Positive electrode active material, preparation method, positive plate, battery, battery pack and electric equipment

Abstract

The invention provides a positive active material, a preparation method, a positive plate, a battery, a battery pack and electric equipment. The positive electrode active material comprises an inner core and a coating layer coating at least part of the surface of the inner core, in the direction away from the inner core, the coating layer comprises a first coating layer and a second coating layer which are stacked, the first coating layer comprises an active lithium salt, the second coating layer comprises a lithium-containing compound, and the porosity of the second coating layer is not higher than 5%; anions of the active lithium salt comprise inorganic acid radical ions and / or organic acid radical ions, and pKa of acid formed by the inorganic acid radical ions is not higher than 6. The positive electrode active material is composed of a special coating layer, so that the positive electrode active material has a higher first effect and a lower expansion rate, and the cycle performance, the safety performance and the energy density of the battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a positive electrode active material, a preparation method, a positive electrode sheet, a battery, a battery pack and an electrical equipment. BACKGROUND

[0002] Secondary batteries (such as lithium ion batteries) have become the core carrier of modern energy storage due to their high energy density, long cycle life and environmental friendliness. They are widely used in consumer electronics (such as smart phones, notebook computers), electric vehicles (such as electric cars, electric bicycles) and large-scale energy storage systems (such as power grid peak shaving, renewable energy matching) and other fields. With the promotion of carbon neutralization, the market's demand for the comprehensive performance of secondary batteries continues to increase, especially in energy efficiency and safety reliability.

[0003] In the actual application of secondary batteries, the first coulombic efficiency (first efficiency) and the expansion rate of the electrode sheet become the key indicators restricting performance upgrading. High first efficiency can reduce the irreversible loss of active lithium, directly improving the battery capacity and energy density; and low expansion is the core prerequisite for ensuring the stability of the battery structure and prolonging the cycle life. If the first efficiency is low, the actual available capacity of the battery will be significantly reduced; and excessive expansion of the battery will cause the interface side reaction to intensify, the internal resistance to rise, and even cause the safety hazard of the separator to be punctured, which seriously limits the commercialization process of high energy density batteries.

[0004] Therefore, how to simultaneously make the battery have higher first efficiency and lower expansion rate is a technical problem to be solved by those skilled in the art. SUMMARY

[0005] The present application provides a positive electrode active material, which has a special coating layer composition, so that the battery has higher first efficiency and lower expansion rate, which helps to improve the cycle performance, energy density and safety performance of the battery.

[0006] The present application provides a preparation method of a positive electrode active material, which is used to realize the preparation of the above-mentioned positive electrode active material.

[0007] The present application also provides a positive electrode sheet comprising the above-mentioned positive electrode active material, which helps to inhibit the loss of active lithium during the formation process of the battery, and the expansion of the electrode sheet itself is also controlled, so that the performance of the battery in cycle performance, safety performance and energy density can be improved.

[0008] The present application also provides a battery comprising the above-mentioned positive electrode sheet, which has higher first efficiency and is not prone to deformation, so that the cycle performance, safety performance and energy density performance are excellent.

[0009] The application also provides a battery pack comprising the above battery, which has excellent cycle performance, safety performance and energy density.

[0010] The application also provides a power consuming device comprising the above battery or battery pack, which has longer standby time and higher safety.

[0011] The application provides a positive electrode active material comprising a core and a coating layer coated on at least part of the surface of the core; in the direction away from the core, the coating layer comprises a first coating layer and a second coating layer arranged in a stack, the first coating layer comprises an active lithium salt, the second coating layer comprises a lithium-containing compound, and the porosity of the second coating layer is not higher than 5%.

[0012] The anion of the active lithium salt comprises inorganic acid radical ions and / or organic acid radical ions, and the pKa of the acid formed by the inorganic acid radical ions is not higher than 6.

[0013] The positive electrode active material as described above, wherein at least any one of the following conditions is met:

[0014] a) the mass percentage of the active lithium salt in the first coating layer is not lower than 50wt%;

[0015] b) the mass percentage of the active lithium salt in the first coating layer is not higher than 70wt%;

[0016] c) the mass percentage of the first coating layer in the positive electrode active material is 0.1wt%-0.3wt%;

[0017] d) the thickness of the first coating layer is 5nm-10nm;

[0018] e) the pH of the first coating layer is 7.5-8.5;

[0019] f) the thickness of the coating layer is 10nm-40nm.

[0020] The positive electrode active material as described above, wherein at least any one of the following conditions is met:

[0021] g) the porosity of the second coating layer is not lower than 2%;

[0022] h) the thickness of the second coating layer is 5nm-15nm;

[0023] i) the mass percentage of the second coating layer in the positive electrode active material is 0.1wt%-0.5wt%.

[0024] The positive electrode active material as described above, wherein the lithium-containing compound comprises at least one of inorganic lithium-containing compound comprising at least one of Li2CO3, LiOH, Li2S, LiBF4, LiPO2F2, and organic lithium-containing compound comprising at least one of LiBOB, LiDFOB, LiFSI, LiCF3SO3.

[0025] Preferably, in the second coating layer, the mass percentage of the inorganic lithium-containing compound in the lithium-containing compound is 40wt%-100wt%.

[0026] The positive electrode active material as described above, wherein the coating layer further comprises a conductive layer, and preferably at least one of the following conditions is satisfied:

[0027] A) the conductive layer is located between the first coating layer and the second coating layer;

[0028] B) the conductive layer is located on the surface of the second coating layer away from the first coating layer;

[0029] C) the thickness of the conductive layer is 5nm-15nm.

[0030] The positive electrode active material as described above, wherein the conductive layer comprises a MXene material, and the MXene material at least satisfies any one of the following conditions:

[0031] D) the electronic conductivity of the MXene material is greater than 10 3 S / m;

[0032] E) the mass percentage of the MXene material in the positive electrode active material is 1wt%-5wt%;

[0033] F) the interlayer spacing of the MXene material is 0.5nm-1.5nm;

[0034] G) the defect density of the MXene material is less than 10 2 / μm

[0035] H) the MXene material comprises at least one of Ti3C2T m , Nb4C3T m , T comprises an oxygen-containing group, a fluorine-containing group, and m>0.

[0036] The positive electrode active material as described above, wherein the core comprises at least one of lithium cobaltate, lithium nickelate, lithium manganate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium iron phosphate, lithium nickel manganate, and lithium manganese iron phosphate material.

[0037] And / or, the active lithium salt includes at least one of LiCl, LiNO3, LiF, LiBr, Li2SO4, Li3PO4, Li2C2O4, lithium maleate, and lithium citrate.

[0038] This application also provides a method for preparing the above-described positive electrode active material, comprising the following steps:

[0039] The core is mixed with acid and subjected to acid treatment to obtain a solid first intermediate. The first intermediate and a lithium-containing compound are then ball-milled to obtain the positive electrode active material; the pK of the acid is... a No higher than 6.

[0040] The preparation method described above, wherein at least one of the following conditions is satisfied:

[0041] I) The acid treatment temperature is 30℃-50℃;

[0042] J) The concentration of the acid is 0.1 mol / L-0.3 mol / L;

[0043] K) After the ball milling treatment, the system is further subjected to annealing. Preferably, the annealing temperature is 300℃-500℃.

