Lithium ion battery and electric device

Abstract

The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery and an electric device. In the present invention, a tetraether nitrile additive is introduced into an electrolyte of a silicon negative electrode battery to be combined with a diisocyanate additive, and the content of a silicon negative electrode material is controlled, such that an ether bond structure of the tetraether nitrile compound is used to transport Li+ during discharging to achieve the purpose of improving rate discharge and low-temperature discharge performance while ensuring that the surface stability of positive and negative electrodes is improved, thereby improving the cycle performance of high-voltage LiCoO2 and high-silicon negative electrode systems.

Description

Lithium-ion battery and power-consuming device Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium ion battery and an electrical device. Background Art

[0002] Lithium-ion batteries, characterized by high voltage, high safety, and long cycle life, play a vital role in our lives. Lithium-ion batteries are also developing towards higher energy density, placing increasing demands on the specific capacity of positive and negative electrode active materials. Increasing the specific capacity of positive electrode materials can be primarily achieved by increasing the voltage. Currently, the voltage of LiCoO2 positive electrode active materials has generally been increased to 4.48V, with 4.53V and 4.55V materials under development. While high voltage brings higher specific capacity, it also leads to reduced stability of the positive electrode material and electrolyte, and a shorter cycle life. Graphite, currently the mainstream negative electrode active material, has achieved a specific capacity of 360-365 mAh / g, essentially approaching its theoretical specific capacity (372 mAh / g). Further improvement is difficult, so the most effective approach is to develop new negative electrode active materials. Currently, the main negative electrode active materials under development include tin-based materials, silicon-based materials, and lithium titanate (LTO). Silicon-based negative electrode materials hold the greatest potential for application. Silicon-based negative electrode materials have a theoretical capacity of 4200mAh / g, which is much higher than that of graphite materials. Furthermore, the raw materials are abundant, and the cost can be reduced to an extremely low level after large-scale mass production. Major lithium battery manufacturers are developing silicon-based negative electrode batteries or have development plans for them in the future. However, silicon-based negative electrodes currently have some significant disadvantages, such as large volume changes (150-300%) during charge and discharge, low initial efficiency, and HF in the electrolyte can also corrode silicon particles. Traditional electrolytes have poor stability and are no longer suitable for new positive and negative electrode systems.

[0003] Application No. CN202310606579.5 discloses an electrolyte and a lithium-ion battery. The electrolyte comprises an additive X containing hydroxyl and nitrile groups. Under high-voltage operating conditions, the hydroxyl groups undergo oxidative dehydrogenation reactions to produce hydrogen radicals, which capture and bind oxygen radicals generated during the phase transition. Additive X exhibits excellent oxidation resistance, facilitating the formation of a uniform CEI film on the surface of the positive electrode material. While this additive can alleviate the degradation of the electrochemical performance of lithium-ion batteries under high voltage, it cannot form a stable SEI on the surface of the silicon anode, thereby improving the cycling performance of high-voltage LiCoO2 and high-silicon anode systems.

[0004] Summary of the Invention

[0005] The present invention addresses the deficiencies in the prior art and provides a lithium-ion battery to solve the above-mentioned technical problems.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode active material comprises a silicon negative electrode material, and the content of the silicon negative electrode material is 10-30 wt% of the total weight of the negative electrode active material; the electrolyte comprises a lithium salt, an organic solvent, and a first additive, wherein the first additive comprises an additive A having a structure of Formula I and an additive B having a structure of Formula II;

[0008] Wherein, R1-R6 are each independently selected from substituted or unsubstituted C1-C10 carbon atoms, alkylene groups or alkylene groups; the content of the additive A accounts for 0.05-5wt% of the total amount of the electrolyte, and the content of the additive B accounts for 0.03-8wt% of the total amount of the electrolyte.

[0009] Preferably, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP).

[0010] Preferably, the content of the additive A accounts for 0.1-3 wt% of the total amount of the electrolyte, and the content of the additive B accounts for 0.1-5 wt% of the total amount of the electrolyte.

[0011] Preferably, the additive A has a structure as shown in formula (III):

[0012] Preferably, the additive B is at least one of the structures shown in formula (IV) and formula (V):

[0013] Preferably, the lithium salt is selected from one or a combination of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiODFP), lithium tetrafluorooxalatophosphate (LiOTFP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) and lithium bis(fluorosulfonyl imide) (LiFSI).

