Positive electrode active material, secondary battery, and electrical device

Abstract

A positive electrode active material, a secondary battery, and an electrical device. The positive electrode active material comprises a secondary particle formed by agglomeration of primary particles. In the SEM image of the cross section of the secondary particle, the number of grain boundaries per unit cross section area is α section / μm2, and the grain boundary length per unit cross section area is β μm / μm2. The secondary particle satisfies: 0.15≤β / α≤0.4. By regulating and controlling the number of grain boundaries and the grain boundary length, the release capability of the material structure for the stress is improved, the oxygen stability of the material is improved, the cycle life of the secondary battery is further prolonged, and the gas production performance and dynamic performance are improved.

Description

Positive electrode active material, secondary battery and electric device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on September 15, 2023, with application number 202311196126.6 and application name “Positive Electrode Active Materials, Secondary Batteries and Electrical Devices”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The embodiments of the present application relate to, but are not limited to, the field of battery technology, and specifically to a positive electrode active material, a secondary battery, and an electrical device. Background Art

[0003] Polycrystalline ternary materials have been widely used in high-power and high-nickel batteries due to their higher initial efficiency and better power performance. However, polycrystalline ternary materials can deteriorate in cycling and gas production due to particle cracking and lattice oxygen loss, which greatly limits the battery's power performance and reduces its application range. Technical issues

[0004] The present application provides a positive electrode active material, a secondary battery and an electrical device to solve the problems of cracking and oxygen loss of high-nickel polycrystalline particles. Technical Solutions

[0005] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0006] In a first aspect, the present application provides a positive electrode active material, comprising secondary particles formed by agglomeration of primary particles, wherein in a SEM image of a cross section of the secondary particles, the number of grain boundaries per unit cross-sectional area is α bars / μm 2 , the grain boundary length per unit cross-sectional area is βμm / μm 2 , the secondary particles satisfy:

[0007] 0.15≤β / α≤0.4.

[0008] Optionally, the secondary particles have pores, and in the SEM image of the cross section of the secondary particles, the number of pores per unit cross-sectional area is γ / μm 2 , the secondary particles satisfy: γ≤30.

[0009] Optionally, in the SEM image of the cross section of the secondary particle, the cross-sectional figure of the primary particle has a longest side and a side that does not intersect with the longest side; wherein the sum of the lengths of the longest side and the side per unit cross-sectional area is R μm / μm 2 , satisfying: R / β≥60%.

[0010] Optionally, the positive electrode active material further satisfies: an oil absorption value of 1 mL / g to 80 mL / g.

[0011] Optionally, the positive electrode active material further satisfies: the Dv10 of the positive electrode active material is from 1 μm to 13 μm, the Dv50 of the positive electrode active material is from 2 μm to 16 μm, and the Dv90 of the positive electrode active material is from 3 μm to 20 μm; wherein, Dv10 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 10%; Dv50 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 50%; Dv90 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 90%.

[0012] Optionally, the positive electrode active material further satisfies: the specific surface area of ​​the positive electrode active material is from 0.2m 2 / g to 2.5m 2 / g.

[0013] Optionally, the secondary particles further satisfy at least one of the following characteristics:

[0014] d)1≤α≤50;

[0015] e)0.15≤β≤20.

[0016] Optionally, the positive electrode active material includes Li θ (Ni a Co b Mn c ) 1-x M x O y G z ; Wherein, 0.95≤θ≤1.1, 0.3≤a≤0.9, 0≤b≤0.15, 0≤c≤0.5, 0≤x≤0.1, 1≤y≤2, 0≤z≤1, y+z=2; M is selected from at least one of Al, Mg, B, Ca, Zn, Sb, W, Bi, Cr, Sr, Y, W, Zr, Ti, La, Nb, Mo, V; G is selected from at least one of F, S, Cl, N.

[0017] Optionally, the positive electrode active material further comprises a coating element, and the coating element is provided on the surface of the secondary particles and / or the primary particles;

[0018] The coating element is selected from at least one of Al, Mg, B, Ba, Co, Si, Sn, P, Ca, Zn, Sb, W, Bi, Cr, Sr, Y, W, Zr, Ti, La, Nb, and Mo;

[0019] The total content of the coating elements per unit surface area in the positive electrode active material is from 0.1 mg / m 2 to 20 mg / m 2 .

[0020] Optionally, the residual lithium content per unit surface area of ​​the positive electrode active material is from 0.1 mg / m 2 to 8 mg / m 2 .

[0021] In a second aspect, the present application further provides a secondary battery, comprising a positive electrode current collector and a positive electrode plate disposed on the positive electrode current collector, wherein the positive electrode plate comprises the positive electrode active material.

[0022] In a third aspect, the present application also provides an electrical device comprising the secondary battery. Beneficial effects

[0023] Compared with the prior art, the present invention provides a positive electrode active material comprising secondary particles formed by agglomeration of primary particles. In the SEM image of the cross section of the secondary particles, the number of grain boundaries per unit cross-sectional area is α bars / μm. 2 , the grain boundary length per unit cross-sectional area is βμm / μm 2 , the secondary particles meet the following conditions: 0.15≤β / α≤0.4. This application improves the stress release capability of the material structure and improves the material's oxygen stability by regulating the number of grain boundaries, crystal plane orientation, and cross-sectional pore structure. This further increases the cycle life of the secondary battery, as well as its gas production and kinetic performance.

[0024] It is understandable that the secondary battery and the electrical device provided in the embodiments of the present application have all the technical features and beneficial effects of the above-mentioned positive electrode active materials, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a cross-sectional SEM image of the positive electrode active material prepared in Example 1 of the present application.

[0026] Implementation Methods of the Application

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. The described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts are within the scope of protection of this application.

[0028] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the components and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application.

[0029] Compared to single-crystal ternary materials, polycrystalline ternary materials offer higher initial efficiency and better power performance. However, particle cracking and lattice oxygen loss are the primary causes of deteriorating cycling and gas production performance in secondary batteries using polycrystalline materials. Alleviating or even preventing particle breakage after high compaction and long cycling, and reducing lattice oxygen loss, are key issues in addressing the cycling and gas production issues of polycrystalline ternary materials.

[0030] Therefore, based on the above problems, the present application provides a positive electrode active material, a secondary battery and an electric device.

