Lithium ion battery cathode material, preparation method and application thereof

Abstract

The application discloses a lithium ion battery positive electrode material and a preparation method and application thereof, and belongs to the technical field of new energy materials. The lithium ion battery positive electrode material provided by the application comprises a hollow shell layer, and the hollow shell layer forms an internal cavity; the hollow shell layer comprises an inner layer and a coating layer on the outer surface of the inner layer; along the direction from the inner layer to the coating layer, the inner layer comprises a fast ion conductor layer and a layered lithium composite oxide layer. The lithium ion battery positive electrode material provided by the application can effectively reduce the impedance of the lithium ion battery positive electrode material in use. The application further provides a preparation method and application of the lithium ion battery positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy materials, in particular to a lithium ion battery cathode material and a preparation method and application thereof. BACKGROUND

[0002] A battery for a vehicle requires a battery with high output power, which requires that the internal resistance of the battery be kept at a low level. For example, if the reaction resistance within the battery (especially the reaction resistance in the positive electrode) can be reduced, a battery with lower internal resistance and more excellent output performance can be obtained.

[0003] A lithium secondary battery using a lithium composite oxide with a layered structure as a positive electrode active material has excellent initial characteristics (for example, low internal resistance, suitable for higher output power) and excellent durability. However, as market requirements improve, the power performance of the above-mentioned layered lithium composite oxide needs to be further improved. Researchers have attempted to increase the internal porosity of the positive electrode active material (for example, to construct small-particle hollow / porous materials) to facilitate greater contact between the electrolyte and the positive electrode active material, which can shorten the lithium ion solid-phase diffusion path while ensuring a lower cobalt content in the positive electrode active material, ultimately improving its power performance.

[0004] However, during use, high specific surface area is usually accompanied by a higher rate of side reactions with the electrolyte, which can cause the cycle performance of the layered lithium composite oxide to decrease. In addition, if the hollow secondary spherical particles are completely closed, the inner wall can only participate in the reaction through solid-phase diffusion, and the reaction kinetics is much lower than that of the solid-liquid interface reaction.

[0005] In summary, the rate and / or power performance of the existing layered lithium composite oxide needs to be improved. SUMMARY

[0006] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a lithium ion battery cathode material that can effectively reduce the impedance of the lithium ion battery cathode material when in use.

[0007] The present application also provides a preparation method of the above-mentioned lithium ion battery cathode material.

[0008] The present application also provides a lithium ion secondary battery comprising the above-mentioned lithium ion battery cathode material.

[0009] According to an embodiment of the first aspect of the present application, a lithium ion battery cathode material is provided, which comprises a hollow shell layer, the hollow shell layer forming an internal cavity;

[0010] The hollow shell layer comprises an inner layer and a coating layer on the outer surface of the inner layer;

[0011] The inner layer comprises a fast ion conductor layer and a layered lithium composite oxide layer in the direction from the inner layer to the cladding layer.

[0012] The lithium ion battery cathode material according to the embodiment of the application has at least the following beneficial effects:

[0013] The lithium ion battery cathode material provided by the application can significantly reduce the internal resistance during use and effectively inhibit the side reaction between the lithium ion battery cathode material and the electrolyte.

[0014] For the cathode material with a hollow structure, after the electrolyte penetrates into the internal cavity, the inner and outer surfaces of the hollow shell layer will directly contact the electrolyte, which will inevitably accelerate the side reaction between the lithium ion battery cathode material and the electrolyte, although the internal resistance will be reduced due to the increase of active sites. In the lithium ion battery cathode material provided by the application, the inner surface of the inner layer is provided with a fast ion conductor layer, and a cladding layer is further included, which is equivalent to wrapping the core material layered lithium composite oxide layer, thereby inhibiting the interface side reaction and enhancing the structural stability. Moreover, the internal fast ion conductor layer has high lithium ion conductivity, so it will not hinder the transmission of lithium ions, and thus will not increase the interface impedance.

[0015] Further, the lithium ion battery cathode material provided by the application also has the effect of reducing the internal impedance and improving the cycle effect of the hollow material. The main principle is that the diffusion path of lithium ions in the solid is shortened, and the internal cavity also accommodates the volume change of the lithium ion battery cathode material during the cycle process, more contact sites, and more uniform interface reaction.

[0016] Overall, the lithium ion battery cathode material provided by the application has a significant synergistic effect between the internal cavity structure, the fast ion conductor layer and the cladding layer.

[0017] According to some embodiments of the application, the cladding layer comprises a fast ion conductor compound. The fast ion conductor compound is a LiM2O type compound. In this way, the ion conductivity can be further improved, the impedance can be reduced, and the rate performance can be improved on the basis of forming a physical barrier and improving the cycle performance. At the same time, the fast ion conductor layer can work together to achieve efficient lithium ion conduction of the lithium ion battery cathode material.

[0018] According to some embodiments of the application, the cladding layer contains element M2; and M2 is selected from at least one of B, Al, La, Ta, Ti, Zr, W, Nb and Ba.

[0019] When M2 includes any one of Zr, W, La, Nb, Ti and Ta, the cladding layer contains a fast ion conductor substance, which can improve the Li+ The diffusion rate is significantly reduced, the interface impedance is reduced, and the power performance is improved. When M2 includes B, the coating layer formed by Li-B-O can repair the cyclic micro-cracks, reduce the direct contact of the electrolyte with the interior of the lithium ion battery positive electrode material, inhibit the interface side reaction, and enhance the interface stability; when M2 includes Al, the coating layer has ion conductivity and interface passivation ability, and improves the rate performance and cycle performance. In addition, when M2 includes Ta, Ti, Zr, W, and Nb, the high bond energy of the M2-O bond can anchor the surface oxygen, inhibit the release of oxygen, enhance the thermal stability of the layered lithium composite oxide, and inhibit the conversion of the layered structure to spinel or rock salt phase during high-voltage charging; when M2 includes La, La has strong "oxygen affinity" and can form a stable passivation layer with oxygen, stabilize the structure, and inhibit excessive growth of CEI. When M2 includes W, Li2WO4 forms a stable coating layer, is resistant to HF corrosion, high-valence W 6+ induces surface passivation; when M2 includes Nb, the compound of Nb can inhibit the decomposition of the electrolyte and the dissolution of the transition metal, inhibit the interface side reaction, and when M2 includes Ba, Ba has a large ionic radius and tends to preferentially occupy the surface or interstitial sites of the crystal lattice, reduce the grain boundary impedance, and provide a wider channel for lithium ion diffusion.

[0020] According to some embodiments of the present application, in the coating layer, M2 is at least one of W, B, Al, and Ti.