[0014] Preferably, the content of the lithium salt compound accounts for 0.1-25 wt % of the total mass of the electrolyte.

[0015] Preferably, the electrolyte further includes a second additive, which includes one or a combination of 1,3,6-hexanetrinitrile (HTCN), adiponitrile (ADN), 1,3-propane sultone (PS), diethylene sulfate (DTD), fluoroethylene carbonate (FEC), tris(trimethylsilyl) borate (TMSB), and tris(trimethylsilyl) phosphate (TMSP).

[0016] Preferably, the mass of the second additive accounts for 0.1-20 wt % of the total mass of the electrolyte.

[0017] Another object of the present invention is to provide an electrical device made using the above lithium-ion battery.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] By introducing tetraether nitrile additives into the electrolyte and combining them with diisocyanate additives, the ether bond structure of tetraether nitrile compounds is utilized to transfer Li+ during discharge while ensuring the improvement of the surface stability of the positive and negative electrodes. + , to improve the performance of rate discharge and low-temperature discharge. When the voltage of the positive electrode is higher than 4.45V, the dissolution of transition metal ions usually occurs. As the voltage increases, the dissolution of transition metal ions will be aggravated. In theory, the aprotic solvent used in the electrolyte will only oxidize at a voltage above 6V, but under the influence of low solvent purity and the catalytic effect of transition metal ions, the electrolyte solvent will generally oxidize when the voltage is higher than 4.45V. The higher the voltage, the more serious the oxidation of the electrolyte solvent. The oxidation potential of nitrile compounds is as high as 6.7V. Adding nitrile compounds as electrolyte additives can effectively reduce the oxidation of the electrolyte at high voltage and effectively improve the cycle performance of the battery at high voltage. The cyano group (-CN) of the nitrile compound can effectively complex with Co ions, effectively reducing the negative reaction caused by it to the electrolyte. The tetraether nitrile compound can use the ether bond contained in its own structure to transport Li + The discharge performance is significantly better than that of fatty nitriles. Isocyanates can form films efficiently on the surfaces of positive and negative electrodes, and the polymer SEI formed can effectively protect the positive and negative active materials, maintain high stability during the cycle, and reduce the volume change and Li +SEI rupture caused by deintercalation. At the same time, the -NCO group of isocyanate can react with H2O and HF in the electrolyte, reducing the decomposition of lithium salts and the dissolution of positive transition metal ions caused by the two, while inhibiting the corrosion of HF on the negative silicon material, thereby extending the cycle life of the battery. Under high temperature and long-term cycle conditions, the H2O in the electrolyte will react with LiPF6, causing the latter to decompose and produce HF and PF5. PF, as a Lewis acid, will catalyze the continued decomposition of LiPF6, forming a chain reaction, deteriorating the cycle performance, and increasing the impedance. The specific reaction is as follows: LiPF6→PF5+LiF PF5+H2O→POF3+HF

[0020] Therefore, by adding isocyanate, this chain reaction can be blocked, the hydrolysis of LiPF6 can be prevented, and the cycle life of the lithium-ion battery can be effectively extended.

[0021] The silicon doping amount suitable for this solution is 10-30wt%, that is, only when the content of silicon negative electrode material is 10-30wt% of the total weight of the negative electrode active material, additives A and additive B can play a role and jointly improve the cycle performance and other key performance of the silicon negative electrode system. When the silicon doping amount is lower than 10wt%, there is no significant difference between the negative electrode system and the ordinary graphite system, and the improvement effect of this additive combination on the system is relatively small. When the silicon doping amount is higher than 30wt%, the volume change of the silicon negative electrode during charging and discharging is too large, and the SEI stability is seriously deteriorated. This additive combination is also unable to improve the stability of the SEI. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0023] Example 1

[0024] Preparation of electrolyte:

[0025] In an argon-filled glove box, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a mass ratio of 2:2:3:3 to obtain a solvent, and then 14 wt% of lithium hexafluorophosphate (LiPF6) based on the total weight of the electrolyte was slowly added to the solvent. Finally, 2.5 wt% of additive A, 2.5 wt% of additive B, 4 wt% of 1,3-propane sultone (PS), and 1 wt% of tris(trimethylsilyl)borate (TMSB) based on the total weight of the electrolyte were added, and the mixture was stirred evenly to obtain a lithium-ion battery electrolyte.

