Method for in-situ coating magnesium borate on lithium ion battery cathode material

Abstract

The application belongs to the technical field of lithium ion battery electrode materials, and discloses a method for in-situ coating of magnesium borate on a lithium ion battery positive electrode material. By adjusting the feeding ratio of a magnesium source and a boron source, and by using the positive charge layer on the surface of the lithium ion battery positive electrode material, the borohydride groups with negative charges dispersed in the solution, and the magnesium ion groups with positive charges, a positive-negative-positive charge distribution layer is constructed. Then, through a hydrolysis reaction, a uniform and complete amorphous magnesium borate coating is in-situ coated on the surface of the positive electrode material, a series of in-situ coating of magnesium borate (Mg2B2O5, Mg3B2O6, MgB4O7) is realized, and a lithium ion battery positive electrode material with good interface stability in air and electrolyte is prepared. The method provided by the application has remarkable effects, simple and efficient steps, low cost, and is easy to realize industrialized preparation.

Description

Technical Field

[0001] This invention relates to a method for in-situ coating magnesium borate onto a lithium-ion battery cathode material, belonging to the technical field of lithium-ion battery cathode materials. Background Technology

[0002] Lithium-ion batteries possess advantages such as high specific capacity, high operating voltage, wide operating temperature range, low self-discharge rate, long cycle life, no memory effect, no pollution, light weight, and good safety performance, making them widely used in 3C consumer electronics, electric vehicles and ships, aerospace, military, and energy storage power stations. Meanwhile, thanks to strong government support for the new energy vehicle industry, China's lithium-ion battery industry has developed rapidly. The development of lithium-ion batteries is moving towards higher energy density, more stable cycle performance, and more reliable safety performance. However, currently, the cathode material for lithium-ion batteries has become a bottleneck restricting their development.

[0003] Currently, lithium iron phosphate (LFP) and lithium cobalt oxide (LCO) cathode materials are relatively mature in application, used in power batteries and 3C consumer electronics products, respectively. Nickel-cobalt-manganese (NiCoMn) and nickel-cobalt-aluminum (NiCoA) cathode materials are less mature, while lithium-rich manganese-based cathode materials are mainly in the research and development stage. The main problems with these cathode materials in practical applications include poor surface stability, demanding storage conditions, and severe interfacial side reactions between the electrolyte and the cathode material, especially at high voltages. These problems can seriously affect the battery's energy density and lifespan, and in some cases, even lead to safety accidents.

[0004] Currently, the mainstream solution to the problems encountered in the aforementioned practical applications is to use coating methods. A surface coating layer on the cathode material can improve the material's corrosion resistance and reduce interfacial side reactions between the material and the electrolyte. Common coating materials include oxides, fluorides, and lithium-ion conductors. These coating methods are often simple mechanical mixing or sol-gel methods. Due to the inherent wettability and surface electropositivity of the cathode material, it is difficult to achieve uniform and complete coating with these materials. Furthermore, the interaction between the coating material and the substrate material is relatively weak. After a short period of cycling, some coating materials may separate from the cathode material at the interface, causing the protective effect of the coating layer to fail. This, in turn, significantly reduces the battery's lifespan, energy density, and safety. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a method for in-situ coating magnesium borate onto lithium-ion battery cathode materials, aiming to improve the cycle stability of lithium-ion battery cathode materials.

[0007] (II) The technical solution of the present invention is as follows:

[0008] A method for in-situ coating magnesium borate onto a lithium-ion battery cathode material, comprising the following steps:

[0009] Step S1: Add a certain amount of lithium-ion battery cathode material, magnesium source, and organic solvent to a stirring device, and set a certain stirring speed and stirring time. The lithium-ion battery cathode material is one or more of the following: nickel-cobalt-manganese ternary cathode material, nickel-cobalt-aluminum ternary cathode material, lithium-rich manganese-based cathode material, lithium iron phosphate cathode material, lithium manganese oxide cathode material, and lithium cobalt oxide cathode material.