[0021] According to some embodiments of the present application, in the coating layer, M2 is a combination of Ti and Al. The molar ratio of Ti and Al is 1-3:1. For example, it can be about 1:1, 1.5:1, 2:1, 2.5:1, or about 3:1.

[0022] According to some embodiments of the present application, in the coating layer, M2 is a combination of W and B. The molar ratio of W and B is 4-8:1. For example, it can be about 4:1, 5:1, 6:1, 7:1, or about 8:1.

[0023] According to some embodiments of the present application, in the coating layer, M2 is a combination of Al, W, and B. The molar ratio of Al, W, and B is 1:2-4:0.3-0.6. For example, it can be about 1:2:0.3, 1:3:0.5, 1:4:0.6, 1:2:0.6, 1:2:0.4, or 1:4:0.3.

[0024] The combination of the above-mentioned several M2 elements has the dual effects of improving the cycle performance and the power performance.

[0025] According to some embodiments of the present application, in the lithium ion battery positive electrode material, the chemical formula of the part other than the coating layer is Li a Ni x Coy Mn z M1 w O 2±b wherein, 1.03≤a≤1.3, 0.3≤x≤0.9, 0≤y≤0.4, 0≤z≤0.4, 0≤w≤0.03, x+y+z+w=1, 0≤b≤0.1;

[0026] M1 is selected from at least one of Zr, W, Mg, La, Ta, Sb, Ti, Sr, Al and Nb. Wherein,

[0027] M1 is mainly enriched in the fast ion conductor layer and can form a certain doping to the layered lithium composite oxide layer. Its role is as follows: the fast ion conductor layer including Zr, W and La can improve Li + diffusion rate, improve power performance; in addition, the doping of Zr, W, Mg or Al can stabilize the lattice structure of the layered lithium composite oxide layer, inhibit cation mixing, and improve cycle performance; Zr 4+ can also occupy the transition metal layer in the layered lithium composite oxide layer, stabilize the layered structure, inhibit cation mixing and lattice oxygen loss, inhibit oxygen precipitation and phase change, and improve cycle stability; W can form a strong W-O bond, reduce the activity of lattice oxygen, inhibit the formation of oxygen vacancies and oxygen loss, reduce irreversible phase change, relieve volume expansion stress during cycling, reduce microcracks, improve cycle stability, reduce interface side reactions, and improve rate performance; Mg² + has an ion radius close to that of Ni² + , can occupy Ni sites, inhibit Li / Ni mixing, stabilize the layered structure of the layered lithium composite oxide layer, and at the same time expand the interlayer distance, promote Li + diffusion, and improve the thermal stability and cycle life of the lithium ion battery cathode material; La³ + tends to occupy grain boundary or surface sites, form a stable fast ion conductor, improve Li + diffusion rate, and inhibit grain boundary crack propagation and transition metal dissolution; Al³ + can replace part of Ni³ + , inhibit cation mixing, and the high bond energy of Al-O bond enhances the stability of the layered structure in the layered lithium composite oxide layer, inhibiting the transformation of the layered structure to spinel or rock salt phase during high-pressure charging. Sb can be doped into the transition metal layer without affecting the layered structure, and can expand the (003) plane spacing to reduce the Li diffusion energy barrier, Ti 4+ substitutes transition metal sites, inhibits cation mixing, stabilizes the oxygen layer structure, improves cycle stability, initial efficiency, and improves rate performance; Sr² +Generally occupies the lithium site, widens the lithium layer spacing, stabilizes the structure and promotes lithium ion diffusion, improves cycle stability; the high bond energy of Nb-O bond effectively inhibits oxygen loss and cation mixing, significantly improves cycle life, enhances structural stability, and improves rate performance.

[0028] Li a Ni x Co y Mn z M1 w O 2±b The range of w can widen the migration channel of lithium ions, improve ionic conductivity, and inhibit lattice distortion while not reducing capacity.

[0029] According to some embodiments of the present application, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b For example, it can be about 0.3, 0.4, 0.5, 0.6, or about 0.7.

[0030] According to some embodiments of the present application, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b For example, it can be about 0.1, 0.2, 0.3, or about 0.4.

[0031] According to some embodiments of the present application, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b For example, it can be about 0.1, 0.2, 0.3, or about 0.4.

[0032] According to some embodiments of the present application, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b For example, it can be about 0.001, 0.003, 0.005, 0.008, 0.01, or about 0.02.

[0033] According to some embodiments of the present application, the chemical formula Li a Nix Co y Mn z M1 w O 2±b M1 is selected from at least one of Zr, W, La, Sb and Al.

[0034] According to some embodiments of the present application, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b M1 is selected from a combination of Zr and W. Wherein the molar ratio of W and Zr is 1-4: 1; for example, it can be about 1:1, 2:1 or about 4:1.

[0035] According to some embodiments of the present application, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b M1 is selected from a combination of W and La. Wherein the molar ratio of W and La is 1-4: 1; for example, it can be about 1:1, 2:1 or about 4:1.

[0036] According to some embodiments of the present application, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b M1 is selected from a combination of Al and W.

[0037] According to some embodiments of the present application, the inner layer is composed of a single layer or double layer of primary particle arrangement. Due to the formation of a single layer or double layer of primary particle arrangement, the gap between the primary particles (loose packing site, or formed after rearrangement and shrinkage of primary particles) is likely to penetrate the inner layer, forming through holes; these through holes act as a rapid channel for electrolyte penetration, allowing the electrolyte to directly penetrate into the secondary sphere of the lithium ion battery anode material, shortening the diffusion distance from the electrolyte to the internal particles, reducing concentration polarization, reducing impedance, significantly improving the utilization rate of active substances (such as the inner layer), improving high-rate performance, reducing interface side reactions (uniform distribution of electrolyte, avoiding local overcharge / overdischarge); in addition, the through holes also provide stress buffer space for volume expansion, disperse stress concentration, reduce the expansion of internal microcracks of the lithium ion battery anode material, inhibit particle pulverization and electrode structure collapse, and prolong the life of the secondary battery including the lithium ion battery anode material. + from the electrolyte to the internal particles, reducing concentration polarization, reducing impedance, significantly improving the utilization rate of active substances (such as the inner layer), improving high-rate performance, reducing interface side reactions (uniform distribution of electrolyte, avoiding local overcharge / overdischarge); in addition, the through holes also provide stress buffer space for volume expansion, disperse stress concentration, reduce the expansion of internal microcracks of the lithium ion battery anode material, inhibit particle pulverization and electrode structure collapse, and prolong the life of the secondary battery including the lithium ion battery anode material.

[0038] Further, compared with the double-layer arrangement, the single-layer arrangement can further improve the contact between the electrolyte and the primary particles, shorten the solid-phase diffusion, improve the rate performance, and meanwhile, the concentrated stress generated by the volume change during the charging and discharging process is smaller, and the structural stability is higher.

