Electrolyte and lithium ion battery
By adding silane phosphate compounds and phosphite compounds to the electrolyte solution of lithium-ion batteries, the problem of poor initial low voltage before the recycled graphite battery is solved, and the efficient cycle and storage performance of the battery is achieved.
Patent Information
- Application Number
- CN202510372081.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-27
- Publication Date
- 2025-06-13
AI Technical Summary
When recycled graphite is processed into a battery as the negative electrode active material of lithium-ion batteries, the proportion of initial low voltage failure before decomposition often increases, resulting in black mist blocks on the cell interface, affecting the cell performance and reducing the yield rate.
An electrolyte solution including lithium salts, organic solvents and additives is used, and the additives include silane phosphate compounds and phosphite compounds. Through the film-forming characteristics and oxidation resistance of these additives, the electrochemical performance and cycle stability of the battery are improved.
It effectively improves the initial voltage before the lithium-ion battery, improves the cycle performance and storage performance of the battery, reduces the bad phenomena in the cell interface, and improves the yield rate.
Smart Images
Figure CN120149550A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte and a lithium ion battery. Background Art
[0002] Compared with other types of rechargeable batteries, lithium-ion batteries have the advantages of high energy density, long life, fast charging speed, environmental friendliness, no memory effect, high operating voltage, and good rate performance. They are widely used in the fields of power and energy storage, and are regarded as a key component of future energy storage solutions. Due to the rapid development of electric vehicles and renewable energy storage systems, the use of lithium-ion batteries has increased dramatically. As a result, more and more waste batteries need to be properly disposed of. As a key main material in lithium-ion batteries, graphite accounts for a large proportion of the recyclable materials of lithium-ion battery products. The recycling and reuse of graphite materials has greatly promoted the positive development of the lithium-ion battery recycling industry.
[0003] The negative electrode active materials of waste lithium-ion batteries are crushed, pickled, purified, coated and other processes to obtain recycled graphite. However, after the recycled graphite is processed into lithium-ion batteries as negative electrode active materials, compared with lithium-ion batteries processed from new graphite, the initial low voltage defect ratio before formation often increases during the battery cell manufacturing process, resulting in the undesirable phenomenon of black fog blocks appearing on the interface of the offline battery cells, affecting the battery cell performance, causing a decrease in the yield rate, and increasing the difficulty of selecting good battery cells. Summary of the invention
[0004] In view of the problems existing in the prior art, the object of the present invention is to provide an electrolyte compatible with recycled graphite; another object of the present invention is to provide a lithium ion battery using recycled graphite as a negative electrode active material.
[0005] The invention discloses an electrolyte comprising a lithium salt, an organic solvent and an additive; the additive comprises a silane phosphate compound and a phosphite compound.
[0006] The lithium salt can be lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(trifluoromethylsulfonyl)imide (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), etc.
[0007] As the organic solvent, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate and the like may be used.
[0008] Utilize the excellent film-forming properties of silane phosphate compounds to form a uniform and dense CEI film on the surface of the positive electrode of the battery. This film can inhibit the cracking of the positive electrode material and prevent the decomposition of the electrolyte, thereby effectively improving the lithium-ion electrochemical performance, and can also improve the cycle stability and lithium deposition performance of the battery. Utilize the antioxidant property of phosphite compounds to offset the influence of oxidizing substances in the battery cell system with recycled graphite as the negative electrode, inhibit the reaction of impurities, and at the same time, it also has slight alkalinity and can slightly reduce the acidity in the electrolyte.
[0009] Furthermore, the silane phosphate compounds include one or more of trimethoxysilylpropyl phosphate, tris(trimethylsilyl) phosphate, triethoxysilylpropyl phosphate, bis(trimethoxysilylpropyl) phosphate, and epoxy silane phosphate.
[0010] Furthermore, the phosphite compounds include one or more of triphenyl phosphite, triethyl phosphite, trimethyl phosphite, and diphenyl phosphite.
[0011] Furthermore, the silane phosphate compound includes tris(trimethylsilyl) phosphate, and the content of tris(trimethylsilyl) phosphate in the electrolyte is 0.5 - 3 wt%.
[0012] Furthermore, the phosphite compound includes triphenyl phosphite, and the content of triphenyl phosphite in the electrolyte is 0.03 - 0.1 wt%.
[0013] Controlling the content of triphenyl phosphite within this range is beneficial to improving the storage performance of lithium-ion batteries.
[0014] Furthermore, the organic solvent includes ethylene carbonate and ethyl methyl carbonate.
[0015] Utilize ethylene carbonate (EC) in the organic solvent of the electrolyte to preferentially form a film on the negative electrode initially, and utilize the phosphonate functional groups derived from the chemical decomposition of silane phosphate compounds to participate in the formation of the SEI film in the form of chemical modification synergistically, and finally obtain an SEI film with a smooth and uniform morphological structure. And at the same time, block the adverse effects of oxidizing substances in the recycled graphite on the battery cell system during the initial wetting process, thereby improving the storage performance and cycle performance of lithium-ion batteries.
