A surface modification method for nickel-cobalt-manganese ternary materials based on ammonolysis reaction

Abstract

The present invention relates to a surface modification method of a nickel-cobalt-manganese ternary material based on an ammonolysis reaction, comprising the following steps: (1) dispersing the nickel-cobalt-manganese ternary material into an ammonolysis solution, in situ constructing a manganese-rich layer on the surface of the nickel-cobalt-manganese ternary material after an ammonolysis reaction, and then separating and drying to obtain a nickel-cobalt-manganese ternary material with a manganese-rich shell structure; the ammonolysis solution is an ammonolysis agent; and (2) subjecting the obtained nickel-cobalt-manganese ternary material with a manganese-rich shell structure to a heat treatment to obtain a surface-modified nickel-cobalt-manganese ternary material.

Description

Technical Field

[0001] The present invention relates to the surface modification of lithium-ion electrode materials, and in particular to a design and preparation method of a manganese-rich shell structure of a nickel-cobalt-manganese ternary material, belonging to the field of chemical energy storage batteries. Background Art

[0002] The rapid development of new energy vehicles has put forward higher requirements on the specific capacity and safety of the positive electrode materials used in power batteries. Among the currently commercialized spinel, olivine and layered positive electrode materials, ternary layered positive electrode materials have attracted widespread attention due to their high specific capacity. Although the increase in nickel content can improve the specific capacity of the ternary positive electrode and reduce the cost, as the nickel content increases, the cycle performance, thermal stability and safety of the ternary positive electrode material will deteriorate sharply, seriously restricting its practical application. The root cause of the above problems is determined by the material properties of the high nickel ternary positive electrode, including the dissolution of metal elements and the strong oxidizing properties of Ni in the charged state. 4+ The side reaction with the electrolyte leads to surface reconstruction, generating a high-resistance NiO phase and releasing active oxygen, which leads to gas production and thermal runaway of the battery. At present, domestic and foreign scholars mainly use coating on the surface of ternary materials to inhibit the dissolution of transition metals and isolate highly active NiO. 4+ Direct contact with the electrolyte solves the above problems.

[0003] Common coating materials such as metal oxides, fluorides, phosphates and other inert substances often only serve to isolate the positive electrode material from the electrolyte. Such coating materials themselves often have very low ionic conductivity and electronic conductivity, and cannot provide active capacity, which will adversely affect the rate performance and capacity of the ternary positive electrode material. The structural design of the manganese-rich shell can maximize the capacity of the nickel-cobalt-manganese ternary positive electrode material while improving the stability and rate performance of the material. At present, the main methods for surface coating of positive electrode materials include co-precipitation, sol-gel method, hydrothermal method, chemical vapor deposition method, atomic deposition method, solid phase ball milling method, etc., but there are still problems such as high cost and uneven coating. The precursor salts of the sol-gel method and hydrothermal method are expensive and have low yields; the chemical vapor deposition method and atomic deposition method have slow processing time, strong toxicity and complex process; the solid phase ball milling method is difficult to obtain a uniform coating layer. From this, it can be seen that developing a method for modifying nickel-cobalt-manganese ternary positive electrode materials that is easy to operate and low-cost, especially designing a manganese-rich shell structure, has high practical value. Summary of the Invention

[0004] To this end, the present invention provides a surface modification method for nickel-cobalt-manganese ternary materials based on an ammonolysis reaction, which comprises the following steps:

[0005] (1) dispersing a nickel-cobalt-manganese ternary material into an ammonolysis solution, in situ constructing a manganese-rich layer on the surface of the nickel-cobalt-manganese ternary material after an ammonolysis reaction, and then separating and drying to obtain a nickel-cobalt-manganese ternary material with a manganese-rich shell structure; the ammonolysis solution is an ammonolysis agent;

[0006] (2) The obtained nickel-cobalt-manganese ternary material with a manganese-rich shell structure is subjected to heat treatment to obtain a surface-modified nickel-cobalt-manganese ternary material.

[0007] In the present invention, a nickel-cobalt-manganese ternary material is dispersed into an ammonolysis solution to obtain a nickel-cobalt-manganese ternary material mixed solution, and an ammonolysis reaction is performed. Taking advantage of the fact that nickel and cobalt ions have a much stronger ability to form coordination compounds with ammonia than manganese ions, the nickel and cobalt in the nickel-cobalt-manganese cathode material are easily dissolved in the ammonolysis solution, while the manganese ions are redeposited on the surface of the larger-diameter nickel-cobalt-manganese ternary material particles, thereby constructing a manganese-rich shell on the surface of the nickel-cobalt-manganese ternary material to obtain a nickel-cobalt-manganese ternary material with a manganese-rich shell structure. The separated and dried nickel-cobalt-manganese ternary material with a manganese-rich shell structure is heat-treated to obtain a surface-modified cathode material.

[0008] Preferably, the nickel-cobalt-manganese ternary material includes a nickel-cobalt-manganese ternary positive electrode material and / or a nickel-cobalt-manganese ternary positive electrode precursor material.

