A cathode material with anion concentration gradient coating, its preparation method and application

Abstract

A cathode material with an anion concentration gradient coating layer, its preparation method, and its application belong to the field of all-solid-state battery technology. The specific scheme is as follows: The preparation method includes the following steps: weighing lithium source and metal source respectively, dissolving or dispersing the above raw materials in an organic solvent, and stirring evenly to obtain a mixture A; adding cathode material to mixture A, stirring and mixing evenly to obtain mixture B; heating mixture B and stirring until the solvent is completely evaporated; heat-treating the obtained mixed powder in an inert atmosphere for a period of time, and then heat-treating it in a hydrogen sulfide carrier gas to obtain a cathode material with a surface anion gradient coating layer; the sulfide solid-state battery cathode material prepared by this method can effectively improve the bidirectional compatibility at the interface, further reduce the reaction energy at the interface, form a stable cathode / electrolyte interface, and comprehensively improve the electrochemical performance of the material.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-solid-state batteries, and particularly relates to a cathode material with an anion concentration gradient coating layer, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, many experts and scholars have predicted that solid-state batteries are an inevitable trend in the future development of lithium battery technology. All-solid-state lithium batteries use solid electrolytes, have no leakage problems, and have advantages such as high temperature resistance, non-flammability, non-volatility, and non-corrosion. Therefore, they have high safety and longer cycle life. Moreover, solid electrolytes can be used in combination with high-voltage and high-capacity cathode materials and lithium metal anodes, so as to有望 obtain a大幅度提高 in energy density, which is in line with the development direction of future new energy energy storage technology.

[0003] With the in-depth study of solid electrolytes, the ionic conductivity of sulfide solid electrolytes is almost comparable to that of organic liquid electrolytes, but the stability of all-solid-state sulfide batteries is still not ideal, mainly limited by interface problems such as cathode / electrolyte and anode / electrolyte in solid-state batteries. Among them, there are cathode interfaces such as physical contact failure, space charge layer effect, and chemical / electrochemical side reactions between traditional oxide cathode materials and sulfide electrolytes. For interface side reactions, due to the relatively high interface reaction energy between conventional oxide cathode materials and sulfide electrolytes, interface chemical reactions are likely to occur, generating by-products that are不利 to lithium ion transport. Therefore, the interfacial diffusion of lithium ions is severely hindered, resulting in problems such as large cathode interface impedance and poor rate performance. Therefore, it is particularly important to perform surface design on the cathode material to reduce the interface reaction energy between the oxide cathode / sulfide electrolyte. Summary of the Invention

[0004] The purpose of the present invention is to solve the cathode / electrolyte interface problem of sulfide solid-state batteries, and provide a cathode material with an anion concentration gradient coating layer, a preparation method thereof, and an application in all-solid-state batteries. The cathode material with an anion concentration gradient coating layer prepared by this method can form a stable interface with sulfide electrolytes, comprehensively improving the electrochemical performance of solid-state batteries.

[0005] In order to achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A cathode material with an anion concentration gradient coating layer includes a cathode material and a coating layer. The average composition of the coating layer is: Li x M y O n S m , 1 < x < 5, 1 < y < 5, 1 < n < 12, 1 < m < 12, M is one or a combination of more of Ti, Nb, Al, Zr. The coating layer is from the outside to the inside, S It should be noted that in the above translation, "有望 obtain a大幅度提高" is a literal translation of the Chinese expression. It might be more accurately expressed as "is expected to achieve a significant increase" in a more natural English sentence. Also, "不利 to lithium ion transport" could be more precisely "unfavorable for lithium ion transport".2- The content gradually decreases, O 2- The content gradually increases.

[0007] Furthermore, the cathode material is an oxide cathode material.

[0008] Furthermore, the oxide cathode material includes one or more combinations of lithium cobalt oxide, lithium manganese oxide, single-crystal ternary materials, and polycrystalline ternary materials, wherein the ternary material includes LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 One or more combinations of O2.

