Lithium ion battery electrolyte and formation method thereof

Abstract

The application discloses a lithium ion battery electrolyte and a formation method thereof, and belongs to the field of lithium ion batteries. The electrolyte comprises a specific compound X and triallyl isocyanurate, and the two groups of additive components are combined to improve the interface stability, inhibit the interface side reaction at high temperature, and improve the cycle stability. The low-temperature pulse formation method comprises the following steps: after the electrolyte is injected into the battery cell, the battery cell is subjected to a standing treatment, the electrolyte is infiltrated into the pole piece in the battery cell, the battery cell after the standing treatment is placed in a low-temperature condition, and the battery cell is formed through pulse charging. Through the low-temperature pulse formation method, the interface components are further optimized, the content of LiF in the positive electrode interface is improved, and the compound X and triallyl isocyanurate are also helpful to the construction of a high-ionic-conductivity and high-strength negative electrode SEI film in the negative electrode interface, so that the battery still has good cycle stability in a high-temperature environment, and the battery can maintain excellent performance under extreme temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery electrolyte and a lithium-ion battery formation method. This method employs a novel formation strategy, utilizing a combination of additives and a low-temperature pulse formation strategy to optimize the electrode interface film composition, thereby enabling the preparation of high-stability, high-rate lithium-ion batteries. Background Technology

[0002] Formation is a crucial step in lithium-ion battery production. During formation, a passivation layer, known as the solid electrolyte interphase (SEI) film, is formed on the surface of the negative electrode. The quality of the SEI film directly affects the battery's cycle life and stability. The positive electrode electrolyte interphase (CEI) film, formed on the surface of the positive electrode, is mainly composed of fluorides and oxides. Its formation mechanism is similar to that of the SEI film, and it also has a certain impact on the battery's safety and lifespan.

[0003] To significantly improve the electrochemical performance of ternary and lithium cobalt oxide lithium-ion batteries, a common strategy in the industry is to modify the cathode interface. This aims to suppress cathode cracking by increasing the content of lithium fluoride (LiF) in the interface film, thereby significantly extending its cycle life. Existing technical solutions mainly include the following, but these traditional modification methods are not perfect, and their limitations cannot be ignored.

[0004] An additive strategy involves adding specific proportions of additives, such as lithium difluorooxalate borate (LiDFOB) or adiponitrile (C6H8N2), to the electrolyte to construct a stable CEI film in situ on the positive electrode surface. This interfacial film effectively reduces interfacial side reactions and improves the stability of the electrode-electrolyte interface. However, when implementing this strategy, the concentration and type of additives must be strictly controlled; even slight deviations can lead to a decline in battery performance. Furthermore, additives may react undesirably with other components in the electrolyte, further deteriorating battery performance.

[0005] Interfacial composition control: This method finely adjusts the composition of the lithium-ion battery electrolyte, including screening solvent molecules and the types or concentrations of anions and cations, to regulate the chemical composition and structure of the interfacial double layer, thereby achieving effective control over the properties of the electrode / electrolyte interface. Although this method can significantly improve interfacial stability, its process is complex, it has extremely high selectivity for the electrolyte, and it may introduce new impurities, posing a potential threat to battery performance.

[0006] Surface coating technology: This mainly employs high-precision methods such as atomic layer deposition (ALD) to uniformly coat the surface of the NCM622 cathode with a thin film of alumina (Al2O3), followed by annealing to achieve surface doping and reduce side reactions between residual lithium compounds (such as lithium hydroxide LiOH and lithium carbonate Li2CO3) and the electrolyte. However, this technology not only requires high-precision equipment and complex processes, resulting in high costs, but also presents significant challenges in controlling the uniformity and thickness of the coating layer, directly impacting the stability of battery performance.

[0007] Silicon anodes possess advantages such as high specific capacity, low delithiation potential, good cleanliness, and abundant resources. However, they suffer from severe volume expansion during lithium insertion / extraction, leading to material pulverization, SEI film instability, and electrode structure damage, thus affecting battery performance and lifespan. Material modification primarily addresses silicon anode expansion through nano-sizing, composite materials, pre-lithiation, improved binders, and optimized electrolyte additives. However, simply using electrolyte additives to improve silicon anode expansion can easily result in high interfacial impedance, hindering lithium-ion transport.

[0008] In conclusion, although these technical solutions have shown some potential in improving the electrochemical performance of batteries, their respective limitations still need to be overcome. Summary of the Invention

[0009] To address the aforementioned challenges, this invention provides a lithium-ion battery electrolyte and its low-temperature pulsed formation method. Through the simple and easy-to-implement method of this invention, an SEI with both high ionic conductivity and low impedance toughness can be formed, which suppresses silicon expansion without increasing the battery's internal resistance. This allows the battery to maintain good cycle stability even at high temperatures, thus helping the battery to maintain excellent performance under extreme temperature conditions.

[0010] This invention provides a lithium-ion battery electrolyte, comprising a lithium salt and an additive, wherein the additive comprises triallyl isocyanurate and compound X, wherein compound X is selected from one or a combination of several of sulfate esters and sulfonic acid derivatives such as 4,4'-diethylene sulfate, pentaerythritol bicyclic sulfate, mannitol carbonate sulfate, triethylene sulfate, and malondisulfonic anhydride.

[0011] Preferably, the lithium-ion battery electrolyte comprises anhydrous organic solvents of esters, including but not limited to one or more of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, and γ-butyrolactone.

[0012] The added mass of triallyl isocyanurate and compound X is 0.1-2% of the total mass of the lithium-ion battery electrolyte, respectively.

