A preparation method of a surface niobium-coated nano-rich-nickel ternary positive electrode material for a lithium ion battery

Abstract

The application discloses a preparation method of a surface niobium-coated nano-rich-nickel ternary positive electrode material for a lithium ion battery. The preparation method comprises the following steps: mixing a transition metal salt solution with a precipitant and a surfactant, and generating a precursor through a solvothermal reaction; mixing the obtained precursor with a lithium source, and calcining to obtain a nano-rich-nickel positive electrode base; and then mixing the base with a niobium source and a lithium source through a wet method, and performing secondary calcination, so that a nano-rich-nickel ternary positive electrode material with a surface uniformly coated with a niobium-based nano layer is finally formed. The material has a nano sheet shape, effectively increases a lithium ion transmission channel, and improves solid-phase diffusion capacity; the surface niobium coating layer enhances the structural stability and mechanical strength of the material, inhibits volume change and surface degradation in a cycle process, so that the cycle life and fast charging performance of the battery are significantly improved while maintaining high specific capacity.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion electrode material technology, and particularly relates to a method for preparing a surface-coated niobium-rich ternary cathode material for lithium-ion batteries. Background Technology

[0002] Currently, the rapid development of the new energy industry has placed higher demands on the energy density, cycle life, and fast-charging performance of energy storage batteries. The National Action Plan for High-Quality Development of Power Batteries (White Paper) clearly states that by 2025, liquid batteries need to achieve a specific energy of over 350Wh / kg, a cycle life of over 1000 cycles or 12 years, and the ability to fast charge at 3C or higher. To achieve these technical indicators, developing key materials that combine high stability with excellent fast charge and discharge performance has become an urgent need for the industry. In lithium-ion battery systems, the capacity of anode materials generally exceeds 350mAh / g, while the capacity of cathode materials is mostly around 200mAh / g, significantly lower than the capacity level that anodes can provide. At the same time, due to their complex crystal structure and high-voltage operating environment, the cycle stability of cathode materials is usually weaker than that of anodes. Therefore, the cathode has become a key link restricting further improvement in the energy density of lithium-ion batteries, and the development of new cathode materials with high specific capacity and long cycle life has become a current research focus. Among numerous cathode materials, ternary layered materials based on nickel-cobalt-manganese (NCM) or nickel-cobalt-aluminum (NCA) are widely used in commercial power batteries due to their high energy density. Compared with lithium iron phosphate (LFP) systems, ternary batteries exhibit higher specific capacity and better rate performance. However, while increasing the nickel content can further improve the specific capacity of the material, its structural stability decreases significantly, capacity decay accelerates during cycling, and safety issues become more prominent. Therefore, currently, commercially used ternary materials are mainly those with a nickel content of less than 60%. To improve the cycle stability of ternary systems under higher energy density requirements, researchers have conducted extensive material modification studies.

[0003] Currently, most common optimization strategies are based on micron-sized spherical ternary materials synthesized via co-precipitation. These materials are secondary spheres formed by the agglomeration of numerous nanoscale primary particles. Their internal grain orientation is anisotropic, leading to stress concentration during lithium-ion insertion / extraction due to anisotropic volume changes. This accelerates particle breakage and pulverization, especially under high-current fast charging conditions, where structural degradation is more pronounced, severely impairing battery cycle performance and safety. Furthermore, such agglomerated structures struggle to form high-specific-surface-area conductive networks on a three-dimensional scale, limiting lithium-ion transport efficiency in the solid phase and consequently affecting the battery's fast-charging capability. Therefore, there is an urgent need to develop novel cathode materials with more stable crystal structures and superior ion transport pathways through material structure design and fabrication process innovation to meet the future demands of high energy density, high safety, and fast charging for next-generation lithium-ion batteries. Summary of the Invention

