Preparation method of positive electrode material for improving cycle stability of lithium ion battery, positive electrode material, positive electrode sheet and lithium ion battery

Abstract

The application provides a preparation method of a positive electrode material for improving cycle stability of a lithium ion battery, a positive electrode material, a positive electrode sheet and the lithium ion battery. a X b Y c CO3 or Ni a X b Y c (OH)2, X is at least one of Al, Co and Mn, Y is at least one of Al, Co and Mn, X is different from Y, a+b+c=1, 1 / 3<=a<1, 0 q P p Q is one of metal elements, P is B element, 1 / 3<=p:q<=6; the precursor, a lithium salt and a modifier are mixed to obtain a mixture; the mixture is subjected to sintering treatment in an oxygen-containing atmosphere to obtain the positive electrode material, the positive electrode material comprises a doped ternary material and a coating layer coated on the surface of the doped ternary material, the structure formula of the doped ternary material is LiNi a‑ q Q q X b Y c O2, the structure formula of the coating layer is Li e P p O o , and e+3p=2o. The preparation method provided by the application not only simplifies the process flow, but also reduces energy consumption and production cost of the positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and in particular to a preparation method of a positive electrode material for improving the cycle stability of a lithium ion battery, the positive electrode material, a positive electrode sheet and the lithium ion battery. BACKGROUND

[0002] At present, lithium ion batteries have become the most promising power batteries due to their good performance and low cost. Among them, ternary positive electrode materials have the advantages of high specific capacity, good cycle performance, stable structure and low cost, and have become a hot research topic among current scholars.

[0003] However, the existing ternary positive electrode materials have the disadvantages of poor structural stability and poor safety, thereby limiting the commercial application of ternary positive electrode materials and ternary positive electrode lithium ion batteries. SUMMARY

[0004] Therefore, the present application provides a preparation method of a positive electrode material for improving the cycle stability of a lithium ion battery, the positive electrode material, a positive electrode sheet and the lithium ion battery.

[0005] To achieve the above-mentioned purpose, the present application provides a preparation method of a positive electrode material for improving the cycle stability of a lithium ion battery, which comprises: providing a precursor, a lithium salt and a modifier, the structural formula of the precursor is at least one of Ni a X b Y c CO3 or Ni a X b Y c (OH)2, X is at least one of Al, Co and Mn, Y is at least one of Al, Co and Mn, X is different from Y, a+b+c=1, 1 / 3≤a<1, 0<b≤1 / 3, 0<c≤1 / 3, the structural formula of the modifier is Q q P p , Q is a metal element, P is one of B and N elements, 1 / 3≤p:q≤6;

[0006] Mixing the precursor, the lithium salt and the modifier to obtain a mixture;

[0007] Performing sintering treatment on the mixture in an oxygen-containing atmosphere to obtain a positive electrode material, the positive electrode material comprises a doped ternary material and a coating layer coated on the surface of the doped ternary material, the structural formula of the doped ternary material is LiNi a-q Q q X b Y c O2, the structural formula of the coating layer is Li e P p O oe+3p=2o.

[0008] In some possible implementations, the modifier is at least one of aluminum diboride, magnesium diboride, titanium diboride, chromium diboride, calcium hexaboride, lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, tantalum nitride, or tungsten nitride.

[0009] In some possible implementations, in the mixture, the proportion of the modifier is 0.5-5 wt.%.

