Lithium ion battery positive electrode material and preparation method and application thereof

Abstract

The invention 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 invention comprises a hollow shell layer, and the hollow shell layer is encircled to form an internal cavity; the hollow shell layer comprises an inner layer and a coating layer on the outer surface of the inner layer; 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. According to the lithium ion battery positive electrode material provided by the invention, the impedance of the lithium ion battery positive electrode material in use can be effectively reduced. The invention also provides a preparation method and application of the lithium ion battery positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and in particular to a lithium-ion battery cathode material, its preparation method, and its application. Background Technology

[0002] Vehicle batteries and other devices that require high output power necessitate suppressing the battery's internal resistance to maintain a low level. For example, reducing the reactive resistance within the battery (especially in the positive electrode) can result in a battery with lower internal resistance and superior output performance.

[0003] Lithium-ion batteries made by using layered lithium composite oxides as cathode active materials exhibit excellent initial characteristics (e.g., low internal resistance, suitable for higher output power) and durability. However, with increasing market demands, the power performance of these layered lithium composite oxides needs further improvement. Researchers are attempting to increase the internal porosity of the cathode active material (e.g., by constructing small-particle hollow / porous materials) to facilitate a larger contact area between the electrolyte and the cathode active material. This allows for a shorter lithium-ion solid-phase diffusion path while maintaining a low cobalt content in the cathode active material, ultimately improving its power performance.

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

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

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a lithium-ion battery cathode material that can effectively reduce the impedance of the lithium-ion battery cathode material during use.

[0007] The present invention also provides a method for preparing the above-mentioned lithium-ion battery cathode material.

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

[0009] According to an embodiment of a first aspect of the present invention, a lithium-ion battery cathode material is provided, the lithium-ion battery cathode material comprising a hollow shell layer, the hollow shell layer surrounding 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 coating layer, the inner layer includes a fast ion conductor layer and a layered lithium composite oxide layer.

[0010] The lithium-ion battery cathode material according to embodiments of the present invention has at least the following beneficial effects: The lithium-ion battery cathode material provided by this invention, due to its structural design, can significantly reduce its internal resistance during use and effectively suppress side reactions between the lithium-ion battery cathode material and the electrolyte. Specifically: For cathode materials with hollow structures, after the electrolyte penetrates into the internal cavity, the inner and outer surfaces of the hollow shell will directly contact the electrolyte. Although the internal resistance will be reduced due to the increase in active sites, it will inevitably accelerate the side reactions between the lithium-ion battery cathode material and the electrolyte. In the lithium-ion battery cathode material provided by this invention, a fast ion conductor layer is provided on the inner surface of the inner layer, and a coating layer is also included, which is equivalent to wrapping the core material layered lithium composite oxide layer, suppressing interfacial side reactions and enhancing structural stability. Moreover, the internal fast ion conductor layer has a high lithium-ion conductivity, so it will not hinder the transport of lithium ions and thus will not increase the interfacial impedance. Furthermore, the lithium-ion battery cathode material provided by this invention also has the common advantages of hollow materials, such as reducing internal impedance and improving cycle performance. The main working principle is that it shortens the diffusion path of lithium ions in the solid, and the internal cavity can accommodate the volume changes of the lithium-ion battery cathode material during cycling. More contact sites also make the interface reaction more uniform.

[0011] Overall, the lithium-ion battery cathode material provided by this invention exhibits a significant synergistic effect among the internal cavity structure, the fast ion conductor layer, and the coating layer.

[0012] According to some embodiments of the present invention, the coating layer comprises a fast ion conductor compound. The fast ion conductor compound is a LiM₂O type compound. Therefore, in addition to forming a physical barrier and improving cycle performance, it can further improve ionic conductivity, reduce impedance, and thus improve rate performance; simultaneously, it can work together with the fast ion conductor layer to achieve efficient lithium-ion conduction throughout the entire lithium-ion battery cathode material.

[0013] According to some embodiments of the present invention, 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. When M2 includes any one of Zr, W, La, Nb, Ti, or Ta, the coating layer contains a fast ion conductor, thereby enhancing the Li... +The diffusion rate is significantly reduced, interface impedance is decreased, and power performance is improved. When M2 includes B, the Li-BO coating layer can repair cycling microcracks and reduce direct contact between the electrolyte and the inside of the lithium-ion battery cathode material, suppressing interface side reactions and enhancing interface stability. When M2 includes Al, the coating layer has both ionic conductivity and interface passivation capability, improving 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 surface oxygen, suppress oxygen release, enhance the thermal stability of the layered lithium composite oxide, and suppress the transformation of the layered structure to the spinel or rock salt phase during high-voltage charging. When M2 includes La, La has a strong "oxygen affinity" and combines with oxygen to form a stable passivation layer, stabilizing the structure and suppressing excessive CEI growth. When M2 includes W, Li2WO4 forms a stable coating layer, resisting HF corrosion, and the high valence of W... 6+ Inducing surface passivation; when M2 includes Nb, the Nb compound can inhibit electrolyte decomposition and transition metal dissolution, and suppress interfacial side reactions. When M2 includes Ba, Ba ions have a large radius and tend to preferentially occupy the lattice surface or interstitial sites, reducing grain boundary impedance and providing a wider channel for lithium ion diffusion.

