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. The positive electrode material comprises a core and a coating layer arranged on the surface of the core, and the coating layer contains lithium polysaccharide sulfate. In the application, the core is coated with lithium polysaccharide sulfate, so that the stability of the positive electrode material is improved, especially the stability in a liquid electrolyte, and the electrical performance of the material is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries (LIBS) are the most promising energy storage devices in power tools, electric vehicles and energy storage systems due to their high energy and power density, long cycle life, low self-discharge rate and high safety. Among them, lithium cobaltate is one of the commonly used materials in current commercial positive electrode materials, and is widely favored by material manufacturers due to its high specific capacity. However, the stability of the conventional lithium cobaltate positive electrode material is poor. SUMMARY

[0003] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a positive electrode material having good stability.

[0004] The present application also provides a preparation method of the positive electrode material.

[0005] The present application also provides a positive electrode.

[0006] The present application also provides a secondary battery.

[0007] The present application also provides the application of the positive electrode material.

[0008] In a first aspect of the present application, a positive electrode material is provided, comprising a core and a coating layer arranged on the surface of the core, wherein the coating layer contains lithium polysaccharide sulfate.

[0009] The positive electrode material according to the embodiments of the present application has at least the following beneficial effects: the core is coated with lithium polysaccharide sulfate in the present application, thereby improving the stability of the positive electrode material, especially in the liquid electrolyte, solving the problem of instability of the positive electrode material (such as lithium cobaltate) in the liquid electrolyte environment, and improving the electrical performance of the material. At the same time, the positive electrode material of the present application has the characteristic of structural stability under high voltage (such as ≥ 4.48V, specifically such as 4.5V, 4.53V, etc.). The positive electrode material of the present application has good application prospects when used in the preparation of battery positive electrodes, secondary batteries or electric devices.

[0010] In this context, lithium polysaccharide sulfate refers to polysaccharide sulfate lithium salt.

[0011] In some embodiments of the present application, the lithium polysaccharide sulfate includes at least one of lithium galactosan sulfate or lithium dextran sulfate.

[0012] In some preferred embodiments of the present application, the lithium polysaccharide sulfate is lithium galactosan sulfate.

[0013] In some preferred embodiments of the present application, the structural formula of lithium galactosan sulfate includes:

[0014]

[0015] In formula (1), the number of R1 is an integer and greater than 0.

[0016] According to the above embodiments, the present application can provide good arranged ion channels and excellent mechanical strength by using lithium galactosan sulfate as a matrix. Compared with the conventional binder PVDF, the sulfate groups in lithium galactosan sulfate can form stable hydrogen bonds with trace amounts of water on the surface of LiCoO2 particles and most oxygen-containing groups such as current collectors (e.g., aluminum foil), which can improve the bonding state between LiCoO2 and the current collector (e.g., aluminum foil), and improve the mechanical properties of the positive electrode material and the battery to which the positive electrode material is applied. Moreover, lithium galactosan sulfate can form a protective barrier between the positive active material (e.g., lithium cobaltate) and the electrolyte, avoiding direct contact between the liquid electrolyte and lithium cobaltate, which can cause corrosion on the surface of lithium cobaltate, while not affecting the lithium ion insertion and extraction efficiency of the positive active material (e.g., lithium cobaltate) with a coating layer, and improving the stability and safety of the traditional lithium battery during the cycling process.

[0017] In addition, galactosan is a kind of polysaccharide composed of galactose monomers, mainly composed of β-1→4 bonded D-galactopyranose residues, and a part of which is composed of 1→6 bonded galactose residues. The galactosan involved in the present application is preferably arabinogalactan, and the structure is shown in formula (2) as follows:

[0018]

[0019] Compared with dextran, galactosan has lower viscosity in aqueous solution, no sticky material aggregation, excellent dispersibility and surface activity. Using galactosan instead of dextran for modification to obtain a positive electrode material containing a coating layer (e.g., using lithium cobaltate coated and modified with lithium sulfate galactosan instead of lithium cobaltate coated and modified with lithium sulfate dextran), the influence on the stirring and coating process (one of the conventional processes for battery production) during battery production can be reduced. Because galactosan and dextran belong to the same class of binders, the viscosity of the slurry can be increased. Compared with the positive electrode material coated and modified with lithium sulfate dextran, the positive electrode material coated and modified with lithium sulfate galactosan is more beneficial to the processing of the slurry during battery production due to its lower viscosity. Therefore, among lithium sulfate galactosan and lithium sulfate dextran, lithium sulfate galactosan is preferred.

[0020] In some embodiments of the present application, the coating layer further contains a solid-state electrolyte.

[0021] In some preferred embodiments of the present application, the solid-state electrolyte comprises at least one of lithium thiophosphate (Li3PS4), lithium lanthanum zirconium oxide, lithium titanium aluminum phosphate, or lithium aluminum germanium phosphate.

[0022] In some more preferred embodiments of the present application, the solid-state electrolyte comprises lithium thiophosphate.

[0023] Through the above embodiments, Li3PS4, as a new type of solid-state electrolyte, has good chemical stability between Li3PS4 and lithium metal compared with traditional solid-state electrolytes, and the good ionic conductivity of Li3PS4 can effectively reduce the cathode electrolyte interface impedance of the positive electrode material and improve the lithium ion transmission efficiency.

