Chloride solid electrolyte coated positive electrode material as well as preparation method and application thereof

Abstract

The invention discloses a chloride solid electrolyte coated positive electrode material as well as a preparation method and application thereof, and belongs to the technical field of all-solid-state batteries. The preparation method comprises the following steps: S1, mixing a positive electrode particle material and a chloride solid electrolyte to obtain a positive electrode mixture; the mass ratio of the positive electrode particle material to the chloride solid electrolyte is (70-95): (5-30); and S2, sintering the positive electrode mixture at a temperature lower than 280 DEG C under the protection of vacuum or inert atmosphere to obtain the chloride solid electrolyte coated positive electrode material. The electrolyte can be sintered for a short time above the melting point of the electrolyte, and in-situ'surface coating 'is uniformly performed on the surfaces of positive electrode particles, so that the coated positive electrode material is obtained. According to the mode, 'point coating 'formed like a ball milling mode can be avoided, and coating defects are reduced; and the situation that the performance of the assembled battery is reduced due to oxygen release of the positive electrode material when high-temperature heating is needed during coating of other inorganic matters can be avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of all-solid-state batteries, and mainly relates to a LACO electrolyte (a chloride solid electrolyte can be synthesized by low-temperature melting, LiAl a Cl b O c , where 0.2 ≤ a ≤ 3, 0 < b ≤ 9, 0 < c ≤ 3, and a + b + c > 1) as an ion conductor, and a preparation method for coating cathode particles, etc. Background Art

[0002] Rechargeable batteries, especially lithium-ion batteries, have been widely used in various electronic devices in recent years. Due to their rapid development, the requirements for high capacity and cycle life have been increasing. Moreover, higher requirements have been put forward for the safety of lithium batteries. In traditional liquid lithium-ion batteries, there is a flammable organic liquid electrolyte, which is prone to safety problems such as thermal runaway, seriously hindering the further development of lithium-ion batteries. Therefore, all-solid-state batteries with high energy density, safety, and low cost will become the future development trend. Compared with traditional liquid lithium-ion batteries, all-solid-state batteries use solid electrolytes that are difficult to volatilize, do not flow easily, and are not flammable, such as inorganic electrolytes such as oxides and sulfides, avoiding problems such as combustion and explosion caused by the impact of the organic electrolyte on the outside world, and having relatively high safety.

[0003] However, existing all-solid-state batteries also have problems such as a small contact area between the cathode material and the sulfide solid electrolyte, which affects battery performance. Currently, methods such as ball milling, stirring and mixing, and annealing can be used to coat some inorganic solid electrolytes on the surface of cathode particle materials in order to increase the contact area with the sulfide solid electrolyte intermediate layer and improve battery performance. However, these methods generally have problems such as uneven coating and coating defects. Among them, the ball milling method is to ball mill and coat the inorganic solid electrolyte on the surface of the cathode particles. This type of coating formed is a "point coating", which is prone to uneven coating and coating defects, making it difficult to effectively improve battery performance. The method of stirring and mixing and annealing often requires high-temperature heating, which is prone to oxygen release from the cathode material, resulting in a decline in the performance of the assembled battery. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the purpose of the present invention is to provide a chloride solid electrolyte-coated cathode material, its preparation method, and application. This method can increase the contact area between the solid electrolyte and the cathode active material, solve the problem of the small interfacial contact area between the traditional solid electrolyte and the cathode active material, and thus is beneficial to the improvement of rate performance, etc.

[0005] The present invention provides a preparation method for a chloride solid electrolyte-coated cathode material, including the following steps:

[0006] S1. Mix the positive electrode particle material and the chloride solid electrolyte to obtain a positive electrode mixture.

[0007] The general formula of the chloride solid electrolyte is LiAl a Cl b O c , where 0.2 ≤ a ≤ 3, 0 < b ≤ 9, 0 < c ≤ 3, and a + b + c > 1; the mass ratio of the positive electrode particle material to the chloride solid electrolyte is 70 - 95:5 - 30.

[0008] S2. Sinter the positive electrode mixture at a temperature below 280°C under vacuum or inert atmosphere protection to obtain a positive electrode material coated with chloride solid electrolyte.

[0009] In some embodiments, step S1 includes: ball-milling and mixing the positive electrode particle material and the chloride solid electrolyte, and then adding a conductive agent for ball-milling to obtain a positive electrode mixture.

[0010] In some embodiments, in step S1, the positive electrode particle material is any one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, binary material nickel cobalt oxide, binary material nickel manganese oxide, ternary material nickel cobalt manganese oxide, and ternary material nickel cobalt aluminum oxide, and the particle size of the positive electrode particle material is 3 - 5 μm; the conductive agent is conductive carbon.

[0011] In some embodiments, in step S1, the synthesis of the chloride solid electrolyte includes: mixing LiAlCl4 and an oxide in a ratio to obtain a precursor, and then performing a low-temperature melting reaction in a reaction device at a temperature below 260°C to obtain a chloride solid electrolyte with the general formula LiAl a Cl b O c ; the oxide is one or more of antimony oxide, molybdenum oxide, bismuth oxide, and arsenic oxide.

