Positive electrode active material, method for manufacturing same, positive electrode sheet, and all-solid-state lithium battery

Abstract

The application provides a positive electrode active material and a preparation method thereof, a positive electrode sheet and a full-solid-state lithium battery, and relates to the field of lithium ion batteries.The positive electrode active material comprises a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer comprises a polyanion lithium salt and conductive carbon, and the thickness of the coating layer is greater than 10 nm and less than 30 nm.In the coating layer of the application, the polyanion lithium salt and the conductive carbon are included, and the two substances cooperate with each other, so that the direct contact between the layered oxide and the solid-state electrolyte can be better isolated, and the side reaction can be avoided.Further, the conductive carbon in the coating layer can reduce the electron transmission impedance, and is beneficial to the improvement of the electrochemical performance of the positive electrode active material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a positive electrode active material, a preparation method thereof, a positive electrode sheet and a full solid-state lithium battery. BACKGROUND

[0002] In recent years, traditional liquid lithium ion batteries face many challenges such as poor safety and limited energy density, while full solid-state batteries use solid-state electrolyte instead of liquid electrolyte, which can significantly improve the safety and energy density of the battery. Among them, sulfide solid-state electrolyte has high ionic conductivity and excellent mechanical properties, and is considered as the most likely solid-state electrolyte to be scaled up. In addition, the selection of positive electrode active material is also one of the key factors to improve the energy density of full solid-state lithium battery, and the layered oxide positive electrode active material (especially high nickel type positive electrode active material) is a relatively excellent candidate positive electrode active material for full solid-state lithium battery, which has the advantages of high capacity and high theoretical energy density. However, the high nickel positive electrode active material will have chemical and electrochemical side reactions when directly contacted with the sulfide solid-state electrolyte, and the by-products can significantly reduce the transport efficiency of lithium ions or electrons; secondly, due to the large electrochemical potential difference between the two, the Li + will redistribute, forming a few nanometers of high resistance layer (i.e. space charge layer) on the sulfide solid-state electrolyte side, and the charge transfer impedance will be enhanced; thirdly, after the sulfide full solid-state positive electrode is cycled at high temperature for many times, P and S elements will migrate to the positive electrode particles, resulting in capacity attenuation of the positive electrode active material. Finally, the volume change of the positive electrode active material particles will cause the interface between the positive electrode active material and the solid-state electrolyte to be detached during the charging and discharging process of the layered oxide positive electrode active material due to the deintercalation of lithium ions, which will affect the capacity performance and safety performance of the solid-state battery.

[0003] At present, the conventional method to solve the above interface problem is to modify the surface of the positive electrode active material by coating, so as to alleviate the interface side reaction. However, these traditional full solid-state positive electrode active material coating technologies have some defects: first, in order to ensure the capacity, the thickness of the coating layer is 5-10 nm, which is easy to be damaged during the preparation of the battery, and the coating layer will also be detached from the material body due to the volume change of the positive electrode particles during the battery cycle, which will affect the electrical performance of the solid-state battery; second, the commonly used full solid-state positive electrode coating layer material has the characteristics of poor electronic conductivity, and the coating is too thick, which will cause insufficient electronic transport path and seriously affect the battery performance. These coating layer defects are the main factors restricting the low capacity, poor rate and cycle of the full solid-state positive electrode.

[0004] Therefore, it is necessary to improve the positive electrode active material and the preparation method thereof. SUMMARY

[0005] The application aims to provide a positive electrode active material, a preparation method thereof, a positive electrode sheet and a full-solid-state lithium battery, so as to solve the above problems.

[0006] To achieve the above object, the application adopts the following technical solutions:

[0007] A positive electrode active material comprises a layered oxide and a coating layer coated on the surface of the layered oxide, wherein the coating layer comprises a polyanion lithium salt and conductive carbon.

[0008] The thickness of the coating layer is greater than 10 nm and less than 30 nm.

[0009] According to an embodiment of the application, the polyanion lithium salt comprises one or more of lithium phosphate, lithium fluorophosphate, lithium sulfate, lithium borate, lithium silicate, lithium pyrophosphate;

[0010] And / or, the layered oxide comprises LiNi a Co b Mn 1-a-b O2, wherein a>0.7, b>0.

[0011] According to an embodiment of the application, the conductive carbon accounts for 0.1-1.0% of the mass of the layered oxide;

[0012] And / or, the conductive carbon accounts for 10.0-40.0% of the mass of the polyanion lithium salt;

[0013] And / or, the polyanion lithium salt accounts for 0.5-5.0% of the mass of the layered oxide.

