A positive electrode material, a method for manufacturing the same, a secondary battery, and a battery module

Abstract

This application relates to a cathode material, comprising: a cathode active material; a first coating layer, the first coating layer coating the cathode active material, the first coating layer having an electrochemical window of 6.0V or higher; and a second coating layer, the second coating layer coating the first coating layer, the second coating layer having a lithium-ion conductivity of 10. ‑3 The positive electrode material of this application, with its double-layer coating, exhibits high electrochemical stability and lithium-ion conductivity at high charging voltages. Furthermore, this application also relates to methods for preparing the aforementioned positive electrode material, secondary batteries, battery modules, battery packs, and power-consuming devices.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a positive electrode material and its preparation method, a secondary battery, a battery module, a battery pack, and an electrical device. Background Technology

[0002] With technological advancements, clean energy sources such as batteries are gradually replacing traditional fossil fuels, providing power for various applications. This has led to higher demands on battery energy density. Improving the battery's charging window to increase its charge / discharge capacity has become one of the key breakthroughs. However, higher charging voltages (above 4.6V) pose greater challenges to the electrochemical stability of the cathode material and the lithium-ion conductivity.

[0003] Therefore, there is an urgent need to develop a cathode material that is electrochemically stable at high charging voltages and has a high lithium-ion conductivity. Summary of the Invention

[0004] 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 at high charging voltage.

[0005] The positive electrode material provided in the first aspect of this application includes: a positive electrode active material, a first coating layer, and a second coating layer. The first coating layer coats the positive electrode active material. The electrochemical window of the first coating layer is 6.0V or higher. The second coating layer coats the first coating layer. The lithium-ion conductivity of the second coating layer is 10. -3 S / cm or higher.

[0006] In the technical solution of this application embodiment, the positive electrode active material is coated with a double layer. 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 electrode active material. The second coating layer has high lithium-ion conductivity and can achieve a high lithium-ion conduction rate.

[0007] In some embodiments, according to the first aspect, a first example of the first aspect is provided, wherein the first covering layer includes Li a MF a+b The second coating layer includes Li a M'Cl a+b Or Li a M' m S a+b ; where M and M' are each independently one or more of Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb, Ge and P; a = 1-7, b = 2-4, m = 1-3.

[0008] In this design, Li a MF a+b It exhibits good stability under high voltage conditions, effectively protecting the positive electrode active material; Li a M'Cl a+b Or Li a M' c S a+b It has high lithium-ion conductivity, enabling high lithium-ion conduction rates.

[0009] In addition, Li a MF a+b Containing F ions, which can complex with transition metal ions in the positive electrode active material, such as Mn, Ni, and Fe ions, prevents them from dissolving and transferring to the negative electrode, thus avoiding damage to the negative electrode's reaction interface and improving the cell's cycle stability. Li a M'Cl a+b It has better moisture stability and can effectively protect Li a MF a+b This is to prevent it from absorbing moisture from the air and undergoing irreversible decomposition.

[0010] In some embodiments, according to the first aspect, a second example of the first aspect is proposed, wherein M and M' are each independently a divalent, trivalent, or tetravalent cation.

[0011] In this design, the smaller ionic radii of divalent, trivalent, or tetravalent cations are more conducive to forming a cubic close-packed anionic arrangement (CCP), making Li... + It is capable of 3D migration in three directions, with trivalent cations being superior to divalent and tetravalent cations.

[0012] In some embodiments, according to the first aspect, a third example of the first aspect is proposed, wherein M and M' are each independently one or more of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, In, Y, Ge and P, and may be selected as one or more of In, Y, Ge and P.

[0013] In this design, further optimization of M and M' is more conducive to improving the electrochemical stability of the cathode material and its lithium-ion conduction rate under high charging voltage.

[0014] In some embodiments, according to the first aspect, a fourth example of the first aspect is proposed, Li a MF a+b It is Li3YF6, and Li a M'Cl a+b It is Li3InCl6.

[0015] In this design, by further optimizing the materials of the first and second coating layers, it is more beneficial to improve the electrochemical stability of the cathode material and its lithium-ion conduction rate under high charging voltage.

[0016] In some embodiments, according to the first aspect, a fifth example of the first aspect is provided, wherein the lithium-ion conductivity of the second coating layer is 10. -2 S / cm or higher.

[0017] In this design, the lithium-ion conductivity of the second coating layer is preferably close to that of the lithium-ion conductivity in the electrolyte. This ensures that lithium ions in the electrolyte can migrate quickly between the solid and liquid phases, avoiding the accumulation of lithium ions at the interface and causing uneven local charge distribution.

[0018] In some embodiments, according to the first aspect, a sixth example of the first aspect is proposed, wherein 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.

[0019] In this design, within this thickness range, the first coating layer exhibits good stability under high voltage conditions, protecting the positive electrode active material and preventing transition metal ions from dissolving and transferring to the negative electrode, thus disrupting the negative electrode's reaction interface and improving the cell's cycle stability. Furthermore, within this thickness range, the second coating layer effectively protects the first coating layer, preventing it from absorbing moisture from the air and undergoing irreversible decomposition.

[0020] In some embodiments, according to the first aspect, a seventh example of the first aspect is proposed, wherein the total thickness of the first covering layer and the second covering layer is less than 10nn.

[0021] In this design, the total thickness of the first and second coating layers is within the aforementioned range, which can protect the positive electrode material while ensuring the conductivity of the positive electrode active material, avoiding an increase in ohmic resistance and internal resistance of the battery cell.

[0022] In some embodiments, according to the first aspect, an eighth example of the first aspect is provided, wherein the positive electrode active material is LiFePO4, LiCoO2, LiMnO4, and LiNi. x Co y M 1-x-y One or more of O2, wherein M is one or more of Mn, Al, Mg, Sn, Y and Cr, 0≤x<1, 0≤y≤1, and x+y≤1.

[0023] In this design, the use of the aforementioned positive electrode active material can optimize the energy density and cycle performance of the battery cell.

[0024] In some embodiments, according to the first aspect, a ninth example of the first aspect is proposed, wherein the positive electrode active material contains at least one of Mn and Co, and the thickness of the first coating layer increases with the increase of Mn content and Co content.

[0025] Since Mn and Co are more easily leached and have a higher leaching rate than other metallic elements, a thicker first coating layer is required to prevent Mn and Co from entering the electrolyte and negative electrode after leaching.

[0026] A second aspect of this application provides a method for preparing a cathode material, including:

[0027] A first coating layer is formed on the surface of the positive electrode active material; and

[0028] A second coating layer is formed by coating the surface of the first coating layer to obtain the cathode material;

[0029] The first coating layer has an electrochemical window of 6.0V or higher, and the second coating layer has a lithium-ion conductivity of 10. -3 S / cm or higher.

[0030] In the technical solution of this application embodiment, the cathode material can be obtained by two coating processes. The preparation process is simple, highly repeatable, and conducive to large-scale industrial production.

[0031] In some embodiments, according to the second aspect, a first example of the second aspect is provided, in which an atomic layer deposition method is used for coating.

[0032] In this design, the coating thickness can be flexibly controlled by adjusting the number of coating layers during atomic layer deposition (ALD). Specifically, the coating thickness can be precisely controlled at the nanometer level, effectively mitigating the increase in resistance of the positive electrode active material caused by coating and reducing the ohmic impedance of the positive electrode. Furthermore, during ALD coating, the precursor gas and solid are in full contact, resulting in more comprehensive and uniform coating. Compared to existing methods that involve ball milling material particles before coating, this method offers advantages such as smaller coating thickness and more uniform and thorough coating.

[0033] In some embodiments, according to the second aspect, a second example of the second aspect is proposed, wherein the first covering layer is Li a MF a+b Where a = 1-7, b = 2-4; the first coating layer is deposited using the first lithium source, fluorine source and the first metal source as precursors.