[0014] According to some embodiments of the present invention, in the coating layer, M2 is at least one of W, B, Al and Ti.

[0015] According to some embodiments of the present invention, in the coating layer, M2 is a combination of Ti and Al. The molar ratio of Ti to Al is 1 to 3:1. Specifically, it can be approximately 1:1, 1.5:1, 2:1, 2.5:1, or approximately 3:1.

[0016] According to some embodiments of the present invention, in the coating layer, M2 is a combination of W and B. The molar ratio of W to B is 4 to 8:1. Specifically, it can be approximately 4:1, 5:1, 6:1, 7:1, or approximately 8:1. According to some embodiments of the present invention, 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. Specifically, it can be approximately 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.

[0017] The combination of the above-mentioned M2 elements has the dual effect of improving both cycle performance and power performance.

[0018] According to some embodiments of the present invention, the chemical formula of the lithium-ion battery cathode material, excluding the coating layer, is Li. a Ni x Co y Mnz 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; M1 is selected from at least one of Zr, W, Mg, La, Ta, Sb, Ti, Sr, Al, and Nb. M1 is mainly enriched in the fast-ion conductor layer and may form some doping in the layered lithium composite oxide layer. Its function is as follows: the fast-ion conductor layer, including Zr, W, and La, can enhance the performance of Li... + Diffusion rate is improved, enhancing power performance; furthermore, doping with Zr, W, Mg, or Al can stabilize the lattice structure of the layered lithium composite oxide layer, suppress cation mixing, and improve cycle performance; Zr 4+ It can also occupy the metallization layer in the layered lithium composite oxide layer, stabilizing the layered structure, inhibiting cation mixing and lattice oxygen loss, suppressing oxygen evolution and phase transition, and improving cycle stability; W can form strong WO bonds, reducing the activity of lattice oxygen, inhibiting oxygen vacancy formation and oxygen loss, and reducing irreversible phase transition; it alleviates volume expansion stress during cycling, reduces microcracks, improves cycle stability, reduces interfacial side reactions, and improves rate performance; Mg² + The ionic radius of Ni² + Proximity allows it to occupy Ni sites, suppressing Li / Ni mixing and stabilizing the layered structure of the layered lithium composite oxide layer. Simultaneously, it increases the interlayer spacing, promoting Li... + Diffusion enhances the thermal stability and cycle life of the lithium-ion battery cathode material; La³ + It tends to occupy grain boundaries or surface sites, forming stable fast ion conductors and enhancing Li + Diffusion rate, inhibiting grain boundary crack propagation and transition metal dissolution; Al³ + Can replace part of Ni³ + This inhibits cation mixing. The high bond energy of the Al-O bond enhances the stability of the layered structure in the layered lithium composite oxide layer, suppressing the transformation of the layered structure to the spinel or rock salt phase during high-voltage charging. Sb can be doped into the transition metal layer without affecting the layered structure, and can expand the (003) interplanar spacing to reduce the Li diffusion barrier. Ti 4+ Sr² replaces transition metal sites, suppresses cation mixing, stabilizes oxygen layer structure, improves cycling stability and first-cycle efficiency, and enhances rate performance. + Typically, it occupies lithium sites, widens the lithium layer spacing, stabilizes the structure, promotes lithium-ion diffusion, and improves cycle stability; the high bond energy of the Nb–O bond effectively inhibits oxygen loss and cation mixing, significantly improves cycle life, enhances structural stability, and improves rate performance.

[0019] Limited Li a Ni x Co y Mn z M1 w O 2±b The range of w can broaden the migration channels of lithium ions, improve ionic conductivity, and suppress lattice distortion without reducing capacity.

[0020] According to some embodiments of the present invention, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b In this case, 0.3 ≤ x ≤ 0.7. For example, it can be approximately 0.3, 0.4, 0.5, 0.6, or approximately 0.7.

[0021] According to some embodiments of the present invention, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b In this case, 0.1 ≤ y ≤ 0.4. For example, it could be approximately 0.1, 0.2, 0.3, or approximately 0.4.

[0022] According to some embodiments of the present invention, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b In this case, 0.1 ≤ z ≤ 0.4. For example, it can be approximately 0.1, 0.2, 0.3, or approximately 0.4.

[0023] According to some embodiments of the present invention, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b In this case, 0.001 ≤ w ≤ 0.02. For example, it can be approximately 0.001, 0.003, 0.005, 0.008, 0.01, or approximately 0.02.

[0024] According to some embodiments of the present invention, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b In this context, M1 is selected from at least one of Zr, W, La, Sb, and Al.

[0025] According to some embodiments of the present invention, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b In this context, M1 is selected from a combination of Zr and W. The molar ratio of W to Zr is 1 to 4:1; for example, it can be approximately 1:1, 2:1, or approximately 4:1.