[0010] In some possible implementations, the precursor is Ni 1 / 3 Co 1 / 3 Mn 1 / 3 (OH)2, Ni 0.5 Co 0.2 Mn 0.3 (OH)2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.83 Co 0.07 Mn 0.1 (OH)2, Ni 0.9 Co 0.05 Mn 0.05 (OH)2, Ni 0.94 Co 0.03 Mn 0.03 (OH)2, Ni 0.96 Co 0.02 Mn 0.02 (OH)2, Ni 1 / 3 Co 1 / 3 Al 1 / 3 (OH)2, Ni 0.5 Co 0.2 Al 0.3 (OH)2, Ni 0.6 Co 0.2 Al 0.2 (OH)2, Ni 0.8 Co 0.1 Al 0.1 (OH)2, Ni 0.83 Co 0.07 Al 0.1 (OH)2, Ni 0.9 Co 0.05 Al 0.05 (OH)2, Ni 0.94 Co 0.03 Al 0.03 (OH)2, Ni 0.96 Co0.02 Al 0.02 (OH)2, Ni 1 / 3 Co 1 / 3 Mn 1 / 3 CO3, Ni 0.5 Co 0.2 Mn 0.3 CO3, Ni 0.6 Co 0.2 Mn 0.2 CO3, Ni 0.8 Co 0.1 Mn 0.1 CO3, Ni 0.83 Co 0.07 Mn 0.1 CO3, Ni 0.9 Co 0.05 Mn 0.05 CO3, Ni 0.94 Co 0.03 Mn 0.03 CO3, Ni 0.96 Co 0.02 Mn 0.02 CO3, Ni 1 / 3 Co 1 / 3 Al 1 / 3 CO3, Ni 0.5 Co 0.2 Al 0.3 CO3, Ni 0.6 Co 0.2 Al 0.2 CO3, Ni 0.8 Co 0.1 Al 0.1 CO3, Ni 0.83 Co 0.07 Al 0.1 CO3, Ni 0.9 Co 0.05 Al 0.05 CO3, Ni 0.94 Co 0.03 Al 0.03 CO3, Ni 0.96 Co 0.02 Al 0.02 at least one of CO3.

[0011] In some possible implementations, a molar ratio of the lithium salt to the precursor is 1.0-1.1:1; the lithium salt is at least one of lithium nitrate, lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium acetate, or lithium bromide.

[0012] In some possible implementations, a thickness of the coating layer is 1-50 nm, and a particle size of the doped ternary material is 5-20 µm.

[0013] In some possible implementation manners, the oxygen-containing atmosphere is oxygen or air, and the sintering treatment is performed at a temperature of 500-1000°C for 4-20 hours.

[0014] The application further provides a positive electrode material, which comprises a doped ternary material and a coating layer coated on the surface of the doped ternary material, wherein the doped ternary material has a structural formula of LiNi a-q Q q X b Y c O2, and the coating layer has a structural formula of Li e P p O o X is at least one of Al, Co and Mn, Y is at least one of Al, Co and Mn, X is different from Y, a+b+c=1, 1 / 3≤a<1, 0

[0015] The application further provides a positive electrode sheet, which comprises a conductive agent, a binder and the positive electrode sheet.

[0016] The application further provides a lithium ion battery, which comprises the positive electrode sheet.

[0017] In the application, the mixture is subjected to sintering treatment in an oxygen-containing atmosphere to obtain the positive electrode material. The preparation method provided by the application only adopts one sintering process, reduces multiple steps such as pre-sintering, secondary sintering and pretreatment (such as grinding) before pre-sintering or secondary sintering, simplifies the process flow, reduces energy consumption and lowers the production cost of the positive electrode material. Meanwhile, the doped ternary material in the positive electrode material obtained by the application has a stable crystal structure, which can improve the cycle stability of the positive electrode material. In addition, the non-metallic elements in the modifier react with lithium to generate a coating material with conductivity, which not only blocks the corrosion of the electrolyte on the doped ternary material, but also further improves the interface conductivity of the positive electrode material, so that the battery prepared from the positive electrode material has better cycle stability. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 FIG. 1 is an X-ray diffraction pattern of the positive electrode material prepared in Example 1 of the application.

[0019] Figure 2 FIG. 2 is a scanning electron microscope (SEM) image of the positive electrode material prepared in Example 1 of the application.

[0020] Figure 3 FIG. 3 is an element distribution mapping image of the positive electrode material prepared in Example 1 of the application.

[0021] Figure 4 In the figure (a) and (b) are respectively scanning electron microscope image and Mg element distribution line scanning graph of the cross section of the positive electrode material prepared in Example 1 of the present application.

[0022] Figure 5 In the figure (a) and (b) are respectively X-ray photoelectron spectroscopy graph of Li-O bond and B-O bond of the positive electrode material prepared in Example 1 of the present application.

[0023] Figure 6 X-ray diffraction graph of the positive electrode material prepared in Example 2 of the present application.

[0024] Figure 7 Scanning electron microscope image of the positive electrode material prepared in Example 2 of the present application.

[0025] Figure 8 X-ray diffraction graph of the positive electrode material prepared in Example 3 of the present application.

[0026] Figure 9 Scanning electron microscope image of the positive electrode material prepared in Example 3 of the present application.

