A positive electrode material, a preparation method and application thereof

Abstract

The application discloses a positive electrode material and a preparation method and application thereof, and belongs to the technical field of secondary battery materials. The positive electrode material provided by the application comprises a core and a shell. The core comprises lithium nickel cobalt manganese oxide. The shell is wrapped around the core, and the material of the shell comprises porous transition metal phosphide. The positive electrode material provided by the application can significantly improve the cycle stability and rate performance due to the design and collocation of the structure and the material. The application further provides a preparation method and application of the positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of secondary battery materials technology, and in particular to a cathode material, its preparation method, and its application. Background Technology

[0002] Currently, lithium-ion batteries (LIBs) have become a rapidly growing energy storage technology, widely used in mobile phones, portable electronics, and electric vehicles. Lithium cobalt oxide (LiCoO2) was the first commercially available cathode material for lithium-ion batteries. Due to its high material density and electrode compaction density, lithium-ion batteries using lithium cobalt oxide cathodes have the highest volumetric energy density. Meanwhile, lithium iron phosphate has also been extensively studied, but its low energy density prevents it from meeting requirements in certain sub-sectors of high-density power batteries and 3C batteries.

[0003] Besides lithium cobalt oxide and lithium iron phosphate, lithium nickel cobalt manganese oxide (ternary cathode material) has also been extensively studied. Lithium nickel cobalt manganese oxide possesses high energy density and low cost, making it the most promising cathode material for development. However, its structure changes under high voltage. To improve its structural stability at high voltages, doping and coating techniques are commonly used to improve the material's structural stability and surface morphology, overcome material defects, and thus meet the requirements for higher voltage applications, thereby increasing its specific capacity.

[0004] However, existing coating and doping technologies have not significantly improved the high-voltage stability of ternary cathode materials. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a cathode material that can effectively improve the cycle stability of the obtained cathode material, as well as the kinetic performance (reduced impedance, improved rate performance) of lithium-ion batteries including said cathode material.

[0006] The present invention also provides a method for preparing the above-mentioned cathode material.

[0007] The present invention also provides a lithium-ion battery comprising the above-described positive electrode material.

[0008] The present invention also provides applications of the above-mentioned lithium-ion batteries.

[0009] According to an embodiment of a first aspect of the present invention, a positive electrode material is provided, the positive electrode material comprising:

[0010] The core includes a positive electrode active ingredient;

[0011] A shell that encloses the core, the shell being made of a porous transition metal phosphide.

[0012] The cathode material according to embodiments of the present invention has at least the following beneficial effects:

[0013] (1) The positive electrode material provided by this invention has a porous structure in the shell, which improves its liquid retention capacity and can significantly improve the kinetic performance of the battery. If it is paired with a high-kinetic electrolyte, the improvement in kinetics is even more significant. Specifically, it improves the transport performance and rate performance of active ions.

[0014] The porous structure can also accommodate the volume changes of the cathode material during charging and discharging, thereby improving the cycle stability of the obtained cathode material.

[0015] (2) In the cathode material provided by the present invention, the shell material is a transition metal phosphide, which has high stability, thus improving the cycle stability of the obtained cathode material and its stability under high pressure conditions.

[0016] According to some embodiments of the present invention, the particle size of the nucleus is 2 to 8 μm.

[0017] According to some embodiments of the present invention, the positive electrode active component includes at least one of lithium nickel cobalt manganese oxide and lithium cobalt oxide.

[0018] According to some embodiments of the present invention, the core further includes dopant atoms.

[0019] The doped atoms include at least one of aluminum, magnesium, zirconium, titanium and fluorine atoms.

[0020] According to some embodiments of the present invention, the molar ratio of nickel, cobalt and manganese in the lithium nickel cobalt manganese oxide includes, but is not limited to, at least one of the following ratios: 1:1:1, 4:4:2, 5:2:2, 6:2:2, 7:1.5:1.5, 8:1:1 or 9:0.8:0.2.

[0021] According to some embodiments of the present invention, the thickness of the shell is 200–500 nm.

[0022] According to some embodiments of the present invention, the shell material also includes transition metals.

[0023] According to some embodiments of the present invention, the porosity of the porous transition metal phosphide is 25-45%. Higher porosity allows for the storage of more electrolyte, improving the electrolyte retention capacity of the battery cell including the positive electrode material. Furthermore, when combined with a high-kinetics electrolyte, it can effectively reduce the cell impedance.