[0026] According to some embodiments of the present invention, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b In this context, M1 is selected from a combination of W and La. The molar ratio of W to La is 1 to 4:1; for example, it can be approximately 1:1, 2:1, or approximately 4:1.

[0027] According to some embodiments of the present invention, the chemical formula Li a Ni x Co y Mn z M1 w O 2±b In this context, M1 is selected from a combination of Al and W.

[0028] According to some embodiments of the present invention, the inner layer is composed of a single or double layer of primary particle arrangement. Because it is formed by a single or double layer of primary particle arrangement, the gaps between the primary particles (in areas of relatively loose packing, or formed after rearrangement and shrinkage of primary particles) are likely to penetrate the inner layer, forming through-holes; these through-holes serve as rapid channels for electrolyte permeation, allowing the electrolyte to directly penetrate into the secondary spheres of the lithium-ion battery positive electrode material, shortening the Li-ion battery's lifespan. + The diffusion distance from the electrolyte to the internal particles reduces concentration polarization, lowers impedance, significantly improves the utilization rate of active materials (such as the inner layer), enhances high-rate performance, and reduces interfacial side reactions (uniform electrolyte distribution avoids local overcharging / over-discharging). In addition, the through-holes provide stress buffer space for volume expansion, disperse stress concentration, reduce the propagation of microcracks inside the lithium-ion battery cathode material, inhibit particle pulverization and electrode structure collapse, and extend the life of secondary batteries including the lithium-ion battery cathode material.

[0029] Furthermore, compared to double-layer arrangement, single-layer arrangement can further improve the contact between electrolyte and primary particles, shorten solid-phase diffusion, and improve rate performance; at the same time, the concentrated stress generated by volume change during charging and discharging is smaller, resulting in higher structural stability.

[0030] According to some embodiments of the present invention, the number of through holes in a single lithium-ion battery cathode material is 1 to 5. For example, it can be 1, 2, 3, 4 or 5.

[0031] According to some embodiments of the present invention, the diameter of the through hole is 0.1~0.2μm.

[0032] According to some embodiments of the present invention, the average thickness of the hollow shell is 0.4~0.8 μm. For example, it can be 0.4 μm, 0.6 μm or 0.8 μm.

[0033] The diameter / number of the through holes and the thickness of the inner layer / hollow shell / internal cavity were determined by cross-sectional SEM observation.

[0034] According to some embodiments of the present invention, the hollow portion accounts for 40-50% of the cross-sectional area of ​​the lithium-ion battery cathode material.

[0035] According to some embodiments of the present invention, in the lithium-ion battery cathode material, the thickness ratio of the hollow shell layer to the internal cavity is 0.14.

[0036] In this invention, information such as the area ratio of the hollow portion and the diameter ratio of the internal cavity needs to be obtained by cutting the positive electrode material in the middle and measuring it on the SEM image.

[0037] According to some embodiments of the present invention, the lithium-ion battery cathode material further includes a core located within the internal cavity. This allows for improved tap density of the lithium-ion battery cathode material while retaining the advantages of the internal cavity; it also provides an additional internal lithium-ion transport channel, mitigating the problem of ineffective lithium-ion transport (lack of lithium insertion / extraction transport processes) caused by the internal cavity; simultaneously, the core can also provide some support, alleviating stress generated during processing or cycling.

[0038] According to some embodiments of the present invention, the core and the inner layer may be in contact or not in contact.

[0039] According to some embodiments of the present invention, the surface of the core is enriched with a fast ion conductor material. The fast ion conductor material and the fast ion conductor layer are made of the same material.

[0040] According to some embodiments of the present invention, 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.

[0041] According to some embodiments of the present invention, the particle size distribution Span ((D90-D10) / D50) of the lithium-ion battery cathode material is 0.8 to 1.3. For example, it can be about 0.9, 1.0, 1.1 or about 1.2.

[0042] According to some embodiments of the present invention, the specific surface area of ​​the lithium-ion battery cathode material is ≥1.8 m². 2 / g. For example, it could be approximately 2.0m. 2 / g, 2.5m 2 / g, 3.0m 2 / g or approximately 3.5m 2 / g.

[0043] According to some embodiments of the present invention, the oil absorption capacity of the lithium-ion battery cathode material is 30 mL / 100g to 70 mL / 100g. Specifically, it can be approximately 40 mL / 100g, 50 mL / 100g, 52 mL / 100g, 55 mL / 100g, 60 mL / 100g, or 65 mL / 100g, or a range of any two of the above values.

[0044] According to an embodiment of a second aspect of the present invention, a method for preparing the lithium-ion battery cathode material described in the first aspect of the present invention is provided, the method comprising 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.

[0045] Since the preparation method employs all the technical solutions of the lithium-ion battery cathode materials described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Specifically: The outer layer is a dense layer and preferentially interacts with Li. +Upon contact and reaction, a layered lithium composite oxide layer is formed. The middle layer is more porous, with smaller primary particle size and higher surface energy. During the sintering process in step S2, it moves and diffuses inward and outward to form the internal cavity; it migrates outward to form the fast ion conductor layer, and migrates inward to form the fast ion conductor material covering the core. Since the fast ion conductor layer is formed by the diffusion of the middle layer inward and outward, there is no very clear boundary between it and the layered lithium composite oxide layer; and M1 may also be partially doped into the layered lithium composite oxide layer in addition to forming the fast ion conductor layer.