[0009] A method for preparing the above-mentioned cathode material includes the following steps:

[0010] Step 1: Take lithium source and metal M source as raw materials, dissolve them in or uniformly disperse them in an organic solvent to obtain mixture A; the metal M is one or more of Ti, Nb, Al, Zr;

[0011] Step 2: Mix the positive electrode material with mixture A to obtain mixture B;

[0012] Step 3: Dry the mixture B, then heat-treat the mixed powder in an inert atmosphere, and then heat-treat it under a carrier gas containing hydrogen sulfide to obtain the cathode material with an anion concentration gradient coating.

[0013] Furthermore, the lithium source is one or more of lithium oxide, lithium hydroxide, lithium ethoxide, lithium nitrate, and lithium acetate; the metal M source is one or more of titanium dioxide, niobium pentoxide, aluminum oxide, zirconium dioxide, niobium ethoxide, tetrabutyl titanate, aluminum nitrate, aluminum sec-butoxide, aluminum isopropoxide, zirconium acetate, zirconium nitrate, and zirconium oxynitrate; and the organic solvent is one or more of anhydrous ethanol, isopropanol, ethylene glycol, and acetone.

[0014] Furthermore, in step one, the mass ratio of the lithium source to the metal M source is 1:1 to 10; the mass ratio of the raw material to the organic solvent is 0.5% to 10%:100%.

[0015] Furthermore, in step two, the mass ratio of the positive electrode material to the raw material is 100%:0.1% to 20%.

[0016] Furthermore, in step three, the temperature for drying mixture B is 40–100°C, the temperature for heat treatment in an inert atmosphere is 200°C–800°C, and the time is 0.5–10 h, and the temperature for heat treatment in a carrier gas containing hydrogen sulfide is 200°C–800°C, and the time is 0.5–5 h.

[0017] Furthermore, in step three, the carrier gas includes one or a combination of two of argon and nitrogen.

[0018] An application of the aforementioned cathode material in a sulfide all-solid-state battery, wherein the cathode material of the sulfide all-solid-state battery comprises the cathode material having an anion concentration gradient coating layer and a sulfide electrolyte.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. This invention utilizes in-situ gas phase reaction to carry out in-situ sulfide reaction on the oxide coating layer pre-formed on the oxide cathode surface. The gas phase reaction has high uniformity. During the heat treatment process, hydrogen sulfide reacts with the oxide coating material, causing sulfur to replace oxygen in the oxide at its original position. The reaction gradually weakens from the outside to the inside, thereby forming a coating layer with an anion concentration gradient.

[0021] 2. This invention forms an interface buffer layer with an anion concentration gradient on the surface of the positive electrode material. The positive electrode active material is a lithium oxide material, which has good structural stability, high ionic conductivity, and extremely low electronic conductivity. It has stable electrochemical performance with the oxide positive electrode, thereby improving the charging and discharging efficiency of the positive electrode.

[0022] 3. The coating layer with an anion concentration gradient constructed in this invention serves as an interface buffer layer. The sulfide electrolyte layer is made of a lithium-oxygen sulfide material. The surface layer of this lithium-oxygen sulfide material is in direct contact with the sulfide electrolyte, reducing the interfacial reaction energy and suppressing interfacial side reactions. Furthermore, it reduces the chemical potential difference between the material and the sulfide electrolyte, preventing the formation of a lithium-ion depletion layer in the electrolyte, significantly reducing interfacial impedance, and improving the performance of the solid-state battery.

[0023] 4. The sulfide solid-state battery cathode material prepared by this method can effectively improve the bidirectional compatibility at the interface, further reduce the reaction energy at the interface, form a stable cathode / electrolyte interface, and comprehensively improve the electrochemical performance of the material.

