WO2023245659A1

WO2023245659A1 - Positive electrode material and preparation method therefor, secondary battery, and battery module

Info

Publication number: WO2023245659A1
Application number: PCT/CN2022/101270
Authority: WO
Inventors: 朱翠翠; 王少飞; 魏奕民; 李杨; 欧阳楚英
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2022-06-24
Filing date: 2022-06-24
Publication date: 2023-12-28
Also published as: WO2023245912A1

Abstract

The present application relates to a positive electrode material, comprising: a positive electrode active material; a first coating layer, the first coating layer covering the positive electrode active material, and an electrochemical window of the first coating layer being 6.0 V or more; and a second coating layer, the second coating layer covering the first coating layer, and the lithium ion conductivity of the second coating layer being 10-3 S/cm or more. The positive electrode material having a double coating structure of the present application has high electrochemical stability and lithium ion conductivity at a high charging voltage. In addition, the present application further relates to a preparation method for the positive electrode material, a secondary battery, a battery module, a battery pack, and an electrical device.

Description

Cathode material and preparation method thereof, secondary battery, battery module

Technical field

This application belongs to the field of battery technology, and specifically relates to a cathode material and its preparation method, secondary batteries, battery modules, battery packs and electrical devices.

Background technique

With the development of technology, clean energy sources such as batteries are gradually replacing traditional fossil energy sources to provide power for various scenarios. People have put forward higher requirements for the energy density of batteries. Increasing the charging window of the battery to increase the battery charging and discharging capacity has become one of the current breakthroughs. However, higher charging voltages (above 4.6V) pose greater challenges to the electrochemical stability of the cathode material and the lithium ion conduction rate.

Therefore, there is an urgent need to develop a cathode material that is electrochemically stable under high charging voltage and has a high lithium ion conductivity rate.

Contents of the invention

In view of the problems existing in the background technology, this application provides a cathode material that has high electrochemical stability and lithium ion conduction rate under high charging voltage.

The cathode material provided in the first aspect of this application includes: a cathode active material, a first coating layer and a second coating layer. The first coating layer covers the positive electrode active material. The electrochemical window of the first cladding layer is above 6.0V. The second coating layer covers the first coating layer. The lithium ion conductivity of the second coating layer is 10 ^-3 S/cm or more.

In the technical solution of the embodiment of the present application, the cathode active material is double-coated, wherein the electrochemical window of the first coating layer is above 6.0V, which has good stability under high voltage conditions and can protect the cathode. Active material; the second coating layer has high lithium ion conductivity and can achieve high lithium ion conduction rate.

In some embodiments, according to the first aspect, a first example of the first aspect is proposed, the first cladding layer includes Li _a MF _a+b ; the second cladding layer includes Li _a M'C _a+b or Li _a M' _m S _a+b ; where M and M' are each independently Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al , one or more of Ga, In, Nb, Ge and P; a=1-7, b=2-4, m=1-3.

In this design, Li _a MF _a+b has good stability under high voltage conditions and can protect the positive active material; Li _a M'Cl _a+b or Li _a M' _c S _a+b has high lithium ion Conductivity, enabling high lithium ion conduction rates.

In addition, Li _a MF _a+b contains F ions, which can complex transition metal ions in the positive electrode active material, such as Mn, Ni, Fe, etc., to prevent their dissolution and transfer to the negative electrode and damage the reaction interface of the negative electrode, thus improving the Cell cycle stability. Li _a M'Cl _a+b has better moisture stability and can effectively protect Li _a MF _a+b from absorbing moisture in the air and causing irreversible decomposition.

In some embodiments, according to the first aspect, a second example of the first aspect is provided, M and M' are each independently a di, tri or tetravalent cation.

In this design, the ionic radius of di, trivalent or tetravalent cations is smaller, which is more conducive to the formation of a cubic close-packed anion arrangement (CCP), allowing Li ⁺ to carry out 3D migration in three directions, among which trivalent cations are preferred. for divalent and tetravalent cations.

In some embodiments, according to the first aspect, a third example of the first aspect is proposed, M and M' are each independently Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc , one or more of In, Y, Ge and P, optionally one or more of In, Y, Ge and P.

In this design, by further optimizing M and M’, it is more conducive to improving the electrochemical stability of the cathode material under high charging voltage and its lithium ion conduction rate.

In some embodiments, according to the first aspect, a fourth example of the first aspect is provided, Li _a MF _a+b is Li ₃ YF ₆ , and Li _a M'Cl _a+b is Li ₃ InCl ₆ .

In this design, by further optimizing the materials of the first coating layer and the second coating layer, it is more conducive to improving the electrochemical stability of the cathode material under high charging voltage and its lithium ion conduction rate.

In some embodiments, according to the first aspect, a fifth example of the first aspect is proposed, the lithium ion conductivity of the second cladding layer is 10 ^-2 S/cm or more.

In this design, the lithium ion conductivity of the second coating layer is preferably close to the lithium ion conductivity in the electrolyte, which can ensure that lithium ions in the electrolyte can quickly migrate between the solid and liquid phases and avoid lithium ions at the interface. The accumulation of ions causes uneven local charge distribution.

In some embodiments, according to the first aspect, a sixth example of the first aspect is proposed, the thickness of the first cladding layer is 3-10 nm, optionally 3-5 nm; and/or the thickness of the second cladding layer 1-5nm, optional 1-2nm.

In this design, within this thickness range, the first coating layer has good stability under high voltage conditions and can protect the positive active material while preventing transition metal ions in the positive active material from dissolving and transferring to the negative electrode and damaging the negative electrode. reaction interface, thereby improving the cycle stability of the battery core. In addition, within this thickness range, the second coating layer can effectively protect the first coating layer from absorbing moisture in the air and causing irreversible decomposition.

In some embodiments, according to the first aspect, a seventh example of the first aspect is proposed, the total thickness of the first cladding layer and the second cladding layer is less than 10 nm.

In this design, the total thickness of the first coating layer and the second coating layer is within the above range, which can protect the cathode material, while ensuring the conductivity of the cathode active material, avoiding increasing ohmic impedance and increasing the battery core's Internal resistance.

In some embodiments, according to the first aspect, an eighth example of the first aspect is proposed, the positive active material is one or more of LiFePO ₄ , LiCoO ₂ , LiMnO ₄ and _LiNix Co _y M _1-xy O ₂ species, where M is one or more of Mn, Al, Mg, Sn, Y and Cr, 0≤x<1, 0≤y≤1, and x+y≤1.