[0013] Preferably, the additive further includes other functional substances, which include one or more of sulfonate compounds, sulfate compounds, unsaturated cyclic carbonate compounds, borate compounds, trimethylsilyl ester compounds, heterocyclic compounds and nitrile compounds, but does not contain lithium fluoride salt additives;

[0014] The other functional substances are added at a mass of 0.1% to 8% of the total mass of the lithium-ion battery electrolyte;

[0015] The lithium salt is lithium hexafluorophosphate (LiPF6).

[0016] The concentration of the lithium salt in the lithium-ion battery electrolyte is 0.5~2M.

[0017] This invention provides a low-temperature pulsed formation method for lithium-ion batteries, comprising the following steps:

[0018] After the electrolyte is injected, the battery cell is left to stand to allow the electrolyte to wet the electrodes in the battery cell; the electrolyte is the lithium-ion battery electrolyte described above.

[0019] The cells that have undergone static treatment are formed by pulse charging under low temperature conditions of -10~0℃ to obtain the formed lithium-ion battery.

[0020] Preferably, the temperature of the static treatment is 40~50℃ and the time is more than 20 hours; the low temperature condition is -6~-1℃.

[0021] Preferably, the current generated is 0.05~0.1C.

[0022] Preferably, the pulse charging lasts for 20-40 seconds, and the device is left to stand after charging until the upper limit charging voltage is reached.

[0023] Preferably, after charging for 20-40 seconds, the resting time is 20-40 seconds.

[0024] Preferably, the battery cell after electrolyte injection is obtained by the following steps: injecting electrolyte into the battery cell assembled with electrodes and separator, with an injection coefficient of 1Ah / 4~5g, and then sealing it.

[0025] Preferably, after the formation is completed, the gas is released and the battery is sealed; the sealed battery is then placed at 40~50°C and aged for more than 20 hours to obtain an aged lithium-ion battery.

[0026] The three allyl groups of triallyl isocyanurate are more easily broken at reduction potentials than in carbonate solvents, generating free radicals that participate in SEI film formation. The low-temperature pulsed formation method employed in this invention involves the instantaneous activation of allyl group breakage at the negative electrode / electrolyte interface by a pulsed current, leading to free radical polymerization. During the pulse interval, free radical chain growth is terminated, preventing the formation of a dense cross-linked layer. This allows sufficient time for the orderly binding of compound X decomposition products, achieving precise control over the SEI composition and structure. This strategy avoids the formation of a dense cross-linked layer while allowing triallyl isocyanurate polymer fragments to orderly bind with inorganic lithium salts such as sulfide salts, LiF, and Li₂CO₃, forming a high-ionic-conductivity and high-strength interface (i.e., a high-ionic-conductivity and low-impedance toughness SEI).

[0027] The low-temperature pulsed formation method employed in this invention can directly form a LiF-rich CEI interface film "in situ" on the cathode surface. The core innovation of this strategy lies in its ingenious utilization of the decomposition reaction of LiPF6 at -10 to 0°C, making the reaction pathway more inclined to generate LiF rather than other byproducts. Simultaneously, the pulsed charging method employed in this invention significantly suppresses the polarization at the interface, increasing the decomposition time (decomposition amount) of LiPF6 and thus substantially increasing the LiF content in the CEI film. This transformation not only successfully avoids many disadvantages of traditional strategies but also achieves a qualitative leap in the LiF content within the CEI. Experimental data conclusively demonstrate that the CEI constructed using the formation method of this invention exhibits a significantly increased LiF proportion, undoubtedly leading to a significant improvement in the electrochemical performance of the battery.

[0028] In summary, the low-temperature pulsed formation strategy pioneered by this invention can precisely optimize the composition and structure of CEI and SEI. This strategy not only successfully avoids the disadvantages of traditional electrolytes and formation strategies, but also achieves a significant improvement in the electrochemical performance and stability of the battery. Therefore, this strategy will undoubtedly have broad application prospects in the field of lithium-ion batteries. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of pulse charging formation in an application example of the present invention;

[0030] Figure 2 This is a SEM comparison image of NCM622 material formed by low-temperature pulse formation after 1000 cycles, as described in Application Example 4 of this invention.

[0031] Figure 3 This is a comparison of the XPS Li 1s spectra of the CEI film formed by low-temperature pulse formation in Example 4 of this invention;

[0032] Figure 4 This is a comparison diagram of EIS of a negative electrode symmetrical battery in Example 4 of the application of this invention;

[0033] Figure 5 This is a comparison chart of the thickness expansion rate of the battery in Application Example 4 of this invention after 200 cycles;

[0034] Figure 6 This is a comparison chart of the rate performance of NCM622 / Si-C pouch cells using low-temperature pulse and conventional constant-current formation strategies, as shown in Application Example 4 of this invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention.

[0036] This invention first provides a lithium-ion battery electrolyte, comprising a lithium salt and an additive. The additive includes triallyl isocyanurate and compound X. Compound X is selected from one or more of the following sulfate esters and sulfonic acid derivatives: 4,4'-diethylene sulfate, pentaerythritol bicyclic sulfate, mannitol carbonate sulfate, tripolyvinyl sulfate, and malondisulfonic anhydride. Further, compound X is 4,4'-diethylene sulfate.

[0037] In an embodiment of the present invention, the electrolyte is used in a lithium-ion battery, wherein the lithium salt is preferably lithium hexafluorophosphate (LiPF6); the lithium-ion battery electrolyte can not only construct a LiF-rich interfacial film at the positive electrode interface, but also enable compound X and triallyl isocyanurate to effectively act on the negative electrode interface, thereby improving battery performance.

