High-nickel ternary positive electrode active material and preparation method, positive electrode and lithium ion battery

Abstract

The application provides a high-nickel ternary positive electrode active material, a preparation method of the high-nickel ternary positive electrode active material, a positive electrode and a lithium ion battery, and the chemical general formula of the high-nickel ternary positive electrode active material is LiNi a Co b M 1‑a‑b O 2‑ x S x , wherein the M metal is one or more of aluminum and manganese, 1 > a > b > 0, and 0.01 <= x <= 0.08. The preparation method of the high-nickel ternary positive electrode active material comprises the following steps: S1, weighing soluble nickel salt, cobalt salt, M metal salt, lithium salt and sulfide according to the stoichiometric amount, wherein the M metal salt is one or more of aluminum salt and manganese salt; S2, dissolving the soluble nickel salt, the cobalt salt and the M metal salt in water to obtain a transition metal solution; S3, adding the lithium salt and the sulfide into the transition metal solution and sol-gelizing the lithium salt and the sulfide to obtain a sol; S4, heating the sol to gelate the sol and drying the sol to obtain a dry gel; and S5, sintering the dry gel to obtain the high-nickel ternary positive electrode active material.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a high-nickel ternary cathode active material, a preparation method thereof, a cathode, and a lithium-ion battery. Background Art

[0002] In recent years, lithium-ion batteries have played an important role in practical devices such as portable electronic devices, electric vehicles (EVs), and plug-in hybrid electric vehicles (PHEVs) due to their high energy and high power. Among them, LiCoO2 with high energy density, good safety and stability, long cycle life, and low environmental pollution stands out among various cathode materials and has become the most widely used commercial lithium-ion battery. However, due to its relatively low capacity (145 mAh g 4+ ), and high cost, people have to find an electrode material that can both maintain high capacity and have excellent cycle performance.

[0003] For a long time, LiNiO2 has been considered as a substitute for LiCoO2. Because it has a similar layered structure to LiCoO2 and a higher reversible capacity (>180 mAh g -1 ). However, the application of LiNiO2 is not only affected by the adverse effects caused by Li / Ni cation mixing, but also because LiNiO2 is relatively easy to decompose to produce lithium-deficient compounds (Li d NiO 2-d , where 0 < d < 1). Coupled with the difficulty in preparing the material itself, it is almost impossible for LiNiO2 to be mass-produced and used practically. After extensive research, the most effective strategy is to replace Ni with a certain amount of Co 3+ and Al 3+ to form a LiNi 3+ Co a Al b Al 1-a-b O2 (also known as NCA, 1 > a > b > 0) solid solution. Because the introduced Co and Al can improve the structural stability of the material by controlling the phase change during charge and discharge. Although the electrochemical performance and thermal stability have been improved, the NCA material still needs to be improved to meet the requirements of high-performance lithium-ion batteries. Because at the end of the charging process, the unstable Ni existing in highly delithiated compounds such as Li 1-d Ni 0.8 Co 0.15 Al 0.05 O2 releases oxygen by decomposition, causing the material to rapidly transform into a more stable NiO-like rock salt phase NCA, resulting in capacity decay and potential safety hazards. [[ID=4 ,2]] Summary of the Invention

[0004] ​To address the aforementioned problems, the inventors, through repeated research, discovered that anion doping of materials to modify their structure is an effective approach. For example, because F anions have high electronegativity, it has been verified that their addition not only enhances the two-dimensional layered properties of the material, but also, due to the stronger bond energy of MF bonds compared to MO bonds, inhibits the dissolution of Co, thus effectively improving the structural stability of the material.

[0005] Through extensive experimental research, the inventors discovered that using another type of anion doping, namely S... 2- Ion doping, replacing some of the oxygen ions in the material, has a better effect on the structure and electrochemical performance of NCA materials. Furthermore, combining the sol-gel process with S... 2- Ion doping simultaneously coats the surface of NCA with a layer of lithium (e.g., lithium sulfate), further modifying NCA and not only exhibiting good electrochemical performance but also improving the material's storage stability. Furthermore, the inventors have discovered that this method (sulfur doping combined with sol-gel method) is applicable not only to NCA ternary cathode active materials but also to NCM (i.e., lithium nickel manganese chromate) ternary cathode active materials, and based on this, the present invention was completed.

[0006] The first aspect of this invention provides a high-nickel ternary cathode active material.

[0007] The second aspect of this invention provides a method for preparing a high-nickel ternary cathode active material.

[0008] A third aspect of the present invention provides a positive electrode for a lithium-ion battery.

[0009] A fourth aspect of the present invention provides a lithium-ion battery.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0011] According to a first aspect of the present invention, a high-nickel ternary cathode active material is provided, wherein the general chemical formula of the high-nickel ternary cathode active material is LiNi. a Co b M 1-a-b O 2-x S x The M metal is one or more of aluminum and manganese, 1>a>b>0, and 0.01≤x≤0.08. Preferably, 0.01≤x≤0.03.

