A lithium-rich borate oxide lithium supplement, a preparation method and application thereof

Abstract

The application discloses a lithium-rich boron oxide lithium supplement, a preparation method and application thereof, and is prepared from lithium carbonate, boric acid and a phosphorus source. In a lithium battery system with LFP as a positive electrode and a silicon-based material as a negative electrode, the lithium supplement can reduce the interface impedance with an electrolyte through lithium borate coated with phosphorus, can effectively supplement active lithium in the first charge-discharge process of the lithium battery, and can improve the first coulomb efficiency of the battery. The lithium supplement can form a good interface contact with the electrolyte, can stabilize the interface, can relieve the volume expansion of the silicon-based negative electrode and the instability of the SEI film, and can effectively improve the cycle performance of the lithium battery.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, and specifically relates to a lithium-rich boron oxide lithium supplement agent, its preparation method, and its application. Background Technology

[0002] Silicon-based anode materials have excellent electrochemical performance. The theoretical lithium intercalation capacity of pure silicon is as high as 4200 mAh / g, which is more than ten times that of traditional graphite anodes (theoretical capacity 372 mAh / g). Even after modification with silicon oxide or carbon composite, its actual capacity is still much higher than that of graphite. It is a key anode material to replace graphite and break through the energy density bottleneck of batteries. However, its own defects such as low conductivity, low initial coulombic efficiency, and volume expansion seriously restrict its large-scale industrial application.

[0003] Currently, the problems of low conductivity and volume expansion are generally addressed through carbon composites, nanostructuring, and the introduction of more stable conductive materials. The low initial coulombic efficiency is addressed by adding lithium replenishers. Unmodified silicon and silicon oxide materials typically have an initial coulombic efficiency of only 70%–85%, far below the minimum standard of 90% required for practical application. This is mainly because the silicon surface reacts violently with the electrolyte, forming a large amount of irreversible solid electrolyte interphase (SEI) film, which consumes a significant amount of active lithium. Adding lithium replenishers can compensate for the loss of active lithium during SEI film formation, thereby stabilizing battery energy density and improving battery performance. The commonly used lithium replenishing agents for silicon-based anodes are inorganic compounds, with lithium borate, lithium iron phosphate, lithium nickel oxide, and lithium triphosphide being the most representative. However, due to their inherent defects, single inorganic compound lithium replenishing agents can no longer meet the electrochemical requirements of silicon-based anodes. For example, lithium borate is easy to produce due to its excellent air and humidity stability, and the boron species in its decomposition products can participate in the construction of a stable electrode / electrolyte interface film (CEI / SEI), effectively suppressing transition metal dissolution and side reaction gas generation, significantly improving battery cycle stability. It also has the advantages of inexpensive raw materials, non-toxicity, and safety, making it suitable for various high-energy systems such as silicon-based anodes and all-solid-state batteries. However, it also has defects such as low lithium replenishment capacity, its own insulation properties, and high lithium release potential, especially in low-voltage battery systems where its lithium replenishment effect is limited.

[0004] Therefore, developing a high-capacity, high-stability lithium replenishing agent that is highly compatible with silicon-based anodes is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a lithium-rich boron oxide lithium supplement agent, its preparation method, and its application. This lithium supplement agent has high specific capacity and strong stability, and by acting in the silicon-based anode of lithium batteries, it can effectively improve the energy density of the battery.

[0006] This invention is achieved through the following technical solution: The lithium-rich boron oxide lithium supplement of the present invention is a phosphorus-coated lithium supplement composed of lithium borate and a phosphorus coating layer. The raw materials include lithium carbonate, boric acid and phosphorus source.

[0007] According to the lithium-rich boron oxide lithium supplement agent, the particle size distribution of the lithium supplement agent is D100 of 1-15 μm and D50 of 3-5 μm; the thickness of the phosphorus coating layer is 10-50 nm.

[0008] According to the lithium-rich boron oxide lithium supplement agent, the molar ratio of lithium carbonate to boric acid is 1.5:1.

[0009] According to the lithium-rich boron oxide lithium supplement agent, the phosphorus source is any one of lithium dihydrogen phosphate, phosphoric acid, or trimethyl phosphate, and its amount is 0.05 to 0.1 times the mass of the lithium carbonate.

[0010] This invention discloses a method for preparing a lithium-rich boron oxide lithium supplement, comprising the following steps: (1) A measured amount of lithium carbonate and boric acid are ball-milled at 100-200 r / min for 20-30 min under an argon atmosphere, and then calcined at 400-500℃ for 2-4 h under an argon atmosphere; (2) Then raise the temperature to 700-800℃ at a rate of 2-3℃ / min and continue calcining for 6-8 hours; (3) After cooling to room temperature, add a quantitative phosphorus source and mix. Then, ball mill at 100-200 r / min for 30-60 min under argon atmosphere. Then, calcine at 550-600℃ under argon atmosphere for 2-4 h. After cooling, pulverize with nitrogen gas flow to obtain lithium supplement powder with D100∈1-10μm and D50∈3-5μm.

[0011] The present invention relates to the application of lithium-rich boron oxide lithium supplement in silicon-based anodes of lithium batteries.