[0046] Furthermore, in step S2, the temperature of the first heat preservation platform ensures the melting / decomposition of the lithium salt, promoting lithium penetration into the crystal lattice and lattice transformation. The temperature of the second heat preservation platform, on the one hand, avoids excessively low temperatures affecting the crystallinity of the resulting lithium-ion battery cathode material, preventing the formation of amorphous materials and ensuring the formation of internal cavities; on the other hand, it also avoids excessively large primary particle fusion growth due to excessively high temperatures, which could lead to structural collapse, thus also ensuring the formation of internal cavities. In addition, the higher the temperature, the higher the degree of crystallinity. After meeting the basic crystallinity requirements, as the degree of crystallinity increases, the number of active sites decreases, the lithium-ion transport speed decreases, and the impedance increases. The temperature of the second heat preservation platform provided by this invention precisely meets the basic crystallinity requirements and avoids over-crystallization.

[0047] According to some embodiments of the present invention, 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, and 0.4≤a≤0.6. Furthermore, the ranges of values ​​for 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 The range and selection are as follows. The specific value of 'a' is selected from 0.4, 0.45, 0.5, 0.55, 0.6; or a range of values ​​consisting of any two of the above points.

[0048] According to some embodiments of the present invention, in step S1, the core is formed by a primary accumulation of sheet-like or plate-like particles.

[0049] According to some embodiments of the present invention, in step S1, the outer layer has a radially arranged structure. Thus, during the calcination process in step S2, a single-layer or multi-layer inner layer structure with a primary particle arrangement can be formed.

[0050] According to some embodiments of the present invention, in step S1, the preparation process of the precursor includes the following steps: S1a. A mixed metal salt solution, an alkaline solution, and an ammonia solution are mixed in parallel flow to carry out a first coprecipitation reaction to obtain the core; the pH range of the first coprecipitation reaction is 10.00~12.50; S1b. Adjust and maintain the pH of the system obtained in step S1a to 7.00~8.60; and introduce the mixed metal salt solution, carbonate solution and M1-containing solution into it in parallel, and the second co-precipitation reaction yields the intermediate layer; S1c. Filter to obtain the solid material obtained in step S1b; re-pulp, adjust and maintain the pH of the obtained slurry at 9.00~11.00; and introduce the mixed metal salt solution, alkali solution and ammonia solution into it in parallel, and perform a third co-precipitation reaction to obtain the outer layer.

[0051] According to the synthesis method of the precursor, by adjusting the pH of different steps and the type of precipitant, the outer layer can form a relatively dense large particle structure, while the primary particles of the middle layer are smaller in size, more loose, and have high porosity.

[0052] According to some embodiments of the present invention, in step S1a, the co-current mixing is to introduce the mixed metal salt solution, alkaline solution and ammonia solution into the bottom liquid in a co-current manner.

[0053] According to some embodiments of the present invention, the base liquid 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.

[0054] According to some embodiments of the present invention, the pH of the base solution is 10 to 12; specifically, it may be about 10, 11 or about 12.

[0055] According to some embodiments of the present invention, in step S1a, the mixed metal salt solution includes nickel ions.

[0056] According to some embodiments of the present invention, in step S1a, the mixed metal salt solution further includes at least one of cobalt ions and manganese ions.

[0057] The types and proportions of ions in the mixed metal salt solution can be determined based on the transition metals in the lithium-ion battery cathode material 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 can be mixed in any proportion.

[0058] According to some embodiments of the present invention, in step S1a, the total concentration of transition metal ions in the mixed metal salt solution is 1.5~2.2 mol / L. Specifically, it can be approximately 1.5 mol / L or 2.0 mol / L.

[0059] According to some embodiments of the present invention, in step S1a, the solute of the alkaline solution includes at least one of sodium hydroxide and potassium hydroxide.

[0060] According to some embodiments of the present invention, in step S1a, the concentration of the alkaline 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, or 10 mol / L.

[0061] According to some embodiments of the present invention, in step S1a, the concentration of the ammonia solution is 4-6 mol / L. Specifically, it can be about 4 mol / L, 4.5 mol / L, 5 mol / L, 6.5 mol / L, or about 6 mol / L.

[0062] According to some embodiments of the present invention, 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.

[0063] According to some embodiments of the present invention, in step S1a, the first coprecipitation reaction is carried out under stirring. The linear velocity of the stirring impeller is 4~9 m / s. Specifically, it can be approximately 4 m / s, 4.5 m / s, 5 m / s, 5.5 m / s, 6 m / s, 7 m / s, 8 m / s, or 9 m / s.

[0064] According to some embodiments of the present invention, 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.

[0065] According to some embodiments of the present invention, in step S1a, the pH of the first coprecipitation process is 10 to 12; for example, it can be about 10, 11 or about 12.