[0012] In some embodiments, in the synthesis of the chloride solid electrolyte in step S1, the temperature of the low-temperature melting reaction is 200 - 250°C, the heating rate in the reaction device is 2 - 5°C / min, and the reaction time is 1 - 3 h.

[0013] In some embodiments, in step S2, the sintering temperature is 160 - 260°C, the time is 1 - 3 h, and the heating rate is 1 - 5°C / min.

[0014] In some embodiments, in step S2, the sintering device is a vacuum tube furnace, a muffle furnace, or a constant temperature oven.

[0015] The present invention provides a chloride solid electrolyte-coated cathode material obtained by the preparation method as described above, including: cathode particles and a chloride solid electrolyte LiAl a Cl b O c coated on its surface, where 0.2 ≤ a ≤ 3, 0 < b ≤ 9, 0 < c ≤ 3, and a + b + c > 1; the mass ratio of the cathode particles to the chloride solid electrolyte is 70-95:5-30.

[0016] In addition, the present invention provides the application of the chloride solid electrolyte-coated cathode material in the preparation of a solid-state battery.

[0017] In some embodiments, in the solid-state battery, a sulfide solid electrolyte is used as the electrolyte layer, the chloride solid electrolyte-coated cathode material is located on the positive electrode side of the electrolyte layer, and a lithium sheet is used as the negative electrode.

[0018] Compared with the prior art, the present invention uses a chloride solid electrolyte with the general formula LiAl a Cl b O c (0.2 ≤ a ≤ 3, 0 < b ≤ 9, 0 < c ≤ 3, and a + b + c > 1), which is mixed with a cathode particle material in a certain proportion to obtain a cathode mixture, and then sintered at a temperature below 280°C under vacuum or inert atmosphere protection to obtain a chloride solid electrolyte-coated cathode material. The chloride solid electrolyte selected by the present invention as the coating material has ionic conductivity (can be called an ion conductor), which can enhance the ability of ions to quickly embed or escape from the cathode active material, is beneficial to ion transport and capacity utilization; and coats this ion conductor on the surface of the cathode particles in a low-temperature melting manner (sintering below 280°C), that is, it can be sintered for a short time above the melting point of the electrolyte, and uniformly perform in-situ "bread coating" on the surface of the cathode particles to obtain the coated cathode material. This method of the present invention can avoid the "point coating" formed by the ball milling method and reduce coating defects; it can also avoid the problems such as high-temperature heating required for other inorganic coatings and easy oxygen release of the cathode material, which may cause the performance of the assembled battery to decline. In addition, it can also avoid problems such as the deterioration of the electrolyte in organic solvents caused by polymer coating. Description of the Drawings

[0019] Figure 1 is the XRD image of the chloride solid electrolyte in Example 1;

[0020] Figure 2 is the EIS test result of the chloride solid electrolyte in Example 1;

[0021] Figure 3 is the scanning electron microscope (SEM) test result of NCM811 (uncoated);

[0022] Figure 4 SEM test results of the coated cathode material sample of Example 1;

[0023] Figure 5 SEM test results of the cathode mixed material sample of Comparative Example 1. Detailed implementation manners

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. Unless otherwise defined, all the professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0025] The present invention provides a preparation method of a chloride solid electrolyte coated cathode material, including the following steps:

[0026] S1. Mix the cathode particle material and the chloride solid electrolyte to obtain a cathode mixed material; the general formula of the chloride solid electrolyte is LiAl a Cl b O c , where 0.2 ≤ a ≤ 3, 0 < b ≤ 9, 0 < c ≤ 3, and a + b + c > 1; the mass ratio of the cathode particle material to the chloride solid electrolyte is 70 - 95:5 - 30;

[0027] S2. Sinter the cathode mixed material at a temperature below 280°C under vacuum or inert atmosphere protection to obtain the chloride solid electrolyte coated cathode material.

[0028] The present invention mainly provides a method for surface modification of the cathode material, which can increase the contact area between the solid electrolyte and the cathode active material and is beneficial to improving the rate performance, etc.

[0029] In the embodiments of the present invention, the cathode particle is used as the main matrix, and the LACO electrolyte with high ionic conductivity is used as an ion conductor through a low-temperature melting method and is in-situ coated and combined on the matrix to form a coating material layer.

[0030] Among them, the LACO electrolyte is the chloride solid electrolyte LiAl a Cl b O c; In this general formula, 0.2 ≤ a ≤ 3 (preferably a = 1), 0 < b ≤ 9 (preferably 1 ≤ b ≤ 5, such as 2.38, 2.5, 2.8, etc.), 0 < c ≤ 3 (preferably 0.1 ≤ c ≤ 1.9, such as 0.25, 0.6, 0.75, 0.81, etc.), and a + b + c > 1. In some embodiments, the chloride solid electrolyte is LiAlCl 2.5 O 0.75 electrolyte, LiAlCl 2.8 O 0.6 electrolyte, LiAlCl 2.38 O 0.81 electrolyte, LiAlCl 2.8 O 0.6 electrolyte. This chloride solid electrolyte has ionic conductivity. As an ion conductor, it has high ionic conductivity, can enhance the ability of lithium ions to rapidly intercalate into and / or deintercalate from the positive electrode active material after assembling the battery, and is beneficial to ion transport and capacity utilization, etc.