[0004] This invention aims to provide a niobium-coated nickel-rich ternary nanomaterial for lithium-ion battery cathodes and its preparation method. This material possesses high specific energy, long cycle stability, and excellent fast-charging performance. The nickel-rich ternary cathode material is synthesized using a surfactant-assisted solvothermal method, forming a nanosheet structure with regularly arranged grains, effectively improving the material's overall electrochemical performance. Surface coating with niobium further enhances the Young's modulus and mechanical strength of the material surface, suppressing surface degradation during cycling. Simultaneously, the nanosheet structure provides more three-dimensional transport paths for lithium-ion diffusion, significantly improving high-rate performance and effectively mitigating volume changes during charge and discharge, thereby achieving a long cycle life.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a surface-coated niobium-rich ternary cathode material for lithium-ion batteries includes the following steps:

[0007] Step 1: Dissolve the transition metal salt solution in a mixed solvent consisting of deionized water and ethanol;

[0008] A mixed solution including a precipitant and a surfactant is slowly added under magnetic stirring to obtain a reaction solution, wherein the molar ratio of transition metal salt, precipitant and surfactant is 1:2:1.

[0009] Step 2: Under temperature control, stir and mix the obtained reaction solution evenly, and transfer the reaction solution into the inner liner of the reaction vessel; place the reaction vessel in a forced-air drying oven to carry out a solvothermal reaction to synthesize the transition metal oxide precursor;

[0010] Step 3: After the reaction vessel has cooled naturally, remove the suspension from the inner liner, wash it by centrifugation with deionized water and ethanol, and dry the resulting precipitate in a forced-air drying oven to obtain the dried powder.

[0011] Step 4: Grind the dried powder evenly, add lithium hydroxide monohydrate and ethanol, mix evenly by ball milling, and dry again to obtain mixed and dried powder.

[0012] Step 5: Place the mixed and dried powder in a tube furnace and calcine it in an oxygen atmosphere to obtain nano-nickel-rich cathode substrate powder.

[0013] Step 6: Mix and grind the nano-nickel-rich cathode substrate powder with ammonium niobate and lithium acetate, then add deionized water to facilitate magnetic stirring, and under heating conditions, use magnetic stirring to completely evaporate the liquid to obtain powder.

[0014] Step 7: Calcine the powder obtained in step 6 in a tube furnace under an oxygen atmosphere to obtain a niobium-coated nickel-rich ternary cathode material, wherein the niobium-coated nickel-rich ternary cathode material is in the form of nano-sized particles.

[0015] Preferably, the transition metal salt is nickel acetate, manganese acetate, or cobalt acetate. The precipitant is urea, and the surfactant is hexadecyltrimethylammonium bromide or polyvinylpyrrolidone. In step 1, the volume ratio of deionized water to ethanol in the mixed solvent is 1:1. In step 2, the solvothermal reaction temperature is 150°C, and the reaction time is 5–8 hours.

[0016] The crystal growth rate can be adjusted by controlling the proportion of surfactant added; too low a proportion can easily lead to particle agglomeration, while too high a proportion will introduce too much carbon-containing impurities, affecting electrochemical performance. Controlling the ratio of water to ethanol solvent to 1:1 helps to regulate crystal size; pure water easily leads to agglomeration, while too much ethanol is not conducive to sufficient crystal growth.

[0017] Preferably, the calcination procedure in step 5 is as follows: heating at a rate of 5°C / min, calcining at 500°C for 4 hours, calcining at 750°C for 10 hours, and an oxygen flow rate of 50 sccm.

[0018] Preferably, the amount of niobium ammonium oxalate added in step 6 is 1%–2% of the mass of the nano-nickel-rich cathode substrate powder, the molar ratio of niobium ammonium oxalate to lithium acetate is 1:1, and the heating temperature is 90°C. It should be noted that the optimal molar ratio of niobium ammonium oxalate to lithium acetate is 1:1. If niobium ammonium oxalate is excessive, the excess niobium cannot form complete LiNbO3, but instead forms other niobium-rich oxides, whose ionic conductivity is lower than that of lithium niobate, hindering the entry and exit of lithium ions and leading to a decrease in battery capacity and rate performance. If lithium acetate is excessive, the excess lithium salt will form lithium residues at high temperatures, increasing interfacial impedance and accelerating the decline in battery performance.