In this design, the above-mentioned positive active material can be used to optimize the energy density and cycle performance of the battery core.

In some embodiments, according to the first aspect, a ninth example of the first aspect is proposed, the positive active material contains at least one of Mn and Co, and the thickness of the first coating layer increases with the increase of the Mn content and the Co content. increase.

Since Mn and Co are easier to dissolve than other metal elements, and the amount of dissolution is higher, it is necessary to use a thicker first coating layer for coating to prevent Mn and Co from entering the electrolyte and negative electrode after dissolution.

The second aspect of this application provides a method for preparing a cathode material, including:

Coating the surface of the positive electrode active material to form a first coating layer; and

Coating the surface of the first coating layer to form a second coating layer to obtain a positive electrode material;

Wherein, the electrochemical window of the first cladding layer is above 6.0V, and the lithium ion conductivity of the second cladding layer is above 10 ^-3 S/cm.

In the technical solution of the embodiment of the present application, the cathode material can be obtained by coating twice. The preparation process is simple and highly repeatable, which is conducive to industrial large-scale production.

In some embodiments, according to the second aspect, the first example of the second aspect is provided, and the atomic layer deposition method is used for coating.

In this design, when using the atomic layer deposition method for coating, the coating thickness can be flexibly controlled by controlling the number of coating turns. In particular, the coating thickness can be precisely controlled at the nanometer level, effectively improving the cathode activity caused by coating. A condition in which the resistance of a substance increases, reducing the ohmic impedance of the positive electrode. In addition, during the coating process using atomic layer deposition, the precursor gas is fully in contact with the solid, which can achieve more comprehensive and uniform coating. Compared with the method in the prior art of ball milling to pulverize material particles and then coating them, the method has the advantages of small coating thickness and uniform and sufficient coating.

In some embodiments, according to the second aspect, a second example of the second aspect is provided, the first cladding layer is Li _a MF _a+b . The first cladding layer is deposited using RLi, R'F _c and R ₁ M as precursors. The deposition temperature is 200-300°C. Among them, RLi is selected from one or more of lithium halide, alkyl lithium, lithium carboxylate, lithium alkoxide, and ester lithium, and R'F _c is a fluorinated alkane, a fluorinated carboxylic acid, a fluorinated alcohol, and a fluorinated ester. One or more of them, RLi, R'F _c boiling point is between 70 and 300℃. R ₁ M is selected from one or more metal alkyls, metal carboxylates, metal alcohols, and ester metals, and has a boiling point between 70 and 300°C. M is selected from one or more of Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb and Ge, a=1-7, b=2-4, and c is an integer from 1 to 10.

In this design, by optimizing the precursor and deposition temperature, it is more conducive to forming the first cladding layer comprehensively and uniformly.

In some embodiments, according to the second aspect, a third example of the second aspect is proposed, the molar ratio of RLi, R′F _c and R ₁ M is (a*c):(a+b):c.

In this design, by optimizing the molar ratio of RLi, R'F _c and R ₁ M, the first coating layer can cover the cathode active material more uniformly and comprehensively, which is beneficial to improving the electrical performance of the cathode material under high charging voltage. Chemical stability.

In some embodiments, according to the second aspect, a fourth example of the second aspect is proposed, the second cladding layer is Li _a M'Cl _a+b ; with RLi, R'Cl _c and R ₂ M' as precursors The second coating layer is deposited by volume injection, and the deposition temperature is 200-300°C; wherein, RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide, and ester lithium, and R'Cl _c is chlorine One or more of alkanes, chlorocarboxylic acids, chloroalcohols and chloroesters, RLi, R'Cl _c boiling point is between 70 and 300°C, R ₂ M' is selected from alkyl metals, carboxylic acids One or more metals, alcohol metals, and ester metals, with a boiling point between 70 and 300°C; M' is selected from Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu , one or more of Lu, Yb, Ti, Zr, Al, Ga, In, Nb and Ge, a=1-7, b=2-4, c is an integer from 1 to 10. Alternatively, the second cladding layer is Li _a M' _m S _a+b , and the second cladding layer is deposited using RLi, R'S and R ₂ M' as precursors, and the deposition temperature is 200-300°C; where, RLi Selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide and ester lithium, R'S is one or more of thioalkane, thiocarboxylic acid, thiol, thioester and sulfonate ester or There are many kinds, the boiling point of RLi and R'S is between 70~300℃, _R2M ' is phosphorous acid, the boiling point is between 70~300℃; M' is P, a=1-7, b=2-5 , m is an integer from 1 to 5.

In this design, by optimizing the precursor and deposition temperature, it is more conducive to the comprehensive and uniform formation of the second cladding layer.

In some embodiments, according to the second aspect, a fifth example of the second aspect is proposed, the molar ratio of RLi, R'Cl _c and R ₂ M' is (a*c):(a+b):c. The molar ratio of RLi, R'S and R ₂ M' is a:(a+b):m.

In this design, by optimizing the molar ratio of RLi, R'Cl _c and R ₂ M' and the molar ratio of RLi, R'S and R ₂ M', the second coating layer can be made to cover the first coating more uniformly and comprehensively. layer, which is conducive to improving the lithium ion conduction rate of the cathode material and protecting the first coating layer from absorbing moisture in the air and causing irreversible decomposition.

In some embodiments, according to the second aspect, a sixth example of the second aspect is proposed. After forming the second coating layer, the cathode material is calcined in a protective atmosphere.

In this design, calcination after coating has the following advantages: (1) It can improve the crystallinity of the first coating layer and the second coating layer to form a cubic close-packed anion arrangement composition (CCP), which helps to form 3D The lithium ion transmission channel improves the rate performance and cycle stability of the cell; (2) It helps to carry out replacement at the junction of the positive active material and the first coating layer and the junction of the first coating layer and the second coating layer. Good atoms fuse to form a transition layer, which reduces the grain boundary resistance caused by the coating interface and reduces the impedance of the battery core.

In some embodiments, according to the second aspect, a seventh example of the second aspect is proposed, the calcination temperature is 150-500°C, optionally 150-300°C; the calcination time is 1-24h, optionally 4-20h .

In this design, optimizing the calcination temperature and calcination time is conducive to improving the calcination effect, which is conducive to improving the crystallinity of the first coating layer and the second coating layer, and is conducive to the interaction between the extremely active material and the first coating layer. The junction and the junction between the first cladding layer and the second cladding layer form a transition layer.

