Manufacturing method of low-temperature lithium ion battery

Abstract

The invention relates to the technical field of lithium ion battery treatment, in particular to a manufacturing method of a low-temperature lithium ion battery, the low-temperature lithium ion battery comprises a positive plate, a negative plate, a diaphragm and an electrolyte; the positive plate comprises a positive current collector and a positive material coated on the positive current collector, the positive material comprises a positive active material, a binder, a conductive agent and lithium titanium aluminum phosphate, and the negative plate comprises a negative active material, sodium carboxymethyl cellulose, a binder, a conductive agent and a copper foil. The LATP particles are added into the positive electrode material and the diaphragm is coated with the LATP coating, so that the charge transfer impedance at low temperature is remarkably reduced, SP, CNT, graphene, LATP and other conductive agents are mixed in the positive electrode, SBR and PAA mixed binder with excellent low-temperature performance are adopted in the negative electrode, the low-temperature performance is improved, and the rate discharge capacity and long cycle stability of the battery are also improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery processing technology, specifically a method for manufacturing a low-temperature lithium-ion battery. Background Technology

[0002] With the rapid development of portable electronic devices, power tools, energy storage systems, and special equipment (such as cold chain logistics, military navigation, and drones), higher demands are being placed on the performance of power supplies over a wide temperature range, especially in low-temperature environments. Lithium-ion batteries are widely used due to their advantages such as high energy density and long cycle life. However, in low-temperature environments (such as below 0°C), the electrolyte viscosity of conventional lithium-ion batteries increases, the ionic conductivity decreases, and the charge transfer impedance at the electrode interface increases significantly, leading to a sharp decline in battery discharge capacity and even failure to function properly.

[0003] Existing technologies typically improve low-temperature performance by modifying positive and negative electrode materials, applying composite separators, or designing specialized electrolytes. For example, optimizing conductive agents to construct highly efficient conductive networks reduces electrode impedance. However, the discharge efficiency of these methods at extremely low temperatures (such as -40°C) still needs improvement, making it difficult to meet the growing demands of applications in cold environments. Therefore, developing a lithium-ion battery that maintains good cycle life while exhibiting excellent low-temperature performance (especially maintaining high capacity retention at -40°C) has significant technological and market value. Summary of the Invention

[0004] The purpose of this invention is to provide a method for manufacturing a low-temperature lithium-ion battery, in order to solve the problem that the existing technologies mentioned in the background art, which usually improve low-temperature performance by improving positive and negative electrode materials, applying composite membranes, or designing special electrolytes, still have insufficient discharge efficiency under extremely low temperature conditions, making it difficult to meet the growing demand for applications in cold environments.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for manufacturing a low-temperature lithium-ion battery, comprising a low-temperature lithium-ion battery, The low-temperature lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; The positive electrode sheet includes a positive current collector and a positive electrode material coated on the positive current collector. The positive electrode material includes a positive electrode active material, a binder, a conductive agent, and lithium aluminum titanium phosphate (LATP), with the following mass ratios: 95%–97%; 1.0–1.5%; 1%–1.5%; 1–3%. The negative electrode sheet comprises a negative electrode active material, sodium carboxymethyl cellulose (CMC), a binder, a conductive agent, and copper foil. The mass ratio of the negative electrode active material, the sodium carboxymethyl cellulose (CMC), the binder, and the conductive agent is 94–95%, 1.2–1.5%, 1.5–2.0%, and 2–2.5%, respectively.

[0006] Preferably, the manufacturing process of the low-temperature lithium-ion battery is as follows: ① Preparation of the positive electrode sheet: The positive electrode active material, binder, conductive agent, lithium aluminum titanium phosphate (LATP), and solvent are mixed evenly in the following mass ratios: 95%–97%; 0.5%–1.5%; 0.5%–1.5%; 1%–3%; 25%–35% to obtain a positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector, and after drying and rolling, a positive electrode sheet is obtained. ② Preparation of negative electrode sheet: The negative electrode active material, sodium carboxymethyl cellulose (CMC), conductive agent, binder and solvent are mixed evenly in the following mass ratios: 94-95%; 1.2-1.5%; 2-2.5%; 1.5-2.0%; 120-130% to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on the surface of copper foil, dried and rolled to obtain the negative electrode sheet. ③ Battery assembly: The positive electrode obtained in step ① and the negative electrode obtained in step ② are assembled with a lithium aluminum titanium phosphate (LATP) coated modified separator to obtain a battery cell. Low-temperature electrolyte is injected, and after formation and capacity testing, a low-temperature lithium-ion battery is obtained.