[0038] In addition, the additives also include other functional substances, such as those with film-forming function; the other functional substances include one or more of sulfonate compounds, sulfate compounds, unsaturated cyclic carbonate compounds, borate compounds, trimethylsilyl ester compounds, heterocyclic compounds and nitrile compounds, but do not contain lithium fluoride salt additives.

[0039] The electrolyte described in this embodiment of the invention is a non-aqueous electrolyte, which may include anhydrous organic solvents such as esters, and may further be one or more of the following: ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4-butyrolactone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, ethyl butyrate, and γ-butyrolactone.

[0040] In embodiments of the present invention, the added mass of triallyl isocyanurate and compound X is 0.1% to 2% of the total mass of the lithium-ion battery electrolyte, respectively; the added mass of other functional substances is 0.1% to 8% of the total mass of the lithium-ion battery electrolyte. Specifically, the concentration of the lithium salt in the lithium-ion battery electrolyte is 0.5 to 2 M.

[0041] Based on the electrolyte described above, this invention provides a low-temperature pulsed formation method for lithium-ion batteries, specifically including the following steps:

[0042] Preparation of the example ternary electrolyte system - Preparation of the basic electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EMC:DEC:FEC = 24:6:8:30:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. 1.5% of 1,3-propanesulfonate lactone and 0.5% of vinylene carbonate were added. This served as the basic ternary electrolyte. Triallyl isocyanurate and compound X were then added to obtain the final product.

[0043] The low-temperature pulsed formation method is as follows:

[0044] The battery cell, after being injected with the electrolyte, is left to stand; the battery cell after standing is then formed by pulse charging at a low temperature of -10 to 0°C to obtain a formed lithium-ion battery.

[0045] The formation method provided by this invention can significantly improve the electrochemical performance and cycle stability of lithium-ion batteries.

[0046] The research system of this invention embodiment can be specifically an NCM622 / Si-C soft-pack battery (the active material of the positive electrode is NCM622, and graphite or graphite mixed with 10% silicon carbon is the negative electrode active material), or the positive electrode active material is LCO, NCM523, NCM811, etc. (NCM active materials are mainly composed of three elements: nickel (Ni), cobalt (Co), and manganese (Mn), and the numbers represent the proportion of these three elements).

[0047] In this invention, positive and negative electrode sheets can be prepared separately, and then assembled to form a battery cell. For example, NCM622 and graphite mixed with 10% silicon carbon are used as the positive and negative electrode active materials, respectively. Then, they are mixed with conductive agents and binders in corresponding proportions, and the active materials are uniformly coated onto the current collector through a coating process. The conductive agent is usually one or more of carbon black and carbon nanotubes, and the binder is mainly polyvinylidene fluoride (PVDF), styrene-butadiene latex (SBR), polyacrylic acid (PAA), and sodium carboxymethyl cellulose (CMC). The mass ratio of the active material can be above 85%, specifically between 95% and 98%. The solvent involved can be N-methylpyrrolidone (NMP) or water (generally deionized water).

[0048] Specifically, in embodiments of the present invention, positive and negative electrode sheets and separators (such as conventional polyolefin separators) can be assembled in a stacked manner to form a cell for a soft-pack battery, and aluminum-plastic film can be used to encapsulate it.

[0049] Subsequently, in this embodiment of the invention, the electrolyte is injected into the prepared battery cell. Preferably, the injection volume and rate of the electrolyte are strictly controlled, with an injection coefficient typically of 1Ah / 3.2g, to ensure uniform distribution and sufficient wetting of the electrolyte inside the battery cell, while simultaneously sealing the battery.

[0050] After electrolyte injection, in this embodiment of the invention, the sealed battery cell undergoes a high-temperature static treatment, that is, it is left to stand for a certain period of time under certain high-temperature conditions. The purpose of this step is to allow the electrolyte to fully wet the electrode plates and the separator. The static treatment temperature is preferably 40~50℃, more preferably 45℃; it can be left to stand for 24 hours to allow the electrolyte to fully wet the electrode plates.

[0051] This invention allows a pouch cell battery, after being left to stand at high temperature, to be placed in a low-temperature oven at -10 to 0°C for pulse charging formation. The core advantage of this invention lies in the -6 to -1°C low-temperature pulse formation strategy; after high-temperature standing, the battery can be transferred to a -6°C low-temperature environment for pulse charging formation. Preferably, the pulse charging lasts for 20 to 40 seconds, followed by standing, preferably for 20 to 40 seconds, until the upper limit charging voltage is reached; the formation current is preferably 0.05 to 0.1C, for example, 0.08A. This step, by lowering the temperature to a specific level and using pulse charging, promotes the decomposition of LiPF6 on the positive electrode surface, thereby generating a LiF-rich CEI; and adjusts the composition of the negative electrode interface film to form a high-ionic-conductivity, high-toughness SEI film.

[0052] In the embodiments of the present invention, the pulsed formation scheme combines the characteristics of traditional constant current charging and pulse charging (traditional pulses are generally at the microsecond level). This scheme can effectively charge the battery (e.g., each charging time is preferably 30s), and it has the characteristic of pulse, that is, after charging, the battery can be left to stand for 30s. During the standing period, the polarization phenomenon in the battery formation process can be effectively eliminated, which greatly extends the decomposition time of LiPF6 (but the amount of decomposition is still negligible in essence, but compared with the traditional constant current charging method, the amount of decomposition is greatly improved). Intermittent pulse charging can avoid excessive polymerization of triallyl isocyanurate, thereby ensuring that the content of inorganic components in the CEI film and SEI film can meet the requirements of the battery at high rates.