[0009] Preferably, the particle size of the nickel-cobalt-manganese positive electrode material is 1 to 100 μm.

[0010] Preferably, the composition of the nickel-cobalt-manganese ternary positive electrode material is LiNi b Co c Mn 1-b-c O2, where 0<b<1, 0<c<1.

[0011] Preferably, the nickel-cobalt-manganese ternary positive electrode precursor material is composed of Ni 1-y-z Co y Mn z (OH)2, wherein 0<y<1, 0<z<1.

[0012] Preferably, the ammonia solution is an ammonia solution, and the mass fraction of ammonia in the ammonia solution is 5% to 25wt%.

[0013] Preferably, the solvent of the ammonolysis agent is at least one of distilled water, methanol, ethanol, isopropanol, n-butanol, isobutanol, cyclohexanol, acetone, cyclohexanone, glycerol and ethyl acetate.

[0014] Preferably, the ammonia solution further comprises an additive, and the additive is selected from one of H2O, KMnO4, H2O2, K2Cr2O7, K2FeO4, NaBiO3, K2MnO4 and NaClO; the amount ratio of the additive to the nickel-cobalt-manganese ternary material is (0-0.10):1, preferably (0.01-0.10):1.

[0015] Preferably, the nickel-cobalt-manganese ternary material is dispersed into the ammoniolysis solution to obtain a nickel-cobalt-manganese ternary material mixed solution; the solid content of the nickel-cobalt-manganese ternary material in the nickel-cobalt-manganese ternary material mixed solution is 2wt% to 20wt%; and the dispersion method is one of ultrasonic dispersion, magnetic stirring, and mechanical stirring.

[0016] Preferably, the ammonolysis temperature of the ammonolysis reaction is 20-100° C., and the time is 0.5 h to 36 h; preferably, stirring is performed during the ammonolysis reaction.

[0017] Preferably, the drying is vacuum drying, the drying temperature is 60-120° C., and the drying time is 24-48 hours.

[0018] Preferably, the heat treatment temperature is 600-800° C., the heat treatment time is 2-10 hours, and the heat treatment atmosphere is pure oxygen or air.

[0019] Preferably, the nickel-cobalt-manganese ternary material with a manganese-rich shell structure is mixed with a lithium-containing oxide and then sintered. The lithium-containing oxide material includes LiOH·H2O, LiNO3, Li2CO3, Li2O and Li2O 2中 At least one; the molar ratio of the nickel-cobalt-manganese ternary material of the manganese-rich shell structure to the lithium-containing oxide is 1: (1.01 to 1.10).

[0020] Preferably, the sintering process includes: a one-step sintering process or a two-step sintering process;

[0021] The sintering temperature of the one-step sintering process is 600-850°C, the holding time is 10h-20h, and the atmosphere is pure oxygen or air; preferably, the heating rate of the one-step sintering process is 2-5°C / min;

[0022] The two-step sintering process includes: the first step is sintering at a temperature of 300-500°C and a holding time of 2h-4h; the second step is sintering at a temperature of 700-850°C and a holding time of 10h-20h; the atmosphere is pure oxygen or air; preferably, the heating rate of the two-step sintering process is 2-5°C / min.

[0023] On the other hand, the present invention provides a surface-modified nickel-cobalt-manganese ternary material prepared according to the above-mentioned surface modification method.

[0024] In another aspect, the present invention provides a lithium-ion battery comprising: the surface-modified nickel-cobalt-manganese ternary material as a positive electrode material, a negative electrode material, and a separator or solid electrolyte for separating the positive electrode material and the negative electrode material.

[0025] Preferably, the separator or solid electrolyte includes: PP, celgard, garnet-type solid electrolyte, NASICON-type solid electrolyte, sulfide solid electrolyte or perovskite-type solid electrolyte.

[0026] Preferably, the negative electrode is graphite, silicon carbon, silicon dioxide, silicon alloy, tin oxide, metallic lithium or lithium alloy.

[0027] Compared with the prior art, the present invention has achieved the following technical effects:

[0028] The basic principle of this invention is that the three metal ions of nickel, cobalt and manganese form a coordination compound with ammonia, causing the nickel-cobalt-manganese ternary material to slowly dissolve in the ammonia, resulting in an ammonolysis reaction. Taking advantage of the fact that nickel ions have a much stronger ability to form coordination compounds with ammonia than cobalt and manganese ions, the nickel ions in the nickel-cobalt-manganese ternary material dissolve easily in the ammonia, while the cobalt and manganese ions redeposit on the surface of the nickel-cobalt-manganese ternary material particles, thereby forming a manganese-rich shell on the material particles.

[0029] In addition, by utilizing the basic principle of this ammonolysis reaction and adding additives to the ammonia-nickel-cobalt-manganese ternary material system, the redox reaction between the additive with oxidizing ability and the nickel, cobalt, and manganese metal ions can be promoted, so that the redox reaction is not limited to the surface of the precursor particles, allowing the redox reaction to proceed completely. The insoluble reaction products of the redox reaction will be deposited on the surface of the precursor particles, thereby making full use of the oxidant for coating. By in situ construction of the manganese-rich shell layer, the cycle stability and rate performance of the nickel-cobalt-manganese ternary material can be effectively improved.