[0024] In some embodiments of the present application, the coating layer comprises a solid-state electrolyte layer and a lithium polysaccharide sulfate layer, the solid-state electrolyte layer is arranged between the core and the lithium polysaccharide sulfate layer, the solid-state electrolyte layer contains a solid-state electrolyte, and the lithium polysaccharide sulfate layer contains lithium polysaccharide sulfate.

[0025] Through the above embodiments, the present application uses lithium polysaccharide sulfate (such as lithium galactosan sulfate) as a substrate and Li3PS4 as a coating to prepare a solid-state electrolyte film layer for surface coating of a traditional positive electrode material (such as lithium cobaltate), which not only improves the structural stability of the positive electrode material in a liquid electrolyte without changing the structure of the traditional positive electrode material, but also enhances the ionic conductivity of the positive electrode material and reduces the impedance.

[0026] In addition, the solid-state electrolyte layer is arranged between the core and the lithium polysaccharide sulfate layer, and the lithium polysaccharide sulfate as the outer layer of the coating layer can form stable hydrogen bonds with trace amounts of water on the surface of the positive active material (such as LiCoO2) particles and most oxygen-containing groups of the current collector (such as aluminum foil), which can improve the bonding state between the positive active material (such as LiCoO2) and the current collector (such as aluminum foil) and improve the mechanical properties.

[0027] In some preferred embodiments of the present application, the thickness of the lithium polysaccharide sulfate layer is 2-12 nm.

[0028] In some more preferred embodiments of the present application, the thickness of the lithium polysaccharide sulfate layer is 5-8 nm.

[0029] In some preferred embodiments of the present application, the thickness of the solid-state electrolyte layer is 5-20 nm.

[0030] In some more preferred embodiments of the present application, the thickness of the solid-state electrolyte layer is 10-15 nm.

[0031] In some preferred embodiments of the present application, the mass ratio of the solid-state electrolyte layer to the core is (0.1-10):(90-99.5).

[0032] In some more preferred embodiments of the present application, the mass ratio of the solid-state electrolyte layer to the core is (0.5-6):(90-99.5).

[0033] In some preferred embodiments of the present application, the mass fraction of the lithium polysulfate layer in the positive electrode material is 0.1-10%.

[0034] In some more preferred embodiments of the present application, the mass fraction of the lithium polysulfate layer in the positive electrode material is 0.5-5%.

[0035] In some more preferred embodiments of the present application, the mass fraction of the lithium polysulfate layer in the positive electrode material is 0.5-2.5%.

[0036] In some preferred embodiments of the present application, the mass ratio of the lithium polysulfate layer, the solid-state electrolyte layer and the core is (0.1-10):(0.1-10):(90-99.5).

[0037] In some more preferred embodiments of the present application, the mass ratio of the lithium polysulfate layer, the solid-state electrolyte layer and the core is (0.5-5):(0.5-6):(90-99.5).

[0038] In some embodiments of the present application, the core comprises an active material.

[0039] In some preferred embodiments of the present application, the active material comprises at least one of lithium manganate, lithium cobaltate or lithium iron phosphate.

[0040] In some more preferred embodiments of the present application, the active material comprises lithium cobaltate (LiCoO2).

[0041] At present, for the conventional lithium cobaltate material, in order to realize its high capacity as much as possible, the cut-off voltage is usually improved, but when charging and discharging at high voltage, a large number of lithium ions are deintercalated from the bulk phase, and the perfect layered structure will cause the transition metal (TM) layer of the layered lattice to have a strong sliding tendency, thereby causing irreversible phase transition, resulting in problems such as cycle diving; in addition to the instability of the intrinsic bulk phase structure, the formation of the cathode electrolyte interface (CEI) at high voltage, oxygen escape and cobalt ion dissolution and other problems are also more obvious. Therefore, the conventional lithium cobaltate has poor stability.

[0042] And in the application, the lithium polysaccharide sulfate (such as lithium sulfate galactose) and the solid electrolyte are used to coat the surface of the lithium cobalt oxide to modify the lithium cobalt oxide, improve the stability of the lithium cobalt oxide in the liquid electrolyte, and improve the structural stability of the lithium cobalt oxide at high voltage. The positive electrode material in the application can meet the charging and discharging requirements in the 4.48V system, and can also meet the charging and discharging requirements in the 4.5V and 4.53V systems.

[0043] In some embodiments of the application, the Dv50 of the positive electrode material is 2-6 μm. 05 2-6 μm.

[0044] In some embodiments of the application, the Dv50 of the positive electrode material is 2-6 μm. v50 12-20 μm.

[0045] In some embodiments of the application, the Dv50 of the positive electrode material is 2-6 μm.

[0046] In some embodiments of the application, the preparation method comprises the following steps: preparing a solid electrolyte layer on the surface of the inner core, and then preparing a lithium polysaccharide sulfate layer to obtain the positive electrode material.

[0047] In some embodiments of the application, the preparation method comprises the following steps:

[0048] S1, sintering the mixture I containing the solid electrolyte and the active material to obtain the active material coated with the solid electrolyte;

[0049] S2, heating the mixture II containing the active material coated with the solid electrolyte and the lithium polysaccharide sulfate to obtain the positive electrode material.