[0066] According to some embodiments of the present invention, in step S1a, the ammonia concentration during the first co-precipitation process is 3~10 g / L. Specifically, it can be approximately 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.

[0067] According to some embodiments of the present invention, in step S1a, the kernel accounts for 10-20% of the particle size of the precursor. For example, it can be about 10%, 12%, 14%, 15%, 16%, 18%, or about 20%.

[0068] Unless otherwise specified, the particle size percentage in this invention refers to the proportion of D50.

[0069] According to some embodiments of the present invention, in step S1b, the reagent used to adjust the pH includes dilute sulfuric acid. The concentration of the dilute sulfuric acid is 1~6 mol / L; more specifically, it can be 2 mol / L or 4 mol / L.

[0070] According to some embodiments of the present invention, in step S1b, the pH is 7.5 to 8.5; for example, it can be about 7.5, 7.6, 7.8, 8.0, 8.2 or about 8.5.

[0071] According to some embodiments of the present invention, in step S1b, the solute of the carbonate solution includes at least one of sodium carbonate and potassium carbonate.

[0072] According to some embodiments of the present invention, 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.

[0073] According to some embodiments of the present invention, in step S1b, the molar ratio of carbonate ions and metal ions (including those in mixed metal salt solutions and solutions containing M1) introduced per unit time is 1 to 1.12:1; for example, it can be about 1:1, 1.1:1, or about 1.12:1.

[0074] According to some embodiments of the present invention, in step S1b, the particle size percentage of the obtained product and the precursor is 70-80%. Specifically, 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. Specifically, it can be about 1 μm, 1.5 μm, 2.0 μm, or about 2.5 μm.

[0075] According to some embodiments of the present invention, in step S1c, the liquid used for pulping includes water, the ammonia solution, and the alkali solution.

[0076] According to some embodiments of the present invention, 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.

[0077] According to some embodiments of the present invention, in step S1c, the pH of the slurry is 9.5 to 10.5. For example, it can be about 9.5, 10, or about 10.5.

[0078] According to some embodiments of the present invention, in step S1c, the oxygen concentration in the atmosphere of the third coprecipitation reaction is <5%.

[0079] According to some embodiments of the present invention, 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.

[0080] According to some embodiments of the present invention, the method for preparing the precursor further includes solid-liquid separation, aging, washing and drying steps after step S1c.

[0081] According to some embodiments of the present invention, in step S1, the precursor D50 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.

[0082] Since the precursor morphology affects the morphology of the lithium-ion battery cathode material, and the coating layer is relatively thin, it has little impact on the particle size. Therefore, the particle size (particle size distribution) of the precursor is basically the same as the particle size of the final lithium-ion battery cathode material.

[0083] According to some embodiments of the present invention, in step S2, the molar ratio of lithium in the precursor and the lithium salt is 1:1.05 to 1.2. For example, it can be about 1:1.05, 1:1.1, 1:1.15 or about 1:1.2.

[0084] According to some embodiments of the present invention, the temperature of the first insulation platform is 480~600°C. For example, it can be about 500°C, 520°C, 550°C, 580°C or about 600°C.

[0085] According to some embodiments of the present invention, in step S2, the insulation time of the first insulation platform is 2 to 6 hours. For example, it can be about 2 hours, 3 hours, 4 hours, 5 hours, or about 6 hours.

[0086] According to some embodiments of the present invention, the temperature of the second insulation platform is 800~920°C. For example, it can be approximately 800°C, 820°C, 850°C, 880°C, 900°C, or approximately 920°C.

[0087] According to some embodiments of the present invention, in step S2, the insulation time of the second insulation platform is 8 to 16 hours. For example, it can be about 8 hours, 10 hours, 12 hours, 14 hours, or about 16 hours.

[0088] According to some embodiments of the present invention, 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.

[0089] According to some embodiments of the present invention, in step S3, M2 accounts for 6000~20000 ppm of the product obtained in step S2. Within this range, the coating layer does not block the lithium-ion transport channels and can provide good physical isolation.

[0090] According to some embodiments of the present invention, in step S3, M2 accounts for 0.6~2 mol% of the molar percentage of (Ni+Co+Mn+M1+M2) in the lithium-ion battery cathode material. For example, it can be about 0.6%, 0.8%, 1.0%, 1.5% or about 2%.

[0091] According to some embodiments of the present invention, in step S3, the temperature of the mixed secondary sintering is 300~600°C. Specifically, it can be about 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, or about 600°C. Within this temperature range, the reaction of the mixed secondary sintering can be ensured to be complete, and the reduction of coating uniformity and conductivity due to excessive sintering can be avoided. Thus, side reactions of unreacted raw materials and electrolytes are avoided, as is the increase in interfacial impedance, ultimately significantly improving the gain effect of the coating layer on cycle performance and rate performance.

[0092] According to some embodiments of the present invention, in step S3, the duration of the mixed calcination is 4 to 10 hours. For example, it can be approximately 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or approximately 10 hours.