[0031] In the embodiments of the present invention, the synthesis of this ion conductor is preferably carried out. That is, the synthesis of the chloride solid electrolyte includes: using LiAlCl4 and Sb2O3 as raw materials for synthesizing the ion conductor, mixing them according to the molar ratio, and pre-mixing can be carried out at different rotation speeds using a mixing device to obtain the precursor of the ion conductor; then carrying out a low-temperature melting reaction at a temperature lower than 260 °C in a reaction device to obtain a chloride solid electrolyte with the general formula LiAl a Cl b O c (that is, an ion conductor, LACO electrolyte).

[0032] Specifically, the molar ratio of the raw materials LiAlCl4 and Sb2O3 can be 1:0.2 - 0.27, and further can be 1:0.2, 1:0.25, 1:0.27, etc.; SbCl3 gas will be generated and sublimated after the reaction of the two. Sb2O3 can also be replaced by metal or metalloid oxides such as MoO3, Bi2O3, As2O3, etc. The chlorides generated during the reaction will also sublime as the reaction proceeds. Specifically, the mixing device can be a conventional planetary ball mill, powder grinder, high-energy nano ball mill in the art; the rotation speed of ball milling can be 300 - 600 rpm, and specifically can be 400 rpm / min, 450 rpm / min, 500 rpm / min, 550 rpm / min, etc.

[0033] After obtaining the precursor, the embodiment of the present invention transfers it to a reaction device, which can be a vacuum tube furnace, a muffle furnace, or a constant temperature oven; the conditions for its low-temperature melting reaction include: a heating rate of 2 to 5°C / min, heating to 200 to 250°C, keeping warm for 1 to 3 hours, and a cooling rate of 2 to 5°C / min to obtain the final electrolyte product.

[0034] Next, the present embodiment mixes the obtained ion conductor with the positive electrode granular material. To ensure uniform mixing of the positive electrode material and the ion conductor, the positive electrode granules and the ion conductor are mixed in proportion using a mixing device. Step S1 includes: first, weighing the positive electrode granular material and the chloride solid electrolyte (also known as the ion conductor) in proportion and ball milling the mixture; then, weighing an appropriate amount of conductive agent, adding the mixture, and continuing the ball milling to obtain the positive electrode mixture.

[0035] Specifically, the positive electrode particle material can be any one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, binary material lithium nickel cobalt oxide, binary material lithium nickel manganese oxide, ternary material lithium nickel cobalt manganese oxide and ternary material lithium nickel cobalt aluminum oxide; for example, NCM811 material (ternary material lithium nickel cobalt manganese oxide, nickel, cobalt, manganese mass proportions are 80%, 10%, 10% respectively), SC-NCM811 material (this material is a single crystal material, the full name is Single Crystal-NCM811), and lithium cobalt oxide LiCoO2 can be used. In addition, the conductive agent is preferably conductive carbon, which can be a commercially available Super P product.

[0036] Specifically, the mass ratio of the positive electrode particle material: ion conductor: conductive carbon is 70:29.5:0.5 to 95:5:0, wherein the conductive carbon may or may not be added. The mass ratio of the three can further be 75:24.5:0.5, 80:19.5:0.5, 85:14.5:0.5, etc., which facilitates coating. Specifically, the mixing equipment used can be a planetary ball mill, a pulverizer, or a high-energy nano ball mill, for example, using a pulverizer for mixing or ball milling.

[0037] In step S2 of the embodiment of the present invention, the positive electrode mixture is sintered at a temperature below 280°C under vacuum or inert atmosphere. Specifically, the positive electrode mixture is protectively sintered above the melting temperature of the ion conductor (generally greater than or equal to 160°C), thereby uniformly coating the surface of the positive electrode particles with the ion conductor. This method of the embodiment of the present invention not only enhances the rapid insertion and extraction of ions into or out of the positive electrode active material, but also does not affect the elemental composition of the positive electrode particles, thereby improving the electrochemical performance of the battery.

[0038] Specifically, the sintering temperature of the positive electrode mixture can be 160°C to 260°C, and further can be 180°C, 200°C, 260°C, etc.; specifically, the sintering holding time of the positive electrode mixture can be 1 to 3 hours, such as 1h, 1.5h, 2h, etc.

[0039] Specifically, the heating rate of sintering the positive electrode mixture can be 1 to 5°C / min, and further can be 2°C / min, 5°C / min, etc.; specifically, the sintering equipment for the positive electrode mixture can be a muffle furnace, a vacuum tube furnace, a constant temperature oven, etc. The ambient atmosphere during the sintering process can be nitrogen, argon, vacuum conditions, etc. Among them, the purity of inert gases such as nitrogen and argon is usually 99.99%.