[0014] According to an embodiment of the application, the coating layer further comprises lithium fluoride, and the lithium fluoride accounts for 0.5-5.0% of the mass of the layered oxide.

[0015] The application further provides a preparation method of the positive electrode active material as described above, comprising:

[0016] Mixing the layered oxide, the polyanion compound, the lithium source and the organic carbon source, and performing heat treatment under the protection of inert gas to obtain the positive electrode active material.

[0017] According to an embodiment of the application, the polyanion compound comprises one or more of phosphate, fluorophosphate, sulfate, borate, silicate and pyrophosphate; wherein the phosphate comprises ammonium phosphate; the fluorophosphate comprises at least one of ammonium hexafluorophosphate, lithium hexafluorophosphate and sodium hexafluorophosphate.

[0018] And / or, the lithium source comprises a lithium salt or a hydrate of the lithium salt, and the lithium salt comprises one or more of lithium carbonate, lithium hydroxide and lithium sulfate.

[0019] And / or, the organic carbon source is composed of carbon, hydrogen, oxygen elements.

[0020] And / or, the organic carbon source includes one or more of glucose, sucrose, and starch.

[0021] According to the embodiments of the present application, when the polyanion compound is one or more of ammonium phosphate, ammonium fluorophosphate, and ammonium sulfate, the polyanion compound accounts for 0.6-7.5% of the mass of the layered oxide, the lithium salt accounts for 0.5-6.6% of the mass of the layered oxide, and the organic carbon source accounts for 0.5-2.5% of the mass of the layered oxide.

[0022] When the polyanion compound is ammonium borate, the polyanion compound accounts for 1.4-14.5% of the mass of the layered oxide, the lithium salt accounts for 0.8-8.0% of the mass of the layered oxide, and the organic carbon source accounts for 0.5-2.5% of the mass of the layered oxide.

[0023] According to the embodiments of the present application, the inert gas includes nitrogen or argon.

[0024] And / or, the temperature of the heat treatment is 400-1000℃.

[0025] And / or, the time of the heat treatment is 1-10h.

[0026] The present application also provides a positive electrode sheet, which includes a current collector and a functional layer located on one side of the current collector, and the material forming the functional layer includes a sulfide electrolyte, a conductive agent, and a positive electrode active material.

[0027] The positive electrode active material is the positive electrode active material described above or the positive electrode active material prepared by the preparation method described above.

[0028] The present application also provides a full-solid-state lithium battery, which includes the positive electrode sheet described above.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] The sulfide solid-state electrolyte will decompose at high voltage, and its products include polyanion by-products such as phosphate, sulfate, and sulfite. The coating layer of the present application has good chemical stability and electrochemical stability with the by-products. At the same time, the coating layer of the present application contains a polyanion lithium salt, which can effectively inhibit the migration of P and S elements in the sulfide solid-state electrolyte to the layered oxide, and can effectively protect the layered oxide.

[0031] If the coating layer only contains the polyanion compound, the coating layer has poor electronic conductivity, resulting in large electron transmission impedance of the positive electrode active material. The conductive carbon in the coating layer of the present application can effectively solve the problem of electron transmission, and significantly improve the capacity, rate performance, and cycle stability of the solid-state battery.

[0032] In summary, the polyanion lithium salt and the conductive carbon cooperate with each other to significantly improve the electrochemical performance of the positive electrode active material. Moreover, the thickness of the coating layer of the present application is 10 nm to 30 nm, which can make the positive electrode active material have high mechanical performance, and is beneficial to improve the cycle performance of the positive electrode active material.

[0033] The present application also provides a preparation method of the positive electrode active material. The positive electrode active material prepared by the method has high electronic conductivity and high mechanical strength, which can effectively reduce the interface side reaction between the layered oxide and the sulfide solid-state electrolyte, reduce the initial impedance in the full solid-state positive electrode, and significantly improve the capacity, initial efficiency, rate, and cycle performance of the full solid-state battery. Moreover, the method of the present application has the advantages of simple operation and low production cost, which is beneficial to large-scale industrial production.

[0034] The positive electrode sheet and the full solid-state lithium battery of the present application both have excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as limiting the scope of the present application.

