A method for preparing a low-strain stable concentration gradient cathode material

Abstract

The application provides a preparation method of a low-strain stable concentration gradient positive electrode material, and belongs to the technical field of high-performance lithium ion battery materials, and comprises the following steps: (a) solution preparation: preparing a nickel salt aqueous solution, a cobalt salt aqueous solution, a mixed solution a containing a cobalt salt and boron elements, a precipitant aqueous solution b and a complexing agent aqueous solution c; (b) precursor preparation: continuously pumping the mixed solution a containing the cobalt salt and the boron elements into the nickel salt aqueous solution, uniformly mixing and pumping into a reaction kettle, simultaneously adjusting the flow rates of the precipitant aqueous solution b and the complexing agent c, and obtaining a precursor [Ni 0.9‑x Co 0.1 B x ](OH)2 after reaction aging; (c) high-temperature solid-phase calcination: uniformly mixing the obtained precursor with a lithium source, an Al source and a Mn source, sintering, then cooling, crushing, sieving and obtaining the positive electrode material. The concentration gradient positive electrode material prepared by the method can better exert the energy density and cycle stability of a high-Ni positive electrode, and has a large application prospect.

Description

Technical Field

[0001] This invention belongs to the field of high-performance lithium-ion battery materials technology, specifically relating to a method for preparing a nickel-rich layer oxygen concentration gradient cathode material with a low-strain stable structure. Background Technology

[0002] The performance of lithium-ion batteries for electric vehicles largely depends on the cathode material. Nickel-rich layered oxide cathode materials, as one of the most promising cathode materials, have attracted much attention due to their higher energy density. However, the inherent structural instability and parasitic interfacial reactions of cathode materials with high Ni content lead to rapid capacity decay. To overcome these scientific problems, nickel-rich cathode materials must exhibit excellent mechanical stability, meaning they should not exhibit severe microcracks even under high-charge conditions.

[0003] Related studies have shown that concentration gradient cathodes can effectively mitigate the stress accumulation caused by internal anisotropy during deep charging, thereby suppressing the formation of severe microcracks during cycling. Simultaneously, the stable manganese-rich surface structure can effectively alleviate surface parasitic reactions to some extent. However, with further increases in energy density and the expansion of the core (nickel-rich) portion, stress accumulation also increases, and the generation and propagation of microcracks become more pronounced. Furthermore, the manganese-rich surface of the concentration gradient cathode still retains some Ni. 4+ Exposed to electrolytes, materials are prone to parasitic reactions, and repeated charging and discharging processes can lead to material degradation and performance decline. Summary of the Invention

[0004] This invention proposes a method for preparing a concentration gradient cathode material with a low-strain stable structure. Specifically, a solution containing cobalt salt and boron salt is gradually pumped into a nickel salt solution, while controlling the nickel content added to the reactor to gradually decrease and the cobalt and boron contents to gradually increase, thereby preparing a concentration gradient precursor [Ni 0.9-x Co 0.1 B x [OH]2 (0.01≤x≤0.1). The precursor, lithium source, Al, and Mn were then subjected to a high-temperature solid-state reaction to obtain a concentration gradient cathode material with a low-strain stable structure. Boron, as a bulk dopant, can reduce the volumetric strain within the particles, enhancing structural integrity and mechanical properties; manganese, as a surface modifier, modifies the surface microstructure, thereby suppressing parasitic reactions at the surface and interface. Therefore, this synergistic modification strategy can improve the stability of the material's internal structure and surface, significantly increasing its cycle life.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a concentration gradient cathode material with a low-strain stable structure, the method comprising the following steps:

[0007] (a) Solution preparation: Prepare aqueous solutions of nickel salt, cobalt salt, a mixed solution containing cobalt salt and boron, b precipitant, and c complexing agent.

[0008] (b) Precursor preparation: The precipitant aqueous solution b and complexing agent aqueous solution c prepared in step (a) are added to a continuously stirred liquid phase reactor as the initial reaction base liquid, and the pH value is controlled between 10 and 13.

[0009] After the reaction begins, a mixed solution (a) containing cobalt salt and boron is continuously pumped into an aqueous nickel salt solution and mixed thoroughly. This mixture is then pumped into the reactor at a controlled flow rate. Simultaneously, the flow rates of the precipitant solution (b) and the complexing agent (c) are adjusted to control the pH and complexing agent concentration within the aforementioned ranges. The purpose of this step is to adjust the composition of the transition metals to obtain a precursor with a concentration gradient.