[0007] Preferably, the positive current collector is made of aluminum foil.

[0008] Preferably, the positive electrode active material is lithium cobalt oxide or a ternary material, the magnetic material content of the positive electrode active material is ≤30 ppb, the moisture content is ≤300 ppm, the binder is polyvinylidene fluoride (PVDF) with a molecular weight of not less than 1.1 million, and the conductive agent is a mixture of at least two selected from conductive carbon fiber (VGCF), carbon nanotubes (CNT), conductive carbon black (SP), and lithium aluminum titanium phosphate (LATP).

[0009] Preferably, the negative electrode active material is high-ratio artificial graphite, the binder is one or both of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA), and the conductive agent is one or more selected from carbon nanotubes (CNT), conductive carbon fiber (VGCF), conductive carbon black, conductive graphite, acetylene black, and graphene composite conductive agent.

[0010] Preferably, the separator is a polyolefin separator coated with lithium aluminum titanium phosphate (LATP) on one or both sides, with a coating thickness of 2-3 micrometers, and the conductivity of the low-temperature electrolyte is not less than 10.0 ms / cm.

[0011] Preferably, the welding tabs, winding, packaging, and liquid injection processes of the low-temperature lithium-ion battery all adopt common processes in this industry.

[0012] Compared with the prior art, the beneficial effects of this invention are as follows: By synergistically adding LATP particles to the positive electrode material and coating the separator with an LATP coating, an additional fast lithium-ion transport channel is constructed. As a fast lithium-ion conductor, LATP has extremely high ionic conductivity at both room temperature and low temperature, which can effectively optimize the solid-liquid interface characteristics between the positive electrode material and the liquid electrolyte, and significantly reduce the charge transfer impedance at low temperature. The positive electrode uses high molecular weight PVDF, which can achieve excellent bonding effect with a small amount. By mixing and using multiple conductive agents such as SP, CNT, graphene and LATP, a highly efficient three-dimensional electronic conductive network is constructed. The negative electrode uses a mixed binder of SBR and PAA with excellent low-temperature performance, which enhances the mechanical stability of the electrode and the interfacial compatibility at low temperature. The low magnetic content of the positive and negative electrode materials also reduces the negative impact of impurities on electrochemical performance, which not only improves low-temperature performance, but also enhances the rate discharge capability and long-cycle stability of the battery. In addition to adjustments in slurry preparation and separator selection, the remaining processes (such as coating, rolling, winding, encapsulation, liquid injection, etc.) all adopt industry-standard processes, which are easy to achieve large-scale production. Detailed Implementation

[0013] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] One embodiment of the present invention provides a method for manufacturing a low-temperature lithium-ion battery, comprising a low-temperature lithium-ion battery. Low-temperature lithium-ion batteries consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode sheet includes a positive current collector and a positive electrode material coated on the current collector. The positive electrode material includes a positive electrode active material, a binder, a conductive agent, and lithium aluminum titanium phosphate (LATP), with the following mass ratios: 95%–97%; 1.0–1.5%; 1%–1.5%; 1–3%. The negative electrode sheet includes a negative electrode active material, sodium carboxymethyl cellulose (CMC), binder, conductive agent and copper foil. The mass ratio of the negative electrode active material, sodium carboxymethyl cellulose (CMC), binder and conductive agent is 94-95%; 1.2-1.5%; 1.5-2.0%; 2-2.5%.