[0093] According to an embodiment of a third aspect of the present invention, a lithium-ion secondary battery is provided, wherein the raw materials for preparing the lithium-ion secondary battery include the lithium-ion battery cathode material described in the first aspect of the present invention, or the lithium-ion battery cathode material prepared by the preparation method described in the second aspect of the present invention.

[0094] Since the lithium-ion secondary battery adopts all the technical solutions of the lithium-ion battery cathode material or preparation method of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0095] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0096] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0097] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a cross-sectional SEM image of the lithium-ion battery cathode material obtained in Example 1 of the present invention.

[0098] Figure 2 This is a SEM image of the lithium-ion battery cathode material obtained in Example 1 of the present invention.

[0099] Figure 3 This is a SEM image of the lithium-ion battery cathode material obtained in Comparative Example 2 of this invention.

[0100] Figure 4 This is a SEM image of the lithium-ion battery cathode material obtained in Comparative Example 3 of this invention.

[0101] Figure 5 This is a cross-sectional mapping pattern of the lithium-ion battery cathode material obtained in Example 6 of the present invention. Detailed Implementation

[0102] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0103] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0104] Example 1 This example demonstrates the preparation of a lithium-ion battery cathode material, with the following specific steps: S1. Preparation of precursors: S1a. A mixed metal salt solution of nickel, cobalt, and manganese (molar ratio of nickel, cobalt, and manganese is 5:2:3, 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 introduced into a base solution with an ammonia concentration of 8 g / L and a pH of 11.0 at a flow rate of 100 mL / min (this is only for the reaction volume in this example; it can be adjusted in actual production). The reaction temperature is 60℃, the stirring speed is 5 m / s (linear velocity, corresponding to a blade speed of 50 Hz), and 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 adjustment system (controlled by the flow rate of the sodium hydroxide aqueous solution); the ammonia concentration is 8 g / L (controlled by the flow rate of the ammonia aqueous solution), forming a dense core composed of primary particles with a plate-like or flaky morphology, allowing the precursor to grow to D50 = 0.5 μm. S1b. Introduce 2 mol / L dilute sulfuric acid to lower the pH of the system obtained in step S1a to 7.8. Introduce a mixed metal salt solution of nickel, cobalt, and manganese (same as step S1a), a sodium tungstate solution (6 g / L), and a sodium carbonate solution (approximately 1.8 mol / L) into the bottom liquid of the reactor at a flow rate of 180 mL / min (only for the reaction volume in this example). Control the molar ratio of transition metal ions (including W) to carbonate ions introduced per unit time to be 1:1.1. Allow the material to grow to a D50 of approximately 2.5 μm, forming an intermediate layer composed of fine particulate W-doped carbonate precursors, wherein the molar percentage of W element in step S1 (Ni+Co+Mn+M1) is 0.3 mol% (controlling the flow rate ratio of the mixed metal salt solution and the sodium tungstate solution).

[0105] S1c. After filtering the reaction slurry obtained in step S1b, seed crystals (solid product) are obtained. The above seed crystals are added to the reactor, along with pure water, ammonia, and NaOH. The ammonia concentration is 10 g / L. The pH of the slurry is adjusted to 10 (this pH and ammonia concentration are maintained during subsequent co-precipitation). A mixed metal salt solution of nickel, cobalt, and manganese with the same composition and flow rate as in step S1a, an alkaline solution, and an ammonia solution are introduced. The stirring speed is 5 m / s, and nitrogen gas is introduced to make the oxygen concentration <5%. The material grows to a D50 of about 3.2 μm, forming a plate-like hydroxide precursor that constitutes a radially arranged outer layer.

[0106] The reaction slurry was filtered, aged, washed, and dried to obtain the precursor, which had a D50 particle size of approximately 3.2 μm.

[0107] S2. The precursor synthesized in step S1 and LiOH are uniformly mixed at a lithium metal ratio of 1.12. Under oxygen, the mixture is heated to 500°C and held for 4 hours, and then sintered at 850°C for 12 hours to obtain the intermediate product.

[0108] S3. Mix the above intermediate product with Al2O3 and TiO2 (M2 is Al and Ti), where Al:Ti = 1:1. The total molar amount of the coating element M2 accounts for 2 mol% of the molar percentage of the obtained cathode material elements (Ni+Co+Mn+M1+M2). Sinter at 450℃ for 6 h, cool and sieve to obtain the lithium-ion battery cathode material.

[0109] The lithium-ion battery cathode material obtained in this example has a hollow shell and an internal cavity formed by the hollow shell. The hollow shell consists of an inner layer and a covering layer on the outer surface of the inner layer; Along the direction from the inner layer to the coating layer, the inner layer includes a fast ion conductor layer and a layered lithium composite oxide layer stacked together; The core exists within the internal cavity. The core has a certain probability of being free within the internal cavity and also has a certain probability of being connected to the fast ion conductor layer. The outer surface of the core also has an enriched fast ion conductor layer.

[0110] The fast ion conductor layer contains lithium tungstate.