[0012] In other words, relative to the number of oxygen and sulfur atoms, the sulfur doping amount can be (0.5-4) at%. For example, the percentage can be 0.5at%, 1at%, 1.5at%, 2at%, 2.5at%, 3at%, 3.5at%, 4at%, etc. In other words, x can take values ​​of 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, and 0.08. The corresponding general formula for high-nickel ternary cathode active materials is LiNi. a Co b M 1-a-b O 1.99 S 0.01 LiNi a Co b M 1-a-b O 1.98 S 0.02 LiNi a Co b M 1-a-b O 1.97 S 0.03 LiNi a Co b M 1-a-b O 1.96 S 0.04 LiNi a Co b M 1-a-b O 1.95 S 0.05 LiNi a Co b M 1-a-b O 1.94 S 0.06 LiNi a Co b M 1-a- b O 1.93 S 0.07 LiNi a Co b M 1-a-b O 1.92 S 0.08 Preferably, the sulfur doping amount can be 0.5 at% to 2 at% (i.e., x is 0.01 to 0.03), and the corresponding general formula for high-nickel ternary cathode active materials is LiNi. a Co b M 1-a-b O 1.99 S 0.01 LiNi a Co b M 1-a- b O 1.98 S 0.02 LiNia Co b M 1-a-b O 1.97 S 0.03 More preferably, the sulfur doping amount is 1 at%, i.e., x is 0.02, corresponding to the general formula of the high-nickel ternary cathode active material being LiNi. a Co b M 1-a-b O 1.98 S 0.02 .

[0013] According to a second aspect of the present invention, a method for preparing a ternary cathode active material is provided, wherein the high-nickel ternary cathode active material has the general chemical formula LiNi. a Co b M 1-a-b O 2-x S x Wherein, the metal M is one or more of aluminum and manganese, 1>a>b>0, and 0.01≤x≤0.08, the process includes the following steps:

[0014] S1, weigh soluble nickel salt, cobalt salt, M metal salt, lithium salt and sulfide according to stoichiometry, wherein the M metal salt is one or more of aluminum salt and manganese salt;

[0015] S2, dissolve the soluble nickel salt, cobalt salt, and M metal salt in water to obtain a transition metal solution;

[0016] S3, the lithium salt and sulfide are added to the transition metal solution and sol-gelled to obtain a sol;

[0017] S4, the sol is heated to gel and then dried to obtain a dry gel;

[0018] S5, the dry gel is sintered to obtain the high-nickel ternary cathode active material.

[0019] Furthermore, in step S1, the soluble nickel salt, cobalt salt, M metal salt, and lithium salt include nitrates of each metal.

[0020] Furthermore, the sulfide includes lithium sulfide or hydrogen sulfide.

[0021] Further, step S3 includes:

[0022] S31, Prepare an aqueous solution of a complexing agent, wherein the complexing agent is citric acid;

[0023] S32, the transition metal solution is added dropwise to the complexing agent aqueous solution, and an ammonia aqueous solution is added to adjust the pH value to 7-8 to form a transition metal complex;

[0024] S33, after forming a transition metal complex, the lithium salt and sulfide are added to the system and stirred to obtain the sol.

[0025] Furthermore, in step S32, the complexing agent aqueous solution is heated by a water bath at a temperature of 40-50°C.

[0026] Furthermore, in step S3, the molar ratio of citric acid to the total of all metal elements shall not be less than 2:1, and in step S32, the complexation reaction shall be carried out under stirring conditions for a time of more than 5 hours.

[0027] Furthermore, in step S4, the reaction system is heated in a water bath during the gelation process, with the water bath temperature being 80℃-100℃, and drying is carried out in a vacuum drying oven at a temperature of 100-120℃ for 2-10 hours.

[0028] Further, step S5 includes:

[0029] S51, the dry gel is pre-fired in a tube furnace with flowing oxygen, the pre-fired temperature is 400-550℃, and the pre-fired time is 3-6h.

[0030] S52, after pre-firing, further heating is carried out for calcination, the calcination temperature is 700-850℃, and the calcination time is 12-24h.

[0031] Furthermore, in step S5, the heating rate is 1-3℃ / min, and the oxygen flow rate is 0.2-1.0L / min.

[0032] The positive electrode according to a third aspect embodiment of the present invention comprises:

[0033] Positive current collector;

[0034] A positive electrode active material layer is disposed on the surface of the positive electrode current collector, and the positive electrode active material layer contains the high-nickel ternary positive electrode active material described in the first aspect embodiment, or the high-nickel ternary positive electrode active material prepared by the preparation method of any embodiment of the second aspect.