[0015] Furthermore, the manufacturing process of low-temperature lithium-ion batteries is as follows: ① Preparation of the positive electrode sheet: The positive electrode active material, binder, conductive agent, lithium aluminum titanium phosphate (LATP), and solvent are mixed evenly in the following mass ratios: 95%–97%; 0.5%–1.5%; 0.5%–1.5%; 1%–3%; 25%–35% to obtain a positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector, and after drying and rolling, a positive electrode sheet is obtained. ② Preparation of negative electrode sheet: The negative electrode active material, sodium carboxymethyl cellulose (CMC), conductive agent, binder and solvent are mixed evenly in the following mass ratios: 94-95%; 1.2-1.5%; 2-2.5%; 1.5-2.0%; 120-130% to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on the surface of copper foil, dried and rolled to obtain the negative electrode sheet. ③ Battery assembly: The positive electrode obtained in step ① and the negative electrode obtained in step ② are assembled with a lithium aluminum titanium phosphate (LATP) coated modified separator to obtain a battery cell. Low-temperature electrolyte is injected, and after formation and capacity testing, a low-temperature lithium-ion battery is obtained.

[0016] Furthermore, the positive electrode current collector is made of aluminum foil. Aluminum foil has excellent electrochemical stability and corrosion resistance at the positive potential of lithium-ion batteries. It is also lightweight, has good conductivity, and is moderately priced. As a mechanical support for the positive electrode active material coating and a current collection channel for electron conduction, it efficiently transfers current from the external circuit to the active material particles.

[0017] Furthermore, the positive electrode active material is lithium cobalt oxide or a ternary material, and the magnetic material content of the positive electrode active material is ≤30 ppb, and the moisture content is ≤300%. To minimize side reactions, self-discharge, and safety hazards (such as gas generation) caused by impurities, the purity and electrochemical stability are ensured. The binder is polyvinylidene fluoride (PVDF) with a molecular weight of not less than 1.1 million. Its longer polymer chain provides stronger adhesion and better flexibility with a smaller addition amount, which helps maintain the integrity of the electrode structure during cycling. At the same time, it reduces the proportion of inactive materials and improves energy density. The conductive agent is a mixture of at least two of conductive carbon fiber (VGCF), carbon nanotubes (CNT), conductive carbon black (SP), and lithium aluminum titanium phosphate (LATP). Conductive carbon black (SP) provides point-to-point basic contact. Carbon nanotubes (CNT) and conductive carbon fiber (VGCF) act as conductive bridges, connecting active particles over long distances and significantly reducing the overall impedance of the electrode. Lithium aluminum titanium phosphate (LATP) acts as an inorganic binder to enhance the structure, establishing additional high-speed lithium-ion transport channels between active particles, optimizing ion transport at the solid-liquid interface, and significantly reducing charge transfer impedance at low temperatures. This is one of the core innovations for improving rate performance and low-temperature performance.

[0018] Furthermore, the negative electrode active material is high-rate artificial graphite, and the binder is one or both of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA). While ensuring the electrode structure is robust, it adapts to the volume change of the material at low temperatures and maintains good electrode integrity. The conductive agent is one or more selected from carbon nanotubes (CNT), conductive carbon fiber (VGCF), conductive carbon black, conductive graphite, acetylene black, and graphene composite conductive agent. Its function is similar to that of the positive electrode, constructing the electronic conductive network of the negative electrode, ensuring unobstructed electron transport between graphite particles, and supporting high-rate charging and discharging. The combined use of multiple conductive agents can form a more complete and efficient conductive system.

[0019] Furthermore, the separator is a polyolefin separator coated with lithium aluminum titanium phosphate (LATP) on one or both sides, with a coating thickness of 2-3 micrometers. This improves the separator's heat resistance and electrolyte wettability, and allows it to work synergistically with the LATP particles in the positive electrode to further reduce the ion transport resistance of the entire battery system. Especially at low temperatures, it effectively alleviates the performance degradation caused by the decrease in electrolyte ionic conductivity. The conductivity of the low-temperature electrolyte is not less than 10.0 ms / cm, ensuring that sufficient ion migration ability can still be maintained at even lower temperatures, and forming a stable interface film with the electrode material.

[0020] Furthermore, the welding of tabs, winding, packaging, and liquid injection processes for low-temperature lithium-ion batteries all adopt industry-standard processes. Adopting standard processes means that existing mature lithium-ion battery production lines can be used for manufacturing without huge equipment investments, which greatly reduces the industrialization threshold and technical risks, and is conducive to the rapid promotion and application of the technology.