[0010] When the particle size of the precursor increases to 10-12 μm, heating is stopped, and after aging for 10-15 h, the product is sequentially washed with water, filtered, and dried to obtain the precursor [Ni] for spherical lithium-ion battery gradient cathode materials. 0.9-x Co 0.1 B x ](OH)2.

[0011] (c) High-temperature solid-state calcination: In order to obtain the concentration gradient cathode material, the precursor of the lithium-ion battery gradient cathode material is mixed uniformly with lithium source, Al source and Mn source, and then the mixture is sintered in a tube furnace in an oxygen atmosphere. After that, the product is cooled, crushed and sieved to obtain the lithium-ion battery concentration gradient cathode material with low strain stable structure.

[0012] Preferably, in step (a), the nickel salt is selected from nickel sulfate, nickel chloride, and nickel nitrate, and the cobalt salt is selected from cobalt sulfate, cobalt chloride, and cobalt nitrate.

[0013] Preferably, the precipitant is selected from at least one of ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and lithium carbonate, with sodium hydroxide being the most preferred.

[0014] Preferably, the complexing agent is selected from at least one of ammonia, EDTA, ammonium nitrate, ammonium sulfate, ammonium chloride, and ammonium acetate, with ammonia being the most preferred.

[0015] Preferably, in step (a), the concentration of the nickel salt aqueous solution is 0.5-2 mol / L, used to prepare the precursor core; the concentration of the cobalt salt aqueous solution is 0.5-2 mol / L, used as the initial cobalt source; the concentration of the boron-containing aqueous solution is 0.5-2 mol / L, used as the initial dopant source; the cobalt salt aqueous solution and the boron-containing aqueous solution are mixed evenly to obtain mixed solution a; the concentration of the precipitant aqueous solution b is 0.01 mol / L to 5 mol / L, and the concentration of the complexing agent aqueous solution c is 0.02 mol / L to 15 mol / L.

[0016] Preferably, in step (b), the solution is first deoxygenated using a protective gas before the coprecipitation reaction, and the precipitation reactor is filled with a protective gas selected from at least one of nitrogen, helium, or argon.

[0017] Preferably, the concentration of the complexing agent in the reactor is maintained at 0.4-0.8 mol / L, the flow rate of the nickel salt solution is 0.8-1.0 L / h, and the flow rate of the mixed solution of cobalt and boron salts is 0.2-0.5 L / h.

[0018] Preferably, the co-precipitation time is 10-20 h and the reaction temperature is 50-60 °C.

[0019] Preferably, in step (c), the lithium source is selected from at least one of LiOH·H2O, LiNO3, and Li2CO3; the Al source is selected from at least one of NaAlO2, Al(OH)3·3H2O, and Al(NO3)3·9H2O; and the manganese source is selected from at least one of MnO, MnO2, Mn2O3, Mn3O4, and MnCO3.

[0020] Preferably, the high-temperature solid-state sintering process is as follows: in an oxygen atmosphere, the temperature is first raised to 450℃~600℃ and held for 3~8h, and then the temperature is further raised to 700℃~800℃ and sintered for 8~15h.

[0021] This invention also provides a concentration gradient cathode material with the chemical formula LiNi prepared by the method. x Co y Al 1-x-y-z B z O2, where 0.8≤x≤1, 0.05≤y≤0.1, 0.01≤z≤0.02.

[0022] The present invention also provides the application of the concentration gradient cathode material with the low strain stable structure described above in lithium-ion batteries.

[0023] In this invention, boron is added as a bulk dopant during precursor preparation. Al is added as a surface dopant during the high-temperature solid-state reaction. The reason is as follows: during the preparation of the concentration gradient precursor, both the pH value and ammonia concentration change slightly with the cation concentration. These parameters are not constant; the purpose is to ensure that the elements in the concentration gradient reach thermodynamic equilibrium, thereby ensuring better electrochemical performance of the cathode material. However, Al has a high Kk content. SP K with Ni and Co SP Even slight variations in pH value can cause Al to nucleate itself or become unevenly doped into the bulk phase, affecting its electrochemical performance. Therefore, Al needs to be added during solid-state sintering.