[0035] Furthermore, the positive electrode active material layer also contains a conductive agent and a binder. The conductive agent is selected from any one or more of conductive carbon black, conductive graphite, carbon nanotubes, carbon fibers, and graphene. The binder is selected from any one or more of polyvinylidene fluoride, polytetrafluoroethylene, sodium alginate, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0036] The lithium-ion battery according to a fourth aspect of the present invention includes the positive electrode described in any embodiment of the third aspect.

[0037] The above-described technical solution of the present invention has at least one of the following beneficial effects:

[0038] According to embodiments of the present invention, the high-nickel ternary cathode active material, using sulfur doping, exhibits excellent cycle stability, especially with a significant improvement in long-term cycle stability at 1C rate.

[0039] Furthermore, the high-nickel ternary cathode active material according to embodiments of the present invention, by using sulfur doping, can significantly reduce cation mixing and effectively improve the structural stability of the material;

[0040] Furthermore, the sol-gel method using nitrates was used to achieve S 2- Achieving LiSO4 coating on the surface of NCA / NCM materials while simultaneously doping with ions results in bifunctional modification of these materials. This bifunctional modified NCA / NCM material not only exhibits excellent electrochemical performance but also improves storage stability. Attached Figure Description

[0041] Figure 1 The XRD patterns of the high-nickel ternary cathode active materials obtained in each embodiment and comparative example are shown.

[0042] Figure 2 The rate performance of the high-nickel ternary cathode active materials obtained in the examples and comparative examples is shown.

[0043] Figure 3 The AC impedance spectra of the high-nickel ternary cathode active materials obtained in the examples and comparative examples are shown.

[0044] Figure 4 The long-cycle performance of the cathode prepared from the high-nickel ternary cathode active material obtained in the examples and comparative examples is shown at 1C rate.

[0045] Figure 5 The electrical performance of lithium-ion batteries prepared from various materials before and after storage is shown. (a) and (b) show the first three cycles of voltammetry of NCA and S0.02-NCA after storage, respectively; (c) and (d) show the first three charge-discharge curves of NCA and S0.02-NCA after storage, respectively; (e) shows the rate performance comparison of NCA material before and after storage; and (f) shows the rate performance comparison of S0.02-NCA material before and after storage.

[0046] Figure 6 The comparison of the cyclic stability of NCA materials at 1C rate before and after storage is shown;

[0047] Figure 7The comparison of the cycling stability of S0.02-NCA material at 1C rate before and after storage is shown. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0049] The high-nickel ternary cathode active material and its preparation method according to embodiments of the present invention are described in detail below.

[0050] According to the first aspect of the present invention, a high-nickel ternary cathode active material is provided for use in a lithium-ion battery, wherein the general chemical formula of the high-nickel ternary cathode active material is LiNi. a Co b M 1-a-b O 2-x S x Wherein, the metal M is one or more of aluminum and manganese, 1>a>b>0, and 0.01≤x≤0.08.

[0051] The preparation method of the above-mentioned high-nickel ternary cathode active material is described below, that is, the preparation method of the high-nickel ternary cathode active material according to the embodiments of the present invention.

[0052] The method for preparing high-nickel ternary cathode active material according to an embodiment of the present invention includes the following steps:

[0053] S1, weigh out soluble nickel salt, cobalt salt, M metal salt, lithium salt and sulfide according to stoichiometry, wherein the M metal salt is one or more of aluminum salt and manganese salt.

[0054] In other words, first, weigh out all the starting materials.

[0055] According to some embodiments of the present invention, the soluble nickel salt, cobalt salt, M metal salt, and lithium salt include nitrates of each metal.

[0056] More specifically, the nickel salt can be nickel nitrate, the cobalt salt can be cobalt nitrate, the M metal salt can be aluminum nitrate or manganese nitrate, and the lithium salt can be lithium nitrate, etc. Considering the good solubility of nitrates and the fact that no impurity removal is required after sol-gel and pre-calcination, they are preferred.

[0057] Furthermore, the sulfide used as a dopant source can be, for example, lithium sulfide or hydrogen sulfide. Lithium sulfide is preferred because it does not introduce impurities and is easier to transport and store than hydrogen sulfide as a raw material.

[0058] It is important to note that when using lithium sulfide as a doping source, lithium is also introduced. Therefore, when weighing, the lithium introduced by lithium sulfide needs to be combined with the lithium introduced by the aforementioned soluble lithium salt (i.e., lithium nitrate or lithium oxalate) for calculation.

[0059] S2, dissolve the soluble nickel salt, cobalt salt, and M metal salt in water to obtain a transition metal solution.

[0060] In other words, firstly, the transition metal salt that constitutes the NCA or NCM material is dissolved in water to obtain a transition metal solution (also known as a transition metal aqueous solution).

[0061] S3, the lithium salt and sulfide are added to the transition metal solution and sol-gelled to obtain a sol.

[0062] In other words, after the transition metal salt is uniformly dissolved to form a transition metal solution, lithium and sulfides as anion doping sources are added to form a sol.