[0039] According to some embodiments of the present application, the number of the through holes in the single lithium ion battery positive electrode material is 1-5. For example, it can be 1, 2, 3, 4 or 5.

[0040] According to some embodiments of the present application, the aperture of the through hole is 0.1-0.2 μm.

[0041] According to some embodiments of the present application, the average thickness of the hollow shell layer is 0.4-0.8 μm. For example, it can be 0.4 μm, 0.6 μm or 0.8 μm.

[0042] The aperture / number of the through hole, the thickness of the inner layer / hollow shell / inner cavity are determined by cross-sectional SEM observation.

[0043] According to some embodiments of the present application, in the cross section of the lithium ion battery positive electrode material, the hollow portion accounts for 40-50% of the area.

[0044] According to some embodiments of the present application, in the lithium ion battery positive electrode material, the thickness ratio of the hollow shell layer and the inner cavity is 0.14.

[0045] In the present application, the hollow portion area ratio and the diameter ratio of the inner cavity are all measured on the SEM graph by cutting the positive electrode material in the middle.

[0046] According to some embodiments of the present application, the lithium ion battery positive electrode material further comprises a core body located in the inner cavity. Thus, the tap density of the lithium ion battery positive electrode material can be improved while the advantages of the inner cavity are possessed; additionally, the internal transport channel of lithium ions is provided, and the problem of invalid transport of lithium ions (no transport process of lithium intercalation and deintercalation) caused by the inner cavity is solved; meanwhile, the core body can also provide certain support to relieve the stress generated during processing or cycling.

[0047] According to some embodiments of the present application, the core body is in contact with or not in contact with the inner layer.

[0048] According to some embodiments of the present application, the surface of the core body is enriched with fast ion conductor substances. The fast ion conductor substances and the fast ion conductor layer are made of the same material.

[0049] According to some embodiments of the present application, the D50 of the lithium ion battery cathode material is 2-10 μm. For example, it can be about 2 μm, 2.5 μm, 2.8 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or about 10 μm.

[0050] According to some embodiments of the present application, the particle size distribution Span ((D90-D10) / D50) of the lithium ion battery cathode material is 0.8-1.3. For example, it can be about 0.9, 1.0, 1.1 or about 1.2.

[0051] According to some embodiments of the present application, the specific surface area of the lithium ion battery cathode material is ≥1.8 m 2 / g. For example, it can be about 2.0 m 2 / g, 2.5 m 2 / g, 3.0 m 2 / g or about 3.5 m 2 / g.

[0052] According to some embodiments of the present application, the oil absorption of the lithium ion battery cathode material is 30 mL / 100 g-70 mL / 100 g. For example, it can be about 40 mL / 100 g, 50 mL / 100 g, 52 mL / 100 g, 55 mL / 100 g, 60 mL / 100 g, 65 mL / 100 g or a range value formed by any two of the above point values.

[0053] According to some embodiments of the second aspect of the present application, the preparation method of the lithium ion battery cathode material according to the embodiments of the first aspect of the present application is provided, and the preparation method comprises the following steps:

[0054] S1. Preparation of a precursor: the precursor comprises an inner core, an intermediate layer and an outer layer from the core to the surface, the intermediate layer is looser than the inner core and the outer layer; the inner core and the outer layer are transition metal hydroxides, and the intermediate layer is a transition metal carbonate doped with M1 elements;

[0055] S2. Mixing and calcining the precursor obtained in step S1 and lithium salt in an oxidizing atmosphere; the mixing and calcining comprises a first holding platform and a second holding platform in sequence; the temperature of the first holding platform is 480-600 ℃; the temperature of the second holding platform is 800-920 ℃;

[0056] S3. Mixing and calcining the product obtained in step S2 and a coating agent.

[0057] Since the preparation method adopts all the technical solutions of the lithium ion battery cathode material according to the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments. Specifically:

[0058] The outer layer is a dense layer, and is preferentially in contact with Li + The intermediate layer is relatively loose, and the primary particles have a smaller particle size and a higher surface energy, and move and diffuse in the inward and outward directions during the sintering process in step S2, to form the internal cavity; the fast ion conductor layer is formed by outward migration, and the fast ion conductor material covering the core is formed by inward migration. Since the fast ion conductor layer is formed by inward and outward diffusion of the intermediate layer, there is no very obvious boundary between the fast ion conductor layer and the layered lithium composite oxide layer; and part of M1 may be doped into the layered lithium composite oxide layer in addition to forming the fast ion conductor layer.

[0059] Further, in step S2, the temperature of the first holding platform can ensure that the lithium salt is melted / decomposed, promote the penetration of lithium into the crystal lattice, and convert the crystal lattice; the temperature of the second holding platform can avoid the influence of too low temperature on the crystallinity of the obtained lithium ion battery positive electrode material, avoid the formation of amorphous material, and ensure the formation of the internal cavity; on the other hand, it can also avoid the fusion growth of the primary particles caused by too high temperature, which may lead to structural collapse, thereby ensuring the formation of the internal cavity. In addition, the higher the temperature, the higher the crystallinity, and when the basic crystallization requirement is met, with the increase of the crystallinity, the active site decreases, the lithium ion transmission speed decreases, and the impedance increases; the temperature of the second holding platform provided by the present application can exactly meet the basic crystallization requirement and avoid excessive crystallization.

[0060] According to some embodiments of the present application, in step S1, the chemical formula of the precursor is Ni x Co y Mn z M1 w (OH) 2a CO 3(1-a) , wherein 0.3≤x≤0.9, 0≤y≤0.4, 0≤z≤0.4, 0≤w≤0.1, x+y+z+w=1, 0.4≤a≤0.6. Further, the value ranges of x, y, z, and w and the selection of M1 refer to the chemical formula Li a Ni x Co y Mn z M1 w O 2±b and the selection. The specific value of a is selected from 0.4, 0.45, 0.5, 0.55, 0.6; or a range value composed of any two of the above point values.

[0061] According to some embodiments of the present application, in step S1, the core is formed by stacking of the flaky or platy primary particles.

[0062] According to some embodiments of the present application, in step S1, the outer layer has a radial arrangement structure. Thus, in the calcination process of step S2, a single-layer or multi-layer primary particle arrangement inner layer structure can be formed.