[0044] L) After separation, the product after acid treatment is further subjected to annealing to obtain the first intermediate; the annealing temperature is 200℃-500℃ and the annealing time is 1h-4h.

[0045] The acid M) includes at least one of HCl, HNO3, HF, HBr, H2SO4, H3PO4, H2C2O4, maleic acid, and citric acid.

[0046] The preparation method described above involves mixing the first intermediate with a conductive layer material to obtain a second intermediate, and then mixing the second intermediate with the lithium-containing compound to obtain the positive electrode active material; or,

[0047] The first intermediate is mixed with a lithium-containing compound to obtain a second intermediate, and then the second intermediate is mixed with a conductive layer material to obtain the positive electrode active material.

[0048] This application provides a positive electrode sheet comprising the positive electrode active material described in any one of the above claims, or comprising the positive electrode active material prepared by the method described in any one of the above claims.

[0049] This application provides a battery, which includes the positive electrode sheet described above.

[0050] This application provides a battery pack comprising at least two batteries as described above.

[0051] The application provides a power utilization device comprising the battery or the battery pack.

[0052] The positive electrode active material has a core-shell structure, specifically, the surface of the inner core is sequentially coated with a first coating layer containing active lithium salt and a second coating layer containing lithium compound and having low porosity. The lithium-containing components in the first coating layer and the second coating layer synergize to form a transmission channel with lithium affinity. On this basis, the active lithium salt in the first coating layer not only compensates for the lithium consumption of the battery during formation, but also builds abundant lithium ion coordination sites, reduces the retention of lithium ions by the positive electrode electrolyte interface film, and improves the initial efficiency of the material. At the same time, the special porosity of the second coating layer makes it have a relatively dense structure, so that the deformation of the positive electrode active material caused by lattice expansion during repeated lithium ion extraction and insertion can be significantly inhibited. Therefore, the high initial efficiency and low expansion characteristics of the positive electrode active material of the application improve the cycle performance, energy density and safety performance of the battery. DETAILED DESCRIPTION

[0053] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0054] During the use of the battery, during the first charge and discharge of the lithium ion battery, in addition to part of the lithium ions participating in the formation of the solid electrolyte interface film (SEI film) and being lost, the lithium ions migrated from the negative electrode during the discharge process are often trapped in the solid electrolyte interface film (CEI film) on the surface of the positive electrode active material and are difficult to completely insert into the positive electrode active material. At the same time, during the insertion and extraction of lithium ions, the lattice structure of the positive electrode active material will change in volume, causing large lattice strain. With the increase of the number of charge and discharge cycles, the lattice strain is continuously accumulated, promoting the macroscopic expansion of the particles. More importantly, there are differences in lithium ion transport rate in different regions of the positive electrode active material, leading to uneven stress distribution. This uneven stress gradually accumulates in the cycle, further aggravating the particle expansion, seriously damaging the material structure stability and affecting the cycle life of the battery.

[0055] In order to effectively improve the initial efficiency of the battery and inhibit the swelling deformation of the battery in the cycle process, the negative electrode pre-lithiation and high-performance binder are currently used to optimize the performance of the battery. Among them, the negative electrode pre-lithiation is a lithium supplement treatment for the negative electrode material (such as silicon-based material, hard carbon, etc.), which pre-supplies lithium ions that are consumed irreversibly in the first charge-discharge process due to the formation of SEI film, but has inherent defects such as complex process, harsh environmental requirements, high safety risk and high cost; and the use of a binder system with stronger toughness and elasticity (such as polyacrylic acid, polyimide or multiple binders) in the pole piece can better buffer the huge volume change of the active material in the cycle process and maintain the integrity of the electrode structure, but also faces challenges such as cost increase, poor compatibility with existing production process and difficult balance of comprehensive performance.

[0056] Based on this, the first aspect of the present application provides a positive electrode active material, which comprises a core and a coating layer coated on a part of the surface of the core; in the direction away from the core, the coating layer comprises a first coating layer and a second coating layer arranged in layers, the first coating layer comprises an active lithium salt, and the second coating layer comprises a lithium-containing compound, the porosity of the second coating layer is not higher than 5%; the anion of the active lithium salt comprises inorganic acid radical ion and / or organic acid radical ion, and the inorganic acid radical ion forms an acid with a pK a not higher than 6.

[0057] Specifically, the positive electrode active material of the present application is a core-layer coating structure comprising a core and a coating layer, wherein at least part of the surface of the core is coated with the coating layer. In detail, the coating layer comprises a first coating layer and a second coating layer arranged in layers, the first coating layer is coated on at least part of the surface of the core, and at least part of the surface of the first coating layer away from the core is coated with the second coating layer.

[0058] The present application does not limit the composition of the core, which can be a positive electrode active material with lithium ions as active ions commonly used in the art, and the present application also does not specifically limit the particle size of the core.

[0059] In the present application, the first coating layer comprises an active lithium salt. In detail, the active lithium salt of the present application has a composition of LiR, wherein R is the anion of the active lithium salt. The anion can be at least one of inorganic acid radical ion and organic acid radical ion, that is, the active lithium salt of the present application comprises at least one of inorganic lithium salt and organic lithium salt. It should be explained that the inorganic acid radical ion of the present application refers to that it can form an inorganic acid HR with hydrogen ion, and the organic acid radical ion refers to that it can form an organic acid HR with hydrogen ion, wherein the inorganic acid and the organic acid can be monobasic acid or polybasic acid, which is not particularly limited in the present application. It is worth mentioning that when the anion of the present application is inorganic acid radical ion, the pK a of the inorganic acid HR formed by the inorganic acid radical ion and hydrogen ion is not higher than 6. The pK aThe negative logarithm of the dissociation constant of HR, generally calculated according to the following formula:

[0060]

[0061]

[0062] wherein Ka is the dissociation constant of the inorganic acid HR in aqueous solution at 25℃ under 1 atm; C H+ is the hydrogen ion concentration of HR at the dissociation equilibrium, mol / L; C R- is the R ion concentration of HR at the dissociation equilibrium, mol / L; C HR is the HR concentration of HR at the dissociation equilibrium, mol / L.

[0063] It should be noted that when the inorganic acid is a polyacid, when the pK a The anion thereof can be used as the anion in the active lithium salt according to the present application.

[0064] For the lithium-containing compound in the second coating layer, the present application does not make special limitations, which can be a lithium-containing compound commonly used in the art.

[0065] The positive electrode active material according to the present application exhibits significant improvement in key performance indicators such as energy density, cycle stability and safety, and its technical advantages are derived from the innovative design of the composition and structure of the double-layer coating and the precise regulation of the porosity parameter.

[0066] At the interface transmission mechanism level, the first coating layer includes an active lithium salt, and the second coating layer includes a lithium-containing compound. The first coating layer and the second coating layer cooperate through the lithium-containing components, which on the one hand can significantly supplement the consumption of lithium salt in the battery during the formation of the SEI film in the formation process, thereby ensuring that there are enough lithium ions to migrate to the positive electrode during the discharge process; on the other hand, the two also construct a transmission channel with lithium affinity. Specifically, the active lithium salt component in the first coating layer can form additional lithium ion coordination sites, forming a low-impedance transmission path at the CEI film interface, effectively reducing the interface transfer energy barrier during lithium ion deintercalation. This structural design enables lithium ions to pass through the coating layer structure in a more efficient path, reducing the trapping of lithium ions by the CEI film, thereby significantly improving the first coulombic efficiency of the battery.