[0010] Step S2: Prepare a certain concentration of metal borohydride compound. While stirring continuously, add the metal borohydride compound dropwise to the stirring device mentioned above. After the dropwise addition is complete, set a certain stirring time. After stirring is completed, a mixed solution is obtained. The metal borohydride compound is one of sodium borohydride, potassium borohydride, and lithium borohydride. By utilizing the positive charge on the surface of the lithium-ion battery positive electrode material, the negatively charged borohydride groups dispersed in the solution, and the positively charged magnesium ion groups, a "positive-negative-positive" charge distribution layer is constructed.

[0011] Step S3: The above mixed solution is filtered, dried, calcined, washed, and dried again to obtain a uniform and complete in-situ magnesium borate (Mg2B2O5, Mg3B2O6, MgB4O7) coated lithium-ion battery cathode material. The drying temperature is 80-120℃ and the drying time is 12-24h.

[0012] More preferably, the magnesium source in step S1 is one of magnesium nitrate nonahydrate, magnesium chloride hexahydrate, and magnesium acetate tetrahydrate, the organic solvent is one of anhydrous methanol and anhydrous ethanol, the mass ratio of lithium-ion battery cathode material to organic solvent is 1:10-50, the stirring rate is 20-300 r / min, and the stirring time is 0.5-2 h.

[0013] More preferably, the dropping rate in step S2 is 5-50 ml / min; the stirring time is 3-6 h.

[0014] More preferably, the molar ratio of magnesium source and boron source in step S1 and step S2 is 1:4-3:2;

[0015] More preferably, the calcination temperature in step S3 is 400-600℃, the calcination time is 0.5-2h, the calcination temperature is low and the time is short, the calcination atmosphere is air, no special atmosphere environment is required, which has great advantages in terms of cost, the heating rate is 5-20℃ / min, and the washing liquid is industrial pure water.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0017] 1. This invention utilizes the positively charged layer inherent on the surface of the lithium-ion battery cathode material, the negatively charged borohydride groups dispersed in the solution, and the positively charged magnesium ion groups to construct a "positive-negative-positive" charge distribution layer. The borohydride groups preferentially bind to the surface of the cathode material, and then, through a hydrolysis reaction, the borohydride groups are converted into metaborate groups. The metaborate groups act as a "bridge," binding both the cathode material and the magnesium ions dispersed in the solution. The magnesium ions and metaborate groups combine to form magnesium metaborate, which is uniformly dispersed on the surface of the cathode material. Finally, through a low-temperature calcination process, a uniform and complete amorphous magnesium borate coating is in situ coated on the surface of the cathode material, achieving a series of magnesium borate (Mg2B2O5, Mg3B2O6, MgB4O7) in situ coatings. Magnesium borate has properties such as corrosion resistance and reinforcing effect, and does not affect the transport of lithium ions. Its application in the field of battery materials can produce lithium-ion battery cathode materials with good interfacial stability in both air and electrolyte. The method provided by this invention has significant effects, simple and efficient steps, low cost, and is easy to industrialize.

[0018] 2. A complete and uniform magnesium borate coating was applied to the material surface using an in-situ coating strategy;

[0019] 3. According to the method of the present invention, the outer shell of the final product is magnesium borate and the inner core is a lithium-ion battery cathode material. The outer shell can suppress side reactions between the material surface and the electrolyte, stabilize the internal structure of the material, and improve the lithium-ion transport rate. The inner core can provide high specific capacity, thereby giving the material good electrochemical performance. Attached Figure Description

[0020] Figure 1 SEM image of Example 1;

[0021] Figure 2 SEM image of Comparative Example 1;

[0022] Figure 3 Surface distribution diagram of element B in Example 1;

[0023] Figure 4 Comparison of discharge specific capacity of Example 1 and Comparative Example 1 in the first 300 cycles (2.8-4.5V, 1C);

[0024] Figure 5 SEM image of Comparative Example 2;

[0025] Figure 6 SEM image of Example 2;

[0026] Figure 7 Comparison of discharge specific capacity of Example 2 and Comparative Example 2 in the first 500 cycles (2.0-4.8V, 1C).

