Cathode sheet, lithium ion battery positive electrode lithium supplement material and preparation method thereof

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a positive plate, a lithium ion battery positive electrode lithium supplement material and a preparation method thereof. The preparation method comprises the following steps: preparing a positive electrode lithium supplement material matrix; mixing the positive electrode lithium supplement material matrix and a carbon source with ethanol as a solvent to obtain a mixed solution; and calcining the mixed solution after volatilizing the solvent in an inert atmosphere to obtain a lithium ion battery positive electrode lithium supplement material with carbon coating on the surface. The application has the advantages of simple process, convenient operation, improved electronic conductivity and ion diffusion coefficient of the obtained lithium ion battery positive electrode lithium supplement material with carbon coating, improved rate performance and cycle performance, and the use of the lithium ion battery positive electrode lithium supplement material with carbon coating as a positive electrode lithium supplement additive can effectively improve the battery capacity without reducing the cycle performance and rate performance of the battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, and particularly relates to a positive electrode sheet, a lithium-ion battery positive electrode lithium replenishment material, and a method for preparing the same. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic products and new energy vehicles due to their advantages such as high energy density, long cycle life, high operating voltage, low self-discharge, and environmental friendliness.

[0003] Currently, graphite is the most commonly used lithium-ion anode material, but its capacity has reached its limit. To improve battery energy density, high-specific-capacity silicon-based anode materials have become the most promising next-generation commercial lithium-ion battery anode materials. However, silicon-based anodes suffer from severe volume effects and low initial coulombic efficiency during charge and discharge, while the initial coulombic efficiency of cathode materials is much higher than that of anodes. The low initial efficiency of anodes leads to the loss of cyclic lithium, reducing battery capacity. Therefore, the concept of lithium replenishment has emerged.

[0004] Lithium replenishment is further divided into positive electrode lithium replenishment, negative electrode lithium replenishment, and electrochemical lithium replenishment. Positive electrode lithium replenishment has the best industrial application prospects due to its high safety and the fact that it does not require changes to existing battery manufacturing processes. Positive electrode lithium replenishment generally involves adding lithium replenishing materials as additives during the positive electrode homogenization process. After the battery cell is manufactured, during the first charge and discharge, the positive electrode lithium replenishing material, due to its high specific capacity and low initial efficiency, releases a large number of lithium ions during normal charging to replenish the lithium ions consumed in the formation of the SEI film on the negative electrode. During discharge, due to its low initial efficiency, it does not accept a large number of lithium ions, thereby increasing the battery capacity.

[0005] Existing lithium replenishment materials generally suffer from drawbacks such as unstable cycling and poor rate performance. For example, the lithium replenishment material Li2NiO2 has an unstable structure and is prone to side reactions with the electrolyte at high potentials. At the same time, the material has a large impedance, thus the addition of lithium replenishment materials affects the cycle performance and rate performance of the battery. Summary of the Invention

[0006] The purpose of this invention is to provide a lithium-ion battery cathode replenishment material, aiming to solve the technical problems of unstable cycling and poor rate performance of existing cathode replenishment materials.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a lithium-ion battery cathode lithium replenishment material, comprising a lithium-rich material Li2NiO2 matrix and a coating layer covering the surface of the lithium-rich material Li2NiO2 matrix, wherein the material of the coating layer is carbon.

[0008] Another object of the present invention is to provide a method for preparing lithium-ion battery cathode lithium replenishment material, comprising the following steps:

[0009] Preparation of cathode lithium supplementation material matrix;

[0010] The positive electrode lithium replenishment material matrix and the carbon source are mixed with ethanol as a solvent to obtain a mixed solution;

[0011] After the solvent is evaporated from the mixed solution, it is calcined in an inert atmosphere to obtain a lithium-ion battery positive electrode lithium replenishment material with carbon coating on its surface.

[0012] Furthermore, the carbon content in the lithium-ion battery cathode replenishment material with carbon coating on its surface is 0.5% to 3%.

[0013] Furthermore, the positive electrode lithium replenishment material matrix and carbon source are mixed with ethanol as a solvent and then ultrasonically dispersed for 0.5h to 2h.

[0014] Furthermore, the process of calcining the mixed solution in an inert atmosphere after the solvent evaporates includes the following steps: after the solvent evaporates from the mixed solution, a dry product is obtained; an organic carbon source is added to the dry product and a first sintering is performed in an inert atmosphere; after cooling, an inorganic carbon source is added and a second sintering is performed in an inert atmosphere; the temperature and time of the second sintering are both greater than the temperature and time of the first sintering.