A third aspect of the application provides a secondary battery, including the cathode material described in the first aspect of the application or the cathode material obtained according to the preparation method described in the second aspect of the application.

In the technical solutions of the embodiments of the present application, since the positive electrode material of the first aspect of the present application or the positive electrode material prepared according to the method of the second aspect of the present application is used, the secondary battery of the present application also has high charging voltage. electrochemical stability and lithium ion conduction rate.

A fourth aspect of the application provides a battery module, including the secondary battery described in the third aspect of the application.

In the technical solutions of the embodiments of the present application, since the positive electrode material of the first aspect of the present application or the positive electrode material prepared according to the method of the second aspect of the present application is used, the battery module of the present application has high electric capacity under high charging voltage. Chemical stability and lithium ion conduction rate.

A fifth aspect of this application provides a battery pack, including the battery module described in the fourth aspect of this application.

In the technical solutions of the embodiments of the present application, since the positive electrode material of the first aspect of the present application or the positive electrode material prepared according to the method of the second aspect of the present application is used, the battery pack of the present application has high electric capacity under high charging voltage. Chemical stability and lithium ion conduction rate.

A sixth aspect of this application provides an electrical device, including at least one of the secondary battery described in the third aspect of this application, the battery module described in the fourth aspect of this application, and the battery pack described in the fifth aspect of this application. A sort of.

In the technical solutions of the embodiments of the present application, since the positive electrode material of the first aspect of the present application or the positive electrode material prepared according to the method of the second aspect of the present application is used, the electrical device of the present application has high charging voltage under high charging voltage. Electrochemical stability and lithium ion conduction rate.

The above description is only an overview of the technical solutions of the present application. In order to have a clearer understanding of the technical means of the present application, they can be implemented according to the contents of the description, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, Specific embodiments of the present application are listed below.

Description of the drawings

In order to explain the technical solutions of the embodiments of the present invention more clearly, the drawings required to be used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. Those of ordinary skill in the art can also obtain other drawings based on the drawings without exerting creative efforts.

Figure 1 is an AC impedance spectrum of a symmetrical battery composed of positive electrode plates prepared in Examples and Comparative Examples of the present invention.

FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application.

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

Figure 4 is a schematic diagram of a battery module according to an embodiment of the present application.

Figure 5 is a schematic diagram of a battery pack according to an embodiment of the present application.

FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5 .

FIG. 7 is a schematic diagram of a power consumption device using a secondary battery as a power source according to an embodiment of the present application.

Explanation of reference symbols:

1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 top cover assembly.

Detailed ways

In order to make the invention purpose, technical solutions and beneficial technical effects of the present application clearer, the present application will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are only for explaining the present application and are not intended to limit the present application.

For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range. In addition, although not explicitly stated, every point or individual value between the endpoints of a range is included in the range. Thus, each point or single value may serve as a lower or upper limit on its own in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" are inclusive, and "multiple" in "one or more" means two or more (including two) .

The above summary of the present application is not intended to describe each disclosed embodiment or every implementation in the present application. The following description illustrates exemplary embodiments in more detail. At various points throughout this application, guidance is provided through a series of examples, which may be used in various combinations. In each instance, the enumerations are representative only and should not be construed as exhaustive.

With the development of technology, people have put forward higher requirements for the energy density of batteries. Increasing the battery's charge and discharge capacity by increasing the battery's charging window has become one of the current breakthroughs. However, during the charging process, since the lithium ions in the cathode material are continuously released, when the charging voltage rises to a certain value, it will cause irreversible transformation or even collapse of the crystal structure, resulting in the electrochemical stability of the cathode material and the lithium ion conduction rate. Reduce and deteriorate battery performance. Therefore, there is an urgent need to develop a cathode material that is electrochemically stable under high charging voltage and has high lithium ion conduction rate.

The inventor found that coating the cathode material with lithium-containing halide Li _a MX _b (where M is a metal ion and The improvement in stability and lithium ion conduction rate is not very satisfactory.

After in-depth research, the inventor designed a cathode material that significantly improved the electrochemical stability of the cathode active material under high charging voltage by sequentially coating the surface of the cathode active material with a first coating layer and a second coating layer. and lithium ion conductivity rate. Among them, the electrochemical window of the first coating layer is above 6.0V, which has good stability under high voltage conditions and can protect the positive active material; the lithium ion conductivity of the second coating layer is 10 ^-3 S/ cm and above, it has high lithium ion conductivity and can achieve high lithium ion conduction rate.

The technical solutions described in the embodiments of this application are applicable to cathode materials, and are also applicable to the preparation process of cathode materials, secondary batteries using cathode materials, battery modules using secondary batteries, battery packs using battery modules, and secondary batteries. A power consumption device for at least one of a battery module and a battery pack.

In a first aspect, according to some embodiments of the present application, the present application provides a cathode material, including a cathode active material, a first coating layer and a second coating layer. The first coating layer covers the positive electrode active material. The electrochemical window of the first cladding layer is above 6.0V. The second coating layer covers the first coating layer. The lithium ion conductivity of the second coating layer is 10 ^-3 S/cm or more.

In the technical solution of the embodiment of the present application, the positive electrode active material is double-layer coated, wherein the electrochemical window of the first coating layer is above 6.0V, which has good stability under high voltage conditions and can protect Positive active material; the second coating layer has high lithium ion conductivity and can achieve high lithium ion conductivity rate.

In some specific embodiments, the electrochemical window of the first cladding layer may be, for example, 6.0V, 6.5V, 7.0V, 7.5V, 8.0V, 8.5V, 9.0V, 9.5V, 10.0V or 10.5V, etc.

In some embodiments, according to the first aspect, a first example of the first aspect is provided, the first cladding layer includes Li _a MF _a+b . The second cladding layer includes Li _a M'Cl _a+b or Li _a M' _m Sa _+b . Wherein, M and M' are each independently Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb, Ge and One or more of P; a=1-7, b=2-4, m=1-3.

In addition, Li _a MF _a+b contains F ions, which can complex transition metal ions in the positive electrode active material, such as Mn, Ni, Fe, etc., to prevent their dissolution and transfer to the negative electrode and damage the reaction interface of the negative electrode, thus improving the Cell cycle stability. Li _a M'Cl _a+b has better moisture stability and can even be prepared through a water solvent method, which can effectively protect Li _a MF _a+b and prevent it from absorbing moisture in the air and causing irreversible decomposition.