[0050] At present, the commonly used solid electrolyte film coating methods include electrode support coating method and magnetron sputtering method. The electrode support coating method uses a doctor blade to coat the slurry on the positive electrode to form a film by means of flow casting technology. Although this method can ensure good contact between the solid electrolyte film and the electrode, it may increase the possibility of mixing the solid electrolyte film layer and the electrode layer together, and reduce the thickness uniformity and mechanical strength of the coating layer. The magnetron sputtering method can realize uniform deposition of the solid electrolyte on the surface of the lithium cobalt oxide positive electrode material, but it needs to control the voltage and gas pressure to ensure good sputtering efficiency, which is relatively complex.

[0051] In the application, the solid electrolyte is mixed with the positive electrode active material (such as LiCoO2) and sintered to obtain the positive electrode active material coated with the solid electrolyte, and then mixed with the lithium polysaccharide sulfate (such as lithium sulfate galactose) to obtain the final product. The method is simple and easy to operate.

[0052] In some preferred embodiments of the application, in step S1, the sintering temperature is 550-750°C.

[0053] In some preferred embodiments of the present application, in step S1, the sintering time is 4-7h. Preferably, the sintering time is 5-6h.

[0054] In some preferred embodiments of the present application, in step S1, in the mixture I, the mass ratio of the solid-state electrolyte and the active material is (0.1-10):(90-99.9).

[0055] In some more preferred embodiments of the present application, in step S1, in the mixture I, the mass ratio of the solid-state electrolyte and the active material is (0.5-6):(94-99.5).

[0056] In some preferred embodiments of the present application, in step S1, the mixture I is ground before sintering.

[0057] In some more preferred embodiments of the present application, the grinding comprises ball milling.

[0058] In some preferred embodiments of the present application, in step S1, the mixture I comprising a ball milling solvent, a solid-state electrolyte and an active material is ball milled, dried and then sintered.

[0059] In some more preferred embodiments of the present application, in step S1, the ball milling solvent comprises at least one of isopropyl alcohol, ethanol, ethylene glycol or acetone.

[0060] In some more preferred embodiments of the present application, in step S1, the ball milling solvent comprises isopropyl alcohol.

[0061] In some more preferred embodiments of the present application, in step S1, the ball milling speed is 800-1200rpm.

[0062] In some more preferred embodiments of the present application, in step S1, the ball milling time is 3-5h.

[0063] In some more preferred embodiments of the present application, in step S1, the drying temperature is 70-90℃.

[0064] In some more preferred embodiments of the present application, in step S1, the drying time is 6-10h.

[0065] In some preferred embodiments of the present application, in step S2, in the mixture II, the mass ratio of the lithium polysulfate-coated active material and the solid-state electrolyte is (0.5-6):(94-99.5).

[0066] In some preferred embodiments of the present application, in step S2, the mixture II containing the solid-state electrolyte-coated active material, lithium polysaccharide sulfate and solvent I is heated to obtain the positive electrode material.

[0067] In some more preferred embodiments of the present application, in the mixture II, the total mass fraction of the lithium polysaccharide sulfate is 0.5-4% based on the total mass of the solid-state electrolyte-coated active material and the lithium polysaccharide sulfate.

[0068] In some more preferred embodiments of the present application, in step S2, the solvent I includes at least one of N,N-dimethylformamide, tetrahydrofuran, acetone or dichloromethane.

[0069] In some more preferred embodiments of the present application, in step S2, the solid-state electrolyte-coated active material, the lithium polysaccharide sulfate and the solvent I are mixed to obtain the mixture II, and the mixture II is stirred and heated to remove the solvent I to obtain the positive electrode material.

[0070] In some more preferred embodiments of the present application, in step S2, after the solvent I is removed, the positive electrode material is obtained by drying.

[0071] In some preferred embodiments of the present application, in step S2, the solid-state electrolyte-coated active material, the lithium polysaccharide sulfate and the solvent I are mixed to obtain the mixture II, and the mixture II is stirred and heated, incubated, dried to remove the solvent I to obtain the positive electrode material.

[0072] In some more preferred embodiments of the present application, in step S2, the stirring and heating temperature is 50-70℃.

[0073] In some more preferred embodiments of the present application, in step S2, the incubation temperature is 105-125℃.

[0074] In some more preferred embodiments of the present application, in step S2, the incubation time is 3-5h.

[0075] In some more preferred embodiments of the present application, in step S2, the solvent I is removed by evaporation under reduced pressure.

[0076] In some more preferred embodiments of the present application, in step S2, the drying temperature is 90-110℃.

[0077] In some more preferred embodiments of the present application, in step S2, the drying time is 20-30h.

[0078] In some embodiments of the present application, the preparation method further comprises preparing the core.

[0079] In some preferred embodiments of the present application, the core comprises lithium cobaltate, which is prepared by sol-gel method.

[0080] In the present application, the LiCoO2 is prepared by sol-gel method, which is beneficial to the coating of the material and the bulk diffusion of the coated material, thus integrating the advantages of doping and coating in one. Meanwhile, the nanoparticles increase the specific surface area of the lithium cobaltate cathode material, which is beneficial to the deintercalation and intercalation of lithium ions and improves the cycle performance.

[0081] In some more preferred embodiments of the present application, the preparation of the lithium cobaltate comprises the following steps:

[0082] The mixture containing lithium acetate and cobalt carbonate is adjusted in pH to obtain a gel, which is calcined to obtain the lithium cobaltate.

