Lithium cobalt oxide material for in-situ construction of interface coating and bulk phase doping as well as preparation method and application of lithium cobalt oxide material

Abstract

The invention discloses a lithium cobalt oxide material for in-situ construction of an interface coating and bulk phase doping, and a preparation method and application thereof, and belongs to the field of lithium ion batteries. The method comprises the following steps: treating by using sodium borohydride: in a glove box filled with protective gas, weighing lithium cobalt oxide and sodium borohydride, grinding and uniformly mixing; putting a mixture ground by using sodium borohydride into a quartz tube, sealing with flame, and then feeding into a muffle furnace for high-temperature sintering; and taking out the sintered sample, immediately transferring into a glove box filled with argon, cooling to room temperature, and grinding to obtain the lithium cobalt oxide material treated by sodium borohydride. The LiCoO2 positive electrode material modified by the method shows good long cycle stability and extremely high energy density in an all-solid-state lithium ion battery based on sulfide electrolyte, and a new thought is provided for a modification method of a solid-state battery positive electrode and realization of a high-energy-density solid-state battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, and specifically relates to a one-step in-situ construction method for interfacial coating and bulk doping of lithium cobalt oxide materials using a single reagent treatment, the preparation method thereof, and its application in high-performance all-solid-state lithium-ion batteries. Background Technology

[0002] Since the successful commercialization of lithium-ion batteries (LIBs) in 1991, their excellent performance has led to their widespread application in various electronic products and electric vehicles, profoundly impacting our daily lives. However, currently commercially available lithium-ion batteries, due to the use of organic liquid electrolytes, still suffer from numerous problems such as low energy density, easy leakage and flammability of organic electrolytes, poor environmental compatibility, and high cost. To address these issues, researchers have proposed all-solid-state lithium-ion batteries (ASSLIBs) with high energy density and high safety, which have become a research hotspot in recent years. The global solid-state battery industry is developing rapidly, with Europe being one of the earliest regions to promote its industrialization, and Japan and South Korea also actively engaged in related work. It is estimated that the Chinese solid-state battery market will reach 20 billion RMB by 2030.

[0003] Although all-solid-state lithium-ion batteries (ASSLIB) have promising prospects, they still face significant challenges in practical applications. These challenges include interfacial issues at the cathode interface, such as space charge layer formation, element diffusion, and poor contact between the cathode material and the solid electrolyte; and particle breakage and internal particle isolation within the cathode material itself. These problems lead to high interfacial impedance and continuous capacity decay in ASSLIBs. Current methods for modifying the lithium cobalt oxide cathode in ASSLIBs include coating with materials such as LiNbO3, LiAlPO4, and LiMgPO4, or using materials such as Mg... 2+ Al 3+ Ti 4+ Doping with cations has yielded good results. However, current modification methods are relatively complex, and there are few reports of methods that can directly construct an interfacial coating on the surface of lithium cobalt oxide materials in one step while simultaneously forming bulk doping. Summary of the Invention

[0004] To overcome the shortcomings and deficiencies of existing solid-state batteries and the cumbersome nature of existing modification techniques, this invention provides a one-step in-situ synergistic modification technique. This technique utilizes a single reagent (sodium borohydride, NaBH4) to perform a one-step thermal treatment on lithium cobalt oxide (LiCoO2) cathode material, simultaneously achieving surface and interface modification and bulk structure enhancement of the lithium cobalt oxide (LiCoO2) cathode material. When sodium borohydride is used to reduce the surface of lithium cobalt oxide, the surface is reduced to cobalt suboxide (CoO) with low cobalt (+2 valence), isolating the direct contact between lithium cobalt oxide and the electrolyte, fundamentally inhibiting the occurrence of interfacial reactions; simultaneously, the Na in sodium borohydride... + It will enter the lithium cobalt oxide lattice and replace part of the Li. + This creates a "pillar effect," stabilizing the lithium cobalt oxide lattice during electrochemical cycling; furthermore, the boron in sodium borohydride reacts with Li... + The combination forms Li3BO3, accelerating the formation of Li + The transmission.