[0027] Figure 10 X-ray diffraction graph of the positive electrode material prepared in Comparative Example 1 of the present application.

[0028] Figure 11 Scanning electron microscope image of the positive electrode material prepared in Comparative Example 1 of the present application.

[0029] Figure 12 X-ray diffraction graph of the positive electrode material prepared in Comparative Example 2 of the present application.

[0030] Figure 13 Scanning electron microscope image of the positive electrode material prepared in Comparative Example 2 of the present application.

[0031] Figure 14 X-ray diffraction graph of the positive electrode material prepared in Comparative Example 3 of the present application.

[0032] Figure 15 Scanning electron microscope image of the positive electrode material prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0033] Embodiments of the present application are described in detail below. The embodiments described below with reference to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0034] In the description of the specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in one or more embodiments or examples.

[0035] At present, the ternary positive electrode material can generally use surface coating or bulk doping to improve the stability of the material. However, the existing surface coating and bulk doping cannot simultaneously solve the problems of poor cycle stability and poor safety of the ternary positive electrode material, and the preparation method of the surface coating or bulk doping also has the disadvantages of complicated process, large energy consumption, large preparation cost and the like.

[0036] Therefore, the present application provides a preparation method of a positive electrode material for improving the cycle stability of a lithium ion battery, comprising the following steps:

[0037] S1. Providing a precursor, a lithium salt and a modifier, the structural formula of the precursor is Ni a X b Y c CO3 or Ni a X b Y c (OH)2, X is at least one of Al, Co, Mn, Y is at least one of Al, Co, Mn, X is different from Y, a+b+c=1, 1 / 3≤a<1, 0 q P p , Q is one of metal elements, P is one of B, N elements, 1 / 3≤p:q≤6;

[0038] S2. Mixing the precursor, the lithium salt and the modifier to obtain a mixture.

[0039] S3. Sintering treatment is performed on the mixture in an oxygen-containing atmosphere to obtain a sintered product, and then the sintered product is ground and sieved to obtain a positive electrode material, the positive electrode material comprises a doped ternary material and a coating layer coated on the surface of the doped ternary material, the structural formula of the doped ternary material is LiNi a-q Q q X b Y c O2, the structural formula of the coating layer is Li e P p O oX is at least one of Al, Co, and Mn, Y is at least one of Al, Co, and Mn, X is different from Y, a+b+c=1, 1 / 3≤a<1, 0

[0040] In the present application, the mixture is sintered in an oxygen-containing atmosphere to obtain the positive electrode material. The preparation method provided in the present application only uses one sintering process, reduces the multiple steps of the existing pre-sintering, secondary sintering, and pretreatment (such as grinding) before pre-sintering or secondary sintering, not only simplifies the process flow, but also reduces the energy consumption and the production cost of the positive electrode material.

[0041] In some embodiments, the modifier is at least one of aluminum diboride, magnesium diboride, titanium diboride, chromium diboride, calcium hexaboride, lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, tantalum nitride, or tungsten nitride. During the sintering of the modifier and the precursor, the metal elements in the modifier replace part of the metal elements in the precursor, so that the doped ternary material forms a bulk doping. The doped ternary material has a stable crystal structure, which can improve the stability of the positive electrode material in circulation. Since the non-metal elements in the modifier react with lithium to form a conductive coating material, the coating material not only separates water and carbon dioxide in the air from the doped ternary material, avoiding the formation of "residual alkali" on the surface of the doped ternary material, but also blocks the corrosion of the electrolyte to the doped ternary material, slowing down the cracking and structure collapse of the doped ternary material particles. Through this method, bulk doping and surface coating of the doped ternary material are simultaneously realized, improving the stability of the positive electrode material.

[0042] In some embodiments, the proportion of the modifier in the mixture is 0.5-5 wt.%. If the proportion of the modifier is less than 0.5 wt.%, the proportion of the modifier is too small, and the influence on the doped ternary material is small, or a coating layer cannot be formed on the surface of the doped ternary material; if the proportion of the modifier is greater than 5 wt.%, the modifier will react with the doped ternary material, consume part of the doped ternary material, and reduce the specific capacity of the positive electrode material.

[0043] In some embodiments, the proportion of the modifier can be 0.5 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, or 5 wt.%.