[0034] In some embodiments, according to the second aspect, a third example of the second aspect is proposed, wherein the first lithium source is RLi, and the fluorine source is R'F. cThe first metal source is R1M. The deposition temperature is 200-300℃. RLi is selected from one or more of lithium halides, alkyl lithium, lithium carboxylate, lithium alkoxides, and lithium esters, and R'F... c It is one or more of fluoroalkanes, fluorocarboxylic acids, fluoroalcohols, and fluoroesters, RLi, R'F c Boiling point between 70 and 300 °C. R1M is selected from one or more of alkyl metals, carboxylic acid metals, alcohol metals, and ester metals, with 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, where c is an integer from 1 to 10.

[0035] In this design, by optimizing the precursor and deposition temperature, it is more conducive to the comprehensive and uniform formation of the first coating layer.

[0036] In some embodiments, according to the second aspect, a fourth example of the second aspect is proposed, RLi, R'F c The molar ratio of R1M to R1M is (a*c):(a+b):c. Optionally, RLi and R'F... c The molar ratio of R1M to R1M is (1-70):(3-11):(1-10).

[0037] In this design, by optimizing RLi and R'F c The molar ratio of R1M to R1M enables the first coating layer to more uniformly and comprehensively coat the positive electrode active material, which is beneficial to improving the electrochemical stability of the positive electrode material under high charging voltage.

[0038] In some embodiments, according to the second aspect, a fifth example of the second aspect is proposed, wherein the second covering layer is Li. a M'Cl a+b a = 1-7, b = 2-4; the second coating layer is deposited using the second lithium source, chlorine source and the second metal source as precursors.

[0039] In some embodiments, according to the second aspect, a sixth example of the second aspect is proposed, wherein the second lithium source is RLi, and the chlorine source is R'Cl. c The second metal source is R2M'. The deposition temperature is 200-300℃. RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester, and R'Cl... c It is one or more of chloroalkanes, chlorocarboxylic acids, chloroalcohols, and chloroesters, RLi, R'Cl cThe boiling point is between 70 and 300 °C. R2M' is selected from one or more of alkyl metals, carboxylic acid metals, alcohol metals, and ester metals, with 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, and c is an integer from 1 to 10.

[0040] In some embodiments, according to the second aspect, a seventh example of the second aspect is proposed, RLi, R'Cl c The molar ratio of RLi and R'M' is (a*c):(a+b):c. Optionally, RLi and R'Cl... c The molar ratio of R2M' to R2M' is (1-70):(3-11):(1-10).

[0041] In some embodiments, according to the second aspect, an eighth example of the second aspect is proposed, wherein the second covering layer is Li a M' m S a+b , where a = 1-7, b = 2-5, and m is an integer from 1 to 5; the second coating layer is deposited using the third lithium source, sulfur source, and M' source as precursors.

[0042] In some embodiments, according to the second aspect, a ninth example of the second aspect is provided, wherein the third lithium source is RLi. The sulfur source is R'S. The M' source is R2M'. The deposition temperature is 200-300°C. Wherein, RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alcohol, and lithium ester; R'S is one or more of thioalkanes, thiocarboxylic acids, thioalcohols, thioesters, and sulfonates; the boiling points of RLi and R'S are between 70 and 300°C; R2M' is phosphorous acid with a boiling point between 70 and 300°C; and M' is phosphorus (P).

[0043] Optimizing the precursor and deposition temperature makes it easier to form a second coating layer in a comprehensive and uniform manner.

[0044] In some embodiments, according to the second aspect, a tenth example of the second aspect is proposed, wherein the molar ratio of RLi, R'S and R2M' is a∶(a+b)∶m. Optionally, the molar ratio of RLi, R'S and R2M' is (1-7)∶(3-12)∶(1-5).

[0045] By optimizing RLi and R'Cl c The molar ratio of R2M' to RLi, R'S and R2M' enables the second coating layer to more uniformly and comprehensively coat the first coating layer, which is beneficial to improving the lithium-ion conduction rate of the cathode material and protecting the first coating layer from irreversible decomposition due to the absorption of moisture from the air.

[0046] In some embodiments, according to the second aspect, an eleventh example of the second aspect is provided, wherein after the second coating layer is formed, the cathode material is calcined in a protective atmosphere.

[0047] 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, forming a cubic close-packed anion arrangement (CCP), which helps to form a 3D lithium-ion transport channel, improve the rate performance and cycle stability of the battery cell; (2) It helps to achieve better atomic fusion at the junction of the positive electrode active material and the first coating layer and at the junction of the first coating layer and the second coating layer, forming a transition layer, reducing the grain boundary resistance caused by the coating interface, and reducing the impedance of the battery cell.

[0048] In some embodiments, according to the second aspect, a twelfth example of the second aspect is provided, wherein the calcination temperature is 150-500°C, optionally 150-300°C; and the calcination time is 1-24h, optionally 4-20h.

[0049] In this design, optimizing the calcination temperature and calcination time is beneficial to improving the calcination effect, which in turn helps to increase the crystallinity of the first coating layer and the second coating layer, and helps to form a transition layer at the interface between the highly active material and the first coating layer, as well as at the interface between the first coating layer and the second coating layer.

[0050] A third aspect of this application provides a secondary battery, comprising the positive electrode material described in the first aspect of this application or the positive electrode material obtained according to the preparation method described in the second aspect of this application.

[0051] In the technical solutions of this application, since the positive electrode material of the first aspect of this application or the positive electrode material prepared according to the method of the second aspect of this application is used, the secondary battery of this application also has high electrochemical stability and lithium-ion conduction rate under high charging voltage.

[0052] A fourth aspect of this application provides a battery module including the secondary battery described in the third aspect of this application.

[0053] In the technical solutions of this application embodiment, since the positive electrode material of the first aspect of this application or the positive electrode material prepared according to the method of the second aspect of this application is used, the battery module of this application has high electrochemical stability and lithium-ion conduction rate under high charging voltage.

[0054] The fifth aspect of this application provides a battery pack including the battery module described in the fourth aspect of this application.

[0055] In the technical solutions of this application embodiment, since the positive electrode material of the first aspect of this application or the positive electrode material prepared according to the method of the second aspect of this application is used, the battery pack of this application has high electrochemical stability and lithium-ion conduction rate at high charging voltage.

[0056] A sixth aspect of this application provides an electrical device comprising 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.

[0057] In the technical solutions of this application embodiment, since the positive electrode material of the first aspect of this application or the positive electrode material prepared according to the method of the second aspect of this application is used, the electrical device of this application has high electrochemical stability and lithium-ion conduction rate under high charging voltage.

[0058] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application, it can be implemented according to the contents of the specification. In order to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0059] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings 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. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0060] Figure 1 The AC impedance spectrum is shown for a symmetrical battery composed of the positive electrode sheets prepared in Examples 1 and 4 of this invention.

[0061] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0062] Figure 3 yes Figure 2 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0063] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0064] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0065] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0066] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0067] Explanation of reference numerals in the attached figures:

[0068] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0069] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.

[0070] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0071] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more (including two).

[0072] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0073] With technological advancements, higher demands are being placed on battery energy density. Improving the battery's charge / discharge capacity by extending its charging window has become a key breakthrough. However, during charging, lithium ions continuously escape from the cathode material. When the charging voltage rises to a certain value, this can cause irreversible crystal structure degradation or even collapse, leading to decreased electrochemical stability and lithium-ion conductivity, thus degrading cell performance. Therefore, there is an urgent need to develop a cathode material that is electrochemically stable at high charging voltages and possesses high lithium-ion conductivity.