[0016] Furthermore, the volume ratio of ethylene carbonate to ethyl methyl carbonate is 2 - 4:7.
[0017] Furthermore, the lithium salt includes lithium hexafluorophosphate, and the concentration of lithium hexafluorophosphate in the electrolyte is 1 - 1.4 mol / L.
[0018] The present invention also discloses a lithium-ion battery, which includes a positive electrode, a negative electrode, a separator, and the electrolyte as described above; wherein, the active material of the negative electrode includes recycled graphite.
[0019] The positive active material of the positive electrode can be lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium iron manganese phosphate, lithium manganate, etc.
[0020] Further, the active material of the positive electrode includes lithium iron phosphate.
[0021] An electrolyte provided by the present application simultaneously adds a silane phosphate compound and a phosphite compound, which improves the stability of the electrochemical reaction of the lithium-ion battery with recycled graphite as the negative active material and increases the initial voltage before formation of the lithium-ion battery prepared with recycled graphite as the negative active material. Description of the Drawings
[0022] Figure 1 is a graph of the potential change during the electrode soaking process of the lithium-ion battery cells prepared in the examples and comparative examples of the present invention;
[0023] Figure 2 is a diagram of the negative electrode interface after full charge and disassembly of the lithium-ion battery prepared in the examples and comparative examples of the present invention;
[0024] Figure 3 is a SEM diagram of the negative electrode graphite of the lithium-ion battery prepared in the examples and comparative examples of the present invention;
[0025] Figure 4 is a graph of the relationship between the number of cycles and the capacity retention rate of the lithium-ion battery prepared in the examples and comparative examples of the present invention. Detailed Embodiments
[0026] To make the technical solution of the present invention clearer, the following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments.
[0027] Example 1
[0028] Prepare the electrolyte:
[0029] Mix EC (ethylene carbonate) and EMC (ethyl methyl carbonate) evenly at a volume ratio of 3:7, and add LiPF 6 (lithium hexafluorophosphate) while stirring to prepare a 1.2 mol / L solution, and then add additives of TMSP (tris(trimethylsilyl) phosphate) and TPPi (triphenyl phosphite) to the above solution, so that the content of TMSP in the electrolyte is 0.5 wt%, and the content of TPPi in the electrolyte is 0.03 wt%, thus obtaining the electrolyte.
[0030] Example 2
[0031] Prepare electrolyte solution:
[0032] Mix EC and EMC evenly at a volume ratio of 3:7, and add LiPF while stirring 6 Prepare a 1.2 mol / L solution, and then add TMSP and TPPi additives to the above solution so that the content of TMSP in the electrolyte solution is 1.5 wt% and the content of TPPi in the electrolyte solution is 0.07 wt%, thus obtaining the electrolyte solution.
[0033] Example 3
[0034] Prepare electrolyte solution:
[0035] Mix EC and EMC evenly at a volume ratio of 3:7, and add LiPF while stirring 6 Prepare a 1.2 mol / L solution, and then add TMSP and TPPi additives to the above solution so that the content of TMSP in the electrolyte solution is 3 wt% and the content of TPPi in the electrolyte solution is 0.1 wt%, thus obtaining the electrolyte solution.
[0036] Example 4
[0037] Prepare electrolyte solution:
[0038] Mix EC and EMC evenly at a volume ratio of 3:7, and add LiPF while stirring 6 Prepare a 1.2 mol / L solution, and then add TMSP and TPPi additives to the above solution so that the content of TMSP in the electrolyte solution is 5 wt% and the content of TPPi in the electrolyte solution is 0.2 wt%, thus obtaining the electrolyte solution.
[0039] Example 5
[0040] Prepare electrolyte solution:
[0041] Add LiPF to EMC while stirring 6 Prepare a 1.2 mol / L solution, and then add TMSP and TPPi additives to the above solution so that the content of TMSP in the electrolyte solution is 1.5 wt% and the content of TPPi in the electrolyte solution is 0.07 wt%, thus obtaining the electrolyte solution.
[0042] Comparative Example 1
[0043] Prepare electrolyte solution:
[0044] Mix EC and EMC evenly at a volume ratio of 3:7, and add LiPF while stirring 6 Prepare a 1.2 mol / L solution, thus obtaining the electrolyte solution.
[0045] Comparative Example 2
[0046] Prepare the electrolyte solution:
[0047] Mix EC and EMC evenly at a volume ratio of 3:7, and add LiPF while stirring 6 Prepare a 1.2 mol / L solution, and then add the TMSP additive to the above solution so that the content of TMSP in the electrolyte solution is 1.5 wt%, thus obtaining the electrolyte solution.
