Solid-state electrolyte-coated graphite negative electrode material, and preparation method therefor and use thereof

Abstract

A solid-state electrolyte-coated graphite negative electrode material, and a preparation method therefor and a use thereof. The graphite negative electrode material comprises a matrix material and a solid-state electrolyte material coated on the surface of the matrix material, and the solid-state electrolyte material comprises a Ti-containing solid-state electrolyte, wherein the Ti-containing solid-state electrolyte comprises Ti3+ and Ti4+, and the molar ratio of Ti3+ to Ti4+ is y, and y satisfies 0.1≤y≤10; and the mass ratio of the Ti-containing solid-state electrolyte to the matrix material is x, and x satisfies 0.001≤x≤0.1.

Description

Solid-state electrolyte-coated graphite negative electrode material and preparation method and application thereof

[0001] Cross-reference to Related Applications

[0002] This application claims priority to the Chinese patent application No. 202410947485.9, filed on July 16, 2024, entitled "Solid-state electrolyte-coated graphite negative electrode material and preparation method and application thereof", the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application belongs to the technical field of lithium ion battery negative electrode materials, and specifically relates to a solid-state electrolyte-coated graphite negative electrode material and a preparation method and application thereof. BACKGROUND

[0004] Lithium ion batteries are widely used in consumer electronics, electric transportation, and energy storage, etc. as an important energy storage device. As a common negative electrode material of lithium ion batteries, graphite material has the advantages of high energy density, long cycle life, low price, and environmental friendliness. However, graphite material still has the problems of poor rate performance and lithium precipitation. Therefore, how to improve the electrochemical reaction process on the surface of graphite and improve the electrode reaction kinetics has become an important research direction in the field of graphite material preparation technology. The existing technical solutions mainly coat a layer of conductive material such as carbon nanotubes and metal nanoparticles on the surface of graphite, which can effectively improve the electronic conductivity, reduce the charge transfer resistance, and improve the lithium diffusion coefficient. In addition, some researches coat a layer of solid electrolyte on the surface of graphite to improve the ionic conductivity alone. However, the existing coating methods have the problem of uneven coating, which will cause the performance of graphite material to be unstable and affect the performance of the battery. Secondly, the existing coating methods such as magnetron sputtering often have high cost, which limits their application in large-scale production. Finally, the electrochemical reaction on the surface of the negative electrode needs to consider the mixed conductivity of ions and electrons, and the existing coating schemes often cannot simultaneously improve the electronic conductivity and ionic conductivity, which limits the rate charge-discharge performance of the battery and causes lithium precipitation.

[0005] SUMMARY

[0006] The main purpose of the present application is to provide a solid-state electrolyte-coated graphite negative electrode material and a preparation method and application thereof, which aims to simultaneously improve the ionic conductivity and electronic conductivity of the graphite negative electrode material to improve the problems of poor rate performance and lithium precipitation of graphite material.

[0007] To achieve the aforementioned purposes of the application, the technical solutions adopted by the present application include:

[0008] The embodiment of the present application provides a solid-state electrolyte coated graphite negative electrode material, which comprises a base material and a solid-state electrolyte material coated on the surface of the base material, and the solid-state electrolyte material comprises a Ti-containing solid-state electrolyte;

[0009] The Ti-containing solid-state electrolyte comprises Ti 3+ and Ti 4+ , Ti 3+ , Ti 4+ , and the molar ratio of Ti and Ti is y, and 0.1<=y<=10; the mass ratio of the Ti-containing solid-state electrolyte and the base material is x, and 0.001<=x<=0.1.

[0010] The embodiment of the present application also provides a preparation method of the solid-state electrolyte coated graphite negative electrode material.

[0011] The first mixed solution at least comprising a titanium source, an easily hydrolyzable / difficult complexing raw material and a complexing agent is mixed with the second mixed solution at least comprising a lithium source and an easily hydrolyzable / easy complexing raw material, and then the base material is added to obtain a third mixed solution;

[0012] And the third mixed solution is freeze-dried and heat-treated to obtain the solid-state electrolyte coated graphite negative electrode material.

[0013] The embodiment of the present application also provides the use of the solid-state electrolyte coated graphite negative electrode material in the preparation of a battery negative electrode sheet or a lithium ion battery.

[0014] The embodiment of the present application also provides a lithium ion battery comprising at least the solid-state electrolyte coated graphite negative electrode material.

[0015] Compared with the prior art, the embodiment of the present application has the beneficial effects that the Ti element in the solid-state electrolyte material in the graphite negative electrode material has the effects of conducting lithium ions and electrons, can effectively improve the electrode reaction kinetics on the surface of the graphite negative electrode material, and the graphite negative electrode material has good rate performance and low-temperature performance. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiment or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0017] Fig. 1 is a preparation flowchart of the solid-state electrolyte coated graphite negative electrode material in a typical embodiment of the present application;

[0018] Figure 2 is a diagram of the fitting results of the XPS Ti2p spectrum of the sample of Example 3 of the present application;

[0019] Figure 3 is a high-resolution SEM photograph of the graphite negative electrode material of Example 4 of the present application;

[0020] Figure 4 is a diagram of the fitting results of the XPS Ti2p spectrum of the sample of Comparative Example 1 of the present application;

[0021] Figure 5 is a diagram of the fitting results of the XPS Ti2p spectrum of the sample of Comparative Example 3 of the present application;

[0022] Figure 6 is a diagram of the lithium extraction at 10 degrees Celsius of the soft- package batteries of different examples and comparative examples of the present application;

[0023] Figure 7 is a schematic diagram of the equivalent fitting circuit used in the present application. DETAILED DESCRIPTION

[0024] In view of the defects of the prior art, the present inventors have long studied and practiced and have come up with the technical solution of the present application. The technical solution of the present application will be described clearly and completely below. Obviously, the described examples are only some of the examples of the present application, but not all of the examples. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0025] Specifically, as one aspect of the technical solution of the present application, the graphite negative electrode material coated with a solid-state electrolyte includes a base material and a solid-state electrolyte material coated on the surface of the base material, and the solid-state electrolyte material includes a Ti-containing solid-state electrolyte.