[0005] The method of this invention is an in-situ modification method, using NaBH4 as a modifier. During heat treatment, NaBH4 acts not only as a reducing agent but also as a Na+ modifier. + NaBH4 serves as both a doping source and a Li3BO3 generation source. This single reagent plays a multifunctional role, simplifying the process of modifying LiCoO2 cathode materials, reducing costs and complexity, and enabling low-cost, high-volume processing of lithium cobalt oxide cathode materials.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing lithium cobalt oxide materials with in-situ interface coating and bulk doping is disclosed. This method utilizes a single sodium borohydride reagent and a one-step thermal treatment to in-situ synergistically modify lithium cobalt oxide, forming a CoO / Li3BO3 composite interface coating layer on the surface of the LiCoO2 cathode material. Simultaneously, Na... + Doping is introduced into the bulk phase of LiCoO2 cathode material, replacing Li + Bulk doping is achieved at specific locations; the method is as follows: (1) Using a single sodium borohydride treatment: In a glove box filled with protective gas, weigh lithium cobalt oxide and sodium borohydride, place them in an agate mortar and grind them evenly; (2) The mixture that has been ground with sodium borohydride in step (1) is placed into a quartz tube, sealed with a flame, and then sent into a muffle furnace for high-temperature sintering. (3) After the sintered sample is taken out, it is immediately transferred to a glove box filled with argon gas, cooled to room temperature and then ground to obtain lithium cobalt oxide material treated with sodium borohydride.

[0007] Further, in step (1), the mass ratio of sodium borohydride to lithium cobalt oxide is 0.5~2:100.

[0008] Furthermore, in step (1), the grinding time is not less than 30 minutes.

[0009] Furthermore, in step (1), the protective gas is nitrogen or an inert gas.

[0010] Furthermore, in step (2), the quartz tube has the following specifications: od×id=13×10 mm and a length of 25 cm.

[0011] Furthermore, in step (2), the high-temperature sintering temperature is 645~655℃ and the time is 115~125min.

[0012] Furthermore, in step (3), the grinding time is not less than 30 minutes.

[0013] A lithium cobalt oxide material prepared by the above preparation method.

[0014] Application of a lithium cobalt oxide material prepared by the above preparation method in a high-performance all-solid-state lithium-ion battery.

[0015] The advantages of this invention over the prior art are as follows: (1) This invention does not require external introduction. It utilizes the redox reaction between sodium borohydride and the surface of lithium cobalt oxide to construct an interfacial coating in situ and simultaneously form bulk doping. The strong reducing property of NaBH4 reduces the Co on the surface of lithium cobalt oxide. 3+ Restored to Co 2+ A uniform layer of cobalt suboxide (CoO) is formed. Simultaneously, the reaction releases Li... + When combined with element B, lithium-ion conductor Li3BO3 is generated in situ, forming a unique CoO / Li3BO3 composite coating. CoO acts as a physical barrier, fundamentally isolating direct contact between lithium cobalt oxide and the sulfide solid electrolyte, suppressing harmful interfacial side reactions (such as element interdiffusion and space charge layer effect). Meanwhile, Li3BO3, as an excellent lithium-ion conductor, ensures efficient lithium-ion transport at the interface and reduces interfacial impedance.

[0016] (2) Na + The introduction of Na+ plays a "pillar effect" in the layered structure of lithium cobalt oxide. + The ionic radius is greater than that of Li + It can effectively expand the interlayer spacing of lithium cobalt oxide and stabilize the crystal structure during electrochemical cycling, suppressing phase transitions and particle breakage, thereby significantly improving the structural stability and long cycle life of the material.

[0017] (3) The process of this invention is simple, and the whole process only involves grinding and one sintering. The steps are simple, easy to control and repeat.

[0018] (4) The reaction is carried out in a closed quartz tube, which is safe and controllable, avoids the emission of harmful substances, and meets the requirements of green manufacturing. In addition, the reaction of the present invention is sufficient, which is conducive to stable output. Attached Figure Description

[0019] Figure 1 The images show the XRD patterns of the lithium cobalt oxide cathode materials prepared in Examples 1, 2, 3 and Comparative Example 1 of this invention.

[0020] Figure 2 This is a SEM image of the lithium cobalt oxide cathode material prepared in Example 1 of the present invention.

[0021] Figure 3 This is a SEM EDS-mapping image of the lithium cobalt oxide cathode material prepared in Example 1 of the present invention.

[0022] Figure 4 This is a TEM image of the lithium cobalt oxide cathode material prepared in Example 1 of the present invention.