[0024] Furthermore, the Mn element used in this invention also serves as a surface modifier, so it needs to be added during the high-temperature solid-state process. This allows for the effective formation of a passivation layer on the surface of the gradient cathode material, protecting it from parasitic reactions.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] As the energy density of cathode materials further increases, the core (nickel-rich) portion expands, leading to increased stress accumulation. This means that the volumetric strain (ΔV / V) of the lattice changes drastically during charge and discharge, and the generation and propagation of microcracks become increasingly pronounced with each cycle. Furthermore, even in concentration gradient cathodes with manganese-rich surfaces, some Ni remains. 4+ Exposed to the electrolyte, the material is prone to parasitic reactions, and repeated charge and discharge processes can lead to material degradation and performance decline (see Comparative Examples 1 and 2).

[0027] (1) The low strain stable structure of the concentration gradient cathode material prepared by the present invention is to refine the primary particles of the concentration gradient cathode material by bulk doping with element B, so as to reduce the inherent instability of Ni-rich cathode, thereby further reducing the accumulation of strain energy and avoiding the formation and propagation of internal microcracks to a certain extent.

[0028] (2) The low-strain stable concentration gradient cathode material prepared by this invention uses surface doping elements Al and Mn to modify the surface interface of the gradient cathode material, forming a thin passivation layer on the surface to resist electrolyte corrosion, effectively solving the parasitic reactions at the surface interface of existing high-nickel layer oxygen gradient cathode materials during cycling. In particular, the abundance and low cost of these doping elements, along with their excellent stability, make them a surface dopant with great industrial application prospects.

[0029] Therefore, the concentration gradient cathode material prepared by this invention can better leverage the energy density and cycle stability of high-Ni cathodes, making it a high-energy-density cathode material with great application prospects. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 The image shown is a scanning electron microscope (SEM) image of an example.

[0032] Figure 2 The cyclic voltammetry (CV) curves for the second cycle of the example and comparative example 1 are shown below.

[0033] Figure 3 The CV curves for the 50th and 100th laps of the example are shown.

[0034] Figure 4 The CV curves for the 50th and 100th laps of Comparative Example 1 are shown.

[0035] Figure 5 The following are charge / discharge rate curves for different embodiments;

[0036] Figure 6 This is a graph showing the charge / discharge rate curves for Comparative Example 1.

[0037] Figure 7 This is a graph showing the charge / discharge rate curves for Comparative Example 3. Detailed Implementation

[0038] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0039] Example

[0040] (a) Solution preparation: Dissolve NiSO4·6H2O in deionized water to prepare a nickel salt aqueous solution with a concentration of 2 mol / L; dissolve CoSO4·7H2O and B2O3 in deionized water and prepare a mixed solution a with a concentration of 2 mol / L by molar ratio Co:B = 10:1.

[0041] Prepare a 4.0 mol / L ammonia solution as a complexing agent and a 2 mol / L sodium hydroxide solution as a precipitant. Dilute the ammonia solution to 0.4 mol / L to prepare the complexing agent solution c; dilute the sodium hydroxide solution to 1 mol / L to prepare the precipitant solution b.

[0042] (b) Precursor preparation: The prepared aqueous solutions of precipitant b and complexing agent c are added to a continuously stirred liquid-phase reactor as the initial reaction base liquid, and the pH value is controlled between 11 and 12. The concentration of complexing agent in the reactor is maintained at 0.4-0.8 mol / L.

[0043] After the reaction begins, a mixed solution a containing cobalt salt and boron is continuously pumped into an aqueous nickel salt solution at a flow rate of 0.3 L / h to ensure homogeneity. The resulting nickel salt solution is then pumped into the reactor at a flow rate of 0.8 L / h, while simultaneously adjusting the flow rate of the precipitant aqueous solution b to maintain the pH between 11 and 12. The flow rate of the complexing agent aqueous solution c is controlled to maintain the concentration of the complexing agent within the aforementioned range in the reactor. By adjusting the composition of the transition metals, a precursor with a concentration gradient is obtained. The reaction temperature is controlled at 50-60℃.

[0044] When the particle size increased to 10-12 μm, the reaction time was approximately 15 h. After the reaction was complete, heating was turned off, and the product was aged for 12 h. The product was then washed with water, filtered, and dried at 120 °C to obtain the precursor [Ni] for spherical lithium-ion battery gradient cathode material. 0.89 Co 0.1 B 0.01 ](OH)2.