[0053] This low-temperature pulsed formation strategy cleverly utilizes low-temperature conditions to promote the effective decomposition of trace amounts of LiPF6, while employing pulsed charging to alleviate interfacial polarization and further regulate the electrode interface composition. Specifically, in the CEI layer formed at -6°C, the LiF content is significantly increased, and the negative electrode interface impedance is greatly reduced, resulting in a significant improvement in battery rate performance. Compared to traditional regulation and modification methods, the method proposed in this invention exhibits unparalleled advantages. It not only avoids adverse side reactions but also enables the battery to maintain excellent performance under extreme temperature conditions; the battery also demonstrates excellent cycle stability at high temperatures.

[0054] After formation is complete, the aluminum-plastic film can be cut open and a vacuum pump can be applied to release the gas. In this embodiment of the invention, the battery can undergo a second final sealing process (relative to the first sealing, this is the second encapsulation, which is a conventional operation technique). This step mainly releases the gas generated during the formation stage, and the encapsulation ensures the airtightness of the cell, preventing electrolyte leakage and the intrusion of external impurities.

[0055] In embodiments of the present invention, the formed battery needs to undergo an aging process. The purpose of this step is to allow the battery to undergo sufficient charge-discharge cycles under specific temperature and current conditions to further stabilize the battery's performance and extend its service life. For example, the packaged battery can be placed at 40~50°C for more than 20 hours (e.g., placed at 45°C for high-temperature aging for 24 hours) to obtain an aged lithium-ion battery.

[0056] This invention eliminates the use of lithium fluoride salt additives commonly used in conventional methods during the formation process, thus reducing electrolyte costs. Preferably, this invention promotes the spontaneous decomposition reaction of LiPF6 on the cathode surface by controlling the formation temperature at -6°C, shifting the chemical equilibrium towards the formation of a LiF-rich CEI. This process not only simplifies the preparation procedure but also significantly increases the LiF content in the CEI, showing a significant increase compared to constant-current formation at 25°C. Furthermore, the instantaneous activation of the triallyl isocyanurate by the pulsed current leads to allyl cleavage and free radical polymerization, while the pulse interval terminates free radical chain growth, preventing the formation of a dense cross-linked layer. This allows sufficient time for the orderly binding of compound X decomposition products, achieving precise control of the SEI composition and structure, forming a high-ionic-conductivity and high-strength interface, and suppressing high-temperature interfacial side reactions.

[0057] Thanks to the formation of LiF-rich CEI and low-resistance, high-toughness SEI film on the negative electrode, the prepared battery has significantly improved cycle stability, rate performance and thermal safety at high temperature (45℃).

[0058] In an embodiment of the present invention, the battery performance testing method includes:

[0059] 1) Loop testing

[0060] NCM622 / Si-C:

[0061] Xinwei's test procedure settings: At 25℃ / 45℃, constant current charging at 1C is applied until the charging cutoff voltage is 4.4V, then constant voltage charging is applied until the current drops to 0.05C, and then constant current discharge at 1C is applied until 3.0V to obtain the capacity retention rate of different formulations at 25℃ / 45℃.

[0062] Capacity retention rate = Last week discharge capacity / Initial discharge capacity × 100%.

[0063] LCO / AG:

[0064] Xinwei's test procedure settings: At 25℃ / 45℃, charge at a constant current of 1C to the charging cutoff voltage of 4.55V, then charge at a constant voltage until the current drops to 0.05C, and then discharge at a constant current of 1C to 3.0V to obtain the capacity retention rate of different formulations at 25℃ / 45℃.

[0065] Capacity retention rate = Last week discharge capacity / Initial discharge capacity × 100%.

[0066] 2) Ratio Performance Test

[0067] The battery was tested at different rates: 0.5C, 1C, 1.5C, 2C, 3C, and 5C.

[0068] 3) Thickness expansion rate

[0069] Thickness expansion rate = (Cell thickness in the last week - Initial cell thickness) / Initial discharge capacity × 100%.

[0070] 4) ACR growth rate

[0071] ACR growth rate = (last week cell ACR - initial cell ACR) / initial ACR × 100%.

[0072] 5) Hot box test

[0073] The temperature chamber is heated from the ambient temperature to 130°C at a rate of 5°C / min and maintained at this temperature for 30 minutes before heating is stopped; the battery is considered to have passed if it does not catch fire or explode; after passing the 130°C hot chamber test, the temperature is increased by 1°C each time, and the final failure temperature is recorded.

[0074] To better understand the technical content of this application, specific embodiments are provided below to further illustrate the application. All raw materials involved are commercially available conventional products and are not subject to any special restrictions.

[0075] Preparation of the basic electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EMC:DEC:FEC = 24:6:8:30:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. 1.5% of 1,3-propanesulfonate lactone and 0.5% of vinylene carbonate were added.

[0076] It is used as a ternary basic electrolyte, and then triallyl isocyanurate and compound X are added to obtain the final product.

[0077] Application Example 1

[0078] The battery system is an NCM622 / Si-C pouch cell.

[0079] Electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EMC:DEC:FEC = 24:6:8:30:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. 1.5% of 1,3-propanesulfonate lactone and 0.5% of vinylene carbonate were added.

[0080] Chemical formation process steps:

[0081] 1. Preparation of positive and negative electrode sheets

[0082] NCM622, graphite, and SiC were used as the positive and negative electrode active materials, respectively. These materials were then mixed with conductive agents and binders in corresponding proportions, and a precise coating process was used to uniformly coat the active materials onto the current collector. Details are as follows:

[0083] Preparation of the positive electrode sheet: The positive electrode material NCM622, conductive agent carbon black (Super P), carbon nanotubes (CNTs, in a 5% NMP solution), and binder polyvinylidene fluoride (PVDF, in a 5% NMP solution) were weighed and mixed at a mass ratio of 97:0.7:0.8:1.5. After mixing, an appropriate amount of NMP was added to control the theoretical solid content to 65%. The mixture was homogenized using a homogenizer to obtain the positive electrode slurry. The positive electrode slurry was then uniformly coated onto a 12μm thick aluminum foil. After drying, rolling, and double-sided coating, the surface density was 380 g / m². 2 The compacted density is 3.6 g / cm³. 3 After cutting, a 50 mm × 70 mm positive electrode sheet is obtained.