[0040] In the embodiment of the present invention, the above-mentioned low-temperature melting method is used to coat the surface of the positive electrode particles with LACO electrolyte as an ion conductor. This method not only enables the ion conductor to uniformly cover the surface of the positive electrode particles to form a "bread coating" with fewer coating defects, but also the coated LACO electrolyte has ion conductivity, which is beneficial to the rapid insertion and extraction of lithium ions from the positive electrode material. Therefore, the electrochemical performance such as the capacity and rate of the battery can be improved, and there is no phenomenon of deterioration in the solvent.

[0041] The embodiment of the present invention provides a positive electrode material coated with a chloride solid electrolyte obtained by the preparation method as described above, which includes: positive electrode particles and a chloride solid electrolyte LiAl a Cl b O c , where 0.2 ≤ a ≤ 3, 0 < b ≤ 9, 0 < c ≤ 3, and a + b + c > 1; the mass ratio of the positive electrode particles to the chloride solid electrolyte is 70 to 95:5 to 30.

[0042] Specifically, the positive electrode material coated with a chloride solid electrolyte further includes a conductive agent, which is preferably conductive carbon. The materials, ratios, etc. of the positive electrode particles, chloride solid electrolyte, and conductive carbon are as described above and will not be elaborated here one by one.

[0043] The present invention also provides the application of the positive electrode material coated with a chloride solid electrolyte in the preparation of a solid-state battery; based on the excellent performance of the positive electrode material coated with a chloride solid electrolyte, the electrochemical performance of the battery can be improved.

[0044] In the solid-state battery described in some embodiments of the present invention, a sulfide solid electrolyte is used as the electrolyte layer, the positive electrode material coated with a chloride solid electrolyte is located on the positive electrode side of the electrolyte layer, and a lithium sheet is used as the negative electrode, and the battery performance is good. Among them, the sulfide solid electrolyte that can be used includes but is not limited to: 70Li2S - 30P2S5, Li 10 Ge / SiP2S12 , Li6PS5X (X = Cl, Br, I), commercially available products can be used without special restrictions. The chloride solid electrolyte coated positive electrode material of the present invention is beneficial for interfacial contact with the electrolyte interlayer. This is because the LACO halide electrolyte has a wide electrochemical window, which can inhibit the occurrence of interfacial side reactions, thereby improving the stability of the electrolyte interlayer under high pressure conditions.

[0045] In order to better understand the technical content of this application, the following specific examples are provided to further illustrate this application. The raw materials involved are all commercially available conventional products and are not particularly limited.

[0046] Example 1

[0047] 1. LiAlCl 2.5 O 0.75 Preparation of electrolyte:

[0048] LiAlCl4 and Sb2O3 were mixed in a molar ratio of 1:0.25, and then premixed using a planetary ball mill at 500 rpm / min for 2 h. The ball-milled precursor powder was then placed in a vacuum atmosphere tube furnace for sintering at a heating rate of 2 °C / min to 250 °C. After holding for 2 h, the cooling rate was 2 °C / min, and the gas flow rate throughout the process was 2 L / min to obtain LiAlCl 2.5 O 0.75 electrolytes.

[0049] The characterization test results of the electrolyte can be found in Figure 1 and Figure 2 , Figure 1 Its X-ray diffraction pattern (XRD) is Figure 2 This is the electrochemical impedance spectroscopy (EIS), which shows the crystal structure and ion conductor properties of the chloride solid electrolyte.

[0050] 2. Preparation of electrolyte-coated positive electrode material (NCM811):

[0051] 1. Preparation of positive electrode mixture:

[0052] NCM811, LiAlCl 2.5 O 0.75 and Super P in a ratio of 75:24.5:0.5. First, weigh the synthesized LiAlCl 2.5 O 0.75and NCM811, using a planetary ball mill at 420 rpm / min for half an hour; secondly, Super P was added to the mixed powder in the first step, and ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain a mixture of positive electrode particles and electrolyte, i.e., a positive electrode mixture.

[0053] 2. Electrolyte in situ coating of cathode mixture:

[0054] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a muffle furnace in a glove box (argon atmosphere) at a temperature not lower than LiAlCl 2.5 O 0.75 The melting point of the electrolyte (≥160°C) was reached, that is, the cathode particles were in situ coated at 200°C for 2h and the heating rate was 2°C / min to form a chloride solid electrolyte coated cathode material, which was recorded as NCM811@LiAlCl 2.5 O 0.75 ; The same applies to the following text.

[0055] Example 2

[0056] 1. LiAlCl 2.8 O 0.6 Preparation of electrolyte:

[0057] LiAlCl4 and Sb2O3 were mixed in a molar ratio of 1:0.2, and then premixed using a planetary ball mill at 300 rpm / min for 2 h. The ball-milled precursor powder was then placed in a vacuum atmosphere tube furnace for sintering at a heating rate of 2 °C / min to 250 °C. After holding for 2 h, the cooling rate was 2 °C / min, and the gas flow rate throughout the process was 2 L / min to obtain LiAlCl 2.8 O 0.6 electrolytes.