In addition, the chloride ions in Li _a M'Cl _a+b have a larger ionic radius than the fluoride ions in Li _a MF _a+b , which is more conducive to the formation of cubic close-packed anion arrangement composition (CCP), so that Li ⁺ can carry out 3D migration in three directions, shuttling through the tetrahedral gap in the Oct1-(Tet1 or Tet2)-Oct2 and Oct1-Tet3-Oct3 pathways respectively. Therefore, it has higher lithium ion conductivity and can achieve high Lithium ion conduction rate.

In some embodiments, M and M' are both trivalent cations.

In this application, M and M' may be the same cation or different cations.

In some specific embodiments, M in Li _a MF _a+b can be Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, One or more of Ga, In, Nb and Ge. Wherein, a can be an integer from 1 to 7, and b can be an integer from 2 to 4. For example, a can be 1, 2, or 3; b can be 2, 3, or 4.

In some specific embodiments, M' in Li _a M'Cl _a+b can be Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr , one or more of Al, Ga, In, Nb and Ge. Wherein, a can be an integer from 1 to 3, and b can be an integer from 2 to 4. For example, a can be 1, 2, or 3; b can be 2, 3, or 4.

In some specific embodiments, M' in Li _a M' _m Sa _+b may be P. Alternatively, Li _a M' _m S _a+b may be Li7P3S11.

In some specific embodiments, the thickness of the first cladding layer may be, for example, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm, 8.5nm, 9nm, 9.5 nm or 10nm. Within this thickness range, the first coating layer has good stability under high voltage conditions and can protect the positive active material while preventing transition metal ions in the positive active material from dissolving and transferring to the negative electrode and damaging the reaction interface of the negative electrode. Thereby improving the cycle stability of the battery core.

In some specific embodiments, the thickness of the second cladding layer may be, for example, 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm or 5 nm. Within this thickness range, the second coating layer can effectively protect the first coating layer from absorbing moisture in the air and causing irreversible decomposition.

In some embodiments, the thickness of the first cladding layer is greater than the thickness of the second cladding layer. The main reason for this design is that Li _a MF _a+b in the first coating layer is in direct contact with the positive active material and is the first to contact the eluted transition metal ions. Therefore, a certain coating thickness is required to avoid transition metal ions. Ion spillover. However, the thickness of the first coating layer should not be too thick (optional 3-5nm). An excessively thick first coating layer will reduce the lithium ion conductivity and electronic conductivity in the positive electrode active material, hindering the charging and discharging process. The deintercalation process of lithium ions inside the positive active material particles increases the polarization of the battery core. In addition, the thickness of the second coating layer should not be too large. It only needs to cover the first coating layer to avoid direct contact with air. Therefore, the thickness of the second coating layer can be selected from 1 to 2 nm.

In some specific embodiments, the total thickness of the first cladding layer and the second cladding layer is less than 8 nm, such as 4 nm, 4.5 nm, 5 nm, 5.5 nm, 6 nm, 6.5 nm, 7 nm, 7.5 nm or 8 nm. Optionally, the total thickness of the first cladding layer and the second cladding layer is 4-7 nm.

The cathode active material in this application can also be other cathode active materials commonly used in this field.

In this design, when atomic layer deposition (ALD) is used for coating, the coating thickness can be flexibly controlled by controlling the number of coating turns. In particular, the coating thickness can be precisely controlled at the nanometer level, effectively improving the effects of coating. When the resistance of the positive active material increases, the ohmic impedance of the positive electrode decreases. In addition, during the coating process using atomic layer deposition, the precursor gas is fully in contact with the solid, which can achieve more comprehensive and uniform coating. Compared with the method in the prior art of ball milling to pulverize material particles and then coating them, the method has the advantages of small coating thickness and uniform and sufficient coating.

As mentioned above, the thickness of the first cladding layer and the second cladding layer can be controlled by controlling the number of turns of ALD coating. Generally, the coating thickness of each turn of ALD is about 0.1nm, so for the first cladding layer material The number of coating turns of (Li _a MF _a+b ) should be set to 30-100 turns, optional 30-50 turns; and the second coating layer material (Li _a M'Cl _a+b or Li _a M' The number of coating turns for _c S _a+b should be set to 10-50 turns, and 10-20 turns are optional. The number of coating turns of the first coating layer material and the second coating layer material respectively corresponds to the thickness of the first coating layer and the second coating layer.

In some specific embodiments, an atomic layer deposition method is used to coat the surface of the positive electrode active material to form a first coating layer; and an atomic layer deposition method is used to coat the surface of the first coating layer to form a second coating layer.

In some specific embodiments, RLi may be methyllithium, n-butyllithium or lithium tert-butoxide.

In some embodiments, R'F _c can be fluoroethylene carbonate.

In some specific embodiments, the deposition temperature may be, for example, 250-300°C. Within this deposition temperature range, the first coating layer can be well formed to cover the positive electrode active material.

Since RLi, R′F _c and R ₁ M need to participate in the deposition process in a gaseous state, they need to be heated to vaporize them before entering the reaction chamber. This application has no special restrictions on their heating temperature, as long as they can be vaporized. For example, RLi is lithium tert-butoxide. The heating temperature of lithium tert-butoxide can be 150-200℃, and 160-170℃ is optional. _R'Fc may be fluoroethylene carbonate. The heating temperature of fluoroethylene carbonate can be 200~300℃, and 240℃ is optional. R ₁ M may be tris(2,2,6,6-tetramethyl-3,5-heptanedioate)yttrium. The heating temperature of tris(2,2,6,6-tetramethyl-3,5-heptanedione acid)yttrium can be 200-300°C, optionally 290°C.

In "(a*c):(a+b):c", "a" refers to the number of lithium atoms contained in Li _a MF _a+b , and "a+b" refers to Li _a MF _a The number of fluorine atoms contained in _+b , "c" refers to the number of F atoms contained in R'F _c , and "a*c" refers to the product of a and c.

In some embodiments, according to the second aspect, a fourth example of the second aspect is provided, and the second cladding layer is Li _a M'Cl _a+b . The second cladding layer is deposited using RLi, R'Cl _c and R ₂ M' as precursors. The deposition temperature is 200-300°C. Among them, RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide, and ester lithium, and R'Cl _c is one of chlorinated alkanes, chlorocarboxylic acids, chlorohydrins, and chloroesters. or more, RLi, R'Cl _c boiling point is between 70 ~ 300℃. R ₂ M' is selected from one or more metal alkyls, metal carboxylates, metal alcohols, and ester metals, and has a boiling point between 70 and 300°C. M' is selected from one or more of Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb and Ge , a=1-7, b=2-4, c is an integer from 1 to 10.