[0027] Figure 8 SEM image of Comparative Example 3;

[0028] Figure 9 SEM image of Example 3;

[0029] Figure 10 Comparison of discharge specific capacity of Example 3 and Comparative Example 3 in the first 200 cycles (2.8-4.5V, 1C). Detailed Implementation

[0030] The following description is based on the principles and features of the present invention. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0031] Example 1

[0032] Step S1: Accurately weigh 100g of nickel-cobalt-manganese ternary cathode material (LiNi) using an analytical balance. 0.8 Co 0.1 Mn 0.1 Add O2), 20g magnesium nitrate hexahydrate and 500g anhydrous ethanol to the stirring device, adjust the speed to 50r / min, and stir for 1h;

[0033] Step S2: Accurately weigh 2g of sodium borohydride using an analytical balance, measure 260ml of anhydrous ethanol using a graduated cylinder, add it to a 500ml beaker, stir to dissolve it, and prepare a 0.2M sodium borohydride anhydrous ethanol solution. While stirring continuously, add it dropwise to the stirring device at a rate of 10ml / min. After the addition is complete, stir again for 3 hours to obtain a mixed solution.

[0034] Step S3: Filter the above mixed solution to obtain a filter cake. Place the filter cake in a vacuum drying oven, set the drying temperature to 100℃, and the drying time to 12h. Place the dried filter cake in a corundum calcining boat and transfer it to a vacuum atmosphere furnace. Set the calcination temperature to 500℃, the calcination time to 1h, the calcination atmosphere to air, and the heating rate to 10℃ / min. After it cools naturally, take out the sintered product and place it in a stirring device. Add 1000ml of industrial pure water, adjust the rotation speed to 300r / min, and the stirring time to 0.5h. After stirring, filter the product and wash it 2-3 times with industrial pure water. Finally, transfer the filter residue to a vacuum drying oven, set the drying temperature to 100℃, and the drying time to 12h. After drying, obtain in-situ magnesium borate (Mg3B2O6) coated nickel-cobalt-manganese ternary cathode material.

[0035] Comparative Example 1

[0036] The difference between this comparative example and Example 1 is that the nickel-cobalt-manganese ternary cathode material (LiNi) used in step 1 of Example 1 is replaced with a different material. 0.8 Co 0.1 Mn 0.1 O2) was replaced with unmodified nickel-cobalt-manganese ternary cathode material (LiNi). 0.8 Co 0.1 Mn 0.1 O2).

[0037] Example 2

[0038] Step S1: Accurately weigh 100g of lithium-rich manganese-based cathode material (Li) using an analytical balance. 1.2 Ni 0.167 Co 0.167 Mn 0.666 Add O2), 20g magnesium nitrate hexahydrate and 500g anhydrous ethanol to the stirring device, adjust the speed to 50r / min, and stir for 1h;

[0039] Step S2: Accurately weigh 2g of sodium borohydride using an analytical balance, measure 260ml of anhydrous ethanol using a graduated cylinder, add it to a 500ml beaker, stir to dissolve, and prepare a 0.2M sodium borohydride anhydrous ethanol solution. While the above stirring device is stirring continuously, add it dropwise to the stirring device at a rate of 10ml / min. After the addition is complete, stir again for 3 hours to obtain a mixed solution.

[0040] Step S3: Filter the above mixed solution to obtain a filter cake. Place the filter cake in a vacuum drying oven and set the drying temperature to 100℃ for 12 hours. Place the dried filter cake in a corundum calcining boat and transfer it to a vacuum atmosphere furnace. Set the calcination temperature to 500℃ for 1 hour and the calcination atmosphere to air. The heating rate is 10℃ / min. After it cools naturally, take out the sintered product and place it in a stirring device. Add 1000 ml of industrial pure water, adjust the rotation speed to 300 r / min, and stir for 0.5 hours. After stirring, filter the product and wash it 2-3 times with industrial pure water. Finally, transfer the filter residue to a vacuum drying oven and dry it at 100℃ for 12 hours. After drying, a lithium-rich manganese-based cathode material coated with magnesium borate (Mg3B2O6) is obtained.

[0041] Comparative Example 2

[0042] The difference between this comparative example and Example 2 is that the lithium-rich manganese-based cathode material (Li) used in step 1 of Example 2 is replaced with a different one. 1.2 Ni 0.167 Co 0.167 Mn 0.666 O2) was replaced with unmodified lithium-rich manganese-based cathode material (Li).1.2 Ni 0.167 Co 0.167 Mn 0.666 O2).