[0067] In terms of structural stability optimization, the second coating layer adopts a densification structure design with a specific porosity range. By controlling the porosity parameter, a continuous and dense ion transport network is formed between the particles, effectively suppressing the lattice distortion and volume expansion caused by repeated lithium ion deintercalation, uniformly dispersing the uneven stress caused by the difference in lithium ion transmission rate in different regions of the core, and reducing the unit cell expansion rate. Moreover, the dense packing structure strengthens the interfacial bonding strength between the first coating layer and the second coating layer, avoiding interlayer peeling even during long-term cycling, and ensuring the structural stability of the positive electrode active material. Therefore, the lower deformation expansion rate and higher structural stability of the positive electrode active material of the present application can ensure the normal deintercalation of lithium ions, reduce the probability of side reactions with electrolyte, and greatly improve the cycle performance, energy density and safety performance of the battery.

[0068] Notably, when the mass percentage of active lithium salt in the first coating layer is not less than 50wt%, the CEI film has a lower retention rate of lithium ions, and more lithium ions deintercalated from the negative electrode can be intercalated into the positive electrode, thereby significantly improving the initial efficiency of the positive electrode active material. In addition to lithium salts, the remaining components in the first coating layer can be other compounds containing lithium elements, such as lithium hydroxide and lithium carbonate.

[0069] In a specific embodiment, the mass percentage of active lithium salt in the first coating layer is not higher than 70wt%. At this time, when the mass percentage of active lithium salt in the first coating layer is within the above range, the porosity of the active material as a whole can be ensured to be within a reasonable range, maintaining stable contact between the coating layer and the core and improving the cycle performance of the battery.

[0070] In the specific implementation of the present application, the mass percentage of the first coating layer in the positive electrode active material is generally controlled to be 0.01wt% or more. Reasonably controlling the mass percentage of the first coating layer in the positive electrode active material is beneficial to further improve the initial efficiency of the battery, and therefore the mass content of the first coating layer can be controlled to be 0.1wt% or more. The inventors have found that as the mass of the first coating layer increases within a certain range, the initial charge-discharge efficiency and cycle performance of the lithium ion battery both first show an increasing trend and then remain basically unchanged, and therefore the mass percentage of the first coating layer in the positive electrode active material is generally controlled to be within the range of 0.1wt%-0.3wt%.

[0071] In addition, in order to further achieve a balance between cycle stability and transmission kinetics, the transmission rate of lithium ions is not affected while ensuring cycle performance. In an embodiment, the thickness of the first coating layer is 5nm-10nm. In addition, the thickness of the coating layer is controlled to be 10nm-40nm, which further reduces the dissolution of transition metals in the core and improves the transmission of lithium ions to a certain extent.

[0072] In one embodiment, the pH of the first coating layer is 7.5-8.5. The inventors have found that when the pH of the first coating layer is controlled in this range, the cycle performance of the battery can be further improved. The presumed reason can be that, on the one hand, this pH can stabilize the lattice oxygen in the core, so that the positive active material of the application still has excellent structural stability even after the completion of lithium ion extraction, greatly avoiding structural collapse due to oxygen anion migration. On the other hand, this pH value can promote the bonding of the first coating layer with the core and the second coating layer respectively, improve the interfacial adhesion, and inhibit the shedding of the coating layer during charging and discharging.

[0073] In addition, while maintaining structural integrity, the application also limits the lower limit of the porosity of the second coating layer. Specifically, the porosity of the second coating layer is not less than 2%. The retention of moderate pore channels in the second coating layer can also buffer the stress of the core deformation during charging and discharging, and ensure certain electrolyte wettability performance, thereby further balancing the structural stability and ion diffusion performance of the positive active material.

[0074] Similarly, in order to further inhibit the expansion of the core during charging and discharging, the mass percentage of the second coating layer in the positive active material can be controlled to be 0.1wt%-0.5wt%.

[0075] In another embodiment, when the thickness of the second coating layer is 5nm-15nm, the binding force of the second coating layer to the core is further improved under the premise of ensuring normal transmission of lithium ions, ensuring that the positive active material has excellent structural stability during long-term cycling, and making the optimization of the cycle performance of the battery more significant.

[0076] The lithium-containing compound in the application includes at least one of an inorganic lithium-containing compound and an organic lithium-containing compound. In the specific selection of the lithium-containing compound, the inorganic lithium-containing compound may, for example, include at least one of Li2CO3, LiOH, Li2S, LiBF4, LiPO2F2, and the organic lithium-containing compound may, for example, include at least one of LiBOB, LiDFOB, LiFSI, and LiCF3SO3.

[0077] In addition, in the second coating layer, when the mass percentage of the inorganic lithium-containing compound in the lithium-containing compound is 40wt%-100wt%, it is helpful to further improve the cycle performance of the battery. It should be noted that when the inorganic lithium-containing compound in the lithium-containing compound is less than 100% in the second coating layer, the remaining components in the lithium-containing compound include organic lithium-containing compounds.

[0078] Further, in order to improve the fast charging performance of the positive electrode active material, the coating layer in the positive electrode active material of the present application can further comprise a conductive layer. The conductive layer can be located between the first coating layer and the second coating layer, or can be located on the surface of the second coating layer away from the first coating layer. That is, in the direction away from the core, the coating layer comprises the first coating layer, the conductive layer and the second coating layer in sequence, or the coating layer comprises the first coating layer, the second coating layer and the conductive layer in sequence. The conductive layer comprises a conductive material, which can help to improve the electronic conductivity of the positive electrode active material, thereby improving the fast charging performance of the battery.

[0079] In addition, while ensuring that the electronic conductivity of the positive electrode active material is improved, in order to further take into account the energy density of the battery, the thickness of the conductive layer can be controlled. Through the research of the inventors, when the thickness of the conductive layer is 5-15 nm, the fast charging performance of the battery can be significantly improved while ensuring the energy density.

[0080] The present application does not limit the specific selection of the conductive material, which can be a common conductive material in the art. Exemplarily, it can include carbon-based materials (carbon black, carbon nanotubes, graphene, conductive graphite), conductive polymers (polypyrrole, polyaniline, poly 3,4-ethylenedioxythiophene), metal oxides (ZnO, TiO2, RuO2), metal sulfides (TiS2, MoS2), etc.

[0081] The inventors found that when the conductive material comprises MXene material, not only the transition metal and the strong covalence of M-X bond therein make it have higher electronic conductivity, but also its larger interlayer spacing ensures a certain lithium ion conduction efficiency. This electronic-ion synergistic optimization mechanism not only improves the fast charging performance of the battery, but also further optimizes the cycle performance and initial efficiency.

[0082] The chemical formula of the MXene material of the present application is M n+1 X n T m wherein M is at least one of transition metals; X is carbon or nitrogen element, which is used to form a strong covalent bond with M; T represents a surface terminal group. n>0, m>0.

[0083] In a specific embodiment, in order to significantly improve the electronic conductivity of the positive electrode active material, in the conductive layer, MXene material with electronic conductivity greater than 10 3 S / m can be selected.