[0063] According to some embodiments of the present application, in step S1, the preparation process of the precursor comprises the following steps:

[0064] S1a. Mixing the mixed metal salt solution, the lye and the ammonia solution in parallel flow to perform a first co-precipitation reaction to obtain the inner core; the pH range of the first co-precipitation reaction is 10.00-12.50;

[0065] S1b. Adjusting and maintaining the pH of the system obtained in step S1a to be 7.00-8.60; and introducing the mixed metal salt solution, the carbonate solution and the M1-containing solution into the system in parallel flow to perform a second co-precipitation reaction to obtain the intermediate layer;

[0066] S1c. Filtering the solid material obtained in step S1b; reslurrying, adjusting and maintaining the pH of the obtained slurry to be 9.00-11.00; and introducing the mixed metal salt solution, the lye and the ammonia solution into the system in parallel flow to perform a third co-precipitation reaction to obtain the outer layer.

[0067] According to the synthesis method of the precursor, by adjusting the pH of different steps and the types of precipitants, the outer layer can form a relatively dense large-particle structure, and the primary particles in the intermediate layer are smaller and more loose with high porosity.

[0068] According to some embodiments of the present application, in step S1a, the parallel flow mixing is introducing the mixed metal salt solution, the lye and the ammonia solution into a bottom solution in parallel flow.

[0069] According to some embodiments of the present application, the bottom solution contains ammonia; wherein the ammonia concentration is 3-10 g / L. For example, it can be about 5 g / L, 7.5 g / L, 8.0 g / L, 8.5 g / L or 9.5 g / L.

[0070] According to some embodiments of the present application, the pH of the bottom solution is 10-12; for example, it can be about 10, 11 or about 12.

[0071] According to some embodiments of the present application, in step S1a, the mixed metal salt solution comprises nickel ions.

[0072] According to some embodiments of the present application, in step S1a, the mixed metal salt solution further comprises at least one of cobalt ions and manganese ions.

[0073] The type of ions and the ratio of internal ions in the mixed metal salt solution can be determined according to the transition metal in the positive electrode material of the lithium ion battery actually needed to be produced; for example, it can be Ni:Co:Mn=5:2:3, or Ni:Co:Mn=1:1:1, or Ni:Co:Mn=6:2:2, or Ni:Co:Mn=8:1:1, or Ni, Co and Mn are mixed in any ratio.

[0074] According to some embodiments of the present application, in step S1a, the total concentration of transition metal ions in the mixed metal salt solution is 1.5-2.2 mol / L. For example, it can be about 1.5 mol / L, 2.0 mol / L.

[0075] According to some embodiments of the present application, in step S1a, the solute of the alkali solution includes at least one of sodium hydroxide and potassium hydroxide.

[0076] According to some embodiments of the present application, in step S1a, the concentration of the alkali solution is 3-10.8 mol / L. For example, it can be about 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 6 mol / L, 7 mol / L, 8 mol / L, 9 mol / L, 10 mol / L.

[0077] According to some embodiments of the present application, in step S1a, the concentration of the ammonia solution is 4-6 mol / L. For example, it can be about 4 mol / L, 4.5 mol / L, 5 mol / L, 6.5 mol / L or about 6 mol / L.

[0078] According to some embodiments of the present application, in step S1a, the temperature of the first coprecipitation reaction is 50-70°C. For example, it can be about 50°C, 55°C, 60°C, 65°C or about 70°C.

[0079] According to some embodiments of the present application, in step S1a, the first coprecipitation reaction is carried out under stirring. The paddle linear speed of the stirring is 4-9 m / s. For example, it can be about 4 m / s, 4.5 m / s, 5 m / s, 5.5 m / s, 6 m / s, 7 m / s, 8 m / s, 9 m / s.

[0080] According to some embodiments of the present application, in step S1a, the first coprecipitation reaction is carried out in a protective atmosphere. The protective atmosphere includes at least one of nitrogen and argon.

[0081] According to some embodiments of the present application, in step S1a, the pH during the first coprecipitation is 10-12; for example, it can be about 10, 11 or about 12.

[0082] According to some embodiments of the present application, in step Sla, the concentration of the process ammonia in the first co-precipitation process is 3-10 g / L. For example, it can be about 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 6 mol / L, 7.5 g / L, 8.0 g / L, 8.5 g / L, 9 mol / L, or 10 mol / L.

[0083] According to some embodiments of the present application, in step Sla, the percentage of the core in the particle size of the precursor is 10-20%. For example, it can be about 10%, 12%, 14%, 15%, 16%, 18%, or about 20%.

[0084] Unless otherwise specified, the percentage of particle size in the present application is the ratio of D50.

[0085] According to some embodiments of the present application, in step S1b, the reagent for adjusting the pH includes dilute sulfuric acid. The concentration of the dilute sulfuric acid is 1-6 mol / L; further specifically, it can be 2 mol / L or 4 mol / L.

[0086] According to some embodiments of the present application, in step S1b, the pH is 7.5-8.5; for example, it can be about 7.5, 7.6, 7.8, 8.0, 8.2, or about 8.5.

[0087] According to some embodiments of the present application, in step S1b, the solute of the carbonate solution includes at least one of sodium carbonate and potassium carbonate.

[0088] According to some embodiments of the present application, in step S1b, the concentration of the carbonate solution is 1.4-2 mol / L. For example, it can be about 1.4 mol / L, 1.8 mol / L, or about 2.0 mol / L.

[0089] According to some embodiments of the present application, in step S1b, the molar ratio of the carbonate ions and the metal ions (including those in the mixed metal salt solution and the M1-containing solution) introduced per unit time is 1-1.12:1; for example, it can be about 1:1, 1.1:1, or about 1.12:1.

[0090] According to some embodiments of the present application, in step S1b, the percentage of the particle size of the obtained product and the precursor is 70-80%. For example, it can be about 70%, 72%, 74%, 76%, 78%, or about 80%. The specific particle size range of the product obtained in step S1b is 1-2.5 μm. For example, it can be about 1 μm, 1.5 μm, 2.0 μm, or about 2.5 μm.

[0091] According to some embodiments of the present application, in step S1c, the pulping liquid comprises water, the ammonia solution and the alkali solution.

[0092] According to some embodiments of the present application, in step S1c, the ammonia concentration of the slurry is 0-20 g / L. For example, it can be about 5 g / L, 10 g / L, 15 g / L or about 20 g / L.

[0093] According to some embodiments of the present application, in step S1c, the pH of the slurry is 9.5-10.5. For example, it can be about 9.5, 10 or about 10.5.

[0094] According to some embodiments of the present application, in step S1c, the oxygen concentration in the atmosphere of the third co-precipitation reaction is <5%.

[0095] According to some embodiments of the present application, in step S1c, the ammonia concentration of the third co-precipitation reaction is 0-20 g / L. For example, it can be about 5 g / L, 10 g / L, 15 g / L or about 20 g / L.

[0096] According to some embodiments of the present application, the preparation method of the precursor further comprises the steps of solid-liquid separation, aging, washing and drying after step S1c.