[0044] In some embodiments, the thickness of the cladding layer is 1-50 nm. The thickness of the cladding layer can be 1 nm, 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm. If the thickness of the cladding layer is small, the effect of blocking the corrosion of the electrolyte and improving the interface conductive capacity is not obvious. If the thickness of the cladding layer is large, the transmission of lithium ions in the lithium ion battery will be affected, and thus the specific capacity of the lithium ion battery will be affected.

[0045] In some embodiments, the particle size of the doped ternary material is 5-20 µm. The particle size can be 5 µm, 10 µm, 15 µm, or 20 µm.

[0046] In some embodiments, the precursor is Ni 1 / 3 Co 1 / 3 Mn 1 / 3 (OH)2, Ni 0.5 Co 0.2 Mn 0.3 (OH)2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.83 Co 0.07 Mn 0.1 (OH)2, Ni 0.9 Co 0.05 Mn 0.05 (OH)2, Ni 0.94 Co 0.03 Mn 0.03 (OH)2, Ni 0.96 Co 0.02 Mn 0.02 (OH)2, Ni 1 / 3 Co 1 / 3 Al 1 / 3 (OH)2, Ni 0.5 Co 0.2 Al 0.3 (OH)2, Ni 0.6 Co 0.2 Al 0.2 (OH)2, Ni 0.8 Co 0.1 Al 0.1 (OH)2, Ni 0.83 Co 0.07 Al 0.1 (OH)2, Ni 0.9 Co 0.05 Al 0.05 (OH)2, Ni 0.94 Co 0.03 Al0.03 (OH)2, Ni 0.96 Co 0.02 Al 0.02 (OH)2, Ni 1 / 3 Co 1 / 3 Mn 1 / 3 CO3, Ni 0.5 Co 0.2 Mn 0.3 CO3, Ni 0.6 Co 0.2 Mn 0.2 CO3, Ni 0.8 Co 0.1 Mn 0.1 CO3, Ni 0.83 Co 0.07 Mn 0.1 CO3, Ni 0.9 Co 0.05 Mn 0.05 CO3, Ni 0.94 Co 0.03 Mn 0.03 CO3, Ni 0.96 Co 0.02 Mn 0.02 CO3, Ni 1 / 3 Co 1 / 3 Al 1 / 3 CO3, Ni 0.5 Co 0.2 Al 0.3 CO3, Ni 0.6 Co 0.2 Al 0.2 CO3, Ni 0.8 Co 0.1 Al 0.1 CO3, Ni 0.83 Co 0.07 Al 0.1 CO3, Ni 0.9 Co 0.05 Al 0.05 CO3, Ni 0.94 Co 0.03 Al 0.03 CO3, Ni 0.96 Co 0.02 Al 0.02 at least one of CO3.

[0047] In some embodiments, the molar ratio of the lithium salt to the precursor is 1.0-1.1 : 1. In some embodiments, the molar ratio of the lithium salt to the precursor is 1 : 1, 1.05: 1, or 1.1 : 1.

[0048] In some embodiments, the oxygen-containing atmosphere is oxygen or air, and the sintering treatment is at a temperature of 500-1000℃ for 4-20h. The sintering treatment can specifically be at a temperature of 500℃ with a temperature increasing rate of 5℃ / min, and then at a temperature of 1000℃ with a temperature increasing rate of 2℃ / min.

[0049] In some embodiments, the lithium salt is at least one of lithium nitrate, lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium acetate, or lithium bromide.

[0050] In some embodiments, the grinding can be manual grinding using a agate mortar or automatic grinding using a ball mill, and the sieving can be manual sieving using a sieve or automatic sieving using a vibrating sieve. In some embodiments, the sieve used in the sieving is 200-500 mesh, for example, 200 mesh, 300 mesh, 400 mesh, or 500 mesh.

[0051] The application also provides a positive electrode material prepared by the preparation method. The positive electrode material comprises a doped ternary material and a coating layer coated on the surface of the doped ternary material, and the structure formula of the doped ternary material is LiNi a-q Q q X b Y c O2, and the structure formula of the coating layer is Li e P p O o , X is at least one of Al, Co, and Mn, Y is at least one of Al, Co, and Mn, X is different from Y, a+b+c=1, 1 / 3≤a<1, 0

[0052] The application also provides a positive electrode sheet, which comprises a positive electrode material, a conductive agent, and a binder.

[0053] In some embodiments, the conductive agent comprises at least one of carbon black, acetylene black, Super P, Ketjen black, conductive carbon fiber, graphite, graphene, polypyrrole, or carbon nanotube.