[0063] After repeated research, the inventors finally designed a sol-gel process, which not only achieves S 2- Ion doping, along with LiSO4 coating on the surface of NCA (or NCM) materials, not only exhibits excellent electrochemical performance but also improves the storage stability of the materials.

[0064] According to some embodiments of the present invention, the specific process for preparing the sol includes:

[0065] S31, Prepare an aqueous solution of a complexing agent, wherein the complexing agent is citric acid.

[0066] Specifically, for example, a certain amount of citric acid can be weighed, dissolved in deionized water under magnetic stirring, and stirring can be continued to form an aqueous solution of citric acid, which is also a complexing agent aqueous solution.

[0067] Here, in order to improve the solubility of citric acid, citric acid can be dissolved in water under water bath heating to form the complexing agent aqueous solution.

[0068] Here, regarding the amount of complexing agent used, for example, the total molar ratio of citric acid to all transition metals can be 1-3:1, preferably 2:1. Using citric acid as a complexing agent enables the formation of stable complexes with transition metals, thereby forming a stable sol.

[0069] S32, the transition metal solution is added dropwise to the complexing agent aqueous solution, and an ammonia aqueous solution is added to adjust the pH value to 7-8, thereby forming a transition metal complex.

[0070] In other words, after preparing the transition metal solution and the complexing agent aqueous solution respectively, the transition metal solution and the complexing agent aqueous solution are mixed, and the pH value is changed to cause the citric acid to undergo a complexation reaction with the transition metal to form a stable transition metal complex.

[0071] In some embodiments of the present invention, specifically, an aqueous solution of citric acid is placed in a constant-temperature water bath under magnetic stirring, and a transition metal solution is added dropwise to the aqueous solution of citric acid, while an appropriate amount of ammonia is added to adjust the pH value of the solution. The solution is stirred thoroughly to ensure that the transition metal ions are complexed as completely as possible.

[0072] In order to allow the transition metal to undergo a sufficient complexation reaction, the titration rate is set at, for example, 10-30 ml / min, preferably 20 ml / min.

[0073] In addition, to ensure that the complexation reaction proceeds fully, it is preferable to carry out the complexation reaction under stirring conditions for a time of 5 hours or more.

[0074] S33, after forming a transition metal complex, the lithium salt and sulfide are added to the system and stirred to obtain the sol.

[0075] In other words, after the transition metal complex is formed, lithium salt and sulfide as a dopant source are added to the system to obtain a sol.

[0076] In other words, since the transition metal forms a stable transition metal complex, the lithium salt added thereafter will coat the surface of the transition metal complex, forming a core-shell structure. Subsequently, through gelation and pre-calcination, this core-shell structure is transformed into an NCA (or NCM) material with Li salt coating on the surface. This not only exhibits good electrochemical performance, but also has a certain effect on improving the storage stability of the material.

[0077] S4, the sol is heated to gel and then dried to obtain a dry gel.

[0078] In other words, after lithium salt and sulfide are added and stirred to form a sol, heating causes the sol to undergo a cross-linking reaction, generating a gel. This means that the transition metal complexes are further cross-linked to achieve gelation, thus forming a gel.

[0079] According to some embodiments of the present invention, during the gelation process (that is, the process of changing from a fluid sol to a solidified gel), the reaction system is heated in a water bath at a temperature of 80°C-100°C. By adding water slowly, the rate of water evaporation can be controlled, preventing incomplete gelation caused by excessively rapid water evaporation.

[0080] After the gel has completely solidified, i.e., the gelation process is complete, the wet gel needs to be dried. Drying can be carried out in a vacuum drying oven at a temperature of 100-120℃ for 2-10 hours.

[0081] S5, the dry gel is sintered to obtain the high-nickel ternary cathode active material.

[0082] After the moisture has fully evaporated, in order to obtain a high-nickel ternary cathode active material, the dry gel needs to be heated to cause a solid-phase reaction.

[0083] According to some embodiments of the present invention, step S5 includes:

[0084] S51, the dry gel is pre-fired in a tube furnace with flowing oxygen, the pre-fired temperature is 400-550℃, and the pre-fired time is 3-6h.

[0085] S52, after pre-firing, further heating is carried out for calcination, the calcination temperature is 700-850℃, and the calcination time is 12-24h.

[0086] Furthermore, in step S5, the heating rate is 1-3℃ / min, and the oxygen flow rate is 0.2-1.0L / min. Controlling the heating rate can, on the one hand, avoid insufficient doping and solid-phase reactions due to excessively rapid heating, and on the other hand, avoid abnormal grain growth due to excessively slow heating rates.

[0087] The cathode obtained using the above-mentioned high-nickel ternary cathode active material is described below.

[0088] The positive electrode according to an embodiment of the present invention comprises:

[0089] Positive current collector;

[0090] A positive electrode active material layer is disposed on the surface of the positive electrode current collector, and the positive electrode active material layer contains the high-nickel ternary positive electrode active material described in any of the above embodiments.