[0026] The structure of additive A is as follows:

[0027] The structure of Additive B is as follows:

[0028] Preparation of positive electrode sheet:

[0029] The positive electrode membrane includes positive electrode active material lithium cobalt oxide (LiCoO2), conductive agent (Super P), and binder polyvinylidene fluoride (PVDF), which are mixed in a weight ratio of 97:1.7:1.3, added to N-methylpyrrolidone (NMP), and mixed evenly to prepare lithium-ion battery positive electrode slurry. The positive electrode slurry is coated on the current collector aluminum foil, dried at 85°C and cold pressed, and then trimmed, cut and stripped, and dried at 85°C under vacuum conditions for 4 hours. The pole ears are welded to prepare the lithium-ion battery positive electrode sheet.

[0030] Preparation of negative electrode sheet:

[0031] The negative electrode membrane includes negative electrode active materials graphite and SiC (or SiO x ), conductive agent carbon nanotubes (CNT), thickener sodium carboxymethyl cellulose (CMC) and binder polyacrylic acid (PAA). A mixture of graphite and SiC in a weight ratio of 80:20 is used as the negative electrode active material. The materials are mixed in a weight ratio of negative electrode active material: conductive agent carbon nanotubes (CNT): thickener sodium carboxymethyl cellulose (CMC): binder polyacrylic acid (PAA) = 93.5:1.3:1.2:4, and deionized water is added and mixed evenly to prepare a negative electrode slurry; the negative electrode slurry is coated on the current collector copper foil, dried at 85°C and then cold pressed. Then, after trimming, cutting, and slitting, it is dried at 85°C under vacuum conditions for 12 hours to obtain the lithium-ion battery negative electrode sheet.

[0032] Preparation of lithium-ion batteries:

[0033] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive and negative electrode sheets, and the bare battery cell is wound and placed in an aluminum-plastic film outer package. The prepared electrolyte is injected into the dried battery, and the battery is packaged, allowed to stand, formed, shaped, and capacity divided to complete the preparation of the lithium-ion soft-pack battery.

[0034] Example 2: The only difference from Example 1 is that the content of additive A is 0.05 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0035] Example 3: The only difference from Example 1 is that the content of additive B is 0.03 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0036] Example 4: The only difference from Example 1 is that the content of additive A is 5 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0037] Example 5: The only difference from Example 1 is that the content of additive B is 8 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0038] Example 6: The only difference from Example 1 is that the content of additive A is 0.1 wt % of the total weight of the electrolyte. By adjusting the solvent content to keep the total amount of the electrolyte unchanged, the voltage upper limit of the cathode active material is increased from 4.53 V to 4.55 V.

[0039] Example 7: The only difference from Example 1 is that the content of additive A is 3 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0040] Example 8: The only difference from Example 1 is that the content of additive B is 0.1 wt% of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0041] Example 9: The only difference from Example 1 is that the content of additive B is 5 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0042] Example 10: The only difference from Example 1 is that the structure of additive B is as follows:

[0043] Example 11: The only difference between Example 1 and Example 1 is that the additive B is 2,6-toluene diisocyanate.

[0044] Example 12: The only difference from Example 1 is that the weight ratio of graphite to SiC is 90:10, and the total weight of the negative electrode active material remains unchanged.

[0045] Example 13: The only difference from Example 1 is that the weight ratio of graphite to SiC is 70:30, and the total weight of the negative electrode active material remains unchanged.

[0046] Comparative Example 1: The only difference between this example and Example 1 is that additive A is not added, and the total amount of the electrolyte remains unchanged by adjusting the solvent content.

[0047] Comparative Example 2: The only difference between this example and Example 1 is that the additive B is not added, and the total amount of the electrolyte remains unchanged by adjusting the solvent content.

[0048] Comparative Example 3: The only difference from Example 1 is that the additive A is changed to adiponitrile, i.e. ADN, and the dosage remains unchanged, which is 2.5 wt% of the total weight of the electrolyte.

[0049] Comparative Example 4: The only difference from Example 1 is that the additive A is changed to 1,3,6-hexanetricarbonitrile, namely HTCN, and the amount used remains unchanged, which is 2.5 wt% of the total weight of the electrolyte.