[0036] Figure 1 FIG. 1 is a structural schematic diagram of the positive electrode active material of the present application;

[0037] Figure 2 FIG. 2 is a TEM diagram of the positive electrode active material in Example 1;

[0038] Figure 3 FIG. 3 is a structural schematic diagram of the positive electrode active material in Example 2;

[0039] Figure 4 FIG. 4 is a TEM diagram of the positive electrode active material in Comparative Example 2;

[0040] Figure 5 FIG. 5 is a TEM diagram of the positive electrode active material in Comparative Example 3;

[0041] Figure 6 FIG. 6 is a structural schematic diagram of the full solid-state half battery. DETAILED DESCRIPTION

[0042] As used herein:

[0043] "comprises," "comprising," "has," "having," "includes," "including," "contains," "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0044] The transitional phrase "consisting of" excludes any element, step, or ingredient not specified. If used in the claims, this phrase shall not be construed to mean that the claimed composition, process, or method does not incudes elements, steps, or ingredients not specified in the claims. The transitional phrase "consisting of" shall be interpreted in the same way as "consists of" as defined above.

[0045] When expressing a range, concentration, or other value or parameter either as a range, a preferred range, or a series of upper preferred values and lower preferred values, it is to be understood that every range of values between the upper and lower preferred values are specifically contemplated regardless of whether such specific range is explicitly stated herein. For example, where a range of "1 to 5" is disclosed, it is to be understood that the range of "1 to 4," "1 to 3," "1 to 2," "1 to 2 and 4 to 5," "1 to 3 and 5," etc., are also contemplated. When a range of values is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within that range.

[0046] In these examples, unless otherwise indicated, the parts and percentages are by mass.

[0047] "Mass parts" refers to a basic unit of measurement that represents the proportional relationship of the mass of multiple components, 1 part can represent any unit mass, such as 1 g, 2.689 g, etc. If we say that the mass parts of component A is a parts, and the mass parts of component B is b parts, it means that the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK, and the mass of component B is bK (K is an arbitrary number, representing a multiple factor). It must not be misunderstood that, unlike mass parts, the sum of the mass parts of all components is not limited to 100 parts.

[0048] "and / or" is used to indicate one or both of the stated circumstances can occur, for example, A and / or B includes (A and B) and (A or B).

[0049] The present application provides a positive electrode active material, referring to Figure 1, including a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer including a polyanion lithium salt and conductive carbon;

[0050] The thickness of the coating layer is greater than 10 nm and less than 30 nm.

[0051] For example, the thickness of the coating layer can be 10.5 nm, 14 nm, 15 nm, 16 nm, 20 nm, 25 nm, 30 nm, or any value between greater than 10 nm and less than 30 nm.

[0052] The present application can improve the mechanical properties and electrochemical properties of the positive electrode active material by surface coating modification of the layered oxide. Specifically, the coating layer of the present application includes a polyanion lithium salt and conductive carbon, and the two substances cooperate with each other to better isolate the layered oxide from direct contact with the solid-state electrolyte and avoid side reactions. Moreover, the conductive carbon in the coating layer can reduce the electron transport impedance, which is beneficial to the improvement of the electrochemical properties of the positive electrode active material.

[0053] Moreover, compared with conventional positive electrode active materials with a coating structure, the thickness of the coating layer of the present application is greater, and when the thickness of the coating layer is within the range of the present application, the structure of the coating layer is stable and not easy to fall off, which can effectively avoid the direct contact between the layered oxide and the sulfide solid-state electrolyte and avoid the occurrence of the positive electrode interface side reaction of the all-solid-state lithium battery.

[0054] In addition, when the thickness of the coating layer is within the range of the present application, the mechanical strength of the layered oxide can also be improved, the ball cracking of the positive electrode active material due to high-pressure pressing during the battery preparation process and the ball cracking of the layered oxide due to volume change during the battery cycle process can be alleviated, and the interface contact loss between the positive electrode active material and the solid-state electrolyte can be reduced.

[0055] According to an embodiment of the present application, the polyanion lithium salt includes one or more of lithium phosphate, lithium fluorophosphate, lithium sulfate, lithium borate, lithium silicate, and lithium pyrophosphate;

[0056] And / or, the layered oxide includes LiNi a Co b Mn 1-a-b O2, wherein a≥0.7, b≥0.

[0057] Further, a can be 0.8, b can be 0.1, and the layered oxide can be LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811).

[0058] According to embodiments of the present application, the conductive carbon accounts for 0.1-1.0% of the mass of the layered oxide. If the mass ratio of the conductive carbon to the layered oxide is too low, the conductive carbon cannot significantly improve the conductivity. If the mass ratio of the conductive carbon to the layered oxide is too high, the excessive conductive carbon can catalyze the oxidative decomposition of the sulfide solid-state electrolyte, affecting the performance of the battery.

[0059] For example, the conductive carbon accounts for 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any value between 0.1-1.0% of the mass of the layered oxide.

[0060] For example, the conductive carbon accounts for 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any value between 0.1-1.0% of the mass of the layered oxide.