[0023] Figure 5 This is a TEM EDS-mapping image of the lithium cobalt oxide cathode material prepared in Example 1 of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, so as to fully and clearly convey the implementation of the present invention to those skilled in the art. However, it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0025] This invention proposes a one-step in-situ synergistic modification technique that simultaneously achieves surface and interface modification and bulk structure enhancement of lithium cobalt oxide (LiCoO2) cathode materials using a single reagent (sodium borohydride, NaBH4). Sodium borohydride is used as the single modifier, and the lithium cobalt oxide cathode material is heat-treated in one step. Utilizing the strong reducing properties of NaBH4, a composite interfacial coating of cobalt suboxide (CoO) and Li3BO3 is formed on the surface of the LiCoO2 cathode material; simultaneously, the Na in sodium borohydride... + Doping is introduced into the bulk phase of LiCoO2 cathode material, replacing Li + Location. The CoO / Li3BO3 composite interface layer can effectively solve the severe interfacial reaction between the cathode material and the electrolyte in solid-state batteries, while Na... +By incorporating the bulk phase of the LiCoO2 cathode material, the stability of the LiCoO2 cathode material during battery cycling can be maintained. The LiCoO2 cathode material modified by this method exhibits excellent long-cycle stability and extremely high energy density in all-solid-state lithium-ion batteries based on sulfide electrolytes, providing a new approach for modifying solid-state battery cathodes and realizing high-energy-density solid-state batteries.

[0026] Example 1: Preparation process of lithium cobalt oxide (LCO) cathode treated with sodium borohydride and assembly of its all-solid-state battery; (1) Weigh 2g of lithium cobalt oxide positive electrode into an agate mortar using a balance in a glove box filled with nitrogen, and then weigh sodium borohydride with a mass fraction of 0.5% of lithium cobalt oxide into the mortar and grind and mix for 30min. (2) Place the ground sample into a quartz tube and seal it with a flame; (3) Transfer the sealed quartz tube into a muffle furnace for sintering. Raise the temperature to 650°C at a rate of 5°C / min for a total of 126 min. After the temperature rise is complete, continue sintering at 650°C for 120 min. (4) The sintered sample was immediately transferred to an argon-filled glove box. After cooling to room temperature, it was removed and transferred to an agate mortar for grinding for 30 minutes to obtain the sodium borohydride-treated lithium cobalt oxide cathode material (NBH-LCO-05). Its XRD pattern is shown below. Figure 1 As shown, the peak value of CoO can be slightly observed; the SEM image is as follows. Figure 2 As shown in the figure, the prepared material surface is smooth and free of cracks; combined with the SEM EDS-mapping image as shown... Figure 3 As shown, TEM image Figure 4 The diagram shown is a TEMEDS-mapping diagram. Figure 5 As shown, Na and B elements are uniformly distributed in the bulk phase and surface of the lithium cobalt oxide cathode material, and the surface coating layer is about 25~30 nanometers. The material was taken out and ground in an agate mortar for 30 minutes according to the mass ratio of lithium cobalt oxide cathode material: lithium phosphorus sulfur chlorine electrolyte: conductive carbon (NBH-LCO-05: LPSCL: Super P) = 150:100:5 to prepare a mixed cathode material. Then, 5mg of the mixed cathode material, 250mg of LPSCL, and lithium indium alloy as the negative electrode were added into a mold and pressed into a solid-state battery.

[0027] Example 2: Preparation process of lithium cobalt oxide (LCO) cathode treated with sodium borohydride and assembly of its all-solid-state battery (1) Weigh 2g of lithium cobalt oxide positive electrode into an agate mortar using a balance in a glove box filled with argon gas, and then add 1% sodium borohydride of lithium cobalt oxide into the mortar and grind and mix for 30min. (2) Place the ground sample into a quartz tube and seal it with a flame; (3) Transfer the sealed quartz tube into a muffle furnace for sintering. Raise the temperature to 650°C at a rate of 5°C / min for a total of 126 min. After the temperature rise is complete, continue sintering at 650°C for 120 min. (4) The sintered sample was immediately transferred to an argon-filled glove box. After cooling to room temperature, it was removed and transferred to an agate mortar for grinding. The grinding time was 30 minutes to obtain the sodium borohydride-treated lithium cobalt oxide cathode material (NBH-LCO-1). Its XRD pattern is as follows: Figure 1 As shown; the material is taken out and ground in an agate mortar for 30 minutes according to the mass ratio of lithium cobalt oxide positive electrode material: lithium phosphorus sulfur chlorine electrolyte: conductive carbon (NBH-LCO-1: LPSCL: Super P) = 150: 100: 5 to make mixed positive electrode material; then, according to the ratio of 5mg of mixed positive electrode material, 250mg of LPSCL, and lithium indium alloy as negative electrode, it is added into a mold and pressed into a solid battery.