[0111] Based on the feed ratio, the chemical formula of the lithium-ion battery cathode 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 2.085 The outer shell comprises lithium zirconate and lithium antimony oxide; the remaining parts have the chemical formula Li. 1.1 (Ni)0.5 Co 0.2 Mn 0.3 ) 0.997 M1 0.003 O 2.05 .

[0112] Example 2 This example prepares a lithium-ion battery cathode material, which differs from Example 1 in that: 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.

[0113] Example 3 This example prepares a lithium-ion battery cathode material, which differs from Example 1 in that: 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.

[0114] Example 4 This example prepares a lithium-ion battery cathode material, which differs from Example 1 in that: In step S1b, the sodium tungstate solution is replaced with a mixed solution of lanthanum sulfate and sodium tungstate of equal concentration and flow rate, wherein the molar ratio of W to La is 1:1.

[0115] Example 5 This example prepares a lithium-ion battery cathode material, which differs from Example 1 in that: In step S1b, the sodium tungstate solution is replaced with a mixed solution of zirconium sulfate and sodium tungstate of equal concentration and flow rate, wherein the molar ratio of W to Zr is 1:1.

[0116] Example 6 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S3, the coating reagent is a combination of tungsten oxide and boric acid, where W:B = 6:1 (molar ratio).

[0117] Example 7 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S3, the coating reagent is a combination of alumina, tungsten oxide and boric acid, wherein Al:W:B = 1:3:0.5 (molar ratio).

[0118] Example 8 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S2, the temperature of the second insulation platform is 800℃.

[0119] Example 9 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S2, the temperature of the second insulation platform is 910℃.

[0120] Example 10 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S1b, the molar percentage of element M1 in step S1 (Ni+Co+Mn+M1) is 3 mol.

[0121] Example 11 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: The steps in step S1c are as follows: After filtering the reaction slurry obtained in step S1b, seed crystals (solid product) are obtained. The seed crystals are added to the reactor, along with pure water, ammonia, and NaOH. The ammonia concentration is 12 g / L. The pH of the slurry is adjusted to 10 (this pH and ammonia concentration are maintained during subsequent co-precipitation). A mixed metal salt solution of nickel, cobalt, and manganese with the same composition as in step S1a (flow rate 150 mL / min), an alkaline solution, and an ammonia solution are introduced. The stirring speed is 4 m / s, and nitrogen gas is introduced to make the oxygen concentration <5%. The material grows to a D50 of about 3.2 μm, forming a short-plate-shaped hydroxide precursor with no dominant orientation among the primary particles.

[0122] The reaction slurry was filtered, aged, washed, and dried to obtain the precursor, which had a D50 particle size of approximately 3.2 μm.

[0123] Comparative Example 1 This example prepares a lithium-ion battery cathode material, which differs from Example 1 in that: In step S1b, sodium tungstate solution is not introduced.

[0124] Comparative Example 2 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S2, the temperature of the second insulation platform is 950℃.

[0125] Comparative Example 3 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S2, the temperature of the second insulation platform is 780℃.

[0126] Comparative Example 4 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S1b, the pH is not adjusted, and the pH of the system is maintained at 11.

[0127] Comparative Example 5 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: Step S3 is not included.

[0128] Comparative Example 6 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: In step S1b, no compound solution of M1 is added; In step S2, the same amount of M1 as in Example 4 is added.

[0129] Comparative Example 7 This example prepares a lithium-ion battery cathode material, which differs from Example 4 in that: Step S1a is excluded; the reaction time of step S1b is maintained, and the reaction time in step S1c is extended to obtain a precursor with D50 equivalent to that of Example 4.

[0130] Application examples This example provides a lithium secondary battery, as detailed below.

[0131] The above-prepared positive electrode material, conductive agent SuperP, and binder polyvinylidene fluoride (PVDF) were mixed with N-methylpyrrolidone (NMP) at a mass ratio of 90:5:5 and stirred evenly to form a positive electrode slurry (solid content approximately 40%). This slurry was coated onto current collector aluminum foil, dried at 105°C, and then rolled at room temperature until the areal density reached 2.7~3.0 g / cm³. 3 Then, the material is punched and cut into φ14mm round sheets to form the positive electrode sheet; wherein the positive electrode material is from the examples or comparative examples.

[0132] Assemble the button cells inside the glove box: Following the sequence of "negative electrode shell - nickel foam - lithium sheet (φ18mm) - 8 drops of electrolyte - separator (φ22mm, 16μm thick) - 8 drops of electrolyte - positive electrode sheet - positive electrode shell," the electrolyte is composed of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (EC:EMC:DMC volume ratio = 1:1:1), containing 1.0M LiPF6; the battery casing (positive and negative electrode shells) is 24mm in size. Place the assembled button cells in the mold cavity of a hydraulic sealing machine (purchased from Shenzhen Kejing Zhida Technology Co., Ltd.), lock them, and apply pressure >450kg / cm². 2 Then unlock it and take out the sealed button cell battery, which is the lithium secondary battery obtained in this example.