[0031] A positive electrode active material includes secondary particles formed by agglomeration of primary particles, wherein the number of grain boundaries per unit cross-sectional area in a SEM image of a cross-sectional surface of the secondary particles is α / μm. 2 , the grain boundary length per unit cross-sectional area is βμm / μm 2 , the secondary particles satisfy: 0.15≤β / α≤0.4.

[0032] It can be understood that the number of grain boundaries per unit cross-sectional area α refers to the number of grain boundaries contained in a unit area of ​​the material. The grain boundary is the interface between adjacent grains. The number of grain boundaries per unit cross-sectional area can be obtained by selecting multiple areas in the SEM image and calculating the ratio of the total number of grain boundaries in multiple areas to the total area to obtain the number of grain boundaries per unit cross-sectional area. When calculating the total number of regional grain boundaries, the edge of the selected area contains incomplete grain boundaries, and the incomplete grain boundary is also calculated as one grain boundary. The length of the grain boundary per unit cross-sectional area β refers to the total length of the grain boundaries in a unit area of ​​the material. The physical meaning of β / α is the length of the unit grain boundary, which can reflect the stability of the material. There are many defects at the grain boundaries, and the side reactions between the material and the electrolyte are intense. Controlling the number of grain boundaries and the grain boundary length to a moderate level can ensure that the electrolyte can effectively infiltrate the primary particles while reducing the occurrence of side reactions between the surface of the positive active material and the electrolyte at the grain boundaries, thereby improving the cycle, gas production and rate performance.

[0033] In some embodiments, the secondary particles satisfy: 1≤α≤50; for example, α can be any value of 1, 2, 5, 8, 10, 15, 20, 25, 30, 35, 40, 45 and 50, or a range between any two values.

[0034] When the value of α is within the above range, it can ensure that the electrolyte can effectively infiltrate the primary particles while reducing the occurrence of side reactions between the surface of the positive electrode active material and the electrolyte at the grain boundary, thereby improving the cycle, gas production and rate performance.

[0035] In some embodiments, the secondary particles satisfy: 0.15≤β≤20; for example, β can be any one of 0.15, 0.35, 0.75, 1, 2, 5, 8, 10, 15 and 20, or a range between any two values.

[0036] When the value of β is within the above range, the oxygen stability of the material can be further effectively improved, lattice oxygen loss can be reduced, and the circulation and gas production performance can be improved.

[0037] In some embodiments, the secondary particles have pores, which are formed by the accumulation of primary particles. In the SEM image of the cross section of the secondary particles, the number of pores per unit cross-sectional area is γ / μm. 2 The secondary particles satisfy the following requirement: γ≤30. For example, γ can be any value among 0.3, 0.5, 0.8, 1.0, 0.5, 2.0, 3.0, 5.0, 6.0, 8.0, 10.0, 12.0, 15.0, 18.0, 20.0, 22.0, 25.0, 28.0, and 30.0, or a range between any two values. The number of pores per unit cross-sectional area can be determined by selecting multiple regions in the SEM image and calculating the ratio of the total number of pores in these regions to the total area. When calculating the number of pores, if the edges of the selected region include non-full pores such as half pores, they are counted as full pores.

[0038] In some embodiments, the secondary particles have pores, the pore diameter is D μm, and satisfies: 0.01≤D≤4; for example, D can be any one of 0.01, 0.1, 1, 2, 3 and 4 or a range between any two values, optionally, D μm is from 0.01 μm to 0.2 μm, or D μm is from 0.05 μm to 0.1 μm.

[0039] It can be understood that the number of pores per unit cross-sectional area γ and the size of the pore diameter D are moderate, which can maximize the release of stress accumulated after high compaction and long cycling, alleviate particle cracking, and improve cycling and gas production performance; at the same time, the appropriate number of cross-sectional pores can enhance the wettability of the electrolyte to the particles and improve the rate performance.

[0040] In some embodiments, in the SEM image of the cross section of the secondary particle, the cross-sectional shape of the primary particle has a longest side and a side that does not intersect with the longest side; wherein the sum of the lengths of the longest side and the side per unit cross-sectional area is R μm / μm 2, satisfying: R / β ≥ 60%. By regulating the crystal plane orientation so that more than 60% of the total length of the grain boundary is contributed by the side edges of the primary particle cross-section, the material's oxygen stability can be effectively improved, lattice oxygen loss can be reduced, and thus improved circulation and gas production performance. In some embodiments, R / β ≤ 90%. For example, the value of R / β can be in the range of one or any two of 60%, 65%, 73%, 78%, 80%, 83%, 86%, 88%, and 90%.

[0041] It can be understood that the side edges in the cross-sectional figure actually correspond to the surface of the primary particle. Taking the long polygonal primary particle as an example, the longest face and the face that does not intersect with the longest face are the side faces, the side faces are the (003) faces, and the remaining faces are the front faces, the front face is the (102) face. Therefore, in the cross-sectional figure of the primary particle, the side faces correspond to the above edges. Since the oxygen vacancy formation energy of the (003) face is greater than that of the (102) face, the oxygen stability of the side faces is higher and it is less likely to lose oxygen. Therefore, when R / β≥60% is satisfied, the oxygen stability of the material can be further improved and the lattice oxygen loss can be reduced.

[0042] In some embodiments, the positive electrode active material has an oil absorption value ranging from 1 mL / g to 80 mL / g; for example, the oil absorption value can be any one of 1 mL / g, 2 mL / g, 3 mL / g, 5 mL / g, 8 mL / g, 10 mL / g, 15 mL / g, 20 mL / g, 25 mL / g, 30 mL / g, 35 mL / g, 40 mL / g, 45 mL / g, 50 mL / g, 55 mL / g, 60 mL / g, 65 mL / g, 70 mL / g, 75 mL / g, and 80 mL / g, or a range between any two of these values. The oil absorption value depends on factors such as the effective internal and external surface area of ​​the material, the number of cross-sectional pores, and the cross-sectional pore size, and can reflect the wettability of the material by the electrolyte. When the oil absorption value is within the above range, the material can have good wettability and rate performance, while effectively reducing the degree of particle cracking, ensuring long-term circulation of the material and reducing gas production.