[0015] Furthermore, the temperature of the first calcination is 300℃~400℃, and the time is 3h~5h.

[0016] Furthermore, the second sintering temperature is 600℃~700℃, and the time is 8h~10h.

[0017] Furthermore, the organic carbon source is at least one of citric acid or ascorbic acid.

[0018] Furthermore, the inorganic carbon source is at least one of carbon black, carbon gel, acetylene black, or graphene.

[0019] Furthermore, the step of preparing the positive electrode lithium supplementation material matrix includes: calcining high-purity Li2CO3 in an inert atmosphere at a calcination temperature of 600-800℃ to obtain high-purity Li2O; mixing the high-purity Li2O and NiO in a molar ratio of (1-1.2):1 and calcining in an inert atmosphere for 6-10 hours at a calcination temperature of 500-800℃.

[0020] Another object of the present invention is to provide a positive electrode sheet, which is obtained by homogenizing and coating the above-mentioned lithium-ion battery positive electrode lithium replenishing material, lithium replenishing modification material, binder, conductive agent and solvent, wherein the lithium-ion battery positive electrode lithium replenishing material is prepared by the above-mentioned lithium-ion battery positive electrode lithium replenishing material preparation method.

[0021] The beneficial effects of this invention are as follows: The preparation method of the lithium-ion battery positive electrode lithium replenishment material of this invention is simple and convenient, and can avoid the introduction of moisture, significantly reducing the surface alkali content. The resulting carbon-coated lithium-ion battery positive electrode lithium replenishment material has improved electronic conductivity and ion diffusion coefficient, as well as improved rate performance and cycle performance. Using this carbon-coated lithium-ion battery positive electrode lithium replenishment material as a positive electrode lithium replenishment additive can effectively improve battery capacity without reducing battery cycle performance and rate performance. Ethanol is selected as a solvent, and its raw materials are cheap, readily available, and volatile, making it suitable for large-scale rapid preparation of carbon-coated lithium-ion battery positive electrode lithium replenishment materials. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A flowchart illustrating the preparation method of lithium-ion battery cathode lithium replenishment material provided in an embodiment of the present invention;

[0024] Figure 2 To utilize Figure 1 SEM image of carbon-coated lithium-ion battery cathode lithium replenishment material prepared by the method shown.

[0025] Figure 3 The image shows the cycle performance curves of a full cell prepared using the products obtained in one embodiment of the present invention, as well as Comparative Examples 1 and 2, as positive electrode materials for lithium-ion batteries. Detailed Implementation

[0026] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] In the description of this invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0029] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0030] The lithium-ion battery cathode lithium replenishment material provided in this invention includes a lithium-rich material Li2NiO2 matrix and a coating layer covering the surface of the Li2NiO2 matrix. The coating layer is made of carbon, and the carbon content can be 0.5% to 3%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc. Using a Li2NiO2 cathode lithium replenishment material with a carbon coating layer on its surface can effectively improve the electronic conductivity and ion diffusion coefficient of the material, improve interface stability, and thus improve the rate performance and cycle performance of the material.

[0031] like Figure 1 As shown, the preparation method of the lithium-ion battery cathode lithium replenishment material provided in this embodiment of the invention includes the following steps:

[0032] Step S100: Prepare the positive electrode lithium replenishment material matrix.

[0033] Step S200: The prepared positive electrode lithium supplement material matrix and carbon source are mixed with ethanol as a solvent to obtain a mixed solution. For example, ultrasonic dispersion or ball milling under an inert atmosphere is performed after mixing to make it uniformly mixed, thereby obtaining a mixed solution.

[0034] Step S300: After evaporating the ethanol from the obtained mixed solution, calcine it in an inert atmosphere to obtain a lithium-ion battery positive electrode lithium replenishment material with carbon coating on the surface.

[0035] The method for preparing lithium-ion battery cathode lithium replenishment material provided in this embodiment is simple, convenient to operate, and avoids the introduction of moisture, significantly reducing the surface alkali content. The resulting carbon-coated lithium-ion battery cathode lithium replenishment material has improved electronic conductivity and ion diffusion coefficient, as well as improved rate performance and cycle performance. Using this carbon-coated lithium-ion battery cathode lithium replenishment material as a cathode lithium replenishment additive can effectively improve battery capacity without reducing battery cycle performance and rate performance. Ethanol is selected as the solvent because its raw materials are cheap, readily available, and volatile, making it suitable for large-scale rapid preparation of carbon-coated lithium-ion cathode lithium replenishment materials.