[0084] In addition, when the mass percentage of the conductive layer in the positive electrode active material is 1wt%-5wt%, the fast charging performance of the battery can be significantly improved while ensuring the energy density.

[0085] Further, in order to balance the electron-ion conductivity of the MXene material, the MXene material with an interlayer spacing of 0.5 nm-1.5 nm can be selected. The interlayer spacing can ensure the smooth transmission of lithium ions and to a certain extent, ensure the interlayer contact, avoiding the influence of electron conductivity.

[0086] In addition, in order to further improve the cycle performance of the battery, a MXene material with a defect density of less than 10 / μm 2 The inventors found that as the defect density of the MXene material increases, the defects will act as active sites for side reactions with the electrolyte, resulting in lithium ion transition consumption and battery gas expansion.

[0087] In the MXene material, different M, X and T functional groups can adjust the electronic structure, interlayer spacing and interface reaction activity of the MXene material, and thus control the electrochemical performance and structural stability. Through the inventors' extensive research, when the MXene material includes at least one of Ti3C2T m , Nb4C3T m , T includes an oxygen-containing group and a fluorine-containing group, and m>0, the MXene material has strong electron-ion double conductivity, and the battery including the positive electrode active material has outstanding performance in terms of fast charging performance and cycle performance.

[0088] As described above, the present application does not limit the selection of the core. For example, the core includes at least one of lithium cobaltate, lithium nickelate, lithium manganate, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium iron phosphate, lithium nickel manganate, and lithium manganese iron phosphate material. Specifically, the above positive electrode active material can be metal-doped or undoped.

[0089] When the active lithium salt is specifically selected, the active lithium salt in the first coating layer may, for example, include at least one of LiCl, LiNO3, LiF, LiBr, Li2SO4, Li3PO4, Li2C2O4 (lithium oxalate), lithium maleate, and lithium citrate.

[0090] The second aspect of the present application also provides a preparation method of the positive electrode active material of the first aspect. Specifically, the preparation method of the present application includes the following steps:

[0091] The core is mixed with an acid for acid treatment, and a solid first intermediate is separated. The first intermediate and a lithium-containing compound are subjected to ball milling treatment to obtain the positive electrode active material. The pK a of the acid is not higher than 6.

[0092] Generally, in the process of preparing the core, there is a residual alkali layer formed by the lithium source on the surface of the core. In the present application, the core is subjected to acid treatment with acid. In the acid treatment process, the acid penetrates into the residual alkali layer and reacts with the residual alkali layer, and finally a first coating layer is formed on the surface of the core, i.e. a solid first intermediate is obtained. Subsequently, the lithium-containing compound is ball milled with the first intermediate to form a second coating layer on the surface of the first coating layer, thereby obtaining the positive electrode active material of the present application.

[0093] It should be noted that when the lithium-containing compound is coated on the surface of the first intermediate, a suitable ball milling treatment is selected to obtain a second coating layer with a porosity of not less than 5%. In the ball milling process, mechanical force promotes the reaction between the lithium-containing compound and the surface of the intermediate to form a second coating layer that is uniform, dense, stable and has high mechanical strength, thereby avoiding excessive expansion of the positive electrode active material due to stress concentration, effectively inhibiting the expansion of the positive electrode active material, and improving the structural stability and cycle performance of the positive electrode active material.

[0094] In a specific embodiment, the acid treatment comprises stirring the mixture comprising the core and the acid at 30-50°C. In the stirring process, the acid gradually enters the residual alkali layer and reacts with the residual alkali to form an active lithium salt. In the stirring process, the stirring speed can be controlled to be 100-300 r / min, and the stirring time can be controlled to be 1-3 h.

[0095] Further, specifically, using an aqueous acid solution for acid treatment can ensure a more gentle reaction. In a specific embodiment, the acid concentration is 0.1-0.3 mol / L. Generally, after the acid treatment is completed, in order to ensure the interfacial contact strength of the first coating layer and the core, the product of the acid treatment can be subjected to annealing treatment. Exemplarily, the annealing temperature is 200-500°C, and the annealing time is 1-4 h.

[0096] In addition, when the ball milling is performed, the lithium-containing compound and the first intermediate can be placed together in a zirconia ball mill tank, zirconia grinding balls are added in a mass ratio of 10:1-15:1, the rotation speed is set to 300-400 r / min, and the ball milling is performed for 30-90 min to complete the coating of the lithium-containing compound and form the second coating layer.

[0097] Further, after the ball milling is completed, the system after ball milling can also be subjected to annealing. Through annealing, the interfacial adhesion between the second coating layer and the surface of the first intermediate can be further increased, thereby prolonging the service life of the positive electrode active material. Exemplarily, the annealing temperature is 300-500°C, and the annealing time is 1-5 h.

[0098] Further, when the coating layer includes the conductive layer, a conductive material coating treatment also needs to be performed. Specifically, the implementation timing of the conductive material coating treatment can be determined according to the physical structure of the target positive electrode active material.

[0099] When the conductive layer needs to be located between the first coating layer and the second coating layer, the conductive material can be mixed with the first intermediate after acid treatment, and then the coating treatment of the lithium compound is performed.

[0100] When the conductive layer needs to be located away from the surface of the first coating layer to the surface of the second coating layer, the first intermediate is mixed with the lithium-containing compound to obtain a second intermediate, and then the second intermediate is mixed with the conductive layer material to obtain the positive electrode active material.

[0101] Exemplarily, the mixing treatment of the conductive material includes: stirring the solution including the product to be coated and the conductive material at 40-60°C; the product to be coated is the first intermediate after acid treatment, or the second intermediate after the coating treatment of the lithium compound.

[0102] In detail, the solvent of the solution can be NMP. Before the stirring treatment, in order to ensure the efficiency of the conductive material coating, the conductive material can be first mixed with NMP by ultrasonic, for example, at a power of 200-300 W for 1-2 h, so that the conductive material is uniformly dispersed. Then, the product to be coated is added, and the stirring speed is 100-300 r / min at 40-60°C for 3-5 h. At the same time, the mass ratio of the product to be coated to the conductive material is (20:1)-(50:1), which is beneficial to control the thickness of the conductive layer and the mass percentage in the positive electrode active material.

[0103] In addition, when the acid treatment is performed, the acid can include at least one of HCl, HNO3, HF, HBr, H2SO4, H3PO4, H2C2O4, maleic acid, and citric acid.

[0104] The third aspect of the present application provides a positive electrode sheet including the positive electrode active material of the first aspect or the positive electrode active material prepared by the preparation method of the second aspect. Therefore, the positive electrode sheet of the present application has a significant improvement in the initial efficiency, energy density, cycle performance, and safety performance of the battery.

[0105] The positive electrode sheet of the present application specifically includes a positive electrode current collector and a positive electrode active layer including the positive electrode active material arranged on at least one surface of the positive electrode current collector.

[0106] In particular, in the preparation of the positive electrode sheet, for example, the positive electrode active material of the present application can be dispersed with a positive electrode conductive agent and a positive electrode binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and the mixture is stirred to form a uniform positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector, and then dried, rolled and cut to obtain the positive electrode sheet. In a particular embodiment, the positive electrode active layer comprises 70-99 wt% of the positive electrode active material, 0.5-15 wt% of the positive electrode conductive agent, and 0.5-15 wt% of the positive electrode binder, and further comprises 80-98 wt% of the positive electrode active material, 1-10 wt% of the positive electrode conductive agent, and 1-10 wt% of the positive electrode binder.