Alternatively, the second cladding layer is Li _a M' _m S _a+b , and the second cladding layer is deposited using RLi, R'S and R ₂ M' as precursors, and the deposition temperature is 200-300°C; where, RLi Selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide and ester lithium, R'S is one or more of thioalkane, thiocarboxylic acid, thiol, thioester and sulfonate ester or There are many kinds, the boiling point of RLi and R'S is between 70~300℃, _R2M ' is phosphorous acid, the boiling point is between 70~300℃; M' is P, a=1-7, b=2-5 , m is an integer from 1 to 5.

In some embodiments, R'Cl _c can be chloroethylene carbonate.

In some embodiments, R'S can be methyl methanesulfonate.

In some specific embodiments, the deposition temperature may be, for example, 250-300°C. The second cladding layer can be well formed to cover the first cladding layer within this deposition temperature range.

Since RLi, R'Cl _c , R'S and R ₂ M' need to participate in the deposition process in a gaseous state, they need to be heated to vaporize them before entering the reaction chamber. This application has no special restrictions on their heating temperature, as long as they can be vaporized. For example, RLi is lithium tert-butoxide. The heating temperature of lithium tert-butoxide can be 150-200°C, optionally 160-170°C; R'Cl _c is chloroethylene carbonate. The heating temperature of chloroethylene carbonate can be 200~300℃, and 240℃ is optional. R ₂ M' can be triethylindium, and the heating temperature of triethylindium can be 100 to 300°C, and 190°C is optional.

In "(a*c):(a+b):c", "a" refers to the number of lithium atoms contained in Li _a M'Cl _a+b , and "a+b" refers to Li _a The number of chlorine atoms contained in M'Cl _a+b , "c" refers to the number of Cl atoms contained in R'Cl _c , and "a*c" refers to the product of a and c.

In "a:(a+b):m", "a" refers to the number of lithium atoms contained in Li _a M' _m S _a+b , and "a+b" refers to Li _a M' _m The number of sulfur atoms contained in S _a+b , "m" refers to the number of M' atoms contained in Li _a M' _m S _a+b .

Specifically, coating using atomic layer deposition includes the following steps.

First, the positive active material powder is put into the reactor, the reactor is evacuated and an inert gas is introduced to purge the atmosphere. During purging, the flow rate of the inert gas is controlled so that the positive active material can be dispersed. Optionally, the inert gas is one or more of argon, helium and nitrogen.

Then, RLi, R′F _c and R ₁ M are used as precursors to deposit the first cladding layer. Specifically, depositing the first coating layer includes: alternating pulses of a precursor and an inert gas purge into the reactor according to the above molar ratio. For example, RLi is introduced first, and then the inert gas is purged; then R'F _c is introduced, and at the end the inert gas is purged; then R ₁ M is introduced, and at the end the inert gas is purged, and so on for a cycle. Each completion of this cycle represents a circle of Li _a MF _a+b coating on the surface of the cathode active material powder. The number of times this process is repeated is determined by the thickness of the first cladding layer. In some embodiments of the present application, the inert gas is one or more of argon, helium, and nitrogen. In this application, the injection pulses of RLi, R'F _c and R ₁ M are determined by the molar ratio of the three.

After the coating of the first coating layer is completed, the inert gas can be continued to be introduced for atmosphere purging to clean the pipeline.

After that, RLi, R'Cl _c and R ₂ M are used as precursors to deposit the second cladding layer. Specifically, depositing the second cladding layer includes: alternating pulses of precursor and inert gas purge into the reactor according to the above molar ratio, thereby depositing Li _a M'Cl _a+b on the surface of the first cladding layer. For example, RLi is introduced first, and then the inert gas is purged; then R'Cl _c is introduced, and the inert gas is purged after the end; R ₂ M' is then introduced, and the inert gas is purged after the end. This is a cycle. Each completion of this cycle represents a circle of Li _a M'Cl _a+b covering the surface of the first coating layer. The number of times this process is repeated is determined by the thickness of the second cladding layer. In some embodiments of the present application, the inert gas is one or more of argon, helium, and nitrogen. In this application, the injection pulses of RLi, R'Cl _c and R ₂ M' are determined by the molar ratio of the three.

Alternatively, after that, RLi, R'S and R ₂ M' are used as precursors to deposit the second cladding layer. Specifically, depositing the second cladding layer includes: alternating pulses of precursor and inert gas purge into the reactor according to the above molar ratio, thereby depositing Li _a M' _m S _a+b on the surface of the first cladding layer . For example, RLi is introduced first, and then the inert gas is purged; then R'S is introduced, and at the end the inert gas is purged; then R ₂ M' is introduced, and at the end the inert gas is purged, and so on. cycle. Each completion of this cycle represents a circle of LiaM' _m Sa _+b covering the surface of the second coating layer. The coating thickness of each turn is about 0.1nm, and the number of repetitions of this process is determined by the thickness of the second coating layer. In some embodiments of the present application, the inert gas is one or more of argon, helium, and nitrogen. In this application, the injection pulses of RLi, R'S and R ₂ M' are determined by the molar ratio of the three.

In some specific embodiments, the calcination temperature may be, for example, 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, or 500°C.

In some specific embodiments, the calcination time may be 4-20 h.

In some specific embodiments, the protective atmosphere may be one or more of argon, helium, and nitrogen.

In some embodiments, calcination can be performed in a tube furnace or a box furnace.

In addition, the secondary battery, battery module, battery pack and electric device of the present application will be described below with appropriate reference to the drawings.

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

Typically, a secondary battery includes a positive electrode plate, a negative electrode plate, an electrolyte and a separator. During the charging and discharging process of the battery, active ions are inserted and detached back and forth between the positive and negative electrodes. The electrolyte plays a role in conducting ions between the positive and negative electrodes. The isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows ions to pass through.

[Positive pole piece]

The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. The positive electrode film layer includes the positive electrode material of the first aspect of the present application or the positive electrode obtained according to the preparation method of the second aspect of the present application. Material.