[0043] Example 3

[0044] Step S1: Accurately weigh 100g of nickel-cobalt-aluminum ternary cathode material (LiNi) using an analytical balance. 0.8 Co 0.1 Mn 0.1 Add O2), 17g magnesium nitrate hexahydrate and 500g anhydrous ethanol to the stirring device, adjust the speed to 50r / min, and stir for 1h;

[0045] Step S2: Accurately weigh 2.5g of sodium borohydride using an analytical balance, measure 330ml of anhydrous ethanol using a graduated cylinder, add it to a 500ml beaker, stir to dissolve, and prepare a 0.2M sodium borohydride anhydrous ethanol solution. While the above stirring device is stirring continuously, add it dropwise to the stirring device at a rate of 10ml / min. After the addition is complete, stir again for 3 hours to obtain a mixed solution.

[0046] Step S3: Filter the above mixed solution to obtain a filter cake. Place the filter cake in a vacuum drying oven, set the drying temperature to 100℃, and the drying time to 12h. Place the dried filter cake in a corundum calcining boat and transfer it to a vacuum atmosphere furnace. Set the calcination temperature to 500℃, the calcination time to 1h, the calcination atmosphere to air, and the heating rate to 10℃ / min. After it cools naturally, take out the sintered product and place it in a stirring device. Add 1000ml of industrial pure water, adjust the rotation speed to 300r / min, and the stirring time to 0.5h. After stirring, filter the product and wash it 2-3 times with industrial pure water. Finally, transfer the filter residue to a vacuum drying oven, dry it at 100℃, and dry it for 12h. After drying, you will obtain in-situ magnesium borate (Mg2B2O5) coated nickel-cobalt-aluminum ternary cathode material.

[0047] Comparative Example 3

[0048] The difference between this comparative example and Example 3 is that the nickel-cobalt-aluminum ternary cathode material (LiNi) used in step 1 of Example 3 is replaced with a different material. 0.8 Co 0.1 Al 0.1 O2) was replaced with unmodified nickel-cobalt-aluminum ternary cathode material (LiNi). 0.8 Co 0.1 Al 0.1 O2).

[0049] Performance testing

[0050] All tests in this experiment were conducted using a 2025 model coin cell as a benchmark. First, the prepared composite material was used as the positive electrode active material, PVDF (model 5130) as the binder, SP and KS-6 as conductive agents, and NMP as the solvent. The materials were mixed in a mass ratio of active material: binder: conductive agent of 85:5:10 until a homogeneous slurry was formed. The prepared positive electrode slurry was then uniformly coated onto aluminum foil using a preheating apparatus, and subsequently transferred to a vacuum drying oven at 120°C for 12 hours. The required thickness for electrode rolling was calculated based on the compaction density, and the rolled electrodes were then cut into uniform thicknesses with a diameter of 12 mm using a cutting machine. These were then assembled into coin cells in a vacuum glove box. A lithium foil was used as the counter electrode, a Celgard 2300 separator was used, and a LiFP6-based electrolyte was employed.

[0051] Figures 1-2 SEM images of Example 1 and Comparative Example 1 are shown respectively. As can be seen from the images, the nickel-cobalt-manganese ternary material of Comparative Example 1 has a smooth surface, clear edges, and no coating layer. The nickel-cobalt-manganese ternary material of Example 1 has complete and uniform magnesium borate nanosheets distributed on its surface.

[0052] Figure 3 The EDS surface distribution diagram of Example 1 is shown, which shows that the Mg and B elements are evenly distributed on the surface of the nickel-cobalt-manganese ternary material.

[0053] Figure 4 Cycling performance graphs of the products obtained in Comparative Example 1 and Example 1 of the present invention are shown respectively. As can be seen from the graphs, at a current density of 1C, the initial discharge capacity of the material in Comparative Example 1 is 204.3 mAh / g, and the capacity retention rate after 300 cycles is only 64.1%; while the initial discharge capacity of the product obtained in Example 1 of the present invention is 165.1 mAh / g, and the capacity retention rate after 300 cycles is as high as 98.1%, indicating that the cycling stability of the material is significantly improved after in-situ magnesium borate coating.