[0026] The Ti-containing solid-state electrolyte includes Ti 3+ and Ti 4+ , and the molar ratio of Ti 3+ / Ti 4+ is y, and satisfies 0.1≤y≤10; the mass ratio of the Ti-containing solid-state electrolyte to the base material is x, and satisfies 0.001≤x≤0.1.

[0027] The solid-state electrolyte material coated on the surface of the base material in the present application is a Ti-containing solid-state electrolyte, which is different from the traditional lithium-ion solid-state electrolyte. The Ti-containing solid-state electrolyte has the functions of conducting lithium ions and electrons, accelerates the electrode reaction, and effectively improves the surface dynamics of the graphite negative electrode material. The Ti-containing solid-state electrolyte has the characteristics of conducting lithium ions and electrons at the same time, which is achieved by adjusting the valence state of Ti elements in the material and the proportion of Ti elements with different valence states.

[0028] In some preferred embodiments, the Ti 3+ / Ti 4+ The molar ratio value y of the Ti-containing solid-state electrolyte and the base material satisfies 0.5≤y≤7.5.

[0029] In some preferred embodiments, the mass ratio value x of the Ti-containing solid-state electrolyte and the base material satisfies 0.005≤x≤0.05.

[0030] In the present application, the graphite is coated with the solid-state electrolyte. When the coating amount is too small, the solid-state electrolyte is not enough to cover the surface of the graphite, and thus the improvement of the surface reaction kinetics of the graphite negative electrode is limited. Meanwhile, since the solid-state electrolyte itself cannot contribute to the capacity, the specific capacity of the graphite negative electrode material will decrease continuously with the continuous increase of the coating amount of the solid-state electrolyte. Therefore, the coating amount of the solid-state electrolyte has a preferred range value.

[0031] In some preferred embodiments, the Ti 3+ / Ti 4+ The molar ratio value y of the Ti-containing solid-state electrolyte and the base material satisfies 0.5≤y≤7.5.

[0032] In some preferred embodiments, the solid-state electrolyte material is uniformly coated on the surface of the base material in the form of point-like coating or island-like coating.

[0033] In some preferred embodiments, the particle size of the solid-state electrolyte material is 10-500 nm.

[0034] In some preferred embodiments, the base material includes artificial graphite and / or natural graphite, and is not limited thereto.

[0035] In some preferred embodiments, the Ti-containing solid-state electrolyte includes any one or a combination of lithium lanthanum titanium oxide solid-state electrolyte, titanium aluminum lithium phosphate solid-state electrolyte, and Ti-doped lithium lanthanum zirconium oxide solid-state electrolyte, and is not limited thereto.

[0036] The graphite negative electrode material in the present application comprises a base material and a solid electrolyte material coated on the surface of the base material. The solid electrolyte material is coated on the base material in a dot or island shape, covering part of the surface of the graphite and being uniformly coated. The size of the solid electrolyte material is generally in nanometer scale, which is 10-500 nm as observed by electron microscopy. Such coating structure can significantly increase the contact area of the solid electrolyte and the base material, effectively accelerate the electron and ion migration kinetics on the surface of the graphite negative electrode material, thereby improving the rate capability and low-temperature performance. The solid electrolyte material coated on the surface of the base material contains Ti element, and the valence of the Ti element includes trivalent and tetravalent. Since the crystal contains homonuclear ions with different oxidation states, the electric charge can be transferred between different oxidation state ions, so the electronic conductivity of the Ti element itself is greatly improved compared with the solid electrolyte containing only tetravalent Ti element. The traditional solid electrolyte is only a good conductor of lithium ions. The solid electrolyte containing Ti in the present application can conduct electrons on the basis of effectively conducting lithium ions, i.e., it is a mixed good conductor of lithium ions and electrons. The Ti element in the mixed good conductor of lithium ions and electrons in the solid electrolyte is in a mixed valence state of trivalent and tetravalent. The mixed good conductor of lithium ions and electrons can effectively improve the rate capability and low-temperature performance of the graphite negative electrode material. 3+ / Ti 4 The raw materials contain a certain proportion of titanium source, and the titanium source only contains tetravalent Ti and does not contain trivalent Ti. The key to obtaining trivalent Ti is to mix the solid electrolyte and the graphite in a suitable proportion under a non-oxidizing atmosphere, in which the carbon material acts as a reducing agent to reduce part of the tetravalent Ti in the solid electrolyte to trivalent Ti. The non-oxidizing atmosphere prevents the carbon material from being oxidized and avoids the oxidation of trivalent Ti. In addition, the specific heat treatment temperature and holding time are used to obtain the target solid electrolyte material, thereby obtaining high lithium ion conductivity. Under the required process conditions, the solid electrolyte coated negative electrode material with high lithium ion conductivity and high electronic conductivity can be obtained by the above heat treatment.

[0037] Another aspect of the embodiments of the present application also provides a preparation method of the aforementioned solid electrolyte coated graphite negative electrode material, which comprises:

[0038] mixing a first mixed solution containing at least a titanium source, a material easy to hydrolyze / difficult to complex, and a complexing agent with a second mixed solution containing at least a lithium source, a material not easy to hydrolyze / easy to complex, and then adding a base material to obtain a third mixed solution;

[0039] and freeze-drying and heat-treating the third mixed solution to obtain the solid electrolyte coated graphite negative electrode material.

[0040] In some preferred embodiments, the titanium source comprises C 16 H 36 O4Ti and / or Ti4(OCH3) 16, and the like, but are not limited thereto.

[0041] In some preferred embodiments, the easily hydrolyzable / difficultly complexing raw material includes Al(NO3)3.9H2O, C9H 21 In some preferred embodiments, the easily hydrolyzable / difficultly complexing raw material includes Al(NO3)3.9H2O, C9H

[0042] In some preferred embodiments, the complexing agent includes any one or more of a combination of citric acid, malic acid, malonic acid, succinic acid, lactic acid, and ethylenediaminetetraacetic acid, and the like, but is not limited thereto.