[0074] The inventors discovered that using lithium-containing halides (Li)a MX b (Where M is a metal ion and X is a halide ion) Coating the cathode material can protect the cathode to a certain extent, but the effect of coating the cathode material with a single halide on improving electrochemical stability and lithium-ion conduction rate is not very satisfactory.

[0075] Through in-depth research, the inventors designed a cathode material by sequentially coating the surface of the cathode active material with a first coating layer and a second coating layer, significantly improving the electrochemical stability and lithium-ion conductivity of the active material under high charging voltages. Specifically, the first coating layer has an electrochemical window above 6.0V, exhibiting good stability under high voltage conditions and protecting the cathode active material; the second coating layer has a lithium-ion conductivity of 10⁻⁶. -3 With a value of S / cm or higher, it has high lithium-ion conductivity and can achieve a high lithium-ion conduction rate.

[0076] The technical solutions described in the embodiments of this application are applicable to cathode materials, and also to cathode material preparation processes, secondary batteries using cathode materials, battery modules using secondary batteries, battery packs using battery modules, and electrical devices using at least one of secondary batteries, battery modules, and battery packs.

[0077] In a first aspect, according to some embodiments of this application, this application provides a positive electrode material, including a positive electrode active material, a first coating layer, and a second coating layer. The first coating layer coats the positive electrode active material. The electrochemical window of the first coating layer is 6.0V or higher. The second coating layer coats the first coating layer. The lithium-ion conductivity of the second coating layer is 10. -3 S / cm or higher.

[0078] In the technical solution of this application embodiment, the positive electrode active material is coated with a double layer. 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 electrode active material. The second coating layer has high lithium-ion conductivity and can achieve a high lithium-ion conduction rate.

[0079] The "electrochemical window" refers to the voltage range within which a substance can remain stable and not undergo redox reactions under electrochemical conditions.

[0080] "Lithium-ion conductivity" is a parameter referring to the ease with which electric charge flows in a substance. Conductivity is represented by the Greek letter σ. The standard unit of conductivity σ is Siemens per meter (abbreviated as S / m), which is the reciprocal of resistivity ρ, i.e., σ = 1 / ρ.

[0081] In some specific embodiments, the electrochemical window of the first coating 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.

[0082] In some embodiments, according to the first aspect, a first example of the first aspect is provided, wherein the first covering layer includes Li a MF a+b The second coating layer includes Li a M'Cl a+b Or Li a M' m S a+b Where M and M' are each independently one or more of Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb, Ge and P; a = 1-7, b = 2-4, m = 1-3.

[0083] In this design, Li a MF a+b It exhibits good stability under high voltage conditions, effectively protecting the positive electrode active material; Li a M'Cl a+b Or Li a M' c S a+b It has high lithium-ion conductivity, enabling high lithium-ion conduction rates.

[0084] In addition, Li a MF a+b Containing F ions, which can complex with transition metal ions in the positive electrode active material, such as Mn, Ni, and Fe ions, prevents them from dissolving and transferring to the negative electrode, thus avoiding damage to the negative electrode's reaction interface and improving the cell's cycle stability. Li a M'Cl a+b It exhibits better moisture stability and can even be prepared using an aqueous solvent method, effectively protecting Li. a MF a+b This is to prevent it from absorbing moisture from the air and undergoing irreversible decomposition.

[0085] In addition, Li a M'Cl a+b The chloride ions in it are compared to those in Li a MF a+b The fluoride ions in Li have a larger ionic radius, which is more conducive to the formation of a cubic close-packed anionic arrangement (CCP), making Li... +It can perform 3D migration in three directions, shuttling through the tetrahedral gap via Oct1-(Tet1 or Tet2)-Oct2 and Oct1-Tet3-Oct3 pathways, respectively, thus exhibiting higher lithium-ion conductivity and achieving a high lithium-ion conduction rate.

[0086] In some embodiments, according to the first aspect, a second example of the first aspect is proposed, wherein M and M' are each independently a divalent, trivalent, or tetravalent cation.

[0087] In this design, the smaller ionic radii of divalent, trivalent, or tetravalent cations are more conducive to forming a cubic close-packed anionic arrangement (CCP), making Li... + It is capable of 3D migration in three directions, with trivalent cations being superior to divalent and tetravalent cations.

[0088] In some specific embodiments, both M and M' are trivalent cations.

[0089] In some embodiments, according to the first aspect, a third example of the first aspect is proposed, wherein M and M' are each independently one or more of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, In, Y, Ge and P, and may be selected as one or more of In, Y, Ge and P.

[0090] In this design, further optimization of M and M' is more conducive to improving the electrochemical stability of the cathode material and its lithium-ion conduction rate under high charging voltage.

[0091] In this application, M and M' can be the same cation or different cations.

[0092] In some specific embodiments, Li a MF a+b M can be 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 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.

[0093] In some specific embodiments, Li a M'Cl a+b M' in the given information can be 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 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.

[0094] In some specific embodiments, Li a M' m S a+b M' in this context can be P. Alternatively, Li a M' m S a+b It can be Li7P3S 11 .

[0095] In some embodiments, according to the first aspect, a fourth example of the first aspect is proposed, Li a MF a+b It is Li3YF6, and Li a M'Cl a+b It is Li3InCl6.

[0096] In this design, by further optimizing the materials of the first and second coating layers, it is more beneficial to improve the electrochemical stability of the cathode material and its lithium-ion conduction rate under high charging voltage.

[0097] In some embodiments, according to the first aspect, a fifth example of the first aspect is provided, wherein the lithium-ion conductivity of the second coating layer is 10. -2 S / cm or higher.

[0098] In this design, the lithium-ion conductivity of the second coating layer is preferably close to that of the lithium-ion conductivity in the electrolyte. This ensures that lithium ions in the electrolyte can migrate quickly between the solid and liquid phases, avoiding the accumulation of lithium ions at the interface and causing uneven local charge distribution.

[0099] In some embodiments, according to the first aspect, a sixth example of the first aspect is proposed, wherein 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.

[0100] In this design, within this thickness range, the first coating layer exhibits good stability under high voltage conditions, protecting the positive electrode active material and preventing transition metal ions from dissolving and transferring to the negative electrode, thus disrupting the negative electrode's reaction interface and improving the cell's cycle stability. Furthermore, within this thickness range, the second coating layer effectively protects the first coating layer, preventing it from absorbing moisture from the air and undergoing irreversible decomposition.

[0101] In some specific embodiments, the thickness of the first coating layer can be, for example, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 5.5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm, 8.5nm, 9nm, 9.5nm, or 10nm. Within this thickness range, the first coating layer exhibits good stability under high voltage conditions, protecting the positive electrode active material while preventing transition metal ions in the positive electrode active material from dissolving and transferring to the negative electrode, thus avoiding damage to the reaction interface of the negative electrode and improving the cycle stability of the cell.

[0102] In some specific embodiments, the thickness of the second coating layer can 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, preventing it from absorbing moisture from the air and undergoing irreversible decomposition.

[0103] In some specific embodiments, the thickness of the first coating layer is greater than the thickness of the second coating layer. The main reason for this design is that the Li in the first coating layer... a MF a+b The first coating layer, which comes into direct contact with the positive electrode active material, is the first to come into contact with the dissolved transition metal ions. Therefore, a certain coating thickness is required to prevent the leakage of transition metal ions. However, the thickness of the first coating layer should not be too thick (3-5 nm is acceptable). An excessively thick first coating layer will reduce the lithium-ion conductivity and electronic conductivity in the positive electrode active material, hindering the insertion and extraction of lithium ions within the positive electrode active material particles during charging and discharging, and increasing the polarization of the cell. In addition, the thickness of the second coating layer should not be too large either; it only needs to cover the first coating layer to prevent direct contact with air. Therefore, the thickness of the second coating layer can be selected as 1-2 nm.