[0097] According to some embodiments of the present application, in step S1, the D50 of the precursor is 2-10 μm. For example, it can be about 2 μm, 2.5 μm, 2.8 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or about 10 μm.

[0098] Due to the influence of the precursor morphology on the morphology of the lithium ion battery cathode material, and the relatively thin coating layer, the particle size (particle size distribution) of the precursor and the final lithium ion battery cathode material are basically equivalent.

[0099] According to some embodiments of the present application, in step S2, the molar ratio of the precursor to lithium in the lithium salt is 1:1.05-1.2. For example, it can be about 1:1.05, 1:1.1, 1:1.15 or about 1:1.2.

[0100] According to some embodiments of the present application, the temperature of the first holding platform is 480-600°C. For example, it can be about 500°C, 520°C, 550°C, 580°C or about 600°C.

[0101] According to some embodiments of the present application, in step S2, the holding time of the first holding platform is 2-6 h. For example, it can be about 2 h, 3 h, 4 h, 5 h or about 6 h.

[0102] According to some embodiments of the present application, the temperature of the second holding platform is 800-920℃. For example, it can be about 800℃, 820℃, 850℃, 880℃, 900℃ or about 920℃.

[0103] According to some embodiments of the present application, the holding time of the second holding platform in step S2 is 8-16h. For example, it can be about 8h, 10h, 12h, 14h or about 16h.

[0104] According to some embodiments of the present application, in step S3, the coating agent is an oxide or acid oxide of M2, wherein M2 is at least one selected from B, Al, La, Ta, Ti, Zr, W, Nb and Ba.

[0105] According to some embodiments of the present application, in step S3, the proportion of M2 in the product obtained in step S2 is 6000-20000ppm. Within this range, the coating layer does not block the transmission channel of lithium ions and can play a good physical isolation role.

[0106] According to some embodiments of the present application, in step S3, the molar percentage of M2 in (Ni+Co+Mn+M1+M2) in the lithium ion battery cathode material is 0.6-2mol%. For example, it can be about 0.6%, 0.8%, 1.0%, 1.5% or about 2%.

[0107] According to some embodiments of the present application, in step S3, the temperature of the mixed second firing is 300-600℃. For example, it can be about 300℃, 350℃, 400℃, 450℃, 500℃, 550℃ or about 600℃. Within this temperature range, it can ensure that the mixed second firing is completely reacted, and also avoid the decrease of the uniformity of coating and conductivity caused by excessive sintering; thus, it avoids the side reaction of unreacted raw materials and electrolyte, and also avoids the increase of interface impedance, and finally significantly improves the gain effect of the coating layer on the cycle performance and rate performance.

[0108] According to some embodiments of the present application, in step S3, the time length of the mixed second firing is 4-10h. For example, it can be about 4h, 5h, 6h, 7h, 8h, 9h or about 10h.

[0109] According to some embodiments of the third aspect of the present application, a lithium ion secondary battery is provided, and the raw materials for preparing the lithium ion secondary battery include the lithium ion battery cathode material according to the first aspect of the present application or the lithium ion battery cathode material prepared by the preparation method according to the second aspect of the present application.

[0110] Since the lithium ion secondary battery adopts the lithium ion battery cathode material or the preparation method of the above-mentioned embodiments, all the beneficial effects brought by the technical solutions of the above-mentioned embodiments are at least possessed.

[0111] Unless otherwise specified, "about" in the present application actually means that the allowed error is within ±2%, for example, about 100 actually means 100±2%×100.

[0112] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0113] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0114] Figure 1 is a cross-sectional SEM image of the lithium ion battery cathode material obtained in Example 1 of the present application.

[0115] Figure 2 is a SEM image of the lithium ion battery cathode material obtained in Example 1 of the present application.

[0116] Figure 3 is a SEM image of the lithium ion battery cathode material obtained in Comparative Example 2 of the present application.

[0117] Figure 4 is a SEM image of the lithium ion battery cathode material obtained in Comparative Example 3 of the present application.

[0118] Figure 5 is a cross-sectional mapping atlas of the lithium ion battery cathode material obtained in Example 6 of the present application. DETAILED DESCRIPTION

[0119] The concept and technical effects of the present application will be described clearly and completely in combination with the embodiments below, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0120] In the description of the application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the application. In this specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0121] Embodiment 1

[0122] In this example, a lithium ion battery positive electrode material is prepared, and the specific steps are as follows:

[0123] S1. Preparation of precursor:

[0124] S1a. Into the bottom solution with ammonia concentration of 8 g / L and pH of 11.00, nickel, cobalt and manganese mixed metal salt solution (molar ratio of nickel, cobalt and manganese is 5:2:3, and total concentration of nickel, cobalt and manganese is 2 mol / L), NaOH aqueous solution (4 mol / L) and ammonia aqueous solution (5 mol / L) are flowed in at a flow rate of 100 mL / min (only for the reaction volume of this example, which can be adjusted in actual production), the reaction temperature is 60°C, the stirring speed is 5 m / s (linear speed, corresponding to paddle speed of 50 Hz), the precipitation reaction is carried out under the protection of nitrogen, the pH of the reaction is maintained at 11.0 by an automatic pH adjusting system (by controlling the flow rate of sodium hydroxide solution), the ammonia concentration is 8 g / L (by controlling the flow rate of ammonia solution), a dense core composed of flaky or plate-like primary particles is formed, and the precursor is grown to D50=0.5 μm;

[0125] S1b. 2 mol / L dilute sulfuric acid is flowed in, the pH of the system obtained in step S1a is reduced to 7.8, nickel, cobalt and manganese mixed metal salt solution (synchronous step S1a), sodium tungstate solution (6 g / L) and sodium carbonate solution (about 1.8 mol / L) are flowed into the reaction kettle bottom solution at a flow rate of 180 mL / min (only for the reaction volume of this example), and the molar ratio of the over metal ions (including W) and carbonate flowed in per unit time is controlled to be 1:1.1; the material is grown to D50 about 2.5 μm, and an intermediate layer composed of fine particle-like W-doped carbonate precursor is formed, wherein the molar percentage of W element in step S1 (Ni+Co+Mn+M1) is 0.3 mol% (the flow rate ratio of mixed metal salt solution and sodium tungstate solution is controlled).

[0126] S1c. The reaction slurry obtained in step S1b is filtered to obtain a crystal seed (solid product); the crystal seed is put into a reaction kettle, pure water, ammonia water and NaOH are added, the ammonia concentration is 10 g / L, the pH of the slurry is adjusted to 10 (the pH and ammonia concentration are maintained in the subsequent co-precipitation), and a mixed metal salt solution of nickel, cobalt and manganese with the same composition as in step S1a (the composition flow rate is synchronized with step S1a), an alkali solution and an ammonia solution are flowed in, the stirring speed is 5 m / s, nitrogen is flowed in to make the oxygen concentration < 5%, and the material is grown to a D50 of about 3.2 μm to form a flaky hydroxide precursor constituting a radially arranged outer layer.