[0061] For example, the conductive carbon accounts for 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any value between 0.1-1.0% of the mass of the layered oxide.

[0062] For example, the conductive carbon accounts for 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any value between 0.1-1.0% of the mass of the layered oxide.

[0063] For example, the conductive carbon accounts for 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any value between 0.1-1.0% of the mass of the layered oxide.

[0064] According to embodiments of the present application, the coating layer further comprises lithium fluoride, and the lithium fluoride accounts for 0.5-5.0% of the mass of the layered oxide. Lithium fluoride has excellent high-pressure stability and ionic conductivity. Lithium fluoride can cooperate with the polyanion lithium salt and the conductive carbon to further improve the transmission of ions and electrons and reduce the interface side reaction, which is conducive to further improving the electrochemical performance of the all-solid-state cathode.

[0065] For example, the lithium fluoride accounts for 0.5%, 1%, 1.5%, 2%, 2.5%, 2.7%, 3%, 3.5%, 4%, 4.5%, 5% or any value between 0.5% and 5.0% of the mass of the layered oxide.

[0066] The application also provides a preparation method of the positive electrode active material as described above, comprising:

[0067] The layered oxide, the polyanion compound, the lithium source and the organic carbon source are mixed, and heat treatment is performed under the protection of an inert gas to obtain the positive electrode active material.

[0068] According to an embodiment of the application, the polyanion compound comprises one or more of a phosphate, a fluorophosphate, a sulfate, a borate, a silicate and a pyrophosphate; wherein the phosphate comprises ammonium phosphate; and the fluorophosphate comprises at least one of ammonium hexafluorophosphate, lithium hexafluorophosphate and sodium hexafluorophosphate. These kinds of polyanion compounds have a relatively low melting point, which is conducive to forming a uniform coating layer on the surface of the layered oxide during heat treatment, so as to isolate the layered oxide and the solid-state electrolyte and alleviate the interface side reaction.

[0069] The polyanion compound is preferably a fluorophosphate. When the polyanion compound is a fluorophosphate, lithium fluoride can be formed in the coating layer. Lithium fluoride has excellent high-voltage stability and ionic conductivity. The lithium fluoride in the coating layer supports and cooperates with each other with the polyanion lithium salt and the conductive carbon, which can more effectively improve the transmission of ions and electrons and reduce the interface side reaction, thereby improving the electrochemical performance of the all-solid-state positive electrode. Specifically, the capacity, the initial efficiency, the rate capability and the cycle performance of the all-solid-state positive electrode can be improved.

[0070] According to an embodiment of the application, the lithium source comprises a lithium salt or a hydrate of the lithium salt, and the lithium salt comprises one or more of lithium carbonate, lithium hydroxide and lithium sulfate.

[0071] And / or, the organic carbon source is composed of carbon, hydrogen and oxygen elements.

[0072] According to an embodiment of the application, the organic carbon source comprises one or more of glucose, sucrose and starch.

[0073] According to the embodiments of the present application, when the polyanionic compound is one or more of ammonium phosphate, ammonium fluorophosphate, ammonium sulfate, the polyanionic compound accounts for 0.6-7.5% of the mass of the layered oxide, the lithium source accounts for 0.5-6.6% of the mass of the layered oxide, and the organic carbon source accounts for 0.5-2.5% of the mass of the layered oxide. When the content of each component is within the above range, it is beneficial to generate a cladding layer with moderate thickness, and the positive electrode active material can have higher capacity, excellent conductivity, etc. If the content of the polyanionic compound is too low, the cladding layer will be too thin, and if the content of the anionic compound is too high, the cladding layer will be too thick; if the content of the lithium source is too low, the polyanionic compound will consume lattice lithium ions of the layered oxide during heat treatment, resulting in reduced capacity, and if the content of the lithium source is too high, the excess lithium ions will form free lithium attached to the surface of the layered oxide, affecting the performance of the battery; if the content of the organic carbon source is too low, the final product formed will have insufficient conductivity, and if the content of the organic carbon source is too high, there will be too much conductive carbon, promoting the decomposition of the sulfide solid electrolyte.

[0074] For example, when the polyanionic compound is one or more of ammonium phosphate, ammonium fluorophosphate, ammonium sulfate, the polyanionic compound accounts for 0.6%, 1%, 1.5%, 2%, 2.5%, 2.6%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.4%, 6.5%, 7%, 7.5%, or any value between 0.6-7.5% of the mass of the layered oxide, the lithium salt accounts for 0.5%, 1%, 1.5%, 2%, 2.2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.4%, 5.5%, 6%, 6.6%, or any value between 0.5-6.6% of the mass of the layered oxide, and the organic carbon source accounts for 0.5%, 1%, 1.3%, 1.5%, 2%, 2.5%, or any value between 0.5-2.5% of the mass of the layered oxide.