[0083] In some more preferred embodiments of the present application, ammonia is used to adjust the pH.

[0084] In some more preferred embodiments of the present application, the calcination temperature is 800-1000℃.

[0085] In some more preferred embodiments of the present application, the calcination time is 12-20h.

[0086] In some more preferred embodiments of the present application, the calcination is performed under a protective atmosphere.

[0087] In some more preferred embodiments of the present application, the protective atmosphere is nitrogen atmosphere.

[0088] In some more preferred embodiments of the present application, the preparation of the lithium cobaltate comprises the following steps: the mixture of lithium acetate, cobalt carbonate and water is adjusted in pH to obtain a sol, then water is removed to obtain a gel, which is dried and calcined to obtain the lithium cobaltate.

[0089] In some more preferred embodiments of the present application, the drying is performed by reduced pressure drying at 90-120℃.

[0090] In some embodiments of the present application, the preparation method further comprises the preparation of a solid electrolyte.

[0091] In some preferred embodiments of the present application, the solid electrolyte comprises lithium thiophosphates, and the preparation of the lithium thiophosphates specifically comprises the following steps: the mixture containing P2S5 and Li2S is ball milled and heat treated to obtain lithium thiophosphates.

[0092] In some more preferred embodiments of the present application, the ball milling time is 12-16h.

[0093] In some more preferred embodiments of the present application, the lithium thiophosphate is prepared by the following steps: ball-milling a mixture of P2S5 and Li2S, tabletting, heat-treating to obtain the lithium thiophosphate.

[0094] In some more preferred embodiments of the present application, the heat-treating is first heating and then holding.

[0095] In some more preferred embodiments of the present application, the holding temperature is 235-255℃.

[0096] In some more preferred embodiments of the present application, the holding time is 0.5-2h.

[0097] In some more preferred embodiments of the present application, the heat-treating is in a closed environment.

[0098] In some embodiments of the present application, the preparation method further comprises preparing lithium polysaccharide sulfate.

[0099] In some preferred embodiments of the present application, the lithium polysaccharide sulfate comprises lithium galactosan sulfate, and the preparation steps of the lithium galactosan sulfate comprise the following steps: esterification of galactosan with chlorosulfonic acid, and then reacting with LiOH to obtain the lithium galactosan sulfate.

[0100] In some more preferred embodiments of the present application, the lithium galactosan sulfate is prepared by the following steps: stirring and heating a mixture of galactosan and chlorosulfonic acid, cooling, adding LiOH solution to obtain the lithium galactosan sulfate.

[0101] In some more preferred embodiments of the present application, the stirring and heating temperature is 50-70℃.

[0102] In some more preferred embodiments of the present application, the stirring and heating time is 1-5h.

[0103] In some more preferred embodiments of the present application, the stirring and heating time is 2-4h.

[0104] In some more preferred embodiments of the present application, the lithium galactosan sulfate is prepared by the following steps: stirring and heating a mixture of galactosan, chlorosulfonic acid and solvent II, cooling, adding LiOH solution, dialysis, lyophilization to obtain the lithium galactosan sulfate.

[0105] In some more preferable embodiments of the present application, the preparation of the lithium galactosan sulfate specifically comprises the following operations: heating and stirring a mixture of galactosan, chlorosulfonic acid and solvent II, cooling to obtain an esterification product, adding water, adding a LiOH solution to pH = 6.5-7.5, dialysis, freeze-drying, vacuum drying to obtain the lithium galactosan sulfate.

[0106] In some more preferable embodiments of the present application, the temperature of the vacuum drying is 100-120℃, and the drying time is 20-28h.

[0107] In a third aspect of the present application, a positive electrode is provided, which is prepared from the material comprising the above positive electrode material.

[0108] Through the above embodiments, the positive electrode in the present application can be applied to a secondary battery, has the characteristics of structural stability at high voltage, can meet the charge-discharge requirements in the 4.48V system, and can meet the charge-discharge requirements in the 4.5V and 4.53V systems.

[0109] In a fourth aspect of the present application, a secondary battery is provided, which contains the above positive electrode.

[0110] In some embodiments of the present application, the secondary battery comprises at least one of a lithium ion battery or a sodium ion battery.

[0111] In a fifth aspect of the present application, the above positive electrode material is applied to the preparation of an electrical device. BRIEF DESCRIPTION OF DRAWINGS

[0112] The present application will be further described below in conjunction with the drawings and examples, in which:

[0113] Figure 1 The XRD test result graph of the raw material-LiCoO2 and Li3PS4-coated LiCoO2 of Example 4 of the present application;

[0114] Figure 2 The interface contrast graph of the electrode sheet after cycling of the battery prepared in Example 7 and the comparative example of the present application. DETAILED DESCRIPTION

[0115] The concept and technical effects of the present application will be described below in conjunction with examples, so as to fully understand the purpose, features and effects of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0116] Example 1

[0117] The present embodiment discloses a positive electrode material, which comprises Li3PS4-coated LiCoO2 solid electrolyte, and specifically, the positive electrode material comprises an inner core (lithium cobaltate) and a solid electrolyte layer arranged on the surface of the inner core. The preparation process of the positive electrode material comprises the following steps:

[0118] (I) Preparation of Li3PS4-coated LiCoO2 solid electrolyte, which comprises the following steps:

[0119] First, 0.5 g of Li3PS4 solid particles and 99.5 g of nano lithium cobaltate are added to 250 mL of isopropyl alcohol (commercially available from Aldrich) and ball-milled for 3 h at a rotation speed of 1000 rpm. Then, the mixture is dried at 80°C for 8 h and sintered at 650°C for 5-6 h to obtain 100 g of Li3PS4-modified LiCoO2 powder (referred to as Li3PS4-coated LiCoO2). The thickness of the Li3PS4 coating layer (i.e., the solid electrolyte layer) is about 10-15 nm.