[0054] In some embodiments, the binder comprises at least one of polyethylene oxide, polyethoxylated ethylene, polyvinyl chloride, polyvinylidene fluoride, polymethyl ethylene carbonate, polymethyl ethylene carbonate, polyvinylpyrrolidone, polypropylene carbonate, chlorinated polyethylene, or polyvinyl carbonate.

[0055] The specific preparation process of the positive electrode sheet comprises the following steps:

[0056] (1) mixing the cathode material, conductive agent, binder, stirring for 0.5-5h, to obtain a mixture component; wherein, in the mixture component, the mass percentage of the cathode material is 60~90%, the mass percentage of the conductive agent is 5~30%, and the mass percentage of the binder is 5~10%.

[0057] (2) adding N-methyl pyrrolidone to the mixture component, stirring for 2-12h, to obtain a mixed slurry; wherein, the stirring speed is 100~1000r / min.

[0058] (3) coating the mixed slurry on an aluminum foil, drying to obtain a cathode sheet. The drying temperature is 60~120℃, and the time is 4~20h.

[0059] In some embodiments, the diameter size of the cathode sheet is 8-14mm, and the load is 1-20mg.

[0060] The application also provides a lithium ion battery, comprising a cathode sheet, a lithium anode sheet, and a separator.

[0061] In some embodiments, the lithium ion battery further comprises an electrolyte, a gasket, a spring, a negative electrode shell, and a positive electrode shell. The cathode sheet, the lithium anode sheet, the separator, the gasket, and the spring are assembled in the negative electrode shell and the positive electrode shell in an inert gas atmosphere, and the electrolyte fills in the negative electrode shell and the positive electrode shell. The lithium ion battery can be a button cell.

[0062] In some embodiments, the electrolyte contains a metal lithium salt and a solvent, and the concentration of the metal lithium salt is 1~2 mol / L.

[0063] In some embodiments, the metal lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisfluorosulfonylimide.

[0064] In some embodiments, the solvent comprises at least one of at least one of ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and fluoroethylene carbonate.

[0065] The scheme of the application will be explained below in combination with embodiments. Those skilled in the art will understand that the following examples are only for explaining the application, and cannot be understood as limiting the application. Unless otherwise stated, the reagents, software, and instruments involved in the following embodiments, which are not specifically stated, are all conventional commercially available products or open source.

[0066] Example 1

[0067] Preparation of the cathode material:

[0068] Providing Ni 0.8 Co 0.1Mn 0.1 (OH)2, MgB2and LiOH H2O;

[0069] mixing the Ni 0.8 Co 0.1 Mn 0.1 (OH)2, MgB2and LiOH H2O, to obtain a mixture, wherein the mass molar ratio of the LiOH H2O to Ni 0.8 Co 0.1 Mn 0.1 (OH)2is 1.03:1, and the proportion of MgB2in the mixture is 1 wt.%.

[0070] The mixture is placed in a tube furnace, heated to 500°C at a heating rate of 5°C / min under a pure oxygen atmosphere, and then heated to 780°C at a heating rate of 2°C / min after holding for 5h, and then cooled to low temperature with the furnace, to obtain a positive electrode material, and the structure formula of the obtained positive electrode material is LiNi 0.79 Mg 0.01 Co 0.1 Mn 0.1 O2-0.02Li3BO3, wherein the doped ternary material is LiNi 0.79 Mg 0.01 Co 0.1 Mn 0.1 O2, and the coating layer is Li3BO3.

[0071] Preparation of a positive electrode sheet:

[0072] Providing acetylene black, polyvinylidene fluoride, N-methyl pyrrolidone and aluminum foil;

[0073] Mixing the positive electrode material, acetylene black and polyvinylidene fluoride, stirring for 1h, to obtain a mixture component. The mass ratio of the positive electrode material, acetylene black and polyvinylidene fluoride is 8:1:1, and the mass of the positive electrode material, acetylene black and polyvinylidene fluoride is 500mg.

[0074] Adding N-methyl pyrrolidone to the mixture component, stirring for 4h, to obtain a mixed slurry, coating the mixed slurry on the aluminum foil, and drying to obtain a positive electrode sheet with a diameter size of 12mm and a load of ~5mg.