[0075] When the polyanionic compound is ammonium borate, the polyanionic compound accounts for 1.4-14.5% of the mass of the layered oxide, the lithium source accounts for 0.8-8.0% of the mass of the layered oxide, and the organic carbon source accounts for 0.5-2.5% of the mass of the layered oxide.

[0076] Further, the ammonium fluorophosphate includes ammonium hexafluorophosphate.

[0077] According to the embodiments of the present application, the inert gas includes nitrogen or argon;

[0078] And / or, the temperature of the heat treatment is 400-1000°C;

[0079] For example, the temperature of the heat treatment can be 400℃, 500℃, 600℃, 700℃, 800℃, 900℃, 1000℃, or any value between 400-1000℃.

[0080] For example, the time of the heat treatment can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or any value between 1-10h.

[0081] For example, the time of the heat treatment can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or any value between 1-10h.

[0082] The application also provides a positive electrode sheet, comprising a current collector and a functional layer on one side of the current collector, the material forming the functional layer comprising a sulfide electrolyte, a conductive agent, and a positive electrode active material.

[0083] The positive electrode active material is the positive electrode active material described above or prepared by the preparation method described above.

[0084] The application also provides a full solid-state lithium battery, comprising the positive electrode sheet described above.

[0085] The embodiments of the application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only for illustration of the application and should not be regarded as limiting the scope of the application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0086] Example 1

[0087] The positive electrode active material in Example 1 comprises a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer comprising a polyanion lithium salt and a conductive carbon; the thickness of the coating layer is greater than 10nm and less than 30nm, the polyanion lithium salt comprises lithium phosphate, and the layered oxide comprises LiNi 0.8 Co 0.1 Mn 0.1 O2, the polyanion lithium salt accounts for 2% of the mass of the layered oxide, the conductive carbon accounts for 0.5% of the mass of the layered oxide, and the conductive carbon accounts for 25% of the mass of the polyanion lithium salt.

[0088] Accurately weigh 10g of NCM811 ternary positive electrode material, 0.26g of ammonium phosphate, 0.22g of lithium hydroxide monohydrate, and 0.13g of glucose, mix them uniformly in a ball mill, then transfer them to a tube furnace for sintering treatment, the sintering conditions are 700℃ for 5h, nitrogen needs to be introduced throughout the sintering process, and finally the positive electrode active material is obtained.

[0089] Figure 2For the TEM image of the positive electrode active material in Example 1, a sample was prepared by Figure 2 It can be seen that the thickness of the coating layer is 15 nm.

[0090] Example 2

[0091] Reference Figure 3 The positive electrode active material in Example 2 includes a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer includes a polyanion lithium salt, lithium fluoride and conductive carbon; the thickness of the coating layer is greater than 10 nm and less than 30 nm, the polyanion lithium salt includes lithium phosphate, and the layered oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2, the polyanion lithium salt accounts for 2% of the mass of the layered oxide, the lithium fluoride accounts for 2.7% of the mass of the layered oxide, and the conductive carbon accounts for 0.5% of the mass of the layered oxide, and the conductive carbon accounts for 25% of the mass of the polyanion lithium salt.

[0092] Accurately weigh NCM811 ternary positive electrode material, ammonium hexafluorophosphate, lithium hydroxide monohydrate, and glucose 10 g, 0.25 g, 0.66 g, and 0.13 g respectively, and uniformly mix them in a ball mill, then transfer them to a tube furnace for sintering treatment, the sintering conditions are 700°C and 5h, nitrogen needs to be introduced throughout the sintering process, and finally the positive electrode active material is obtained.

[0093] Example 3

[0094] The positive electrode active material in Example 3 includes a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer includes a polyanion lithium salt and conductive carbon; the thickness of the coating layer is greater than 10 nm and less than 30 nm, the polyanion lithium salt includes lithium phosphate, and the layered oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2, the polyanion lithium salt accounts for 0.5% of the mass of the layered oxide, the conductive carbon accounts for 0.2% of the mass of the layered oxide, and the conductive carbon accounts for 40% of the mass of the polyanion lithium salt.

[0095] Accurately weigh NCM811 ternary positive electrode material, ammonium phosphate, lithium hydroxide monohydrate, and glucose 10 g, 0.06 g, 0.05 g, and 0.05 g respectively, and uniformly mix them in a ball mill, then transfer them to a tube furnace for sintering treatment, the sintering conditions are 700°C and 5h, nitrogen needs to be introduced throughout the sintering process, and finally the positive electrode active material is obtained.