As an example, the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming metal materials (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on polymer material substrates (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the cathode active material may be a cathode active material known in the art for use in batteries. As an example, the cathode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials of batteries can also be used. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium Manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi1/3Co1/3Mn1/3O2 (can also be abbreviated to NCM333), LiNi0.5Co0.2Mn0.3O2 (can also be abbreviated to NCM523), LiNi0 .5Co0.25Mn0.25O2 (can also be abbreviated to NCM211), LiNi0.6Co0.2Mn0.2O2 (can also be abbreviated to NCM622), LiNi0.8Co0.1Mn0.1O2 (can also be abbreviated to NCM811), lithium nickel cobalt aluminum oxide (such as LiNi0.85Co0.15Al0.05O2) and at least one of its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include but are not limited to lithium iron phosphate (such as LiFePO4 (also referred to as LFP) ), at least one of composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), composite materials of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and composite materials of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer optionally further includes a binder. As examples, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer optionally further 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.

In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode piece can be obtained.

[Negative pole piece]

The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, where the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material. The composite current collector can be formed by forming metal materials (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyterephthalate It is formed on substrates such as ethylene glycol ester (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative active material may be a negative active material known in the art for batteries. As an example, the negative active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, and the like. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon carbon composites, silicon nitrogen composites and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as battery negative electrode active materials can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.

In some embodiments, the negative electrode film layer optionally further includes a binder. The binder can be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polysodium acrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), poly At least one of methacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer optionally further includes a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethylcellulose (CMC-Na)) and the like.

In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative active materials, conductive agents, binders and any other components in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode piece can be obtained.

[Electrolyte]

The electrolyte plays a role in conducting ions between the positive and negative electrodes. There is no specific restriction on the type of electrolyte in this application, and it can be selected according to needs. For example, the electrolyte can be liquid, gel, or completely solid.

In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes electrolyte salts and solvents.

In some embodiments, the electrolyte salt may be selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, trifluoromethane At least one of lithium sulfonate, lithium difluorophosphate, lithium difluoroborate, lithium dioxaloborate, lithium difluorodioxalate phosphate and lithium tetrafluoroxalate phosphate.

In some embodiments, the solvent may be selected from the group consisting of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, Butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate At least one of ester, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

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

[Isolation film]

In some embodiments, the secondary battery further includes a separator film. There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation film can be a single-layer film or a multi-layer composite film, with no special restrictions. When the isolation film is a multi-layer composite film, the materials of each layer can be the same or different, and there is no particular limitation.

In some embodiments, the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer packaging. The outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.

This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. For example, FIG. 2 shows a square-structured secondary battery 5 as an 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 side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 can cover the opening to close the accommodation cavity. The positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the containing cavity. The electrolyte soaks into the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in the battery module can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery module.

Figure 4 is a battery module 4 as an example. Referring to FIG. 4 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 . Of course, it can also be arranged in any other way. Furthermore, the plurality of secondary batteries 5 can be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.

In some embodiments, the above-mentioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select the specific number according to the application and capacity of the battery pack.

Figures 5 and 6 show the battery pack 1 as an example. Referring to FIGS. 5 and 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3 . The upper box 2 can be covered with the lower box 3 and form a closed space for accommodating the battery module 4 . Multiple battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided by the present application. The secondary battery, battery module, or battery pack may be used as a power source for the electrical device, or may be used as an energy storage unit for the electrical device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, and electric golf carts). , electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

As the power-consuming device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

Fig. 7 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, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electrical device, a battery pack or battery module can be used.

As another example, the device may be a mobile phone, a tablet, a laptop, etc. The device is usually required to be thin and light, and a secondary battery can be used as a power source.

The present invention will be further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the invention and are not intended to limit the scope of the invention.

Preparation of cathode materials

Example 1

First, the cathode active material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811 for short) powder is put into the atomic layer deposition reactor, the reactor is evacuated and argon gas is introduced for atmosphere purging, and the argon gas flow rate is controlled to make LiFePO _4. The powder can be dispersed evenly.

Then, according to the molar ratio of 3:6:1, lithium tert-butoxide, fluoroethylene carbonate and tris(2,2,6,6-tetramethyl) were introduced into the 200°C reactor in an alternating pulse manner. (3,5-heptanedione acid) yttrium gas and argon gas was introduced for atmosphere purging. Specifically, lithium tert-butoxide was first introduced, and then an inert gas was introduced for purging; then fluoroethylene carbonate was introduced ester, and then pass in an inert gas to purge; then pass in tris(2,2,6,6-tetramethyl-3,5-heptanedione acid) yttrium, and then pass in an inert gas to purge, so A cycle. Each completion of this cycle represents a circle of Li ₃ YF ₆ coating on the surface of LiFePO ₄ powder. Among them, the injection temperature, injection pulse and argon purge time of lithium tert-butoxide are 160°C, 3s and 15s respectively, and the injection temperature, injection pulse and argon purge time of fluoroethylene carbonate are respectively 240℃, 6s and 15s, the injection temperature, injection pulse and argon purge time of tris(2,2,6,6-tetramethyl-3,5-heptanedioic acid)yttrium are 290℃ respectively. 1s. After repeated coating for 30 times, the preparation of the first coating layer is completed, and the thickness of the first coating layer is about 3 nm.

After that, continue to pass in argon gas to purge the atmosphere to clean the pipeline.

Next, according to the molar ratio of 3:6:1, lithium tert-butoxide, chloroethylene carbonate and triethyl indium were introduced into the 200°C reactor in an alternating pulse manner, and argon gas was introduced for atmosphere Purge, specifically, first pass in lithium tert-butoxide, and then pass in inert gas to purge; then pass in chloroethylene carbonate, and then pass in inert gas to purge; then pass in triethyl indium, and end Then inert gas is introduced to purge, and this is a cycle. Each completion of this cycle represents a circle of Li ₃ InCl ₆ coating on the surface of the first coating layer. Among them, the injection temperature, injection pulse and argon purge time of lithium tert-butoxide are 160°C, 3s and 15s respectively, and the injection temperature, injection pulse and argon purge time of chloroethylene carbonate are respectively 125°C, 6s and 15s, and the injection temperature, injection pulse and argon purge time of triethylindium are 189°C, 1s and 15s respectively. After repeated coating for 10 rounds, the preparation of the second coating layer is completed, and the thickness of the second coating layer is about 1 nm.

Then, the obtained material was transferred to a tube furnace and calcined at 260°C for 4 hours using Ar as a protective gas to obtain a double-layer coated cathode material.