[0024] According to some embodiments of the present invention, the pore size of the porous transition metal phosphide is 2 to 7 nm.

[0025] According to some embodiments of the present invention, the pores in the porous transition metal phosphide are continuous channels. This can shorten the lithium-ion transport distance and improve the kinetic performance of the battery.

[0026] According to some embodiments of the present invention, the porous transition metal phosphide is made of at least one of nickel phosphide, manganese phosphide and cobalt phosphide.

[0027] According to some embodiments of the present invention, the mass ratio of the core to the shell is 2 to 9:1.

[0028] According to some embodiments of the present invention, the mass ratio of the core to the shell is 2.3 to 9:1, specifically 7:3, 7:1 or 3:1.

[0029] According to an embodiment of a second aspect of the present invention, a method for preparing the cathode material is provided, the method comprising ball milling and mixing the core and the porous transition metal phosphide followed by annealing.

[0030] Since the preparation method adopts all the technical solutions of the cathode material in the above embodiments, it has at least all the beneficial effects brought about by the technical solutions in the above embodiments.

[0031] Furthermore, the preparation method provided by the present invention is simple and easy to implement, with low cost, and can effectively improve the cycle life of the obtained cathode material and the lithium-ion battery including the cathode material.

[0032] According to some embodiments of the present invention, the method for obtaining the porous transition metal phosphide includes: obtaining a mixture of transition metal and non-porous transition metal phosphide by melt spinning method, and then acid etching the mixture.

[0033] According to some embodiments of the present invention, the method for obtaining the nucleus includes co-precipitating an aqueous solution of a transition metal salt and an aqueous solution of a precipitant in an organic solvent containing an aqueous solution of a complexing agent to obtain a precursor of the nucleus.

[0034] According to some embodiments of the present invention, the method for obtaining the core further includes sintering the precursor and the lithium source after mixing.

[0035] According to some embodiments of the present invention, the method for preparing the positive electrode material includes the following steps:

[0036] S1. Material Preparation:

[0037] To obtain porous transition metal phosphides: After obtaining a mixture of transition metal and non-porous transition metal phosphides by melt spinning method, the mixture is acid-etched.

[0038] Core acquisition: A co-precipitation reaction is carried out between an aqueous solution of a transition metal salt and an aqueous solution of a precipitant in an organic solvent containing an aqueous solution of a complexing agent. The resulting precursor is then mixed with a lithium source and sintered.

[0039] S2. Encapsulation: The core and the porous transition metal phosphide are ball-milled and then annealed.

[0040] Therefore, in the process of obtaining the nucleus, the use of organic solvents can promote the mixing of the raw materials for the preparation of the nucleus and control the rate of the coprecipitation reaction.

[0041] In the acquisition of porous transition metal phosphides, the melt-spinning method is used, resulting in a smaller and more uniform pore size. Furthermore, the porosity of the obtained porous transition metal phosphides can be adjusted by adjusting the parameters of the melt-spinning method.

[0042] The porous transition metal phosphides prepared by a combination of strip spinning and acid etching have continuous pores. These continuous pores mean that most of the pores are interconnected, allowing lithium ions to pass through most of them. Specifically, based on the dealloying principle, the dealloying process involves the corrosion of the active metal (transition metal) and the recombination of the inert metal or inert phase (transition metal phosphide), thereby forming the continuous pores.

[0043] According to some embodiments of the present invention, in step S1, the transition metal accounts for less than 20% of the mass ratio of the mixture. For example, it can be 10-18%, and more specifically, it can be about 15%.

[0044] According to the alloy phase diagram, when the mass fraction of transition metal (e.g., nickel) in the mixture is less than 20%, the components appearing in the transition metal and phosphorus phase diagram are transition metal and transition metal phosphides (e.g., nickel and nickel phosphide). That is, the product obtained by the melt spinning method is a mixture of the two.

[0045] According to some embodiments of the present invention, the steps of the melt-spinning method are as follows:

[0046] S1a. Place the transition metal and the non-porous transition metal phosphide in a vacuum quartz tube;

[0047] S1b. When the mixture obtained in step S1 is ignited by electric arc to the molten state, the cooling water is turned on and the copper roller is turned on. The copper roller rotates below the quartz tube and throws out strips.