[0050] Comparative Example 5: The only difference between this example and Example 1 is that the weight ratio of graphite to SiC is 95:5, and the total weight of the negative electrode active material remains unchanged.

[0051] Comparative Example 6: The only difference between this example and Example 1 is that the weight ratio of graphite to SiC is 65:35, and the total weight of the negative electrode active material remains unchanged.

[0052] Comparative Example 7: The only difference between this example and Example 1 is that the content of additive A is 0.02 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0053] Comparative Example 8: The only difference between this example and Example 1 is that the content of additive A is 6 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0054] Comparative Example 9: The only difference between this example and Example 1 is that the content of additive B is 0.02 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0055] Comparative Example 10: The only difference between this example and Example 1 is that the content of additive B is 10 wt % of the total weight of the electrolyte, and the total amount of the electrolyte is kept unchanged by adjusting the solvent content.

[0056] Table 1 Process parameters of Examples and Comparative Examples

[0057] Relevant performance tests were performed on the batteries prepared in Examples 1-13 and Comparative Examples 1-10.

[0058] (1) Normal temperature cycle performance test: In a 25°C environment, the divided battery is charged to 4.53V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. After 400 cycles of charge and discharge, the capacity retention rate at the 400th week is calculated. The calculation formula is as follows:

[0059] 400th cycle capacity retention rate (%) = (400th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0060] (2) High temperature cycle performance test: In a 45°C environment, the divided battery is charged to 4.53V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. After 300 cycles of charge and discharge, the capacity retention rate at the 300th week is calculated. The calculation formula is as follows:

[0061] 300th cycle capacity retention rate (%) = (300th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0062] (3) 85℃ 24h high temperature storage test: The battery was placed at room temperature and charged and discharged once at 0.5C (4.53V-3.0V), and the discharge capacity C0 of the battery before storage was recorded. The battery was then charged to 4.53V at a constant current and constant voltage (100% SOC). A PPG battery thickness gauge (600g) was used to test the thickness d1 of the battery before high temperature storage. The battery was placed in an 85℃ constant temperature box and stored for 24h. After the storage was completed, the battery was taken out and the thermal thickness d2 of the battery after storage was tested. The thickness expansion rate of the battery after storage at 85℃ for 24h was calculated. After the battery was cooled at room temperature for 24h, the battery was again discharged at a constant current of 0.5C to 3.0V, and then charged to 4.53V at a constant current and constant voltage of 0.5C. The discharge capacity C1 and charge capacity C2 of the battery after storage were recorded. The capacity remaining rate and recovery rate of the battery after storage at 85℃ for 24h were calculated as follows:

[0063] Thickness expansion ratio after storage at 85℃ for 24h = (d2-d1) / d1×100%;

[0064] After storage at 85℃ for 24h, the remaining capacity is C1 / C0×100%.

[0065] After storage at 85°C for 24 hours, the capacity recovery rate = C2 / C0×100%.

[0066] (4) Low temperature discharge performance test: The battery was placed in a 25°C incubator for 2 hours, and then charged to 100% SOC at a constant current and constant voltage of 0.2C, with a cut-off current of 0.02C, and then discharged to 3.0V at a rate of 0.5C. This cycle was repeated three times, and the capacity at the third discharge was taken as C0. The battery was charged to 100% SOC at a constant current and constant voltage of 0.2C, and then placed in a -10°C low temperature box for 2 hours, and then discharged to 3.0V at a current of 0.2C. The capacity was obtained as C1. The discharge capacity retention rate of the battery in a -10°C environment was calculated using the following formula:

[0067] -10℃ low temperature discharge capacity retention rate = C1 / C0×100%.

[0068] Table 2 Performance test results of the embodiments and comparative examples

[0069] From the comparison of the test results of Examples 1-13 and Comparative Examples 1-10 in Table 2, it can be seen that:

[0070] Introducing additive A in the embodiment can effectively improve the normal temperature and high temperature cycle performance of the battery, and is conducive to improving the high temperature storage performance of the battery. The oxidation potential of nitrile compounds is as high as 6.7V. Adding nitrile compounds as electrolyte additives can effectively reduce the oxidation of electrolyte under high voltage, effectively improve the cycle performance of the battery under high voltage. And the cyano group (-CN) that nitrile compounds have can effectively be complexed with Co ions, effectively reducing the side reaction caused to the electrolyte. And tetraether nitrile compounds can utilize the ether bond contained in its own structure to transmit Li+, and discharge performance is obviously better than fatty nitrile, which can reduce the low temperature performance deterioration risk brought by nitrile structure.