[0043] In some embodiments, the Dv10 of the positive electrode active material ranges from 1 μm to 13 μm, the Dv50 of the positive electrode active material ranges from 2 μm to 16 μm, and the Dv90 of the positive electrode active material ranges from 3 μm to 20 μm. Dv10 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 10%; Dv50 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 50%; and Dv90 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 90%. It is understood that a suitable particle size range can ensure a moderate specific surface area of ​​the positive electrode active material and a moderate lithium ion transport distance, effectively improving the material's cycle and rate performance.

[0044] In some embodiments, when the value of Dv10 is within the above range, the distribution of the positive electrode active material particles in the positive electrode active material layer can be further improved, and the overall performance of the secondary battery can be further improved.

[0045] In some embodiments, when the value of Dv50 or Dv90 is within the above range, the proportion of large particles in the positive electrode active particles can be controlled, the distribution of positive electrode active material particles in the positive electrode active material layer can be in a better state, and the overall performance of the secondary battery can be improved.

[0046] In some embodiments, the specific surface area of ​​the positive electrode active material is from 0.2 m 2 / g to 2.5m 2 / g; For example, the specific surface area of ​​the positive electrode active material can be 0.2m 2 / g, 0.5m 2 / g, 0.8m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 2.0m 2 / g and 2.5m 2 / g, or any value or range between any two values. It is understood that a suitable specific surface area range can facilitate sufficient contact between the electrolyte and the positive electrode active material, reduce interfacial side reactions, and improve cycle and gas production performance. It can also reduce the amount of conductive agent and binder used, lower battery costs, and increase battery energy density.

[0047] In some embodiments, the number of grain boundaries per unit cross-sectional area α can be calculated by the following formula: α=N0 / (L0 / P0×W0 / P0);

[0048] Among them, N0 represents the number of primary particles and primary particle boundaries in the SEM image of the cross section of the secondary particle, and the unit is bar; L0 represents the actual measured length of the SEM image of the cross section of the secondary particle, and the unit is μm; W0 represents the actual measured width of the SEM image of the cross section of the secondary particle, and the unit is μm; / P0 represents the ratio of the measured value of the scale line segment length to the indicated value of the scale line segment in the SEM image of the cross section of the secondary particle, and the unit is μm / nm.

[0049] In some embodiments, the grain boundary length per unit cross-sectional area β can be calculated by the following formula: β=S0 / (L0 / P0×W0 / P0);

[0050] Among them, S0 represents the total length of the interface between primary particles and primary particles in the SEM image of the cross section of the secondary particles, in μm; L0 represents the actual measured length of the SEM image of the cross section of the secondary particles, in μm; W0 represents the actual measured width of the SEM image of the cross section of the secondary particles, in μm; P0 represents the ratio of the measured value of the scale line segment length to the indicated value of the scale line segment in the SEM image of the cross section of the secondary particles, in μm / nm.

[0051] In some embodiments, the number of holes per unit cross-sectional area γ can be calculated by the following formula: γ = H0 / (L0 / P0×W0 / P0);

[0052] Wherein, H0 represents the total number of pores with a diameter greater than 10 nm in the SEM image of the cross section of the secondary particle, in pieces; L0 represents the actual measured length of the SEM image of the cross section of the secondary particle, in μm; W0 represents the actual measured width of the SEM image of the cross section of the secondary particle, in μm; P0 represents the ratio of the measured value of the scale line segment length to the indicated value of the scale line segment in the SEM image of the cross section of the secondary particle, in μm / nm.

[0053] Taking Figure 1 as an example, after ion cutting the positive electrode active material, a SEM examination of the particle cross-section was performed. A single particle with a secondary particle diameter of Dv50±10% was selected and an SEM image of that particle at a magnification of 30K was obtained. The SEM image only includes the cross-section of that particle. In Figure 1, A represents the side view of a primary particle, and B represents the front view of a primary particle. For polygonal primary particles, the longest side and any side that does not intersect with the longest side are considered side views, while the remaining sides are considered front views. If a face is both a side view of one primary particle and the front view of another, it is counted as a side view.

[0054] In some embodiments, N0 can be directly determined from the intersection point in Figure 1; S0 can be directly determined from the total length of the boundary line segment in Figure 1; H0 can be directly determined from the pores in Figure 1, which is the sum of the number of pores; L0 and W0 represent the actual measured dimensions of the length and width of Figure 1, respectively; P0 can be understood as the proportional relationship between the value indicated by the scale segment in Figure 1 and the actual dimension of the segment measured by a ruler, which is used to convert the size of the corresponding secondary particles. Taking Figure 1 as an example, P0 represents the actual measured length corresponding to a scale of 200 nm.

[0055] In some embodiments, the positive electrode active material includes Li θ (Ni a Co b Mn c ) 1-x M x O y G z; Wherein, 0.95≤θ≤1.1, 0.3≤a≤0.9, 0≤b≤0.15, 0≤c≤0.5, 0≤x≤0.1, 1≤y≤2, 0≤z≤1, y+z=2; M is selected from at least one of Al, Mg, B, Ca, Zn, Sb, W, Bi, Cr, Sr, Y, W, Zr, Ti, La, Nb, Mo, V; G is selected from at least one of F, S, Cl, N.

[0056] The positive electrode active material further includes a coating element, which is disposed on the surface of the secondary particles and / or the primary particles; the coating element is selected from at least one of Al, Mg, B, Ba, Co, Si, Sn, P, Ca, Zn, Sb, W, Bi, Cr, Sr, Y, W, Zr, Ti, La, Nb, and Mo; and the total content of the coating element per unit surface area in the positive electrode active material is 0.1 to 20 mg / m 2 The total content of coating elements per unit surface area = the total mass of coating elements per unit mass of positive electrode active material / the specific surface area of ​​the positive electrode active material.

[0057] It's understandable that the total amount of coating elements per unit particle surface area more accurately reflects the content of the coating material on the particle surface. An appropriate coating amount effectively reduces side reactions at the interface between the material and the electrolyte, improving cycling and gas production performance. Furthermore, when the total amount of coating elements per unit particle surface area falls within the aforementioned range, it increases the lithium ion transport rate at the surface of the positive electrode active material, contributing to the optimal battery kinetic performance.