[0043] In some preferred embodiments, the lithium source includes any one or more of a combination of LiOH, Li2CO3, and LiNO3, and the like, but is not limited thereto.

[0044] In some preferred embodiments, the not easily hydrolyzable / easily complexing raw material includes NH4H2PO4, and the like, but is not limited thereto.

[0045] In some preferred embodiments, the first mixed solution further includes a first solvent, and the first solvent includes any one or more of a combination of anhydrous ethanol, isopropyl alcohol, and methanol, and the like, but is not limited thereto.

[0046] In some preferred embodiments, the second mixed solution further includes a second solvent, and the second solvent includes any one or more of a combination of anhydrous ethanol, isopropyl alcohol, and methanol, and the like, but is not limited thereto.

[0047] In some preferred embodiments, the molar ratio of the complexing agent to the sum of the moles of metal ions other than lithium ions in the easily hydrolyzable / difficultly complexing raw material is 0.7-5:1.

[0048] In some preferred embodiments, the molar ratio of the titanium source to the easily hydrolyzable / difficultly complexing raw material is 0.1-9:1.

[0049] In some preferred embodiments, the molar ratio of the titanium source to the not easily hydrolyzable / easily complexing raw material is 0.02-10:1.

[0050] In some preferred embodiments, the molar ratio of the titanium source to the lithium source is 0.02-12:1.

[0051] In some preferred embodiments, the mass ratio of the titanium source to the base material is 0.002:0.3.

[0052] In some preferred embodiments, the temperature of the heat treatment is 500-1200℃.

[0053] In some preferred embodiments, the time of the heat treatment is 4-15h.

[0054] In some preferred embodiments, the atmosphere used in the heat treatment is a non-oxidizing atmosphere, which includes any one or a combination of nitrogen, argon, helium, argon-hydrogen mixed gas, and the like, but is not limited thereto.

[0055] In some more specific embodiments, the method for preparing the solid-state electrolyte-coated graphite negative electrode material includes the following steps:

[0056] Step one: dissolving a titanium source and easily hydrolyzable / difficultly complexing raw materials and a complexing agent into a solvent to obtain a first mixed solution;

[0057] Step two: dissolving a lithium source and not easily hydrolyzable / easily complexing raw materials into a solvent to obtain a second mixed solution;

[0058] Step three: mixing the first mixed solution and the second mixed solution, and adding graphite to obtain a third mixed solution;

[0059] Step four: freeze-drying the third mixed solution to obtain a dried powder.

[0060] Step five: heat-treating the dried powder to obtain a solid-state electrolyte-coated graphite material.

[0061] The Ti-containing solid-state electrolyte includes one or more of lithium lanthanum titanium oxide solid-state electrolyte, titanium aluminum lithium phosphate, lithium lanthanum zirconium oxide, and the like.

[0062] Optionally, in some embodiments of the present application, the third mixed solution includes LiNO3, La(NO3)3, and C 16 H 36 O4Ti.

[0063] Optionally, in some embodiments of the present application, the complexing agent is one or more of citric acid, malic acid, malonic acid, succinic acid, succinic acid, lactic acid, and ethylenediaminetetraacetic acid.

[0064] Optionally, in some embodiments of the present application, the third mixed solution in step four is subjected to freeze-drying, which can achieve uniform coating of the Ti-containing solid-state electrolyte on the graphite negative electrode material.

[0065] Optionally, in some embodiments of the present application, the holding temperature of the heat treatment is in the range of 500°C to 1200°C, and the holding time of the heat treatment is in the range of 4h to 15h, and the heat treatment is performed in a nitrogen atmosphere.

[0066] In the solid-state electrolyte-coated graphite negative electrode material with excellent comprehensive performance under suitable heat treatment conditions (temperature, time, atmosphere) in the present application, the mass ratio x of the solid-state electrolyte to the graphite and the Ti 3+ / Ti 4+ The ratio y has a certain optimal range, which can be obtained by linear fitting, 6≤y+2.044x≤8.

[0067] In some preferred embodiments, the preparation process of the solid-state electrolyte-coated graphite negative electrode material in the present application is shown in Figure 1.

[0068] Another aspect of the embodiments of the present application also provides the use of the aforementioned solid-state electrolyte-coated graphite negative electrode material in the preparation of a battery negative electrode sheet or a lithium ion battery.

[0069] Another aspect of the embodiments of the present application also provides a lithium ion battery comprising at least the aforementioned solid-state electrolyte-coated graphite negative electrode material.

[0070] The technical solutions of the present application will be further described in detail below in combination with several preferred embodiments and the accompanying drawings. The embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0071] The experimental materials used in the following examples are commercially available from conventional biochemical reagent companies, unless otherwise specified.

[0072] Example 1

[0073] Step 1: 150 mL of anhydrous ethanol was first added to a beaker, and a magnetic stirrer was added for magnetic stirring. Then 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O and 1.04 g of malonic acid were added in sequence, respectively. After the previous raw material was fully dissolved, the next raw material was added to obtain a first mixed solution.

[0074] Step 2: 150 mL of anhydrous ethanol was first added to a beaker, and 0.48 g of LiNO3 and 1.50 g of NH4H2PO4 were added, respectively, to obtain a second mixed solution.

[0075] Step 3: The second mixed solution and the first mixed solution were mixed, and 955.03 g of graphite was added. After sufficient stirring, a third mixed solution was obtained.

[0076] Step 4: The third mixed solution was freeze-dried. The solution was first frozen with liquid nitrogen, and then dried using a freeze dryer to obtain a dry powder.

[0077] Step 5: The refined powder was heat-treated at 600 degrees under a nitrogen atmosphere for 15 h to obtain a solid-state electrolyte-coated graphite negative electrode material, wherein the solid-state electrolyte is Li 1.4 Al 0.4 Ti 1.6 (PO4)2.6 .