[0107] In particular, the material of the positive electrode current collector can be at least one of aluminum foil and nickel foil; the positive electrode conductive agent can be at least one selected from carbon black, acetylene black, graphene, ketjen black, and carbon fiber; and the positive electrode binder can be at least one selected from polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, oxirane-containing polymer, polyvinylpyrrolidone, and polyurethane.

[0108] The fourth aspect of the present application also provides a battery comprising the positive electrode sheet described above. The battery provided by the present application has the advantages corresponding to the positive electrode active material described above, which will not be repeated here.

[0109] In the present application, unless otherwise specified, the coating, drying, rolling and other processes involved are conventional operations in the art, and the equipment used can be conventional equipment in the art, which will not be particularly limited.

[0110] Generally, the battery comprises an electrolyte or a solid electrolyte, a battery cell, and a shell packaging the battery cell, the electrolyte or the solid electrolyte is placed in the battery cell in the shell, and the battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet. The battery cell can be a laminated battery cell, i.e., the battery cell is formed by interleaving and stacking the positive electrode sheet, the separator and the negative electrode sheet; or the battery cell can also be a wound battery cell, i.e., the battery cell is formed by stacking and winding the positive electrode sheet, the separator and the negative electrode sheet.

[0111] Specifically, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active layer on at least one side surface of the negative electrode current collector. Specifically, the negative electrode active layer can be provided on one side surface of the negative electrode current collector, or the negative electrode active layer can be provided on both side surfaces of the negative electrode current collector in the thickness direction.

[0112] Specifically, the negative active layer can include a negative active material, a negative conductive agent, and a negative binder, which can all be conventional materials in the art. For example, the negative active material can include one or more of natural graphite, artificial graphite, petroleum coke, silicon-carbon materials, the negative conductive agent can include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, ketjen black, carbon fiber, and the negative binder can include one or more of sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0113] The present application can employ a conventional negative current collector in the art, for example, the negative current collector includes a copper foil.

[0114] The negative electrode sheet of the present application can be prepared by a conventional method in the art, for example, by a coating method. Specifically, the negative active material, the negative conductive agent, the negative binder, and the like, which are components for forming the negative active layer, can be dispersed in a solvent, for example, including water, to prepare a negative electrode slurry, which is then coated on the surface of the negative current collector, and after drying, rolling, and the like, the negative electrode sheet is prepared. The coating, drying, rolling, and the like, are conventional operations for preparing a negative electrode sheet by a coating method, and are not particularly limited.

[0115] The electrolyte of the present application can be a conventional electrolyte in the art, for example, the electrolyte is a non-aqueous electrolyte, which can specifically include an organic solvent, an additive, and an electrolyte salt. The organic solvent can include one or more of ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC), the additive can include fluoroethylene carbonate (FEC), and the electrolyte salt can include a lithium salt, for example, lithium hexafluorophosphate (LiPF6), but is not limited thereto.

[0116] The solid-state electrolyte of the present application can be a conventional solid-state electrolyte in the art, for example, a sulfide electrolyte, an oxide electrolyte, a polymer electrolyte, a halide electrolyte, and the like.

[0117] In the present application, a separator is used to separate the positive electrode sheet and the negative electrode sheet to prevent the positive electrode sheet and the negative electrode sheet from being in contact and short-circuited. A conventional separator in the art can be employed, and is not particularly limited. For example, the separator material can be a separator made of one or more of high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide, and polyvinylidene fluoride.

[0118] In this application, conventional housing materials in the art can be used to encapsulate the battery cell. The housing may include flexible packaging materials such as aluminum-plastic film, but is not limited to this.

[0119] This application describes how components such as positive electrode sheets, separators, and negative electrode sheets can be assembled into a battery using conventional methods in the art. For example, positive electrode sheets, separators, and negative electrode sheets can be stacked alternately to produce a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and subjected to conventional processes such as electrolyte injection and encapsulation to obtain a battery. Alternatively, when using a solid electrolyte, positive electrode sheets, solid electrolyte, and negative electrode sheets can be stacked alternately to produce a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and subjected to conventional processes such as encapsulation to obtain a battery.

[0120] This application also provides a battery pack comprising at least two of the above-described batteries, which has advantages corresponding to the above-described positive electrode active materials, which will not be elaborated further.

[0121] At least two cells in a battery pack are each individual cells connected together to form the battery pack. These cells can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without particular limitation.

[0122] This application also provides an electrical device, including the above-mentioned battery or battery pack, which has advantages corresponding to the above-mentioned positive electrode active material, which will not be elaborated further.

[0123] The electrical equipment used in this application can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., without any particular limitation.

[0124] The positive electrode active material of this application will be described in detail below through specific embodiments.

[0125] Example 1

[0126] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0127] 1) At 35℃, according to the core (specifically LiNi) 0.8 Co 0.1 Mn 0.1 O2) and acid (specifically, an aqueous solution of HF with a concentration of 0.2 mol / L) were mixed in a mass ratio of 1:0.2, stirred for 2 hours, filtered to obtain powder, and annealed at 450°C for 3 hours to obtain the first intermediate.

[0128] 2) ultrasonic dispersion of the MXene material (specifically Ti3C2T2) into an N-methylpyrrolidone solution to obtain an ultrasonic dispersion liquid, mixing the first intermediate and the ultrasonic dispersion liquid at 45°C to obtain a mixed solution, controlling the mass ratio of the first intermediate: MXene material = 25:1, stirring the mixed solution for 4h, and centrifugal filtration to obtain a second intermediate;

[0129] 3) ball milling of the mixture of the second intermediate and a lithium-containing compound (specifically Li2CO3 and Li2S, molar ratio of Li2CO3:Li2S = 1:2) for 1h, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.3 wt%, and annealing the product after ball milling at 500°C in an inert atmosphere for 4h to obtain the positive electrode active material.

[0130] Example 2

[0131] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, and the difference lies in that step 1) comprises: mixing at 35°C according to the core (specifically LiNi 0.8 Co 0.1 Mn 0.1 O2): acid liquid (specifically an aqueous solution of HF with a concentration of 0.16 mol / L) mass ratio = 1:0.15, stirring for 1.5h, filtering to obtain a powder, and annealing the powder at 480°C for 2h to obtain the first intermediate.

[0132] Example 3

[0133] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, and the difference lies in that step 1) comprises: mixing at 35°C according to the core (specifically LiNi 0.8 Co 0.1 Mn 0.1 O2): acid liquid (specifically an aqueous solution of HF with a concentration of 0.25 mol / L) mass ratio = 1:0.3, stirring for 1.5h, filtering to obtain a powder, and annealing the powder at 480°C for 2h to obtain the first intermediate.

[0134] Example 4

[0135] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, and the difference lies in that step 1) comprises: mixing at 35°C according to the core (specifically LiNi 0.8 Co 0.1 Mn 0.1 O2): acid liquid (specifically an aqueous solution of HF with a concentration of 0.3 mol / L) mass ratio = 1:0.35, stirring for 1.5h, filtering to obtain a powder, and annealing the powder at 480°C for 2h to obtain the first intermediate.