[0048] The width and thickness of the strip are determined by the size of the opening at the bottom of the quartz tube and the rotational speed of the copper roller. As the opening of the quartz tube increases and the rotational speed of the copper roller decreases, the width of the strip varies between 0.3 and 2.2 mm, and the length varies between 10 and 70 mm.

[0049] According to some embodiments of the present invention, in step S1a, the diameter of the quartz tube opening is 0.5 to 2.5 mm.

[0050] According to some embodiments of the present invention, in step S1a, the transition metal includes at least one of nickel, cobalt and manganese.

[0051] According to some embodiments of the present invention, in step S1a, the non-porous transition metal phosphide includes at least one of Ni3P, Co3P and Mn3P.

[0052] According to some embodiments of the present invention, in step S1b, the rotational speed of the copper roller is between 1000 r / min and 6000 r / min. By adjusting this rotational speed, the porosity of the obtained porous transition metal phosphide can be adjusted over a certain period of time.

[0053] According to some embodiments of the present invention, in step S1, the acid used for acid etching is hydrochloric acid.

[0054] The concentration of the hydrochloric acid is 0.8–1.2 mol / L. For example, it can be approximately 1 mol / L.

[0055] Because transition metal phosphides are stable and insoluble in common chemical reagents such as dilute acids and alkalis, hydrochloric acid etching can remove the transition metals from the resulting mixture, thereby forming the porous structure.

[0056] According to some embodiments of the present invention, in step S1, the acid etching temperature is 45-50°C, specifically about 45°C.

[0057] According to some embodiments of the present invention, in step S1, the acid etching time is 24 to 28 hours, specifically about 24 hours. By adjusting this time, the porosity of the obtained porous transition metal phosphide can be adjusted to a certain extent.

[0058] According to some embodiments of the present invention, in step S1, the acquisition of the porous transition metal phosphide further includes cleaning and drying the obtained solid product after acid etching.

[0059] The cleaning includes cleaning with at least one of water and ethanol.

[0060] According to some embodiments of the present invention, in step S1, the concentration of the transition metal salt aqueous solution is 2.8 to 3.5 mol / L. For example, it can be about 3 mol / L.

[0061] According to some embodiments of the present invention, the solute in the transition metal salt aqueous solution includes nickel salt, manganese salt and cobalt salt.

[0062] According to some embodiments of the present invention, the solute in the aqueous solution of the transition metal salt includes at least one of sulfate, nitrate, acetate and hydrochloride.

[0063] According to some embodiments of the present invention, the solute in the transition metal salt aqueous solution further includes a doped metal salt.

[0064] The concentration of the doped metal salt in the aqueous solution of the transition metal salt is 0.04–0.06 mol / L. For example, it can be approximately 0.05 mol / L.

[0065] The doped metal salt includes at least one of aluminum salt, magnesium salt, titanium salt, and zirconium salt.

[0066] The doped metal salt includes at least one of chloride, sulfate and nitrate.

[0067] The doped metal salt includes at least one of aluminum chloride, magnesium chloride, and titanium chloride. For example, it can specifically be aluminum chloride.

[0068] According to some embodiments of the present invention, the solute in the aqueous precipitant solution includes at least one of sodium carbonate, potassium carbonate, sodium hydroxide, and potassium hydroxide.

[0069] According to some embodiments of the present invention, the concentration of the precipitant aqueous solution is 1.0 to 1.2 mol / L. For example, it can be about 1 mol / L.

[0070] According to some embodiments of the present invention, the volume ratio of the transition metal salt aqueous solution to the precipitant aqueous solution is 1:1 to 1.2; for example, it can be about 1:1.

[0071] According to some embodiments of the present invention, the solute in the complexing agent aqueous solution includes ammonia.

[0072] According to some embodiments of the present invention, the concentration of the complexing agent aqueous solution is 0.4 to 0.6 mol / L. For example, it can be about 0.5 mol / L.

[0073] According to some embodiments of the present invention, the volume ratio of the transition metal salt aqueous solution to the complexing agent aqueous solution is 1:1 to 1.2; for example, it can be about 1:1.

[0074] According to some embodiments of the present invention, the organic solvent includes at least one of ethanol, isobutanol, and N,N-dimethylformamide.