[0036] In step S100, the step of preparing the positive electrode lithium supplementation material matrix includes: selecting high-purity Li2CO3 and ball milling and calcining it in an inert atmosphere at a calcination temperature of 600-800℃ to obtain high-purity Li2O; mixing the high-purity Li2O and NiO in a molar ratio of Li2O:LiO=(1~1.2):1 and ball milling it in an inert atmosphere for 10-30h at a ball milling condition of 300-500rpm, and then calcining it in an inert atmosphere for 6-10h at a calcination temperature of 500-800℃.

[0037] In step S300, the carbon content in the lithium-ion battery positive electrode lithium replenishment material with carbon coating on its surface is 0.5% to 3%, for example 0.5%, 1%, 1.5%, 2%, 2.5%, and 3%.

[0038] In step S200, the positive electrode lithium replenishment material matrix and the carbon source are mixed with ethanol as a solvent and then mechanically stirred for a certain period of time, such as 5 min to 10 min, followed by ultrasonic dispersion for 0.5 h to 2 h. Ultrasonic dispersion has small vibration and large acceleration, which makes the carbon source uniformly distributed on the surface of the positive electrode lithium replenishment material matrix.

[0039] In step S300, the process of calcining the mixed solution in an inert atmosphere after the solvent has evaporated includes the following steps: drying the mixed solution at 60℃~80℃ to obtain a dried product, such as evaporating ethanol in a water bath, adding an organic carbon source to the dried product and performing a first sintering in an inert atmosphere, cooling, adding an inorganic carbon source, and performing a second sintering in an inert atmosphere. The temperature and time of the second sintering are both greater than those of the first sintering. An organic carbon source is used in the first sintering to ensure that the carbon source can be uniformly dissolved in the ethanol solvent and that the carbon source is distributed at the molecular level in the positive electrode lithium supplement material matrix. An inorganic carbon source is used in the second sintering to allow the carbon source to be directly and uniformly mixed with the positive electrode lithium supplement material matrix before high-temperature sintering.

[0040] In one embodiment, the temperature of the first calcination is 300°C to 400°C, and the sintering time is 3 hours to 5 hours.

[0041] In one embodiment, the temperature of the second sintering is 600℃~700℃, and the sintering time is 8h~10h.

[0042] In one embodiment, the organic carbon source is at least one of citric acid or ascorbic acid.

[0043] In one embodiment, the inorganic carbon source is at least one of carbon black, carbon gel, acetylene black, graphene, or carbon nanotubes.

[0044] The positive electrode sheet provided in this embodiment of the invention comprises a slurry obtained by homogenizing the lithium-ion battery positive electrode lithium replenishing material, lithium replenishing modification material, binder, conductive agent, and solvent described in the above embodiments. This lithium-ion battery positive electrode lithium replenishing material is prepared using the preparation method described in the above embodiments. The carbon-coated lithium-ion battery positive electrode lithium replenishing material content is 1%-20% of the total weight of the positive electrode material. The positive electrode material is at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and ternary materials; the negative electrode is at least one of silicon-based materials, silicon-oxygen-graphite composite materials, or silicon-carbon-graphite composite materials.

[0045] Example 1

[0046] High-purity Li₂CO₃ (purity > 99.99%) was selected and ball-milled and calcined in an inert atmosphere at a temperature of 600-800℃ to obtain high-purity product Li₂O (purity > 99.9%). The high-purity Li₂O and high-purity NiO were ball-milled in a nitrogen atmosphere at 350 rpm for 10 h, and then calcined in a nitrogen atmosphere for 4 h at a temperature of 650℃ to obtain Li₂NiO₂ material. An appropriate amount of citric acid was weighed and added to Li₂NiO₂. The mixture was mechanically stirred and ultrasonically dispersed for 1 hour using ethanol as a solvent. After obtaining a mixed solution, the solvent was evaporated by stirring in a water bath. The resulting dried product was then subjected to a first sintering under a nitrogen atmosphere at 350℃ for 4 hours. After cooling, it was ground with acetylene black until fully sintered, and then subjected to a second sintering under an inert atmosphere at 600-700℃ for 8-10 hours. This yielded a carbon-coated lithium-ion battery cathode lithium replenishment material. The carbon content of this material was 1%. A scanning electron microscope (SEM) image of the carbon-coated lithium-ion battery cathode lithium replenishment material matrix is ​​shown below. Figure 2 As shown in the figure, the carbon-coated lithium-ion cathode lithium replenishment material prepared in Example 1 has an irregular block structure and good particle dispersion. The particle size D50 is 14 μm, meaning that half of the particles have a particle size of less than 14 μm.