[0096] Example 4

[0097] The positive electrode active material in Example 4 includes a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer including a polyanion lithium salt and conductive carbon; the thickness of the coating layer is greater than 10 nm and less than 30 nm, the polyanion lithium salt includes lithium phosphate, and the layered oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2, the polyanion lithium salt accounts for 5% of the mass of the layered oxide, the conductive carbon accounts for 1% of the mass of the layered oxide, and the conductive carbon accounts for 20% of the mass of the polyanion lithium salt.

[0098] Accurately weigh 10 g of NCM811 ternary positive electrode material, 0.64 g of ammonium phosphate, 0.54 g of lithium hydroxide monohydrate, and 0.25 g of glucose, uniformly mix them in a ball mill, then transfer them to a tube furnace for sintering treatment, the sintering condition is 700 ℃ for 5 h, nitrogen needs to be introduced throughout the sintering process, and finally the positive electrode active material is obtained.

[0099] Comparative Example 1

[0100] Accurately weigh 10 g of NCM811 ternary positive electrode material, 0.26 g of ammonium phosphate, 0.22 g of lithium hydroxide monohydrate, and 0.13 g of glucose, uniformly mix them in a ball mill, then transfer them to a tube furnace for sintering treatment, the sintering condition is 300 ℃ for 5 h, nitrogen needs to be introduced throughout the sintering process, and finally the positive electrode active material is obtained.

[0101] Comparative Example 2

[0102] The positive electrode active material in Comparative Example 2 includes a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer including a polyanion lithium salt and conductive carbon; the polyanion lithium salt includes lithium phosphate, and the layered oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2, the polyanion lithium salt accounts for 0.3% of the mass of the layered oxide, the conductive carbon accounts for 0.1% of the mass of the layered oxide, and the conductive carbon accounts for 33% of the mass of the polyanion lithium salt.

[0103] Accurately weigh 10 g of NCM811 ternary positive electrode material, 0.04 g of ammonium phosphate, 0.03 g of lithium hydroxide monohydrate, and 0.03 g of glucose, uniformly mix them in a ball mill, then transfer them to a tube furnace for sintering treatment, the sintering condition is 700 ℃ for 5 h, nitrogen needs to be introduced throughout the sintering process, and finally the positive electrode active material is obtained.

[0104] Figure 4 The TEM image of the positive electrode active material in Comparative Example 2 is as shown in FIG. 2. Figure 4 It can be seen that the thickness of the coating layer is 5-10 nm.

[0105] Comparative Example 3

[0106] The positive electrode active material in Comparative Example 3 includes a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer including a polyanion lithium salt and conductive carbon; the polyanion lithium salt includes lithium phosphate, and the layered oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2, the polyanion lithium salt accounts for 5.5% of the mass of the layered oxide, the conductive carbon accounts for 1.5% of the mass of the layered oxide, and the conductive carbon accounts for 27% of the mass of the polyanion lithium salt.

[0107] The NCM811 ternary positive electrode material, ammonium phosphate, lithium hydroxide monohydrate, and glucose were accurately weighed at 10 g, 0.72 g, 0.6 g, and 0.38 g respectively, uniformly mixed in a ball mill, and then transferred to a tube furnace for sintering treatment, with the sintering conditions being 700°C and 5h, and nitrogen being introduced throughout the sintering process. Finally, the positive electrode active material was obtained.

[0108] Figure 5 The TEM image of the positive electrode active material in Comparative Example 3 is shown in FIG. 3. Figure 5 It can be seen that the thickness of the coating layer is 30-35 nm.

[0109] Comparative Example 4

[0110] The positive electrode active material in Comparative Example 4 includes a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer including a polyanion lithium salt; the polyanion lithium salt includes lithium phosphate, and the layered oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2, the polyanion lithium salt accounts for 2% of the mass of the layered oxide.

[0111] The NCM811 ternary positive electrode material, ammonium phosphate, and lithium hydroxide monohydrate were accurately weighed at 10 g, 0.26 g, and 0.22 g respectively, uniformly mixed in a ball mill, and then transferred to a tube furnace for sintering treatment, with the sintering conditions being 700°C and 5h, and nitrogen being introduced throughout the sintering process. Finally, the positive electrode active material was obtained.

[0112] Comparative Example 5

[0113] Comparative Example 5 uses a liquid phase method to prepare a positive electrode active material.