Examples 2-14, 16 and 18-26

The cathode material was prepared according to the method of Example 1, except that the parameters listed in Table 1 below are different from those of Example 1.

Example 15

The cathode material was prepared according to the method of Example 1, except that lithium tert-butoxide and fluoroethylene carbonate were introduced into the 200°C reactor in an alternating pulse manner at a molar ratio of 3:7:1. and tetraethylgermanium and pass in argon gas for atmosphere purge; other parameters are detailed in Table 1 below.

Example 17

The cathode material was prepared according to the method of Example 1, except that lithium tert-butoxide, phosphorous acid and methyl were introduced into the 200°C reactor in an alternating pulse manner at a molar ratio of 7:11:3. Methyl sulfonate and pass in argon gas for atmosphere purge; other parameters are detailed in Table 1 below.

Comparative example 1

The cathode material was prepared according to the method of Example 1, except that 1) the deposition sequence was adjusted so that the first coating layer was Li ₃ InCl ₆ and the second coating layer was Li ₃ YF ₆ ; 2) the deposition sequence was not used in the tubular Calcined in the furnace.

Comparative example 2

The cathode material was prepared according to the method of Example 1, except that 1) only 4 nm thick Li ₃ YF ₆ was coated on the surface of the cathode active material powder as the first coating layer, and there was no second coating layer; 2) Not calcined in tube furnace.

Comparative example 3

The cathode material was prepared according to the method of Example 1, except that 1) only 4 nm thick Li ₃ InCl ₆ was coated on the surface of the cathode active material powder as the first coating layer, and there was no second coating layer; 2) Not calcined in tube furnace.

Comparative example 4

The cathode material was prepared according to the method of Example 1. The difference is that 1) first, the surface of the cathode active material powder is coated with one circle of Li ₃ InCl ₆ , and then coated with three circles of Li ₃ YF ₆ . This is a cycle, and the process is repeated. After 10 cycles, the thickness of the resulting mixed coating layer is 4 nm; 2) It is not calcined in a tube furnace.

Comparative example 5

This comparison ratio is the blank control group. Only NCM811 powder is provided without any processing.

The coating parameters of Examples 1-26 and Comparative Examples 1-5 are as shown in Table 1 below.

The positive electrode materials prepared in Examples 1-26 and Comparative Examples 1-5 were used to prepare button batteries and symmetrical batteries according to the following general preparation methods.

Preparing button cells

Preparation of positive electrode plate:

Add the binder polyvinylidene fluoride (PVDF) to the solvent N-methylpyrrolidone (NMP) and stir continuously until the PVDF is completely dissolved. Then add the conductive carbon black and stir to disperse. Then add the prepared cathode material, continue stirring, and disperse evenly (NCM811: conductive carbon black: PVDF = 96:2:2, the ratio is the mass ratio). Use a 200μm spatula to directly apply the stirred slurry to a thickness of 12μm. On the aluminum foil, after drying for 6 hours under air blast conditions at 100°C, the positive electrode pieces with a diameter of 16mm were punched out.

Preparation of negative electrode plate:

Use the die-cut 18μm lithium sheet as the negative electrode. Before use, use a brush to remove a small amount of impurities and possible oxides on the surface to expose the silver-white metallic luster.

Button battery assembly:

In the glove box (water and oxygen content ≤ 0.1ppm), place the negative electrode shell, negative electrode plate, isolation film (polypropylene), positive electrode plate, gasket, shrapnel, and positive electrode shell in order. Add electrolyte dropwise during the placement process. solution (1.0 mol/L lithium hexafluorophosphate) 120 μL, and let it stand for 2 hours. The resulting button battery was used to test the battery cycle performance.

Preparing symmetrical cells

Prepare the positive electrode tab according to the method for preparing the positive electrode tab of a button battery. Assemble the fresh positive electrode sheet, polypropylene isolation film, and electrolyte (1.0 mol/L lithium hexafluorophosphate, 120 μL) into a symmetrical battery with a positive electrode, and let it stand for 2 hours in a 25°C incubator to ensure the infiltration of the electrolyte. The resulting symmetrical cells were used for impedance testing.

Electrical performance test

1. Capacity retention test of button battery

The capacity retention rate test process is as follows: at 25°C, charge the prepared button battery with a constant current of 1/3C to 4.2V, then charge with a constant voltage of 4.2V until the current is 0.05C, leave it for 5 minutes, and then charge it with a constant current of 1/3C. Discharge from 3C to 2.8V, and the resulting capacity is recorded as the initial capacity C ₀ . Repeat the above steps for the same button battery, and record the discharge capacity C _n of the button battery after the nth cycle. Then the capacity retention rate of the button battery after each cycle P _n =C _n /C ₀ *100 %.

The capacity retention data in Table 1 is the data measured after 100 cycles under the above test conditions, that is, the value of P ₁₀₀ .

2. Symmetrical battery AC impedance test

The prepared symmetrical battery was tested for AC impedance. The AC impedance test is carried out using the electrochemical workstation impedance test module, voltage disturbance mode PEIS, disturbance voltage 5mV, frequency range: 200kHZ-30mHZ, 0-5V voltage range, 0-5V voltage protection, the test data is calculated as the negative number of the imaginary part of the impedance (-Z”) is the ordinate, and the real part Z is the abscissa. The AC impedance spectrum data is obtained, as shown in Figure 1.

Fitting processing of impedance test data:

Use Z-fit software to fit the data recorded in the AC impedance test. Select the fitting circuit as R _s +C ₁ /R _SEI +C ₂ /R _ct +W, where R _s is the ohmic impedance, mainly related to the positive electrode material. _It _is related to _the conductivity of The SEI film hinders the migration of lithium ions; C ₂ is the electric double layer capacitance of the charge transfer interface; W is the semi-infinite diffusion diffusion element that reflects the impact of diffusion on impedance. The judgment basis of fitting requires: the error is less than 5%, and the intersection point with the real part should have a deviation of less than 5% from the _Rs obtained by fitting. Only fitting results that meet the above requirements can be accepted. Extract R _ct and R _s from the fitting results and record them in Table 1.

Table 1: Coating parameters and electrical performance test data

As can be seen from Table 1, the capacity retention rate of Example 1 is significantly higher than that of Comparative Examples 1-5, which shows that the electrochemical stability and cycle performance of Example 1 are significantly better than Comparative Examples 1-5. It can be seen that the double-layer coating of the present application can significantly improve the electrochemical stability of the cathode material under high charging voltage.