[0012] According to the application described, the lithium-rich boron oxide lithium supplement is added to the negative electrode material prepared with silicon dioxide to form a lithium battery negative electrode.

[0013] According to the application described, the amount of the lithium-rich boron oxide lithium supplementer added to the silicon-based anode material is 1~3wt%.

[0014] Beneficial effects of this invention: The lithium-rich phosphide lithium replenisher provided by this invention, in a lithium battery system with LFP as the positive electrode and silicon-based material as the negative electrode, can reduce the interfacial impedance between lithium borate and electrolyte through phosphorus-coated lithium borate, enabling lithium borate to effectively replenish active lithium during the first charge and discharge process of the lithium battery, thereby improving the battery's first coulombic efficiency; through the formation of good interfacial contact between the lithium replenisher and the electrolyte, the interface is stabilized, alleviating the volume expansion of the silicon-based negative electrode and the instability of the SEI film, effectively improving the cycle performance of the lithium battery. Attached Figure Description

[0015] Figure 1 The particle size distribution diagram prepared in Example 1; Figure 2 The SEM image prepared in Example 1. Detailed Implementation

[0016] The following is a further explanation of the content of this invention: This invention relates to a lithium-rich boron oxide lithium supplement, which is a phosphorus-coated lithium supplement composed of lithium borate and a phosphorus coating layer. The raw materials include lithium carbonate, boric acid, and a phosphorus source. The molar ratio of lithium carbonate to boric acid is 1.5:1. The phosphorus source is any one of lithium dihydrogen phosphate, phosphoric acid, or trimethyl phosphate, and its amount is 0.05 to 0.1 times the mass of the lithium carbonate.

[0017] The particle size distribution of the lithium supplement is D100 of 1–15 μm and D50 of 3–5 μm; the thickness of the phosphorus coating layer is 10–50 nm.

[0018] The preparation method of the lithium-rich boron oxide lithium supplement of the present invention includes the following steps: (1) A measured amount of lithium carbonate and boric acid are ball-milled at 100-200 r / min for 20-30 min under an argon atmosphere, and then calcined at 400-500℃ for 2-4 h under an argon atmosphere; (2) Then raise the temperature to 700-800℃ at a rate of 2-3℃ / min and continue calcining for 6-8 hours; (3) After cooling to room temperature, add a quantitative phosphorus source and mix. Then, ball mill at 100-200 r / min for 30-60 min under argon atmosphere. Then, calcine at 550-600℃ under argon atmosphere for 2-4 h. After cooling, pulverize with nitrogen gas flow to obtain lithium supplement powder with D100∈1-10μm and D50∈3-5μm.

[0019] The present invention relates to the application of lithium-rich boron oxide lithium supplement in silicon-based anodes of lithium batteries. The lithium-rich boron oxide lithium supplement is added to the anode material prepared with silicon dioxide, and the amount of lithium-rich boron oxide lithium supplement added to the silicon-based anode material is 1~3wt%.

[0020] All of the above raw materials are commercially available. The silicon-based material is made of nano-sized silicon dioxide with an average particle size of 15nm.

[0021] The preparation of the lithium-rich boron oxide lithium supplement of the present invention will be described below with specific parameters. Example 1

[0022] Step 1: Add 110.84g of lithium carbonate and 61.83g of boric acid to a ball mill and ball mill at 100r / min for 20min under an argon atmosphere. Then transfer it to an atmosphere furnace and calcine at 400℃ for 2h under an argon atmosphere. Then raise the temperature to 700℃ at a rate of 2℃ / min and continue calcining for 6h.

[0023] Step 2: After cooling to room temperature, transfer the material to a ball mill, add 5.6g of lithium dihydrogen phosphate, and ball mill for 30min at 100r / min under an argon atmosphere. Then transfer it to an atmosphere furnace and calcine at 550℃ for 2h under an argon atmosphere. After cooling to room temperature, pulverize the material using a nitrogen gas flow to obtain 78.06g of the target product, lithium-rich boron oxide lithium supplement, denoted as A.

[0024] The product was tested and found to have a moisture content of 0.01%; the particle size D50 was 4.21 and the D100 was 8.92.

[0025] Example 2

[0026] Step 1: Add 110.84g of lithium carbonate and 61.83g of boric acid to a ball mill and ball mill at 200r / min for 30min under an argon atmosphere. Then transfer it to an atmosphere furnace and calcine at 500℃ for 4h under an argon atmosphere. Then raise the temperature to 800℃ at a rate of 3℃ / min and continue calcining for 8h.

[0027] Step 2: After cooling to room temperature, transfer the material to a ball mill, add 11.1g of lithium dihydrogen phosphate, and ball mill for 1 hour at 200r / min under an argon atmosphere. Then transfer it to an atmosphere furnace and calcine at 600℃ under an argon atmosphere for 4 hours. After cooling to room temperature, pulverize the material using a nitrogen gas flow to obtain 82.23g of the target product, lithium-rich boron oxide lithium supplement, denoted as B.

[0028] The product was tested and found to have a moisture content of 0.01%; the particle size D50 was 4.35 and the D100 was 8.64.

