Positive electrode material with surface modification of sulfur element, preparation method thereof and solid-state lithium battery

Abstract

The application discloses a positive electrode material with a sulfur element surface modification, a preparation method thereof and a solid-state lithium battery, and relates to the technical field of lithium batteries. x or LiM2O4-2xS 2x wherein M is one or more of Co, Ni and Mn, 0.05

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium batteries, in particular to a positive electrode material with surface modification of sulfur element, a preparation method thereof and a solid-state lithium battery. BACKGROUND

[0002] Lithium batteries have been widely used in digital products, power and energy storage fields. The existing commercialized lithium batteries mainly use liquid electrolyte, which has problems such as easy volatilization, easy corrosion, flammability, explosion risk and poor thermal stability. During use, thermal runaway may occur, which may cause safety problems. The solid-state lithium battery uses solid electrolyte instead of liquid electrolyte, which can fundamentally solve the safety problem of lithium batteries.

[0003] Among the solid-state electrolytes used in solid-state lithium batteries, sulfide solid-state electrolytes have the optimal ionic conductivity and suitable processing performance, and are considered as a strong candidate material for solid-state lithium batteries. However, the stability of sulfide solid-state electrolytes is poor, and the electrochemical window is narrow. When in contact with high-voltage oxide positive electrode materials, a series of side reactions may occur, which reduces the ionic conductivity of sulfides and leads to the performance degradation of the battery.

[0004] Therefore, it is necessary to modify the surface of the positive electrode material, so that the surface of the positive electrode material can be compatible with sulfides, reduce the interfacial resistance, reduce the side reactions on the interface, and maintain the electrochemical stability of the positive electrode. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a positive electrode material with surface modification of sulfur element, a preparation method thereof and a solid-state lithium battery.

[0006] The positive electrode material with surface modification of sulfur element disclosed by the present application is LiMO2-xS x or LiM2O4-2xS 2x wherein M is one or more of Co, Ni and Mn, and 0.05 < x < 0.3.

[0007] The preparation method of the positive electrode material with surface modification of sulfur element disclosed by the present application comprises the following steps:

[0008] S1. 100 parts of positive electrode substrate are added to 900-1200 parts of sulfurizing agent solution to obtain a dispersion liquid;

[0009] S2. The dispersion liquid is added to a reaction kettle for reaction to obtain an intermediate product;

[0010] S3. The intermediate product is cleaned and dried to obtain the positive electrode material with surface modification of sulfur element.

[0011] According to an embodiment of the present application, the positive electrode substrate is one or more of layered oxides, spinel oxides.

[0012] According to an embodiment of the present application, the positive electrode substrate is one or more of lithium cobaltate, lithium nickelate, ternary materials, lithium manganate, lithium nickel manganate.

[0013] According to an embodiment of the present application, the sulfurizing agent solution comprises a sulfurizing agent and a solvent, wherein the content of the sulfurizing agent is 0.5-10 parts.

[0014] According to an embodiment of the present application, the sulfurizing agent is one or more of sodium sulfide, thiourea.

[0015] According to an embodiment of the present application, the solvent is one or more of water, ethanol, methanol, acetone, NMP, THF, DMF.

[0016] According to an embodiment of the present application, in the S2 step, the reaction temperature is 140-210℃, the stirring rate is 300-800 rpm, and the reaction time is 4-12 h.

[0017] According to an embodiment of the present application, in the S3 step, the intermediate product is washed with deionized water, and the intermediate product is vacuum dried at 60-80℃.

[0018] The solid-state lithium battery disclosed in the present application is characterized in that the solid-state lithium battery comprises the sulfur element surface modified positive electrode material as described above.

[0019] Compared with the prior art, the sulfur element surface modified positive electrode material, the preparation method thereof, and the solid-state lithium battery have the following advantages:

[0020] The preparation method of the sulfur element surface modified positive electrode material of the present application forms a sulfur-rich layer doping modification on the surface of the positive electrode material through ion exchange reaction of the sulfurizing agent, so as to improve the interface compatibility of the positive electrode material and the sulfide solid-state electrolyte, reduce the interface contact resistance, have faster charge transfer capacity, and thus improve the performance of the sulfide solid-state lithium battery. DETAILED DESCRIPTION

[0021] The embodiments of the present application will be described below. Many practical details will be described in the following description for the purpose of clear illustration. However, it should be understood that these practical details should not be used to limit the present application. That is, in some embodiments of the present application, these practical details are not necessary. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it. When the combination of technical solutions contradicts each other or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0022] The application discloses a positive electrode material with surface modification of sulfur elements, which has a chemical formula of LiMO2-xS x or LiM2O4-2xS 2x wherein M is one or more of Co, Ni and Mn, and 0.05 < x < 0.3.