[0084] Preparation of the negative electrode: The negative electrode material is artificial graphite (specific capacity 355 mAh·g). -1 The following components were mixed: silicon carbide (Si-C), conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC, 1.5% deionized aqueous solution), binder styrene-butadiene rubber (SBR, 48% deionized aqueous solution), and polyacrylic acid (PAA) at a mass ratio of 85:10:0.6:1.5:1.5. After mixing, deionized water was added, and the theoretical solid content was controlled to be 52%. The mixture was homogenized using a homogenizer to obtain a negative electrode slurry. The negative electrode slurry was then uniformly coated onto a 6μm thick copper foil. After drying, rolling, and double-sided coating, the surface density was 164g / m². 2 The compacted density is 1.65 g / cm³. 3 After cutting, a 52 mm × 72 mm negative electrode sheet is obtained. Furthermore, the N / P ratio of the positive and negative electrodes is 1.1.

[0085] Preparation of the diaphragm: A polyethylene diaphragm coated with alumina on one side was used as the isolation membrane and was left to stand in a dry room with a dew point of -35°C for 72 h before use.

[0086] 2. Cell fabrication

[0087] The positive and negative electrode sheets and the separator are stacked to form the cell of a soft-pack battery, and then encapsulated with an aluminum-plastic film.

[0088] 3. Injection

[0089] The electrolyte is injected into the cell at an injection rate of 1 Ah / 3.2 g; the injection volume and speed are strictly controlled to ensure uniform distribution and full wetting of the electrolyte inside the cell. Simultaneously, the battery is sealed.

[0090] 4. High-temperature standing

[0091] After the liquid injection is completed, the sealed battery is left to stand at 45°C for 24 hours.

[0092] 5. -6℃ low-temperature pulse

[0093] After completing the high-temperature settling process, the battery is transferred to a -6°C low-temperature oven for pulse charging formation; such as Figure 1 As shown, the pulsed generation process involves charging for 30 seconds and resting for 30 seconds until the upper limit of the charging voltage is reached, with a generation current of 0.05C.

[0094] Furthermore, the control group batteries were formed using a constant current charging method at 45°C (i.e., using a conventional constant current formation strategy, charging the batteries at a constant current at 45°C, with the battery clamp pressure and other parameters being consistent with general testing).

[0095] 6. Second final seal

[0096] After formation is completed, the battery undergoes a second final sealing process.

[0097] 7. Aging

[0098] The formed battery was placed at 45°C for high-temperature aging for 24 hours.

[0099] Batteries aged using two different formation methods were subjected to cycle performance tests, including 1000 cycles.

[0100] Application Example 2

[0101] The battery system is an NCM622 / Si-C pouch cell (designed capacity of 1.6Ah).

[0102] Electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) are mixed thoroughly at a mass ratio of EC:PC:EMC:DEC:FEC = 24:6:8:30:8. Lithium hexafluorophosphate (LiPF6) is slowly added to the solution at a molar ratio of 1.2 mol / L. 1,3-propanesulfonate lactone is added at a content of 1.5%, vinylene carbonate at a content of 0.5%, and 4,4'-ethylene bisulfate at a content of 0.5%.

[0103] Chemical formation process steps:

[0104] 1. Preparation of positive and negative electrode sheets

[0105] NCM622 and graphite and silicon carbon are used as positive and negative electrode active materials, respectively. They are then mixed with conductive agents and binders in the corresponding proportions, and the active materials are uniformly coated on the current collector through a precise coating process.

[0106] 2. Cell fabrication

[0107] The positive and negative electrode plates and the separator are stacked to form the cell of the soft-pack battery, and then encapsulated with an aluminum-plastic film.

[0108] 3. Injection

[0109] The electrolyte is injected into the cell at an injection rate of 1 Ah / 3.2 g; the injection volume and speed are strictly controlled to ensure uniform distribution and full wetting of the electrolyte inside the cell. Simultaneously, the battery is sealed.

[0110] 4. High-temperature standing

[0111] After the liquid injection is completed, the sealed battery is left to stand at 45°C for 24 hours.

[0112] 5. -6℃ low-temperature pulse

[0113] After completing the high-temperature settling process, the battery is transferred to a -6°C low-temperature oven for pulse charging formation; such as Figure 1 As shown, the pulsed generation process involves charging for 30 seconds and resting for 30 seconds until the upper limit of the charging voltage is reached, with a generation current of 0.05C.

[0114] Furthermore, the control group batteries were formed using a constant current charging method at 45°C (i.e., using a conventional constant current formation strategy, charging the batteries at a constant current at 45°C, with the battery clamp pressure and other parameters being consistent with general testing).

[0115] 6. Second final seal

[0116] After formation is completed, the battery undergoes a second final sealing process.

[0117] 7. Aging

[0118] The formed battery was placed at 45°C for high-temperature aging for 24 hours.

[0119] Batteries aged using two different formation methods were subjected to cycle performance tests, including 1000 cycles.

[0120] Application Example 3

[0121] The battery system is an NCM622 / Si-C pouch cell (designed capacity of 1.6Ah).