[0091] Furthermore, the positive electrode active material layer also contains a conductive agent and a binder. The conductive agent improves its conductivity, while the binder helps to increase the bonding strength between the positive electrode active material layer and the positive electrode current collector.

[0092] Specifically, the conductive agent is selected from any one or more of conductive carbon black, conductive graphite, carbon nanotubes, carbon fibers, and graphene.

[0093] In addition, the adhesive is any one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), sodium alginate (SA), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0094] Using one or more of PVDF, PTFE, sodium alginate, CMC, and SBR as binders can further improve the interfacial contact performance between the positive electrode active material layer and the positive electrode current collector, as well as the battery performance.

[0095] Specifically, PVDF has a high dielectric constant, good chemical stability and temperature characteristics, which have a positive effect on improving the adhesion between the positive electrode active material layer and the positive electrode current collector.

[0096] PTFE is a high-molecular-weight chemical material containing polytetrafluoroethylene. PTFE is produced by the free radical polymerization of tetrafluoroethylene. PTFE possesses advantages such as high temperature resistance (operating temperature up to 250℃), low temperature resistance (maintaining 5% elongation even at -196℃), and corrosion resistance (exhibiting inertness to most chemicals and solvents, and resistance to strong acids, alkalis, water, and various organic solvents).

[0097] Using sodium alginate (SA) as a binder, metal ion-coordinated sodium alginate is formed on the surface of metal fluoride particles during electrode manufacturing, successfully inhibiting the dissolution of the layered oxide material. In other words, copper-manganese layered oxides can be in-situ crosslinked with the SA binder, forming a conformal complex layer on the surface of the copper-manganese layered oxide particles. This effectively inhibits the dissolution of metal ions in the copper-manganese layered oxide in the electrolyte, enhancing the reversibility of the positive electrode.

[0098] CMC is widely used as a binder for anode materials in aqueous systems. CMC can achieve larger battery capacity, improve battery cycle life, and reduce battery internal resistance.

[0099] SBR binder has high bonding strength, good mechanical stability and workability. When used as a binder in the battery industry, it has good bonding effect and stable quality.

[0100] There are no particular limitations on the method for depositing a positive electrode active material layer on the surface of the positive electrode current collector; for example, it may include:

[0101] Disperse 60-100 parts by weight of the above-mentioned high-nickel ternary positive electrode active material, 0-10 parts by weight of the conductive agent and 0-10 parts by weight of the binder in a solvent (e.g., water, methanol, ethanol, etc.) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the surface of the positive electrode current collector.

[0102] The positive electrode obtained above can be used to construct a lithium-ion battery.

[0103] The following examples further illustrate the preparation of the high-nickel ternary cathode active material, the cathode, and the lithium-ion battery according to the present invention.

[0104] It should be noted that the following embodiments only use NCA material as an example for illustration. However, those skilled in the art should understand that the method according to the present invention is also applicable to NCM material and should be understood to fall within the scope of the claims in this field.

[0105] Example 1: Preparation of sulfur-doped NCA material S0.02-NCA (LiNi 0.8 Co 0.15 Al 0.05 S 0.02 O 1.98 )

[0106] (1) Citric acid (C6H8O7·H2O) was dissolved in 50 ml of deionized water under magnetic stirring to obtain citric acid solution.

[0107] (2) Dissolve nickel nitrate (Ni(NO3)2·6H2O), cobalt nitrate (Co(NO3)2·6H2O), and aluminum nitrate (Al(NO3)3·9H2O) in 50 ml of deionized water to form a transition metal nitrate solution (the molar ratio of the transition metal elements is Ni∶Co∶Al=0.8∶0.15∶0.05).

[0108] The molar ratio of citric acid to nickel nitrate is 2:1.

[0109] (3) Place the citric acid solution in a water bath at 45°C under magnetic stirring, and add the transition metal nitrate solution dropwise.

[0110] After the addition is complete, add an appropriate amount of ammonia water to adjust the pH of the solution to 7.5.

[0111] Afterward, the solution was stirred thoroughly for 5 hours to allow the transition metal ions to complex as completely as possible.

[0112] (4) Raise the water bath temperature to 80°C and stir continuously, then add lithium nitrate (LiNO3) solution.

[0113] After the lithium nitrate solution is added and just before the sol is about to form, a lithium sulfide (Li2S) solution (1% sulfur doping) is added.

[0114] The total amount of lithium (i.e., the total amount of lithium nitrate and lithium sulfide) is in a molar ratio of 1:0.8 to nickel.

[0115] (5) After the sol is formed, continue to evaporate the water. After the sol becomes a wet gel, dry it in a vacuum drying oven at 120°C for 12 hours to obtain a dry gel (precursor).