[0023] The application discloses a preparation method of the positive electrode material with surface modification of sulfur elements, which comprises the following steps:

[0024] S1. 100 parts of a positive electrode substrate are added into 900-1200 parts of a sulfurizing agent solution to obtain a dispersion liquid;

[0025] S2. The dispersion liquid is added into a reaction kettle to perform a reaction, so as to obtain an intermediate product;

[0026] S3. The intermediate product is cleaned and dried to obtain the positive electrode material with surface modification of sulfur elements.

[0027] Further, the positive electrode substrate in the step S1 is one or more of a layered oxide and a spinel oxide. The layered oxide has a chemical formula of LiMO2, and M is one or more of Co, Ni and Mn. The spinel oxide has a chemical formula of LiM2O4, and M is Mn or Mn and Ni, and the ratio of Mn to Ni is 3:1. Specifically, the positive electrode substrate is one or more of lithium cobaltate, lithium nickelate, a ternary material, lithium manganate (LiMn2O4) and lithium nickel manganate (LiNi 0.5 Mn 1.5 O4).

[0028] Further, the sulfurizing agent solution in the step S1 comprises a sulfurizing agent and a solvent, wherein the content of the sulfurizing agent is 0.5-10 parts. Specifically, the sulfurizing agent is one or more of sodium sulfide (Na2S) and thiourea, and the solvent is one or more of water, ethanol, methanol, acetone, NMP, THF and DMF.

[0029] Further, in the step S2, the reaction temperature is 140-210℃, the stirring rate is 300-800 rpm, and the reaction time is 4-12 h.

[0030] Further, in the step S3, the cleaning of the intermediate product adopts deionized water, and the drying of the intermediate product is vacuum drying at 60-80℃.

[0031] The application further discloses a solid-state lithium battery comprising the positive electrode material with surface modification of sulfur elements.

[0032] Furthermore, the solid-state lithium battery includes a positive electrode, a negative electrode, and a sulfide solid electrolyte, with the sulfide solid electrolyte located between the positive and negative electrodes. Specifically, the positive electrode includes a positive current collector and a positive active material layer, the positive active material layer being coated on one or both surfaces of the positive current collector; the positive active material layer includes a conductive agent, a binder, a sulfide solid electrolyte, and the aforementioned sulfur-modified positive electrode material, and the sulfide solid electrolyte accounts for less than 20% of the positive active material layer. The negative electrode includes a negative current collector and a negative active material layer, the negative active material layer being coated on one or both surfaces of the negative current collector.

[0033] Furthermore, the method for preparing this solid-state lithium battery includes the following steps:

[0034] P1. The positive electrode is obtained;

[0035] P2. Obtain the negative electrode;

[0036] P3. Solid-state lithium batteries were produced.

[0037] Among them, the sulfide solid electrolytes are glassy states of 70Li₂S·30P₂S₅, 75Li₂S·25P₂S₅, 80Li₂S·20P₂S₅, 55(66Li₂S·33P₂S₅)·45LiI, 95(60Li₂S·40SiS₂)·5Li₃BO₃(Li₃AlO₃), 77(75Li₂S·25P₂S₅)·33LiBH₄, 40Li₂S·28SiS₂·30LiI, 30Li₂S·26B₂S₃·33LiI, and glass-ceramic states of Li₇P₃S₅. 11 Li7P 2.9 S 10.85 Mo 0.01 Li7P 2.9 Mn 0.1 S 10.7 I 0.3 Argyrodite-type Li6PS5Cl, Li6PS5Br, Li7PS6, Li7Ge3PS 12 Li 6.35 P 0.65 Si 0.35 S5Br, Li 6.6 P 0.4 Ge 0.6 S5I, Thio-LiSICON's Li 3.25 Ge 0.25 P 0.75 S4, Li4SnS4, Li 11 AlP2S 12 Li 3.833 Sn 0.833 As0.166 S4, Li in a crystalline state 10 GeP2S 12 , Li 10 SnP2S 12 , Li 10 SiP2S 12 , Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 , 70Li2S·30P2S5-1,4-butanediol, 75Li2S·25P2S5-PFPE, 77.5Li2S·22.5P2S5-methly-imine. The negative active material layer is one or more of graphite, silicon, silicon-carbon, silicon monoxide, lithium metal.

