A Lithium-Ion Battery Electrolyte Doped with Mesoporous Molecular Sieve and Its Application

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a lithium-ion battery electrolyte doped with mesoporous molecular sieve and its application. The electrolyte includes an electrolyte lithium salt, a solvent and an additive; the additive is a mesoporous lithiated molecular sieve, and the mass content of the additive accounts for 1-6% of the total mass of the electrolyte. By adding mesoporous lithium molecular sieve to the electrolyte of the present invention, the contents of water and metal impurities in the electrolyte can be reduced, and the self-discharge of the lithium-ion battery can be effectively reduced, thereby improving the battery performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a lithium-ion battery electrolyte doped with mesoporous molecular sieve and its application. Background Art

[0002] Due to its high energy density, power density, long cycle life, flexibility, light weight and other characteristics, lithium-ion batteries have been widely used in many fields, ranging from large-scale energy storage power stations to electric vehicles and various electronic devices, etc. It is the most important technology among various energy storage technologies. As a medium for conducting ions and electrons, the electrolyte plays a very important role in battery performance. It has been found that there are many impurities in the lithium-ion battery electrolyte, such as water, metal impurity ions such as HF, Al, Cr, Cu, Fe, Na, Ni, etc. The impurities in the electrolyte will cause the continuous reduction of the battery specific capacity and cycle efficiency. When the impurity concentration exceeds a certain content, the lithium-ion battery will be completely damaged. Therefore, it is necessary to strengthen the analysis of impurity content and impurity removal technology to improve the stability and safety of the battery.

[0003] Researchers have proposed many impurity removal methods, which can be simply divided into two categories from the technical principle: one is to modify the electrode material, such as pretreating the graphite electrode with Li2SO4, surface coating the positive electrode material, etc. However, this scheme is difficult to reduce the water content to a very low level, and has high cost, complex process, and even reduces the battery capacity, with certain drawbacks. The other is to use lithiated molecular sieve for impurity removal treatment. While the molecular sieve removes water, HF can also be removed. At the same time, other metal ions will also exchange with the lithium ions of the lithiated molecular sieve, further reducing the ion content. Because 4A molecular sieve has outstanding performance in adsorbing water, and 5A molecular sieve can well adsorb the heteroalcohol in the solvent while adsorbing water, so generally 4A and 5A molecular sieves are mixed in a ratio of 1:1 during production to dehydrate the solvent. However, the A-type molecular sieve is characterized by a small pore size, which is not conducive to the diffusion of the electrolyte therein. Therefore, preparing mesoporous A-type molecular sieve can reduce the self-discharge phenomenon of the battery on the basis of successful impurity removal, and then improve its performance in the battery, which has important practical significance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the current impurity removal methods, and provide a lithium-ion battery electrolyte doped with mesoporous molecular sieve and its application. This electrolyte can significantly reduce the self-discharge of the battery, and can remove impurities such as water and metals, thereby improving the performance of the battery.

[0005] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] On the one hand, the present invention provides a lithium-ion battery electrolyte doped with mesoporous molecular sieve. The electrolyte includes an electrolyte lithium salt, a solvent, and an additive. The additive is a mesoporous lithiated molecular sieve, and the mass content of the additive accounts for 1-6% of the total mass of the electrolyte.

[0007] In the above technical solution, further, the electrolyte lithium salt is LiPF6 or LiBF4, and the concentration of the electrolyte lithium salt in the electrolyte is 0.6-1.4 mol / L.

[0008] In the above technical solution, further, the solvent is dimethyl carbonate and / or ethyl methyl carbonate, and the volume ratio of dimethyl carbonate to ethyl methyl carbonate is 0:3-3:0.

[0009] In the above technical solution, further, the preparation method of the mesoporous lithiated molecular sieve includes the following steps:

[0010] 1) Dissolve the triblock copolymer P123 in deionized water, stir at 35 °C until clear, then add mesitylene, and stir for 1-4 h to obtain solution A;

[0011] 2) Add a silicon source to solution A and stir for 2-6 h to obtain solution B;

[0012] 3) Dissolve an aluminum source in an NaOH solution to obtain solution C;

[0013] 4) Add solution C to solution B, stir at 40 °C for 2-4 h, then transfer to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallize at 80-120 °C for 6-14 h, filter, and wash;

[0014] 5) Transfer the filter cake obtained in step 4) to an oven for drying, then transfer to a muffle furnace and calcine at 450-600 °C for 4-8 h to obtain a mesoporous molecular sieve;

[0015] 6) Prepare a lithiation solution with a concentration of 0.1-1.0 mol / L of a lithium salt, immerse the mesoporous molecular sieve obtained in step 5) in the lithiation solution for ion exchange, stir at 40 °C for 4-8 h, then filter and dry, repeat the exchange 1-2 times again, and finally activate at 150-300 °C for 2-4 h to obtain a mesoporous lithiated molecular sieve.