[0019] Preferably, the calcination procedure in step 7 is as follows: heating at a rate of 5°C / min, calcining at 750°C for 3 hours, with an oxygen flow rate of 50 sccm; the diameter of the nanoparticles is 400–800 nm.

[0020] The nickel-rich ternary cathode material is a nickel-cobalt-manganese ternary system, wherein the molar fraction of nickel is not less than 0.6, the ratio of nickel, cobalt and manganese is variable, and the sum of the molar ratios of the three is 1.

[0021] The beneficial effects of this invention are as follows: A nanostructured nickel-rich ternary cathode material was successfully prepared using a surfactant-assisted solvothermal method combined with niobium surface coating technology. This material maintains high specific capacity while significantly improving cycle life and fast-charging performance. Its nanoscale sheet-like morphology effectively increases lithium-ion transport channels and improves solid-phase diffusion kinetics; the niobium coating layer enhances the material's surface modulus and mechanical stability, significantly suppressing volumetric strain and structural degradation during cycling, thereby improving the overall electrochemical performance and durability of the battery. Attached Figure Description

[0022] Figure 1 This is a microstructure diagram (high magnification) of the nickel-rich ternary cathode material described in this invention.

[0023] Figure 2 This is a microstructure diagram (low magnification) of the nickel-rich ternary cathode material described in this invention.

[0024] Figure 3 The capacity decay diagram of the material prepared in Example 2 of the present invention when used in a lithium-ion battery at a 1C rate in the range of 2.8-4.3V (the comparison sample is the commercial ternary cathode material NCM811);

[0025] Figure 4 The capacity decay diagram of the material prepared in Example 2 of the present invention when used in a lithium-ion battery in the range of 2.8-4.6V and cycled at a 1C rate (the comparison sample is the commercial ternary cathode material NCM811);

[0026] Figure 5 The performance of the material prepared in Example 2 of this invention in lithium-ion batteries under different charge and discharge rates in the range of 2.8-4.6V (the comparison sample is the commercial ternary cathode material NCM811);

[0027] Figure 6 The voltage curve and discharge capacity degradation diagram of the material prepared in Example 2 of this invention when used in a lithium-ion battery in the range of 2.8-4.6V under a 20C charging-0.2C discharging strategy (the comparison sample is the commercial ternary cathode material NCM811). Detailed Implementation

[0028] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0029] Example 1:

[0030] Preparation of transition metal salt solution: Weigh out the appropriate masses of nickel acetate tetrahydrate, manganese acetate tetrahydrate, and cobalt acetate tetrahydrate in a molar ratio of 6:2:2, add 35 mL of deionized water and 35 mL of ethanol, and stir magnetically until completely dissolved; then add urea and hexadecyltrimethylammonium bromide (CTAB), wherein the molar ratio of urea, CTAB, and total transition metal salt is 2:1:1; stir the mixed solution vigorously for 1 hour, transfer it to a polytetrafluoroethylene-lined reactor, place it in a forced-air drying oven, and react at 150°C for 5 hours; after the reaction, collect the suspension, wash it several times by centrifugation with deionized water and ethanol, and dry it at 120°C for 12 hours to obtain precursor powder; mix the precursor powder with lithium hydroxide monohydrate according to the metal element... The nickel-rich cathode substrate was uniformly mixed with lithium at a molar ratio of 1:1.05 in a ball mill, and then calcined in a tube furnace: the temperature was increased at a rate of 5 °C / min under an oxygen atmosphere, held at 500 °C for 4 hours, and then increased to 750 °C for 10 hours with an oxygen flow rate of 50 sccm to obtain a nano-nickel-rich cathode substrate material. The above substrate powder was then ground together with ammonium niobate oxalate and lithium acetate, with the amount of ammonium niobate oxalate added being 1% of the substrate mass and the molar ratio of ammonium niobate oxalate to lithium acetate being 1:1. 5 mL of deionized water was added, and the mixture was magnetically stirred at 90 °C until the liquid was completely evaporated. The resulting powder was then calcined in a tube furnace at a temperature increased to 750 °C at a rate of 5 °C / min under an oxygen atmosphere for 3 hours with an oxygen flow rate maintained at 50 sccm to obtain the final product.