[0075] According to some embodiments of the present invention, the volume ratio of the transition metal salt aqueous solution to the organic solvent is 1:1.8 to 2.2; for example, it can be about 1:2.

[0076] According to some embodiments of the present invention, the temperature of the coprecipitation reaction is 55–65°C. Specifically, it can be about 60°C.

[0077] According to some embodiments of the present invention, the duration of the coprecipitation reaction is 10 to 15 hours. For example, it can be approximately 12 hours.

[0078] According to some embodiments of the present invention, in step S1, the acquisition of the nucleus further includes solid-liquid separation and drying of the solid product after the coprecipitation reaction. The specific operations for solid-liquid separation and drying are not limited; in actual production, operations such as centrifugation, extraction, drying, and freeze-drying can be selected according to production conditions and requirements.

[0079] According to some embodiments of the present invention, in step S1, the lithium source includes at least one of lithium carbonate, anhydrous lithium hydroxide, lithium hydroxide monohydrate, and lithium nitrate.

[0080] According to some embodiments of the present invention, in step S1, the molar ratio of the precursor to the lithium source is 1:1 to 1.05. For example, it can be approximately 1:1.

[0081] The molar ratio here is actually the molar ratio of the transition metal in the precursor to the lithium in the lithium source.

[0082] According to some embodiments of the present invention, in step S1, the sintering atmosphere includes oxygen. This sintering atmosphere is related to the type of core; for example, if the core material is NCM811 or a nickel content of higher, pure oxygen is used. If the material is NCM111 or a material with a lower nickel content, the atmosphere can be dry air. This calcination atmosphere can be determined based on industry experience.

[0083] According to some embodiments of the present invention, the heating rate of the sintering is 5 to 10 °C / min.

[0084] According to some embodiments of the present invention, the sintering includes pre-sintering and high-temperature sintering performed sequentially.

[0085] The pre-sintering temperature is 450–550°C. For example, it can be approximately 500°C.

[0086] The pre-sintering time is 4 to 10 hours.

[0087] The high-temperature sintering temperature is 750–850°C. For example, it could be approximately 800°C.

[0088] The high-temperature sintering time is 8 to 24 hours.

[0089] According to some embodiments of the present invention, in step S2, the mass ratio of the core to the porous transition metal phosphide is 2 to 9:1.

[0090] According to some embodiments of the present invention, in step S2, the ball-to-material ratio in the ball milling mixture is 1:2.5 to 3.5. For example, it can be approximately 1:3.

[0091] According to some embodiments of the present invention, in step S2, the ball milling and mixing are carried out in an ethanol system.

[0092] The role of ethanol includes cleaning the surfaces of each component to promote the full bonding of the shell and core, as well as improving the degree of ball milling mixing.

[0093] In the ball milling process, the mass ratio of ethanol to other solids is 1:2.8 to 3.2. For example, it can be approximately 1:3.

[0094] According to some embodiments of the present invention, in step S2, the ball milling mixing time is 4 to 6 hours. For example, it can be about 5 hours.

[0095] According to some embodiments of the present invention, in step S2, the annealing is carried out in a protective gas. The protective gas includes at least one of nitrogen and an inert gas.

[0096] According to some embodiments of the present invention, in step S2, the annealing time is 250–350°C. For example, it can be approximately 300°C.

[0097] According to some embodiments of the present invention, the annealing time is 4 to 6 hours. For example, it can be about 5 hours.

[0098] According to an embodiment of a third aspect of the present invention, a lithium-ion battery is provided, the lithium-ion battery comprising the aforementioned positive electrode material.

[0099] Since the lithium-ion battery adopts all the technical solutions of the cathode material described in the above embodiments, it possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments. Specifically, the lithium-ion battery has good rate performance, cycle performance, and high voltage performance.

[0100] According to some embodiments of the present invention, the lithium-ion battery includes a cell, the cell including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode;

[0101] The positive electrode includes a positive electrode current collector and a positive electrode coating covering the positive electrode current collector;

[0102] The positive electrode coating includes the positive electrode material.

[0103] According to some embodiments of the present invention, the positive electrode coating further includes a conductive agent, a dispersant, and a binder.

[0104] The conductive agent includes at least one of carbon nanotubes, graphene, and conductive graphite.