[0030] In summary, this method for constructing a manganese-rich shell results in high surface ionic conductivity for the cathode material, resulting in excellent cycling and rate performance. This method is highly practical, employs inexpensive raw materials, is easy to operate, and is readily scalable, demonstrating strong industrial application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is an X-ray diffraction (XRD) pattern of the positive electrode material, including Example 1 and Example 2 that have undergone aminolysis and Comparative Example 1 that has not undergone surface modification;

[0032] Figure 2Table 1 shows the nickel-cobalt-manganese component ratios obtained by ICP-OES testing of the materials, including the nickel-cobalt-manganese positive electrode precursor powder of Comparative Example 1, the nickel-cobalt-manganese positive electrode precursor powder after ammonolysis of Example 1, the supernatant after ammonolysis of Example 1, and the nickel-cobalt-manganese positive electrode precursor powder of Example 2;

[0033] Figure 3A 、 3B 3A and 3C are dQ / dV curves of the positive electrode materials at different cycle numbers, including Example 1 (3A) and Example 2 (3B) modified by aminolysis and Comparative Example 1 (3C) without surface modification;

[0034] Figure 4A-4B This is a comparison chart of the cycling stability of positive electrode materials, including Examples 1, 2, and 3 modified by ammoniolysis, and Comparative Example 1, which has not been surface-modified. The present invention was explored at different concentrations. Example 3 is an example with 2% additive, while Comparative Example 2 is a comparative example with 2% additive but without ammoniolysis. A comparison of the cycling performance of Example 3 and Comparative Example 2 is attached.

[0035] Figure 5 1 is a rate comparison chart of positive electrode materials, including Example 1, Example 2, Example 3 modified by aminolysis, and Comparative Example 1 without surface modification;

[0036] Figure 6 The scanning electron micrographs (SEM) of the cross sections of the positive electrode particles of the positive electrode materials before and after cycling include Example 1 and Example 2 modified by aminolysis and Comparative Example 1 without surface modification. DETAILED DESCRIPTION

[0037] The present invention is further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0038] In the present disclosure, based on the innovative difference in the effects of different metal ions and ligands, ammonia water is used as a ligand, and the three metal ions of nickel, cobalt and manganese and ammonia water are used to form a coordination compound, so that the nickel-cobalt-manganese ternary material is slowly dissolved in ammonia water, and an ammonialysis reaction occurs. By performing surface modification on the lithium-ion positive electrode material, its electrochemical performance and safety are improved, and the modification cost is reduced. The method is easy to operate, simple in principle, and easy to scale up production. The basic principle of ammonialysis is that nickel, cobalt, and manganese metal ions have different abilities to form coordination compounds with ammonia water. Taking K stability as the standard of measurement, for the three metal ions of nickel, cobalt, and manganese, the ability of nickel ions to form coordination compounds with ammonia water is much stronger than that of cobalt and manganese, while manganese hardly forms coordination compounds with ammonia water. Take the ammonialysis of the precursor as an example:

[0039]

[0040] Therefore, nickel can be dissolved through the ammonolysis reaction, while manganese and cobalt will be redeposited on the surface of the particles, thereby building a manganese-rich layer on the surface. The specific results are shown in the attached figure. Figure 2 More specifically, in order to better understand the present invention, the present invention is further described in detail below with reference to specific embodiments.

[0041] Prepare an ammonolysis solution. The ingredients of the ammonolysis solution are restricted. The ammonolysis agent cannot react directly with the additives. The additives should be able to react with one or more of the nickel, cobalt, and manganese metal ions produced by ammonolysis or form a precipitate. The concentration of the ammonolysis agent should not be too low, otherwise the ammonolysis reaction will not be sufficient. The performance changes of the nickel-cobalt-manganese ternary material under different ammonolysis agent concentrations have not been explored. The ammonolysis solution can be a mixture of an ammonolysis agent and additives. The ammonolysis agent is an ammonia solution, and the mass fraction of ammonia can be 5-25%. The additives include one or more of H2O, KMnO4, H2O2, K2Cr2O7, K2FeO4, NaBiO3, K2MnO4, and NaClO. The ratio of the amount of the additive to the amount of the nickel-cobalt-manganese ternary precursor can be 0.01-0.10:1. The role of the additive is to accelerate the formation of the manganese-rich shell and supplement the additional elements. The additive should be able to react with one or more of the nickel, cobalt, and manganese metal ions produced by ammonia decomposition or form a precipitate. For a complete reaction, the amount of the additive can be controlled. Ammonolysis can also be carried out using only ammonia water, with specific results shown in Example 1. Taking KMnO4 as an additive as an example:

[0042] KMnO4 manganese supplementation process:

[0043] Precursor surface:

[0044] M(OH)2+KMnO4→MOOH+MnO2↓

[0045] Metal ions (Ni and Co) released by ammoniation:

[0046] M 2+ +KMnO4→M 3+ +MnO2↓;

[0047] M 3+ +NH3→[M(NH3)6] 3+

[0048] Different forms of manganese ions in ammonia water:

[0049] Mn(+2):Mn(OH)2↓;Mn(+4):MnO2↓

[0050] The metal ions are released through an ammonolysis reaction, and the resulting precipitate from the redox reaction between the metal ions and the additive KMnO4 is deposited on the particle surface, completing the construction of a manganese-rich layer. Modification effects can be achieved even without the addition of additional additives, as shown in Example 1. Other additives serve to supplement or introduce additional elements, such as KMnO4 for additional manganese and K2Cr2O7 for the introduction of chromium.

[0051] The nickel-cobalt-manganese ternary material is dispersed in the ammonium solution to obtain a nickel-cobalt-manganese ternary material mixture. The nickel-cobalt-manganese ternary material includes a nickel-cobalt-manganese ternary positive electrode material and a nickel-cobalt-manganese ternary positive electrode precursor material. The particle size of the nickel-cobalt-manganese ternary material is 1 to 100 μm. Specifically, the nickel-cobalt-manganese ternary positive electrode material is nickel-cobalt-manganese (NCM), and the chemical formula can be expressed as LiNi b Co c Mn 1-b-c O2 (0<b<1, 0<c<1). Specifically, the nickel-cobalt-manganese ternary positive electrode precursor

[0052] The main material is nickel cobalt manganese (NCM (OH) 2), and the chemical formula can be expressed as Ni (1-y-z) Co y Mn z (OH)2(0<y<1, 0<z<1). The solid content of the nickel-cobalt-manganese ternary material mixture can be 2wt%-20wt%. The nickel-cobalt-manganese ternary material can be dispersed by ultrasonic dispersion, and the ultrasonic time is 1-180 minutes.

[0053] Stirring is started, and the nickel-cobalt-manganese ternary material mixture is subjected to an ammonolysis reaction, separated (e.g., centrifuged), and dried to obtain a nickel-cobalt-manganese ternary material with a manganese-rich shell structure. The solvent of the ammonolysis agent is at least one of distilled water, methanol, ethanol, isopropanol, n-butanol, isobutanol, cycloethanol, acetone, cyclohexanone, glycerol, and ethyl acetate, or a combination thereof. The ammonolysis reaction time is 0.5h to 36h, and the temperature is 20 to 100°C. The centrifugal speed can be 1000 to 8000rpm, and the centrifugal time can be 3 to 5min. Drying can be oven drying, natural drying, or vacuum drying. Preferably, the drying temperature is 20 to 150°C, and the drying time is 24 to 48h.

[0054] Optionally, the nickel-cobalt-manganese ternary material with a manganese-rich shell structure is directly heat-treated to obtain a surface-modified nickel-cobalt-manganese ternary material. The heat treatment temperature can be 600-800°C, the heat treatment time can be 2-10h, and the heat treatment atmosphere is pure oxygen or air. The heat treatment, for the nickel-cobalt-manganese ternary positive electrode material, is an annealing treatment so that the material maintains a layered structure. For the nickel-cobalt-manganese ternary precursor material, it is a solid-phase reaction, which causes the nickel-cobalt-manganese ternary precursor material and the lithium source to undergo a solid-phase reaction at high temperature to generate a layered nickel-cobalt-manganese ternary positive electrode material.

[0055] Optionally, a nickel-cobalt-manganese ternary material with a manganese-rich shell structure is used as a precursor material and a lithium-containing compound (for example, LiOH·H2O) is fully mixed in a molar ratio of 1:x, and then sintered in a pure oxygen atmosphere to obtain an active material. Wherein x is 1.01 to 1.10. The lithium oxide-containing material includes at least one of LiOH·H2O, LiNO3, Li2CO3, Li2O, and Li2O2, or a combination thereof. Specifically, the nickel-cobalt-manganese ternary precursor material and a lithium source are subjected to a high-temperature solid-phase reaction under a high-temperature oxygen atmosphere, the nickel-cobalt-manganese precursor material is dehydrated, and after lithium is inserted, it is converted into a layered nickel-cobalt-manganese ternary positive electrode material, and at the same time, a manganese-rich shell is coated on the surface of the material and doped with corresponding elements.

[0056] More preferably, the sintering process includes one-step sintering and two-step sintering. The one-step sintering process has a sintering temperature of 700-850°C, a holding time of 10-20 hours, and a heating rate of 2-5°C / min. The two-step sintering process has a first sintering temperature of 300-500°C, a holding time of 2-4 hours, and a second sintering temperature of 700-850°C, a holding time of 10-20 hours, and a heating rate of 2-5°C / min. The sintering atmosphere is pure oxygen or air.

[0057] The lithium-ion battery of the present invention comprises: a positive electrode, a negative electrode and a separator or solid electrolyte for separating the positive and negative electrode materials. The positive electrode material of the battery is the positive electrode material based on the surface modification of the ion exchange membrane described in the present invention.