[0114] Accurately weigh 0.26 g of ammonium phosphate, 0.22 g of lithium hydroxide monohydrate, and 0.13 g of glucose into a beaker, then add 20 mL of pure water and stir to dissolve, then weigh 10 g of NCM811 ternary positive electrode material, disperse and stir for 10 min, then place it in a 100℃ environment and stir while evaporating until a slurry is formed, then place it in a vacuum drying oven to completely evaporate the water, and finally crush it with a mortar and transfer it to a tube furnace for sintering treatment, with a sintering condition of 700℃ for 5 h, and nitrogen gas being introduced throughout the sintering process, to obtain a positive electrode active material.

[0115] Comparative Example 6

[0116] The positive electrode active material of Comparative Example 6 is NCM811.

[0117] In order to compare with the coated positive electrode material, NCM811 is sintered in a tube furnace, with a sintering condition of 700℃ for 5 h, and nitrogen gas being introduced throughout the sintering process, to obtain a positive electrode active material.

[0118] Comparative Example 7

[0119] The positive electrode active material in Comparative Example 7 includes a layered oxide and a coating layer coated on the surface of the layered oxide, and the coating layer only contains conductive carbon; the layered oxide includes LiNi 0.8 Co 0.1 Mn 0.1 O2, and the conductive carbon accounts for 0.5% of the mass of the layered oxide.

[0120] Accurately weigh 10 g of NCM811 ternary positive electrode material and 0.13 g of glucose into a ball mill for uniform mixing, then transfer it to a tube furnace for sintering treatment, with a sintering condition of 700℃ for 5 h, and nitrogen gas being introduced throughout the sintering process, to obtain a positive electrode active material.

[0121] Performance testing of examples and comparative examples

[0122] The positive electrode active materials prepared in the examples and comparative examples are assembled into solid-state batteries according to the following method, with the specific steps as follows.

[0123] Assembly of all-solid-state half-batteries: The assembled all-solid-state lithium battery is a sulfide electrolyte all-solid-state lithium battery pressed by a pressure mold. Use an agate mortar to grind and mix each positive electrode active material, sulfide electrolyte, and conductive carbon in a mass ratio of 70:30:3 as the functional layer of the positive electrode sheet (composite positive electrode, Figure 6 in the positive electrode sheet), Li6P5SCl (LPSC) as the solid electrolyte, stainless steel sheet as the current collector of the positive electrode sheet and the current collector of the negative electrode sheet, Li-In alloy as the negative electrode, and the structure of the all-solid-state lithium battery is shown in the following Figure 6 .

[0124] Test equipment: LAND battery test system of model CT-2001A from Wuhan Lantian Electronics Co., Ltd., Swiss Watan EIS AC impedance tester (PGSTAT204), Japan Shimazuwa MCT series micro compression testing machine.

[0125] Test method: The capacity, rate performance and cycle performance of the all-solid-state lithium battery were characterized by using the constant current charging and discharging mode. The test temperature was 45℃, and the voltage range was 2.1-3.7V (corresponding to 2.72-4.32V vs. Li / Li + Because the potential of Li-In pair is 0.62V vs. Li / Li +

[0126] The electronic conductivity was tested by assembling ion-blocking solid-state mold batteries, and then the electronic conductivity was calculated by the formula (In the formula, V = 50mV; I is the steady-state current under 50mV bias, L is the thickness of the composite cathode, and S is the cross-sectional area of the mold) at a test temperature of 45℃.

[0127] The particle strength of the cathode active material was tested by using the Japan Shimazuwa MCT series micro compression testing machine.

[0128] Table 1 Comparison table of electrochemical performance of all-solid-state half batteries of examples and comparative examples

[0129]

[0130] From the data in Table 1, the comprehensive performance of Examples 1-4 is better than that of Comparative Examples 1-7.

[0131] Compared with Example 1, the capacity, initial efficiency, rate and cycle of Example 2 are all better, mainly because there is lithium fluoride in the coating layer of Example 2, which has better high-voltage stability and lithium ion conduction capacity. Compared with Example 1, the performance of Example 3 and Example 4 is slightly worse, mainly because of the influence of coating amount and coating thickness.

[0132] Compared with Example 1, the battery performance, electronic conductivity and particle strength of Comparative Example 1 are worse, because the temperature of heat treatment is too low, which cannot form a good coating layer and cannot make the organic carbon source better carbonized.