[0105] The mass ratio of the positive electrode material to the conductive agent is 95:0.5 to 1.5. For example, it can be approximately 95:1.

[0106] The dispersant includes sodium lignosulfonate.

[0107] The mass ratio of the positive electrode material to the dispersant is 95:0.5 to 1.5. For example, it can be approximately 95:1.

[0108] The adhesive includes PVDF.

[0109] The mass ratio of the positive electrode material to the binder is 95:2 to 4. For example, it can be 95:3.

[0110] According to some embodiments of the present invention, the lithium-ion battery further includes an electrolyte comprising LiPO2F2. Thus, the electrolyte and the positive electrode material work synergistically, specifically synergistically with the porous structure in the positive electrode material shell, effectively reducing the impedance of the resulting lithium-ion battery and improving its rate performance.

[0111] According to some embodiments of the present invention, the electrolyte wets the battery cell.

[0112] According to some embodiments of the present invention, the method for preparing the lithium-ion battery includes preparing the positive and negative electrodes using commercially available methods, as well as steps such as rolling, winding, liquid injection, and formation and capacity testing.

[0113] According to an embodiment of the fourth aspect of the present invention, an application of the lithium-ion battery is provided in the fields of power batteries, 3C batteries and energy storage batteries.

[0114] Since the application adopts all the technical solutions of the lithium-ion battery and the cathode material of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments.

[0115] Unless otherwise specified, the term "about" in this invention actually means that the error is allowed to be within ±2%, for example, about 100 is actually 100 ± 2% × 100.

[0116] Unless otherwise specified, "between" in this invention includes the number itself, for example, "between 2 and 3" includes the endpoint values ​​2 and 3.

[0117] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0118] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0119] Figure 1 This refers to the cycle performance of lithium-ion batteries that include the cathode materials obtained in Embodiment 1 and Comparative Example 1 of this invention.

[0120] Figure 2 This is a morphology diagram of the cathode material obtained in Example 1 of the present invention. Detailed Implementation

[0121] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0122] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0123] In the description of this invention, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0124] Example 1

[0125] This embodiment prepares a cathode material, and the specific steps are as follows:

[0126] S1. Material Preparation:

[0127] Obtaining porous nickel phosphide:

[0128] Weigh 15wt% of nickel sheet and 85wt% of Ni2P (CAS: 12035-64-2), and prepare a nickel-phosphide mixture by melt spinning method. The specific operation of melt spinning method is as follows: the nickel sheet and nickel phosphide are loaded into a quartz glass tube (the diameter of the tube opening is 2.0 mm), and the electric arc is turned on under vacuum. When the mixture is in a molten state, the cooling water is turned on, and the copper roller below the quartz tube is turned on to run at a speed of 3000 r / min to spin out the strip.

[0129] Subsequently, the strips were etched at 45°C with a 1 mol / L HCl solution for 24 hours to obtain porous nickel phosphide (np-Ni2P). After repeated washing with deionized water and alcohol, and drying, np-Ni2P powder was obtained.

[0130] Core acquisition:

[0131] NiSO4, CoSO4, and Mn2(SO4)3 were dissolved in water along with the dopant salt in a molar ratio of Ni:Co:Mn = 8:1:1 to form an aqueous solution of transition metal salt with a total metal ion concentration of 3 mol / L, wherein the concentration of the dopant salt was 0.05 mol / L and the dopant salt was AlCl3.

[0132] Prepare a 1 mol / L sodium carbonate aqueous solution as a precipitant aqueous solution;

[0133] Prepare a 0.5 mol / L ammonia solution as a complexing agent aqueous solution;

[0134] The above-mentioned aqueous solutions of transition metal salts, precipitant, complexing agent, and organic solvent ethanol were placed in a reaction vessel at a volume ratio of 1:1:1:1:2 and reacted at 60°C for 12 hours. The precipitate was then filtered and dried to obtain the precursor.

[0135] The obtained precursor was mixed with lithium carbonate at a molar ratio of 1:1 (molar ratio of metal to lithium), then pre-sintered at 500℃ for 5 hours in an oxygen atmosphere, and then sintered at 800℃ in an oxygen atmosphere for 15 hours to obtain the core. The heating rate during the sintering process was 10℃ / min.