[0058] Specifically, the separator or solid electrolyte includes PP, Celgard, garnet-type solid electrolyte, NASICON-type solid electrolyte, sulfide solid electrolyte, perovskite-type solid electrolyte. The negative electrode is graphite, silicon carbon, silicon dioxide, silicon alloy, tin oxide, metallic lithium or lithium alloy.

[0059] Specifically, the surface-modified positive electrode material is uniformly mixed with conductive carbon and a binder to form a slurry, which is then coated onto aluminum foil. A cutting machine is then used to cut the dried slurry-loaded aluminum foil into the desired size for use as the positive electrode. This complete battery is then assembled and tested.

[0060] The following examples are further given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values exemplified below.

[0061] Example 1

[0062] Step 1): preparing a 25% by mass ammonia solution as an ammonolysis solution;

[0063] Step 2): Take another 4g of nickel-cobalt-manganese ternary positive electrode precursor material (Ni 0.83 Co 0.12 Mn 0.05 (OH)2) is mixed with the ammonium solution of step 1) to prepare a precursor mixture according to a solid content of 5%, and ultrasonically dispersed for 10 minutes;

[0064] Step 3): Stir the precursor mixture obtained in step 2) and the nickel-cobalt-manganese ternary positive electrode precursor material in situ to construct a manganese-rich shell. The reaction time is 3 hours and the reaction temperature is 25°C. After the reaction time is over, the precursor mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugal time of 3 minutes. The solid material obtained by centrifugation is dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. A nickel-cobalt-manganese ternary material with a manganese-rich shell structure is obtained;

[0065] Step 4): The ternary precursor material constructed with the manganese-rich shell obtained in step 3) was thoroughly mixed with LiOH·H2O at a molar ratio of 1:1.05 by ball milling. The mixture was then sintered in two steps under a pure oxygen atmosphere: the first step at 400°C for 2 hours and the second step at 750°C for 12 hours. The heating rate was 3°C / min. The active material was obtained.

[0066] The obtained active material was prepared into electrodes and button batteries were assembled. Assembly and testing of CR2025 button batteries: NCM ternary positive electrode material (the final product prepared in the embodiment or comparative example), conductive carbon (Super P:VGCF=1:1), and polyvinylidene fluoride (PVDF) were made into a slurry in a mass ratio of 8:1:1 and coated on aluminum foil. The dried aluminum foil loaded with the slurry was cut into small discs with a diameter of 1.2 cm using a cutting machine as the positive electrode. Metal lithium sheet was used as the negative electrode, Celgard was used as the separator, and 1M carbonate solution was used as the electrolyte (wherein the solvent was a mixed solution of ethylene carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) in a volume ratio of 1:1:1, and the solute was LiPF6). CR2025 button batteries were assembled in an argon glove box.

[0067] Example 2

[0068] Step 1): Prepare a 25% ammonia solution and add 0.21g of KMnO4 as an additive to the ammonia solution to prepare an ammonium solution;

[0069] Step 2): Take another 4g of nickel-cobalt-manganese ternary positive electrode precursor material (Ni 0.83 Co 0.12 Mn 0.05 (OH)2) is mixed with the ammonia solution of step 1), the amount of KMnO4 is 3% of the nickel-cobalt-manganese ternary positive electrode precursor material, and a precursor mixture is prepared according to a solid content of 5%, and ultrasonically dispersed for 10 minutes;

[0070] Step 3): Stir the precursor mixture obtained in step 2) and the nickel-cobalt-manganese ternary positive electrode precursor material in situ to construct a manganese-rich shell. The reaction time is 1.5 hours and the reaction temperature is 25°C. After the reaction time is over, the precursor mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugal time of 3 minutes. The solid material obtained by centrifugation is dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. A nickel-cobalt-manganese ternary material with a manganese-rich shell structure is obtained;

[0071] Step 4): The ternary precursor material constructed with the manganese-rich shell obtained in step 3) was thoroughly mixed with LiOH·H2O at a molar ratio of 1:1.05 by ball milling. The mixture was then sintered in two steps under a pure oxygen atmosphere: the first step at 400°C for 2 hours and the second step at 750°C for 12 hours. The heating rate was 3°C / min. The active material was obtained.

[0072] The active material obtained in Example 2 was prepared into electrodes and button batteries were assembled, following the same process as in Example 1.