[0122] Electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EMC:DEC:FEC = 24:6:8:30:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. 1,3-propanesulfonate lactone was added at a content of 1.5%, vinylene carbonate at a content of 0.5%, and triallyl isocyanurate at a content of 0.5%.

[0123] Process steps:

[0124] 1. Preparation of positive and negative electrode sheets

[0125] NCM622 and graphite and silicon carbon are used as positive and negative electrode active materials, respectively. They are then mixed with conductive agents and binders in the corresponding proportions, and the active materials are uniformly coated on the current collector through a precise coating process.

[0126] 2. Cell fabrication

[0127] The positive and negative electrode plates and the separator are stacked to form the cell of the soft-pack battery, and then encapsulated with an aluminum-plastic film.

[0128] 3. Injection

[0129] The electrolyte is injected into the cell at an injection rate of 1 Ah / 3.2 g; the injection volume and speed are strictly controlled to ensure uniform distribution and full wetting of the electrolyte inside the cell. Simultaneously, the battery is sealed.

[0130] 4. High-temperature standing

[0131] After the liquid injection is completed, the sealed battery is left to stand at 45°C for 24 hours.

[0132] 5. -6℃ low-temperature pulse

[0133] After completing the high-temperature settling process, the battery is transferred to a -6°C low-temperature oven for pulse charging formation; such as Figure 1 As shown, the pulsed generation process involves charging for 30 seconds and resting for 30 seconds until the upper limit of the charging voltage is reached, with a generation current of 0.05C.

[0134] Furthermore, the control group batteries were formed using a constant current charging method at 45°C (i.e., using a conventional constant current formation strategy, charging the batteries at a constant current at 45°C, with the battery clamp pressure and other parameters being consistent with general testing).

[0135] 6. Second final seal

[0136] After formation is completed, the battery undergoes a second final sealing process.

[0137] 7. Aging

[0138] The formed battery was placed at 45°C for high-temperature aging for 24 hours.

[0139] Batteries aged using two different formation methods were subjected to cycle performance tests, including 1000 cycles.

[0140] Application Example 4

[0141] The battery system is an NCM622 / Si-C pouch cell (designed capacity of 1.6Ah).

[0142] Electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EMC:DEC:FEC = 24:6:8:30:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. The content of 1,3-propanesulfonate lactone was 1.5%, the content of vinylene carbonate was 0.5%, the content of 4,4'-vinyl sulfate was 0.5%, and the content of triallyl isocyanurate was 0.3%.

[0143] Process steps:

[0144] 1. Preparation of positive and negative electrode sheets

[0145] NCM622 and graphite and silicon carbon are used as positive and negative electrode active materials, respectively. They are then mixed with conductive agents and binders in the corresponding proportions, and the active materials are uniformly coated on the current collector through a precise coating process.

[0146] 2. Cell fabrication

[0147] The positive and negative electrode plates and the separator are stacked to form the cell of the soft-pack battery, and then encapsulated with an aluminum-plastic film.

[0148] 3. Injection

[0149] The electrolyte is injected into the cell at an injection rate of 1 Ah / 3.2 g; the injection volume and speed are strictly controlled to ensure uniform distribution and full wetting of the electrolyte inside the cell. Simultaneously, the battery is sealed.

[0150] 4. High-temperature standing

[0151] After the liquid injection is completed, the sealed battery is left to stand at 45°C for 24 hours.

[0152] 5. -6℃ low-temperature pulse

[0153] After completing the high-temperature settling process, the battery is transferred to a -6°C low-temperature oven for pulse charging formation; such as Figure 1 As shown, the pulsed generation process involves charging for 30 seconds and resting for 30 seconds until the upper limit of the charging voltage is reached, with a generation current of 0.05C.

[0154] Furthermore, the control group batteries were formed using a constant current charging method at 45°C (i.e., using a conventional constant current formation strategy, charging the batteries at a constant current at 45°C, with the battery clamp pressure and other parameters being consistent with general testing).

[0155] 6. Second final seal

[0156] After formation is completed, the battery undergoes a second final sealing process.

[0157] 7. Aging

[0158] The formed battery was placed at 45°C for high-temperature aging for 24 hours.

[0159] Batteries aged using two different formation methods were subjected to cycle performance tests, including 1000 cycles.

[0160] Application Example 5

[0161] The battery system is an NCM622 / Si-C pouch cell (designed capacity of 1.6Ah).

[0162] Electrolyte: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EMC:DEC:FEC = 24:6:8:30:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. The content of 1,3-propanesulfonate lactone was 1.5%, the content of vinylene carbonate was 0.5%, the content of 4,4'-vinyl sulfate was 1%, and the content of triallyl isocyanurate was 0.3%.

[0163] Process steps:

[0164] 1. Preparation of positive and negative electrode sheets

[0165] NCM622 and graphite and silicon carbon are used as positive and negative electrode active materials, respectively. They are then mixed with conductive agents and binders in the corresponding proportions, and the active materials are uniformly coated on the current collector through a precise coating process.

[0166] 2. Cell fabrication

[0167] The positive and negative electrode plates and the separator are stacked to form the cell of the soft-pack battery, and then encapsulated with an aluminum-plastic film.

[0168] 3. Injection

[0169] The electrolyte is injected into the cell at an injection rate of 1 Ah / 3.2 g; the injection volume and speed are strictly controlled to ensure uniform distribution and full wetting of the electrolyte inside the cell. Simultaneously, the battery is sealed.

[0170] 4. High-temperature standing

[0171] After the liquid injection is completed, the sealed battery is left to stand at 45°C for 24 hours.