[0031] Example 2:

[0032] Preparation of transition metal salt solution: Weigh out the appropriate masses of nickel acetate tetrahydrate, manganese acetate tetrahydrate, and cobalt acetate tetrahydrate in a molar ratio of 8:1:1, add 35 mL of deionized water and 35 mL of ethanol, and stir magnetically until completely dissolved; then add urea and hexadecyltrimethylammonium bromide (CTAB), wherein the molar ratio of urea, CTAB, and total transition metal salt is 2:1:1; stir the mixed solution vigorously for 1 hour, transfer it to a polytetrafluoroethylene-lined reactor, place it in a forced-air drying oven, and react at 150°C for 5 hours; after the reaction, collect the suspension, wash it several times by centrifugation with deionized water and ethanol, and dry it at 120°C for 12 hours to obtain precursor powder; mix the precursor powder with lithium hydroxide monohydrate according to the metal element... The nickel-rich cathode substrate was uniformly mixed with lithium at a molar ratio of 1:1.05 in a ball mill, and then calcined in a tube furnace: the temperature was increased at a rate of 5 °C / min under an oxygen atmosphere, held at 500 °C for 4 hours, and then increased to 750 °C for 10 hours with an oxygen flow rate of 50 sccm to obtain a nano-nickel-rich cathode substrate material. The above substrate powder was then co-ground with ammonium niobate oxalate and lithium acetate, with the amount of ammonium niobate oxalate added being 2% of the substrate mass and the molar ratio of ammonium niobate oxalate to lithium acetate being 1:1. 5 mL of deionized water was added, and the mixture was magnetically stirred at 90 °C until the liquid was completely evaporated. The resulting powder was then calcined in a tube furnace at a temperature increased to 750 °C at a rate of 5 °C / min under an oxygen atmosphere for 3 hours with an oxygen flow rate maintained at 50 sccm to obtain the final product. Figures 3-6 The test results show that this material has excellent electrochemical performance when used as a cathode material in lithium-ion batteries.

[0033] Example 3:

[0034] The only difference between this embodiment and Embodiment 2 is that, in step 1, the surfactant added in the solvothermal reaction is polyvinylpyrrolidone (PVP).

[0035] Example 4:

[0036] The only difference between this embodiment and Embodiment 2 is that in step 1, an excess of precipitant was added to the solvothermal reaction, i.e., the molar ratio of transition metal salt, precipitant, and surfactant (CTAB) was 1:3:1.

[0037] Example 5:

[0038] The only difference between this embodiment and Embodiment 2 is that in step 1, insufficient precipitant was added to the solvothermal reaction, i.e., the molar ratio of transition metal salt, precipitant, and surfactant (CTAB) was 1:0.5:1.

[0039] Example 6:

[0040] The only difference between this embodiment and Embodiment 2 is that in step 1, the volume ratio of deionized water to ethanol added in the solvothermal reaction is 1:2.

[0041] Example 7:

[0042] The only difference between this embodiment and Embodiment 2 is that in step 1, the volume ratio of deionized water to ethanol added in the solvothermal reaction is 2:1.

[0043] Example 8:

[0044] The only difference between this embodiment and Embodiment 2 is that in step 6, the amount of niobium ammonium oxalate added is 0.5% of the mass of the nano-nickel-rich cathode substrate powder.