[0136] S2. Package:

[0137] The ternary cathode material obtained in step S1 and porous nickel phosphide were mixed with ethanol at a mass ratio of 9:1, and the mass ratio of ethanol to all solid materials was 1:3. The mixture was then ball-milled. The ball-to-material ratio of the mixture was 1:3, and the mixing time was 5 hours.

[0138] The cathode material was then annealed at 300°C for 5 hours in an inert gas atmosphere.

[0139] Example 2

[0140] This embodiment prepares a cathode material, which differs from Embodiment 1 in that:

[0141] In step S1, the melt-spinning method, Ni3P is replaced with an equal mass of Co2P (CAS: 126129-99-5). In subsequent steps, porous nickel phosphide is also replaced with porous cobalt phosphide.

[0142] Comparative Example 1

[0143] This comparative example prepared a cathode material, which differs from Example 1 in the following ways:

[0144] This only includes the core acquisition step from Example 1. That is, the core from Example 1 is directly used as the positive electrode material.

[0145] Comparative Example 2

[0146] This comparative example prepared a cathode material, which differs from Example 1 in the following ways:

[0147] S2. Package:

[0148] The ternary cathode material obtained in step S1 is added to ethanol, with the mass ratio of ethanol to all solid materials being 1:3, and then ball-milled for mixing. The ball-to-material ratio for ball milling is 1:3, and the mixing time is 5 hours.

[0149] Then, under an inert gas atmosphere, methane gas was introduced and annealed at 300°C for 5 hours to obtain the carbon-coated cathode material.

[0150] Application examples

[0151] In this application example, lithium-ion batteries were prepared using the cathode materials obtained in Examples 1-2 and Comparative Examples 1-2 as raw materials. The specific steps are as follows:

[0152] The positive electrode material obtained in the specific embodiment, conductive agent SP, dispersant sodium lignosulfonate and binder PVDF are mixed with NMP in a mass ratio of 95:1:1:3 to prepare a positive electrode slurry; the obtained positive electrode slurry is coated on the surface of aluminum foil, rolled and cut to obtain the positive electrode;

[0153] A negative electrode slurry is prepared by mixing graphite (anode material), SBR (solid content 50%), colloid (concentration 2%), and deionized water. The resulting negative electrode slurry is then coated onto a copper foil surface, rolled, and cut to obtain the negative electrode.

[0154] The obtained positive and negative electrodes are wound together to form a bare cell with a coefficient of N / P = 1.02:1. An electrolyte containing LiPO2F2 is injected, and the cell is then processed into a lithium-ion battery through steps such as formation and capacity testing.

[0155] Test case

[0156] This test example first tested the physicochemical properties of the obtained cathode material. Specifically, the pore size and porosity were tested using the BET method; the particle size of the core and cathode material was tested using a particle size analyzer, and the thickness of the coating layer was estimated by subtraction; the morphology of the cathode material was also observed using scanning electron microscopy. The results show that the cathode material obtained in this invention has a distinct coating structure: the surface has a dotted distribution, and the edges of the cathode material are rounded. The morphology of the cathode material obtained in Example 1 is as follows. Figure 2 As shown, the core particle size of the obtained cathode material is 2–8 μm, the shell thickness is 200 nm–500 nm, the shell pore size is 2 nm–7 nm, and the porosity is 25%–45%.

[0157] This test case examines the rate performance of the lithium-ion battery obtained from the application example. Specifically:

[0158] The discharge specific capacity at 0.2C, 0.5C, 1.0C, and 1.5C rates was tested within a voltage range of 3.0–4.45V, and the ratio of the discharge specific capacity at other rates to the discharge specific capacity at 0.2C was calculated. The specific results are shown in Table 1.

[0159] Table 1 Rate performance of the cathode materials obtained in Examples 1-2 and Comparative Examples 1-2

[0160]

[0161]

[0162] Table 1 shows that regardless of whether the cathode material's shell is cobalt phosphide or nickel phosphide, it exhibits excellent rate performance, indicating that the porous structure of the shell improves the kinetic performance of the lithium-ion battery, including the corresponding cathode material (Examples 1-2). In contrast, in Comparative Example 1, the cathode material lacks a shell and therefore has no porous structure, resulting in a significant decrease in its rate performance.

