A method for preparing a single-crystal cathode material, a single-crystal cathode material and a lithium ion battery

Abstract

This invention discloses a method for preparing single-crystal cathode materials, the single-crystal cathode materials, and lithium-ion batteries. The method includes the following steps: mixing a single-crystal cathode material precursor, initial-state grains, and a lithium source, followed by sintering and pulverization to obtain the single-crystal cathode material. The grain size of the single-crystal cathode material precursor differs from the grain size of the initial-state grains. The initial-state grains are monodisperse grains or agglomerated particles composed of several grains, wherein the grain size is 0.1-1 μm, and the agglomerated particles have an average particle size of less than 2 μm, forming monodisperse small-particle-size powder. Based on the fundamental principle of sintering, this method creates a size difference between grains during sintering, allowing large-particle-size grains to rapidly grow by consuming smaller grains, thereby reducing the amount of sintering aid, or even obtaining single-crystal cathode materials without any sintering aid. This achieves the effects of lowering the sintering temperature and significantly increasing the discharge capacity.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a method for preparing single-crystal cathode materials, single-crystal cathode materials and lithium-ion batteries. Background Technology

[0002] With the rapid development of new energy vehicles, the requirements for lithium-ion batteries used in energy storage devices are becoming increasingly stringent, such as longer cycle life, higher charge stability, and lower cost. To improve these performance indicators, single-crystalization of cathode materials is currently a widely feasible method. However, current single-crystal synthesis methods, such as high-temperature sintering with lithium over-lithium, adding sintering aids, molten salt methods, and multiple calcinations, all have significant drawbacks.

[0003] The high-temperature solid-state lithium over-lithiation method promotes grain growth by increasing the amount of lithium over-lithiation and raising the sintering temperature. However, this method generates a large amount of residual alkali, requiring water washing and heat treatment processes, which leads to significant lithium source waste, increases costs, and reduces production efficiency. In particular, high-nickel cathode materials have poor thermal stability and cannot withstand prolonged high-temperature sintering; excessively high sintering temperatures cause surface lithium to volatilize and transform into a rock salt phase.

[0004] The sintering aid method involves adding small amounts of specific metal oxides, such as SrCO3 and BaCO3, to promote grain growth and prepare single-crystal cathode materials at relatively low temperatures. This method is currently widely used in industry. However, sintering aid elements typically lack electrochemical activity, thus their addition is detrimental to the realization of electrochemical capacity.

[0005] The molten salt method involves adding large amounts of molten salts such as Li₂SO₄, Na₂SO₄, alkali metal chlorides LiCl and NaCl, LiOH-LiNO₃-H₃BO₃, Li₂SO₄-Na₂SO₄, or LiOH-LiNO₃. However, this method requires a large amount of molten salt, which must be washed away with water later. This not only increases material consumption and cost, but the water washing process is also very unfriendly to humidity-sensitive high-nickel cathode materials, causing changes in the high-nickel surface structure, including Li⁺ / H⁺ exchange and surface phase transitions. Furthermore, a large amount of molten salt inevitably leaves residues, which may even penetrate the crystal lattice and affect electrochemical performance.

[0006] Multiple calcination involves adding lithium source in stages and calcining repeatedly to prepare single crystals. The first stage adds a insufficient amount of lithium source, followed by high-temperature sintering to grow the grains. The grains are then removed, crushed, and the remaining lithium is added before calcination again to obtain the single crystal material. This method involves many steps and is cumbersome to operate.

[0007] The grain growth process is essentially a transformation from numerous small grains to fewer large grains, thermodynamically manifested as a decrease in surface energy. The size difference between grains is the driving force behind grain growth. Specifically, between two adjacent grains, the larger grain has lower surface energy, thus consuming the higher energy of the smaller grain, which then grows. As adjacent smaller grains are consumed, this process repeats, consuming the next smaller grain, eventually leading to a single crystal. However, during conventional lithium-ion precursor sintering, the grains formed on the secondary spheres are of uniform size, and the driving force for grain growth is the size difference between adjacent grains. Therefore, conventional sintering methods have a weak driving force, resulting in slow grain growth.