[0058] In some embodiments, the residual lithium content per unit surface area of ​​the positive electrode active material is from 0.1 mg / m 2 to 8 mg / m 2 Wherein, the amount of residual lithium per unit surface area = the amount of residual lithium per unit mass of the positive electrode active material / the specific surface area of ​​the positive electrode active material.

[0059] It's understandable that the total amount of residual lithium per unit particle surface area more accurately reflects the residual lithium content on the particle surface. An appropriate amount of residual lithium can effectively improve long-term cycling and gas production performance. A small amount of residual lithium promotes the formation of the positive electrode CEI film, improving cycling and gas production performance. Excessive residual lithium will affect ion and electron transport on the surface of the positive electrode active material, exacerbating the decomposition of HF in the electrolyte, resulting in a decrease in long-term cycling and an increase in gas production.

[0060] In some embodiments, the preparation method of the above-mentioned positive electrode active material includes the following steps: (1) After the sulfate of nickel, cobalt and manganese is configured into a metal salt solution of a certain proportion, the metal salt solution, the complexing agent solution and the sodium hydroxide solution are simultaneously dripped into the reactor, and the parameters are controlled to perform a co-precipitation reaction. After the reaction is completed, the nickel-cobalt-manganese precursor is obtained through aging, filtration, washing and drying. (2) The nickel-cobalt-manganese precursor, lithium source, M source and N source are placed in a mixing device in a certain proportion and mixed evenly, and then placed in an atmosphere furnace for sintering to obtain a ternary material with doped elements. (3) The product obtained by the primary sintering and the coating source are placed in a mixing device and mixed evenly, and then placed in an atmosphere furnace for secondary sintering to obtain a ternary material with a coating.

[0061] In some embodiments, the complexing agent solution is one or more of ammonia water, ammonium bicarbonate, ammonium dihydrogen phosphate, and oxalic acid.

[0062] In some embodiments, the coprecipitation reaction temperature is 50-90°C, the pH is from 7 to 12, the reaction time is from 24h to 200h, and the aging time is from 12h to 48h; by regulating the coprecipitation reaction parameters, the precursor nucleus formation rate is much greater than the crystal growth rate, thereby preparing a precursor with slender whiskers.

[0063] In some embodiments, the lithium source is a lithium-containing compound, specifically one or more of lithium hydroxide, lithium carbonate, lithium phosphate, and lithium oxide; the M source is a carbonate, oxide, nitrate, phosphate, chloride or hydroxide containing one or more elements of Al, Mg, B, Ca, Zn, Sb, W, Bi, Cr, Sr, Y, W, Zr, Ti, La, Nb, Mo, and V; the G source is a compound containing one or more elements of F, S, Cl, and N, and the compound is specifically lithium fluoride, calcium chloride, sodium sulfide, lithium nitride, etc.

[0064] It can be understood that by adding special doping elements and combining the sintering process control, the (003) surface of the ternary material is induced to grow preferentially, and the slender precursor primary particles of the whiskers further grow into long strips, with the side surfaces accounting for the majority, thereby improving the stability of the material and reducing lattice oxygen loss.

[0065] In some embodiments, the coating source is a carbonate, oxide, nitrate, phosphate, chloride or hydroxide containing one or more elements of Al, Mg, B, Ba, Co, Si, Sn, P, Ca, Zn, Sb, W, Bi, Cr, Sr, Y, W, Zr, Ti, La, Nb, Mo.

[0066] In some embodiments, the first sintering temperature is from 400° C. to 1000° C., the sintering time is from 12 h to 48 h, and the oxygen concentration is ≥10%; the second sintering temperature is from 100° C. to 700° C., and the sintering time is from 12 h to 24 h.

[0067] In some embodiments, the present application also provides a secondary battery, comprising a positive electrode current collector and a positive electrode plate disposed on the positive electrode current collector, wherein the positive electrode plate comprises the above-mentioned positive electrode active material.

[0068] In some embodiments, the positive electrode sheet includes a positive electrode active material layer, which may be one or more layers. Each layer of the multi-layer positive electrode active material layer may include the aforementioned positive electrode active material. The positive electrode active material is any substance that can reversibly intercalate and deintercalate metal ions such as lithium ions.

[0069] In some embodiments, the positive electrode plate is a single-sided plate or a double-sided plate. When the positive electrode plate is a single-sided plate, the positive electrode active material layer is disposed on one surface of the positive electrode current collector. When the positive electrode plate is a double-sided plate, the positive electrode active material layer is disposed on both surfaces of the positive electrode current collector. The positive electrode plate may also have both a single-sided positive electrode plate region and a double-sided positive electrode plate region.

[0070] In some embodiments, the preparation method of the positive electrode active material may include: high temperature solid phase method, carbon thermal reduction method, spray drying method, template method or hydrothermal synthesis method.

[0071] In some embodiments, the intermediate product obtained during the preparation of the positive electrode active material can also be crushed and sieved to obtain a positive electrode active material with an optimized particle size distribution and specific surface area. There is no particular limitation on the crushing method, which can be selected according to actual needs, such as using a particle crusher. The preparation method of the positive electrode active material of the present application is not limited to the above preparation method, as long as the formed positive electrode active material has the characteristics shown in this application.

[0072] In addition, the positive electrode active material layer further includes a positive electrode conductor and a positive electrode binder.

[0073] In some embodiments, the type of positive electrode conductive agent is not limited, and any known conductive agent can be used. Examples of positive electrode conductive agents include, but are not limited to, natural graphite, artificial graphite, acetylene black, amorphous carbon such as needle coke, carbon nanotubes, graphene, and the like. The above-mentioned positive electrode conductive agents can be used alone or in any combination.

[0074] In some embodiments, the type of positive electrode binder used in the manufacture of the positive electrode active material layer is not particularly limited. In the case of a coating method, any material can be dissolved or dispersed in the liquid medium used in electrode manufacture. Examples of positive electrode binders may include, but are not limited to, one or more of the following: resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber-like polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymers or their hydrides, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers or their hydrides; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; polymer compositions having ionic conductivity of alkali metal ions (especially lithium ions), etc. The above-mentioned positive electrode binders can be used alone or in any combination.