[0048] Comparative Example 3
[0049] Prepare the electrolyte solution:
[0050] Mix EC and EMC evenly at a volume ratio of 3:7, and add LiPF while stirring 6 Prepare a 1.2 mol / L solution, and then add the TPPi additive to the above solution so that the content of TPPi in the electrolyte solution is 0.07 wt%, thus obtaining the electrolyte solution.
[0051] Assemble the batteries with Examples 1-5 and Comparative Examples 1-3. The specific operations are as follows:
[0052] Mix lithium iron phosphate, conductive agent Super P (conductive carbon black), and PVDF (polyvinylidene fluoride) evenly in an NMP (N-methylpyrrolidone) solvent at a mass ratio of 96%:1%:3% to obtain the positive electrode paste. Coating the positive electrode paste evenly on the front and back sides of a 12 + 1 + 1 μm carbon-coated aluminum foil through an extrusion coater, baking, pressing through a roller press to obtain the positive electrode roll, and then slicing through a hardware die cutter to obtain the positive electrode sheet; mix natural graphite, Super P, CMC (sodium carboxymethyl cellulose), and SBR (styrene-butadiene rubber) evenly in a deionized water solvent at a mass ratio of 95%:1%:1.5%:2.5% to obtain the negative electrode paste. Coating the negative electrode paste evenly on the front and back sides of a 4.5 μm copper foil through an extrusion coater, baking, pressing through a roller press to obtain the negative electrode roll, and then slicing through a hardware die cutter to obtain the negative electrode sheet; separate the above positive and negative electrode sheets with a PP separator for lamination to obtain a bare battery cell, put it into a shell to obtain a semi-finished dry battery cell, inject the electrolyte solutions prepared in Examples 1-5 and Comparative Examples 1-3 above, and seal it once.
[0053] Performance test:
[0054] 1. Place the sealed battery cell in a normal temperature environment and record the potential change during the infiltration process of the battery cell after injection with a paperless recorder for a total of 24 h.
[0055] The results are as Figure 1As shown, after the infiltration of the electrolyte prepared in Examples 1-5 is completed, the potential of the battery cell is above 100 mV, while the final potentials of the battery cells of the electrolytes prepared in Comparative Examples 1-3 are significantly lower than those of Examples 1-5. In particular, the potential of Comparative Example 1 is close to 0 V, indicating that the electrochemical system is continuously affected by side reactions during the infiltration of the electrolyte prepared in Comparative Examples 1-3, resulting in the performance degradation of the battery cell after the production process is offline.
[0056] By adjusting the components of the electrolyte, the present invention can greatly improve the initial voltage before formation of a lithium-ion battery using regenerated graphite as the negative electrode active material. This method is simple and easy to implement, without changing any battery cell production process steps, and only solves this problem at the electrolyte material end.
[0057] 2. After the infiltrated battery cells are formed and divided into capacities, a soft-pack battery cell with a capacity of 30 Ah is obtained. The battery cell is disassembled to check the negative electrode interface and SEM testing is performed. The above battery cells are subjected to charged storage and normal temperature cycle testing, and the specific operations are as follows.
[0058] Charged test:
[0059] The offline battery cells are charged to full capacity at a constant current of 0.5C and a constant voltage, and discharged to 2.5V at a current of 1C (record the discharge retention capacity at this step as Qbegin).
[0060] Normal temperature charged storage: The offline battery cells are charged to full capacity at a constant current of 0.5C and a constant voltage, left to stand at room temperature of 25°C for 28 days, discharged to 2.5V at a current of 1C (record the discharge retention capacity at this step as Q1), left to stand for 10 min, charged to full capacity at a constant current of 0.5C and a constant voltage, left to stand for 10 min, and discharged to 2.5V at a current of 1C (record the discharge recovery capacity at this step as Q2);
[0061] High temperature charged storage: The offline battery cells are charged to full capacity at a constant current of 0.5C and a constant voltage, left to stand at a high temperature of 60°C for 7 days, discharged to 2.5V at a current of 1C (record the discharge retention capacity at this step as Q1), left to stand for 10 min, charged to full capacity at a constant current of 0.5C and a constant voltage, left to stand for 10 min, and discharged to 2.5V at a current of 1C (record the discharge recovery capacity at this step as Q2);
[0062] Capacity retention rate = Q1 / Qbegin; Capacity recovery rate = Q2 / Qbegin, and the test results are shown in Table 1.
[0063] Cycle test:
[0064] The offline lithium-ion battery is charged to full capacity at a constant current of 1C and a constant voltage, left to stand for 30 min, discharged to 2.5V at a current of 1C, left to stand for 30 min. This is one week of cycling. Repeat the above steps and record the capacity decay at different cycle numbers. Capacity (retention) ratio = discharge capacity after each cycle / initial capacity.