[0073] Example 3

[0074] Step 1): Prepare a 25% ammonia solution and add 0.14g of KMnO4 as an additive to the ammonia solution to prepare an ammonium solution;

[0075] Step 2): Take another 4g of nickel-cobalt-manganese ternary positive electrode precursor material (Ni 0.83 Co 0.12 Mn 0.05 (OH)2) is mixed with the ammonia solution of step 1), the amount of KMnO4 is 2% of the nickel-cobalt-manganese ternary positive electrode precursor material, and a precursor mixture is prepared according to a solid content of 5%, and ultrasonic dispersion is performed for 10 minutes;

[0076] Step 3): Stir the precursor mixture obtained in step 2) and the nickel-cobalt-manganese ternary positive electrode precursor material in situ to construct a manganese-rich shell. The reaction time is 1.5 hours and the reaction temperature is 25°C. After the reaction time is over, the precursor mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugal time of 3 minutes. The solid material obtained by centrifugation is dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. A nickel-cobalt-manganese ternary material with a manganese-rich shell structure is obtained;

[0077] Step 4): The ternary precursor material constructed with the manganese-rich shell obtained in step 3) was thoroughly mixed with LiOH·H2O at a molar ratio of 1:1.05 by ball milling. The mixture was then sintered in two steps under a pure oxygen atmosphere: the first step at 400°C for 2 hours and the second step at 750°C for 12 hours. The heating rate was 3°C / min. The active material was obtained.

[0078] The active material obtained in Example 3 was prepared into electrodes and button cells were assembled, following the same process as in Example 1.

[0079] Example 4

[0080] Step 1): Prepare a 25% ammonia solution and add 0.26g of K2Cr2O7 as an additive to the ammonia solution to prepare an ammonium solution;

[0081] Step 2): Take another 4g of nickel-cobalt-manganese ternary positive electrode precursor material (Ni 0.83 Co 0.12 Mn 0.05 (OH)2) is mixed with the ammonia solution of step 1), the amount of K2Cr2O7 is 2% of the nickel-cobalt-manganese ternary positive electrode precursor material, and a precursor mixture is prepared according to a solid content of 5%, and ultrasonically dispersed for 10 minutes;

[0082] Step 3): Stir the precursor mixture obtained in step 2) and the nickel-cobalt-manganese ternary positive electrode precursor material in situ to construct a manganese-rich shell. The reaction time is 1.5 hours and the reaction temperature is 25°C. After the reaction time is over, the precursor mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugal time of 3 minutes. The solid material obtained by centrifugation is dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. A nickel-cobalt-manganese ternary material with a manganese-rich shell structure is obtained;

[0083] Step 4): The ternary precursor material constructed with the manganese-rich shell obtained in step 3) was thoroughly mixed with LiOH·H2O at a molar ratio of 1:1.05 by ball milling. The mixture was then sintered in two steps under a pure oxygen atmosphere: the first step at 400°C for 2 hours, and the second step at 750°C for 12 hours. The heating rate was 3°C / min. This yielded the active material.

[0084] The active material obtained in Example 4 was prepared into electrodes and button cells were assembled, following the same process as in Example 1.

[0085] Comparative Example 1

[0086] Nickel-cobalt-manganese ternary precursor material (Ni 0.83 Co 0.12 Mn 0.05 (OH)2) and LiOH·H2O were thoroughly mixed by ball milling at a molar ratio of 1:1.05. The mixture was then sintered in two steps under a pure oxygen atmosphere: the first step at 400°C for 2 hours; the second step at 750°C for 12 hours. The heating rate was 3°C / min. The active material obtained in Comparative Example 1 was used to prepare electrodes and assemble button cells. The process was the same as in Example 1.

[0087] Comparative Example 2

[0088] Step 1): Prepare an aqueous solution and add 0.14 g of KMnO4 as an additive to the aqueous solution to prepare a solution;

[0089] Step 2): Take another 4g of nickel-cobalt-manganese ternary positive electrode precursor material (Ni 0.83 Co 0.12 Mn 0.05 (OH)2) is mixed with the solution of step 1), the amount of KMnO4 is 2% of the nickel-cobalt-manganese ternary positive electrode precursor material, and a precursor mixture is prepared according to a solid content of 5%, and ultrasonically dispersed for 10 minutes;

[0090] Step 3): Stir the precursor mixture obtained in step 2) and the nickel-cobalt-manganese ternary positive electrode precursor material in situ to construct a manganese-rich shell. The reaction time is 1.5 hours and the reaction temperature is 25°C. After the reaction time is over, the precursor mixture is centrifuged at a centrifugal speed of 3000 rpm and a centrifugal time of 3 minutes. The solid material obtained by centrifugation is dried in a vacuum oven at a drying temperature of 80°C and a drying time of 24 hours. The nickel-cobalt-manganese ternary material is obtained;

[0091] Step 4): The ternary precursor material obtained in step 3) was thoroughly mixed with LiOH·H2O at a molar ratio of 1:1.05 by ball milling. The mixture was then sintered in two steps under a pure oxygen atmosphere: the first step at 400°C for 2 hours, and the second step at 750°C for 12 hours. The heating rate was 3°C / min. The active material was obtained.

[0092] The active material obtained in Comparative Example 2 was prepared into electrodes and button batteries were assembled in the same process as in Example 1.