[0075] In some embodiments, the type of solvent used to form the positive electrode slurry is not limited, as long as it is a solvent that can dissolve or disperse the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder. Examples of solvents used to form the positive electrode slurry may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixed media of alcohol and water. Examples of organic media may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

[0076] The type of positive electrode current collector is not particularly limited and can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and composite materials formed by polymers and metal layers. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0077] There are no particular limitations on the form of the positive electrode current collector. When the positive electrode current collector is a metal material, the form of the positive electrode current collector may include, but is not limited to, metal foil, metal cylinder, metal coil, metal plate, metal foil, expanded metal, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, the form of the positive electrode current collector may include, but is not limited to, carbon plate, carbon film, carbon cylinder, etc.

[0078] In some embodiments, the preparation process of the positive electrode sheet may include stirring, coating, drying, cold pressing, slitting, and cutting. The preparation of the positive electrode sheet includes dispersing the positive electrode active material, positive electrode conductive agent, and positive electrode binder in N-methylpyrrolidone (NMP) in a certain proportion, coating the resulting slurry on aluminum foil, drying, and then cold pressing and slitting to obtain the positive electrode sheet.

[0079] Negative electrode

[0080] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer contains a negative electrode active material, and the negative electrode active material contains graphite.

[0081] The negative electrode sheet can be single-sided or double-sided. When the negative electrode sheet is single-sided, the negative electrode active material layer is disposed on one surface of the negative electrode current collector. When the negative electrode sheet is double-sided, the negative electrode active material layer is disposed on both surfaces of the negative electrode current collector. A negative electrode sheet can also have both a single-sided negative electrode sheet region and a double-sided negative electrode sheet region. When a negative electrode sheet has both a single-sided negative electrode sheet region and a double-sided negative electrode sheet region, the thickness of the negative electrode sheet is the thickness of the double-sided negative electrode sheet region.

[0082] diaphragm

[0083] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. The type of separator is not particularly limited and can be selected based on actual needs. Separators can be polypropylene, polyethylene, spandex, aramid, or a multilayer composite film modified with a coating.

[0084] electrolyte

[0085] In some embodiments, the main components of the electrolyte include a lithium salt, an organic solvent, and an additive. The types and compositions of the lithium salt and organic solvent are not particularly limited and can be selected based on actual needs. The lithium salt may include lithium hexafluorophosphate, and the solvent may include ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propyl propionate.

[0086] In some embodiments, the preparation of a secondary battery includes: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, so that the separator is located between the positive and negative electrode sheets to play an isolating role, and then winding them into a bare battery cell, placing them in a battery shell, and then baking them at 65 to 120°C to remove water, injecting electrolyte, sealing, and obtaining a secondary battery after standing, hot and cold pressing, formation, clamping, and capacity separation.

[0087] In some embodiments, the embodiments of the present application provide an electrical device, which includes the above-mentioned secondary battery. The electrochemical device can be used for but is not limited to backup power supplies, motors, electric vehicles, electric motorcycles, power-assisted bicycles, bicycles, power tools, large household batteries, etc.

[0088] The present invention has been tested many times, and some of the test results are now cited as reference to further describe the invention in detail, and the following is a detailed description of the invention in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0089] Example 1

[0090] The nickel-cobalt-manganese ternary polycrystalline material was prepared by the following steps:

[0091] (1) nickel sulfate, cobalt sulfate, and manganese sulfate were prepared in a molar ratio of 1:1:1 to form a 2 mol / L raw material solution, which was then added dropwise into a continuous stirring reactor simultaneously with 0.5 mol / L ammonia water and 2 mol / L sodium hydroxide solution. The reaction temperature was controlled at 60°C and the pH was 11. The reaction was continued for 72 hours, aged for 12 hours, and finally filtered, washed, and dried to obtain a nickel-cobalt-manganese hydroxide precursor.

[0092] (2) The nickel-cobalt-manganese precursor, Me source (niobium oxide, molybdenum oxide and lithium fluoride in a molar ratio of 1:1:2), and lithium hydroxide were placed in a mixing device at a molar ratio of Li / TM (Ni+Co+Mn) = 1.05:1 and mixed evenly, and then placed in a furnace with an oxygen concentration of 10% at 900°C for 24 hours. After mechanical grinding, a ternary material containing niobium, molybdenum and fluorine elements was obtained;

[0093] (3) The product obtained by the primary sintering and the coating material (zirconium oxide, tungsten oxide, and titanium hydroxide in a molar ratio of 1:1:1) are placed in a mixing device and mixed evenly, and then placed in an atmosphere furnace for sintering at 500°C for 12 hours to obtain a ternary polycrystalline positive electrode active material with a coating layer (the coating elements are Zr, W, and Ti).

[0094] Example 2

[0095] The preparation method was essentially the same as that in Example 1, except that the reaction temperature was 50°C, the pH was 11.5, the reaction time was 60 hours, and the aging time was 8 hours. The primary sintering was performed at 850°C for 18 hours. The Me source consisted of tin oxide, chromium oxide, and lithium sulfide in a molar ratio of 1:1:3, and the coating source consisted of magnesium oxide and barium hydroxide in a molar ratio of 1:1.

[0096] Example 3

[0097] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 5:2:3, the reaction temperature was controlled at 70°C, the reaction pH was 10.5, the reaction time was 80 hours, and the aging time was 15 hours. The primary sintering process was performed at 850°C for 24 hours. The Me source consisted of strontium oxide and yttrium chloride in a 1:2 molar ratio, and the coating source consisted of titanium oxide and bismuth carbonate in a 1:2 molar ratio.

[0098] Example 4

[0099] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 5:2:3, the reaction temperature was controlled at 65°C, the reaction pH was 12, the reaction time was 64 hours, and the aging time was 8 hours. The primary sintering was performed at 850°C for 18 hours. The Me source was lanthanum oxide and tungsten oxide in a molar ratio of 1:1.5, and the coating source was tin oxide and chromium oxide in a molar ratio of 1:1.5.

[0100] Example 5

[0101] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 6:2:2, the reaction temperature was controlled at 40°C, the reaction pH was 10, the reaction time was 80 hours, and the aging time was 15 hours. The primary sintering temperature was 800°C for 12 hours, and the oxygen concentration was 60%. The Me source was niobium hydroxide and molybdenum oxide in a 2:1 molar ratio, and the coating source was strontium oxide and yttrium hydroxide in a 1:2 molar ratio.