[0058] 2. Preparation of electrolyte-coated positive electrode material (NCM811):

[0059] 1. Preparation of positive electrode mixture:

[0060] NCM811, LiAlCl 2.8 O 0.6 and Super P in a ratio of 70:29.5:0.5. First, weigh the synthesized LiAlCl 2.8 O 0.6 and NCM811, using a planetary ball mill at 420 rpm / min for half an hour; secondly, Super P was added to the mixed powder in the first step, and ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain a mixture of positive electrode particles and electrolyte, i.e., a positive electrode mixture.

[0061] 2. Electrolyte in situ coating of cathode mixture:

[0062] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it into a vacuum tube furnace and heat it at a temperature not lower than LiAlCl 2.8 O 0.6 The melting point of the electrolyte (≥160℃) was maintained at 160℃ for 1h, and the heating rate was 1℃ / min to form NCM811@LiAlCl 2.8 O 0.6 .

[0063] Example 3

[0064] 1. LiAlCl 2.38 O 0.81 Preparation of electrolyte:

[0065] LiAlCl4 and Sb2O3 were mixed in a molar ratio of 1:0.27, and then premixed using a planetary ball mill at 600 rpm / min for 2 h. The ball-milled precursor powder was then placed in a muffle furnace in a glove box for sintering. The heating rate was 2 °C / min, and the temperature was raised to 250 °C. After holding for 2 h, the cooling rate was 2 °C / min, and the gas flow rate throughout the process was 2 L / min to obtain LiAlCl 2.38 O 0.81 electrolytes.

[0066] 2. Preparation of electrolyte-coated positive electrode material (NCM811):

[0067] 1. Preparation of positive electrode mixture:

[0068] LiAlCl 2.38 O 0.81 , NCM811 and Super P were mixed in a ratio of 95:5:0. First, the synthesized LiAlCl 2.38 O 0.81 and NCM811, and mixed them using a powder grinder for 5s×20 times to obtain a mixture of positive electrode particles and electrolyte, namely, a positive electrode mixture.

[0069] 2. Electrolyte in situ coating of cathode mixture:

[0070] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a constant temperature oven in a glove box (argon atmosphere) at a temperature not lower than LiAlCl 2.38 O 0.81 The melting point of the electrolyte (≥160℃) was maintained at 260℃ for 3h, and the heating rate was 5℃ / min to form NCM811@LiAlCl 2.38 O 0.81 .

[0071] Example 4

[0072] 1. LiAlCl 2.5 O 0.75 Preparation of electrolyte:

[0073] LiAlCl4 and Sb2O3 were mixed in a molar ratio of 1:0.25, and then premixed using a high-energy nano ball mill at 600 rpm / min for 2 h. The milled precursor powder was then placed in a constant temperature oven for sintering at a heating rate of 2 °C / min to 250 °C. After holding for 2 h, the cooling rate was 2 °C / min, and the gas flow rate throughout the process was 2 L / min to obtain LiAlCl 2.5 O 0.75 electrolytes.

[0074] 2. Preparation of electrolyte-coated cathode material (SC-NCM811):

[0075] 1. Preparation of positive electrode mixture:

[0076] SC-NCM811, LiAlCl 2.5 O 0.75 and Super P in a ratio of 70:29.5:0.5. First, weigh LiAlCl according to the metering ratio. 2.5 O 0.75 and SC-NCM811, using a high-energy nano ball mill at 420 rpm / min for half an hour; secondly, Super P was added to the mixed powder in the first step, and ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain a mixture of positive electrode particles and electrolyte, i.e., a positive electrode mixture.

[0077] 2. Electrolyte in situ coating of cathode mixture:

[0078] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a muffle furnace in a glove box (nitrogen atmosphere) at a temperature not lower than LiAlCl 2.5 O 0.75 The melting point of the electrolyte (≥160°C) was maintained at 160°C for 3 h, and the heating rate was 5°C / min. The SC-NCM811@LiAlCl 2.5 O 0.75 .

[0079] Example 5

[0080] 1. LiAlCl 2.8 O 0.6 Preparation of electrolyte:

[0081] 1. LiAlCl4 and Sb2O3 were mixed in a molar ratio of 1:0.2, and then a powder mixer was used to mix the materials for 5s×20 times. The mixed powder was then placed in a vacuum atmosphere tube furnace for sintering. The heating rate was 2℃ / min. The temperature was raised to 250℃. After keeping the temperature for 2h, the cooling rate was 2℃ / min. The gas flow rate during the whole process was 2L / min. LiAlCl 2.8 O 0.6 electrolytes.

[0082] 2. Preparation of electrolyte-coated positive electrode material (NCM811):

[0083] 1. Preparation of positive electrode mixture:

[0084] NCM811, LiAlCl 2.8 O 0.6 and Super P in a ratio of 95:5:0. First, weigh the synthesized LiAlCl 2.8 O 0.6 and NCM811, using a high-energy nano ball mill at 420 rpm / min for half an hour; secondly, Super P was added to the mixed powder in the first step, and ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain a mixture of positive electrode particles and electrolyte, i.e., a positive electrode mixture.