[0133] Test case The first aspect of this example tested the BET, morphology (and mapping pattern), particle size distribution, and oil absorption value of the lithium-ion battery cathode materials obtained in the examples and comparative examples. The test results of BET and oil absorption value are shown in Table 1. Specifically, the oil absorption amount was tested using a HITEC DABS oil absorption tester. Paraffin oil was added dropwise at a uniform rate during the stirring process of the lithium-ion battery cathode material, and the oil absorption amount was calculated based on the torque value. The morphology was tested using a scanning electron microscope (SEM), specifically testing the overall morphology and cross-sectional morphology. The particle size was measured using a laser particle size analyzer. Combining morphology and particle size tests, it can be seen that the particle size of the obtained lithium-ion battery cathode material is between 2 and 10 μm, with most of it between 2 and 4 μm. The particle size distribution of the lithium-ion battery cathode material obtained in Example 1 is approximately 1.1 ((D90-D10) / D50). The obtained lithium-ion battery cathode material includes a core and a hollow shell layer. The core and the hollow shell layer may or may not be in contact. The hollow shell layer has through holes, and the number of through holes is about two when viewed in a single cross-section. The average thickness of the hollow shell layer is about 0.4 μm, formed by the orderly radial arrangement of primary particles, specifically forming one or two layers. Based on a cross-section from the center, the thickness ratio of the hollow shell layer to the internal cavity is about 0.14, and the hollow portion accounts for about 45% of the area. From the mapping test results, it can be seen that in the cathode material obtained in Example 6, W is coated on the surface of the core and enriched in the fast ion conductor layer and the coating layer. Therefore, it can be seen that the preparation method provided by the present invention does indeed produce a cathode material with the target structure. The morphology of the lithium-ion battery cathode material obtained in Example 1 is as follows: Figures 1-2 As shown, the mapping test results of the cathode material obtained in Example 6 are as follows: Figure 5 As shown, Figure 5 The green dots represent the distribution of W element; the morphology of the lithium-ion battery cathode materials obtained in Comparative Examples 2 and 3 is as follows: Figures 3-4 As shown, the apparent morphology of the lithium-ion battery cathode materials obtained in other embodiments is similar to that of Examples 1 and 6, all possessing a hollow shell and a coating layer. The hollow shell 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 essentially the same, therefore, it cannot migrate inward or outward to form an internal cavity during subsequent calcination. In Comparative Example 6, although an internal cavity is formed, the product does not possess an inner fast ion conductor layer because M1 is not added in step S1b. In Comparative Example 7, since step S1a is not included, the internal structure is also different from that of the lithium-ion battery cathode materials obtained in the embodiments.

[0134] 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%.

[0135] 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℃.

[0136] 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℃.

[0137] The test results are shown in Table 1.

[0138] Table 1. Performance of lithium-ion battery cathode materials obtained in the examples and comparative examples.

[0139] Comparing the results of Examples 1-3, it can be seen that the lithium-ion battery cathode material and its preparation method provided by the present invention are suitable for modifying ternary cathode materials with low nickel content, medium nickel content and high nickel content, and can all achieve relatively excellent electrochemical performance.

[0140] Comparing the results of Examples 1 and 4-5, it can be seen that switching different raw materials can achieve beneficial electrochemical performance, and depending on the selection of M1, there are advantages in terms of cycle retention rate, pre-cycle impedance, and rate capability.

[0141] Comparing the results of Examples 4, 6-7, and Comparative Example 5, it can be seen that using different coating layers significantly improves the capacity retention and rate capability of the resulting lithium-ion battery cathode material. Most importantly, the rate of impedance increase during use is significantly reduced. Furthermore, when M2 is a mixture of Al, W, and B, the resulting lithium-ion battery cathode material exhibits superior cycle performance and lower impedance after cycling. This indicates that, within the experimental range of the examples, coating layers including this combination possess superior inert barrier properties and better lithium-ion conductivity, and it is expected that they will exhibit excellent long-cycle performance under high-rate conditions.

[0142] Comparing the results of Examples 1, 8-9, and 2-3, it can be seen that as the temperature of the second insulation platform increases, the impedance first decreases and then increases.

[0143] Comparing the results of Examples 4, 10-11 and Comparative Example 1, it can be seen that when M1 is not doped, the performance of the obtained cathode material is significantly degraded. As the doping amount of M1 increases, the overall performance of the obtained cathode material shows a trend of first increasing and then decreasing.

[0144] Comparing the results of Example 4, Comparative Example 4, and Comparative Examples 6-7, it can be seen that if the obtained lithium-ion battery cathode material does not have the specific structure required by the present invention, the overall performance of the material will decrease.

[0145] In summary, the lithium-ion battery cathode material provided by this invention, due to its special structural and compositional design, exhibits excellent cycle performance, low impedance, and superior rate performance. Because of these superior properties, this lithium-ion battery cathode material, or lithium-ion secondary batteries incorporating this cathode material, is expected to find wide application in the fields of power batteries, energy storage technology, and communication electronics.

[0146] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

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 coating layer, the inner layer includes a fast ion conductor layer and a layered lithium composite oxide layer.

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

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 chemical formula of the precursor is 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, and x+y+z+w=1.

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 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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