[0172] 5. -6℃ low-temperature pulse

[0173] After completing the high-temperature settling process, the battery is transferred to a -6°C low-temperature oven for pulse charging formation; such as Figure 1 As shown, the pulsed generation process involves charging for 30 seconds and resting for 30 seconds until the upper limit of the charging voltage is reached, with a generation current of 0.05C.

[0174] Furthermore, the control group batteries were formed using a constant current charging method at 45°C (i.e., using a conventional constant current formation strategy, charging the batteries at a constant current at 45°C, with the battery clamp pressure and other parameters being consistent with general testing).

[0175] 6. Second final seal

[0176] After formation is completed, the battery undergoes a second final sealing process.

[0177] 7. Aging

[0178] The formed battery was placed at 45°C for high-temperature aging for 24 hours.

[0179] Batteries aged using two different formation methods were subjected to cycle performance tests, including 1000 cycles.

[0180] The cell preparation in Application Examples 2-5 is basically the same as that in Application Example 1.

[0181] Application Example 6

[0182] The battery system is an LCO / AG soft-pack battery (designed capacity of 2.0Ah), and the formation adopts two methods: low-temperature pulse charging formation and high-temperature formation.

[0183] Preparation of LCO system electrolyte

[0184] Electrolyte preparation: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl acetate (EP), propyl propionate (PP), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EP:PP:FEC = 10:10:15:35:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. 1,3-propanesulfonate lactone (3%), hexanetrionitrile (1.5%), adiponitrile (1.5%), and triallyl isocyanurate (0.3%) were also added.

[0185] Application Example 7

[0186] The battery system is an LCO / AG soft-pack battery (designed capacity of 2.0Ah), and the formation adopts two methods: low-temperature pulse charging formation and high-temperature formation.

[0187] Electrolyte preparation: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl acetate (EP), propyl propionate (PP), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EP:PP:FEC = 10:10:15:35:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. 1,3-propanesulfonate lactone (3%), hexanetrionitrile (1.5%), adiponitrile (1.5%), and mannitol sulfate (2%) were also added.

[0188] Application Example 8

[0189] The battery system is an LCO / AG soft-pack battery (designed capacity of 2.0Ah), and the formation adopts two methods: low-temperature pulse charging formation and high-temperature formation.

[0190] Electrolyte preparation: In an argon-filled glove box (moisture < 0.1 ppm, oxygen < 0.1 ppm), ethylene carbonate (EC), propylene carbonate (PC), propyl acetate (EP), propyl propionate (PP), and fluoroethylene carbonate (FEC) were mixed thoroughly at a mass ratio of EC:PC:EP:PP:FEC = 10:10:15:35:8. Lithium hexafluorophosphate (LiPF6) was slowly added to the solution at a molar ratio of 1.2 mol / L. 1,3-propanesulfonate lactone (3%), hexanetrionitrile (1.5%), adiponitrile (1.5%), mannitol sulfate (2%), and triallyl isocyanurate (0.3%) were also added.

[0191] Figure 1 The pulse formation diagram illustrates the process of transforming the original 0.05C constant current charging mode into a pulse charging mode. In this pulse charging mode, the battery capacity is 1.6Ah, and 0.05C corresponds to 0.08A (the specific operation is as follows: first charge at 0.08A for 30 seconds, then rest for 30 seconds; this process is repeated until the battery reaches its upper charging voltage limit. Because the traditional LiPF6 boundary potential range cannot be directly determined, pulse charging is used throughout the initial formation range to ensure sufficient LiPF6 decomposition). The pulse charging method effectively suppresses interface polarization primarily because at the lithium-ion battery interface, the rate of electron gain and loss is significantly faster than the migration rate of lithium ions. This makes it difficult for lithium ions to complete the deintercalation / intercalation process in the cathode material in a timely manner, resulting in excessive "accumulation" of electrons inside the cathode material. This excessive accumulation of electrons causes the battery's open-circuit voltage to rapidly cross the LiPF6 decomposition voltage range. In pulse charging mode, by periodically introducing rest periods, the excessive "accumulation" of electrons in the positive electrode material can be significantly reduced, thereby allowing the open-circuit voltage of the battery to be maintained within the decomposition voltage range of LiPF6 for as long as possible. Therefore, the pulse charging method in this invention can significantly increase the decomposition amount of LiPF6 compared to constant current charging. The allyl group of triallyl isocyanurate, which is instantaneously activated by the pulse current on the negative electrode side, breaks down and undergoes free radical polymerization. During the pulse interval, the growth of free radical chains is terminated, avoiding the formation of a dense cross-linked layer. This allows sufficient time for the orderly binding of the decomposition products of compound X, achieving precise control of the SEI composition and structure, and forming an interface with high ionic conductivity and high strength.

[0192] Figure 2The images are scanning electron microscope (SEM) images of the cross-section of NCM622 material after formation in Example 4. (a) shows that the NCM622 material with low-temperature pulse formation strategy still maintains its structural integrity after 1000 cycles. (b) shows that the NCM622 material with 45°C constant current formation strategy has crystal breakage after 1000 cycles. The broken crystals cause the CEI film to rupture, so the new interface (generated by the breakage) of the material will come into contact with the electrolyte again. During the cycle, side reactions will occur continuously, resulting in rapid capacity decay of the battery.

[0193] Figure 3 The XPS Li 1s spectrum of the CEI film after formation in Example 4 is shown; a low-temperature pulsed formation strategy (such as...) was employed. Figure 3 (a) shows that, compared to the 45°C constant flow formation method (as shown in the image), Figure 3 As shown in (b), the LiF content on the surface of the NCM622 material was significantly increased. This increase directly promoted a leap in CEI performance, effectively curbing crystal fragmentation and greatly extending the cycle life of the battery. It is worth noting that LiF itself possesses excellent lithium-ion transport efficiency and low electronic conductivity. Therefore, the LiF-rich CEI film not only significantly improves the lithium-ion transport rate, thereby optimizing the battery's rate performance, but also effectively prevents interfacial side reactions, further consolidating and improving the battery's cycle stability and lifespan.