[0045] Example 9:

[0046] The only difference between this embodiment and Embodiment 2 is that in step 6, the amount of niobium ammonium oxalate added is 3% of the mass of the nano-nickel-rich cathode substrate powder.

[0047] Example 10:

[0048] The only difference between this embodiment and embodiment 2 is that in step 6, the obtained powder is heated in a tube furnace at 5°C / min under an oxygen atmosphere and calcined at 650°C for 3 hours with an oxygen flow rate of 50 sccm.

[0049] Example 11:

[0050] The only difference between this embodiment and embodiment 2 is that in step 6, the obtained powder is heated in a tube furnace at 5°C / min under an oxygen atmosphere and calcined at 850°C for 3 hours with an oxygen flow rate of 50 sccm.

[0051] Table 1: Test Results of Examples

[0052]

[0053]

[0054] The above description is only a part of the specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes 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 protection scope of the present invention.

Claims

1. A method for preparing a surface-coated niobium-rich ternary cathode material for lithium-ion batteries, characterized in that, Includes the following steps: Step 1: Dissolve the transition metal salt solution in a mixed solvent consisting of deionized water and ethanol; the volume ratio of deionized water to ethanol is 1:

1. Under magnetic stirring conditions slow A mixed solution including a precipitant and a surfactant is added to obtain a reaction solution, wherein the molar ratio of transition metal salt, precipitant and surfactant is 1:2:1; Step 2: Under temperature control, the obtained reaction solution is stirred and mixed evenly, and the reaction solution is transferred to the inner liner of the reaction vessel; the reaction vessel is placed in a forced-air drying oven to carry out a solvothermal reaction to synthesize the transition metal oxide precursor; the solvothermal reaction temperature is 150℃ and the time is 5 hours. Step 3: After the reaction vessel has cooled naturally, remove the suspension from the inner liner, wash it by centrifugation with deionized water and ethanol, and dry the resulting precipitate in a forced-air drying oven to obtain the dried powder. Step 4: Grind the dried powder evenly, add lithium hydroxide monohydrate and ethanol according to the molar ratio of metal element to lithium in the powder of 1:1.05, mix evenly by ball milling, and dry again to obtain mixed and dried powder. Step 5: Place the mixed and dried powder in a tube furnace and calcine it under an oxygen atmosphere to obtain nano-nickel-rich cathode substrate powder; the calcine procedure is as follows: heat up at a rate of 5 °C / min, calcine at 500 °C for 4 hours, and calcine at 750 °C for 10 hours. Step 6: Mix and grind the nano-nickel-rich cathode substrate powder with ammonium niobate and lithium acetate, then add deionized water to facilitate magnetic stirring. Under heating conditions, the liquid is completely evaporated by magnetic stirring to obtain powder. The amount of ammonium niobate added is 2% of the mass of the nano-nickel-rich cathode substrate powder, and the heating temperature is 90°C. Step 7: The powder obtained in Step 6 is calcined in a tube furnace under an oxygen atmosphere to obtain a niobium-coated nickel-rich ternary cathode material. The niobium-coated nickel-rich ternary cathode material is in the form of nano-sized particles. The calcination procedure is as follows: heating at a rate of 5 °C / min, calcining at 750 °C for 3 hours, with an oxygen flow rate of 50 sccm. The diameter of the nano-sized particles is 400–800 nm. The transition metal salts are nickel acetate, manganese acetate, and cobalt acetate; the molar ratio of nickel acetate, cobalt acetate, and manganese acetate is 8:1:

1. The precipitant is urea, and the surfactant is hexadecyltrimethylammonium bromide.

2. The preparation method according to claim 1, characterized in that, In the calcination process described in step 5, the oxygen flow rate is 50 sccm.

3. The preparation method according to claim 1, characterized in that, In step 6, the molar ratio of ammonium niobate oxalate to lithium acetate is 1:1.

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