[0104] In some embodiments, according to the first aspect, a seventh example of the first aspect is proposed, wherein the total thickness of the first coating layer and the second coating layer is less than 10 nm.

[0105] In this design, the total thickness of the first and second coating layers is within the aforementioned range, which can protect the positive electrode material while ensuring the conductivity of the positive electrode active material, avoiding an increase in ohmic resistance and internal resistance of the battery cell.

[0106] In some specific embodiments, the total thickness of the first coating layer and the second coating layer is less than 8 nm, for example, 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 coating layer and the second coating layer is 4-7 nm.

[0107] In some embodiments, according to the first aspect, an eighth example of the first aspect is provided, wherein the positive electrode active material is LiFePO4, LiCoO2, LiMnO4, and LiNi. x Co y M 1-x-y One or more of O2, wherein M is one or more of Mn, Al, Mg, Sn, Y and Cr, 0≤x<1, 0≤y≤1, and x+y≤1.

[0108] In this design, the use of the aforementioned positive electrode active material can optimize the energy density and cycle performance of the battery cell.

[0109] The positive electrode active material of this application may also be other positive electrode active materials commonly used in the art.

[0110] In some embodiments, according to the first aspect, a ninth example of the first aspect is proposed, wherein the positive electrode active material contains at least one of Mn and Co, and the thickness of the first coating layer increases with the increase of Mn content and Co content.

[0111] Since Mn and Co are more easily leached and have a higher leaching rate than other metallic elements, a thicker first coating layer is required to prevent Mn and Co from entering the electrolyte and negative electrode after leaching.

[0112] A second aspect of this application provides a method for preparing a cathode material, comprising:

[0113] A first coating layer is formed on the surface of the positive electrode active material; and

[0114] A second coating layer is formed by coating the surface of the first coating layer to obtain the cathode material;

[0115] The first coating layer has an electrochemical window of 6.0V or higher, and the second coating layer has a lithium-ion conductivity of 10. -3 S / cm or higher.

[0116] In the technical solution of this application embodiment, the cathode material can be obtained by two coating processes. The preparation process is simple, highly repeatable, and conducive to large-scale industrial production.

[0117] In some embodiments, according to the second aspect, a first example of the second aspect is provided, in which an atomic layer deposition method is used for coating.

[0118] In this design, the atomic layer deposition (ALD) coating method allows for flexible control of the coating thickness by adjusting the number of coating layers. Specifically, it enables precise control of the coating thickness at the nanometer level, effectively mitigating the increase in resistance of the positive electrode active material caused by coating and reducing the ohmic impedance of the positive electrode. Furthermore, the ALD coating process ensures sufficient contact between the precursor gas and the solid, resulting in more comprehensive and uniform coating. Compared to existing methods that involve ball milling material particles before coating, this method offers advantages such as smaller coating thickness and more uniform and thorough coating.

[0119] As mentioned above, the thickness of the first and second coating layers can be controlled by controlling the number of ALD coating layers. Typically, the coating thickness of each ALD layer is approximately 0.1 nm. Therefore, for the first coating layer material (Li... a MF a+b The number of wrapping layers should be set to 30-100, with 30-50 wrapping layers being an option; and the second coating layer material (Li a M'Cl a+b Or Li a M' c S a+b The number of wrapping rings should be set to 10-50 rings, with 10-20 rings being an option. The number of wrapping rings for the first and second coating materials corresponds to the thickness of the first and second coating layers, respectively.

[0120] 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.

[0121] In some embodiments, according to the second aspect, a second example of the second aspect is proposed, wherein the first covering layer is Li a MF a+b Where a = 1-7, b = 2-4. The first coating layer is deposited using the first lithium source, fluorine source and the first metal source as precursors.

[0122] In some embodiments, according to the second aspect, a third example of the second aspect is provided, wherein the first lithium source is RLi, and the fluorine source is R'F. c The first metal source is R1M. The deposition temperature is 200-300℃. RLi is selected from one or more of lithium halides, alkyl lithium, lithium carboxylate, lithium alkoxides, and lithium esters, and R'F... c It is one or more of fluoroalkanes, fluorocarboxylic acids, fluoroalcohols, and fluoroesters, RLi, R'F cBoiling point between 70 and 300 °C. R1M is selected from one or more of alkyl metals, carboxylic acid metals, alcohol metals, and ester metals, with 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, where c is an integer from 1 to 10.

[0123] In this design, by optimizing the precursor and deposition temperature, it is more conducive to the comprehensive and uniform formation of the first coating layer.

[0124] In some specific embodiments, RLi may be lithium methyl, lithium n-butyl, or lithium tert-butoxide, etc.

[0125] In some specific embodiments, R'F c It can be fluoroethylene carbonate.

[0126] 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 formed well to coat the positive electrode active material.

[0127] Due to RLi, R'F c R1M and R2M need to participate in the deposition process in a gaseous state, therefore they need to be heated to vaporize them before entering the reaction chamber. This application does not have a particular limitation on their heating temperature, as long as it allows for vaporization. For example, RLi is lithium tert-butoxide. The heating temperature of lithium tert-butoxide can be 150-200°C, optionally 160-170°C. R'F c It can be fluoroethylene carbonate. The heating temperature of fluoroethylene carbonate can be 200-300℃, optionally 240℃. R1M can be tris(2,2,6,6-tetramethyl-3,5-heptadecanoic acid)yttrium. The heating temperature of tris(2,2,6,6-tetramethyl-3,5-heptadecanoic acid)yttrium can be 200-300℃, optionally 290℃.

[0128] In some embodiments, according to the second aspect, a fourth example of the second aspect is proposed, RLi, R'F c The molar ratio of R1M to R1M is (a*c)∶(a+b)∶c.

[0129] In "(a*c):(a+b):c", "a" refers to Li a MF a+b The number of lithium atoms contained in it, "a+b" refers to the number of lithium atoms in Li. a MF a+b The number of fluorine atoms contained in it, "c" refers to R'F cThe number of F atoms contained in the coating, "a*c" refers to the product of a and c. Optionally, in some first coating layer embodiments, as described above, a = 1-7, b = 2-4, and c is an integer from 1 to 10, then a*c can be 1-70, a+b can be 3-11, and c can be 1-10, so (a*c)∶(a+b)∶c can be (1-70)∶(3-11)∶(1-10), that is, RLi, R'F c The molar ratio of R1M to R1M can be (1-70):(3-11):(1-10). For example, RLi, R'F c The molar ratio of R1M can be (1-10):(3-11):(1-10), (10-20):(3-11):(1-10), (20-30):(3-11):(1-10), (30-40):(3-11):(1-10), (40-50):(3-11):(1-10), (50-60):(3-11):(1-10) or (60-70):(3-11):(1-10).

[0130] In this design, by optimizing RLi and R'F c The molar ratio of R1M to R1M enables the first coating layer to more uniformly and comprehensively coat the positive electrode active material, which is beneficial to improving the electrochemical stability of the positive electrode material under high charging voltage.

[0131] In some embodiments, according to the second aspect, a fifth example of the second aspect is proposed, wherein the second covering layer is Li. a M'Cl a+b Where a = 1-7 and b = 2-4. The second coating layer is deposited using a second lithium source, a chlorine source, and a second metal source as precursors.

[0132] In some embodiments, according to the second aspect, a sixth example of the second aspect is proposed, wherein the second lithium source is RLi, and the chlorine source is R'Cl. c The second metal source is R2M'. The deposition temperature is 200-300℃. RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester, and R'Cl... c It is one or more of chloroalkanes, chlorocarboxylic acids, chloroalcohols, and chloroesters, RLi, R'Cl c The boiling point is between 70 and 300 °C. R2M' is selected from one or more of alkyl metals, carboxylic acid metals, alcohol metals, and ester metals, with 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, where c is an integer from 1 to 10.