[0021] Working principle: The following uses the square soft-pack lithium-ion battery model 483035-400mAh as an example. Step 1: Preparation of the positive electrode: The positive electrode active material lithium cobalt oxide, binder (PVDF with a molecular weight of 1.1 million) and conductive agent are mixed in N-methylpyrrolidone solvent at a mass ratio of 96.5%; 1.1%; 0.7% (CNT + graphene mixture); 0.7% (conductive carbon SP) and dispersed evenly to obtain a positive electrode slurry. The solid content of the slurry is controlled at about 70%. The obtained slurry is evenly coated on both sides of aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0022] Step 2: Negative electrode preparation: The negative electrode active material artificial graphite, thickener CMC, binder SBR, and conductive agent conductive carbon black were mixed in deionized water solvent at a mass ratio of 94.6%, 1.4%, 1.5%, and 2.5% respectively, and dispersed evenly to obtain a negative electrode slurry. The obtained slurry was evenly coated on both sides of copper foil, dried, and cold-pressed with rollers. The compaction density was controlled at 1.55 g / cm³ to obtain a negative electrode sheet with an areal density controlled at 15.8 mg / cm².

[0023] Step 3: Battery Assembly The positive electrode, negative electrode, and LATP double-sided coated modified separator are wound into a core. The core is vacuum baked to remove moisture. The baked core is then placed into an aluminum-plastic film shell, and the tabs are welded and heat-sealed. A low-temperature electrolyte with a conductivity of 10.5 mS / cm (the solvent is a mixed system of ethylene carbonate / ethyl methyl carbonate / dimethyl carbonate, and the lithium salt is LiPF6) is injected. Standardized formation and capacity testing processes are performed to obtain a square soft-pack lithium-ion battery with a rated capacity of 400mAh.

[0024] The following is a description of the testing methods and comparative examples: Example

[0025] The battery cell was obtained by coating the modified diaphragm with LATP, injecting electrolyte, forming, and grading. Example

[0026] The positive electrode material was modified with 1.0 wt% LATP, and the membrane was coated with LATP. After liquid injection, formation, and capacity testing, a battery cell was obtained. Example

[0027] The positive electrode material is modified with 2.0 wt% LATP, and the membrane is coated with LATP, followed by liquid injection, formation, and capacity testing to obtain the battery cell. Example

[0028] The positive electrode material is modified with 3.0 wt% LATP, and the membrane is coated with LATP, followed by liquid injection, formation, and capacity testing to obtain the battery cell.

[0029] Comparative Example The comparative example had no LATP added to the positive electrode and the diaphragm was not coated with LATP, but everything else was the same as in the example.

[0030] Test method: For each scheme, five batteries were numbered and subjected to the following conditions at 25°C: constant current and constant voltage charging at 0.5C to 4.2V, cutoff at 0.02C; discharge at 0.5C to 3.0V and record the capacity C1. 0.5C constant current and constant voltage charging to 4.2V, 0.02C cutoff; 1C discharge to 3.0V to record capacity C2; The capacitor was charged to 4.2V at a constant current and constant voltage of 0.5C at 25℃ and cut off at 0.02C. After being left to stand at -20℃ for 4 hours, it was discharged to 3.0V at 0.5C, and the discharge capacity C3 was recorded.

[0031] The capacitor was charged to 4.2V at a constant current and constant voltage of 0.5C at 25℃ and cut off at 0.02C. After being placed at -40℃ for 4 hours, it was discharged to 3.0V at 0.5C, and the discharge capacity C4 was recorded.

[0032] At 25℃, the capacitor is charged at a constant current and constant voltage of 0.5C to 4.2V, cut off at 0.02C, and discharged at 0.5C to 3.0V. This cycle is repeated for 500 cycles, and the capacity C500 on the 500th cycle is recorded.