[0038] The application replaces oxygen elements on the surface of the positive electrode material with sulfur elements by ion exchange in a simple one-step hydrothermal method, to improve the interface compatibility of oxides and sulfides, and further improve the high-voltage stability of sulfide solid electrolytes. The surface sulfur element coverage of the positive electrode material with sulfur element surface modification is as high as 95%, the thickness of the sulfur element modification is 1-10 nm, and the structure of the positive electrode material after the sulfur element modification is unchanged.

[0039] The application will be further described below in combination with specific embodiments.

[0040] Embodiment one

[0041] A positive electrode material with sulfur element surface modification, with a chemical formula of LiCoO 0.95 S 0.05 .

[0042] A preparation method of the positive electrode material with sulfur element surface modification as described above, comprising the following steps:

[0043] S1. 0.025g of thiourea is added to 50mL of water, stirred at room temperature for 10min to obtain a sulfidation agent solution; then 5g of lithium cobaltate is added to the sulfidation agent solution to obtain a dispersion liquid;

[0044] S2. The dispersion liquid is added to a 100mL reaction kettle, and reacted for 6h at a reaction temperature of 180℃ and a stirring speed of 400rpm to obtain an intermediate product;

[0045] S3. After the intermediate product is washed with deionized water, vacuum drying is performed at 60℃ to obtain the positive electrode material with sulfur element surface modification LiCoO 0.95 S 0.05 , wherein the thickness of the sulfur element modification is 10nm.

[0046] The application also discloses a solid-state lithium battery comprising the sulfur element surface modified positive electrode material as described above.

[0047] The solid-state lithium battery comprises a positive electrode, a negative electrode and a sulfide solid-state electrolyte, and a preparation method thereof comprises the following steps:

[0048] P1. 10% Li 10 GeP2S 12 , 86% LiCoO 0.95 S 0.05 , 2% PTFE and 2% SP are mixed and then rolled on an aluminum foil to obtain a positive electrode;

[0049] P2. 10% Li 10 GeP2S 12 , 10% silicon carbon, 78% graphite and 2% CMC are mixed and then coated on a copper foil with a thickness of 9 um to obtain a negative electrode;

[0050] P3. The positive electrode, Li 10 GeP2S 12 and the negative electrode are combined by hot pressing to obtain a solid-state lithium battery, wherein Li 10 GeP2S 12 is located between the positive electrode and the negative electrode, and the thickness of Li 10 GeP2S 12 is 30 um.

[0051] Example Two

[0052] In this example, the chemical formula of the sulfur element surface modified positive electrode material is LiCoO 1.8 S 0.2 .

[0053] The amount of thiourea in the S1 step is 0.1 g.

[0054] The sulfur element surface modified positive electrode material in the S3 step is LiCoO 1.8 S 0.2 , and the thickness of the sulfur element modification is 50 nm.

[0055] In the P1 step, 10% Li 10 GeP2S 12 , 86% LiCoO 0.95 S 0.05 , 2% PTFE and 2% SP are replaced by 8% Li 10 GeP2S 12 , 88% LiCoO 1.8 S 0.2 , 2% PTFE and 2% SP.

[0056] Example Three

[0057] In this embodiment, relative to embodiment one, the thiourea in step S1 is replaced by Na2S, and the amount is unchanged.

[0058] Embodiment four

[0059] In this embodiment, relative to embodiment two, the lithium cobaltate in step S1 is replaced by ternary material NCM111, and the amount is unchanged.

[0060] Embodiment five

[0061] In this embodiment, relative to embodiment two, the chemical formula of the positive electrode material modified by sulfur element is LiNi 0.6 Co 0.2 Mn 0.2 O 1.85 S 0.15 .

[0062] In step S1, the water is replaced by a mixed solution of water and ethanol, and the volume ratio of water to ethanol is 1:1.

[0063] In step S2, the reaction temperature is 140°C, the stirring rate is 500 rpm, and the reaction time is 8h.

[0064] In step S3, the positive electrode material modified by sulfur element is LiNi 0.6 Co 0.2 Mn 0.2 O 1.85 S 0.15 , and the thickness of the sulfur element modification is 5nm.

[0065] Embodiment six

[0066] In this embodiment, relative to embodiment two, the lithium cobaltate in step S1 is replaced by LiNi 0.5 Mn 1.5 O4, and the amount is unchanged.