[0116] (6) The dry gel precursor was placed in a tube furnace with flowing oxygen and heated to 500°C at a heating rate of 3°C min⁻¹. It was pre-calcined at 500°C for 4 hours, then heated to 750°C for 15 hours. After cooling to room temperature, a sulfur-doped 1 at% NCA cathode material (LiNi) was obtained. 0.8 Co 0.15 Al 0.05 S 0.02 O 1.98 ), marked as S0.02-NCA.

[0117] Example 2: Preparation of sulfur-doped NCA material S0.01-NCA (LiNi 0.8 Co 0.15 Al 0.05 S 0.01 O 1.99 )

[0118] Except for step (4) above, where lithium sulfide is added at 0.05 at%, 0.5 at% NCA cathode material (LiNi) is prepared in the same manner as in Example 1. 0.8 Co 0.15 Al 0.05 S 0.01 O 1.99 ), marked as S0.01-NCA.

[0119] Example 3: Preparation of sulfur-doped NCA material SiO.03-NCA (LiNi 0.8 Co 0.15 Al 0.05 S 0.03 O 1.97 )

[0120] Except for step (4) above, where lithium sulfide was added at 1.5 at%, 1.5 at% NCA cathode material (LiNi) was prepared in the same manner as in Example 1. 0.8 Co 0.15 Al 0.05 S 0.03 O 1.97 ), marked as S0.03-NCA.

[0121] Comparative Example 1: Preparation of Undoped NCA Material - NCA

[0122] Except for step (4) above, in which lithium sulfide is not added, NCA cathode material is prepared in the same manner as in Example 1, and is referred to as NCA.

[0123] Comparative Example 2: Preparation of Fluorine-Doped NCA Material -F0.02-NCA(LiNi) 0.8 Co 0.15 Al 0.05 S 0.02 O 1.98 )

[0124] Except for step (4) above, where lithium fluoride (LiF) is used instead of lithium sulfide, fluorine doping is prepared in the same manner as in Example 1. The fluorine doping amount is 1%, meaning the general formula of the resulting fluorine-doped NCA material is LiNi. 0.8 Co 0.15 Al 0.05 F 0.02 O 1.98 )

[0125] Performance testing

[0126] (I) XRD patterns

[0127] Figure 1 The XRD patterns of the materials prepared in each embodiment (S0.01-NCA, S0.02-NCA, S0.03-NCA) and the comparative example (NCA, F0.02-NCA) are shown.

[0128] Depend on Figure 1 It can be seen that the diffraction peaks of all materials are characteristic diffraction peaks of hexagonal layered NCA, belonging to the α-NaFeO2 structure (R3m space group), and no other impurity peaks were observed. Compared with NCA, the intensity of the (003) peak of doped NCA is increased, resulting in an increase in the peak intensity ratio I(003) / I(104). The I(003) / I(104) ratios of NCA, F0.02-NCA, S0.01-NCA, S0.02-NCA, and S0.03-NCA are 1.10, 1.29, 1.25, 1.30, and 1.26, respectively. The I(003) / I(104) ratio can reflect the degree of cation mixing in the material. When the ratio is greater than 1.2, it indicates that the degree of cation mixing is small. The I(003) / I(104) ratio of the F and S doped samples increased significantly, indicating that F and S doping can significantly reduce the degree of cation mixing by substituting O in the lattice. Among them, F0.02-NCA and S0.02-NCA had the highest ratio (in fact, these two materials also have the best long-term cycling stability).

[0129] Depend on Figure 1As can be seen in (b), compared with NCA, the (003) and (104) peaks of F0.02-NCA are significantly shifted towards smaller angles; while the shift of S-doped NCA is slightly larger than that of F0.02-NCA. This shift indicates that F and S have been incorporated into the layered oxide lattice, partially replacing O. The greater shift of S0.02-NCA compared to F0.02-NCA is likely related to the fact that the radius of the sulfur ion (0.184 nm) is greater than that of the fluorine ion (0.133 nm).

[0130] (II) Electrical Performance Testing

[0131] To conduct electrical performance testing, the high-nickel ternary cathode active materials prepared in the above embodiments and comparative examples were used as active materials for the preparation of lithium-ion batteries. The specific steps are as follows:

[0132] The prepared powder was mixed with acetylene black and polyvinylidene fluoride (PVDF) binder at a mass ratio of 80:10:10. An appropriate amount of N-methylpyrrolidone (NMP) solution was added, and the mixture was ground in a dry environment at room temperature to form a slurry. The slurry was then uniformly coated onto the current collector aluminum foil and dried under an infrared lamp before being cut into (8×8) mm pieces. 2 The electrodes were dried at 110°C for 10 hours under vacuum and then transferred to a glove box for later use.