[0078] Example 2

[0079] Step 1: First, 150 mL of anhydrous ethanol was added into a beaker, and a magnetic stirrer was added for magnetic stirring. Then, 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O, and 1.04 g of malonic acid were added in sequence, respectively. After the previous raw material was fully dissolved, the next raw material was added, to obtain a first mixed solution.

[0080] Step 2: First, 150 mL of anhydrous ethanol was added into a beaker, and 0.48 g of LiNO3 and 1.47 g of NH4H2PO4 were added, respectively, to obtain a second mixed solution.

[0081] Step 3: The second mixed solution and the first mixed solution were mixed, and 191.00 g of graphite was added. After being fully stirred, a third mixed solution was obtained.

[0082] Step 4: The third mixed solution was freeze-dried. First, the solution was frozen using liquid nitrogen, and then dried using a freeze dryer, to obtain a dry powder.

[0083] Step 5: The refined powder was heat-treated at 900 degrees under a nitrogen atmosphere for 8 h, to obtain a solid-state electrolyte-coated graphite anode material, in which the solid-state electrolyte was Li 1.4 Al 0.4 Ti 1.6 (PO4) 2.55 .

[0084] Example 3

[0085] Step 1: First, 150 mL of anhydrous ethanol was added into a beaker, and a magnetic stirrer was added for magnetic stirring. Then, 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O, and 1.18 g of succinic acid were added in sequence, respectively. After the previous raw material was fully dissolved, the next raw material was added, to obtain a first mixed solution.

[0086] Step 2: First, 150 mL of anhydrous ethanol was added into a beaker, and 0.48 g of LiNO3 and 1.47 g of NH4H2PO4 were added, respectively, to obtain a second mixed solution.

[0087] Step 3: The second mixed solution and the first mixed solution were mixed, and 19.10 g of graphite was added. After being fully stirred, a third mixed solution was obtained.

[0088] Step 4: The third mixed solution was freeze-dried. First, the solution was frozen using liquid nitrogen, and then dried using a freeze dryer, to obtain a dry powder.

[0089] Step 5: The refined powder is heat treated at 1200 degrees for 4 hours under nitrogen atmosphere to obtain a solid electrolyte coated graphite anode material, wherein the solid electrolyte is Li 1.4 Al 0.4 Ti 1.6 (PO4) 2.55 .

[0090] Example 4

[0091] Step 1: A beaker is first added with 150 mL of anhydrous ethanol, a magnetic stirrer is added for magnetic stirring, then 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O and 1.92 g of citric acid are added in sequence, after the previous raw material is fully dissolved, the next raw material is added, to obtain a first mixed solution.

[0092] Step 2: A beaker is first added with 150 mL of anhydrous ethanol, 0.48 g of LiNO3 and 1.46 g of NH4H2PO4 are added respectively to obtain a second mixed solution.

[0093] Step 3: The second mixed solution and the first mixed solution are mixed, and 127.34 g of graphite is added, and after being fully stirred, a third mixed solution is obtained.

[0094] Step 4: The third mixed solution is freeze-dried, first using liquid nitrogen to freeze the solution, and then using a freeze dryer to dry, to obtain a dry powder.

[0095] Step 5: The refined powder is heat treated at 925 degrees for 6 hours under nitrogen atmosphere to obtain a solid electrolyte coated graphite anode material, wherein the solid electrolyte is Li 1.4 Al 0.4 Ti 1.6 (PO4) 2.53 .

[0096] Example 5

[0097] Step 1: A beaker is first added with 150 mL of anhydrous ethanol, a magnetic stirrer is added for magnetic stirring, then 3.4 g of Ti(OC4H9)4, 2.42 g of La(NO3)3·6H2O and 3 g of citric acid are added in sequence, after the previous raw material is fully dissolved, the next raw material is added, to obtain a first mixed solution.

[0098] Step 2: A beaker is first added with 150 mL of anhydrous ethanol, 0.23 g of LiNO3 is added to obtain a second mixed solution.

[0099] Step 3: The second mixed solution and the first mixed solution are mixed, and 117.3 g of graphite is added, and after being fully stirred, a third mixed solution is obtained.

[0100] Step 4: The third mixed solution was freeze-dried, first using liquid nitrogen to freeze the solution, and then using a freeze dryer to dry, to obtain a dry powder.

[0101] Step 5: The refined powder was heat-treated at 880 degrees for 6 hours in a nitrogen atmosphere to obtain a solid electrolyte-coated graphite negative electrode material.

[0102] The solid electrolyte-coated graphite negative electrode material in this embodiment has performance comparable to that of Example 1, and the button battery prepared using it also has performance comparable to that of Example 1.

[0103] Example 6

[0104] Step 1: A beaker was first filled with 150 mL of anhydrous ethanol, a magnetic stirrer was added for magnetic stirring, and then 0.43 g of Ti(OC4H9)4, 12.99 g of La(NO3)3·6H2O, 2.31 g of ZrO(NO3)2·6H2O, and 5.04 g of citric acid were added in sequence. After the previous material was fully dissolved, the next material was added, to obtain a first mixed solution.

[0105] Step 2: A beaker was first filled with 150 mL of anhydrous ethanol, and 2.07 g of LiNO3 was added to obtain a second mixed solution.

[0106] Step 3: The second mixed solution and the first mixed solution were mixed, and 117.3 g of graphite was added. After thorough stirring, a third mixed solution was obtained.

[0107] Step 4: The third mixed solution was freeze-dried, first using liquid nitrogen to freeze the solution, and then using a freeze dryer to dry, to obtain a dry powder.

[0108] Step 5: The refined powder was heat-treated at 900 degrees for 8 hours in a nitrogen atmosphere to obtain a solid electrolyte-coated graphite negative electrode material, wherein the solid electrolyte was Li6Ti 0.25 La3Zr2O 11.905 .