[0085] 2. Electrolyte in situ coating of cathode mixture:

[0086] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a muffle furnace in a glove box (argon atmosphere) at a temperature not lower than LiAlCl 2.8 O 0.6 The melting point of the electrolyte (≥160°C) was maintained at 260°C for 1h, and the heating rate was 1°C / min to form NCM811@LiAlCl 2.8 O 0.6 .

[0087] Example 6

[0088] 1. LiAlCl 2.38 O 0.81 Preparation of electrolyte:

[0089] 1. LiAlCl4 and Sb2O3 were mixed in a molar ratio of 1:0.27, and then premixed using a planetary ball mill at 300 rpm / min for 2 hours. The ball-milled precursor powder was then placed in a constant temperature oven in a glove box for sintering. The heating rate was 2°C / min, and the temperature was raised to 250°C. After holding for 2 hours, the cooling rate was 2°C / min, and the gas flow rate throughout the process was 2 liters / min to obtain LiAlCl2.38 O 0.81 electrolytes.

[0090] 2. Preparation of electrolyte-coated positive electrode material (LiCoO2):

[0091] 1. Preparation of positive electrode mixture:

[0092] LiCoO2, LiAlCl 2.38 O 0.81 and Super P in a ratio of 70:29.5:0.5. First, weigh the synthesized LiAlCl 2.38 O 0.81 and LiCoO2, using a high-energy nano ball mill at 420 rpm / min for half an hour; secondly, Super P was added to the mixed powder in the first step, and ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain a mixture of positive electrode particles and electrolyte, i.e., a positive electrode mixture.

[0093] 2. Electrolyte in situ coating of cathode mixture:

[0094] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a vacuum tube furnace and heat it under vacuum conditions not lower than LiAlCl 2.38 O 0.81 The melting point of the electrolyte (≥160℃) is maintained at 160℃ for 1h, and the heating rate is 5℃ / min. The cathode particles are in situ coated to form LiCoO2@LiAlCl 2.38 O 0.81 .

[0095] Example 7

[0096] 1. LiAlCl 2.8 O 0.6 Preparation of electrolyte:

[0097] 1. LiAlCl4 and Sb2O3 were mixed in a molar ratio of 1:0.2, and then premixed using a high-energy nano ball mill at 500 rpm / min for 2 hours. The ball-milled precursor powder was then placed in a muffle furnace in a glove box for sintering. The heating rate was 2°C / min, and the temperature was raised to 250°C. After holding for 2 hours, the cooling rate was 2°C / min, and the gas flow rate throughout the process was 2 liters / min to obtain LiAlCl 2.8 O 0.6 electrolytes.

[0098] 2. Preparation of electrolyte-coated positive electrode material (NCM811):

[0099] 1. Preparation of positive electrode mixture:

[0100] NCM811, LiAlCl 2.8 O 0.6 and Super P in a ratio of 95:5:0. 2.8 O 0.6 and NCM811, and mixed them at 420 rpm / min using a planetary ball mill for half an hour to obtain a mixture of positive electrode particles and electrolyte, namely, a positive electrode mixture.

[0101] 2. Electrolyte in situ coating of cathode mixture:

[0102] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a constant temperature oven in a glove box (nitrogen atmosphere) at a temperature not lower than LiAlCl 2.8 O 0.6 The melting point of the electrolyte (≥160℃) is maintained at 260℃ for 3h, and the heating rate is 1℃ / min to form LiCoO2@LiAlCl 2.8 O 0.6 .

[0103] Example 8

[0104] 1. LiAlCl 2.5 O 0.75 Preparation of electrolyte:

[0105] LiAlCl4 and Sb2O3 were mixed in a molar ratio of 1:0.25, and then premixed using a high-energy nano ball mill at 600 rpm / min for 2 h. The ball-milled precursor powder was then placed in a muffle furnace in a glove box for sintering. The heating rate was 2 °C / min, and the temperature was raised to 250 °C. After holding for 2 h, the cooling rate was 2 °C / min, and the gas flow rate throughout the process was 2 L / min to obtain LiAlCl 2.5 O 0.75 electrolytes.

[0106] 2. Preparation of electrolyte-coated cathode material (SC-NCM811):

[0107] 1. Preparation of positive electrode mixture:

[0108] SC-NCM811, LiAlCl 2.5 O 0.75 and Super P in a ratio of 70:29.5:0.5. First, weigh the synthesized LiAlCl 2.5 O 0.75 , SC-NCM811 and Super P were mixed using a powder grinder at a rate of 5s × 20 times to obtain a mixture of positive electrode particles and electrolyte, namely, a positive electrode mixture.