[0008] Therefore, it is necessary to provide a method for preparing single-crystal cathode materials to overcome the problems existing in the current single-crystal preparation methods. Summary of the Invention

[0009] One objective of this invention is to provide a method for preparing single-crystal cathode materials, thereby addressing the difficulty in preparing single-crystal materials. This method allows for the preparation of single-crystal cathode materials with a lower sintering temperature by adding only a very small amount of sintering aid elements or without any sintering aid, thus enabling the production of single-crystal cathode materials with higher capacity. This method also avoids the structural damage caused by the molten salt washing process.

[0010] The second objective of this invention is to provide a single-crystal cathode material prepared using the method described above.

[0011] The third objective of this invention is to provide a lithium-ion battery.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] This invention provides a method for preparing single-crystal cathode materials, the method comprising the following steps: mixing a single-crystal cathode material precursor, initial-state grains, and a lithium source, and then sintering and pulverizing the mixture to obtain the single-crystal cathode material.

[0014] The initial state grains are monodisperse grains or agglomerated particles composed of several grains, wherein the grain size is 0.1-1μm and the agglomerated particles are monodisperse small-particle-size powders with an average particle size of less than 2μm.

[0015] The amount of initial-state grains added is 0.1%-100% of the mass of the single-crystal cathode material precursor, used to create a grain size difference with the single-crystal cathode material precursor.

[0016] The initial grain size is different from that of the single-crystal cathode material precursor, so there will be differences in the initial grain size after sintering. This results in a phenomenon where the initial grains of sintering vary in size, causing the large grains to absorb the small grains and grow rapidly.

[0017] The single-crystal cathode material precursor includes one of the following: ternary single-crystal cathode material precursor and lithium manganese oxide single-crystal cathode material precursor.

[0018] When the single-crystal cathode material precursor is a ternary single-crystal cathode material precursor, the molar ratio of the total transition metal ions in the single-crystal cathode material precursor to the Li in the lithium source is 1:1-1:2. The initial-state grains are obtained by ball milling, air jet milling or rolling pressing of the ternary single-crystal cathode material precursor, the oxide of the ternary single-crystal cathode material precursor or the ternary layered lithium compound.

[0019] Furthermore, the oxide of the ternary single-crystal cathode material precursor is prepared by heat-treating the ternary single-crystal cathode material precursor at 500℃-900℃ for 5-10 hours.

[0020] Furthermore, the ternary layered lithiation is a lithiation product of a ternary single-crystal cathode material precursor or a ternary single-crystal cathode material precursor oxide, wherein the lithiation temperature is 600℃-900℃ and the lithiation time is 2-12h.

[0021] Furthermore, the ternary single-crystal cathode material precursor can be nickel cobalt manganese hydroxide, nickel cobalt manganese carbonate compound, or nickel cobalt manganese oxalate compound.

[0022] When the precursor of the single-crystal cathode material is a lithium manganese oxide single-crystal cathode material precursor, the molar ratio of Mn in the single-crystal cathode material precursor to Li in the lithium source in the initial state grain is 2:1-1.05, and the initial state grain is obtained by ball milling, air jet milling or rolling of the precursor of the lithium manganese oxide single-crystal cathode material or lithium manganese oxide.

[0023] Furthermore, the sintering process is specifically as follows: in an air or oxygen atmosphere, the temperature is held at 450℃-750℃ for 4-5 hours, and then the temperature is increased to 800℃-960℃ and held for 6-15 hours.

[0024] The method for preparing single-crystal cathode material further includes: during the mixing process, the raw materials being mixed also include a sintering aid.

[0025] Furthermore, the sintering aid element in the sintering aid includes at least one of Sr, Ba, Zr, and Al.

[0026] Furthermore, the amount of the sintering aid element added is 0%-1% of the mass of the single-crystal cathode material precursor.