[0054] Figures 5-6 SEM images of Example 2 and Comparative Example 2 are shown respectively. As can be seen from the images, the lithium-rich manganese-based cathode material of Comparative Example 2 has a smooth surface, clear edges, and no coating layer, while the lithium-rich manganese-based cathode material of Example 2 has a complete and uniform coating layer distributed on its surface.

[0055] Figure 7The cycling performance graphs of the products obtained in Comparative Example 2 and Example 2 of the present invention are shown. As can be seen from the graphs, within a voltage range of 2.0-4.8V and a current density of 1C during cycling tests, the material in Comparative Example 2 exhibits an initial discharge capacity of 252.2 mAh / g and a capacity retention rate of only 59.3% after 500 cycles; while the product obtained in Example 2 of the present invention exhibits an initial discharge capacity of 254.0 mAh / g and a capacity retention rate as high as 90.1% after 500 cycles, indicating that the cycle life of the material is significantly improved after in-situ magnesium borate coating.

[0056] Figures 8-9 High-magnification SEM images of Example 3 and Comparative Example 3 are shown respectively. As can be seen from the images, the nickel-cobalt-aluminum ternary material of Comparative Example 3 has a smooth surface, clear edges, and no coating layer. The primary particles of the nickel-cobalt-aluminum ternary material of Example 3 are coated with a complete magnesium borate coating.

[0057] Figure 10 Cycling performance graphs of the products obtained in Comparative Example 3 and Example 3 of the present invention are shown. As can be seen from the graphs, within a voltage range of 2.8-4.5V and a current density of 1C, the material in Comparative Example 3 exhibits an initial discharge capacity of 201.1 mAh / g and a capacity retention rate of only 78.5% after 200 cycles. In contrast, the product obtained in Example 3 of the present invention exhibits an initial discharge capacity of 200.5 mAh / g and a capacity retention rate as high as 96.7% after 200 cycles, indicating that the cycle life of the material is significantly improved after in-situ magnesium borate coating.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for in-situ coating magnesium borate onto a lithium-ion battery cathode material, the method comprising the following steps: Step S1: Add a certain amount of lithium-ion battery cathode material, magnesium source, and organic solvent to a stirring device, and set a certain stirring speed and stirring time. The lithium-ion battery cathode material is one or more of the following: nickel-cobalt-manganese ternary cathode material, nickel-cobalt-aluminum ternary cathode material, lithium-rich manganese-based cathode material, lithium iron phosphate cathode material, lithium manganese oxide cathode material, and lithium cobalt oxide cathode material. Step S2: Prepare a certain concentration of metal borohydride. While the above-mentioned stirring device is continuously stirring, add the metal borohydride dropwise into the stirring device. After the addition is complete, continue stirring for a certain period of time to obtain a mixed solution. The metal borohydride is one of sodium borohydride, potassium borohydride, or lithium borohydride. Step S3: The above mixed solution is filtered, dried, calcined, washed and dried to obtain a uniform and complete in-situ magnesium borate Mg2B2O5, or Mg3B2O6, or MgB4O7 coated lithium-ion battery cathode material. The drying temperature is 80-120℃ and the drying time is 12-24h. The magnesium source in step S1 is one of magnesium nitrate nonahydrate, magnesium chloride hexahydrate, and magnesium acetate tetrahydrate; the organic solvent is one of anhydrous methanol and anhydrous ethanol; the mass ratio of lithium-ion battery cathode material to organic solvent is 1:10-50; the stirring rate is 20-300 r / min; and the stirring time is 0.5-2 h. The dropping rate in step S2 is 5-50 mL / min; the stirring time is 3-6 h. The molar ratio of magnesium source to metal borohydride in steps S1 and S2 is 1:4-3:

2. In step S3, the calcination temperature is 400-600℃, the calcination time is 0.5-2h, the calcination atmosphere is air, the heating rate is 5-20℃ / min, and the washing liquid is industrial pure water.

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