[0102] Example 6

[0103] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 6:2:2, the reaction temperature was controlled at 45°C, the reaction pH was 10.5, the reaction time was 60 hours, and the aging time was 8 hours. The primary sintering temperature was 800°C, the sintering time was 18 hours, and the oxygen concentration was 70%. The Me source was calcium fluoride and antimony oxide in a molar ratio of 3:2, and the coating source was strontium oxide and yttrium oxide in a molar ratio of 3:1.

[0104] Example 7

[0105] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 8:1:1, the reaction temperature was controlled at 65°C, the reaction pH was 11.5, the reaction time was 144 hours, and the aging time was 6 hours. The primary sintering process was performed at 750°C for 20 hours, and the oxygen concentration was 90%. The Me source was tin phosphate and tungsten oxide in a 1:1 molar ratio, and the coating source was niobium carbonate and molybdenum oxide in a 1:2 molar ratio.

[0106] Example 8

[0107] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 8:1:1, the reaction temperature was controlled at 80°C, the reaction pH was 12, the reaction time was 168 hours, and the aging time was 10 hours. The primary sintering temperature was 750°C, the sintering time was 18 hours, and the oxygen concentration was 90%. The Me source was cobalt oxide and silicon sulfate in a molar ratio of 3:2; the coating source was calcium carbonate and silicon oxide in a molar ratio of 1:1.

[0108] Example 9

[0109] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 90:05:05, the reaction temperature was controlled at 70°C, the reaction pH was 10.5, the reaction time was 144 hours, and the aging time was 12 hours. The primary sintering process was performed at 700°C for 24 hours, and the oxygen concentration was 95%. The metal oxide (ME) source consisted of boric acid, tungsten oxide, and lithium sulfide in a molar ratio of 1:2:1, and the coating source consisted of tin oxide, phosphoric acid, and tungsten oxide in a molar ratio of 1:2:2.

[0110] Example 10

[0111] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 523, the reaction temperature was controlled at 65°C, the reaction pH was 11.5, the reaction time was 168 hours, and the aging time was 12 hours. The primary sintering was performed at 700°C for 18 hours, and the oxygen concentration was 95%. The metal oxide (ME) source was zinc oxide and barium oxide in a 1:2 molar ratio, and the coating source was cobalt oxide and silicon hydroxide in a 1:3 molar ratio.

[0112] Example 11

[0113] The preparation method was essentially the same as that in Example 1, except that the reaction temperature was controlled at 50°C, the pH was 12, the reaction time was 20 hours, and the aging time was 4 hours. The primary sintering temperature was 850°C and the sintering time was 15 hours. The Me source was titanium hydroxide and lanthanum oxide in a molar ratio of 1:3, and the coating source was boron oxide and tungsten oxide in a molar ratio of 3:2.

[0114] Example 12

[0115] The preparation method was essentially the same as that in Example 1, except that the reaction temperature was controlled at 50°C, the pH was 10.5, the reaction time was 64 hours, and the aging time was 8 hours. The primary sintering step was performed at 1000°C for 24 hours. The Me source consisted of aluminum hydroxide and cobalt chloride in a 1:1 molar ratio, and the coating source consisted of zinc carbonate and barium oxide in a 3:1 molar ratio.

[0116] Example 13

[0117] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 5:2:3, the reaction temperature was controlled at 65°C, the reaction pH was 11.5, the reaction time was 64 hours, and the aging time was 12 hours. The primary sintering process was performed at 750°C for 24 hours. The metal oxide (Me) source consisted of zinc oxide, yttrium oxide, and bismuth oxide in a molar ratio of 2:2:3, and the coating source consisted of titanium carbonate and lanthanum oxide in a molar ratio of 1:3.

[0118] Example 14

[0119] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 5:2:3, the reaction temperature was controlled at 60°C, the reaction pH was 12, the reaction time was 64 hours, and the aging time was 8 hours. The primary sintering temperature was 750°C for 8 hours. The Me source was aluminum oxide and tungsten oxide in a 3:2 molar ratio, and the coating source was aluminum hydroxide and cobalt oxide in a 3:4 molar ratio.

[0120] Example 15

[0121] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 6:2:2, the reaction temperature was controlled at 30°C, the reaction pH was 11, the reaction time was 64 hours, and the aging time was 24 hours. The primary sintering process was performed at 850°C for 12 hours, and the oxygen concentration was 80%. No Me source was added, and the coating source consisted of zinc oxide, yttrium oxide, and boric acid in a molar ratio of 3:2:1.

[0122] Example 16

[0123] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 6:2:2, the reaction temperature was controlled at 45°C, the reaction pH was 11.5, the reaction time was 48 hours, and the aging time was 4 hours. The primary sintering process was performed at 800°C for 18 hours, and the oxygen concentration was 10%. The metal oxide (ME) source consisted of titanium hydroxide and silicon nitride in a 1:2 molar ratio, and the coating source consisted of aluminum hydroxide and tungsten oxide in a 3:2 molar ratio.

[0124] Example 17

[0125] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 8:1:1, the reaction temperature was controlled at 50°C, the reaction pH was 11.5, the reaction time was 124 hours, and the aging time was 6 hours. The primary sintering process was performed at 780°C for 24 hours, and the oxygen concentration was 95%. The Me source was tin oxide and lithium phosphate in a molar ratio of 1:3, and the coating source was antimony oxide and molybdenum oxide in a molar ratio of 3:2.

[0126] Example 18

[0127] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 8:1:1, the reaction temperature was controlled at 70°C, the reaction pH was 11, the reaction time was 200 hours, and the aging time was 20 hours. The primary sintering temperature was 750°C, the sintering time was 20 hours, and the oxygen concentration was 90%. The Me source was cobalt oxide and zinc oxide in a 1:1 molar ratio, and the coating source was titanium hydroxide and silicon oxide in a 1:2 molar ratio.

[0128] Example 19

[0129] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 90:05:05, the reaction temperature was controlled at 70°C, the reaction pH was 11.5, the reaction time was 124 hours, and the aging time was 16 hours. The primary sintering process was performed at 700°C for 20 hours, and the oxygen concentration was 95%. The metal oxide (ME) source consisted of chromium oxide, lanthanum oxide, and lithium nitride in a molar ratio of 1:2:1, and the coating source consisted of tin oxide and phosphorus oxide in a molar ratio of 3:2.