[0047] The lithium-ion cathode lithium replenishment material in this example is used to make a lithium battery cathode sheet: the carbon-coated Li2NiO2 cathode lithium replenishment additive prepared in this example is combined with the high-nickel cathode material Li(Ni) 0.8 Co0.1 Mn 0.1 O2, conductive carbon black (SP), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) are homogenized together and coated onto aluminum foil. After drying, a positive electrode sheet is formed. The known positive electrode material is Li(Ni). 0.8 Co 0.1 Mn 0.1 The initial charge / discharge efficiency of O2 is 90%, and the actual discharge capacity is 198 mAh / g.

[0048] The negative electrode uses a graphite negative electrode doped with 10wt% SiO, with an initial charge-discharge efficiency of 83.5% and an actual discharge specific capacity of 483 mAh / g measured in a half-cell. The negative electrode was prepared by homogenizing the active material with conductive carbon black (SP), carbon nanotubes (SWCNT), hydroxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and water, then coating the mixture onto copper foil and drying it. The initial charge-discharge capacity ratio of the positive and negative electrodes was set to 1.05.

[0049] The above positive and negative electrode plates are assembled into a full cell.

[0050] Comparative Example 1

[0051] The high-nickel cathode material Li(Ni) 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (SP), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) are homogenized together and coated onto aluminum foil. After drying, a positive electrode sheet is formed. The known positive electrode material is Li(Ni). 0.8 Co 0.1 Mn 0.1 The initial charge / discharge efficiency of O2 is 90%, and the actual discharge capacity is 198 mAh / g.

[0052] The negative electrode uses a graphite negative electrode doped with 10wt% SiO, with an initial charge-discharge efficiency of 83.5% and an actual discharge specific capacity of 483 mAh / g measured in a half-cell. The negative electrode was prepared by homogenizing the active material with conductive carbon black (SP), carbon nanotubes (SWCNT), hydroxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and water, then coating the mixture onto copper foil and drying it. The initial charge-discharge capacity ratio of the positive and negative electrodes was set to 1.05.

[0053] The above positive and negative electrode plates are assembled into a full cell.

[0054] Comparative Example 2

[0055] High-purity Li₂CO₃ (purity > 99.99%) was selected and ball-milled and calcined in an inert atmosphere at a temperature of 600-800℃ to obtain high-purity product Li₂O (purity > 99.9%). The high-purity Li₂O and high-purity NiO were ball-milled in a nitrogen atmosphere at 350 rpm for 10 h, and then calcined in a nitrogen atmosphere for 4 h at a temperature of 650℃ to obtain Li₂NiO₂ material.

[0056] The uncoated Li2NiO2 cathode lithium supplementation material was used to make a lithium battery cathode sheet: the uncoated Li2NiO2 cathode lithium supplementation additive prepared in this example was combined with the high-nickel cathode material Li(Ni) 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black (SP), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) are homogenized together and coated onto aluminum foil. After drying, a positive electrode sheet is formed. The known positive electrode material is Li(Ni). 0.8 Co 0.1 Mn 0.1 The initial charge / discharge efficiency of O2 is 90%, and the actual discharge capacity is 198 mAh / g.

[0057] The negative electrode uses a graphite negative electrode doped with 10wt% SiO, with an initial charge-discharge efficiency of 83.5% and an actual discharge specific capacity of 483 mAh / g measured in a half-cell. The negative electrode was prepared by homogenizing the active material with conductive carbon black (SP), carbon nanotubes (SWCNT), hydroxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and water, then coating the mixture onto copper foil and drying it. The initial charge-discharge capacity ratio of the positive and negative electrodes was set to 1.05.