[0045] (c) High-temperature solid-state calcination: The precursor [Ni] of the obtained lithium-ion battery gradient cathode material is calcined. 0.89 Co 0.1 B 0.01 Li(OH)₂ was mixed with LiOH·H₂O, Al(OH)₃·3H₂O, and MnO₂ in a molar ratio of Li:(Ni+Co+B):Al:Mn = 1.02:0.95:0.02:0.03 until homogeneous. The mixture was then placed in a tube furnace under an oxygen atmosphere and heat-treated at 500℃ for 6 hours, followed by sintering at 750℃ for 12 hours. The product was then cooled, crushed, and sieved to obtain LiNi as the bulk material. 0.87 Co 0.1 Al 0.02 B 0.01 A low-strain stable lithium-ion battery concentration gradient cathode material with O2. If a manganese-containing coating is considered, the chemical formula of the cathode material is LiNi. 0.8 4Co 0.1 Mn 0.03 Al 0.02 B 0.01 O2.

[0046] (d) Electrochemical Performance Testing: The above-mentioned concentration gradient cathode materials were assembled into coin half-cells for electrochemical performance testing, specifically as follows: A slurry was prepared by mixing cathode materials with a shell concentration gradient of 8:1:1 by mass ratio, acetylene black, and polyvinylidene fluoride (PVDF) with N-methylpyrrolidone (NMP). The slurry was then uniformly coated onto aluminum foil and dried under vacuum at 80°C for 12 hours. Electrodes with a diameter of 12 mm were cut and accurately weighed for later use. The mass loading of NCM active material on each working circular electrode was approximately 2.5 mg cm⁻¹. -2 1M LiPF6 dissolved in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (volume ratio 1:1:1) was used as the electrolyte, lithium foil as the counter electrode, and Celgard 2400 polymer membrane as the separator. The materials were assembled into coin cells in an argon-filled glove box and tested after standing for 12 hours.

[0047] Comparative Example 1

[0048] (a) Solution preparation: NiSO4·6H2O was dissolved in deionized water to prepare a 2 mol / L nickel salt aqueous solution; CoSO4·7H2O was dissolved in deionized water to prepare a 2 mol / L solution a, which does not contain B. The complexing agent aqueous solution c and the precipitant aqueous solution b are the same as in the example.

[0049] (b) Precursor preparation: The difference from the example is that solution a does not contain B, and the obtained precursor is Ni. 0.9 Co 0.1 (OH)2.

[0050] (c) High-temperature solid-state calcination: The difference compared to the example is that a concentration gradient cathode without dopant element B is obtained. The precursor Ni... 0.9 Co 0.1 Li(OH)₂, LiOH·H₂O, Al(OH)₃·3H₂O, and MnO₂ were mixed uniformly in a molar ratio of Li:(Ni + Co):Al:Mn = 1.02:0.95:0.02:0.03, and then sintered to obtain a bulk material of LiNi. 0.88 Co 0.1 Al 0.02 A low-strain stable lithium-ion battery concentration gradient cathode material with O2. If a manganese-containing coating is considered, the chemical formula of the cathode material is LiNi. 0.85 Co 0.1 Mn 0.03 Al 0.02 O2.

[0051] Comparative Example 2

[0052] (a) Solution preparation: Same as in the above examples.

[0053] (b) Precursor preparation: Same as in the above examples.

[0054] (c) High-temperature solid-state calcination: The difference compared to the examples is that a concentration gradient cathode without Mn surface modification is obtained. The precursor [Ni]... 0.89 Co 0.1 B 0.01 Li(OH)₂, LiOH·H₂O, and Al(OH)₃·3H₂O were mixed uniformly in a molar ratio of Li:(Ni + Co + B):Al = 1.02:0.98:0.02. The resulting bulk material was LiNi. 0.87 Co 0.1 Al 0.02 B 0.01 O2 low-strain stable structure lithium-ion battery concentration gradient cathode material.

[0055] Comparative Example 3:

[0056] (a) Solution preparation: Prepare a salt solution containing NiSO4·6H2O, CoSO4·7H2O and B2O3. The molar ratio of nickel ions, cobalt ions and boron ions in the salt solution is 0.89:0.1:0.01. The sum of the concentrations of nickel ions, cobalt ions and boron ions in the salt solution is 2 mol / L.