[0065] As Figure 2As shown, the lithiated graphite at the interface of the electrodes in Examples 1-4 has a uniform color, bright color, and good consistency. In Example 5, since no EC participated in film formation, there were many black spots and white mists on the apparent interface, and the interface was not good; while in Comparative Examples 1-3, due to the occurrence of side reactions, impurities were generated and attached to the negative electrode interface at the initial stage of the battery life after formation, manifested as black mist-like substances on the surface of the lithiated graphite, affecting the cycle life of the battery.
[0066] The smoother the graphite surface and the more uniform the particles after the battery is disassembled, the better the formed SEI film, which is more beneficial for later storage and cycling. As Figure 3 can be seen, the graphite surfaces of the electrodes in Examples 1-4 are smooth and uniform, indicating that the formed SEI film is relatively uniform after formation and has better stability. The graphite of the electrode in Example 5 is very rough because no EC participated in film formation; the graphite surfaces of the electrodes in Comparative Examples 1-3 are relatively rough. There are many large granular substances attached to the surface in Comparative Example 1 and Comparative Example 3. Comparative Example 2 is smoother than Comparative Example 1 and Comparative Example 3, but there are still some small particle protrusions compared with Examples 1-5. All of these affect the storage stability of the battery to a certain extent.
[0067] Table 1 Charge retention test results of examples and comparative examples
[0068] Retention rate at 25°C for 28 days Recovery rate at 25°C for 28 days Retention rate at 60°C for 7 days Recovery rate at 60°C for 7 days Example 1 96.9% 97.5% 96.3% 97.0% Example 2 97.1% 97.7% 96.5% 97.1% Example 3 96.8% 97.6% 96.1% 97.1% Example 4 96.0% 96.4% 94.7% 95.5% Example 5 89.3% 90.8% 85.1% 88.2% Comparative Example 1 94.3% 94.7% 92.7% 93.2% Comparative Example 2 94.5% 95.9% 93.7% 94.1% Comparative Example 3 94.3% 94.6% 92.2% 92.9%
[0069] As can be seen from Table 1, the batteries prepared in Examples 1-3 show higher charge retention rates, indicating that the examples have better storage stability. Compared with Comparative Examples 1-3, the overall charge recovery rate is increased by 3-4%, and it has a good calendar life. In Example 4, due to the relatively large amount of additive TPPi, certain side reactions occurred in the battery system, resulting in relatively poor charge performance, but the charge retention rate is still better than that of Comparative Examples 1-3; in Example 5, due to poor film formation, the reaction between the electrolyte and the lithiated graphite during storage consumed active lithium, resulting in a double decline in the retention rate and the recovery rate.
[0070] From Figure 4 it can be seen that the capacity retention rate of Examples 1-3 is still higher than 90% after 800-1000 cycles, while the capacity retention rate of the comparative examples reaches the standard of 90% within 400 cycles, indicating that the solution of the present invention can effectively improve the cycle performance of the battery.
[0071] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.
Claims
1. An electrolyte, characterized in that: The invention comprises lithium salt, organic solvent and additives; the additives comprise silane phosphate compounds and phosphite compounds.
2. An electrolyte according to claim 1, characterized in that: The silane phosphate compound includes one or more of trimethoxysilyl propyl phosphate, tris(trimethylsilyl) phosphate, triethoxysilyl propyl phosphate, bis(trimethoxysilyl propyl) phosphate, and epoxy silane phosphate.
3. An electrolyte according to claim 1, characterized in that: The phosphite compound includes one or more of triphenyl phosphite, triethyl phosphite, trimethyl phosphite and diphenyl phosphite.
4. An electrolyte according to claim 1, characterized in that: The silane phosphate compound includes tris(trimethylsilane) phosphate, and the content of the tris(trimethylsilane) phosphate in the electrolyte is 0.5-3wt%.
5. An electrolyte according to claim 4, characterized in that: The phosphite compound includes triphenyl phosphite, and the content of the triphenyl phosphite in the electrolyte is 0.03-0.1wt%.
6. An electrolyte according to claim 1, characterized in that: The organic solvent includes ethylene carbonate and ethyl methyl carbonate.
7. An electrolyte according to claim 6, characterized in that: The volume ratio of the ethylene carbonate to the ethyl methyl carbonate is 2-4:
7.
8. An electrolyte according to claim 1, characterized in that: The lithium salt includes lithium hexafluorophosphate, and the concentration of the lithium hexafluorophosphate in the electrolyte is 1-1.4 mol / L.
9. A lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and an electrolyte as claimed in any one of claims 1 to 8; wherein the active material of the negative electrode comprises regenerated graphite.
10. A lithium ion battery according to claim 9, characterized in that: The active material of the positive electrode includes lithium iron phosphate.