[0120] In the positive electrode material, the mass percentage of Li3PS4 in the Li3PS4-coated LiCoO2 is 0.5%.

[0121] The present embodiment also provides a positive electrode, which comprises the positive electrode material prepared in the present embodiment. The preparation process of the positive electrode comprises the following steps: the positive electrode material (Li3PS4-coated LiCoO2), conductive carbon (Super P), and binder polyvinylidene fluoride are dissolved in an N-methylpyrrolidone solvent system at a weight ratio of 90:5:5, and then stirred and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry is coated on an aluminum foil, vacuum dried at 120°C for 12 h, and then cut into a circular piece with a diameter of 14 mm to obtain a positive electrode sheet.

[0122] The present embodiment also provides a lithium ion button cell, which comprises the positive electrode prepared in the present embodiment and further comprises a negative electrode and an electrolyte.

[0123] The negative electrode is metal lithium.

[0124] The electrolyte is a solution prepared by mixing lithium salt LiPF6 and non-aqueous organic solvent at a mass ratio of 8:92, wherein the non-aqueous organic solvent is a solvent obtained by mixing ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) at a mass ratio of 20:30:20:28:2.

[0125] The preparation process of the lithium ion button cell comprises the following steps: the positive electrode sheet, the negative electrode, and the electrolyte prepared above are assembled into a CR2032 button cell in an argon-filled glove box.

[0126] The embodiment further provides a lithium ion button cell comprising the lithium ion button cell prepared in the embodiment.

[0127] Embodiment 2

[0128] The embodiment discloses a positive electrode material, which is different from the positive electrode material in Embodiment 1 only in that the amount of Li3PS4 used in step (I) is 2 g, and the amount of lithium cobaltate used is 98 g. In the positive electrode material prepared in the embodiment, the mass percentage of Li3PS4 in Li3PS4-coated LiCoO2 is 2%.

[0129] The embodiment further provides a positive electrode comprising the positive electrode material prepared in the embodiment, and specifically, the positive electrode is prepared in the same way as in Embodiment 1.

[0130] The embodiment further provides a lithium ion button cell comprising a positive electrode, wherein the positive electrode comprises the positive electrode material prepared in the embodiment, and specifically, the lithium ion button cell is prepared in the same way as in Embodiment 1.

[0131] Embodiment 3

[0132] The embodiment discloses a positive electrode material, which is different from the positive electrode material in Embodiment 1 only in that the amount of Li3PS4 used in step (I) is 4 g, and the amount of lithium cobaltate used is 96 g. In the positive electrode material prepared in the embodiment, the mass percentage of Li3PS4 in Li3PS4-coated LiCoO2 is 4%.

[0133] The embodiment further provides a positive electrode comprising the positive electrode material prepared in the embodiment, and specifically, the positive electrode is prepared in the same way as in Embodiment 1.

[0134] The embodiment further provides a lithium ion button cell comprising a positive electrode, wherein the positive electrode comprises the positive electrode material prepared in the embodiment, and specifically, the lithium ion button cell is prepared in the same way as in Embodiment 1.

[0135] Embodiment 4

[0136] The embodiment discloses a positive electrode material, which is different from the positive electrode material in Embodiment 1 only in that the amount of Li3PS4 used in step (I) is 6 g, and the amount of lithium cobaltate used is 94 g. In the positive electrode material prepared in the embodiment, the mass percentage of Li3PS4 in Li3PS4-coated LiCoO2 is 6%.

[0137] The embodiment further provides a positive electrode comprising the positive electrode material prepared in the embodiment, and specifically, the positive electrode is prepared in the same way as in Embodiment 1.

[0138] The embodiment also provides a lithium ion button cell, which comprises a positive electrode, and the positive electrode comprises the positive electrode material prepared in the embodiment.

[0139] Embodiment 5

[0140] The embodiment discloses a positive electrode material, which is different from the positive electrode material in Embodiment 1 only in that the amount of Li3PS4 used in step (I) is 7 g, and the amount of lithium cobaltate used is 93 g. In the positive electrode material prepared in the embodiment, the mass percentage of Li3PS4 in Li3PS4-coated LiCoO2 is 7%.

[0141] The embodiment also provides a positive electrode, which comprises the positive electrode material prepared in the embodiment, and the positive electrode is prepared according to Embodiment 1.

[0142] The embodiment also provides a lithium ion button cell, which comprises a positive electrode, and the positive electrode comprises the positive electrode material prepared in the embodiment, and the lithium ion button cell is prepared according to Embodiment 1.