[0024] 5. The preparation method of this invention is simple, the manufacturing cost is low, and it has extremely broad application prospects. Attached Figure Description

[0025] Figure 1The electrochemical impedance diagram after the first charge and discharge at 30 °C and 0.2C of the lithium cobalt oxide cathode material with an anion concentration gradient coating layer obtained in Example 1 when applied to a sulfide solid-state battery;

[0026] Figure 2 The charge and discharge cycle performance diagram of the lithium cobalt oxide cathode material with an anion concentration gradient coating layer obtained in Example 1 in a sulfide solid-state battery. Detailed implementation manners

[0027] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Detailed implementation manner one

[0029] A cathode material with an anion concentration gradient coating layer, including a cathode material and a coating layer. The average composition of the coating layer is: Li x M y O n S m , where 1 < x < 5, 1 < y < 5, 1 < n < 12, 1 < m < 12, and M is one or a combination of more than one of Ti, Nb, Al, and Zr. From the outside to the inside of the coating layer, the content of S 2- gradually decreases, and the content of O 2- gradually increases, and the anion concentration gradient is formed by an in-situ gas-phase reaction.

[0030] Furthermore, the cathode material is an oxide cathode material.

[0031] Furthermore, the oxide cathode material includes one or a combination of more than one of lithium cobalt oxide, lithium manganate, single-crystal ternary material, and polycrystalline ternary material. The ternary material includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn<​​​

[0034] Step 1: Take lithium source and metal M source as raw materials, dissolve them in or uniformly disperse them in an organic solvent to obtain mixture A; the metal M is one or more of Ti, Nb, Al, Zr;

[0035] Step 2: Mix the positive electrode material with mixture A to obtain mixture B;

[0036] Step 3: Dry the mixture B, then heat-treat the mixed powder in an inert atmosphere, and then heat-treat it under a carrier gas containing hydrogen sulfide to obtain the cathode material with an anion concentration gradient coating.

[0037] Furthermore, the lithium source is one or more of lithium oxide, lithium hydroxide, lithium ethoxide, lithium nitrate, and lithium acetate; the metal M source is one or more of titanium dioxide, niobium pentoxide, aluminum oxide, zirconium dioxide, niobium ethoxide, tetrabutyl titanate, aluminum nitrate, aluminum sec-butoxide, aluminum isopropoxide, zirconium acetate, zirconium nitrate, and zirconium oxynitrate; and the organic solvent is one or more of anhydrous ethanol, isopropanol, ethylene glycol, and acetone.

[0038] Furthermore, in step one, the mass ratio of the lithium source to the metal M source is 1:1 to 10; the mass ratio of the raw material to the organic solvent is 0.5% to 10%:100%, and the stirring and mixing time is 0.5 to 3 hours.

[0039] Furthermore, in step two, the mass ratio of the positive electrode material to the raw material is 100%:0.1% to 20%, and the stirring and mixing time of the positive electrode material and the mixture A is 0.5-3 hours.

[0040] Furthermore, in step three, the temperature for drying mixture B is 40–100°C, the temperature for heat treatment in an inert atmosphere is 200°C–800°C, and the time is 0.5–10 h, and the temperature for heat treatment in a carrier gas containing hydrogen sulfide is 200°C–800°C, and the time is 0.5–5 h.

[0041] Furthermore, in step three, the carrier gas containing hydrogen sulfide is obtained by thermal decomposition of thiourea in a tube furnace, wherein the carrier gas is one or more of argon and nitrogen, and the mass ratio of thiourea to the mixed powder is 0.1-100:100. Specific Implementation Method 3

[0043] An application of the cathode material described in a specific embodiment, wherein the cathode material having an anion concentration gradient coating layer is used in a sulfide all-solid-state battery.

[0044] Furthermore, in sulfide all-solid-state batteries, the sulfide solid electrolyte is Li7P3S. 11, β-Li3PS4, Li7P2S8I, Li4PS4I, Li6PS5Cl x Li6PS5I y Li6PS5Br z One of them, where x, y, and z all take values ​​from 0 to 1.