[0028] Example 3: Preparation process of lithium cobalt oxide (LCO) cathode treated with sodium borohydride and assembly of its all-solid-state battery; (1) Weigh 2g of lithium cobalt oxide positive electrode into an agate mortar using a balance in a glove box filled with nitrogen, and then add sodium borohydride with a mass fraction of 2% of lithium cobalt oxide into the mortar and grind and mix for 30min. (2) Place the ground sample into a quartz tube and seal it with a flame; (3) Transfer the sealed quartz tube into a muffle furnace for sintering. Raise the temperature to 650°C at a rate of 5°C / min for a total of 126 min. After the temperature rise is complete, continue sintering at 650°C for 120 min. (4) The sintered sample was immediately transferred to an argon-filled glove box. After cooling to room temperature, it was removed and transferred to an agate mortar for grinding. The grinding time was 30 minutes to obtain the sodium borohydride-treated lithium cobalt oxide cathode material (NBH-LCO-2). Its XRD pattern is as follows: Figure 1 As shown; the material is taken out and ground in an agate mortar for 30 minutes according to the mass ratio of lithium cobalt oxide positive electrode material: lithium phosphorus sulfur chlorine electrolyte: conductive carbon (NBH-LCO-2: LPSCL: Super P) = 150: 100: 5 to make mixed positive electrode material; then, according to the mixture of 5mg of positive electrode material, 250mg of LPSCL, and lithium indium alloy as negative electrode, it is added to a mold and pressed into a solid battery.

[0029] Comparative Example 1: Assembly of Bare-LCO all-solid-state battery XRD pattern of the material as follows Figure 1As shown, a mixed positive electrode material was prepared by grinding the lithium cobalt oxide positive electrode material, lithium phosphorus sulfur chlorine electrolyte, and conductive carbon (Bare-LCO: LPSCL: Super P) in a mortar for 30 minutes according to a mass ratio of 150:100:5. Then, 5 mg of the mixed positive electrode material, 250 mg of LPSCL, and lithium indium alloy as the negative electrode were added to a mold and pressed into a solid-state battery.

[0030] Table 1 Example 1 Example 2 Example 3 Comparative Example 1 0.1C rate capacity utilization (mAh / g) 162.6 170.2 154.8 178.4 0.2C multiplier cycle count 100 100 100 100 Remaining capacity (mAh / g) 86.7 112.2 102.9 77.5 Table 1 is a comparison table of the performance of all-solid-state batteries in the examples and the comparative examples. It can be seen that after 100 cycles, the remaining specific capacity of the examples is higher than that of the comparative examples, indicating that the all-solid-state battery assembled with lithium cobalt oxide after the treatment of this technical solution has better electrical performance.

[0031] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing lithium cobalt oxide materials with in-situ constructed interface coating and bulk doping, characterized in that: The method is as follows: (1) Treatment with sodium borohydride: Weigh lithium cobalt oxide and sodium borohydride in a glove box filled with protective gas, and grind and mix them evenly; (2) The mixture that has been ground with sodium borohydride in step (1) is placed into a quartz tube, sealed with a flame, and then sent into a muffle furnace for high-temperature sintering. (3) After the sintered sample is taken out, it is immediately transferred to a glove box filled with argon gas, cooled to room temperature and then ground to obtain lithium cobalt oxide material treated with sodium borohydride.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of sodium borohydride to lithium cobalt oxide is 0.5~2:

100.

3. The preparation method according to claim 1, characterized in that: In step (1), the grinding time shall be no less than 30 minutes.

4. The preparation method according to claim 1, characterized in that: In step (1), the protective gas is nitrogen or an inert gas.

5. The preparation method according to claim 1, characterized in that: In step (2), the quartz tube has the following specifications: od×id=13×10 mm and a length of 25 cm.

6. The preparation method according to claim 1, characterized in that: In step (2), the high-temperature sintering temperature is 645~655℃ and the time is 115~125min.

7. The preparation method according to claim 1, characterized in that: In step (3), the grinding time shall be no less than 30 minutes.

8. A lithium cobalt oxide material prepared by the preparation method according to any one of claims 1 to 7.

9. The application of a lithium cobalt oxide material prepared by the preparation method according to any one of claims 1 to 7 in a high-performance all-solid-state lithium-ion battery.

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