[0016] In the above technical solution, in step 1), the mass concentration of the triblock copolymer P123 is 0.2-2 wt%, and the mass concentration of mesitylene is 0.2-2 wt%; in step 2), the mass concentration of the silicon source calculated as SiO₂ is 5-10 wt%; in step 3), the mass concentration of the aluminum source calculated as Al₂O₃ is 7-12 wt%.

[0017] In the above technical solution, further, in step 2), the silicon source is silica sol, sodium silicate or tetraethyl orthosilicate.

[0018] In the above technical solution, further, in step 3), the aluminum source is sodium aluminate, aluminum isopropoxide or pseudo-boehmite.

[0019] In the above technical solution, further, in step 6), the lithium salt is LiNO3, LiClO4, lithium acetate, lithium carbonate or lithium hydroxide.

[0020] On the other hand, the present invention provides an application of the above lithium-ion battery electrolyte, and the electrolyte is used in a lithium-ion battery with Li3V2(PO4)3 as the positive electrode material.

[0021] In the above technical solution, further, both the positive and negative electrolytes of the lithium-ion battery are the above electrolyte.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. Adding mesoporous lithium molecular sieve to the electrolyte can reduce the content of water and metal impurities in the electrolyte, and can effectively reduce the self-discharge of the lithium-ion battery and improve the battery performance.

[0024] 2. The ethyl methyl carbonate in the electrolyte has stable properties and low reaction activity, so its decomposition voltage is higher, and it can reduce the catalytic ability of Li3V2(PO4)3 with high activity in the full charge state to the electrolyte. Specific Embodiments

[0025] Example 1

[0026] 1) Weigh 0.20 g of triblock copolymer P123 and dissolve it in 14.5 mL of deionized water. Stir at 35 °C until clear, add 0.20 g of mesitylene, and continue stirring for 4 h, denoted as solution A; weigh 5.0 g of silica sol (30%) and add it to solution A, stir for 4 h; separately weigh 1.70 g of sodium aluminate and 2.5 g of NaOH and dissolve them in deionized water, denoted as solution B; then add solution B to solution A, stir at 40 °C for 4 h, transfer to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallize at 100 °C for 10 h, filter, and wash; transfer the filter cake to an oven for drying, and then transfer it to a muffle furnace and calcine at 550 °C for 6 h to obtain mesoporous molecular sieve.

[0027] 2) Preparation of lithium-exchanged molecular sieve: Weigh 6.9 g of lithium nitrate, dissolve it in 100 mL of solution to prepare a 1 mol / L lithium-exchanged solution, take 10 g of the above-obtained mesoporous molecular sieve and immerse it in this solution, stir at 40 °C for 8 h, then filter and dry, repeat the exchange 1 - 2 times again, and finally activate at 200 °C for 4 h.

[0028] Comparative Example 1

[0029] Preparation of ordinary lithiated molecular sieve: The preparation process is the same as that in Example 1, and the only difference is that P123 and mesitylene are not added during the preparation of the molecular sieve.

[0030] Example 2

[0031] The dimethyl carbonate was subjected to water treatment. The purity of the dimethyl carbonate was 99.95%, the initial water content was 201 ppm, and the total metal ion concentration was 15 ppm. Two portions of 500 g of dimethyl carbonate were taken and 10% of the molecular sieves of Example 1 and Comparative Example 1 were added respectively, and treated at room temperature for 5 h. The water content of the treated dimethyl carbonate was detected by a Coulometric moisture tester, and the results were 6.5 and 6.8 ppm respectively. The total concentration of other metal ions detected by an inductively coupled plasma optical emission spectrometer was 5 ppm and 10 ppm. This shows that the molecular sieves obtained in Example 1 and Comparative Example 1 have almost the same effect on removing water from dimethyl carbonate, but the effect of Example 1 on removing metal ions is better than that of Comparative Example 1.