[0045] Example 1

[0046] This embodiment prepares a sulfide solid-state battery cathode material according to the following steps:

[0047] (1) Prepare the precursor solution by weighing 20 mg lithium acetate and 20 mg zirconium acetate, dispersing them in 5 g anhydrous ethanol solvent, and stirring magnetically for 1 h to obtain mixture A;

[0048] (2) Add 2g of lithium cobalt oxide cathode material to the mixture A obtained in step (1) and stir magnetically for 2h to obtain mixture B;

[0049] (3) Place the mixture B obtained in step (2) in a magnetic stirrer and heat it at 60°C until the solvent is completely evaporated;

[0050] (4) The mixed powder obtained in step (3) is heat-treated at 450°C for 2 hours in argon gas, and then heat-treated at 450°C for 1 hour in a carrier gas containing hydrogen sulfide to obtain lithium cobalt oxide cathode material with an anion concentration gradient coating layer.

[0051] Figure 1 The image shows the electrochemical impedance spectroscopy (EIR) diagram after the first charge-discharge cycle at 30°C and 0.2C for the lithium cobalt oxide cathode material with an anion concentration gradient coating obtained in Example 1, applied to a Li6PS5Cl sulfide solid-state battery. Figure 1 It can be seen that the coating modification measure with anion concentration gradient significantly reduces the battery interface impedance.

[0052] Figure 2 The graph shows the charge-discharge cycle performance of the lithium cobalt oxide cathode material with an anion concentration gradient coating obtained in Example 1 in a sulfide solid-state battery. Figure 2 It can be seen that after modification, the interfacial chemical stability is better, the space charge layer effect is smaller, and the capacity performance and cycling stability of the material are significantly improved.

[0053]

[0054] Table 1 shows the theoretically calculated interfacial reaction energy results of the lithium cobalt oxide cathode material with anion concentration gradient coating obtained in Example 1, between the anion concentration gradient coating and the cathode active material and the sulfide electrolyte. As shown in the table, in the anion gradient coating, the inner oxygen-rich coating layer and the active material hardly undergo interfacial side reactions, and the outer sulfur-rich coating layer and the sulfide electrolyte hardly undergo interfacial side reactions. However, the conventional active material or oxide coating layer is still unstable with the sulfide electrolyte. Therefore, the anion concentration gradient coating can bidirectionally stabilize the oxide active material and the sulfide electrolyte.

[0055] Example 2

[0056] This embodiment prepares a sulfide solid-state battery cathode material according to the following steps:

[0057] (1) Prepare the precursor solution by weighing 15 mg lithium ethanol and 15 mg zirconium acetate, dispersing them in 3 g anhydrous ethanol solvent, and stirring magnetically for 1 h to obtain mixture A;

[0058] (2) 2g of ternary cathode material single crystal LiNi 0.8 Co 0.1 Mn 0.1 O2 was added to the mixture A obtained in step (1), and the mixture was magnetically stirred for 2 hours to obtain mixture B;

[0059] (3) Place the mixture B obtained in step (2) in a magnetic stirrer and heat it at 70°C until the solvent is completely evaporated;

[0060] (4) The mixed powder obtained in step (3) is heat-treated at 550°C for 5 hours in argon gas, and then heat-treated at 550°C for 1 hour in a carrier gas containing hydrogen sulfide to obtain a single-crystal LiNi with an anion concentration gradient coating. 0.8 Co 0.1 Mn 0.1 O2.

[0061] Example 3

[0062] This embodiment prepares a sulfide solid-state battery cathode material according to the following steps:

[0063] (1) Prepare the precursor solution by weighing 10 mg lithium acetate and 20 mg tetrabutyl titanate, dispersing them in 5 g anhydrous ethanol solvent, and stirring magnetically for 1 h to obtain mixture A.

[0064] (2) 2g of ternary cathode material polycrystalline LiNi 0.6 Co 0.2 Mn 0.2 O2 was added to the mixture A obtained in step (1), and the mixture was magnetically stirred for 2 hours to obtain mixture B;

[0065] (3) Place the mixture B obtained in step (2) in a magnetic stirrer and heat it at 60°C until the solvent is completely evaporated;

[0066] (4) The mixed powder obtained in step (3) is heat-treated at 750°C for 2 hours in argon gas, and then heat-treated at 750°C for 0.5 hours in a carrier gas containing hydrogen sulfide to obtain polycrystalline LiNi with an anion concentration gradient coating. 0.6 Co 0.2 Mn 0.2 O2.