[0057] (b) Precursor preparation: 10 L of salt solution was added to a reactor under nitrogen atmosphere and at a rotation speed of 500 rpm at a rate of 0.67 L / h. 4 mol / L ammonia solution was added to the reactor as a complexing agent. Simultaneously, 2 mol / L NaOH solution was pumped into the reactor to adjust the alkaline solution flow rate and maintain the pH at 11.3. After co-precipitation for 15 h, the precursor [Ni] was obtained. 0.89 Co 0.1 B 0.01 After the reaction is complete, turn off the heating, age for 12 hours, wash the product with water, filter it, and dry it at 120°C.

[0058] (c) High-temperature solid-state lithium intercalation: The resulting lithium-ion battery cathode material precursor [Ni 0.89 Co 0.1 B 0.01 Li(OH)₂ was mixed with LiOH·H₂O, Al(OH)₃·3H₂O, and MnO₂ in a molar ratio of Li:(Ni+Co+B):Al:Mn = 1.02:0.95:0.02:0.03 until homogeneous. The mixture was then calcined in a muffle furnace at 750℃ for 12 hours. The calcined material was crushed and sieved to obtain homogeneous LiNi₂. 0.87 Co0.1 Al 0.02 B 0.01 O2 cathode material. If a manganese-containing coating is considered, the chemical formula of the cathode material is LiNi. 0.84 Co 0.1 Mn 0.03 Al 0.02 B 0.01 O2.

[0059] The above examples and comparative examples were subjected to SEM and electrochemical tests, and the experimental results are as follows:

[0060] Figure 1 The embodiment body is LiNi 0.88 Co 0.1 Al 0.02 SEM images of O2-based low-strain stable lithium-ion battery concentration gradient cathode materials. A uniform, well-defined spherical appearance with a smooth microstructure can be observed.

[0061] Figure 2 The second cycle CV curves in Examples 1 and Comparative Example 1 show obvious redox peaks (H2-H3). Figure 3 The CV curves of the example after 50 and 100 cycles were analyzed using dQ / dV curves. The H2-H3 redox peaks of the example were still very pronounced. This is attributed to the fact that the concentration gradient material, bulk element doping with B and Mn, and surface modification can suppress the coarsening of primary particles during sintering and induce the primary particles to align radially. B doping can modify the formation energy of the (003) crystal plane, effectively alleviating stress accumulation at the grain boundaries of secondary particles, thereby suppressing the generation of intergranular cracks.

[0062] Figure 4 The CV curves for the 50th and 100th cycles of Comparative Example 1 show that the H2-H3 redox peaks have essentially disappeared. More pronounced polarization was observed, indicating that Comparative Example 1 underwent more irreversible phase transitions and higher interfacial impedance during multiple cycles.

[0063] Figure 5 As an example, the battery was charged and discharged at different rates (0.2C, 0.5C, 1C, 2C, 5C). It was shown that the battery maintained relatively stable performance at high rates (5C). Finally, when the rate returned to 0.2C, the battery still maintained the same electrochemical performance as at the initial 0.2C rate.

[0064] Figure 6The graph shows the charge-discharge curves of Comparative Example 1 battery at different rates. At 0.2C, its electrochemical performance is about 10 mAh / g lower than that of the Example. At higher rates (5C), its electrochemical performance loss is also low due to irreversible redox reactions. Finally, when the rate returns to 0.2C, its performance also decreases to some extent, which is related to... Figures 2-4 The CV curve results are basically consistent with those in Comparative Example 1. It can be seen that in the undoped B, the volumetric strain (ΔV / V) of the lattice changes drastically during repeated charge and discharge, and the resulting stress accumulation also increases. The irreversibility of the structure leads to material degradation and performance decline.

[0065] Figure 7 This is a charge-discharge curve for Comparative Example 3 at different rates. It indicates that at a 0.2C rate, the bulk composition of the prepared uniformly concentrated LiNi is... 0.87 Co 0.1 Al 0.02 B 0.01 The O2 cathode material exhibited similar electrochemical performance to Comparative Example 1. Similarly, with increasing rate, its electrochemical performance deteriorated, returning to its initial capacity of 0.2C, and was only comparable to the performance at 0.5C during the initial 6th-10th cycles. This indicates that the concentration gradient cathode material undergoes an irreversible phase transition, leading to energy density loss.