[0093] Figure 1 The X-ray diffraction (XRD) diagram of the positive electrode is shown. The positive electrode materials include Example 1 which has been surface-modified by an ammonolysis reaction and Comparative Example 1 which has not been surface-modified. All diffraction peaks match well with the typical hexagonal a-NaFeO2 structure (JCPDF card number 01-089-4533, space group R-3m), which represents the main phase of the nickel-cobalt-manganese ternary positive electrode material. The a-NaFeO2 type crystal structure is an ordered rock salt type, with Li and Me ions occupying alternating (111) layers. The nickel-cobalt-manganese ternary positive electrode material has a layered NaFeO2 structure, R-3m space group, with alternating layers formed by LiO6 and MO6 octahedra. From Figure 1 It can be seen that the main diffraction peaks of all samples match well with the JCPDF card with the R-3m space group, indicating that the surface modification by the aminolysis reaction does not change the layered structure of the nickel-cobalt-manganese ternary cathode material.

[0094] Figure 2 The ICP-OES test of the material shows the component ratios obtained. The materials include the nickel-cobalt-manganese ternary positive electrode precursor powder of Comparative Example 1, the nickel-cobalt-manganese ternary positive electrode precursor powder after ammonolysis of Example 1, the supernatant after ammonolysis of Example 1, and the nickel-cobalt-manganese ternary positive electrode precursor powder after ammonolysis and manganese supplementation of Example 2. The test results show that after the ammonolysis reaction, the nickel-cobalt-manganese ternary positive electrode precursor powder of Comparative Example 1, the nickel-cobalt-manganese ternary positive electrode precursor powder after ammonolysis of Example 1, and the nickel-cobalt-manganese ternary positive electrode precursor powder after ammonolysis and manganese supplementation of Example 2 have different components. In Comparative Example 1, the relative ratio of cobalt and manganese in the component of Example 1 remains unchanged, the nickel content decreases, and the manganese content in the component of Example 2 increases significantly. Comparing the nickel-cobalt-manganese ternary positive electrode precursor powder component before ammonolysis and the supernatant after ammonolysis, the ratio of nickel, cobalt and manganese ions in the two undergoes a significant change, with very little cobalt and manganese present in the supernatant. This indicates that after the ammonolysis reaction, nickel is dissolved, while manganese and cobalt remain in the precursor. At the same time, test results show that manganese was successfully added to the precursor through the ammoniolysis-based manganese supplementation strategy, indicating that the surface modification method of nickel-cobalt-manganese ternary cathode materials based on the ammoniolysis reaction can successfully achieve manganese enrichment of the material.

[0095] Figure 3A-3CThe dQ / dV curves of the positive electrode materials at different cycle numbers are shown, and the materials include Example 1 and Example 2 modified by ammonia solution and Comparative Example 1 without surface modification. The dQ / dV curve shows that after cycling, the peak position of the dQ / dV curve of Comparative Example 1 has undergone severe displacement, and the charging peak has moved to the right, indicating that the material has undergone severe polarization during the cycling process; the phase change peak H3-H3 at high voltage has gradually disappeared, indicating that the high-voltage positive electrode material has undergone severe phase change. In contrast, the peak positions of Example 1 and Example 2 have not undergone significant displacement, indicating that the polarization and phase change of the positive electrode material during the cycling process are relatively small. It fully demonstrates that the surface modification method of nickel-cobalt-manganese ternary positive electrode material based on ammonia solution reaction is beneficial to inhibiting the polarization and phase change of the positive electrode material during the cycling process.

[0096] Figures 4A-4B This figure shows a comparison of the cycling stability of cathode materials, including Examples 1, 2, and 3, which underwent ammonolysis modification, and Comparative Examples 1 and 2, which did not undergo ammonolysis modification. The electrochemical cycling test results show that the ammonolysis-based surface modification significantly improves the cycling stability of the resulting cathode materials. This fully demonstrates that the ammonolysis-based surface modification method for nickel-cobalt-manganese ternary materials can improve the stability of cathode materials.

[0097] Figure 5 A comparison chart showing the rate performance of positive electrode materials, including Examples 1, 2, and 3 modified by ammonolysis, and the unmodified Comparative Example 1. The results demonstrate that the rate performance of the nickel-cobalt-manganese ternary positive electrode material, surface-modified by the ammonolysis reaction, is significantly improved, enabling greater capacity release at high rates.

[0098] Figure 6 SEM images of the cross-section of the positive electrode particles before and after the positive electrode material is cycled are shown, and the materials include Example 2 modified by ammoniolysis and Comparative Example 1 that is not modified. The results show that Example 1, Example 2 and Comparative Example 1 are all secondary particles formed by the agglomeration of primary particles. The primary particles are tightly bound before the cycle, and there are no obvious cracks between the secondary particles. After 150 cycles at a rate of 1C, both Example 1 and Example 2 maintained a complete spherical secondary particle morphology, while the positive electrode particles of Comparative Example 1 were obviously broken. This shows that the surface modification method of nickel-cobalt-manganese ternary positive electrode material based on ammoniolysis reaction can inhibit the particle breakage of the positive electrode material during the cycle process.

[0099] The above results fully demonstrate the effectiveness of the surface modification method of nickel-cobalt-manganese ternary materials based on ammonolysis reaction, which can effectively improve the cycle stability and rate performance of nickel-cobalt-manganese ternary positive electrode materials.