[0133] The simulated battery was assembled in an Ar atmosphere glove box (Micarona, model Super 1220 / 750, Microna China Co., Ltd.), using lithium metal as the counter electrode, Celgard 2300 as the separator, and 1M LiPF6 / EC (ethylene carbonate) + EMC (ethyl methyl carbonate) (volume ratio 1:1) as the electrolyte to form a CR2032 coin cell.

[0134] Electrochemical performance testing:

[0135] Electrochemical impedance spectroscopy (EIS) was performed using a CHI 760E electrochemical workstation. Cyclic voltammetry was performed with a scan voltage range of 2.8–4.3 V and a scan rate of 0.1 mV / s. -1 The electrochemical impedance spectroscopy test frequency range is 10. 5 -10 -2 Hz.

[0136] Cyclic voltammetry (CV) tests were performed using a CHI 760E electrochemical workstation. The scan voltage range for cyclic voltammetry was 2.8–4.3 V, and the scan rate was 0.1 mV / s. -1 .

[0137] The battery charge and discharge tests were conducted on a LAND battery performance tester (model CT-2001A), with a charge and discharge range of 2.8-4.3V.

[0138] All the above tests were conducted at a constant temperature of 25℃.

[0139] Depend on Figure 2 As can be seen, all three materials exhibit good rate performance. The maximum discharge specific capacities of NCA, F0.02-NCA, and S0.02-NCA at 0.1C are 189.6, 171.7, and 172.5 mAh g, respectively. -1 When the current is increased to a 2C rate, the maximum discharge specific capacities are 147.0, 134.2, and 140.3 mAh g, respectively. -1 The capacity retention rates were 77.5%, 78.2%, and 81.3%, respectively. This means that NCA had the highest specific capacity, while S0.02-NCA exhibited the best rate performance. When the current rate was reduced again to 0.1C, the discharge specific capacity of all three electrodes essentially recovered.

[0140] Figure 3 The electrochemical impedance spectroscopy (EIS) spectra measured at 50% SOC after 30 rate performance test cycles are shown. In terms of impedance, NCA has the highest impedance, followed by F0.02-NCA, and S0.02-NCA has the lowest impedance; therefore, S0.02-NCA exhibits the best rate performance.

[0141] Figure 4 The long-term cycling stability of NCA, F0.02-NCA, and S0.02-NCA at 1C rate was evaluated. After 1100 cycles, the specific capacities of the three electrodes increased to 153.6, 142.3, and 145.0 mAh g, respectively. -1 The values ​​decreased to 52.1, 86.3, and 102.1 mAh g. -1 The capacity retention rates were 33.9%, 60.6%, and 70.4%, respectively. This demonstrates that the S0.02-NCA electrode exhibits excellent cycle stability.

[0142] (III) Performance Testing Before and After Storage

[0143] Example 4

[0144] The lithium-ion battery obtained using the S0.02-NCA material prepared in Example 1 above was stored in a sealed bag for 3 months, and the stored lithium-ion battery was named stored S0.02-NCA.

[0145] Comparative Example 3:

[0146] The lithium-ion battery obtained using the NCA material prepared in Comparative Example 1 was stored in a sealed bag for 3 months, and the stored material was named stored NCA.

[0147] from Figure 5 As can be seen, compared with the newly prepared material, the NCA after storage exhibits an increased initial charge potential and a decreased discharge potential at a 0.1C rate, with a significant reduction in rate performance. While the stored S0.02-NCA also shows a decrease in initial capacity, its rate performance remains relatively good. The initial charge capacities of the stored NCA and S0.02-NCA materials are 201.7 and 206.1 mAh g⁻¹, respectively. -1 The initial discharge capacities were 157.7 and 165.4 mAh g, respectively. -1 The coulombic efficiencies were 78.2% and 80.3%, respectively; the second discharge capacities were 154.2 and 166.0 mAh g, respectively. -1 The coulombic efficiencies were 91.8% and 93.4%, respectively; the third discharge capacities were 153.4 and 166.3 mAh g, respectively. -1 The coulomb efficiencies were 92.7% and 94.0%, respectively.

[0148] Following rate performance testing, long-term cycle stability testing was conducted on the stored electrode at 1C rate, and the results were compared with those of the electrode before storage. The results are shown in the figures below. Figure 6 and Figure 7 The initial discharge capacities of NCA before and after storage were 153.6 and 104.9 mAh g, respectively. -1 After 200 cycles, the discharge capacity decreased to 117.5 and 75.1 mAh g. -1 The capacity retention rates were 76.5% and 71.6%, respectively. Figure 6 The initial discharge capacity of S0.02-NCA before and after storage was 145 mAh g. -1 After approximately 700 cycles, the discharge capacity remained at 120.1 and 99.8 mAh g. -1 The capacity retention rates were 82.8% and 70.1%, respectively. Figure 7 Therefore, sulfur doping can not only improve the charge-discharge cycle stability of NCA materials, but also improve their storage stability. The main reason is that during the calcination process, a small amount of sulfur will form a lithium sulfate protective layer on the surface of the active material, which will hinder the adverse side reactions between the active material particles and the electrolyte. This is also one of the reasons why the material can obtain excellent cycle performance.