[0136] Example 5

[0137] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that step 1) comprises: mixing the inner core (specifically LiNi 0.8 Co 0.1 Mn 0.1 O2): acid solution (specifically an aqueous solution of HF with a concentration of 0.1 mol / L) at a mass ratio of 1:0.15, stirring for 1.5 h, filtering to obtain a powder, and annealing the powder at 480°C for 2 h to obtain a first intermediate.

[0138] Example 6

[0139] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that step 3) comprises: ball milling the mixture of the second intermediate and the lithium-containing compound (specifically LiDFOB and Li2S, with a molar ratio of LiDFOB:Li2S = 1:1) for 1 h, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.14 wt%, and annealing the product after ball milling at 500°C in an inert atmosphere for 4 h to obtain the positive electrode active material.

[0140] Example 7

[0141] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that step 3) comprises: ball milling the mixture of the second intermediate and the lithium-containing compound (specifically LiBOB and Li2CO3, with a molar ratio of LiBOB:Li2CO3 = 1:2) for 1 h, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.14 wt%, and annealing the product after ball milling at 500°C in an inert atmosphere for 4 h to obtain the positive electrode active material.

[0142] Example 8

[0143] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that step 3) comprises: ball milling the mixture of the second intermediate and the lithium-containing compound (specifically LiDFOB and Li2CO3, with a molar ratio of LiDFOB:Li2CO3 = 1:5) for 1 h, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.6 wt%, and annealing the product after ball milling at 500°C in an inert atmosphere for 4 h to obtain the positive electrode active material.

[0144] Example 9

[0145] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that step 3) comprises: ball milling the mixture of the second intermediate and the lithium-containing compound (specifically, LiDFOB and Li2CO3, molar ratio of LiDFOB:Li2CO3 = 4:1) for 1 h, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.8 wt%, and annealing the product after ball milling at 500°C under an inert atmosphere for 4 h to obtain the positive electrode active material.

[0146] Embodiment 10

[0147] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that step 3) comprises: ball milling the mixture of the second intermediate and the lithium-containing compound (specifically, LiDFOB and Li2CO3, molar ratio of LiDFOB:Li2CO3 = 2:1) for 1 h, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.15 wt%, and annealing the product after ball milling at 500°C under an inert atmosphere for 4 h to obtain the positive electrode active material.

[0148] Embodiment 11

[0149] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that step 3) comprises: ball milling the mixture of the second intermediate and the lithium-containing compound (specifically, Li2CO3 and Li2S, molar ratio of Li2CO3:Li2S = 1:2) for 45 min, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.3 wt%, and annealing the product after ball milling at 500°C under an inert atmosphere for 4 h to obtain the positive electrode active material.

[0150] Embodiment 12

[0151] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that step 3) comprises: ball milling the mixture of the second intermediate and the lithium-containing compound (specifically, Li2CO3 and Li2S, molar ratio of Li2CO3:Li2S = 1:2) for 20 min, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.3 wt%, and annealing the product after ball milling at 500°C under an inert atmosphere for 4 h to obtain the positive electrode active material.

[0152] Embodiment 13

[0153] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that step 3) comprises: ball milling the mixture of the second intermediate and the lithium-containing compound (specifically, Li2CO3 and Li2S, molar ratio of Li2CO3:Li2S = 1:2) for 3 h, controlling the mass percentage of the lithium-containing compound in the mixture to be 0.3 wt%, and annealing the product after ball milling at 500°C under an inert atmosphere for 4 h to obtain the positive electrode active material.

[0154] Example 14

[0155] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that in step 2), the MXene material (specifically Ti3C2T2) is ultrasonically dispersed into the N-methyl pyrrolidone solution to obtain an ultrasonic dispersion solution, the first intermediate is mixed with the ultrasonic dispersion solution at 45°C to obtain a mixed solution, the mass ratio of the first intermediate: MXene material is controlled to be 50:1, the mixed solution is stirred for 4h, and the second intermediate is obtained by centrifugal filtration.

[0156] Example 15

[0157] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that in step 2), the MXene material (specifically Ti3C2T2) is ultrasonically dispersed into the N-methyl pyrrolidone solution to obtain an ultrasonic dispersion solution, the first intermediate is mixed with the ultrasonic dispersion solution at 45°C to obtain a mixed solution, the mass ratio of the first intermediate: MXene material is controlled to be 15:1, the mixed solution is stirred for 4h, and the second intermediate is obtained by centrifugal filtration.

[0158] Example 16

[0159] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that in step 2), the MXene material (specifically Ti3C2T2) is ultrasonically dispersed into the N-methyl pyrrolidone solution to obtain an ultrasonic dispersion solution, the first intermediate is mixed with the ultrasonic dispersion solution at 45°C to obtain a mixed solution, the mass ratio of the first intermediate: MXene material is controlled to be 100:1, the mixed solution is stirred for 4h, and the second intermediate is obtained by centrifugal filtration.

[0160] Example 17

[0161] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that in step 2), the MXene material (specifically Ti3C2T2) is ultrasonically dispersed into the N-methyl pyrrolidone solution to obtain an ultrasonic dispersion solution, the first intermediate is mixed with the ultrasonic dispersion solution at 45°C to obtain a mixed solution, the mass ratio of the first intermediate: MXene material is controlled to be 12:1, the mixed solution is stirred for 4h, and the second intermediate is obtained by centrifugal filtration.

[0162] Example 18

[0163] The preparation method of the positive electrode active material of the present example is basically the same as that of Example 1, except that in step 2), tetramethylammonium hydroxide (TMAOH) is used to insert into the interlayer of Ti3C2T2 material.

[0164] Example 19

[0165] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that in step 2), Ti2C2T2 material is used to replace Ti3C2T2 material.

[0166] Embodiment 20

[0167] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that in step 2), hexadecylamine is inserted into the interlayer of Ti3C2T2 material.

[0168] Embodiment 21

[0169] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that in step 2), carbon black is used to replace Ti3C2T2 material.

[0170] Embodiment 22

[0171] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that in step 1), the inner core (specifically LiNi 0.8 Co 0.1 Mn 0.1 O2) and acid liquid (specifically an aqueous solution of phosphoric acid and oxalic acid, molar ratio of phosphoric acid to oxalic acid = 1:1, concentration of 0.3 mol / L) are mixed at a mass ratio of 1:0.6, stirred for 1.5 h, filtered to obtain a powder, and the powder is annealed at 480°C for 2 h to obtain a first intermediate.

[0172] Embodiment 23

[0173] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that in step 1), the inner core (specifically LiNi 0.8 Co 0.1 Mn 0.1 O2) and acid liquid (specifically an aqueous solution of sulfuric acid, concentration of 0.1 mol / L) are mixed at a mass ratio of 1:0.1, stirred for 1 h, filtered to obtain a powder, and the powder is annealed at 400°C for 3 h to obtain a first intermediate.

[0174] Embodiment 24

[0175] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Embodiment 1, except that in step 1), the inner core is LiMn 0.6 Fe 0.4 PO4.