[0133] In some embodiments, according to the second aspect, a seventh example of the second aspect is proposed, RLi, R'Cl c The molar ratio of R2M' to R2M' is (a*c)∶(a+b)∶c.

[0134] In "(a*c):(a+b):c", "a" refers to Li a M'Cl a+b The number of lithium atoms contained in it, "a+b" refers to the number of lithium atoms in Li. a M'Cl a+b The number of chlorine atoms contained in it, "c" refers to R'Cl c The number of Cl atoms contained in the coating, "a*c" refers to the product of a and c. Optionally, in some second coating layer embodiments, as described above, a = 1-7, b = 2-4, and c is an integer from 1 to 10. Then a*c can be 1-70, a+b can be 3-11, and c can be 1-10. Thus, (a*c)∶(a+b)∶c can be (1-70)∶(3-11)∶(1-10), i.e., RLi, R'Cl c The molar ratio of R2M' to R2M' can be (1-70):(3-11):(1-10). For example, RLi, R'Cl c The molar ratio of R2M' can be (1-10):(3-11):(1-10), (10-20):(3-11):(1-10), (20-30):(3-11):(1-10), (30-40):(3-11):(1-10), (40-50):(3-11):(1-10), (50-60):(3-11):(1-10) or (60-70):(3-11):(1-10).

[0135] In some specific embodiments, RLi may be lithium methyl, lithium n-butyl, or lithium tert-butoxide, etc.

[0136] In some specific embodiments, R'Cl c It can be chloroethylene carbonate.

[0137] In some specific embodiments, the deposition temperature may be, for example, 250-300°C. Within this deposition temperature range, the second coating layer can be formed well to coat the first coating layer.

[0138] In some embodiments, according to the second aspect, an eighth example of the second aspect is proposed, wherein the second covering layer is Li a M' m S a+b Where a = 1-7, b = 2-5, and m is an integer from 1 to 5. A second coating layer was deposited using a third lithium source, a sulfur source, and an M' source as precursors.

[0139] In some embodiments, according to the second aspect, a ninth example of the second aspect is provided, wherein the third lithium source is RLi. The sulfur source is R'S. The M' source is R2M'. The deposition temperature is 200-300°C. Wherein, RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alcohol, and lithium ester; R'S is one or more of thioalkanes, thiocarboxylic acids, thioalcohols, thioesters, and sulfonates; the boiling points of RLi and R'S are between 70 and 300°C; R2M' is phosphorous acid with a boiling point between 70 and 300°C; and M' is phosphorus (P).

[0140] Optimizing the precursor and deposition temperature makes it easier to form a second coating layer in a comprehensive and uniform manner.

[0141] In some specific embodiments, RLi may be lithium methyl, lithium n-butyl, or lithium tert-butoxide, etc.

[0142] In some specific embodiments, R'S may be methyl methanesulfonate.

[0143] In some specific embodiments, the deposition temperature may be, for example, 250-300°C. Within this deposition temperature range, the second coating layer can be formed well to coat the first coating layer.

[0144] Due to RLi, R'Cl c R'S and R2M' need to participate in the deposition process in a gaseous state, therefore they need to be heated to vaporize them before entering the reaction chamber. This application does not impose any particular limitation on their heating temperature, as long as it allows for vaporization. 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 It is ethylene chlorocarbonate. The heating temperature of ethylene chlorocarbonate can be 200-300℃, and 240℃ is optional. R2M' can be triethylin, and the heating temperature of triethylin can be 100-300℃, and 190℃ is optional.

[0145] In some embodiments, according to the second aspect, a tenth example of the second aspect is proposed, wherein the molar ratio of RLi, R'S and R2M' is a∶(a+b)∶m.

[0146] In “a∶(a+b)∶m”, “a” refers to Li a M' m S a+b The number of lithium atoms contained in it, "a+b" refers to the number of lithium atoms in Li. a M' m S a+b The number of sulfur atoms contained in it, "m" refers to the number of sulfur atoms in Li. a M' m S a+bThe number of M' atoms contained in it. Optionally, in some second coating layer embodiments, as described above, a = 1-7, b = 2-5, m is an integer from 1 to 5, then a can be 1-7, a+b can be 3-12, m can be 1-5, then a∶(a+b)∶m can be (1-7)∶(3-12)∶(1-5), that is, the molar ratio of RLi, R'S and R2M' is (1-7)∶(3-12)∶(1-5).

[0147] By optimizing RLi and R'Cl c The molar ratio of R2M' to RLi, R'S and R2M' enables the second coating layer to more uniformly and comprehensively coat the first coating layer, which is beneficial to improving the lithium-ion conduction rate of the cathode material and protecting the first coating layer from irreversible decomposition due to the absorption of moisture from the air.

[0148] Specifically, the coating process using atomic layer deposition includes the following steps.

[0149] First, the positive electrode active material powder is placed in the reactor, the reactor is evacuated, and an inert gas is introduced for atmosphere purging. During purging, the flow rate of the inert gas is controlled to disperse the positive electrode active material. Optionally, the inert gas is one or more of argon, helium, and nitrogen.

[0150] Then, with RLi, R'F c R1M was used as a precursor for sample introduction to deposit the first coating layer. Specifically, depositing the first coating layer included: introducing the precursor and inert gas into the reactor in alternating pulses according to the above molar ratio for purging. For example, RLi was introduced first, followed by inert gas purging after the process; then R'F was introduced. c After the process is complete, an inert gas is introduced for purging; then R1M is introduced, and after that, an inert gas is introduced for purging again. This completes one cycle. Each completed cycle represents the formation of a ring of Li on the surface of the positive electrode active material powder. a MF a+b The number of repetitions of this process is determined by the thickness of the first coating layer. In some embodiments of this application, the inert gas is one or more of argon, helium, and nitrogen. In this application, RLi, R'F c The injection pulses of R1M and R1M are determined by the molar ratio of the three.

[0151] After the first coating layer is completed, inert gas can be continuously introduced for atmosphere purging to clean the pipeline.

[0152] Afterwards, with RLi and R'Cl cR2M was used as a precursor for sample introduction to deposit a second coating layer. Specifically, the deposition of the second coating layer included: purging the reactor with alternating pulses of the precursor and inert gas according to the above molar ratio, thereby depositing Li on the surface of the first coating layer. a M'Cl a+b For example, first introduce RLi, then purge with an inert gas; then introduce R'Cl. c After the process is complete, an inert gas is introduced for purging; then R2M' is introduced, and after that, an inert gas is introduced for purging again. This completes one cycle. Each completion of this cycle represents the coating of the first coating layer with a ring of Li. a M'Cl a+b The number of repetitions of this process is determined by the thickness of the second coating layer. In some embodiments of this application, the inert gas is one or more of argon, helium, and nitrogen. In this application, RLi, R'Cl... c The injection pulses of R2M' and R2M' are determined by the molar ratio of the three.

[0153] Alternatively, a second coating layer can be deposited subsequently using RLi, R'S, and R2M' as precursors. Specifically, depositing the second coating layer includes: purging the reactor with alternating pulses of the precursors and inert gas in the aforementioned molar ratio, thereby depositing Li on the surface of the first coating layer. a M' m S a+b For example, first, RLi is introduced, followed by purging with inert gas; then R'S is introduced, followed by purging with inert gas; then R2M' is introduced, followed by purging with inert gas, and so on, completing one cycle. Each completion of this cycle represents the formation of one ring of LiaM' on the surface of the second coating layer. m S a+b Each coating layer has a thickness of approximately 0.1 nm, and the number of repetitions of this process is determined by the thickness of the second coating layer. In some embodiments of this application, the inert gas is one or more of argon, helium, and nitrogen. In this application, the injection pulses of RLi, R'S, and R2M' are determined by the molar ratio of the three.