[0075] Preparation of a lithium ion battery:

[0076] Providing the positive electrode sheet, lithium negative electrode sheet, electrolyte, separator, gasket, spring, negative electrode shell, positive electrode shell;

[0077] In the glove box filled with argon, the positive electrode, lithium negative electrode, electrolyte, diaphragm, gasket, spring, negative electrode shell, positive electrode shell were assembled into CR2032 button cell as needed.

[0078] The electrolyte contains lithium hexafluorophosphate with a concentration of 1 mol / L and ethylene carbonate, diethyl carbonate, dimethyl carbonate.

[0079] See Figure 1 , the XRD of the positive electrode material of Example One is hexagonal NaFeO2 layered structure, and corresponds to R3m space group, card number is PDF # 70-4314, and there is no obvious impurity phase.

[0080] See Figure 2 and Figure 11 , compared with the positive electrode material obtained by not adding modifier in Comparative Example One, its surface presents uniform convex spherical structure, Figure 2 The surface of the positive electrode material prepared in Example One is flat, which can be understood that the addition of the modifier forms a coating layer on the surface of the ternary material, which covers the convex surface in Comparative Example One to form a surface with smooth structure, which can be explained that the addition of the modifier makes the coating layer on the surface of the positive electrode material.

[0081] See Figure 3 , the element distribution mapping of the positive electrode material contains Mg element and the Mg element is uniformly distributed in the positive electrode material, which indicates that the Mg element is successfully doped into the bulk phase of the positive electrode material, and combined with Figure 4 , it can be known that along the arrow direction in (a) graph, that is, along the center direction of the hemispherical structure of the positive electrode material, from (b) graph, it can be known that the intensity of Mg element in the positive electrode material gradually decreases until stable, which shows that the content of Mg element gradually tends to be stable along the arrow direction in (a) graph, which proves that Mg element has been gradiently doped into the ternary material. Mg element plays a role in supporting the crystal lattice in the crystal structure of the doped ternary material, which can stabilize the structure of the positive electrode material.

[0082] See Figure 5 , in the X-ray photoelectron spectrogram of the positive electrode material, Figure 5 From (a) and (b) in (a) and (b), it can be shown that the positive electrode material surface exists Li-O bond and B-O bond, which is proved to be lithium borate Li3BO3 by matching. Lithium borate has a stable structure, not only does not react with electrolyte, but also can prevent the positive electrode material from being corroded by electrolyte, and secondly has good Li ion conductivity, which can improve the electrical conductivity of the positive electrode material interface.

[0083] Example Two

[0084] The difference between Example One is that the modifier MgB2 is replaced by AlB2 in the preparation of the positive electrode material, and the structural formula of the positive electrode material obtained is LiNi 0.79 Al 0.01 Co 0.1 Mn 0.1 O2-0.02Li3BO3, wherein the ternary material doped in the positive electrode material is LiNi 0.79 Al 0.01 Co 0.1 Mn 0.1 O2, and the coating layer is Li3BO3. Other steps are the same as those of Example One and are not repeated.

[0085] See Figure 6 , the XRD of the positive electrode material of Example Two is similar to that of Example One, both of which are hexagonal NaFeO2layered structure, and there is no impurity phase.

[0086] See Figure 7 Similar to Example One, the positive electrode material of Example Two also produces a coating layer on the surface and also has element doping.

[0087] Example Three

[0088] The difference between Example One is that the modifier MgB2 is replaced by TiB2 in the preparation of the positive electrode material, and the structural formula of the positive electrode material obtained is LiNi 0.79 Ti 0.01 Co 0.1 Mn 0.1 O2-0.02Li3BO3, wherein the ternary material doped in the positive electrode material is LiNi 0.79 Ti 0.01 Co 0.1 Mn 0.1 O2, and the coating layer is Li3BO3. Other steps are the same as those of Example One and are not repeated.

[0089] See Figure 8 , the XRD of the positive electrode material of Example Three is similar to that of Example One, both of which are hexagonal NaFeO2layered structure, and there is no impurity phase.

[0090] See Figure 9 Similar to Example One, the positive electrode material of Example Three also produces a coating layer on the surface and also has element doping.

[0091] Comparative Example One

[0092] The difference between Example One is that no modifier is added in the preparation of the positive electrode material, and the structural formula of the positive electrode material obtained is LiNi 0.80 Co0.1 Mn 0.1 O2. Other steps are the same as Example One, and are not repeated.