[0066] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a concentration gradient cathode material with a low-strain stable structure, characterized in that, The method includes the following steps: (a) Solution preparation: Prepare aqueous solutions of nickel salt and cobalt salt, and mix the aqueous solution of cobalt salt and the aqueous solution containing boron element evenly to obtain mixed solution a; prepare aqueous solutions of precipitant b and complexing agent c; (b) Precursor preparation: The precipitant aqueous solution b and complexing agent aqueous solution c prepared in step (a) are added to a continuously stirred liquid-phase reactor as the initial reaction base liquid, and the pH value is controlled between 10 and 13; after the reaction starts, a mixed solution a containing cobalt salt and boron is continuously pumped into the nickel salt aqueous solution and mixed evenly, and then pumped into the reactor at a certain flow rate, while adjusting the flow rates of precipitant aqueous solution b and complexing agent c; when the particle size of the precursor increases to 10-12 μm, heating is stopped, and after aging for 10-15 h, the product is washed with water, filtered and dried in sequence to obtain the precursor [Ni] of the spherical lithium-ion battery gradient cathode material. 0.9−x Co 0.1 B x (OH)2; (c) High-temperature solid-state calcination: The precursor of the lithium-ion battery gradient cathode material is mixed uniformly with lithium source, Al source and Mn source, and then the mixture is sintered in a tube furnace in an oxygen atmosphere. After that, the product is cooled, crushed and sieved to obtain a concentration gradient cathode material with a low strain stable structure. In step (c), the lithium source is selected from at least one of LiOH·H2O, LiNO3, and Li2CO3; the Al source is selected from at least one of NaAlO2, Al(OH)3·3H2O, and Al(NO3)3·9H2O; and the manganese source is selected from at least one of MnO, MnO2, Mn2O3, Mn3O4, and MnCO3. The high-temperature solid-state sintering process is as follows: in an oxygen atmosphere, the temperature is first raised to 450℃~600℃ and held for 3~8h, and then the temperature is further raised to 700℃~800℃ and sintered for 8~15h.

2. The method for preparing the concentration gradient cathode material with a low strain stable structure according to claim 1, characterized in that, In step (a), the nickel salt is selected from one of nickel sulfate, nickel chloride, and nickel nitrate, and the cobalt salt is selected from one of cobalt sulfate, cobalt chloride, and cobalt nitrate; The precipitant is selected from at least one of ammonia, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, and lithium carbonate. The complexing agent is selected from at least one of ammonia, EDTA, ammonium nitrate, ammonium sulfate, ammonium chloride, and ammonium acetate.

3. The method for preparing the concentration gradient cathode material with a low strain stable structure according to claim 2, characterized in that, In step (a), the concentration of the nickel salt aqueous solution is 0.5-2 mol / L; the concentration of the cobalt salt aqueous solution is 0.5-2 mol / L; and the concentration of the boron-containing aqueous solution is 0.5-2 mol / L. The concentration of the precipitant aqueous solution b is 0.01 mol / L to 5 mol / L, and the concentration of the complexing agent aqueous solution c is 0.02 mol / L to 15 mol / L.

4. The method for preparing the concentration gradient cathode material with a low strain stable structure according to claim 1, characterized in that, In step (b), the solution is first deoxygenated using a protective gas before the coprecipitation reaction. The precipitation reactor is filled with a protective gas selected from at least one of nitrogen, helium, or argon.

5. The method for preparing the concentration gradient cathode material with a low strain stable structure according to claim 4, characterized in that, In step (b), the concentration of the complexing agent in the reactor is maintained at 0.4-0.8 mol / L, the flow rate of the nickel salt solution is 0.8-1.0 L / h, and the flow rate of the mixed solution of cobalt and boron salts is 0.2-0.5 L / h.

6. The method for preparing the concentration gradient cathode material with a low strain stable structure according to claim 4, characterized in that, In step (b), the co-precipitation time is 10-20 h and the reaction temperature is 50-60 °C.

7. The low-strain stable concentration gradient cathode material prepared by the method according to any one of claims 1 to 6, characterized in that, The chemical formula of the concentration gradient cathode material is LiNi. x Co y Al 1-x-y-z B z O2, where 0.8≤x≤1, 0.05≤y≤0.1, 0.01≤z≤0.

02.

8. The application of the low-strain stable structure concentration gradient cathode material according to claim 7 in lithium-ion batteries.

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