[0109] The solid electrolyte-coated graphite negative electrode material in this embodiment has performance comparable to that of Example 1, and the button battery prepared using it also has performance comparable to that of Example 1.

[0110] Comparative Example 1

[0111] Step 1: First, 150 mL of anhydrous ethanol was added into a beaker, and a magnetic stirrer was added for magnetic stirring. Then, 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O, and 1.92 g of citric acid were sequentially added, respectively, and the previous raw material was fully dissolved before adding the next raw material to obtain a first mixed solution.

[0112] Step 2: First, 150 mL of anhydrous ethanol was added into a beaker, and 0.48 g of LiNO3 and 1.44 g of NH4H2PO4 were added, respectively, to obtain a second mixed solution.

[0113] Step 3: The second mixed solution and the first mixed solution were mixed, and 3820.11 g of graphite was added, and after being fully stirred, a third mixed solution was obtained.

[0114] Step 4: The third mixed solution was freeze-dried, first using liquid nitrogen to freeze the solution, and then using a freeze dryer to dry, to obtain a dry powder.

[0115] Step 5: The refined powder was heat-treated at 925 degrees under a nitrogen atmosphere for 6 h to obtain a graphite negative electrode material, wherein the solid-state electrolyte was Li 1.4 Al 0.4 Ti 1.6 (PO4) 2.51 .

[0116] Comparative Example 2

[0117] Step 1: First, 150 mL of anhydrous ethanol was added into a beaker, and a magnetic stirrer was added for magnetic stirring. Then, 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O, and 1.92 g of citric acid were sequentially added, respectively, and the previous raw material was fully dissolved before adding the next raw material to obtain a first mixed solution.

[0118] Step 2: First, 150 mL of anhydrous ethanol was added into a beaker, and 0.48 g of LiNO3 and 1.51 g of NH4H2PO4 were added, respectively, to obtain a second mixed solution.

[0119] Step 3: The second mixed solution and the first mixed solution were mixed, and 19.10 g of graphite was added, and after being fully stirred, a third mixed solution was obtained.

[0120] Step 4: The third mixed solution was freeze-dried, first using liquid nitrogen to freeze the solution, and then using a freeze dryer to dry, to obtain a dry powder.

[0121] Step 5: The refined powder was heat-treated at 925 degrees under a nitrogen atmosphere for 6 h to obtain a graphite negative electrode material, wherein the solid-state electrolyte was Li 1.4 Al 0.4 Ti1.6 (PO4) 2.62 .

[0122] Comparative Example 3

[0123] Step 1: 150 mL of anhydrous ethanol was first added into a beaker, a magnetic bar was added for magnetic stirring, then 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O and 1.92 g of citric acid were sequentially added respectively, after the previous raw material was fully dissolved, the next raw material was added, to obtain a first mixed solution.

[0124] Step 2: 150 mL of anhydrous ethanol was first added into a beaker, 0.48 g of LiNO3 and 1.72 g of NH4H2PO4 were added respectively to obtain a second mixed solution.

[0125] Step 3: The second mixed solution and the first mixed solution were mixed, 127.34 g of graphite was added, and after fully stirring, a third mixed solution was obtained.

[0126] Step 4: The third mixed solution was freeze-dried, the solution was first frozen with liquid nitrogen, and then dried using a freeze dryer to obtain a dry powder.

[0127] Step 5: The refined powder was heat treated at 925 degrees for 6 h in an air atmosphere to prepare a graphite negative electrode material, wherein the solid-state electrolyte is Li 1.4 Al 0.4 Ti 1.6 (PO4)3.

[0128] Comparative Example 4

[0129] Step 1: 150 mL of anhydrous ethanol was first added into a beaker, a magnetic bar was added for magnetic stirring, then 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O and 1.92 g of citric acid were sequentially added respectively, after the previous raw material was fully dissolved, the next raw material was added, to obtain a first mixed solution.

[0130] Step 2: 150 mL of anhydrous ethanol was first added into a beaker, 0.48 g of LiNO3 and 1.55 g of NH4H2PO4 were added respectively to obtain a second mixed solution.

[0131] Step 3: The second mixed solution and the first mixed solution were mixed, 127.34 g of graphite was added, and after fully stirring, a third mixed solution was obtained.

[0132] Step 4: The third mixed solution was freeze-dried, the solution was first frozen with liquid nitrogen, and then dried using a freeze dryer to obtain a dry powder.

[0133] Step 5: The refined powder is subjected to heat treatment at 400 degrees under a nitrogen atmosphere for 6 hours to obtain a graphite negative electrode material, wherein the solid-state electrolyte is Li 1.4 Al 0.4 Ti 1.6 (PO4) 2.7 .

[0134] Comparative Example 5

[0135] Step 1: 150 mL of anhydrous ethanol is first added to a beaker, a magnetic stirrer is added for magnetic stirring, and then 2.72 g of Ti(OC4H9)4, 0.75 g of Al(NO3)3·9H2O and 1.92 g of citric acid are added in sequence. After the previous raw material is fully dissolved, the next raw material is added to obtain a first mixed solution.

[0136] Step 2: 150 mL of anhydrous ethanol is first added to a beaker, and then 0.48 g of LiNO3 and 1.45 g of NH4H2PO4 are added to obtain a second mixed solution.

[0137] Step 3: The second mixed solution and the first mixed solution are mixed, and 127.34 g of graphite is added. After being fully stirred, a third mixed solution is obtained.

[0138] Step 4: The third mixed solution is subjected to freeze-drying. The solution is first frozen using liquid nitrogen, and then dried using a freeze dryer to obtain a dry powder.

[0139] Step 5: The refined powder is subjected to heat treatment at 1350 degrees under a nitrogen atmosphere for 6 hours to obtain a graphite negative electrode material, wherein the solid-state electrolyte is Li 1.4 Al 0.4 Ti 1.6 (PO4) 2.52 .

[0140] The method for making a battery using the graphite negative electrode material of the present application is described below.