[0067] Example 4

[0068] This embodiment prepares a sulfide solid-state battery cathode material according to the following steps:

[0069] (1) Prepare the precursor solution by weighing 20 mg lithium nitrate and 10 mg aluminum isopropoxide, dispersing them in 5 g anhydrous ethanol solvent, and stirring magnetically for 1 h to obtain mixture A;

[0070] (2) Add 3g of lithium cobalt oxide cathode material to the mixture A obtained in step (1) and stir magnetically for 2 hours to obtain mixture B;

[0071] (3) Place the mixture B obtained in step (2) in a magnetic stirrer and heat it at 60°C until the solvent is completely evaporated;

[0072] (4) The mixed powder obtained in step (3) is heat-treated at 650°C for 5 hours in argon gas, and then heat-treated at 550°C for 1 hour in a carrier gas containing hydrogen sulfide to obtain lithium cobalt oxide cathode material with an anion concentration gradient coating.

[0073] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A cathode material having an anion concentration gradient coating layer, characterized in that: It includes a positive electrode material and a coating layer, and the average composition of the coating layer is: Li x M y O n S m , where 1 < x < 5, 1 < y < 5, 1 < n < 12, 1 < m < 12, M is one or a combination of more than one of Ti, Nb, Al, Zr, and from the outside to the inside of the coating layer, the content of S 2- gradually decreases, and the content of O 2- gradually increases.

2. The cathode material with an anion concentration gradient coating layer according to claim 1, characterized in that: The cathode material is an oxide cathode material.

3. The cathode material with an anion concentration gradient coating layer according to claim 2, characterized in that: The oxide cathode material includes one or more combinations of lithium cobalt oxide, lithium manganese oxide, single-crystal ternary materials, and polycrystalline ternary materials, wherein the ternary material includes LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 One or more combinations of O2.

4. A method for preparing the positive electrode material according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: Take lithium source and metal M source as raw materials, dissolve them in or uniformly disperse them in an organic solvent to obtain mixture A; the metal M is one or more of Ti, Nb, Al, Zr; Step 2: Mix the positive electrode material with mixture A to obtain mixture B; Step 3: Dry the mixture B, then heat-treat the mixed powder in an inert atmosphere, and then heat-treat it under a carrier gas containing hydrogen sulfide to obtain the cathode material with an anion concentration gradient coating.

5. The preparation method according to claim 4, characterized in that: The lithium source is one or more of lithium oxide, lithium hydroxide, lithium ethoxide, lithium nitrate, and lithium acetate; the metal M source is one or more of titanium dioxide, niobium pentoxide, aluminum oxide, zirconium dioxide, niobium ethoxide, tetrabutyl titanate, aluminum nitrate, aluminum sec-butoxide, aluminum isopropoxide, zirconium acetate, zirconium nitrate, and zirconium oxynitrate; and the organic solvent is one or more of anhydrous ethanol, isopropanol, ethylene glycol, and acetone.

6. The preparation method according to claim 4, characterized in that: In step one, the mass ratio of the lithium source to the metal M source is 1:1 to 10; the mass ratio of the raw material to the organic solvent is 0.5% to 10%:100%.

7. The preparation method according to claim 4, characterized in that: In step two, the mass ratio of the positive electrode material to the raw material is 100%:0.1% to 20%.

8. The preparation method according to claim 4, characterized in that: In step three, the temperature for drying mixture B is 40-100℃, the temperature for heat treatment in an inert atmosphere is 200℃-800℃ for 0.5-10h, and the temperature for heat treatment in a carrier gas containing hydrogen sulfide is 200℃-800℃ for 0.5-5h.

9. The preparation method according to claim 4, characterized in that: In step three, the carrier gas includes one or a combination of two of argon and nitrogen.

10. The application of the cathode material according to any one of claims 1-3 in a sulfide all-solid-state battery, characterized in that: The cathode material of the sulfide all-solid-state battery includes the cathode material with an anion concentration gradient coating layer and the sulfide electrolyte.

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