[0143] Embodiment 6

[0144] The embodiment discloses a positive electrode material, which comprises Li3PS4-coated LiCoO2, and the positive electrode material specifically comprises a core (lithium cobaltate) and a coating layer arranged on the surface of the core, wherein the coating layer comprises a solid electrolyte layer and a lithium galactosan sulfate layer, the solid electrolyte layer is arranged between the core and the lithium galactosan sulfate layer, and the positive electrode material is prepared according to the following steps.

[0145] (I) Preparation of Li3PS4-coated LiCoO2, which comprises the following steps:

[0146] First, 6 g of Li3PS4 solid particles and 94 g of nano lithium cobaltate are added into 250 mL of isopropyl alcohol (which can be purchased from Aldrich) and are subjected to ball milling at a speed of 1000 rpm for 3 h. Then, the mixture is dried at 80 ℃ for 8 h and is sintered at 650 ℃ for 5-6 h to obtain 100 g of Li3PS4-modified LiCoO2 powder (abbreviated as: Li3PS4-coated LiCoO2), and the thickness of the Li3PS4 coating layer (i.e., the solid electrolyte layer) is about 10-15 nm.

[0147] (II) Lithium galactosan sulfate coating of the Li3PS4-modified LiCoO2 obtained in step (I), which comprises the following steps:

[0148] 2 g of lithium galactosan sulfate powder (lithium galactosan sulfate in this embodiment is prepared by the present application; it can also be purchased from the conventional market, such as formula (1), for example, with a molecular weight of 500.49, which can be purchased from Aladdin), 98 g of Li3PS4-coated LiCoO2 obtained in step (I) and 100 mL of N,N-dimethylformamide (DMF) are mixed, heated to 60°C and stirred until completely dissolved, then heated to 115°C and stirred for 4 h to obtain a mixed solution with a mass fraction of 2% (in the mixed solution, based on the sum of the mass of Li3PS4-coated LiCoO2 and lithium galactosan sulfate, the mass fraction of lithium galactosan sulfate is 2%). Then the solvent (DMF) is removed by rotary evaporation under reduced pressure, and the mixture is dried in a vacuum drying oven at 100°C for 24 h to obtain the positive electrode material, i.e., the modified LiCoO2 coated with lithium galactosan sulfate and solid electrolyte (referred to as double-layer coated LiCoO2), wherein the thickness of the lithium galactosan sulfate coating layer (i.e., the lithium polysaccharide sulfate layer) is about 5-8 nm, and the D v05 50 μm, and D v50 16 μm.

[0149] In the positive electrode material, the mass ratio of lithium galactosan sulfate, Li3PS4 and the inner core is 2:5.88:92.12, and the mass fraction of lithium galactosan sulfate is 2%.

[0150] The present embodiment also provides a positive electrode comprising the positive electrode material prepared in the present embodiment, and the preparation process of the positive electrode is the same as that of Example 1. Specifically, the preparation process of the positive electrode comprises: dissolving the positive electrode material (double-layer coated LiCoO2), conductive carbon (Super P) and binder polyvinylidene fluoride in N-methylpyrrolidone solvent system according to a weight ratio of 90:5:5, thoroughly stirring and mixing to obtain a positive electrode slurry. The positive electrode slurry is coated on an aluminum foil, vacuum dried at 120°C for 12 h, and a circular piece with a diameter of 14 mm is cut to obtain a positive electrode sheet.

[0151] The present embodiment also provides a lithium ion button cell comprising the positive electrode prepared in the present embodiment, and further comprising a negative electrode and an electrolyte.

[0152] The negative electrode is metal lithium.

[0153] The electrolyte is a solution prepared by mixing lithium salt LiPF6 and non-aqueous organic solvent according to a mass ratio of 8:92, wherein the non-aqueous organic solvent is a solvent obtained by mixing ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP) and vinylene carbonate (VC) according to a mass ratio of 20:30:20:28:2.

[0154] The preparation process of the lithium ion button cell comprises assembling the prepared positive electrode sheet, negative electrode and electrolyte into a CR2032 button cell in an argon-filled glove box.

[0155] The embodiment further provides a power utilization device comprising the lithium ion button cell prepared in the embodiment.

[0156] Embodiment 7

[0157] The embodiment discloses a positive electrode material, and the preparation process of the positive electrode material is the same as that of Embodiment 6, and the difference between the positive electrode material and Embodiment 6 is that the amount of lithium sulfate galactan powder is 3 g in step (II), and the amount of modified LiCoO2 obtained in step (I) is 97 g.

[0158] The embodiment further provides a positive electrode, and the positive electrode comprises the positive electrode material prepared in the embodiment, and specifically, the preparation process of the positive electrode is the same as that of Embodiment 6.

[0159] The embodiment further provides a lithium ion button cell, and the lithium ion button cell comprises the positive electrode, the positive electrode comprises the positive electrode material prepared in the embodiment, and specifically, the preparation process of the lithium ion button cell is the same as that of Embodiment 6.

[0160] The embodiment further provides a power utilization device comprising the lithium ion button cell prepared in the embodiment.

[0161] Comparative example

[0162] The comparative example discloses a positive electrode material, and the difference between the positive electrode material and Embodiment 1 is that the lithium cobaltate in the comparative example is not coated with Li3PS4, that is, the positive electrode material in the comparative example is nano lithium cobaltate.