[0141] Button half-cell preparation:

[0142] The solid-state electrolyte-coated graphite material, the conductive agent and the binder are mixed uniformly in a mass ratio of 92:5:3 to prepare a negative electrode aqueous slurry, which is coated on a Cu foil current collector and dried at 90 degrees under vacuum to prepare a negative electrode sheet. In a glove box, a lithium sheet, a separator and the negative electrode sheet are assembled using a button cell shell, and an electrolyte is added dropwise. After sealing and pressurizing, a completed CR2032 button half-cell is obtained.

[0143] Soft package battery preparation:

[0144] The lithium cobalt oxide positive electrode active material, a conductive agent, and a binder are mixed uniformly to prepare a positive electrode NMP slurry, which is coated onto an Al foil and dried in a vacuum to prepare a positive electrode. The solid electrolyte-coated graphite material, a conductive agent, and a binder are mixed uniformly in a mass ratio of 97:1.5:1.5 to prepare a negative electrode aqueous slurry, which is coated onto a Cu foil and dried in a vacuum to prepare a negative electrode. The above positive and negative electrode sheets and an LLZO-coated separator are used to assemble a soft-pack battery using a commercial electrolyte.

[0145] The following describes the preparation of the solid electrolyte-coated graphite negative electrode material of the present application and the testing method of its performance parameters.

[0146] Preparation of solid electrolyte powder:

[0147] In each of the embodiments, the remaining steps remain unchanged, and the only difference is that no graphite is added in step 3. The powder is then subjected to high-energy planetary ball milling, and the ball milling parameters are as follows: 6 mm zirconium oxide balls are used, the mass ratio of zirconium oxide balls to solid electrolyte material is 4:1, the mass ratio of grinding medium isopropyl alcohol to solid electrolyte material is 3:1, the rotation speed is 450 rpm, and the ball milling time is 9 h. The powder after ball milling is dried at 80 degrees for 24 h and ground for 15 min.

[0148] Testing of ionic conductivity:

[0149] Preparation of solid electrolyte sheet: First, the obtained solid electrolyte powder material is ground in an agate mortar for 20 min, 1 g of the powder is taken and pressed into a sheet using a mold with a diameter of 1 / 2 inch, and a hand-operated press is used to apply pressure, with a pressing pressure of 300 MPa. The electrolyte sheet after pressing is subjected to nitrogen atmosphere heat treatment using a box furnace, and the heat treatment parameters are as follows: 1150 degrees for 6 h, the heating rate is 3 degrees per minute, and the cooling stage is furnace cooling. A sintered and dense solid electrolyte sheet is obtained after heat treatment.

[0150] Preparation of PEO-LiTFSI film: PEO (polyethylene oxide, molecular weight 4,000,000), LiTFSI (99.95%), and acetonitrile (99.8%) are used to prepare a PEO-LiTFSI film. PEO and LiTFSI are dried at 60°C for 24 hours under vacuum. The polymer and salt are weighed in an argon glove box to a molar ratio of EO:Li = 6:1. First, LiTFSI is dissolved in acetonitrile to form a transparent solution, then PEO is slowly added to the solution, stirred at room temperature for 24 hours, and then stirred at 60°C for 12 hours to ensure dissolution. The PEO / LiTFSI solution is placed in a polytetrafluoroethylene mold, stirred appropriately to eliminate bubbles, and then left to cool. Vacuum drying is performed for 24 hours to obtain a PEO-LiTFSI film.

[0151] PEO-LiTFSI films have electronic blocking properties, but do not block Li + transport in the low frequency range. PEO-LiTFSI films were pressed on both sides of the solid electrolyte sheet, and then Li sheets were pressed on top, and a battery mold was used to assemble a Li-PEO-LiTFSI-solid electrolyte sheet-PEO-LiTFSI-Li structure for EIS testing.

[0152] EIS testing was performed using an electrochemical workstation, with a test voltage of 50 mV and a frequency range of 300 mHz-7 MHz. The equivalent fitting circuit used after testing is shown in Figure 7. The values of R B and R GB were obtained by fitting, and the sum of the two was the total resistance R, and the ionic conductivity: σ = d / (R x S), where d is the thickness of the solid electrolyte sheet (cm); R is the total resistance of the solid electrolyte (Ω), and S is the effective area of the electrode (cm 2 ).

[0153] Electronic conductivity test:

[0154] The powder used to test electronic conductivity was the solid electrolyte powder, and the determination method was carried out in accordance with the relevant provisions of GB / T 40007-2021 Nanotechnology - Nanomaterials - Contact method for measuring resistivity - General rules. The test result was the electronic conductivity of the material when the pressure was equal to 4 kN.

[0155] The test methods for the various performance parameters of the graphite negative electrode material of the present application are described below.

[0156] XPS test:

[0157] The equipment used was Thermo Scientific K-Alpha, and an appropriate amount of sample was pressed into a tablet and attached to the sample disc. The sample was placed in the sample chamber of the Thermo Scientific K-Alpha XPS instrument, and when the pressure in the sample chamber was less than 2.0 x 10-7 mbar, the sample was sent to the analysis chamber. The spot size was 400 μm, the working voltage was 12 kV, and the filament current was 6 mA; the narrow spectrum scanning energy was 50 eV, and the step size was 0.1 eV. The XPS data was processed using Avantage software, which mainly fitted the Ti 2p spectrum, and the content ratio of Ti 3+ and Ti 4+ was obtained after fitting.

[0158] Median particle size test:

[0159] The determination method was carried out in accordance with the relevant provisions of GB / T 19077 Particle Size Analysis - Laser Diffraction Method.

[0160] Specific surface area test:

[0161] The determination method is carried out according to the relevant provisions of GB / T 19587 gas adsorption BET method for determining the specific surface area of solid matter.

[0162] Tap density test:

[0163] The determination method is carried out according to the relevant provisions of GB / T 5162 determination of tap density of metal powder.