[0130] Example 20

[0131] The preparation method was essentially the same as that in Example 1, except that the nickel, cobalt, and manganese concentrations in the raw material solution were set at 523°C, the reaction temperature was controlled at 65°C, the reaction pH was 10.5, the reaction time was 144 hours, and the aging time was 8 hours. The primary sintering process was performed at 700°C for 18 hours, and the oxygen concentration was 95%. The metal oxide (ME) source consisted of tungsten oxide, boric acid, and aluminum oxide in a 1:2 molar ratio, and the coating source consisted of cobalt carbonate and zinc oxide in a 2:1 molar ratio.

[0132] Example 21

[0133] The preparation method was essentially the same as that of Example 5, except that the reaction temperature was controlled at 60°C, the reaction pH was 11, the reaction time was 120 hours, and the aging time was 12 hours. The primary sintering temperature was 850°C, the sintering time was 24 hours, and the oxygen concentration was 80%. The Me source was calcium oxide and silicon oxide in a molar ratio of 1:3, and the coating source was chromium hydroxide and lanthanum oxide in a molar ratio of 1:4.

[0134] Example 22

[0135] The preparation method was essentially the same as that of Example 7, except that the reaction temperature was controlled at 55°C, the reaction pH was 10.5, the reaction time was 120 hours, and the aging time was 6 hours. The primary sintering was performed at 720°C for 18 hours, and the oxygen concentration was 99%. The Me source was magnesium phosphate, and the coating source was tungsten oxide, boric acid, and aluminum oxide in a molar ratio of 1:2:3.

[0136] Example 23

[0137] The preparation method was essentially the same as that of Example 8, except that the reaction temperature was controlled at 60°C, the reaction pH was 11.5, the reaction time was 180 hours, and the aging time was 12 hours. The primary sintering was performed at 700°C for 24 hours, and the oxygen concentration was 60%. The Me source consisted of titanium oxide, molybdenum oxide, and lithium fluoride in a molar ratio of 1:2:1, and the coating source consisted of calcium carbonate and silicon oxide in a molar ratio of 3:2.

[0138] Comparative Example 1

[0139] The preparation method was essentially the same as that in Example 1, except that the reaction temperature was controlled at 65°C, the reaction pH was 12, the reaction time was 64 hours, and the aging time was 6 hours. The primary sintering was performed at 1000°C for 12 hours. The Me source was zirconium carbonate and tungsten oxide in a 1:1 molar ratio, and the coating source was magnesium phosphate.

[0140] Comparative Example 2

[0141] The preparation method was essentially the same as that in Example 3, except that the reaction temperature was controlled at 65°C, the reaction pH was 10, the reaction time was 120 hours, and the aging time was 10 hours. The primary sintering was performed at 600°C for 28 hours. The Me source was chromium oxide and lanthanum oxide in a 1:1 molar ratio, and the coating source was titanium oxide and molybdenum oxide in a 1:1 molar ratio.

[0142] Comparative Example 3

[0143] The preparation method was essentially the same as that of Example 9, except that the reaction temperature was controlled at 40°C, the reaction pH was 9.5, the reaction time was 120 hours, and the aging time was 15 hours. The primary sintering was performed at 600°C for 48 hours, and the oxygen concentration was 60%. The Me source consisted of tungsten oxide, boric acid, and aluminum hydroxide in a molar ratio of 1:2:1, and the coating source consisted of zirconium hydroxide and tungsten oxide in a molar ratio of 1:2.

[0144] The parameters and systems of the positive electrode active materials prepared in Examples 1-23 and Comparative Examples 1-3 are shown in Table 1 and Table 1.1. θ (Ni a Co b Mn c ) 1-x M x O y G zThe ratio of a, b and c, such as 111 means 1:1:1, 523 means 5:2:3, and 9005 means 9:0.5:0.5.

[0145] Electrochemical performance test:

[0146] The positive electrode active materials from Examples 1-23 and Comparative Examples 1-3 were mixed with the conductive agent SP and the binder PVDF in a ratio of 90:5:5. NMP was added as a solvent and stirred thoroughly to uniformly disperse the slurry. The positive electrode slurry was evenly coated on both sides of the current collector aluminum foil, then dried at 120°C, cold pressed, slit, and cut to obtain positive electrode sheets.

[0147] Graphite, thickener CMC, binder SBR, conductive agent SP, and binder PVDF are mixed in a ratio of 97:1:1:1. Deionized water is added as a solvent and stirred thoroughly to evenly disperse the slurry. The negative electrode slurry is evenly coated on both sides of the current collector copper foil, then dried at 120°C, cold pressed, slit, and cut to obtain the negative electrode sheet.

[0148] The positive electrode sheet, negative electrode sheet, and separator (polypropylene film with a thickness of 12 μm) were wound into a bare cell, then placed in an aluminum-plastic film. After baking, the electrolyte (EC / EMC = 3 / 7, 1M lithium hexafluorophosphate) was injected. After the formation, sealing, and capacity separation processes, a 3Ah soft-pack battery was obtained. The following performance tests were then carried out. The test results are shown in Table 2.

[0149] (1) Gram capacity: At room temperature, the battery was charged at a constant current of 0.33C to 4.2V, then charged at a constant voltage of 4.2V to a current less than 0.05C. After standing for 5 minutes, the battery was discharged at a current of 0.33C to 2.8V to obtain the first discharge gram capacity.

[0150] (2) Rate performance: At room temperature, the battery was charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current was less than 0.05C. After standing for 5 minutes, the battery was discharged at a current of 4C to 2.8V. 4C rate = 4C discharge capacity / 1C discharge capacity × 100%.

[0151] (3) Cyclic performance test: Repeated charge and discharge cycles at 1C current at 45°C, with a charge and discharge cut-off voltage of 2.8V to 4.2V. The 900th cycle capacity retention rate = 900th cycle capacity / first cycle capacity × 100%.

[0152] (4) Storage gas generation test: Charge the battery to 4.2V at a constant current of 1C, then charge it at a constant voltage of 4.2V until the current is less than 0.05C. Place the fully charged battery in an 80℃ oven and test the volume using the water displacement method every other day. Fully charge the battery at 1C every 7 days.