[0176] LiMn 0.6 Fe 0.4The preparation method of PO4 includes: mixing FePO4, MnC2O4 and LiH2PO4, LiOH, wherein the molar ratio of FePO4 and MnC2O4 is 4:6, calcining at 700 DEG C in an inert atmosphere to obtain the core LiMn 0.6 Fe 0.4 PO4; wherein the molar ratio of FePO4+MnC2O4 to LiH2PO4 is 1:0.97, and the molar ratio of FePO4+MnC2O4 to Li is 1:1.06.

[0177] Example 25

[0178] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Example 1, except that the core of step 1) is LiFePO4.

[0179] The preparation method of LiFePO4 includes: mixing FePO4 and LiOH, and calcining at 700 DEG C in an inert atmosphere to obtain the core LiFePO4 of the present embodiment; wherein the molar ratio of FePO4 to LiOH is 1:1.06.

[0180] Example 26

[0181] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Example 1, except that the order of steps 2) and 3) is adjusted after step 1). That is, the present embodiment first performs lithium-containing compound coating treatment, and then performs MXene material coating treatment.

[0182] Example 27

[0183] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Example 1, except that the present embodiment does not perform step 2), that is, the first intermediate product is directly subjected to lithium-containing compound coating treatment.

[0184] Example 28

[0185] The preparation method of the positive electrode active material of the present embodiment is basically the same as that of Example 1, except that step 1) includes: mixing the core (specifically LiNi 0.8 Co 0.1 Mn 0.1 O2) and acid solution (specifically aqueous solution of citric acid with a concentration of 0.3 mol / L) at a mass ratio of 1:0.3, stirring for 3h, filtering to obtain powder, and annealing the powder at 450 DEG C for 3h to obtain the first intermediate.

[0186] Comparative Example 1

[0187] The preparation method of the positive electrode active material of the present comparative example is basically consistent with that of Example 27, except that in step 3), the first intermediate is mixed with a lithium-containing compound (specifically, Li2CO3 and Li2S, the molar ratio of Li2CO3:Li2S = 1:2), and the mass percentage of the lithium-containing compound in the mixture is controlled to be 0.3 wt%, and the mixed product is annealed at 500°C under an inert atmosphere for 4h to obtain the positive electrode active material.

[0188] Comparative Example 2

[0189] The preparation method of the positive electrode active material of the present comparative example is basically consistent with that of Example 27, except that step 1) comprises: mixing the inner core (specifically, LiNi 0.8 Co 0.1 Mn 0.1 O2): acid solution (specifically, an aqueous solution of H2CO3 with a concentration of 0.4 mol / L) at a mass ratio of 1:0.6, stirring for 1.5h, filtering to obtain a powder, and annealing the powder at 480°C for 2h to obtain the first intermediate.

[0190] Assembling a battery

[0191] The positive electrode active materials of the examples and comparative examples are mixed with conductive carbon black and PVDF at a mass ratio of 97:1.5:1.5 to prepare positive electrode sheets. Graphite, conductive carbon black, and polyacrylic acid are mixed at a mass ratio of 100:1:2 to prepare negative electrode sheets. In an Ar atmosphere glove box, the positive electrode sheets, negative electrode sheets, separators, and electrolyte (lithium salt is LiPF6 and LiFSI, the ratio is 7:3, the concentration is 1 mol / L, the solvent is EC:EMC=3:7, the additives are vinylene carbonate and methyl disulfonic acid, and the addition amount is 1 part and 2 parts respectively) are assembled into lithium ion batteries.

[0192] Test Example

[0193] (I) Physical property test

[0194] 1. Material surface coating structure

[0195] The characterization can be performed by field emission transmission electron microscopy. 1 g of the sample is ultrasonically dispersed in 10 mL of anhydrous ethanol for 30 min, and after uniform dispersion, the dispersion liquid is added dropwise on a copper mesh. After drying the copper mesh to be tested, it is placed in an electron microscope for testing. By adjusting the shooting area and magnification, the particles to be shot are locked, and the surface coating structure can be observed. After shooting, the matching energy dispersive X-ray spectrometer is started, and the elements in the coating layer are scanned to obtain the mass proportion of the corresponding elements in the region. According to the element scanning result, the element material composition of each coating layer can be obtained, and according to the element mass proportion, the mass proportion of each coating layer in the entire positive electrode active material can be calculated. The present application uses a Tecnai G2 F300 type transmission electron microscope and an AZtecOne type energy dispersive X-ray spectrometer.

[0196] The surface coating layer can be observed on the surface of the positive electrode material, the first coating layer thickness H1, the second coating layer thickness H2, and the third coating layer thickness H3 can be directly calculated, the active lithium salt, the lithium-containing compound, and the type of conductive layer material can be obtained by EDS characteristic element analysis, the mass percentage of the active lithium salt in the first coating layer w a , the mass percentage of the first coating layer in the positive electrode active material w1, the mass percentage of the second coating layer in the positive electrode active material w2, and the mass percentage of the inorganic lithium-containing compound in the lithium-containing compound in the second coating layer w b , the mass percentage of the conductive layer in the positive electrode active material w3 is calculated by the element percentage of EDS.

[0197] 2, the pH of the first coating layer

[0198] After removing the conductive layer and the second coating layer, the product 2g including the first coating layer is dissolved in 100 mL of deionized water, stirred for 30 min, and the mixed solution is centrifuged and separated, and the supernatant is tested for pH. The pH tester is Leici PHS-2F.

[0199] 3, the porosity v of the second coating layer

[0200] FIB-SEM is used for characterization, and a Thermo Fisher Helios 6 HD FIB-SEM system is used for characterization. The FIB is used to etch the surface of the sample, so that the cross section of the second coating layer is exposed in the SEM observation range, and the SEM is used to reconstruct the three-dimensional structure of the sample coating layer, and the three-dimensional structure model of the coating layer is obtained. The porosity of the coating layer can be obtained by data processing of the three-dimensional model.

[0201] 4, the electronic conductivity p of the conductive material in the conductive layer

[0202] Electronic conductivity needs to be tested using a four-probe resistivity meter. The powder to be tested is pressed into a 40 mm diameter disc, and the disc thickness is measured using a micrometer to obtain the actual thickness of the coating layer. Place the disc in the center of the sample stage, and input the sample thickness. Then slowly lower the four-probe probe until the probe just contacts the sample, and the four-probe instrument current indicator displays a value. Adjust the knob so that the displayed value is consistent with the value given by the computer, and then start the test. Test the middle, top, bottom, left, and right of the 40 mm disc to obtain the resistivity value of the sample. Use the Suzhou crystal lattice ST2253 four-probe resistivity meter to test, and by comparing the conductivity difference between the coated material and the uncoated material, the conductivity of the conductive material can be calculated.

[0203] 5. The interlayer spacing D of the conductive material in the conductive layer

[0204] The material layer spacing needs to be characterized using XRD, and the results are analyzed twice to calculate the layer spacing. The present application uses a Bruker D8 Advance XRD for testing. A quartz glass plate is used as a carrier, and the positive active material powder is uniformly filled into the test portion. The quartz plate is placed into the tester for testing, and the 2θ range is controlled at 2-90°. The XRD results are analyzed, and the Bragg equation is used for analysis to obtain the layer spacing results.