[0164] Compacted density test:

[0165] The determination method is carried out according to the relevant provisions of GB / T 24533-2019 "Lithium ion battery graphite negative electrode material".

[0166] Button cell test:

[0167] Capacity and initial efficiency: assemble CR2032 button semi-solid battery, test the cycle performance of the battery, for graphite-Li system, voltage range 0.005-1.5V, current 0.05C, compare the first circle discharge capacity and charge-discharge efficiency.

[0168] Pouch cell test:

[0169] Rate discharge test: (1) the pouch cell is first charged to 4.35V with 0.5C cross-flow constant voltage, cut off at 0.05C current, stand for 5min, discharged to 3V with 1C constant current, stand for 5min; (2) then charged to 4.35V with 0.5C cross-flow constant voltage, cut off at 0.05C current, stand for 5min, discharged to 3V with 3C constant current, stand for 5min. Calculate and compare the ratio of 3C discharge capacity and 1C discharge capacity. (3) then charged to 4.35V with 0.5C cross-flow constant voltage, cut off at 0.05C current, stand for 5min, discharged to 3V with 5C constant current, stand for 5min. Calculate and compare the ratio of 5C discharge capacity and 1C discharge capacity.

[0170] Rate charge test: (1) the pouch cell is first charged to 4.35V with 0.2C cross-flow constant voltage, cut off at 0.05C current, stand for 5min, discharged to 3V with 0.5C constant current, stand for 5min; (2) then charged to 4.35V with 2.5C cross-flow constant voltage, cut off at 0.05C current, stand for 5min, discharged to 3V with 0.5C constant current, stand for 5min. Calculate and compare the ratio of 2.5C charge capacity and 0.2C charge capacity.

[0171] 0 degree low temperature cycle: use pouch cell to test the cycle performance of the battery, for lithium cobaltate-graphite system, voltage range 3-4.35V, current 0.2C, temperature 0 degree, calculate the capacity retention rate of 50 cycles.

[0172] Low-temperature lithium precipitation: (1) The soft-pack battery was first placed in a thermostat at 10 degrees for 5 minutes, then discharged at 1C constant current to 3V, and then placed for 4 hours; (2) placed for 5 minutes, then charged to 4.35V at constant current and constant voltage, the current was cut off to 50mA, and then placed for 5 minutes, and then discharged at 2C constant current to 3V; (3) repeat step (2), 2C charge-discharge cycle for 10 weeks; (4) disassemble the battery in the glove box, take out the negative electrode sheet, and observe the lithium precipitation. If the sheet is golden without black material, it is not lithium precipitation, and if the sheet appears black material, it is lithium precipitation.

[0173] The graphite negative electrode materials of Examples 1 to 4, Comparative Examples 1 to 5 were tested, and the test results are shown in Tables 1 to 4.

[0174] Table 1 Material ratio and titanium ratio of different examples and comparative examples

[0175] As shown in Table 1, the material ratio and the content ratio of two valence states of titanium of four examples and five comparative examples are summarized. Examples 1 to 4 adopt different solid electrolyte coating ratios, i.e. different mass ratios of solid electrolyte and graphite, and the ratio of Ti 3+ / Ti 4+ of the material obtained according to XPS fitting (Figures 2, 4 and 5 respectively show the XPS Ti2p spectrum fitting results of Example 3, Comparative Example 1 and Comparative Example 3), which depends on specific preparation process parameters, including coating ratio, temperature, time and atmosphere of heat treatment. Under the same process conditions, considering the role of the reducing agent graphite, the content of the reducing agent is reduced, the mass ratio of the solid electrolyte and the graphite is high, and the ratio of Ti 3+ / Ti 4+ will decrease. For example, the solid electrolyte content of Comparative Example 1 is lower than that of Example 4, and the ratio of Ti 3+ / Ti 4+ obtained is larger than that of Example 4; the solid electrolyte content of Comparative Example 2 is higher, and the ratio of Ti 3+ / Ti 4+ obtained is smaller than that of Example 4.

[0176] Comparative Example 3 uses air atmosphere for heat treatment, and trivalent Ti cannot be obtained under the oxidation atmosphere, and there is a problem of graphite oxidation loss, and the material prepared is mainly solid electrolyte powder.

[0177] Through specific tests, it is found that the mass ratio x of the solid electrolyte and the graphite and the ratio of Ti 3+ / Ti 4+The ratio y has a certain optimal range, which can be obtained by linear fitting, 6≤y+2.044x≤8, in the above examples and comparative examples, example 4 meets the preferred range. The morphology of the material prepared in example 4 is shown in figure 3, the nanoscale solid electrolyte small particles are dispersed on the surface of the graphite matrix material, and the dispersion is relatively uniform, and the size of the solid electrolyte particles is generally about 50 nm.

[0178] Table 2: Performance test results of materials of different examples and comparative examples

[0179] Table 2: Performance test results of materials of different examples and comparative examples

[0180] The material prepared in comparative example 3 is mainly solid electrolyte powder, and the corresponding electronic conductivity is greatly reduced, only 1.7*10 -8 S / cm, and the particle size, tap and compacted density of the material are also reduced compared with other examples. Because small particles of solid electrolyte are obtained, the specific surface area is higher than that of other examples.

[0181] Comparative example 4 uses a lower heat treatment temperature than example 4, and comparative example 5 uses a higher heat treatment temperature than example 4. Both of these heat treatment temperatures are not in the temperature range that can obtain the target solid electrolyte, and the coating material on the surface of the substrate finally obtained does not have good lithium ion conductivity. The corresponding test results of lithium ion conductivity are all in the order of 10 -7 Magnitude, much lower than the ion conductivity of example 4.

[0182] Table 3: Discharge test results of materials of different examples and comparative examples

[0183] Table 3 and table 4 are the results measured by preparing solid electrolyte materials into button cells and soft package batteries. The size of the discharge capacity is affected by the content of solid electrolyte. Since it cannot contribute to the capacity itself, the higher the content of solid electrolyte, the lower the corresponding discharge capacity.