[0154] In some embodiments, according to the second aspect, an eleventh example of the second aspect is provided, wherein after the second coating layer is formed, the cathode material is calcined in a protective atmosphere.

[0155] 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, forming a cubic close-packed anion arrangement (CCP), which helps to form a 3D lithium-ion transport channel, improve the rate performance and cycle stability of the battery cell; (2) It helps to achieve better atomic fusion at the junction of the positive electrode active material and the first coating layer and at the junction of the first coating layer and the second coating layer, forming a transition layer, reducing the grain boundary resistance caused by the coating interface, and reducing the impedance of the battery cell.

[0156] In some embodiments, according to the second aspect, a twelfth example of the second aspect is provided, wherein the calcination temperature is 150-500°C, optionally 150-300°C; and the calcination time is 1-24h, optionally 4-20h.

[0157] In this design, optimizing the calcination temperature and calcination time is beneficial to improving the calcination effect, which in turn helps to increase the crystallinity of the first coating layer and the second coating layer, and helps to form a transition layer at the interface between the highly active material and the first coating layer, as well as at the interface between the first coating layer and the second coating layer.

[0158] 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.

[0159] In some specific embodiments, the calcination time can be 4-20 hours.

[0160] In some specific embodiments, the protective atmosphere may be one or more of argon, helium, and nitrogen.

[0161] In some specific embodiments, calcination can be carried out in a tube furnace or a box furnace.

[0162] A third aspect of this application provides a secondary battery, comprising the positive electrode material described in the first aspect of this application or the positive electrode material obtained according to the preparation method described in the second aspect of this application.

[0163] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0164] In one embodiment of this application, a secondary battery is provided.

[0165] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0166] [Positive electrode plate]

[0167] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the positive electrode film layer includes the positive electrode material of the first aspect of this application or the positive electrode material obtained according to the preparation method of the second aspect of this application.

[0168] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0169] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0170] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0171] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0172] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0173] 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 (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0174] [Negative electrode plate]

[0175] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0176] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0177] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0178] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode 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, and lithium titanate, etc. 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, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0179] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of 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).

[0180] In some embodiments, the negative electrode film may optionally include 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.

[0181] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0182] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0183] [Electrolytes]

[0184] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0185] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0186] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0187] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0188] In some embodiments, the electrolyte may optionally include 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 battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0189] [Isolation membrane]

[0190] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0191] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0192] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0193] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0194] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0195] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured secondary battery 5.

[0196] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0197] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0198] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0199] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0200] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0201] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0202] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric 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.

[0203] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0204] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0205] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0206] In the technical solutions of this application, since the positive electrode material of the first aspect of this application or the positive electrode material prepared according to the method of the second aspect of this application is used, the secondary battery of this application also has high electrochemical stability and lithium-ion conduction rate under high charging voltage.

[0207] A fourth aspect of this application provides a battery module including the secondary battery described in the third aspect of this application.

[0208] In the technical solutions of this application embodiment, since the positive electrode material of the first aspect of this application or the positive electrode material prepared according to the method of the second aspect of this application is used, the battery module of this application has high electrochemical stability and lithium-ion conduction rate under high charging voltage.

[0209] The fifth aspect of this application provides a battery pack including the battery module described in the fourth aspect of this application.

[0210] In the technical solutions of this application embodiment, since the positive electrode material of the first aspect of this application or the positive electrode material prepared according to the method of the second aspect of this application is used, the battery pack of this application has high electrochemical stability and lithium-ion conduction rate at high charging voltage.

[0211] A sixth aspect of this application provides an electrical device comprising 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.

[0212] In the technical solutions of this application embodiment, since the positive electrode material of the first aspect of this application or the positive electrode material prepared according to the method of the second aspect of this application is used, the electrical device of this application has high electrochemical stability and lithium-ion conduction rate under high charging voltage.

[0213] The present invention will be further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0214] Preparation of cathode materials

[0215] Example 1

[0216] First, the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) powder is placed in an atomic layer deposition reactor. The reactor is evacuated and argon gas is introduced for atmosphere purging. The argon gas flow rate is controlled to ensure that the LiFePO4 powder is uniformly dispersed.

[0217] Then, lithium tert-butoxide, ethylene fluorocarbonate, and tris(2,2,6,6-tetramethyl-3,5-heptadecanoic acid) yttrium gas were introduced into the reactor at 200°C in an alternating pulse manner at a molar ratio of 3:6:1, followed by purging with argon gas. Specifically, lithium tert-butoxide was introduced first, followed by purging with inert gas; then ethylene fluorocarbonate was introduced, followed by purging with inert gas; then tris(2,2,6,6-tetramethyl-3,5-heptadecanoic acid) yttrium was introduced, followed by purging with inert gas. This process constitutes one cycle. Each completion of this cycle represents the formation of a ring of Li3YF6 on the surface of the LiFePO4 powder. The injection temperature, injection pulse, and argon purge time for lithium tert-butoxide were 160℃, 3s, and 15s, respectively; for fluoroethylene carbonate, the injection temperature, injection pulse, and argon purge time were 240℃, 6s, and 15s, respectively; and for tris(2,2,6,6-tetramethyl-3,5-heptadecanoic acid)yttrium, the injection temperature, injection pulse, and argon purge time were 290℃ and 1s, respectively. After 30 repeated coating cycles, the first coating layer was prepared, with a thickness of approximately 3nm.

[0218] Afterwards, argon gas was continued to be introduced for atmosphere purging to clean the pipeline.

[0219] Next, lithium tert-butoxide, ethylene chloride carbonate, and triethylindium were introduced into a reactor at 200°C using an alternating pulsed flow at a molar ratio of 3:6:1, followed by purging with inert gas. Specifically, lithium tert-butoxide was introduced first, followed by purging with inert gas; then ethylene chloride carbonate was introduced, followed by purging with inert gas; finally, triethylindium was introduced, followed by purging with inert gas. This process constituted one cycle. Each completed cycle represented the coating of the first coating layer with a ring of Li3InCl6. The injection temperature, injection pulse, and argon purging time for lithium tert-butoxide were 160°C, 3 s, and 15 s, respectively; for ethylene chloride carbonate, the injection temperature, injection pulse, and argon purging time were 125°C, 6 s, and 15 s, respectively; and for triethylindium, the injection temperature, injection pulse, and argon purging time were 189°C, 1 s, and 15 s, respectively. After repeating the coating process 10 times, the second coating layer was prepared, with a thickness of approximately 1 nm.

[0220] Then, the obtained material was transferred to a tube furnace and calcined at 260°C for 4 hours with Ar as the protective gas to obtain a double-coated cathode material.

[0221] Examples 2-14, 16 and 18-30

[0222] 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 in Example 1.

[0223] Example 15

[0224] The cathode material was prepared according to the method of Example 1, except that lithium tert-butoxide, ethylene fluorocarbonate and tetraethyl germanium were introduced into a reactor at 200°C in an alternating pulse manner at a molar ratio of 3:7:1, and argon gas was introduced for atmosphere purging; other parameters are detailed in Table 1 below.

[0225] Example 17

[0226] The cathode material was prepared according to the method of Example 1, except that lithium tert-butoxide, phosphorous acid and methyl methanesulfonate were introduced into a reactor at 200°C in an alternating pulse manner at a molar ratio of 7:11:3, and argon gas was introduced for atmosphere purging; other parameters are detailed in Table 1 below.

[0227] Comparative Example 1

[0228] 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 Li3InCl6 and the second coating layer was Li3YF6; 2) it was not calcined in a tube furnace.

[0229] Comparative Example 2

[0230] The cathode material was prepared according to the method of Example 1, except that: 1) only a 4 nm thick Li3YF6 layer was coated on the surface of the cathode active material powder as the first coating layer, and there was no second coating layer; 2) it was not calcined in a tube furnace.