[0205] 6. The defect density N of the conductive material in the conductive layer

[0206] The material defect density needs to be characterized using EPR, and the present application uses a Bruker E580Q EPR for testing. The powder is placed into a quartz sample tube in a glove box, and the sample is placed into the EPR after correction. After the test is completed, the data is processed twice to obtain the surface defect density of the material.

[0207] The above test results are shown in Table 1.

[0208] Table 1

[0209]

[0210] (II) Performance test

[0211] 1. The conductivity of the pole piece

[0212] The pole piece sample is cut into a 40 mm diameter disc, and the four-probe probe is slowly lowered until the probe just contacts the sample. The four-probe instrument current indicator displays a value, and the knob is adjusted so that the displayed value is consistent with the value given by the computer, and then the test is started. The middle, top, bottom, left, and right of the 40 mm disc are tested to obtain the resistivity value of the sample. The reciprocal of the resistivity is the conductivity of the pole piece, and the results are shown in Table 2.

[0213] 2. Cell expansion rate

[0214] The cell parameters of lithium ion batteries at empty and full states were analyzed by XRD data, the cell volumes of the positive active material at empty and full states were compared, and the cell expansion rate of the positive active material was obtained, and the results are shown in Table 2.

[0215] 3. First charge-discharge efficiency

[0216] Charged at 0.2C to the upper limit voltage, and then discharged at 0.2C to the lower limit voltage, and the discharge capacity was divided by the charge capacity, and the results are shown in Table 2.

[0217] 4. Cycle performance

[0218] According to the standard cycle life test method in GB / T 31484-2015, the cycle number of the battery to SOH 80% was tested, and the results are shown in Table 2.

[0219] Table 2

[0220]

[0221] According to Table 2, during the battery cycle process, not only a low cell expansion rate is required, but also a high electrode conductivity is required, the high conductivity ensures the electrochemical performance of the battery, and the low cell expansion rate ensures the life of the battery. Compared with the comparative examples, the positive active material of the present application has the characteristics of high first efficiency and low expansion, and has good conductivity, so the cycle performance and rate performance of the battery are more excellent.

[0222] Finally, it should be noted that: after considering the specification and practicing the invention disclosed herein, other embodiments of the present application will be easily conceived by those skilled in the art. The present application is intended to cover any variations, uses or adaptations of the present application which follow the general principles of the present application and include known or customary technical means in the art which are not disclosed by the present application, and are not limited to the precise structures described above, and various modifications and changes can be made without departing from the scope thereof. The scope of the present application is limited only by the appended claims.

Claims

1. A positive electrode active material, characterized in that, The device includes a core and a coating layer covering at least a portion of the surface of the core; in a direction away from the core, the coating layer includes a first coating layer and a second coating layer stacked together, the first coating layer comprising an active lithium salt, the second coating layer comprising a lithium-containing compound, and the porosity of the second coating layer not exceeding 5%; The anions of the active lithium salt include inorganic acid radicals and / or organic acid radicals, and the pKa of the acid formed by the inorganic acid radicals is not higher than 6.

2. The positive electrode active material according to claim 1, characterized in that, At least one of the following conditions must be met: a) The mass percentage of the active lithium salt in the first coating layer is not less than 50 wt%; b) The mass percentage of the active lithium salt in the first coating layer is not higher than 70 wt%; c) The first coating layer accounts for 0.1wt%-0.3wt% of the mass percentage of the positive electrode active material; d) The thickness of the first coating layer is 5nm-10nm; e) The pH of the first coating layer is 7.5-8.5; f) The thickness of the coating layer is 10nm-40nm.

3. The positive electrode active material according to claim 1 or 2, characterized in that, At least one of the following conditions must be met: g) The porosity of the second coating layer is not less than 2%; h) The thickness of the second coating layer is 5nm-15nm; i) The second coating layer accounts for 0.1%wt-0.5wt% of the mass of the positive electrode active material.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The lithium-containing compound includes at least one of inorganic lithium-containing compounds and organic lithium-containing compounds. The inorganic lithium-containing compound includes at least one of Li2CO3, LiOH, Li2S, LiBF4, and LiPO2F2. The organic lithium-containing compound includes at least one of LiBOB, LiDFOB, LiFSI, and LiCF3SO3. Preferably, in the second coating layer, the inorganic lithium compound accounts for 40wt%-100wt% of the mass percentage of the lithium compound.

5. The positive electrode active material according to any one of claims 1-4, characterized in that, The coating layer further includes a conductive layer, preferably satisfying at least one of the following conditions: A) The conductive layer is located between the first coating layer and the second coating layer; B) The conductive layer is located on the surface of the second coating layer away from the first coating layer; C) The thickness of the conductive layer is 5nm-15nm.

6. The positive electrode active material according to claim 5, characterized in that, The conductive layer comprises an MXene material, wherein the MXene material satisfies at least one of the following conditions: D) The electronic conductivity of the MXene material is greater than 10. 3 S / m; E) The MXene material accounts for 1wt%-5wt% of the mass percentage of the positive electrode active material; F) The interlayer spacing of the MXene material is 0.5 nm to 1.5 nm; G) The defect density of the MXene material is less than 10 defects / μm. 2 ; H) The MXene material includes Ti3C2T m Nb4C3T m At least one of them, T includes an oxygen-containing group and a fluorine-containing group, and m > 0.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The core includes at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate, lithium nickel manganese oxide, and lithium manganese iron phosphate. And / or, the active lithium salt includes at least one of LiCl, LiNO3, LiF, LiBr, Li2SO4, Li3PO4, Li2C2O4, lithium maleate, and lithium citrate.

8. A method for preparing the positive electrode active material according to any one of claims 1-7, characterized in that, Includes the following steps: The core is mixed with acid and subjected to acid treatment to obtain a solid first intermediate. The first intermediate and a lithium-containing compound are then ball-milled to obtain the positive electrode active material; the pK of the acid is... a No higher than 6.

9. The preparation method according to claim 8, characterized in that, At least one of the following conditions must be met: I) The acid treatment temperature is 30℃-50℃; J) The concentration of the acid is 0.1 mol / L-0.3 mol / L; K) After the ball milling treatment, the system is further subjected to annealing. Preferably, the annealing temperature is 300℃-500℃. L) After separation, the product after acid treatment is further subjected to annealing to obtain the first intermediate; the annealing temperature is 200℃-500℃ and the annealing time is 1h-4h. The acid M) includes at least one of HCl, HNO3, HF, HBr, H2SO4, H3PO4, H2C2O4, maleic acid, and citric acid.

10. The preparation method according to claim 8 or 9, characterized in that, The first intermediate is mixed with the conductive layer material to obtain the second intermediate, and then the second intermediate is mixed with the lithium-containing compound to obtain the positive electrode active material. or, The first intermediate is mixed with a lithium-containing compound to obtain a second intermediate, and then the second intermediate is mixed with a conductive layer material to obtain the positive electrode active material.

11. A positive electrode plate, characterized in that, It includes the positive electrode active material according to any one of claims 1-7, or the positive electrode active material prepared by the method according to any one of claims 8-10.

12. A battery, characterized in that, The battery includes the positive electrode as described in claim 11.

13. A battery pack, characterized in that, The battery pack includes at least two batteries as described in claim 12.

14. An electrical appliance, characterized in that, The electrical device includes the battery of claim 12, or the battery pack of claim 13.

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