As can be seen from Table 1, the ohmic impedance R _s and the charge transfer resistance R _ct of Example 1 are both smaller than those of Comparative Examples 1-5. In particular, the charge transfer resistance R _ct is significantly smaller. This shows that the double-layer coating of the present application can significantly reduce the impedance.

In addition, by comparing Examples 1 and 13, it can be seen that the positive electrode material with double layer coating in Example 13 is not calcined, and its ohmic impedance _Rs and charge transfer resistance R _ct are both higher than those in Example 1. This indicates that the calcination process has a beneficial effect on reducing the impedance.

The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can easily think of changes or modifications within the technical scope disclosed in the present invention. All substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

A cathode material, characterized by including:

positive active material;

A first coating layer covers the positive active material, and the electrochemical window of the first coating layer is above 6.0V; and

A second coating layer covers the first coating layer, and the lithium ion conductivity of the second coating layer is 10 -3 S/cm or above.
The cathode material according to claim 1, characterized in that:

The first coating layer includes Li a MF a+b ;

The second coating layer includes Li a M'C a+b or Li a M' m Sa +b ;

Wherein, M and M' are each independently Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb, Ge and one or more of P;

a=1-7, b=2-4, m=1-3.
The cathode material according to claim 2, wherein M and M' are each independently a divalent, trivalent or tetravalent cation.
The cathode material according to claim 2 or 3, characterized in that M and M' are each independently Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, In, Y, One or more of Ge and P, optionally one or more of In, Y, Ge and P.
The cathode material according to any one of claims 2 to 4, characterized in that:

The Li a MF a+b is Li 3 YF 6 , and the Li a M'Cl a+b is Li 3 InCl 6 .
The cathode material according to any one of claims 1 to 5, wherein the lithium ion conductivity of the second coating layer is 10 -2 S/cm or more.
The cathode material according to any one of claims 1 to 6, characterized in that the thickness of the first coating layer is 3-10 nm, optionally 3-5 nm;

And/or, the thickness of the second coating layer is 1-5 nm, optionally 1-2 nm.
The cathode material according to any one of claims 1 to 7, wherein the total thickness of the first coating layer and the second coating layer is 10 nm or less.
The cathode material according to any one of claims 1 to 8, characterized in that the cathode active material is one or more of LiFePO 4 , LiCoO 2 , LiMnO 4 and LiNix Co y M 1-xy O 2 species, where M is one or more of Mn, Al, Mg, Sn, Y and Cr, 0≤x<1, 0≤y≤1, and x+y≤1.
The cathode material according to any one of claims 1 to 9, characterized in that the cathode active material contains at least one of Mn and Co, and the thickness of the first coating layer varies with the Mn content and the Co content. increase by increasing.
A preparation method of cathode material, characterized by including:

Coating the surface of the positive electrode active material to form a first coating layer; and

Coating the surface of the first coating layer to form a second coating layer to obtain a positive electrode material;

Wherein, the electrochemical window of the first cladding layer is 6.0 V or above, and the lithium ion conductivity of the second cladding layer is 10 -3 S/cm or above.
The preparation method according to claim 11, characterized in that the coating is performed by atomic layer deposition.
The preparation method according to claim 11 or 12, characterized in that the first coating layer is Li a MF a+b ; RLi, R'F c and R 1 M are used as precursors to inject and deposit the first Coating layer, the deposition temperature is 200-300°C;

Among them, RLi is selected from one or more of lithium halide, alkyl lithium, lithium carboxylate, lithium alkoxide, and ester lithium, and R'F c is a fluorinated alkane, a fluorinated carboxylic acid, a fluorinated alcohol, and a fluorinated ester. One or more of them, RLi and R'F c have a boiling point between 70 and 300°C, R 1 M is selected from one or more of alkyl metals, carboxylate metals, alcohol metals and ester metals, the boiling point Between 70~300℃; M is selected from Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb and One or more types of Ge, a=1-7, b=2-4, and c is an integer from 1 to 10.
The preparation method according to any one of claims 11 to 13, characterized in that the molar ratio of RLi, R'F c and R 1 M is (a*c):(a+b):c.
The preparation method according to any one of claims 11 to 14, characterized in that the second coating layer is Li a M'Cl a+b ; using RLi, R'Cl c and R 2 M' as precursors The second coating layer is deposited through volume injection, and the deposition temperature is 200-300°C;

Among them, RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide, and ester lithium, and R'Cl c is one of chlorinated alkanes, chlorocarboxylic acids, chlorohydrins, and chloroesters. or more, RLi, R'Cl c has a boiling point between 70 and 300°C, R 2 M' is selected from one or more metal alkyls, carboxylate metals, alcohol metals, and ester metals, and has a boiling point between Between 70~300℃; M' is selected from Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb and Ge One or more of them, a=1-7, b=2-4, c is an integer from 1 to 10;

Alternatively, the second cladding layer is Li a M' m S a+b , and the second cladding layer is deposited using RLi, R'S and R 2 M' as precursors, and the deposition temperature is 200-300°C;

Among them, RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide, and ester lithium, and R'S is thioalkane, thiocarboxylic acid, thiol, thioester, and sulfonate ester. One or more kinds, RLi and R'S have boiling points between 70 and 300°C, R 2 M' is phosphorous acid, and their boiling points are between 70 and 300°C; M' is P, a=1-7, b= 2-5, m is an integer from 1 to 5.
The preparation method according to any one of claims 11 to 15, characterized in that the molar ratio of RLi, R'Cl c and R 2 M' is (a*c):(a+b):c; RLi, The molar ratio of R'S and R 2 M' is a:(a+b):m.
The preparation method according to any one of claims 11 to 16, characterized in that after forming the second coating layer, the positive electrode material is calcined in a protective atmosphere.
The preparation method according to claim 17, characterized in that the calcination temperature is 150-500°C, optionally 150-300°C; the calcination time is 1-24h, optionally 4-20h.
A secondary battery, characterized by comprising the cathode material according to any one of claims 1 to 10 or the cathode material obtained according to the preparation method according to any one of claims 11 to 18.
A battery module comprising the secondary battery according to claim 19.
A battery pack, characterized by comprising the battery module according to claim 20.
An electrical device, characterized by comprising at least one of the secondary battery according to claim 19, the battery module according to claim 20, and the battery pack according to claim 21.