[0071] The introduction of additive B can effectively improve the normal temperature and high temperature cycle performance of the battery, and is conducive to improving the high temperature storage performance of the battery. Isocyanate compounds can efficiently form films on the positive and negative electrode surfaces. The polymer SEI formed by them can effectively protect the positive and negative electrode active materials, maintain high stability during the cycle, and reduce the volume change and Li + SEI rupture caused by deintercalation. At the same time, the -NCO group of isocyanate can react with H2O and HF in the electrolyte, reducing the decomposition of lithium salts and the dissolution of transition metal ions in the positive electrode caused by the two, while inhibiting HF corrosion of the negative electrode silicon material and extending the cycle life of the battery.

[0072] As can be seen from Examples 1-13 and Comparative Examples 1-10, Additives A and B are only suitable for negative electrode systems with a silicon doping content between 10-30%. When the silicon doping content is less than 10%, there is no significant difference between the negative electrode system and the ordinary graphite system. This additive combination cannot be differentiated from the control group and has no significant effect. When the silicon doping content is higher than 30%, the volume change of the silicon negative electrode during charge and discharge is too large, and the SEI stability is seriously deteriorated. This additive combination is also unable to improve the stability of the SEI. Therefore, this additive combination is only suitable for negative electrode systems with a silicon doping content of 10-30%.

[0073] The specific embodiments described herein are merely illustrative of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described embodiments without departing from the present invention or exceeding the scope of the appended claims.

Claims

1. A lithium ion battery comprising a positive electrode, a negative electrode and an electrolyte, It is characterized in that The negative electrode active material of the negative electrode comprises a silicon negative electrode material, and the content of the silicon negative electrode material is 10-30wt% of the total weight of the negative electrode active material; The electrolyte includes a lithium salt, an organic solvent and a first additive, wherein the first additive includes an additive A having a structure of formula I and an additive B having a structure of formula II; Among them, R 1 -R 6 are each independently selected from substituted or unsubstituted C 1 -C 10 of carbon atoms, alkylene or alkylidene; The content of the additive A accounts for 0.05-5wt% of the total amount of the electrolyte, and the content of the additive B accounts for 0.03-8wt% of the total amount of the electrolyte.

2. The lithium ion battery according to claim 1, It is characterized in that The organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC) and propyl propionate (PP).

3. The lithium ion battery according to claim 1, It is characterized in that The content of the additive A accounts for 0.1-3wt% of the total amount of the electrolyte, and the content of the additive B accounts for 0.1-5wt% of the total amount of the electrolyte.

4. The lithium ion battery according to claim 1, It is characterized in that The additive A has a structure as shown in formula (III):

5. The lithium ion battery according to claim 1, It is characterized in that The additive B is at least one of the structures shown in formula (IV) and formula (V):

6. The lithium ion battery according to claim 1, It is characterized in that The lithium salt is selected from lithium hexafluorophosphate (LiPF 6 ), lithium difluorophosphate (LiDFP), lithium difluorobisoxalate phosphate (LiODFP), lithium tetrafluorooxalate phosphate (LiOTFP), lithium bisoxalate borate (LiBOB), lithium difluorooxalate borate (LiODFB), lithium tetrafluoroborate (LiBF 4 ), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), or a combination of the two or more thereof.

7. The lithium ion battery according to claim 1, It is characterized in that The content of the lithium salt accounts for 0.1-25.0 wt % of the total amount of the electrolyte.

8. The lithium ion battery according to claim 1, It is characterized in that The electrolyte also includes a second additive, which includes one or a combination of 1,3,6-hexanetrinitrile (HTCN), adiponitrile (ADN), 1,3-propane sultone (PS), diethylene sulfate (DTD), fluoroethylene carbonate (FEC), tris(trimethylsilyl) borate (TMSB), and tris(trimethylsilyl) phosphate (TMSP).

9. The lithium ion battery according to claim 1, It is characterized in that The mass of the second additive accounts for 0.1-20wt% of the total mass of the electrolyte.

10. An electrical device, It is characterized in that A lithium ion battery comprising any one of claims 1 to 9.

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