[0127] The reaction slurry is filtered, aged, washed and dried to obtain the precursor, and the D50 particle size of the obtained precursor is about 3.2 μm.

[0128] S2. The precursor synthesized in step S1 and LiOH are uniformly mixed at a lithium metal ratio of 1.12, heated to 500°C under oxygen for 4 h, and then sintered at 850°C for 12 h to obtain an intermediate product.

[0129] S3. The intermediate product is mixed with Al2O3 and TiO2 (M2 is Al and Ti), wherein Al:Ti = 1:1, and the total molar amount of the coated element M2 accounts for 2 mol% of the molar percentage of the obtained positive electrode material elements (Ni+Co+Mn+M1+M2), and sintered at 450°C for 6 h, and then sieved after cooling to obtain a lithium ion battery positive electrode material.

[0130] The lithium ion battery positive electrode material obtained in this example has a hollow shell layer and an internal cavity formed around the hollow shell layer;

[0131] The hollow shell layer is composed of an inner layer and a coating layer on the outer surface of the inner layer;

[0132] In the direction from the inner layer to the coating layer, the inner layer comprises a fast ion conductor layer and a layered lithium composite oxide layer arranged in layers;

[0133] The internal cavity contains a core body, which has a certain probability of being free in the internal cavity and also has a certain probability of being connected to the fast ion conductor layer; the outer surface of the core body also has a rich fast ion conductor layer.

[0134] The fast ion conductor layer contains lithium tungstate.

[0135] The chemical formula of the lithium ion battery positive electrode material obtained in this example is Li 1.12 (Ni 0.5 Co 0.2 Mn 0.3 ) 0.978 M1 0.002 M2 0.02 O 2.085Wherein the shell comprises lithium zirconate and lithium antimonate; the rest of the chemical formula is Li 1.1 (Ni 0.5 Co 0.2 Mn 0.3 ) 0.997 M1 0.003 O 2.05 .

[0136] Example 2

[0137] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 1 in that:

[0138] In step S1, the molar ratio of Ni, Co and Mn in the mixed metal salt solution of nickel, cobalt and manganese is 1:1:1.

[0139] Example 3

[0140] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 1 in that:

[0141] In step S1, the molar ratio of Ni, Co and Mn in the mixed metal salt solution of nickel, cobalt and manganese is 8:1:1.

[0142] Example 4

[0143] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 1 in that:

[0144] In step S1b, the sodium tungstate solution is replaced by a mixed solution of lanthanum sulfate and sodium tungstate with the same concentration and flow rate, and the molar ratio of W and La is 1:1.

[0145] Example 5

[0146] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 1 in that:

[0147] In step S1b, the sodium tungstate solution is replaced by a mixed solution of zirconium sulfate and sodium tungstate with the same concentration and flow rate, and the molar ratio of W and Zr is 1:1.

[0148] Example 6

[0149] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 4 in that:

[0150] In step S3, the coating reagent is a combination of tungsten oxide and boric acid, and the molar ratio of W:B is 6:1.

[0151] Example 7

[0152] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 4 in that:

[0153] In step S3, the coating reagent is a combination of aluminum oxide, tungsten oxide and boric acid, wherein Al:W:B = 1:3:0.5 (molar ratio).

[0154] Example 8

[0155] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 4 in that:

[0156] In step S2, the temperature of the second holding platform is 800°C.

[0157] Example 9

[0158] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 4 in that:

[0159] In step S2, the temperature of the second holding platform is 910°C.

[0160] Example 10

[0161] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 4 in that:

[0162] In step S1b, the molar percentage of M1 element in (Ni+Co+Mn+M1) in step S1 is 3 mol%.

[0163] Example 11

[0164] In this example, a lithium ion battery positive electrode material is prepared, which is different from example 4 in that:

[0165] The steps in step S1c are as follows:

[0166] The reaction slurry obtained in step S1b is filtered to obtain seed crystals (solid product); the above seed crystals are put into the reaction kettle, pure water, ammonia water and NaOH are added, the ammonia concentration is 12 g / L, the pH of the slurry is adjusted to 10 (the pH and ammonia concentration are maintained during subsequent co-precipitation), and the same nickel, cobalt and manganese mixed metal salt solution (flow rate 150 mL / min), alkali solution and ammonia solution as in step S1a are flowed in, the stirring speed is 4 m / s, nitrogen is flowed in to make the oxygen concentration <5%, and the material is grown to a D50 of about 3.2 μm, forming a short flake-shaped hydroxide precursor, and there is no dominant arrangement orientation between primary particles.

[0167] The reaction slurry is filtered, aged, washed and dried to obtain the precursor, and the D50 particle size of the obtained precursor is about 3.2 μm.

[0168] Comparative Example 1

[0169] A lithium ion battery cathode material is prepared in this example, which is different from example 1 in that:

[0170] In step S1b, no sodium tungstate solution is added.

[0171] Comparative example 2

[0172] A lithium ion battery cathode material is prepared in this example, which is different from example 4 in that:

[0173] In step S2, the temperature of the second holding platform is 950°C.

[0174] Comparative example 3

[0175] A lithium ion battery cathode material is prepared in this example, which is different from example 4 in that:

[0176] In step S2, the temperature of the second holding platform is 780°C.

[0177] Comparative example 4

[0178] A lithium ion battery cathode material is prepared in this example, which is different from example 4 in that:

[0179] In step S1b, no pH adjustment is made, and the system pH is maintained at 11.

[0180] Comparative example 5

[0181] A lithium ion battery cathode material is prepared in this example, which is different from example 4 in that:

[0182] Step S3 is not included.

[0183] Comparative example 6

[0184] A lithium ion battery cathode material is prepared in this example, which is different from example 4 in that:

[0185] In step S1b, no compound solution of M1 is added;

[0186] In step S2, the same amount of M1 as in example 4 is added.

[0187] Comparative example 7

[0188] A lithium ion battery cathode material is prepared in this example, which is different from example 4 in that:

[0189] Step S1a is not included; the reaction time of step S1b is maintained, and the reaction time in step S1c is extended to obtain a precursor comparable to example 4.

[0190] Application example

[0191] The example provides a lithium secondary battery, which is specifically as follows.

[0192] The positive electrode material prepared above, the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) are mixed and stirred uniformly at a mass ratio of 90:5:5, and then mixed with N-methyl pyrrolidone (NMP) to prepare a positive electrode slurry (solid content of about 40%) which is coated on a current collector aluminum foil, dried at 105°C, and then rolled at room temperature to a surface density of 2.7-3.0 g / cm 3 Then, punching and shearing are performed to obtain a positive electrode sheet with a diameter of 14 mm. The positive electrode material is from the example or the comparative example.