[0194] Figure 4 To apply the symmetrical battery impedance diagram of the negative electrode interface after formation in Example 4, compared with the traditional formation method, the composition of the negative electrode SEI film can be better controlled, forming an organic-inorganic composite high-strength electrode-electrolyte interface film, reducing film impedance; and suppressing the expansion of silicon in the cyclic negative electrode (e.g., Figure 5 (As shown), to reduce the side reactions caused by SEI rupture.

[0195] Figure 6 This is a comparison chart of the rate performance of pouch cells using low-temperature pulse and 45°C constant current formation strategies, as shown in Application Example 4; based on... Figure 6 Compared to batteries that use a 45℃ constant current formation method, batteries using low-temperature pulse formation technology show a significant improvement and optimization in rate performance.

[0196] Tables 1 and 2 show the cycle performance of NCM622 / Si-C and LCO / AG cells with different formation processes and electrolyte formulations, respectively.

[0197] Table 1 NCM622 / Si-C Test Data

[0198]

[0199] Table 2 LCO / AG Test Data

[0200]

[0201] Under both ambient and high-temperature environments, the electrolyte solution of this invention employs a low-temperature pulsed formation strategy, resulting in excellent battery cycle stability. This strategy promotes the effective decomposition of LiPF6 by combining pulsed charging at a low temperature of -6°C, thereby generating a LiF-rich CEI layer on the positive electrode surface. On the negative electrode side, the pulsed current instantaneously activates the allyl group of triallyl isocyanurate, leading to free radical polymerization. During the pulse interval, free radical chain growth is terminated, preventing the formation of a dense cross-linked layer. This allows sufficient time for the orderly binding of compound X decomposition products, achieving precise control over the SEI composition and structure, forming a high-ionic-conductivity and high-strength interface. The stable interface on both the positive and negative electrode sides reduces side reactions at the electrolyte-electrode interface during cycling, especially at high temperatures, significantly improving the battery's electrochemical performance and cycle stability.

[0202] Table 2 shows the thermal test data of the LCO / AG system. The data indicates that the combination of compound X and triallyl isocyanurate improves interfacial thermal stability, reduces high-temperature failure, and enhances safety performance. Further employing low-temperature pulse charging formation increases the LiF content at the positive electrode interface and helps compound X and triallyl isocyanurate construct a high-ionic-conductivity, high-strength negative electrode SEI film at the negative electrode interface, suppressing the dissolution of the interfacial film at high temperatures. This reduces side reactions in the electrolyte at high temperatures, and the lower impedance mitigates heat generation caused by increased polarization during high-temperature cycling, further improving the battery's thermal runaway temperature.

[0203] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium-ion battery electrolyte, comprising a lithium salt and additives, characterized in that, The additive includes triallyl isocyanurate and compound X, wherein compound X is selected from one or a combination of several sulfate esters and sulfonic acid derivatives.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The compound X is selected from one or more of 4,4'-diethylene sulfate, pentaerythritol bicyclic sulfate, mannitol carbonate sulfate, triethylene sulfate, and propylene disulfonic anhydride; The lithium-ion battery electrolyte includes an anhydrous organic solvent of esters. The added mass of triallyl isocyanurate and compound X is 0.1-2% of the total mass of the lithium-ion battery electrolyte, respectively.

3. The lithium-ion battery electrolyte according to claim 1 or 2, characterized in that, The additive also includes other functional substances, which include one or more of sulfonates, sulfates, unsaturated cyclic carbonates, borates, trimethylsilyl esters, heterocyclic compounds, and nitrile compounds, but does not contain lithium fluoride salt additives. The lithium salt is lithium hexafluorophosphate, and its concentration in the lithium-ion battery electrolyte is 0.5~2M.

4. A low-temperature pulsed formation method for lithium-ion batteries, characterized in that, Includes the following steps: The battery cell after being injected with electrolyte is left to stand, allowing the electrolyte to wet the electrodes in the battery cell; the electrolyte is the lithium-ion battery electrolyte according to any one of claims 1-3; The cells that have undergone static treatment are formed by pulse charging under low temperature conditions of -10~0℃ to obtain the formed lithium-ion battery.

5. The low-temperature pulsed formation method according to claim 4, characterized in that, The static treatment is carried out at a temperature of 40~50℃ for a time of more than 20 hours; the low temperature condition is -6~-1℃.

6. The low-temperature pulsed formation method according to any one of claims 4-5, characterized in that, The current generated is 0.05~0.1C.

7. The low-temperature pulsed formation method according to claim 6, characterized in that, The pulse charging process involves charging for 20-40 seconds, followed by resting until the upper limit charging voltage is reached.

8. The low-temperature pulsed formation method according to claim 7, characterized in that, After charging for 20-40 seconds, the resting time is 20-40 seconds.

9. The low-temperature pulsed formation method according to claim 4, characterized in that, The battery cell after electrolyte injection is obtained by the following steps: injecting electrolyte into the battery cell with assembled electrodes and separator, with an injection coefficient of 1Ah / 4~5g, and then sealing it.

10. The low-temperature pulsed formation method according to claim 4, characterized in that, After the formation process is completed, the gas is released and the battery is sealed. The sealed battery is then placed at 40-50°C and aged for more than 20 hours to obtain an aged lithium-ion battery.

Images