[0231] Comparative Example 3

[0232] The cathode material was prepared according to the method of Example 1, except that: 1) only a 4 nm thick Li3InCl6 layer was coated on the surface of the cathode active material powder as the first coating layer, and there was no second coating layer; 2) it was not calcined in a tube furnace.

[0233] Comparative Example 4

[0234] The cathode material was prepared according to the method of Example 1, except that: 1) the surface of the cathode active material powder was first coated with a layer of Li3InCl6, and then coated with three layers of Li3YF6. This is one cycle. The cycle was repeated 10 times, and the thickness of the resulting mixed coating layer was 4 nm; 2) it was not calcined in a tube furnace.

[0235] Comparative Example 5

[0236] This comparative example serves as a blank control group. Only NCM811 powder is provided without any processing.

[0237] The coating parameters for Examples 1-30 and Comparative Examples 1-5 are shown in Table 1 below.

[0238] Using the cathode materials prepared in Examples 1-30 and Comparative Examples 1-5, coin cells and symmetrical cells were prepared according to the following general preparation method.

[0239] Preparation of button cells

[0240] Preparation of the positive electrode sheet:

[0241] Polyvinylidene fluoride (PVDF) binder was added to N-methylpyrrolidone (NMP) solvent and stirred continuously until PVDF was completely dissolved. Then, conductive carbon black was added and stirred to disperse it. Next, the prepared positive electrode material was added and stirred until it was evenly dispersed (NCM811: conductive carbon black: PVDF = 96:2:2, this ratio is by mass). The stirred slurry was directly coated onto a 12μm thick aluminum foil using a 200μm scraper. After drying at 100℃ under forced air for 6 hours, it was punched into positive electrode sheets with a diameter of 16mm.

[0242] Preparation of negative electrode sheet:

[0243] Use 18μm die-cut lithium sheets as the negative electrode. Before use, brush off any small amount of impurities and possible oxides on the surface to expose the silvery-white metallic luster.

[0244] Assembly of button cells:

[0245] Inside a glove box (with water and oxygen content ≤0.1ppm), the negative electrode shell, negative electrode sheet, separator (polypropylene), positive electrode sheet, gasket, spring sheet, and positive electrode shell were placed in sequence. During the placement process, 120μL of electrolyte (1.0mol / L lithium hexafluorophosphate) was added dropwise, and the mixture was left to stand for 2 hours. The resulting coin cell was used to test the battery cycle performance.

[0246] Preparation of symmetric cells

[0247] The positive electrode was prepared according to the method for preparing a coin cell positive electrode. The freshly prepared positive electrode, polypropylene separator, and electrolyte (1.0 mol / L lithium hexafluorophosphate, 120 μL) were assembled into a symmetrical positive electrode cell and placed in a 25°C constant temperature oven for 2 hours to ensure electrolyte wetting. The resulting symmetrical cell was used for impedance testing.

[0248] Characterization of coating layer

[0249] 1. Electrochemical window test of the first coating layer

[0250] The electrochemical window was tested using the linear voltammetry module of an electrochemical workstation. A first coating material obtained by atomic layer deposition (ALD) (this first coating material can be obtained, for example, by using ALD with a first lithium source, a fluorine source, and a first metal source as precursors, depositing the sample onto a smooth Cu foil, and then scraping off the powder to obtain the first coating material; however, this application is not limited to obtaining the first coating material by this method, and other suitable methods can be used) and a binder PVDF were mixed in a 95:5 mass ratio and drop-coated onto the surface of a glassy carbon electrode as the working electrode. A voltammetry curve was tested using 1M LiPF6 as the solution and a lithium sheet as the counter electrode, with a voltage range of 2.5–6.5 V and a scan rate of 0.5 mV / s. The recorded oxidation potential is the electrochemical window.

[0251] 2. Lithium-ion conductivity test of the second coating layer

[0252] Lithium-ion conductivity measurement method:

[0253] The AC impedance test was performed using the impedance test module of the electrochemical workstation, in voltage perturbation mode PEIS, with a perturbation voltage of 5mY and a frequency range of 200kHz to 30MHz. The second coating material obtained by atomic layer deposition (ALD) (the second coating material can be obtained, for example, by using ALD with a second lithium source, a chlorine source, and a second metal source as precursors, or by using a third lithium source, a sulfur source, and a M' source as precursors, depositing the sample onto a smooth Cu foil, and then scraping off the powder to obtain the second coating material; however, this application is not limited to obtaining the second coating material by this method, and other suitable methods can be used) was subjected to impedance testing, and the lithium-ion conductivity of the electrolyte sheet was calculated. Specifically, after obtaining the second coating material, the second coating material was pressed and calcined to form a blocking electrode with a diameter of approximately 6mm and a thickness of approximately 1.3mm. The blocking electrode was then subjected to magnetron sputtering gold sputtering, and then the AC impedance test was performed using the electrochemical workstation. The gold-plated blocking electrode is an ionic conductor and not conductive to electrons. Therefore, before impedance testing, blocking Ag electrodes need to be connected to both sides of the gold-plated blocking electrode. The gold-plated blocking electrode is polished smooth to a certain thickness, coated with silver paste to draw Ag wires, and then subjected to Ag firing in a muffle furnace to ensure close contact between the Ag electrodes and the electrolyte surface. The resistance is measured as R = h / (ρs), where h is the thickness of the solid electrolyte sheet, s is the area of ​​the solid electrolyte sheet, and ρ is the resistivity. The lithium-ion conductivity σ is then calculated using this formula: σ = 1 / ρ.

[0254] Electrical performance testing

[0255] 1. Capacity retention test of button cells

[0256] The capacity retention test procedure is as follows: At 25℃, the prepared coin cell is charged to 4.2V at a constant current of 1 / 3C, then charged to a current of 0.05C at a constant voltage of 4.2V, rested for 5 minutes, and then discharged to 2.8V at 1 / 3C. The resulting capacity is recorded as the initial capacity C0. The above steps are repeated for the same coin cell, and the discharge capacity C of the coin cell after the nth cycle is recorded simultaneously. n Then, the capacity retention rate P of the coin cell after each cycle n =C n / C0*100%.

[0257] The capacity retention rate data in Table 1 were obtained after 100 cycles under the above test conditions, i.e., P 100 The value of .

[0258] 2. Symmetrical Cell AC Impedance Test

[0259] The prepared symmetrical cell underwent AC impedance testing. The AC impedance testing was performed using the impedance testing module of an electrochemical workstation, in PEIS voltage perturbation mode, with a perturbation voltage of 5mV, a frequency range of 200kHz-30MHz, a voltage range of 0-5V, and 0-5V voltage protection. The test data were plotted with the negative imaginary part of the impedance (-Z”) on the ordinate and the real part Z on the abscissa to obtain the AC impedance spectrum data, as shown below. Figure 1 As shown.

[0260] Fitting and processing of impedance test data:

[0261] The data recorded from the AC impedance test were fitted using Z-fit software, with R selected as the fitting circuit. s +C1 / R SEI +C2 / R ct +W, where R s It is an ohmic impedance, mainly related to the conductivity of the positive electrode material; R ct C1 is the charge transfer impedance, which mainly reflects the lithium-ion insertion / extraction rate in the cathode material; C2 is the double-layer capacitance at the SEI interface (solid electrolyte interface); R SEI C1 represents the SEI film impedance, primarily reflecting the SEI film's hindrance to lithium-ion migration; C2 is the double-layer capacitance at the charge transfer interface; W is the semi-infinite diffusion element, reflecting the effect of diffusion on impedance. The fitting criteria require: an error less than 5%, and the intersection point with the real part should be consistent with the fitted R0. s The deviation must be less than 5%. Only fitting results that meet the above requirements can be accepted, and the R-value of the fitting results will be included. ct With R s Extract and record in Table 1.