[0109] 2. Electrolyte in situ coating of cathode mixture:

[0110] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a vacuum tube furnace in a dry room and heat it under vacuum conditions not lower than LiAlCl 2.5 O 0.75 The melting point of the electrolyte (≥160℃) was maintained at 160℃ for 3h and the heating rate was 1℃ / min to form SC-NCM811@LiAlCl 2.5 O 0.75 .

[0111] Comparative Example 1

[0112] NCM811, LiAlCl 2.5 O 0.75 and Super P in a ratio of 80:19.5:0.5. First, weigh the previously synthesized LiAlCl 2.5 O 0.75 and NCM811, using a planetary ball mill at 420 rpm / min to mix for half an hour; then Super P was added to the first step mixed powder, and the ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain positive electrode particles and LiAlCl 2.5 O 0.75 Electrolyte mixture, that is, positive electrode mixture.

[0113] Figure 3 This is the scanning electron microscope test result of NCM811 (uncoated); Figure 4 The scanning electron microscope (SEM) test results of Example 1 are as follows; Figure 5 This is the scanning electron microscope test result of Comparative Example 1.

[0114] It can be clearly seen from the SEM image that the positive electrode particles are spherical before coating, and after coating, the surface of the positive electrode particles is evenly covered with a layer of LiAlCl 2.5 O 0.75 The electrolyte is prepared by using energy dispersive X-ray spectroscopy (EDS) to present the distribution of each element in the positive electrode particles, which shows that the low-temperature melting method can evenly cover the surface of the positive electrode particles with a layer of ion conductor (such as Figure 4 The sample of Example 1 shown). While LiAlCl 2.5 O 0.75 After mixing with NCM811 at room temperature without sintering, the SEM image clearly shows that LiAlCl 2.5 O 0.75The electrolyte is dispersed around the NCM811 particles, and the electrolyte and the cathode particles are still in point-to-point contact, resulting in uneven coating and coating defects, which is not conducive to ion transmission and rate performance improvement. Figure 5 The Comparative Example 1 sample is shown.

[0115] In addition, when the sintering temperature of the in-situ coating is exceeded, the glassy (non-static) coating layer may crystallize due to the high temperature, reducing the protective effect on the positive electrode.

[0116] Comparative Example 2

[0117] Preparation of electrolyte-coated positive electrode material (NCM811):

[0118] 1. Preparation of positive electrode mixture:

[0119] NCM811, LiAlCl 2.5 O 0.75 and Super P in a ratio of 75:24.5:0.5. First, weigh LiAlCl according to the metering ratio. 2.5 O 0.75 and NCM811, using a planetary ball mill at 420 rpm / min for half an hour; secondly, Super P was added to the mixed powder in the first step, and ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain a mixture of positive electrode particles and electrolyte, i.e., a positive electrode mixture.

[0120] 2. Electrolyte in situ coating of cathode mixture:

[0121] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a muffle furnace in a glove box at a temperature not lower than LiAlCl 2.5 O 0.75 The melting point of the electrolyte (≥160°C) was maintained at 280°C for 4h, and the heating rate was 6°C / min to form the comparative sample NCM811@LiAlCl 2.5 O 0.75 .

[0122] Comparative Example 3

[0123] Preparation of electrolyte-coated positive electrode material (NCM811):

[0124] 1. Preparation of positive electrode mixture:

[0125] NCM811, LiAlCl 2.5 O 0.75 and Super P in a ratio of 75:24.5:0.5. First, weigh LiAlCl according to the metering ratio. 2.5 O 0.75and NCM811, using a planetary ball mill at 420 rpm / min for half an hour; secondly, Super P was added to the mixed powder in the first step, and ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain a mixture of positive electrode particles and electrolyte, i.e., a positive electrode mixture.

[0126] 2. Electrolyte in situ coating of cathode mixture:

[0127] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it into a muffle furnace in a dry room at a temperature not lower than LiAlCl 2.5 O 0.75 The melting point of the electrolyte (≥160℃) was obtained by in-situ coating on the positive electrode particles at 200℃ for 2h and a heating rate of 2℃ / min to form the comparative sample NCM811@LiAlCl 2.5 O 0.75 .

[0128] Comparative Example 4

[0129] Preparation of electrolyte-coated positive electrode material (NCM811):

[0130] 1. Preparation of positive electrode mixture:

[0131] NCM811, LiAlCl 2.5 O 0.75 and Super P in a ratio of 50:49.5:0.5. First, weigh LiAlCl according to the metering ratio. 2.5 O 0.75 and NCM811, using a planetary ball mill at 420 rpm / min for half an hour; secondly, Super P was added to the mixed powder in the first step, and ball milling was continued at a speed of 430 rpm / min and a mixing time of 40 minutes to obtain a mixture of positive electrode particles and electrolyte, i.e., a positive electrode mixture.

[0132] 2. Electrolyte in situ coating of cathode mixture:

[0133] Weigh an appropriate amount of cathode mixture into a quartz crucible, then place it in a muffle furnace in a glove box (argon atmosphere) at a temperature not lower than LiAlCl 2.5 O 0.75 The melting point of the electrolyte (≥160℃) was obtained by in-situ coating on the positive electrode particles at 200℃ for 2h and a heating rate of 2℃ / min to form the comparative sample NCM811@LiAlCl 2.5 O 0.75 .