[0149] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A high-nickel ternary positive electrode active material, characterized by, The high-nickel ternary positive electrode active material has a chemical formula of LiNi a Co b M 1-a-b O 2-x S x , wherein M is aluminum or manganese, 1 > a > b > 0, and 0.01 ≤ x ≤ 0.08, and the high-nickel ternary positive electrode active material is obtained by the following method: S1, the soluble nickel salt, cobalt salt, M metal salt, lithium salt and sulfide are weighed according to stoichiometry, wherein the M metal salt is one of aluminum salt and manganese salt; S2, the soluble nickel salt, cobalt salt and M metal salt are dissolved in water to obtain a transition metal solution; S3, the lithium salt and sulfide are added to the transition metal solution and sol-gelized to obtain a sol; S4, the sol is heated to gelate and dried to obtain a dry gel; S5, the dry gel is sintered to obtain the high-nickel ternary positive electrode active material; The step S3 comprises: S31, preparing an aqueous solution of a complexing agent, wherein the complexing agent is citric acid; S32, the transition metal solution is added dropwise into the aqueous solution of the complexing agent, and an aqueous ammonia solution is added to adjust the pH value to 7-8 to form a transition metal complex; S33, after the formation of the transition metal complex, the lithium salt and sulfide are added to the system, and stirring is performed to obtain the sol; The step S5 comprises: S51, the dry gel is pre-sintered in a tubular furnace with flowing oxygen, the pre-sintering temperature is 400-550 DEG C, and the pre-sintering time is 3-6h; S52, after the pre-sintering is completed, further heating is performed for calcination, the calcination temperature is 700-850 DEG C, and the calcination time is 12-24h.

2. A method for producing a high-nickel ternary positive electrode active material, characterized by, The high-nickel ternary positive electrode active material has a chemical formula of LiNi a Co b M 1-a-b O 2-x S x wherein M is aluminum or manganese, 1 > a > b > 0, and 0.01 ≤ x ≤ 0.08, and the method comprises the following steps: S1, the soluble nickel salt, cobalt salt, M metal salt, lithium salt and sulfide are weighed according to stoichiometry, wherein the M metal salt is one of aluminum salt and manganese salt; S2, the soluble nickel salt, cobalt salt and M metal salt are dissolved in water to obtain a transition metal solution; S3, the lithium salt and sulfide are added to the transition metal solution and sol-gelized to obtain a sol; S4, the sol is heated to gelate and dried to obtain a dry gel; S5, the dry gel is sintered to obtain the high-nickel ternary positive electrode active material; The step S3 comprises: S31, preparing an aqueous solution of a complexing agent, wherein the complexing agent is citric acid; S32, the transition metal solution is added dropwise into the aqueous solution of the complexing agent, and an aqueous ammonia solution is added to adjust the pH value to 7-8 to form a transition metal complex; S33, after the formation of the transition metal complex, the lithium salt and sulfide are added to the system, and stirring is performed to obtain the sol; The step S5 comprises: S51, the dry gel is pre-sintered in a tubular furnace with flowing oxygen, the pre-sintering temperature is 400-550 DEG C, and the pre-sintering time is 3-6h; S52, after the pre-sintering is completed, further heating is performed for calcination, the calcination temperature is 700-850 DEG C, and the calcination time is 12-24h.

3. The method of claim 2, wherein, In the step S1, the soluble nickel salt, cobalt salt, M metal salt, lithium salt include nitrate of each metal, and the sulfide includes lithium sulfide or hydrogen sulfide.

4. The method of claim 2, wherein, In the step S32, the aqueous solution of the complexing agent is heated by a water bath, and the temperature of the water bath is 40-50 DEG C.

5. The method of claim 2, wherein, In the step S32, the molar ratio of the citric acid to the total transition metal elements is not less than 2:1, and the complexing reaction is performed under stirring in the step S32, and the complexing reaction time is more than 5h.

6. The method of claim 2, wherein, In the step S4, the reaction system is heated by water bath during the gelation process, the temperature of the water bath is 80-100℃, the drying is carried out in a vacuum drying oven and the drying temperature is 100-120℃, and the drying time is 2-10h.

7. The method of claim 2, wherein, In the step S5, the heating rate is 1-3℃ / min, and the oxygen flow rate is 0.2-1.0L / min.

8. A positive electrode, characterized by comprising: Comprising: a positive electrode current collector; a positive electrode active material layer, which is arranged on the surface of the positive electrode current collector, and contains the high-nickel ternary positive electrode active material according to claim 1, or the high-nickel ternary positive electrode active material prepared by the preparation method according to any one of claims 2-7.

9. A lithium-ion battery, characterized by A positive electrode comprising the positive electrode according to claim 8.

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