[0153] (5) Cyclic Gas Generation Test: After 900 cycles, the battery is discharged to 2.8V and then placed in water to test its volume using the displacement method. The displacement method works by completely submerging the battery in a beaker of water, which is placed on an electronic scale. The change in the scale reading before and after the battery is placed is equal to Ffloat. Using Archimedes' principle, Ffloat = ρgV, the battery volume V can be calculated.

[0154] Table 1

[0155] Table 1.1 (In the table, M elements and G elements refer to the chemical formula of the positive electrode active material Li θ (Ni a Co b Mn c ) 1-x M x O y G z The content of M element refers to the molar percentage of the content of M element in the positive electrode active material to the total content of transition metal elements)

[0156] Table 2

[0157] It can be seen from Tables 1 and 2 that compared with Comparative Example 1, Example 1 has better battery cycle performance, rate performance and gas production performance, indicating that when the β / α value is less than or equal to 0.4, the arrangement of the primary particles inside the secondary particles is more orderly, the contact sites between the electrolyte and the grain boundaries are appropriate, and intergranular cracking is not likely to occur after cycling.

[0158] Compared with Example 2, Example 3 has significantly better rate, cycle and gas production performance than Example 2, indicating that when the β / α value is greater than 0.15, the arrangement of the primary particles inside the secondary particles is more orderly, and intergranular cracking is less likely to occur after circulation.

[0159] Compared with Example 3, Example 9 has significantly better rate, cycle and gas production performance than Example 3, indicating that when the β / α value is greater than 0.15, the arrangement of the primary particles inside the secondary particles is more orderly, and intergranular cracking is less likely to occur after circulation.

[0160] In summary, the positive electrode active material of this embodiment includes secondary particles composed of primary particles. By regulating the number of grain boundaries, crystal plane orientation, and cross-sectional pore structure, the grain boundary length per unit cross-sectional area β and the number of grain boundaries per unit cross-sectional area α of the positive electrode active material satisfy 0.15≤β / α≤0.4. This improves the material structure's ability to release stress, improves the material's oxygen stability, alleviates the problem of polycrystalline particle breakage after high compaction and long cycling, and reduces lattice oxygen loss. As a result, the positive electrode active material of this embodiment has excellent cycle life, low gas generation performance, and good kinetic performance.

[0161] The above is a detailed introduction to a positive electrode active material, a secondary battery and an electrical device provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present application.

Claims

1. A positive electrode active material, wherein It includes secondary particles formed by agglomeration of primary particles, wherein in the SEM image of the cross section of the secondary particles, the number of grain boundaries per unit cross-sectional area is α bars / μm 2 , the grain boundary length per unit cross-sectional area is βμm / μm 2 , the secondary particles satisfy: 0.15≤β / α≤0.

4.

2. The positive electrode active material according to claim 1, wherein The secondary particles have pores. In the SEM image of the cross section of the secondary particles, the number of pores per unit cross-sectional area is γ / μm. 2 , the secondary particles satisfy: γ≤30.

3. The positive electrode active material according to claim 1, wherein In the SEM image of the cross section of the secondary particle, the cross-sectional figure of the primary particle has a longest side and a side that does not intersect with the longest side; wherein the sum of the lengths of the longest side and the side per unit cross-sectional area is R μm / μm 2 , satisfying: R / β≥60%.

4. The positive electrode active material according to claim 1, wherein The positive electrode active material further satisfies: an oil absorption value ranging from 1 mL / g to 80 mL / g.

5. The positive electrode active material according to claim 1, wherein The positive electrode active material further satisfies: the Dv10 of the positive electrode active material ranges from 1 μm to 13 μm, the Dv50 of the positive electrode active material ranges from 2 μm to 16 μm, and the Dv90 of the positive electrode active material ranges from 3 μm to 20 μm; wherein Dv10 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 10%; Dv50 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 50%; and Dv90 is the particle size corresponding to when the cumulative volume percentage of the positive electrode active material reaches 90%.

6. The positive electrode active material according to claim 1, wherein The specific surface area of ​​the positive electrode active material is from 0.2 m 2 / g to 2.5m 2 / g.

7. The positive electrode active material according to claim 1, wherein The secondary particles further satisfy at least one of the following characteristics: a) 1≤α≤50; b) 0.15≤β≤20.

8. The positive electrode active material according to claim 1, wherein The positive electrode active material includes Li θ (Ni a Co b Mn c ) 1-x M x O y G z ; Wherein, 0.95≤θ≤1.1, 0.3≤a≤0.9, 0≤b≤0.15, 0≤c≤0.5, 0≤x≤0.1, 1≤y≤2, 0≤z≤1, y+z=2; M is selected from at least one of Al, Mg, B, Ca, Zn, Sb, W, Bi, Cr, Sr, Y, W, Zr, Ti, La, Nb, Mo, V; G is selected from at least one of F, S, Cl, N.

9. The positive electrode active material according to claim 8, wherein The positive electrode active material includes a coating element, and the coating element is arranged on the surface of the secondary particles and / or the primary particles; the coating element is selected from at least one of Al, Mg, B, Ba, Co, Si, Sn, P, Ca, Zn, Sb, W, Bi, Cr, Sr, Y, W, Zr, Ti, La, Nb, and Mo.

10. The positive electrode active material according to claim 9, wherein In the positive electrode active material, the total content of the coating element per unit surface area is from 0.1 mg / m 2 Up to 20 mg / m 2 .

11. The positive electrode active material according to claim 8, wherein In the positive electrode active material, the residual lithium content per unit surface area is from 0.1 mg / m 2 To 8 mg / m 2 .

12. The positive electrode active material according to claim 1, wherein The secondary particles have pores. The pores of the secondary particles are formed by the accumulation of the primary particles. The pore diameter is D μm, and satisfies: 0.01≤D≤4.

13. The positive electrode active material according to claim 3, wherein R / β≤90％。 14. A secondary battery, wherein: The invention comprises a positive electrode current collector and a positive electrode plate arranged on the positive electrode current collector, wherein the positive electrode plate comprises the positive electrode active material according to any one of claims 1 to 13.

15. An electrical device, wherein: Includes the secondary battery as claimed in claim 14.

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