[0067] Embodiment seven

[0068] In this embodiment, relative to embodiment six, the reaction temperature in step S2 is 160°C, and the reaction time is 6h.

[0069] Embodiment eight

[0070] In this embodiment, relative to embodiment six, the Li 10 GeP2S 12 in steps P1, P2 and P3 is replaced by Li6PS5Cl, and the content is unchanged.

[0071] Embodiment nine

[0072] In this example, relative to Example Eight, Li6PS5C1 in P1, P2 and P3 steps is replaced by Li 3.25 Ge 0.25 P 0.75 S4 and Li4SnS4 in a ratio of 1:3. 3.25 Ge 0.25 P 0.75 S4 and Li4SnS4 in a ratio of 1:3.

[0073] Example Ten

[0074] In this example, relative to Example Nine, copper foil in P2 step is replaced by lithium metal foil with a thickness of 25um.

[0075] Example Eleven

[0076] In this example, relative to Example Ten, 10% Li 3.25 Ge 0.25 P 0.75 S4 and Li4SnS4 in a ratio of 1:3.

[0077] Example Twelve

[0078] In this example, relative to Example Eight, Li6PS5C1 in P3 step has a thickness of 20um.

[0079] Comparative Example One

[0080] A solid-state lithium battery includes a positive electrode, a negative electrode, and a sulfide solid-state electrolyte, and a method for manufacturing the same includes the following steps:

[0081] P1. 10% Li 10 GeP2S 12 S4 and Li4SnS4 in a ratio of 1:3.

[0082] P2. 10% Li 10 GeP2S 12 S4 and Li4SnS4 in a ratio of 1:3.

[0083] P3. The positive electrode, Li 10 GeP2S 12 S4 and Li4SnS4 in a ratio of 1:3. 10 GeP2S 12 S4 and Li4SnS4 in a ratio of 1:3. 10 GeP2S 12 S4 and Li4SnS4 in a ratio of 1:3.

[0084] Comparative Example Two

[0085] In the present comparative example, the lithium cobaltate in the P1 step is replaced by the ternary material NCM622, compared with Comparative Example One.

[0086] Li in the P1, P2 and P3 steps 10 GeP2S 12 is replaced by Li6PS5Cl.

[0087] Comparative Example Three

[0088] In the present comparative example, the lithium cobaltate in the P1 step is replaced by LiNi 0.5 Mn 1.5 O4, compared with Comparative Example One.

[0089] The solid-state lithium batteries prepared in Examples One to Twelve and Comparative Examples One to Three are subjected to performance tests below to study the influence of the sulfur element surface modified cathode material on performance.

[0090] The performance test results are shown in Table 1 below.

[0091] Table 1 Performance Test Results

[0092]

[0093]

[0094] From the comparison between Example One and Comparative Example One and the comparison between Example One and Comparative Example Three, it can be seen that the solid-state lithium battery of Example One is prepared from a sulfur element surface modified cathode material, while the solid-state lithium batteries of Comparative Examples One and Three are prepared from conventional cathode materials. The results show that the interfacial resistance of Example One is much lower than that of Comparative Examples One or Three, and the initial efficiency, the first discharge capacity and the 50th cycle capacity retention rate of Example One are also superior to those of Comparative Examples One or Three.

[0095] From the comparison between Example One and Example Three, it can be seen that the difference between Example One and Example Three lies in the different sulfurizing agents, i.e., thiourea is used in Example One, while Na2S is used in Example Three. The results show that the interfacial resistance of Example One is lower than that of Example Three, and the initial efficiency, the first discharge capacity and the 50th cycle capacity retention rate of Example One are also superior to those of Example Three.

[0096] By comparing Example Two with Example Four, it can be seen that the difference between Example Two and Example Four is the difference of the positive electrode material, Example Two uses lithium cobaltate, while Example Four uses ternary material NCM111. The results show that the interface resistance of Example Two is higher than that of Example Four, the first discharge capacity of Example Two is lower than that of Example Four, and the 50th week capacity retention rate of Example Two is slightly higher than that of Example Four.

[0097] By comparing Example Two with Example Six, it can be seen that the difference between Example Two and Example Six is the difference of the positive electrode material, Example Two uses lithium cobaltate, while Example Six uses LiNi 0.5 Mn 1.5 O4. The results show that the interface resistance of Example Two is lower than that of Example Six, and the initial efficiency, the first discharge capacity and the 50th week capacity retention rate of Example Two are all higher than those of Example Six.