[0133] ​Compared with Example 1, the comprehensive performance of Comparative Example 2 and Comparative Example 3 is worse than that of Example 1, which is due to the fact that the thickness of the coating layer in Comparative Example 2 is too small and the thickness of the coating layer in Comparative Example 3 is too large. Too small or too large thickness of the coating layer will lead to the decline of the electrical performance. Among them, too small thickness of the coating layer is easy to cause the coating layer to break or fall off, which will cause the positive electrode material and the solid-state electrolyte to directly contact, and the side reaction is serious; too large thickness of the coating layer will significantly increase the transmission path of lithium ions and electrons, resulting in the decline of capacity and rate. When the thickness of the coating layer is greater than 10 nm and less than 30 nm, the positive electrode active material can have excellent electrochemical performance.

[0134] Compared with Examples 1-4, the comprehensive performance of Comparative Example 4 is worse than that of Examples 1-4, especially the 1C rate and electronic conductivity, which is mainly due to the fact that there is no conductive carbon inside the coating layer of Comparative Example 4, and the electronic transmission impedance is large.

[0135] Comparative Example 5 is very close to Example 1 in electrical performance and other performances, indicating that the coating effects of the two coating methods (dry method and liquid phase method) are close, but the process flow of liquid phase coating is more complex and the manufacturing cost is higher.

[0136] Compared with Examples 1-4, the capacity, initial efficiency and rate of Comparative Example 6 are worse than those of Examples 1-4, which is mainly because Comparative Example 6 does not contain a coating layer, and the positive electrode active material of Examples 1-4 includes a coating layer. After coating, the interface side reaction between the positive electrode material and the sulfide solid-state electrolyte is reduced, the electronic conductivity of the positive electrode material is significantly increased, and the cycle performance is improved.

[0137] Compared with Examples 1-4, the cycle performance and particle strength of Comparative Example 7 are worse than those of Examples 1-4, which is due to the fact that the coating layer of Comparative Example 7 lacks a polyanion lithium salt.

[0138] Finally, it should be pointed out that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

[0139] Furthermore, to the extent that the terms "comprises", "comprising", "includes", "including" and "has" or any variation thereof are used in the following description and / or claims, such terms are intended to include a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Also, where appropriate to context, the above description and / or the following claims could omit conventional elements well known in the art to which the application pertains. For example, although the application is described in terms of a computer system, the application is not limited to computer systems and can be implemented in any system capable of performing the functions described herein.

Claims

1. A positive electrode sheet for an all-solid-state lithium battery, characterized by comprising: The positive electrode active material comprises a layered oxide and a coating layer coated on the surface of the layered oxide, the coating layer comprising a polyanion lithium salt and conductive carbon; The thickness of the coating layer is greater than 10 nm and less than 30 nm; The polyanion lithium salt is lithium phosphate; The conductive carbon accounts for 0.1-1.0% of the mass of the layered oxide; The layered oxide includes LiNi a Co b Mn 1-a-b O2, wherein a > 0.7 and b > 0. The conductive carbon accounts for 10.0-40.0% of the mass of the polyanion lithium salt; The polyanion lithium salt accounts for 0.5-5.0% of the mass of the layered oxide; The coating layer further comprises lithium fluoride, which accounts for 0.5-5.0% of the mass of the layered oxide. The positive electrode active material is prepared by the following method:

2. The positive electrode sheet for an all-solid-state lithium battery according to claim 1, characterized by, The layered oxide, the polyanion compound, the lithium source, and the organic carbon source are mixed and heat-treated under the protection of an inert gas to obtain the positive electrode active material. The polyanion compound is a fluorophosphate; wherein the fluorophosphate is ammonium hexafluorophosphate; 3. The positive electrode sheet for an all-solid-state lithium battery according to claim 2, characterized by, And / or, the lithium source comprises a lithium salt or a hydrate of a lithium salt, the lithium salt comprising one or more of lithium carbonate, lithium hydroxide, and lithium sulfate; And / or, the organic carbon source is composed of carbon, hydrogen, and oxygen elements; And / or, the organic carbon source comprises one or more of glucose, sucrose, and starch. The polyanion compound accounts for 0.6-7.5% of the mass of the layered oxide, the lithium source accounts for 0.5-6.6% of the mass of the layered oxide, and the organic carbon source accounts for 0.5-2.5% of the mass of the layered oxide.

4. The positive electrode sheet for an all-solid-state lithium battery according to claim 3, characterized by The inert gas comprises nitrogen or argon; 5. The positive electrode sheet for an all-solid-state lithium battery according to claim 2, characterized by And / or, the temperature of the heat treatment is 400-1000°C; And / or, the time of the heat treatment is 1-10 h. The all-solid-state lithium battery comprises the positive electrode sheet for an all-solid-state lithium battery according to any one of claims 1-5.

6. An all-solid-state lithium battery, characterized by, ​

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