[0027] This invention, based on fundamental sintering theory, explores methods to increase grain growth by controlling the initial grain size variation during sintering, without or with minimal sintering aids. This aims to lower the sintering temperature while introducing little to no inert elements, thereby achieving higher capacity. By adding initial-state grains, which differ in size from conventional precursor grains, the resulting layered oxide grains exhibit varying sizes. This breaks the uniformity of initial-state grain size during sintering, increasing the driving force for grain growth. It avoids the problem of slow grain growth caused by uniform grain size on secondary spheres during conventional lithium-ion precursor sintering. This is of great significance for reducing costs and improving product competitiveness.

[0028] The present invention also provides a single-crystal cathode material prepared by the method described above.

[0029] Furthermore, the grain size of the single-crystal cathode material is 1.5-5 μm.

[0030] The present invention also provides a lithium-ion battery comprising the single-crystal cathode material.

[0031] The beneficial effects of this invention are:

[0032] This invention provides a novel method for preparing single-crystal cathode materials, which differs from existing high-temperature sintering methods, sintering aid methods, and molten salt methods. Based on the fundamental principles of sintering, this method adds initial-state grains with sizes different from those in the single-crystal cathode material precursor to create a size difference between grains during sintering. This increases the thermodynamic driving force for grain growth, allowing larger grains to rapidly grow by consuming smaller grains. This reduces the amount of sintering aid required, and can even achieve single-crystal cathode materials without any aid, thus lowering the sintering temperature and significantly increasing the discharge capacity. Attached Figure Description

[0033] Figure 1 SEM of NCM650728 precursor.

[0034] Figure 2 The NCM650728 single crystal prepared in Example 1 with initial grain size controlled at 920℃ / 12h.

[0035] Figure 3 The NCM831106 single crystal prepared in Example 3 with initial grain size controlled at 840℃ / 12h.

[0036] Figure 4 The image shows the electrochemical cycling performance of NCM831106 single crystal prepared in Example 3 with controlled initial grain size at 840℃ / 12h.

[0037] Figure 5SEM images of NCM650728 precursor mixed with lithium as Comparative Example 1, sintered at 970℃ / 12h. Detailed Implementation

[0038] To enable those skilled in the art to better understand the present invention and to make the above-mentioned objects, features, and advantages of the present invention more apparent, specific embodiments of the present invention are further described below. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of various ranges, the endpoint values ​​of various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0039] Example 1: Preparation of Ternary Single-Crystal Cathode Material LiNi 0.65 Co 0.07 Mn 0.28 O2(NCM650728)

[0040] In this embodiment, the precursor is a commercially available hydroxide precursor, Ni. 0.65 Co 0.07 Mn 0.28 (OH)2, its SEM image is as follows Figure 1 As shown, the atomic ratio Ni:Co:Mn = 0.65:0.07:0.28, and the grain size is 0.5-1μm.

[0041] 1) Commercial hydroxide precursors were ball-milled to obtain powder with a grain size of 0.1-0.7 μm and an average particle size of less than 2 μm of agglomerated particles, which was used as the initial grains.

[0042] 2) Mix the commercial hydroxide precursor, the initial crystal grains obtained in step 1), and Li2CO3, wherein TM:Li = 1:1.05 (TM refers to the total transition metal ions in the commercial hydroxide precursor and the initial crystal grains), and the mass of the initial crystal grains is 5% of the mass of the commercial hydroxide precursor.

[0043] 3) The mixture from step 2) is sintered at 720℃ for 4 hours and then at 920℃ for 12 hours in an oxygen atmosphere, followed by airflow pulverization to obtain the single-crystal cathode material LiNi. 0.65 Co 0.07 Mn 0.28 O2, its appearance is as follows Figure 2 As shown.

[0044] Comparative Example 1

[0045] Compared to the preparation process of Example 1, the difference in this comparative example is that no initial state grains are added. The specific preparation process is as follows: a commercial hydroxide precursor and Li₂CO₃ are mixed, wherein TM:Li = 1:1.05 (TM refers to the transition metal ions in the commercial hydroxide precursor), and then sintered in an oxygen atmosphere at 720℃ / 4h and 920℃ / 12h to obtain the product. The morphology of the product is as follows. Figure 5 As shown, from Figure 5 As can be seen, when only lithium is mixed in the precursor, the sintered product still has a polycrystalline morphology.