[0032] Example 3

[0033] The ethyl methyl carbonate was subjected to water treatment. The purity of the ethyl methyl carbonate was 99.96%, the initial water content was 180 ppm, and the total metal ion concentration was 13 ppm. Two portions of 500 g of ethyl methyl carbonate were taken and 10% of the molecular sieves of Example 1 and Comparative Example 1 were added respectively, and treated at room temperature for 5 h. The water content of the treated ethyl methyl carbonate was detected by a Coulometric moisture tester, and the results were 5.4 and 5.5 ppm respectively. The total concentration of other metal ions detected by an inductively coupled plasma optical emission spectrometer was 3 ppm and 7 ppm. This shows that the molecular sieves obtained in Example 1 and Comparative Example 1 have almost the same effect on removing water from dimethyl carbonate, but the effect of Example 1 on removing metal ions is better than that of Comparative Example 1.

[0034] Example 4

[0035] The electrolyte lithium salt is LiPF6 with a concentration of 1 mol / L, the additive is the mesoporous lithium molecular sieve prepared in Example 1 with a mass concentration of 4%, and the solvent is a mixture of dimethyl carbonate and ethyl methyl carbonate (volume ratio 1:1).

[0036] Dissolve Li3V2(PO4)3, conductive carbon black, and binder in a mass ratio of 8:1:1 in an appropriate amount of N-methylpyrrolidone and mix evenly. Coat an electrode film with a thickness of 0.1 mm using a wet film applicator. After drying quickly, cut the electrode film into electrode sheets with a diameter of 10 mm using a slicing machine, weigh them, and calculate the mass of the active material. At the same time, use a lithium sheet as the negative electrode, Celgard 2500 as the separator, add 50 μL of electrolyte, and assemble a button battery in a glove box. Then, conduct electrochemical tests on the battery. First, let it stand for 5 h, perform 10 cycles of charge and discharge at a rate of 0.2C, charge to 4.3V, and then set it aside. After setting it aside for 10 days, discharge it to 3V at a rate of 0.2C. The attenuation rate of the discharge capacity before and after setting it aside is the self-discharge rate of the battery.

[0037] Test results: The self-discharge rate of the battery after setting it aside is 3%.

[0038] Comparative Example 2

[0039] The electrolyte lithium salt is LiPF6 with a concentration of 1 mol / L, the additive is the ordinary lithiated molecular sieve prepared in Comparative Example 1 with a mass concentration of 4%, and the solvent is a mixture of dimethyl carbonate and ethyl methyl carbonate (volume ratio 1:1).

[0040] Test results: The self-discharge rate of the battery after setting it aside is 12%.

[0041] Example 5

[0042] The electrolyte lithium salt is LiBF4 with a concentration of 1 mol / L, the additive is the mesoporous lithium molecular sieve prepared in Example 1 with a mass concentration of 4%, and the solvent is a mixture of dimethyl carbonate and ethyl methyl carbonate (volume ratio 1:1).

[0043] Comparative Example 3

[0044] The electrolyte lithium salt is LiBF4 with a concentration of 1 mol / L, the additive is the ordinary lithiated molecular sieve prepared in Comparative Example 1 with a mass concentration of 4%, and the solvent is a mixture of dimethyl carbonate and ethyl methyl carbonate (volume ratio 1:1).

[0045] Example 6

[0046] The electrolyte lithium salt is LiPF4 with a concentration of 1 mol / L, the additive is the mesoporous lithium molecular sieve prepared in Example 1 with a mass concentration of 4%, and the solvent is ethyl methyl carbonate.

[0047] Comparative Example 4

[0048] The electrolyte lithium salt is LiBF4 with a concentration of 1 mol / L, the additive is the ordinary lithiated molecular sieve prepared in Comparative Example 1 with a mass concentration of 4%, and the solvent is ethyl methyl carbonate.

[0049] Example 7

[0050] The electrolyte lithium salt is LiBF4 with a concentration of 1 mol / L, the additive is the mesoporous lithium molecular sieve prepared in Example 1 with a mass concentration of 4%, and the solvent is dimethyl carbonate.

[0051] Comparative Example 5

[0052] The electrolyte lithium salt is LiBF4 with a concentration of 1 mol / L, the additive is the ordinary lithiated molecular sieve prepared in Comparative Example 1 with a mass concentration of 4%, and the solvent is dimethyl carbonate.

[0053] The battery cathode materials, electrolyte compositions and self-discharge rates of Examples 5-7 and Comparative Examples 3-5 are shown in Table 1.