[0193] The assembly of the coin cell is performed in a glove box: the coin cell is assembled in the order of "negative shell-foam nickel-lithium sheet (φ18 mm)-8 drops of electrolyte-separator (φ22 mm, 16 μm thick)-8 drops of electrolyte-positive electrode sheet-positive shell", wherein the electrolyte is composed of ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) (EC: EMC: DMC volume ratio = 1:1:1) and contains 1.0 M LiPF6; the size of the battery shell (positive shell and negative shell) is 24 mm. The assembled coin cell is placed in a mold groove of a hydraulic sealing machine (purchased from Shenzhen Kejing Zhida Technology Co., Ltd.), locked, and pressed at >450 kg / cm 2 Then, the coin cell is unlocked and taken out, and the sealed coin cell is the lithium secondary battery obtained in the example.

[0194] Test Example

[0195] The first aspect of the example tests the BET, morphology (and mapping atlas), particle size distribution, and oil absorption value of the lithium ion battery positive electrode material obtained in the examples and comparative examples, wherein the test results of the BET and oil absorption value are shown in Table 1. Specifically, the oil absorption amount is tested by using a HITEC DABS oil absorption tester, and paraffin oil is dropped at a constant speed during stirring of the lithium ion battery positive electrode material, and the oil absorption amount is calculated according to the torque value; the morphology is tested by using a scanning electron microscope (SEM), and the overall morphology and cross-sectional morphology are specifically tested, and the particle size is tested by using a laser particle size analyzer. It can be known from the combination of the morphology test and the particle size test that the particle size of the obtained lithium ion battery positive electrode material is between 2-10 μm, most of which is between 2-4 μm, and the particle size distribution of the lithium ion battery positive electrode material obtained in Example 1 is about 1.1 ((D90-D10) / D50); the obtained lithium ion battery positive electrode material includes a core and a hollow shell layer, the core and the hollow shell layer are in contact or not in contact, there are through holes on the hollow shell layer, and the number of through holes on a single cross section is about 2; the average thickness of the hollow shell layer is about 0.4 μm, which is formed by the ordered radial arrangement of primary particles, and specifically forms one layer or two layers; according to the thickness ratio of the hollow shell layer and the internal cavity, the ratio is about 0.14, and the area ratio of the hollow part is about 45%; it can be known from the mapping test results that in the positive electrode material obtained in Example 6, W is coated on the surface of the core and is enriched in the fast ion conductor layer and the coating layer, so it can be known that the preparation method provided by the application indeed obtains the positive electrode material with the target structure. The morphology of the lithium ion battery positive electrode material obtained in Example 1 is shown in Figures 1-2 , the mapping test results of the positive electrode material obtained in Example 6 are shown in Figure 5 , Figure 5 The green points represent the distribution of the W element; the morphology of the lithium ion battery positive electrode material obtained in Comparative Examples 2-3 is shown in Figures 3-4 . It can be known that the apparent morphology of the lithium ion battery positive electrode material obtained in other examples is equivalent to that of Examples 1 and 6, and both have a hollow shell layer and a coating layer, and the hollow shell layer further includes a fast ion conductor layer and a layered lithium composite oxide layer. In Comparative Example 4, since the pH is not adjusted, the density of the intermediate layer and other layers of the precursor is basically the same, so in the subsequent calcination process, it cannot migrate inward and outward to form an internal cavity. In Comparative Example 6, although an internal cavity is formed, since M1 is not added in step S1b, the product does not have a fast ion conductor layer in the inner layer. In Comparative Example 7, since step S1a is not included, the internal structure of the lithium ion battery positive electrode material obtained in the example is also different.

[0196] The second aspect of this example tested the cycle performance and impedance before and after cycling of the lithium-ion battery obtained in the application example. The cycle performance was tested as follows: at 25°C, the charge-discharge cycle characteristics of the coin cell were detected using a Blue Electric test cabinet, with 1C values ​​set to 165 mAh / g (Example 1), 145 mAh / g (Example 2), and 195 mAh / g (Example 3). One cycle of activation was performed at a charge-discharge rate of 0.1C, followed by charge-discharge at 1C within a voltage range of 2.8V to 4.25V. Specifically, the first cycle involved constant current charging at 0.1C to 4.25V, followed by constant voltage charging at 4.25V to a cutoff current of 0.02C, followed by a 5-minute rest, and then discharge at 0.1C to 2.8V, followed by a 5-minute rest. In the second cycle, charge at a constant current of 1C to 4.25V, then charge at a constant voltage of 4.25V until the cutoff current reaches 0.02C. Let it rest for 5 minutes, then discharge at 1C to 2.8V, let it rest for 5 minutes, and record the charge / discharge capacity after the second cycle (the first cycle of 1C charge / discharge). Repeat this cycle for 50 cycles at 1C, and record the charge / discharge capacity after the 51st cycle (the 50th cycle of 1C charge / discharge). Cycle capacity retention (%) = (51st cycle discharge capacity / 2nd cycle discharge capacity) × 100%.

[0197] Pre-cycle impedance test method: At 25℃, the charge-discharge cycle characteristics of the button cell were tested using a Blue Electric test cabinet. The charge-discharge rate was 0.1C, and the charge-discharge was performed in the voltage range of 2.8V~4.25V. Specifically, the cell was charged at a constant current of 0.1C to 4.25V, then charged at a constant voltage of 4.25V to the cutoff current of 0.02C, and left to stand for 5 minutes. The cell was then discharged at 0.1C to 2.8V and left to stand for 5 minutes. Then charge at a constant current of 0.1C to 4.25V, and then charge at a constant voltage of 4.25V to the cutoff current of 0.02C. Let it rest for 5 minutes, then discharge at 0.1C to the median voltage (about 3.79V) and let it stand for 2 hours. Then, at -30℃, use a blue electric test cabinet to test the low temperature impedance. Let it stand at -30℃ for 1 hour, then discharge at 3C for 10 seconds and let it stand. Divide the voltage difference between the voltage before 3C discharge and the voltage at 10 seconds of discharge by the discharge current to obtain the DCR value at -30℃.

[0198] Impedance testing method after cycling: After the above cycling performance test is completed, charge at a constant current of 0.1C to 4.25V, then charge at a constant voltage of 4.25V to the cutoff current of 0.02C, let stand for 5 minutes, discharge at 0.1C to the median voltage (about 3.79V), and let stand for 2 hours. Then, at -30℃, use a blue electric test cabinet to test the low temperature impedance, let stand at -30℃ for 1 hour, then discharge at 3C for 10 seconds and let stand. Divide the voltage difference between the voltage before 3C discharge and the voltage at 10 seconds of discharge by the discharge current to obtain the DCR value at -30℃.