[0163] The comparative example further provides a positive electrode, and the positive electrode comprises the positive electrode material in the comparative example, and specifically, the preparation process of the positive electrode is the same as that of Embodiment 1.

[0164] The comparative example further provides a lithium ion button cell, and the lithium ion button cell comprises the positive electrode, the positive electrode comprises the positive electrode material prepared in the comparative example, and specifically, the preparation process of the lithium ion button cell is the same as that of Embodiment 1.

[0165] Part of the information of the positive electrode material in the above embodiment and comparative example is shown in Table 1.

[0166] Table 1 Information of the positive electrode material in the embodiment and comparative example

[0167]

[0168]

[0169] The lithium cobaltate, Li3PS4 and lithium galactosan sulfate used in the above examples and comparative examples can be purchased from the market or prepared by the following method.

[0170] (1) Preparation of lithium galactosan sulfate powder, comprising the following steps:

[0171] 100 g of galactosan, 163 g of chlorosulfonic acid (HClO3S) and 250 mL of N, N-dimethylformamide (DMF) were heated at 60°C with stirring for 2-4 h, and after cooling to room temperature, an esterification product was obtained. The esterification product was dissolved in 150 mL of water to obtain a solution containing the esterification product. Then a certain amount of LiOH solution was added to the above solution until pH ≈ 7 to obtain a lithium galactosan sulfate solution. Lithium galactosan sulfate was obtained by dialysis and lyophilization. After vacuum drying at 110°C for 24 h, lithium galactosan sulfate solid was obtained, which was ground to obtain lithium galactosan sulfate powder.

[0172] (2) Preparation of nano lithium cobaltate (LiCoO2), prepared by sol-gel method, comprising the following steps:

[0173] Using lithium acetate and cobalt carbonate as raw materials, the cobalt carbonate and lithium acetate were dissolved in deionized water at 80°C in a molar ratio of 1:1.05, and the pH was adjusted with ammonia until a blue sol was obtained (color change as the end point of ammonia adjustment). Then the solvent water was evaporated to form a red wet gel, which was then dried at 110°C under reduced pressure to form a purple-red dry gel. The dry gel was then broken in a high-speed pulverizer at a speed of 5000 r / min (2000-8000 r / min can also be used), the pulverizing time was 5-8 min, the pulverizing times was 5-7 times, and the nano LiCoO2 was obtained by calcining at 920°C for 16-18 h under nitrogen.

[0174] (3) Preparation of Li3PS4 solid-state electrolyte, comprising the following steps:

[0175] Put 616.7 g of P2S5 and 383.3 g of Li2S in a ball mill jar in proportion and ball mill for 14 h, then press the obtained powder into a mold at a pressure of about 360 MPa, and then seal it in a ceramic crucible for heat treatment, with a heating rate of 3°C / min, and a final temperature of 243°C, and heat for 1 h to obtain Li3PS4 solid-state electrolyte.

[0176] Test Example

[0177] The positive electrode materials and lithium ion batteries obtained in the examples and comparative examples were tested for performance in this test example, which specifically included:

[0178] 1. XRD test of raw materials-LiCoO2 and Li3PS4 coated LiCoO2 in Example 4, the test results are as follows: Figure 1As shown, compared with LiCoO2, the diffraction peak position of Li3PS4-coated LiCoO2 did not change, indicating that Li3PS4-coated LiCoO2 did not change the structure of LiCoO2.

[0179] 2. Gram capacity test: At 25°C, the charge and discharge performance of the material was studied by constant current charge and discharge (0.1C), and the voltage range was 3.0V-4.5V; the first charge and discharge efficiency was calculated according to the charge and discharge gram capacity.

[0180] 3. Normal temperature cycle performance test: At 25°C, the button cell was charged to 4.50V at 0.1C constant current and constant voltage, and the cutoff current was 0.05C, then discharged to 3.0V at 0.1C constant current, and the cycle was repeated, and the capacity retention rate at the 50th week was calculated after 80 cycles of charge and discharge, and the calculation formula was as follows:

[0181] The 50th week cycle capacity retention rate (%) = (the 50th week cycle discharge capacity / the first cycle discharge capacity) x 100%.

[0182] 4. Lithium cobaltate crack number test: The morphology of lithium cobaltate was visualized by scanning electron microscopy, and the number of lithium cobaltate cracks was calculated under 1000 times magnification.

[0183] 5. Microstructure test of the interface of the electrode sheet of the battery prepared in Example 7 and the comparative example after cycling, and the test results are shown in Figure 2

[0184] The test results of the above battery performance are shown in Table 2 as follows:

[0185] Table 2 Battery performance test results

[0186]

[0187]

[0188] From the comparison of the test results of Examples 1-5 and the comparative example in Table 2, it can be seen that coating Li3PS4 on the surface of lithium cobaltate can significantly reduce the impedance and improve the cycle retention rate, and with the increase of the coating amount, the improvement effect is more significant, and the performance of Li3PS4 coating amount of 6wt% and 7wt% is similar, so 6wt% is selected as the optimal coating amount. The test data of the comparative example and Examples 6-7 show that when the coating amount of lithium galactosan sulfate sulfate on the surface of lithium cobaltate is 2.0wt% and the coating amount of Li3PS4 is 6.0wt%, the cycle capacity retention rate and the first charge and discharge efficiency of the button cell can be significantly improved. When the coating amount of lithium galactosan sulfate sulfate is too thick (the mass fraction in the positive electrode material is more than 3%), the impedance of the lithium battery will increase.