[0046] Example 2: Preparation of ternary single-crystal cathode material LiNi 0.83 Co 0.11 Mn 0.06 O2(NCM831106)

[0047] In this embodiment, the precursor is a commercially available hydroxide precursor, Ni. 0.83 Co 0.11 Mn 0.06 (OH)2, with a grain size of 0.5-1μm.

[0048] 1) Commercial hydroxide precursors were ball-milled to obtain powder with a grain size of 0.1-0.8 μm and an average particle size of less than 2 μm of agglomerated particles, which was used as the initial grains;

[0049] 2) Mix the commercial hydroxide precursor, the initial crystal grains obtained in step 1), and LiOH·H2O, wherein TM:Li = 1:1.05 (TM refers to the total transition metal ions in the commercial hydroxide precursor and the initial crystal grains), and the mass of the initial crystal grains is 5% of the mass of the commercial hydroxide precursor;

[0050] 3) The mixture from step 2) is sintered at 500℃ for 4 hours and then at 840℃ for 12 hours in an oxygen atmosphere, followed by air jet pulverization to obtain the single-crystal cathode material LiNi. 0.83 Co 0.11 Mn 0.06 O2.

[0051] Example 3: Preparation of ternary single-crystal cathode material LiNi 0.83 Co 0.11 Mn 0.06 O2

[0052] In this embodiment, the precursor is a commercially available hydroxide precursor, Ni. 0.83 Co 0.11 Mn 0.06 (OH)2, with a grain size of 0.5-1μm.

[0053] 1) Preparation of Ni carbonate precursor by co-precipitation method0.83 Co 0.11 Mn 0.06 CO3 was then used to heat-treat the carbonate precursor in air at 800℃ for 6 hours. After ball milling, dispersed nickel-cobalt-manganese oxides with a grain size of 0.1-0.3 μm and an average particle size of less than 2 μm were obtained.

[0054] 2) Mix the commercial hydroxide precursor, the nickel cobalt manganese oxide obtained in step 1), and LiOH·H2O, wherein TM:Li = 1:1.05 (TM refers to the total transition metal ions in the commercial hydroxide precursor and the nickel cobalt manganese oxide), and the mass of the nickel cobalt manganese oxide is 5% of the mass of the commercial hydroxide precursor.

[0055] 3) The mixture from step 2) is sintered at 500℃ for 4 hours and then at 840℃ for 12 hours in an oxygen atmosphere, followed by air jet pulverization to obtain the single-crystal cathode material LiNi. 0.83 Co 0.11 Mn 0.06 O2.

[0056] The single-crystal cathode material LiNi prepared in this embodiment 0.83 Co 0.11 Mn 0.06 SEM image of O2 as follows Figure 3 As shown, the electrochemical performance is as follows Figure 4 As shown, under conditions of 2.8-4.3V, 1C = 200mAh / g rate, and 25℃, the 0.1C discharge capacity is 196mAh / g, and the cycle retention rate is 92.38% after 100 cycles.

[0057] Example 4: Preparation of Zr-doped ternary single-crystal cathode material

[0058] In this embodiment, the precursor is a commercially available hydroxide precursor, Ni. 0.83 Co 0.11 Mn 0.06 (OH)2, with a grain size of 0.5-1μm.

[0059] 1) Mix commercial hydroxide precursors with lithium, TM:Li = 1:1.05 (TM refers to the transition metal ions in the commercial hydroxide precursors), and then sinter at 750℃ / 12h in an oxygen atmosphere to obtain polycrystalline material. Then, the polycrystalline material is ball-milled to obtain lithium compound powder with a grain size of 0.2-0.8μm and an average particle size of less than 2μm for agglomerated particles.

