time of 10+60+60+SOC (60+60+60+60% C60+60% SOC/60+60+60% C) from the following equation). The shorter this time, the more excellent the quick charge performance of the battery.

3. Cycle performance test

And standing the soft package batteries prepared in the examples and the comparative examples for 12h at 25 ℃, then performing constant current discharge to 2.8V at a current of 1C, standing for 5min, performing constant current charge to 4.2V at a current of 0.33C, performing constant voltage charge to 0.05C, standing for 5min, and performing constant current discharge to 2.8V at a current of 1C to obtain the measured initial capacity C0 of the battery. Subsequently, the discharge capacity Cn after each cycle was recorded until the cycle capacity retention rate (Cn/C0.times.100%) was 80% or less, and the number of cycles was recorded, in accordance with the charge of 2C to the cutoff voltage, the discharge of 1C to the cutoff voltage. The more turns represents the better cycle life of the battery.

4. Test results for examples and comparative examples

Batteries of each example and comparative example were prepared separately according to the above-described methods, and each performance parameter was measured, and the results are shown in table 2 below.

Table 2 performance parameters of the batteries of each example and comparative example

From the above examples and comparative examples, it can be seen that: compared with example 1, the average particle size of the natural graphite green pellets in step (1) was adjusted to Dv ₅₀ to 12 μm (example 6) to improve the storage and cycle days of the battery, but deteriorated the kinetic performance thereof; adjusting the average particle diameter of the natural graphite green pellets to Dv ₅₀ of 18 μm (comparative example 1) deteriorates the storage, cycle days, and kinetic properties of the battery; after increasing the first liquid hard carbon coating solids content in step (2) (example 12), the storage, cycling and kinetic performance of the cell are all deteriorated; in the step (1), the negative pressure roasting condition is changed to the roasting temperature of 300 ℃ and the roasting time is 8 hours (example 22), so that the storage, the cycle days and the dynamics performance of the material are all improved; in step (1), unless the first negative pressure firing is performed (comparative example 2), the storage, cycle and kinetic properties of the battery are deteriorated.

The present application is not limited to the above embodiment. The above embodiments are merely examples, and embodiments having substantially the same configuration and the same effects as those of the technical idea within the scope of the present application are included in the technical scope of the present application. Further, various modifications that can be made to the embodiments and other modes of combining some of the constituent elements in the embodiments, which are conceivable to those skilled in the art, are also included in the scope of the present application within the scope not departing from the gist of the present application.

Claims

A method for preparing a negative electrode active material, comprising the steps of:

Carrying out first negative pressure roasting on natural graphite;

Coating a first liquid hard carbon coating precursor on the natural graphite subjected to the first negative pressure roasting, presintering, and forming a primary coating layer; and

And coating a second liquid hard carbon coating precursor on the surface of the primary coating layer, and carbonizing to form a secondary coating layer.
The method according to claim 1, wherein the first negative pressure firing has a vacuum degree of 0 to 0.5 atm, a firing temperature of 120 to 300 ℃ and a firing time of 2 to 8 hours.
The method of claim 1, wherein the coating of the first liquid hard carbon coated precursor on the first negative pressure calcined natural graphite comprises the steps of:

Transferring the natural graphite subjected to the first negative pressure roasting into vacuum coating equipment containing the first liquid hard carbon coating precursor under the vacuum condition, and vacuumizing and stirring for 4-7 h at 120-200 ℃.
The method according to claim 1, wherein the pre-firing temperature is 400-600 ℃ and the pre-firing time is 0.5-2 h.
The method according to any one of claims 1 to 4, further comprising a step of subjecting the natural graphite to a second negative pressure calcination after forming a primary coating layer and before the primary coating layer surface coats a second liquid hard carbon coating precursor.
The method according to claim 5, wherein the second negative pressure firing has a vacuum degree of 0.1 to 0.3 atm, a firing temperature of 100 to 150 ℃ and a firing time of 1 to 3 hours.
The method of claim 5, wherein the coating of the primary coating surface with the second liquid hard carbon coating precursor comprises the steps of:

Transferring the natural graphite subjected to the second negative pressure roasting into vacuum coating equipment filled with the second liquid hard carbon coating precursor under the vacuum condition, and vacuumizing and stirring for 2-4 h at 120-200 ℃.
The preparation method according to any one of claims 1 to 7, wherein the carbonization is performed under an inert gas atmosphere at a temperature of 800 to 1300 ℃ for a time of 4 to 8 hours.
The method according to any one of claims 1 to 7, wherein the first liquid hard carbon-coated precursor includes one or more of a phenolic resin, an epoxy resin, and a petroleum resin, and the mass fraction of the resin in the first liquid hard carbon-coated precursor is 30 to 70%.
The method according to any one of claims 1 to 7, wherein the second liquid hard carbon-coated precursor includes one or more of phenolic resin, epoxy resin, and petroleum resin, and the mass fraction of the resin in the second liquid hard carbon-coated precursor is 10 to 30%.
The production method according to any one of claims 1 to 10, wherein the primary coating layer has a coating mass ratio with respect to the natural graphite of 2to 5%.
The production method according to any one of claims 1 to 10, wherein the coating mass ratio of the secondary coating layer to the natural graphite is 1 to 3%.
The production method according to any one of claims 1 to 12, wherein the natural graphite satisfies at least one of the following conditions a to c before the first negative pressure firing:

a. the volume average particle diameter Dv ₅₀ is 6-15 mu m;

optionally, the volume average particle diameter Dv ₅₀ is 8-12 μm;

b. Volume average particle diameter (Dv ₉₀-Dv ₁₀)/Dv ₅₀ is 1.0 to 1.4;

alternatively, the volume average particle diameter (Dv ₉₀-Dv ₁₀)/Dv ₅₀ is 1.0 to 1.2;

c. The tap density TD is 0.7-1.1 g/cm ³;

Optionally, the tap density TD is 0.8-1.0 g/cm ³.
The production method according to any one of claims 1 to 12, wherein the anode active material satisfies at least one of the following conditions d to g:

d. The volume average particle diameter Dv ₅₀ is 7-17 mu m;

Optionally, the volume average particle diameter Dv ₅₀ is 9-13 μm;

e. Volume average particle diameter (Dv ₉₀-Dv ₁₀)/Dv ₅₀ is 1.0 to 1.3;

alternatively, the volume average particle diameter (Dv ₉₀-Dv ₁₀)/Dv ₅₀ is 1.0 to 1.2;

f. the tap density TD is 0.7-1.1 g/cm ³;

Optionally, the tap density TD is 0.85-0.95 g/cm ³;

g. BET specific surface area is 1.0-5.0 m ²/g;

Alternatively, the BET specific surface area is 1.5 to 3.5m ²/g.
A negative electrode active material, characterized in that the negative electrode active material is produced by the production method of the negative electrode active material according to any one of claims 1 to 14.
A secondary battery comprising the anode active material according to claim 15.
An electric device comprising the secondary battery according to claim 16.