[0093] See Figure 10 The XRD of the positive electrode material of Comparative Example One is a clear hexagonal NaFeO2layered structure corresponding to the R3m space group, card number PDF #70-4314, and no obvious impurities.

[0094] See Figure 11 Compared with Examples One to Three, the positive electrode material of Comparative Example One has no coating layer on the surface.

[0095] Comparative Example Two

[0096] The difference from Example One is that the modifier MgB2is replaced by MgO in the preparation of the positive electrode material. The structural formula of the positive electrode material obtained is LiNi 0.79 Mg 0.01 Co 0.1 Mn 0.1 O2. Other steps are the same as Example One, and are not repeated.

[0097] See Figure 12 The XRD of the positive electrode material of Comparative Example Two is similar to that of Comparative Example One, both of which are hexagonal NaFeO2layered structures and have no impurities.

[0098] See Figure 13 Compared with Examples One to Three, the positive electrode material of Comparative Example Two also has no coating layer on the surface, only realizing the doping of Mg element.

[0099] Comparative Example Three

[0100] The difference from Example One is that the modifier MgB2is replaced by B2O3in the preparation of the positive electrode material. The structural formula of the positive electrode material obtained is LiNi 0.80 Co 0.1 Mn 0.1 O2-0.02Li3BO3. Other steps are the same as Example One, and are not repeated.

[0101] See Figure 14 The XRD of the positive electrode material of Comparative Example Three is similar to that of Comparative Example Two, both of which are hexagonal NaFeO2layered structures and have no impurities.

[0102] See Figure 15 Compared with Examples One to Three, the positive electrode material of Comparative Example Three has no element doping, only surface coating.

[0103] Table 1 Modification results of the positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3

[0104]

[0105] Referring to Table 1, in Examples 1-3, it can be seen that the metal elements in different modifiers are doped into the ternary material, and B in the metal boride chemically reacts with lithium ions to form Li3BO3, achieving bulk doping and surface coating of the ternary material. In Comparative Example 2, only oxides are added for modification, and the metal elements in the oxides can only be doped into the ternary material and do not form a coating layer. In Comparative Example 3, only boron oxide is added for modification, and the boron oxide can only chemically react with lithium ions to form Li3BO3, and the Li3BO3 is only located on the surface of the ternary material and does not form bulk doping.

[0106] The lithium ion batteries prepared in Examples 1-3 and Comparative Examples 1-3 were also subjected to performance tests of first charge specific capacity, first discharge specific capacity, first cycle coulombic efficiency, capacity retention rate after 500 cycles, and coulombic efficiency after 500 cycles at a working voltage of 2.8-4.5 V and a rate of 0.1 C. Table 2.

[0107] Table 2 Comparison of electrochemical performance of lithium ions prepared in Examples 1-3 and Comparative Examples 1-3

[0108]

[0109] As can be seen from Table 2, compared with the lithium ion batteries of Comparative Examples 1-2, the lithium ion batteries of Examples 1-3 have a certain degree of decrease in first charge specific capacity, first discharge specific capacity, and first cycle coulombic efficiency, which is mainly due to the addition of the modifier metal boride, the chemical reaction of boron elements with Li + ions in the lithium salt to form Li3BO3, and the formation of the coating layer on the surface of the doped ternary material. Since the formation of the coating layer consumes part of the Li + ions to some extent, the first charge specific capacity and the first discharge specific capacity of the battery are relatively low.

[0110] However, under high voltage and after a long period of cycling, the capacity retention rate and the coulombic efficiency of the lithium ion batteries of Examples 1-3 are greatly improved compared with Comparative Examples 1-3. This is mainly due to the addition of the modifier metal boride, the doping of metal elements into the ternary material, and the role of supporting the crystal lattice in the crystal lattice, thereby stabilizing the structure of the positive electrode material. In addition, the boron elements in the modifier chemically react with Li +The ion generates a chemical reaction and forms Li3BO3, and the Li3BO3 is coated on the surface of the ternary positive electrode material. The coating layer can isolate the ternary positive electrode material from water and carbon dioxide in the air, avoid the generation of "residual alkali" on the surface of the doped ternary material, resist the corrosion of the electrolyte on the ternary positive electrode material, and further slow down the particle cracking and structure collapse of the doped ternary material particles in the long cycle process, so that the modified ternary positive electrode lithium ion battery has very stable electrochemical performance.