[0134] The samples prepared in the above examples and comparative examples were tested as follows:

[0135] Weigh 0.1g of sulfide solid electrolyte (Li6PS5Cl) as the battery interlayer and press it into a sheet under a pressure of 100MPa; then weigh 18.3mg of the above-mentioned electrolyte-coated positive electrode material and place it on the positive electrode side of the electrolyte interlayer, add carbon-coated aluminum foil and press it into a sheet under a pressure of 300MPa. Then use the lithium sheet as the negative electrode, assemble it into a battery, and test it at different rates.

[0136] The test results are as follows:

[0137] Table 1 Battery performance test results of the embodiments of the present invention and the comparative examples

[0138]

[0139] As can be seen from the above examples, it was unexpectedly discovered in the examples of the present invention that the LACO electrolyte can be uniformly coated on the surface of the positive electrode particles after low-temperature melting. The coating method is surface coating, which is less likely to form coating defects compared to point coating formed by ball milling or stirring. The coated LACO electrolyte has ionic conductivity, which is conducive to the rapid insertion and extraction of ions from the positive electrode material, thereby facilitating the transmission of ions in the battery, the utilization of capacity, and the improvement of rate performance (such as the first-cycle efficiency is above 85%, and the 1C / 0.1C retention rate is above 70%).

[0140] The advantages of the technology of the embodiments of the present invention include: 1. The electrolyte can be evenly coated on the positive electrode particles after sintering in a short time; 2. Low-temperature sintering avoids the need for high-temperature heating required for coating with other inorganic materials, which can easily cause the positive electrode material to release oxygen and thus reduce the performance of the assembled battery; 3. Avoids polymer coating, which causes the electrolyte to deteriorate in organic solvents, and the residual solvent will affect subsequent cycles.

[0141] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a chloride solid electrolyte coated positive electrode material, characterized in that: The following steps are involved: S1, mixing the positive electrode particle material and the chloride solid electrolyte to obtain a positive electrode mixture; The general formula of the chloride solid electrolyte is LiAl a Cl b O c , where 0.2 ≤ a ≤ 3, 0 < b ≤ 9, 0 < c ≤ 3, and a + b + c > 1; the mass ratio of the positive electrode particle material to the chloride solid electrolyte is (70-95):(5-30); S2. Sintering the cathode mixture at a temperature lower than 280° C. under vacuum or inert atmosphere protection to obtain a chloride solid electrolyte coated cathode material.

2. The preparation method according to claim 1, characterized in that The step S1 comprises: ball-milling the positive electrode particle material and the chloride solid electrolyte, and then adding a conductive agent and ball-milling the mixture to obtain a positive electrode mixture.

3. The preparation method according to claim 2, characterized in that In step S1, the positive electrode particle material is any one of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, binary material lithium nickel cobalt oxide, binary material lithium nickel manganese oxide, ternary material lithium nickel cobalt manganese oxide and ternary material lithium nickel cobalt aluminum oxide, and the particle size of the positive electrode particle material is 3 to 5 μm; the conductive agent is conductive carbon.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step S1, the synthesis of the chloride solid electrolyte includes: mixing LiAlCl4 and oxide in proportion to obtain a precursor, and then performing a low-temperature melting reaction below 260°C in a reaction device to obtain a solid electrolyte with the general formula LiAl a Cl b O c The chloride solid electrolyte; the oxide is one or more of antimony oxide, molybdenum oxide, bismuth oxide and arsenic oxide.

5. The preparation method according to claim 4, characterized in that In the synthesis of the chloride solid electrolyte in step S1, the temperature of the low-temperature melting reaction is 200-250° C., the heating rate in the reaction equipment is 2-5° C. / min, and the reaction time is 1-3 hours.

6. The preparation method according to any one of claims 1 to 3, characterized in that In the step S2, the sintering temperature is 160-260°C, the sintering time is 1-3 hours, and the heating rate is 1-5°C / min.

7. The preparation method according to claim 6, characterized in that In the step S2, the sintering equipment is a vacuum tube furnace, a muffle furnace or a constant temperature oven.

8. The chloride solid electrolyte coated cathode material obtained by the preparation method according to any one of claims 1 to 7, comprising: Positive electrode particles and chloride solid electrolyte LiAl coated on their surfaces a Cl b O c , where 0.2 ≤ a ≤ 3, 0 < b ≤ 9, 0 < c ≤ 3, and a + b + c > 1; the mass ratio of the positive electrode particles to the chloride solid electrolyte is (70 - 95):(5 - 30).

9. Use of the chloride solid electrolyte coated cathode material according to claim 8 in the preparation of a solid-state battery.

10. The use according to claim 9, characterized in that In the solid-state battery, a sulfide solid electrolyte is used as the electrolyte layer, the chloride solid electrolyte coated positive electrode material is located on the positive electrode side of the electrolyte layer, and a lithium sheet is used as the negative electrode.

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