[0100] The above embodiments are merely preferred embodiments for the purpose of fully illustrating the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

Claims

1. A surface modification method of nickel-cobalt-manganese ternary material based on ammonolysis reaction, characterized in that: It consists of the following steps: (1) Dispersing a nickel-cobalt-manganese ternary material into an ammonolysis solution, in situ constructing a manganese-rich layer on the surface of the nickel-cobalt-manganese ternary material after an ammonolysis reaction, and then separating and drying to obtain a nickel-cobalt-manganese ternary material with a manganese-rich shell structure; the ammonolysis solution is an ammonolysis agent; the ammonolysis agent is an ammonia solution, and the mass fraction of ammonia in the ammonia solution is 5% to 25wt%; the solvent of the ammonolysis agent is distilled water; the ammonolysis solution also contains an additive, and the additive is selected from one of KMnO4, H2O2, K2Cr2O7, K2FeO4, NaBiO3, K2MnO4 and NaClO; wherein the nickel-cobalt-manganese ternary material includes a nickel-cobalt-manganese ternary positive electrode material or / and a nickel-cobalt-manganese ternary positive electrode precursor material; the composition of the nickel-cobalt-manganese ternary positive electrode material is LiNi b Co c Mn 1-b-c O2, wherein 0<b<1, 0<c<1; the composition of the nickel-cobalt-manganese ternary positive electrode precursor material is Ni 1-y-z Co y Mn z (OH)2, where 0 <y<1,0<z<1; (2) The obtained nickel-cobalt-manganese ternary material with a manganese-rich shell structure is subjected to heat treatment to obtain a surface-modified nickel-cobalt-manganese ternary material.

2. The surface modification method according to claim 1, characterized in that The particle size of the nickel-cobalt-manganese positive electrode material is 1 to 100 μm.

3. The surface modification method according to claim 1, wherein The molar ratio of the additive to the nickel-cobalt-manganese ternary material is (0.01-0.10):

1.

4. The surface modification method according to claim 1, wherein The nickel-cobalt-manganese ternary material is dispersed into an ammonia solution to obtain a nickel-cobalt-manganese ternary material mixed solution; the solid content of the nickel-cobalt-manganese ternary material in the nickel-cobalt-manganese ternary material mixed solution is 2wt% to 20wt%; and the dispersion method is one of ultrasonic dispersion, magnetic stirring, and mechanical stirring.

5. The surface modification method according to claim 1, wherein The ammonolysis reaction temperature is 20-100° C., and the time is 0.5 h to 36 h. The drying is vacuum drying, and the drying temperature is 60-120° C., and the drying time is 24-48 h.

6. The surface modification method according to claim 1, characterized in that Stirring is performed during the aminolysis reaction.

7. The surface modification method according to claim 1, characterized in that The heat treatment temperature is 600-800° C., the heat treatment time is 2-10 hours, and the heat treatment atmosphere is pure oxygen or air.

8. The surface modification method according to claim 1, wherein When the nickel-cobalt-manganese ternary material is a nickel-cobalt-manganese ternary precursor material, the nickel-cobalt-manganese ternary material with a manganese-rich shell structure and a lithium-containing oxide are mixed and sintered to obtain a surface-modified nickel-cobalt-manganese ternary material; The lithium-containing oxide material includes at least one of LiOH·H2O, LiNO3, Li2CO3, Li2O and Li2O2; the molar ratio of the nickel-cobalt-manganese ternary material with a manganese-rich shell structure to the lithium-containing oxide is 1:(1.01-1.10).

9. The surface modification method according to claim 8, characterized in that The sintering process includes: a one-step sintering process or a two-step sintering process; The sintering temperature of the one-step sintering process is 600-850°C, the holding time is 10h-20h, and the atmosphere is pure oxygen or air; The two-step sintering process includes: the first step is sintering at a temperature of 300-500° C. and a holding time of 2-4 hours; the second step is sintering at a temperature of 700-850° C. and a holding time of 10-20 hours; the atmosphere is pure oxygen or air.

10. The surface modification method according to claim 9, characterized in that The heating rate of the one-step sintering process is 2-5°C / min; the heating rate of the two-step sintering process is 2-5°C / min.

11. A surface-modified nickel-cobalt-manganese ternary material prepared by the surface modification method according to any one of claims 1 to 10.

12. A lithium ion battery, characterized in that: include: The surface-modified nickel-cobalt-manganese ternary material according to claim 11 is used as a positive electrode material, a negative electrode material, and a diaphragm or solid electrolyte for separating the positive electrode material and the negative electrode material.

13. The lithium-ion battery according to claim 12, wherein: The separator or solid electrolyte includes: PP, celgard, garnet solid electrolyte, NASICON solid electrolyte, sulfide solid electrolyte or perovskite solid electrolyte.

14. The lithium-ion battery according to claim 12, wherein: The negative electrode is graphite, silicon carbon, silicon dioxide, silicon alloy, tin oxide, metallic lithium or lithium alloy.

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