[0184] As shown in table 4, the graphite material coated with solid electrolyte has significantly improved performance of charge and discharge, which is mainly due to the high ion and electron conductivity of the solid electrolyte coated on the surface of the matrix material. Example 4 has the best ion and electron conductivity, and its corresponding charge and discharge performance is the best. As shown in figure 6, due to the improved kinetic performance of graphite, in the low temperature test, the 0 degree 50 cycle capacity retention rate and lithium precipitation of example also show good results.

[0185] Table 4: Soft package battery test results of materials of different examples and comparative examples

[0186] In addition, the inventors of the present application have also carried out tests with other raw materials, process operations and process conditions described in the specification with reference to the foregoing examples, and all ideal results have been obtained.

[0187] It should be understood that the technical solutions of the present application are not limited to the specific implementation cases described above, and any technical modification made according to the technical solutions of the present application without departing from the purpose of the present application and the scope protected by the claims falls within the protection scope of the present application. Industrial applicability

[0188] The present application provides a solid-state electrolyte coated graphite negative electrode material and its preparation method and application, wherein the Ti element in the solid-state electrolyte material has the functions of conducting lithium ions and electrons at the same time, which can effectively improve the surface electrode reaction kinetics of the graphite negative electrode material, and the graphite negative electrode material has good rate performance and low temperature performance.

[0189] In addition, it can be understood that the solid-state electrolyte coated graphite negative electrode material and its preparation method and application of the present application can be reproduced, and can be widely applied in the technical field of lithium ion battery negative electrode materials.

Claims

1. A solid-state electrolyte-coated graphite anode material, characterized by, The solid-state electrolyte material includes a Ti-containing solid-state electrolyte; The Ti-containing solid-state electrolyte comprises Ti 3+ and Ti 4+ , Ti 3+ , and Ti 4+ , and the molar ratio of Ti to the other metal element is y, and satisfies 0.1≤y≤10; the mass ratio of the Ti-containing solid-state electrolyte to the base material is x, and satisfies 0.001≤x≤0.

1.

2. The graphite negative electrode material of claim 1, wherein: the Ti 3+ / Ti 4+ the molar ratio y of Ti to Al satisfies 0.5 ≤ y ≤ 7.5; The mass ratio x of the Ti-containing solid-state electrolyte to the base material satisfies 0.005≤x≤0.05; and / or, the Ti 3+ / Ti 4+ The molar ratio y of the Ti and the mass ratio x of the Ti-containing solid-state electrolyte and the base material satisfy: 6 ≤ y + 2.044x ≤ 8.

3. The graphite negative electrode material of claim 1, wherein: The solid-state electrolyte material is uniformly coated on the surface of the base material in a dot-shaped or island-shaped manner.

4. The graphite negative electrode material of claim 1, wherein: The particle size of the solid-state electrolyte material is 10-500 nm; The base material includes artificial graphite and / or natural graphite; The Ti-containing solid-state electrolyte includes any one or more of lithium lanthanum titanium oxide solid-state electrolyte, lithium titanium aluminum phosphate solid-state electrolyte, and Ti-doped lithium lanthanum zirconium oxide solid-state electrolyte.

5. The method of producing the solid-state electrolyte-coated graphite negative electrode material according to any one of claims 1 to 4, characterized by, The method includes: Mixing a first mixed solution containing at least a titanium source, a hydrolyzable / difficult-to-complex raw material, and a complexing agent with a second mixed solution containing at least a lithium source and an easy-to-hydrolyze / difficult-to-complex raw material, and then adding a base material to obtain a third mixed solution; Freezing and drying the third mixed solution and performing heat treatment to obtain a solid-state electrolyte-coated graphite negative electrode material.

6. The method of claim 5, wherein: The titanium source includes C 16 H 36 O4Ti and / or Ti4(OCH3) 16 ; and / or, the easily hydrolyzable / difficultly complexing raw material includes a combination of any one or more of Al(NO3)3.9H2O, C9H 21 AlO3, Al(NO3)3, ZrO(NO3)2, La(NO3)3; and / or, the complexing agent includes a combination of any one or more of citric acid, malic acid, malonic acid, succinic acid, succinic acid, lactic acid, ethylenediaminetetraacetic acid. The lithium source includes any one or more of LiOH, Li2CO3, and LiNO3; and / or the easy-to-hydrolyze / difficult-to-complex raw material includes NH4H2PO4; The first mixed solution further includes a first solvent, and the first solvent includes any one or more of anhydrous ethanol, isopropanol, and methanol; The second mixed solution further includes a second solvent, and the second solvent includes any one or more of anhydrous ethanol, isopropanol, and methanol.

7. The method of claim 5, wherein: The molar ratio of the complexing agent to the sum of the moles of metal ions other than lithium ions in the hydrolyzable / difficult-to-complex raw material is 0.7-5:1; The molar ratio of the titanium source to the hydrolyzable / difficult-to-complex raw material is 0.1-9:1; The molar ratio of the titanium source to the easy-to-hydrolyze / difficult-to-complex raw material is 0.02-10:1; The molar ratio of the titanium source to the lithium source is 0.02-12:1; The mass ratio of the titanium source to the base material is 0.002:0.

3.

8. The method of claim 5, wherein: The temperature of the heat treatment is 500-1200℃; The time of the heat treatment is 4-15 h; The atmosphere used in the heat treatment is a non-oxidizing atmosphere, and the non-oxidizing atmosphere includes any one or more of nitrogen, argon, helium, and argon-hydrogen mixed gas.

9. Use of the solid-state electrolyte-coated graphite negative electrode material in any one of claims 1-4 in the preparation of a battery negative electrode sheet or a lithium ion battery.

10. A lithium-ion battery, characterized by, The solid-state electrolyte-coated graphite negative electrode material includes at least the solid-state electrolyte-coated graphite negative electrode material in any one of claims 1-4.

Images