[0111] The above embodiments are only used to illustrate the technical solutions of the present application and are not limited. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the present application.

Claims

1. A method for producing a positive electrode material for improving cycle stability of a lithium ion battery, characterized by, The preparation method comprises: A precursor, a lithium salt and a modifier are provided, the structural formula of the precursor is Ni a X b Y c CO3 or Ni a X b Y c at least one of (OH)2, X is at least one of Al, Co, Mn, Y is at least one of Al, Co, Mn, X is different from Y, a+b+c=1, 1 / 3≤a<1, 0 q P p , Q is a metal element, P is a B element, 1 / 3≤p:q≤6; mixing the precursor, the lithium salt and the modifier to obtain a mixture; sintering treatment is performed on the mixture in an oxygen-containing atmosphere, which is oxygen or air, heating to 500°C at a heating rate of 5°C / min, holding for 5h, then heating to 780°C at a heating rate of 2°C / min, holding for 11h, to obtain a positive electrode material, the positive electrode material comprising a doped ternary material and a coating layer coated on the surface of the doped ternary material, the structural formula of the doped ternary material being LiNi a-q Q q X b Y c O2, the structural formula of the coating layer being Li e P p O o , e+3p=2o, the thickness of the coating layer being 1-50nm, and the particle size of the doped ternary material being 5-20µm.

2. The method for preparing the cathode material as described in claim 1, characterized in that, The modifier is at least one of aluminum diboride, magnesium diboride, titanium diboride, chromium diboride, and calcium hexaboride.

3. The method for preparing the cathode material as described in claim 1, characterized in that, In the mixture, the proportion of the modifier is 0.5-5 wt.%.

4. The method for preparing the cathode material as described in claim 1, characterized in that, The precursor is Ni 1 / 3 Co 1 / 3 Mn 1 / 3 (OH)2, Ni 0.5 Co 0.2 Mn 0.3 (OH)2, Ni 0.6 Co 0.2 Mn 0.2 (OH)2, Ni 0.8 Co 0.1 Mn 0.1 (OH)2, Ni 0.83 Co 0.07 Mn 0.1 (OH)2, Ni 0.9 Co 0.05 Mn 0.05 (OH)2, Ni 0.94 Co 0.03 Mn 0.03 (OH)2, Ni 0.96 Co 0.02 Mn 0.02 (OH)2, Ni 1 / 3 Co 1 / 3 Al 1 / 3 (OH)2, Ni 0.5 Co 0.2 Al 0.3 (OH)2, Ni 0.6 Co 0.2 Al 0.2 (OH)2, Ni 0.8 Co 0.1 Al 0.1 (OH)2, Ni 0.83 Co 0.07 Al 0.1 (OH)2, Ni 0.9 Co 0.05 Al 0.05 (OH)2, Ni 0.94 Co 0.03 Al 0.03 (OH)2, Ni 0.96 Co 0.02 Al 0.02 (OH)2, Ni 1 / 3 Co 1 / 3 Mn 1 / 3CO3, Ni 0.5 Co 0.2 Mn 0.3 CO3, Ni 0.6 Co 0.2 Mn 0.2 CO3, Ni 0.8 Co 0.1 Mn 0.1 CO3, Ni 0.83 Co 0.07 Mn 0.1 CO3, Ni 0.9 Co 0.05 Mn 0.05 CO3, Ni 0.94 Co 0.03 Mn 0.03 CO3, Ni 0.96 Co 0.02 Mn 0.02 CO3, Ni 1 / 3 Co 1 / 3 Al 1 / 3 CO3, Ni 0.5 Co 0.2 Al 0.3 CO3, Ni 0.6 Co 0.2 Al 0.2 CO3, Ni 0.8 Co 0.1 Al 0.1 CO3, Ni 0.83 Co 0.07 Al 0.1 CO3, Ni 0.9 Co 0.05 Al 0.05 CO3, Ni 0.94 Co 0.03 Al 0.03 CO3, Ni 0.96 Co 0.02 Al 0.02 at least one of CO3, Ni 5. The method for preparing the cathode material as described in claim 1, characterized in that, The molar ratio of the lithium salt to the precursor is 1.0-1.1:

1. The lithium salt is at least one of lithium nitrate, lithium carbonate, lithium hydroxide, lithium hydroxide monohydrate, lithium acetate, or lithium bromide.

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