[0058] The aforementioned positive and negative electrode plates were assembled into a full cell. The capacity and cycle performance of the full cells from the embodiments and comparative examples of this invention were tested using constant current followed by constant voltage charging and constant current discharging methods, respectively. The pre-charge / discharge current was 0.2C, the cycle charge / discharge current was +0.5C / -1C, and the charge / discharge voltage range was 2.5-4.2V. The cycle capacities of the embodiments and comparative examples are as follows: Figure 3 Table 1 shows a comparison of the performance parameter data tested in the Example, Comparative Example 1, and Comparative Example 2.

[0059] Table 1

[0060]

[0061] As can be seen from the test results in Table 1, in the embodiments, the actual charge-discharge specific capacity of the lithium-ion battery cathode material with the additives of the present invention added is significantly higher than that of the lithium-ion battery cathode material without additives in Comparative Example 1, and the battery capacity can be increased by about 110mAh. Furthermore, it can be seen from the embodiments and Comparative Example 2 that the impedance of the cathode sheet made of carbon-coated Li2NiO2 is significantly lower than that of the cathode sheet made of uncoated Li2NiO2. Figure 3 It can be seen that the capacity of the embodiments is significantly higher than that of Comparative Example 1, while the cycle decay trends are similar; the cycle trend of the embodiments of the present invention is significantly better than that of Comparative Example 2. Because the addition of carbon-coated lithium-ion battery cathode lithium replenishment material can release a large number of lithium ions to replenish the lithium ions consumed by the silicon-based anode material in forming the SEI film, the utilization rate of the cathode material is improved, resulting in a higher specific capacity, and thus improving the overall battery capacity. Simultaneously, the use of carbon-coated cathode lithium replenishment material Li2NiO2 can effectively improve the electronic conductivity and ion diffusion coefficient of the material, improve interface stability, and thus improve the rate performance and cycle performance of the material. Carbon-coated cathode lithium replenishment material Li2NiO2, as a cathode lithium replenishment additive, can effectively improve the battery capacity without reducing the battery's cycle performance and rate performance.

[0062] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery cathode lithium replenishment material, characterized in that, It includes a lithium-rich material Li2NiO2 matrix and a coating layer covering the surface of the lithium-rich material Li2NiO2 matrix, wherein the coating layer is made of carbon. The preparation steps of the lithium-ion battery cathode lithium replenishment material are as follows: Preparation of cathode lithium supplementation material matrix; The positive electrode lithium replenishment material matrix and the carbon source are mixed with ethanol as a solvent to obtain a mixed solution, wherein the carbon source is an organic carbon source; After the solvent is evaporated from the mixed solution, it is calcined in an inert atmosphere to obtain a lithium-ion battery positive electrode lithium replenishment material with carbon coating on the surface. The content of the carbon-coated lithium-ion battery positive electrode lithium replenishment material is 1%-20% of the total weight of the positive electrode material. The process of calcining the mixed solution in an inert atmosphere after the solvent evaporates includes the following steps: after the solvent evaporates from the mixed solution, a dry product is obtained, and a first sintering is performed in an inert atmosphere. After cooling, an inorganic carbon source is added and a second sintering is performed in an inert atmosphere. The temperature and time of the second sintering are both greater than those of the first sintering. The temperature of the first sintering is 300℃~400℃, and the time is 3 h~5 h; The second sintering temperature is 600℃~700℃, and the time is 8 h~10 h; The inorganic carbon source is at least one of carbon black, carbon gel, acetylene black, or graphene. The organic carbon source is at least one of citric acid or ascorbic acid; The steps for preparing the cathode lithium supplementation material matrix include: calcining high-purity Li2CO3 in an inert atmosphere at a temperature of 600-800℃ to obtain high-purity Li2O; mixing the high-purity Li2O and NiO in a molar ratio of (1~1.2):1 and ball-milling them in an inert atmosphere for 10-30 hours at a milling rate of 300-500 rpm; and then calcining them in an inert atmosphere for 6-10 hours at a temperature of 500-800℃.

2. The lithium-ion battery cathode lithium replenishment material according to claim 1, characterized in that: The carbon content in the lithium-ion battery cathode lithium replenishment material with carbon coating on its surface is 0.5% to 3%.

3. The lithium-ion battery cathode lithium replenishment material according to claim 1, characterized in that: The positive electrode lithium replenishment material matrix and carbon source were mixed with ethanol as solvent and then ultrasonically dispersed for 0.5 h to 2 h.

4. A positive electrode plate, characterized in that: The lithium-ion battery cathode lithium replenishing material, lithium replenishing modification material, binder, conductive agent and solvent are homogenized and coated according to any one of claims 1 to 3.

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