[0060] 2) Mix the commercial hydroxide precursor, the lithium powder from step 1), and LiOH·H2O, and add ZrO2 doping, TM:Zr:Li=0.998:0.002:1.05 (TM refers to the total transition metal ions in the commercial hydroxide precursor and the lithium powder), and the mass of the lithium powder is 3% of the mass of the commercial hydroxide precursor;

[0061] 3) The material mixed in step 2) is sintered at 500℃ for 4 hours and 840℃ for 12 hours in an oxygen atmosphere, and then pulverized by airflow to obtain the single crystal cathode material.

[0062] Example 5: Preparation of single-crystal spinel cathode material LiMn2O4

[0063] In this embodiment, the precursor is commercially available Mn3O4 with a grain size of 0.4-0.9 μm.

[0064] 1) Commercial Mn3O4 was ball-milled to a grain size of 0.1-0.5 μm and an average particle size of less than 2 μm for agglomerated particles, which were then used as the initial grains;

[0065] 2) Mix commercial Mn3O4 with a lithium source, the lithium source being LiOH·H2O, TM:Li = 2:1.05 (TM refers to the transition metal ions in commercial Mn3O4), and then add the initial state grains from step 1), the mass of which is 3% of the mass of commercial Mn3O4;

[0066] 3) The material mixed in step 2) is sintered at 500℃ / 4h and 850℃ / 12h in an oxygen atmosphere, and then pulverized by airflow to obtain the single crystal spinel cathode material LiMn2O4.

Claims

1. A method for preparing single-crystal cathode materials, characterized in that, The method includes the following steps: mixing a single-crystal cathode material precursor, initial-state grains, and a lithium source, then sintering and pulverizing to obtain a single-crystal cathode material; When the single-crystal cathode material precursor is a ternary single-crystal cathode material precursor, the grain size of the single-crystal cathode material precursor is 0.5~1μm; the initial state grains are monodisperse grains or agglomerated particles composed of several grains, wherein the grain size is 0.1-0.8μm, and the agglomerated particles are monodisperse small-particle-size powders with an average particle size of less than 2μm. The amount of initial state grains added is 3%-5% of the mass of the single-crystal cathode material precursor, and is used to react with the single-crystal cathode material. The precursor material is constructed with different grain sizes; the initial grains are obtained by ball milling, air jet milling or roll pressing of the ternary single-crystal cathode material precursor or the oxide of the ternary single-crystal cathode material precursor; the molar ratio of the total transition metal ions in the single-crystal cathode material precursor to Li in the lithium source is 1:(1~2); the oxide of the ternary single-crystal cathode material precursor is obtained by heat treatment of the ternary single-crystal cathode material precursor at 500℃-900℃ for 5-10h; When the single-crystal cathode material precursor is a lithium manganese oxide single-crystal cathode material precursor, the grain size of the single-crystal cathode material precursor is 0.4~0.9μm; the initial state grains are monodisperse grains or agglomerated particles composed of several grains, wherein the grain size is 0.1-0.5μm, and the agglomerated particles are monodisperse small-particle-size powders with an average particle size of less than 2μm. The amount of initial state grains added is 3% of the mass of the single-crystal cathode material precursor, used to create a grain size difference with the single-crystal cathode material precursor; the initial state grains are obtained by ball milling, air jet milling, or roll pressing of the lithium manganese oxide single-crystal cathode material precursor; the molar ratio of Mn in the single-crystal cathode material precursor to Li in the lithium source is 2:(1~1.05).

2. The method according to claim 1, characterized in that, The precursor of the ternary single-crystal cathode material is nickel cobalt manganese hydroxide, nickel cobalt manganese carbonate compound, or nickel cobalt manganese oxalate compound.

3. The method according to claim 1, characterized in that, The sintering process is as follows: in an air or oxygen atmosphere, the temperature is held at 450℃-750℃ for 4-5 hours, and then the temperature is raised to 800℃-960℃ and held for 6-15 hours.

4. The method according to claim 1, characterized in that, The method further includes: during the mixing process, the raw materials being mixed also include a sintering aid; The sintering aid element in the sintering aid includes at least one of Sr, Ba, Zr, and Al; The amount of the sintering aid element added is 0%-1% of the mass of the single-crystal cathode material precursor.

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