[0054] Table 1

[0055] Group Positive electrode Electrolyte lithium salt Solvent Additive Self-discharge rate Example 5 <![CDATA[Li3V2(PO4)3]]> <![CDATA[LiBF4]]> DMC + EMC Mesoporous lithium molecular sieve 8％ Comparative Example 2 <![CDATA[Li3V2(PO4)3]]> <![CDATA[LiBF4]]> DMC + EMC Ordinary lithium molecular sieve 17％ Example 6 <![CDATA[Li3V2(PO4)3]]> <![CDATA[LiBF4]]> EMC Mesoporous lithium molecular sieve 9％ Comparative Example 3 <![CDATA[Li3V2(PO4)3]]> <![CDATA[LiBF4]]> EMC Ordinary lithium molecular sieve 20％ Example 7 <![CDATA[Li3V2(PO4)3]]> <![CDATA[LiBF4]]> DMC Mesoporous lithium molecular sieve 7％ Comparative Example 4 <![CDATA[Li3V2(PO4)3]]> <![CDATA[LiBF4]]> DMC Ordinary lithium molecular sieve 16％

[0056] As can be seen from Table 1, adding the mesoporous lithium molecular sieve can play a role in reducing the self-discharge rate of the battery under different battery materials and electrolyte compositions.

[0057] The content described in the present invention is not limited to the content of the embodiments described in the present invention.

[0058] Specific examples are used in this article to illustrate the embodiments of the present invention. The descriptions of the above embodiments are only for helping to understand the present invention. It should be noted that for those skilled in the art of this technology, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A mesoporous molecular sieve-doped lithium-ion battery electrolyte, characterized in that: The electrolyte includes an electrolyte lithium salt, a solvent, and an additive; the additive is a mesoporous lithiated molecular sieve, and the mass content of the additive accounts for 1-6% of the total mass of the electrolyte; The preparation method of the mesoporous lithiated molecular sieve includes the following steps: 1) Dissolve the triblock copolymer P123 in deionized water, stir at 35 °C until clear, then add mesitylene, and stir for 1-4 h to obtain solution A; 2) Add a silicon source to solution A and stir for 2-6 h to obtain solution B; 3) Dissolve an aluminum source in a NaOH solution to obtain solution C; 4) Add solution C to solution B, stir at 40 °C for 2-4 h, then transfer it to a stainless steel reaction kettle with a polytetrafluoroethylene lining, crystallize at 80-120 °C for 6-14 h, filter, and wash; 5) Transfer the filter cake obtained in step 4) to an oven for drying, then transfer it to a muffle furnace and calcine at 450-600 °C for 4-8 h to obtain a mesoporous molecular sieve; 6) Prepare a lithiating solution with a concentration of 0.1-1.0 mol / L of a lithium salt, immerse the mesoporous molecular sieve obtained in step 5) in the lithiating solution for ion exchange, stir at 40 °C for 4-8 h, then filter and dry, repeat the exchange 1-2 times again, and finally activate at 150-300 °C for 2-4 h to obtain a mesoporous lithiated molecular sieve.

2. The lithium-ion battery electrolyte according to claim 1, wherein: The electrolyte lithium salt is LiPF6 or LiBF4, and the concentration of the electrolyte lithium salt in the electrolyte is 0.6-1.4 mol / L.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that: The solvent is dimethyl carbonate and / or ethyl methyl carbonate, and the volume ratio of dimethyl carbonate to ethyl methyl carbonate is 0:3-3:

0.

4. The lithium-ion battery electrolyte according to claim 1, wherein: In step 1), the mass concentration of the triblock copolymer P123 is 0.2-2 wt%, and the mass concentration of mesitylene is 0.2-2 wt%; In step 2), the mass concentration of the silicon source calculated as SiO2 is 5-10 wt%; In step 3), the mass concentration of the aluminum source calculated as Al2O3 is 7-12 wt%.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that: In step 2), the silicon source is silica sol, sodium silicate, or tetraethyl orthosilicate.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that: In step 3), the aluminum source is sodium aluminate, aluminum isopropoxide, or pseudo-boehmite.

7. The lithium-ion battery electrolyte according to claim 1, wherein: In step 6), the lithium salt is LiNO3, LiClO4, lithium acetate, lithium carbonate, or lithium hydroxide.

8. Use of the lithium-ion battery electrolyte according to any one of claims 1 to 7, characterized in that: The electrolyte is used in a lithium-ion battery with Li3V2(PO4)3 as the positive electrode material.

9. The application according to claim 8, characterized in that: The positive and negative electrode electrolytes of the lithium-ion battery are both the electrolytes described in any one of claims 1-7.