[0033] The following table shows the test results for the examples and comparative examples: Table 1.1 Capacity test data at room temperature (25℃)

[0034] Table 1.2 Discharge efficiency at -20℃ and 0.5C

[0035] Table 1.3 Discharge efficiency at -40℃ and 0.5C

[0036] Table 1.4 500 charge-discharge cycles at 0.5C

[0037] According to the data in Tables 1.1 to 1.4, all four examples and comparative batteries exhibited excellent low-temperature discharge performance. Specifically, Example 1, which used a LATP-modified separator, showed a significant improvement in low-temperature discharge performance and cycle performance compared to the comparative example. Furthermore, the data from Examples 2 to 4 indicate that adding LATP to the cathode material can further improve the low-temperature discharge performance of the battery. Comparative analysis shows that, based on the use of an LATP-modified separator, the improvement effect on performance is comparable when the amount of LATP added to the cathode material is 2wt% and 3wt%. The design scheme of this invention achieves excellent low-temperature performance of the battery through synergistic optimization of the positive and negative electrode design and separator modification.

[0038] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for manufacturing a low-temperature lithium-ion battery, characterized in that, Including low-temperature lithium-ion batteries, The low-temperature lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; The positive electrode sheet includes a positive current collector and a positive electrode material coated on the positive current collector. The positive electrode material includes a positive electrode active material, a binder, a conductive agent, and lithium aluminum titanium phosphate (LATP), with the following mass ratios: 95%–97%; 1.0–1.5%; 1%–1.5%; 1–3%. The negative electrode sheet comprises a negative electrode active material, sodium carboxymethyl cellulose (CMC), a binder, a conductive agent, and copper foil. The mass ratio of the negative electrode active material, the sodium carboxymethyl cellulose (CMC), the binder, and the conductive agent is 94–95%, 1.2–1.5%, 1.5–2.0%, and 2–2.5%, respectively.

2. The method for manufacturing a low-temperature lithium-ion battery according to claim 1, characterized in that, The manufacturing process of the low-temperature lithium-ion battery is as follows: ① Preparation of the positive electrode sheet: The positive electrode active material, binder, conductive agent, lithium aluminum titanium phosphate (LATP), and solvent are mixed evenly in the following mass ratios: 95%–97%; 0.5%–1.5%; 0.5%–1.5%; 1%–3%; 25%–35% to obtain a positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector, and after drying and rolling, a positive electrode sheet is obtained. ② Preparation of negative electrode sheet: The negative electrode active material, sodium carboxymethyl cellulose (CMC), conductive agent, binder and solvent are mixed evenly in the following mass ratios: 94-95%; 1.2-1.5%; 2-2.5%; 1.5-2.0%; 120-130% to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on the surface of copper foil, dried and rolled to obtain the negative electrode sheet. ③ Battery assembly: The positive electrode obtained in step ① and the negative electrode obtained in step ② are assembled with a lithium aluminum titanium phosphate (LATP) coated modified separator to obtain a battery cell. Low-temperature electrolyte is injected, and after formation and capacity testing, a low-temperature lithium-ion battery is obtained.

3. The method for manufacturing a low-temperature lithium-ion battery according to claim 1, characterized in that, The positive current collector is made of aluminum foil.

4. The method for manufacturing a low-temperature lithium-ion battery according to claim 1, characterized in that, The positive electrode active material is lithium cobalt oxide or a ternary material, the magnetic material content of the positive electrode active material is ≤30 ppb, the moisture content is ≤300 ppm, the binder is polyvinylidene fluoride (PVDF) with a molecular weight of not less than 1.1 million, and the conductive agent is a mixture of at least two selected from conductive carbon fiber (VGCF), carbon nanotubes (CNT), conductive carbon black (SP), and lithium aluminum titanium phosphate (LATP).

5. The method for manufacturing a low-temperature lithium-ion battery according to claim 1, characterized in that, The negative electrode active material is high-ratio artificial graphite, the binder is one or both of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA), and the conductive agent is one or more selected from carbon nanotubes (CNT), conductive carbon fibers (VGCF), conductive carbon black, conductive graphite, acetylene black, and graphene composite conductive agents.

6. The method for manufacturing a low-temperature lithium-ion battery according to claim 1, characterized in that, The diaphragm is a polyolefin diaphragm coated with lithium aluminum titanium phosphate (LATP) on one or both sides, with a coating thickness of 2-3 micrometers, and the conductivity of the low-temperature electrolyte is not less than 10.0 ms / cm.

7. The method for manufacturing a low-temperature lithium-ion battery according to claim 1, characterized in that, The welding of tabs, winding, packaging, and electrolyte injection processes for the low-temperature lithium-ion battery all adopt common processes in this industry.

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