[0029] Example 3

[0030] Step 1: Add 110.84g of lithium carbonate and 61.83g of boric acid to a ball mill and ball mill at 150r / min for 20min under an argon atmosphere. Then transfer it to an atmosphere furnace and calcine at 450℃ for 3h under an argon atmosphere. Then raise the temperature to 750℃ at a rate of 2.5℃ / min and continue calcining for 7h.

[0031] Step 2: After cooling to room temperature, transfer the material to a ball mill, add 8.3g of phosphoric acid, and ball mill for 45 minutes at 150r / min under an argon atmosphere. Then transfer it to an atmosphere furnace and calcine at 580℃ for 3 hours under an argon atmosphere. After cooling to room temperature, pulverize the material using a nitrogen gas flow to obtain 79.98g of the target product, lithium-rich boron oxide lithium supplement, denoted as C.

[0032] The product was tested and found to have a moisture content of 0.01%; the particle size D50 was 4.06 and the D100 was 8.59.

[0033] The lithium replenishing agents prepared in Examples 1-3 were used to prepare lithium batteries and their performance was tested. Preparation of positive electrode: LFP, PVDF and Sp are mixed evenly in NMP solution at a mass ratio of 94:3:3 and then coated onto aluminum foil; the aluminum foil is dried in a vacuum oven at 120℃ and then cut into positive electrode sheets with a diameter of 1.2cm and stored in a sealed container.

[0034] Preparation of negative electrode: CMC+SBR, SP, silicon dioxide, and A / B / C were mixed evenly in deionized water at a mass ratio of 5:8:85:2, and then vacuum degassed. The slurry was then coated onto the surface of Cu foil and dried in a vacuum oven at 80℃ for 2 hours to obtain a negative electrode. The negative electrode was then rolled and cut into negative electrode sheets with a diameter of 1.4 cm, sealed and stored. The negative electrode sheets were labeled as SiO-A / SiO-B / SiO-C and blank silicon-based negative electrode sheets without lithium supplementation, respectively. The mass ratio of silicon dioxide, SP, and CMC+SBR was 87:8:5.

[0035] Assembly and testing of full cells: LFPs were assembled with blank silicon-based negative electrodes, SiO-A, SiO-B and SiO-C negative electrodes to form CR2032 cells. The ratio of the unit area capacity of the negative electrode to the unit area capacity of the positive electrode was 1.2:1. Charge and discharge tests were performed in the LANBTS test cabinet within the voltage range of 2.5-3.8 V.

[0036] The test results are shown in the table below: , , The results in Tables 1 and 2 show that the lithium battery using the lithium-rich boron oxide provided by this invention as the negative electrode lithium replenishment agent has a significantly higher first-charge specific capacity than the lithium battery without the lithium replenishment agent. Its first coulombic efficiency is increased from 80% to over 90%, which effectively improves the energy density, increases the capacity retention rate, and extends the battery life.

[0037] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A lithium-rich boron oxide lithium supplement, characterized in that it is... A phosphorus-coated lithium supplement composed of lithium borate and a phosphorus coating layer, the raw materials of which include lithium carbonate, boric acid and phosphorus source.

2. The lithium-rich boron oxide lithium supplement agent according to claim 1, characterized in that, The lithium supplement has a particle size distribution of D100 of 1–15 μm and D50 of 3–5 μm; the phosphorus coating thickness is 10–50 nm.

3. The lithium-rich boron oxide lithium supplement agent according to claim 1, characterized in that, The molar ratio of lithium carbonate to boric acid is 1.5:

1.

4. The lithium-rich boron oxide lithium supplement agent according to claim 1, characterized in that, The phosphorus source is any one of lithium dihydrogen phosphate, phosphoric acid, or trimethyl phosphate, and its amount is 0.05 to 0.1 times the mass of the lithium carbonate.

5. A method for preparing a lithium-rich boron oxide lithium supplement agent according to any one of claims 1-4, characterized in that, Includes the following steps: (1) A measured amount of lithium carbonate and boric acid are ball-milled at 100-200 r / min for 20-30 min under an argon atmosphere, and then calcined at 400-500℃ for 2-4 h under an argon atmosphere; (2) Then raise the temperature to 700-800℃ at a rate of 2-3℃ / min and continue calcining for 6-8 hours; (3) After cooling to room temperature, add a quantitative phosphorus source and mix. Then, ball mill at 100-200 r / min for 30-60 min under argon atmosphere. Then, calcine at 550-600℃ under argon atmosphere for 2-4 h. After cooling, pulverize with nitrogen gas flow to obtain lithium supplement powder with D100∈1-10μm and D50∈3-5μm.

6. The application of the lithium-rich boron oxide lithium supplement agent as described in claim 1 in the silicon-based anode of a lithium battery.

7. The application according to claim 6, characterized in that, The lithium-rich boron oxide lithium supplementer is added to the negative electrode material prepared with silicon dioxide to make a lithium battery negative electrode.

8. The application according to claim 6, characterized in that, The amount of the lithium-rich boron oxide lithium supplementer added to the silicon-based anode material is 1~3wt%.

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