[0199] The test results are shown in Table 1.

[0200] Table 1 Performance of the positive electrode material of the lithium ion battery obtained in the examples and comparative examples

[0201]

[0202] It can be seen from the results of Comparative Examples 1-3 that the lithium ion battery positive electrode material and the preparation method thereof provided by the application are suitable for modification of low-nickel, medium-nickel and high-nickel ternary positive electrode materials, and excellent electrochemical performance can be achieved.

[0203] It can be seen from the results of Comparative Example 1 and Examples 4-5 that beneficial electrochemical performance can be achieved by switching different raw materials, and according to the selection of M1, there are advantages in cycle retention rate, pre-cycle impedance and rate.

[0204] It can be seen from the results of Comparative Example 4, Examples 6-7 and Comparative Example 5 that the capacity retention rate and the rate of the lithium ion battery positive electrode material obtained by using different coating layers are significantly improved, and most importantly, the impedance increase rate during use is significantly reduced. In addition, when M2 is a mixture of Al, W and B, the cycle performance of the lithium ion battery positive electrode material obtained is better, and the post-cycle impedance is lower, which indicates that within the test range of the examples, the coating layer including this combination has better inert barrier performance and better lithium ion conductivity, and it can be expected that the long cycle performance under high rate conditions is excellent.

[0205] It can be seen from the results of Comparative Example 1, Examples 8-9 and Comparative Examples 2-3 that with the increase of the second holding platform temperature, the impedance shows a trend of first decreasing and then increasing.

[0206] It can be seen from the results of Comparative Example 4, Examples 10-11 and Comparative Example 1 that when M1 is not doped, the performance of the positive electrode material obtained is significantly deteriorated, and with the increase of the amount of M1 doping, the overall performance of the positive electrode material obtained shows a trend of first increasing and then decreasing.

[0207] It can be seen from the results of Comparative Example 4, Comparative Example 4, Comparative Examples 6-7 that if the lithium ion battery positive electrode material obtained does not have the specific structure required by the application, the overall performance of the material will decrease.

[0208] In conclusion, the lithium ion battery cathode material provided by the application has excellent cycle performance, low impedance and excellent rate performance due to the special structure design and special component design. Due to the above excellent performance, the lithium ion battery cathode material or the lithium ion secondary battery including the lithium ion battery cathode material is expected to be widely applied in the field of power batteries, the field of energy storage technology and the field of communication electronics.

[0209] The embodiments of the application are described in detail above with reference to the drawings, but the application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the application. In addition, the embodiments of the application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A lithium-ion battery cathode material, characterized in that, The lithium-ion battery cathode material includes a hollow shell layer, which surrounds and forms an internal cavity; The hollow shell layer includes an inner layer and a covering layer on the outer surface of the inner layer; Along the direction from the inner layer to the outer coating layer, the inner layer includes a fast ion conductor layer and a layered lithium composite oxide layer; The preparation method includes the following steps: S1. Preparation of precursor: The precursor includes a core, an intermediate layer and an outer layer from the core to the surface, the intermediate layer being more porous than the core and the outer layer; the core and the outer layer are transition metal hydroxides, and the intermediate layer is a transition metal carbonate doped with M1 element; M1 is selected from at least one of Zr, W, Mg, La, Ta, Sb, Ti, Sr, Al, and Nb; S2. In an oxidizing atmosphere, the precursor obtained in step S1 and the lithium salt are mixed and calcined; the mixed calcination includes a first heat preservation platform and a second heat preservation platform in sequence; the temperature of the first heat preservation platform is 480~600℃; the temperature of the second heat preservation platform is 800~920℃; S3. Mix the product obtained in step S2 with the coating agent and calcine.

2. The lithium-ion battery cathode material according to claim 1, characterized in that, In the lithium-ion battery cathode material, the chemical formula of the parts other than the coating layer is Li. a Ni x Co y Mn z M1 w O 2±b , where 1.03≤a≤1.3, 0.3≤x≤0.9, 0≤y≤0.4, 0≤z≤0.4, 0≤w≤0.03, x+y+z+w=1, 0≤b≤0.

1.

3. The lithium-ion battery cathode material according to claim 1, characterized in that, The coating layer comprises a fast ion conductor compound; and / or, the coating layer contains element M2; and M2 is selected from at least one of B, Al, La, Ta, Ti, Zr, W, Nb and Ba.

4. The lithium-ion battery cathode material according to claim 1, characterized in that, The lithium-ion battery cathode material also includes a core, which is located in the internal cavity.

5. The lithium-ion battery cathode material according to any one of claims 1 to 4, characterized in that, The inner layer consists of a single or double layer of primary particle arrangement.

6. The lithium-ion battery cathode material according to any one of claims 1 to 4, characterized in that, The lithium-ion battery cathode material satisfies at least one of the following parameters: (a) D50 is 2~10μm; (b) Particle size distribution Span (D90-D10 / D50) is 0.8~1.3; (c) Specific surface area ≥ 1.8 m² 2 / g.

7. A method for preparing a lithium-ion battery cathode material as described in any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: S1. Preparation of precursor: The precursor includes a core, an intermediate layer and an outer layer from the core to the surface, the intermediate layer being more porous than the core and the outer layer; the core and the outer layer are transition metal hydroxides, and the intermediate layer is a transition metal carbonate doped with M1 element; S2. In an oxidizing atmosphere, the precursor obtained in step S1 and the lithium salt are mixed and calcined; the mixed calcination includes a first heat preservation platform and a second heat preservation platform in sequence; the temperature of the first heat preservation platform is 480~600℃; the temperature of the second heat preservation platform is 800~920℃; S3. Mix the product obtained in step S2 with the coating agent and calcine.

8. The preparation method according to claim 7, characterized in that, In step S1, the precursor has the chemical formula Ni. x Co y Mn z M1 w (OH) 2a CO 3(1-a) Where 0.3≤x≤0.9, 0≤y≤0.4, 0≤z≤0.4, 0≤w≤0.1, x+y+z+w=1; 0.4≤a≤0.

6.

9. The preparation method according to claim 7, characterized in that, In step S3, the coating agent is an oxide or acid of M2, wherein M2 is selected from at least one of B, Al, La, Ta, Ti, Zr, W, Nb and Ba.

10. A lithium-ion secondary battery, characterized in that, The raw materials for preparing the lithium-ion secondary battery include the lithium-ion battery cathode material according to any one of claims 1 to 6, or the lithium-ion battery cathode material prepared by the preparation method according to any one of claims 7 to 9.

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