[0098] By comparing Example Six with Example Eight, it can be seen that the difference between Example Six and Example Eight is the difference of the solid-state electrolyte, Example Six uses Li 10 GeP2S 12 , while Example Eight uses Li6PS5Cl. The results show that the interface resistance of Example Six is lower than that of Example Eight, and the initial efficiency, the first discharge capacity and the 50th week capacity retention rate of Example Six are all higher than those of Example Eight.

[0099] By comparing Example Eight with Example Nine, it can be seen that the difference between Example Eight and Example Nine is the difference of the solid-state electrolyte, Example Eight uses Li6PS5Cl, while Example Nine uses Li 3.25 Ge 0.25 P 0.75 S4 and Li4SnS4 mixed electrolyte. The results show that the interface resistance of Example Eight is higher than that of Example Nine, and the initial efficiency and the first discharge capacity of Example Eight are both lower than those of Example Nine.

[0100] By comparing Example Nine with Example Ten, it can be seen that the difference between Example Nine and Example Ten is the difference of the negative electrode current collector, Example Nine uses copper foil, while Example Ten uses lithium metal foil. The results show that the interface resistance of Example Nine is lower than that of Example Ten, the initial efficiency and the first discharge capacity of Example Nine are both higher than those of Example Ten, and the 50th week capacity retention rate of Example Nine is lower than that of Example Ten.

[0101] By comparing Example 10 and Example 11, it can be seen that the difference between Example 10 and Example 11 is the difference in the negative active material, Example 10 uses 10% Li 3.25 Ge 0.25 P 0.75 S4 and Li4SnS4 mixed electrolyte, 10% silicon carbon, 78% graphite and 2% CMC, while Example 11 uses 5% lithium metal and 95% graphite. The results show that the interface resistance of Example 10 is higher than that of Example 11, the initial efficiency of Example 10 is lower than that of Example 11, and the first discharge capacity and 50-week capacity retention rate of Example 10 are higher than those of Example 11.

[0102] By comparing Example 8 and Example 12, it can be seen that the difference between Example 8 and Example 12 is the difference in the thickness of the solid-state electrolyte, the thickness of Example 8 is 30um, and the thickness of Example 12 is 20um. The results show that the interface resistance of Example 8 is higher than that of Example 12, the initial efficiency and the first discharge capacity of Example 8 are higher than those of Example 12, and the 50-week capacity retention rate of Example 8 is lower than that of Example 12.

[0103] In general, Examples 1 to 12 use sulfur element surface modified positive electrode materials, Comparative Examples 1 to 3 use conventional positive electrode materials, by comparison, Examples 1 to 12 have lower interface resistance, faster charge transfer capacity, and better stability of solid-state lithium battery under high and low pressure cycling.

[0104] The above only describes the embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the scope of the claims of the present application.

Claims

1. A method for producing a positive electrode material having a sulfur element surface modification, characterized by, The method comprises the following steps: S1. 100 parts of positive electrode substrate is added into 900-1200 parts of vulcanizing agent solution to obtain a dispersion liquid; S2. The dispersion liquid is added into a reaction kettle for reaction to obtain an intermediate product; S3. The intermediate product is cleaned and dried to obtain a positive electrode material with sulfur element surface modification; In the S2 step, the reaction temperature is 180-210℃, the stirring rate is 300-800 rpm, and the reaction time is 4-12 h; In the S3 step, the cleaning of the intermediate product uses deionized water, and the drying of the intermediate product is vacuum drying at 60-80℃; The sulfur element surface-modified cathode material is LiM02-xS x or LiM2O4-2xS 2x wherein M is one or more of Co, Ni, Mn, and 0.05 The vulcanizing agent solution comprises a vulcanizing agent and a solvent, wherein the content of the vulcanizing agent is 0.5-10 parts; The vulcanizing agent is thiourea.

2. The method for producing a positive electrode material of claim 1, wherein The positive electrode substrate is one or more of layered oxides and spinel oxides.

3. The method of producing a sulfur element surface-modified positive electrode material according to claim 2, characterized by, The positive electrode substrate is one or more of lithium cobaltate, lithium nickelate, ternary material, lithium manganate, and lithium nickel manganate.

4. The method of producing a sulfur element surface-modified positive electrode material according to claim 1, characterized by, The solvent is one or more of water, ethanol, methanol, acetone, NMP, THF, and DMF.

5. A solid-state lithium battery, characterized by, The solid-state lithium battery comprises the positive electrode material with sulfur element surface modification according to claim 1.

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