[0262] Table 1: Coating parameters and electrical performance test data

[0263]

[0264]

[0265]

[0266]

[0267] As shown in Table 1, the capacity retention rate of Example 1 is significantly higher than that of Comparative Examples 1-5, indicating that the electrochemical stability and cycling performance of Example 1 are significantly better than those of Comparative Examples 1-5. Therefore, the double-layer coating of this application can significantly improve the electrochemical stability of the cathode material under high charging voltage.

[0268] As can be seen from Table 1, the ohmic impedance R in Example 1 is... s and charge transfer impedance Rct All are less than those in comparative examples 1-5, especially the charge transfer impedance R. ct Significantly smaller. This indicates that the double-layer coating of this application can significantly reduce impedance.

[0269] Furthermore, a comparison of Examples 1 and 13 shows that the double-layer coated cathode material in Example 13 was not calcined, and its ohmic impedance R s and charge transfer impedance R ct All were higher than in Example 1. This indicates that the calcination process has a beneficial effect on reducing impedance.

[0270] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A positive electrode material, characterized in that, include: Positive electrode active material; A first coating layer, wherein the first coating layer coats the positive electrode active material, and the electrochemical window of the first coating layer is above 6.0 V; as well as 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 higher.

2. 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'Cl a+b Or Li a M' m S a+b ; Wherein, M and M' are each independently one or more of Sc, Y, La, Gd, Tb, Dy, Tm, Ho, Sm, Er, Eu, Lu, Yb, Ti, Zr, Al, Ga, In, Nb, Ge and P; a = 1-7, b = 2-4, m = 1-3.

3. The cathode material according to claim 2, characterized in that, M and M' are each independently divalent, trivalent, or tetravalent cations.

4. The cathode material according to claim 2 or 3, characterized in that, M and M' are each independently one or more of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, In, Y, Ge, and P.

5. The positive electrode material according to claim 4, characterized in that, M and M' are each independently one or more of In, Y, Ge, and P.

6. The cathode material according to claim 2, characterized in that, The Li a MF a+b It is Li3YF6, and the Li a M'Cl a+b It is Li3InCl6.

7. The cathode material according to claim 1, characterized in that, The lithium-ion conductivity of the second coating layer is 10. -2 S / cm or higher.

8. The positive electrode material according to claim 1, characterized in that, The thickness of the first coating layer is 3-10 nm; And / or, the thickness of the second coating layer is 1-5 nm.

9. The cathode material according to claim 8, characterized in that, The thickness of the first coating layer is 3-5 nm; And / or, the thickness of the second coating layer is 1-2 nm.

10. The cathode material according to claim 1, characterized in that, The total thickness of the first coating layer and the second coating layer is less than 10 nm.

11. The cathode material according to claim 1, characterized in that, The positive electrode active material is LiFePO4, LiCoO2, LiMnO4, and LiNi. x Co y M 1-x-y One or more of O2, wherein M is one or more of Mn, Al, Mg, Sn, Y and Cr, 0≤x<1, 0≤y≤1, and x+y≤1.

12. The cathode material according to claim 1, characterized in that, The positive electrode active material contains at least one of Mn and Co, and the thickness of the first coating layer increases with the increase of Mn content and Co content.

13. A method for preparing a positive electrode material, characterized in that, include: A first coating layer is formed on the surface of the positive electrode active material; as well as A second coating layer is formed by coating the surface of the first coating layer to obtain the positive electrode material; The first coating layer has an electrochemical window of 6.0 V or higher, and the second coating layer has a lithium-ion conductivity of 10. -3 S / cm or higher.

14. The preparation method according to claim 13, characterized in that, The coating was performed using atomic layer deposition.

15. The preparation method according to claim 13 or 14, characterized in that, The first coating layer is Li a MF a+b , where a = 1-7, b = 2-4; the first coating layer is deposited using the first lithium source, fluorine source and the first metal source as precursors.

16. The preparation method according to claim 15, characterized in that, The first lithium source is RLi, and the fluorine source is R'F. c The first metal source is R1M, and the deposition temperature is 200-300℃; Wherein, RLi is selected from one or more of lithium halides, alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester, and R'F c It is one or more of fluoroalkanes, fluorocarboxylic acids, fluoroalcohols, and fluoroesters, RLi, R'F c The boiling point is between 70 and 300 °C. R1M is selected from one or more of alkyl metals, carboxylic acid metals, alcohol metals, and ester metals, with 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. c is an integer from 1 to 10.

17. The preparation method according to claim 16, characterized in that, The molar ratio of RLi, R'Fc, and R1M is .

18. The preparation method according to claim 17, characterized in that, The molar ratio of RLi, R'Fc and R1M is (1-70):(3-11):(1-10).

19. The preparation method according to claim 13, characterized in that, The second coating layer is Li a M'Cl a+b , where a = 1-7, b = 2-4; the second coating layer is deposited using the second lithium source, chlorine source and the second metal source as precursors.

20. The preparation method according to claim 19, characterized in that, The second lithium source is RLi, and the chlorine source is R'Cl. c The second metal source is R2M', and the deposition temperature is 200-300℃; Wherein, RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alkoxide, and lithium ester, and R'Cl c It is one or more of chloroalkanes, chlorocarboxylic acids, chloroalcohols, and chloroesters, RLi, R'Cl c The boiling point is between 70 and 300 °C. R2M' is selected from one or more of alkyl metals, carboxylic acid metals, alcohol metals, and ester metals, with 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, and c is an integer from 1 to 10.

21. The preparation method according to claim 20, characterized in that, RLi、R'Cl c The molar ratio of R2M' to R2M' is .

22. The preparation method according to claim 21, characterized in that, RLi、R'Cl c The molar ratio of R2M' to R2M' is (1-70):(3-11):(1-10).

23. The preparation method according to claim 13, characterized in that, The second coating layer is Li a M' m S a+b , where a = 1-7, b = 2-5, and m is an integer from 1 to 5; the second coating layer is deposited using the third lithium source, sulfur source, and M' source as precursors.

24. The preparation method according to claim 23, characterized in that, The third lithium source is RLi, the sulfur source is R'S, the M' source is R2M', and the deposition temperature is 200-300℃; Wherein, RLi is selected from one or more of alkyl lithium, lithium carboxylate, lithium alcohol, and lithium ester; R'S is one or more of thioalkanes, thiocarboxylic acids, thioalcohols, thioesters, and sulfonates; the boiling points of RLi and R'S are between 70 and 300 °C; R2M' is phosphorous acid with a boiling point between 70 and 300 °C; and M' is P.

25. The preparation method according to claim 24, characterized in that, The molar ratio of RLi, R'S and R2M' is a: (a+b) : m.

26. The preparation method according to claim 25, characterized in that, The molar ratio of RLi, R'S and R2M' is (1-7):(3-12):(1-5).

27. The preparation method according to claim 13, characterized in that, After the second coating layer is formed, the cathode material is calcined in a protective atmosphere.

28. The preparation method according to claim 27, characterized in that, The calcination temperature is 150-500℃, and the calcination time is 1-24h.

29. The preparation method according to claim 28, characterized in that, The calcination temperature is 150-300℃, and the calcination time is 4-20h.

30. A secondary battery, characterized in that, This includes the cathode material according to any one of claims 1-12 or the cathode material obtained by the preparation method according to any one of claims 13 to 29.

31. A battery module, characterized in that, Includes the secondary battery as described in claim 30.

32. A battery pack, characterized in that, Includes the battery module as described in claim 31.

33. An electrical appliance, characterized in that, It includes at least one of the secondary battery of claim 30, the battery module of claim 31, and the battery pack of claim 32.

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