[0189] ​As can be seen from the above, lithium galactosan sulfate can improve the material stability of lithium cobaltate, Li3PS4 can effectively reduce the impedance of lithium battery and improve the ion conductivity, and the combination of the two can effectively improve the cycle capacity retention rate of lithium cobaltate positive electrode material.

[0190] The lithium galactosan sulfate and Li3PS4 are used as coating materials to coat the surface of the traditional lithium cobaltate positive electrode material, without changing the structure of lithium cobaltate, the structural stability of the lithium cobaltate positive electrode material in the liquid electrolyte is improved, the ion conductivity of the lithium cobaltate positive electrode material is enhanced, and the impedance is reduced. Specifically, the lithium galactosan sulfate is used as a matrix to provide good ion channel arrangement and excellent mechanical strength. Compared with the traditional binder PVDF, the sulfate group in the lithium galactosan sulfate can form stable hydrogen bonds with the trace amount of water on the surface of LiCoO2 particles and most oxygen-containing groups such as aluminum foil, so that the bonding state between LiCoO2 and aluminum foil can be improved, and the mechanical properties can be improved. Moreover, the lithium galactosan sulfate can form a protective barrier between lithium cobaltate and electrolyte, so that the corrosion of the surface of lithium cobaltate caused by the direct contact between the liquid electrolyte and lithium cobaltate is avoided, while the lithium ion insertion and migration efficiency of the modified lithium cobaltate is not affected, and the stability and safety of the traditional lithium battery in the cycle process are improved. As a new type of solid-state electrolyte, compared with the traditional solid-state electrolyte, the chemical stability between Li3PS4 and metal lithium is good, the good ion conductivity of Li3PS4 can effectively reduce the cathode electrolyte interface impedance of lithium cobaltate positive electrode material, and improve the lithium ion transmission efficiency. The battery prepared by using the positive electrode material prepared in the embodiment of the present application has the characteristics of structural stability at high voltage, can meet the charge and discharge requirements in the 4.48V system, and can meet the charge and discharge requirements in the 4.5V and 4.53V systems.

[0191] Meanwhile, the LiCoO2 is prepared by the sol-gel method, which is beneficial to the coating of the material and the bulk diffusion of the coating material, so that the advantages of doping and coating are integrated. At the same time, the nanoparticles increase the specific surface area of the lithium cobaltate positive electrode material, which is beneficial to the deintercalation and intercalation of lithium ions, and improves the cycle performance.

[0192] It should be noted that, in this paper, "room temperature" and "normal temperature" are about 25℃ unless otherwise specified; the meaning of "about" related to numerical values in this paper is an error of ±2%.

[0193] The embodiments of the present application are described in detail above in combination with the drawings, but the present application 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 purpose of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A positive electrode material, characterized in that, The cathode material comprises a core and a coating layer disposed on the surface of the core. The core includes an active material. The coating layer includes a solid electrolyte layer and a lithium polysaccharide sulfate layer. The solid electrolyte layer is disposed between the core and the lithium polysaccharide sulfate layer. The solid electrolyte layer contains a solid electrolyte, which is lithium thiophosphate. The lithium polysaccharide sulfate layer contains lithium polysaccharide sulfate, which is lithium galactomannan sulfate. The mass ratio of the solid electrolyte layer to the core is (0.1-10):(90-99.5). In the cathode material, the mass fraction of the lithium polysaccharide sulfate layer is 0.1-10%.

2. The cathode material according to claim 1, characterized in that, The thickness of the lithium sulfate polysaccharide layer is 2-12 nm.

3. The cathode material according to claim 1, characterized in that, The thickness of the solid electrolyte layer is 5-20 nm.

4. The cathode material according to claim 1, characterized in that, The active material includes at least one of lithium manganese oxide, lithium cobalt oxide, or lithium iron phosphate.

5. A method for preparing the positive electrode material according to any one of claims 1-4, characterized in that, The process includes the following steps: preparing a solid electrolyte layer on the core surface, and then preparing a lithium sulfate polysaccharide layer to obtain the cathode material.

6. The method for preparing the cathode material according to claim 5, characterized in that, The preparation method includes the following steps: S1, sinter the mixture I containing solid electrolyte and active material to obtain active material coated with solid electrolyte; S2, a mixture II of active material containing solid electrolyte coating and lithium sulfate polysaccharide is heated to obtain the positive electrode material.

7. The method for preparing the cathode material according to claim 5, characterized in that, The preparation method further includes the preparation of lithium polysaccharide sulfate; the lithium polysaccharide sulfate includes lithium galactomannan sulfate, and the preparation steps of the lithium galactomannan sulfate include the following operations: galactomannan is esterified with chlorosulfonic acid, and then reacted with LiOH to obtain the lithium galactomannan sulfate.

8. A positive electrode, characterized in that, The positive electrode is made of a material comprising the positive electrode material as described in any one of claims 1-4.

9. A secondary battery, characterized in that, The secondary battery contains the positive electrode as described in claim 8.

10. The application of the cathode material according to any one of claims 1-4 in the preparation of electrical devices.

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