[0163] This test also tested the cycle performance of the lithium-ion batteries obtained in the application examples. Specifically, within a voltage range of 3.0–4.45V, charge-discharge cycles were performed at room temperature at a rate of 0.7C, with 24 hours per day, and the capacity retention rate (ratio of the discharge capacity to the first week's capacity) was calculated over 10 days. The test results showed that the lithium-ion batteries using the cathode materials obtained in Examples 1 and 2 still maintained a capacity retention rate of 85% or higher after 10 days of cycling. However, the lithium-ion batteries using the cathode material obtained in Comparative Example 1 showed a capacity retention rate that dropped to 70% or even lower after 9 days of cycling. Specific test results are as follows... Figure 1 As shown, the cathode material obtained by this invention, through its special structural design and the passivation effect of the shell, can significantly protect the core. This protection, combined with the pores in the shell, can significantly improve its high-voltage, long-cycle performance.

[0164] This test case also tested the liquid retention coefficient during the fabrication process of the lithium-ion battery in the application example, as well as the room temperature impedance of the lithium-ion battery at 50% SOC. Specific test results are shown in Table 2.

[0165] Table 2 shows the performance of lithium-ion batteries using the cathode materials obtained in Examples 1-2 and Comparative Examples 1-2.

[0166] Liquid retention coefficient Impedance RT 50% SOC mΩ Example 1 1.43 19 Example 2 1.41 21 Comparative Example 1 1.25 33 Comparative Example 2 1.26 28

[0167] The results show that the liquid retention coefficient of the lithium-ion battery using the cathode materials obtained in Examples 1 and 2 is significantly higher than that of the lithium-ion battery using the cathode materials obtained in Comparative Examples 1 and 2. This indicates that the porous structure rich in phosphides can increase the liquid retention performance of the battery. Furthermore, Table 2 also shows that the impedance of the lithium-ion battery is significantly reduced when using the cathode materials obtained in Examples 1 and 2. This demonstrates that the cathode material provided by the present invention, due to its porous surface structure, can achieve lower impedance when combined with a high-kinetics electrolyte.

[0168] In summary, the cathode material provided by this invention, due to the porous transition metal phosphide coating, not only improves the rate performance of lithium-ion batteries including the corresponding cathode material, but also enhances their cycle life, reduces phase transitions during cycling, and makes cycling more stable. Because the resulting lithium-ion battery exhibits excellent cycle stability and rate performance, it is expected to find wide application in the fields of power batteries, 3C batteries, and energy storage batteries.

[0169] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A positive electrode material, characterized in that, The cathode material includes: The core includes a positive electrode active component; the positive electrode active component includes at least one of lithium nickel cobalt manganese oxide and lithium cobalt oxide; A shell enclosing the core, the shell being made of a porous transition metal phosphide; the pores in the porous transition metal phosphide are continuous channels; The mass ratio of the core to the shell is 2 to 9:1; The porosity of the porous transition metal phosphide is 25-45%; The method for obtaining the porous transition metal phosphide includes: obtaining a mixture of transition metal and non-porous transition metal phosphide by melt spinning method, and then acid etching the mixture.

2. The cathode material according to claim 1, characterized in that, The porous transition metal phosphide is made of at least one of nickel phosphide, manganese phosphide, and cobalt phosphide.

3. A method for preparing the cathode material as described in any one of claims 1 to 2, characterized in that, The preparation method includes ball milling and mixing the core and the porous transition metal phosphide, followed by annealing; the method for obtaining the porous transition metal phosphide includes: obtaining a mixture of transition metal and non-porous transition metal phosphide by melt spinning method, and then acid etching the mixture; The acid used for the acid etching is hydrochloric acid with a concentration of 0.8–1.2 mol / L; The ball milling and mixing were carried out in an ethanol system.

4. The preparation method according to claim 3, characterized in that, The method for obtaining the nucleus includes co-precipitating an aqueous solution of a transition metal salt and an aqueous solution of a precipitant in an organic solvent containing an aqueous solution of a complexing agent to obtain the precursor of the nucleus.

5. The preparation method according to claim 4, characterized in that, The method for obtaining the core also includes sintering the precursor and lithium source after mixing them.

6. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode material and electrolyte as described in any one of claims 1 to 2; The electrolyte contains LiPO2F2.

7. An application of the lithium-ion battery as described in claim 6 in the fields of power batteries, 3C batteries and energy storage batteries.

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