A method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range

Abstract

The present invention relates to the field of lithium-ion battery manufacturing, and specifically to a method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range. The method includes positive electrode preparation, negative electrode preparation, and composite manganese-based lithium battery preparation, wherein lithium manganese oxide, lithium iron manganese phosphate, a conductive agent, a binder, etc. are used to sequentially prepare a positive electrode slurry, a positive electrode coil, and a positive electrode sheet, and artificial graphite, a thickener, a conductive agent, a binder, etc. are used to sequentially prepare a negative electrode slurry, a negative electrode coil, and a negative electrode sheet; a core package consisting of two positive electrode sheets, a negative electrode sheet, and a diaphragm is continuously ultrasonically welded and loaded into an aluminum shell, and a cover plate and an aluminum shell are laser welded to melt into a whole. After liquid injection, formation, and aging, a composite manganese-based lithium battery suitable for use in a wide temperature range is obtained, which can continuously and stably operate in a wide temperature range of ‑40°C to 55°C, solving the problems of low energy density and poor low-temperature performance of lithium iron phosphate batteries, poor safety of ternary lithium batteries that cannot be punctured, and poor cycle performance of lithium manganese oxide batteries.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion battery manufacturing, and in particular to a method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range. Background Art

[0002] In recent years, lithium-ion batteries have been continuously upgraded, with gradually improving electrical performance and enhanced environmental adaptability. They have been widely used in fields such as machining, automobile manufacturing, electronics production, and the new energy industry. The current mainstream lithium batteries in the market include lithium iron phosphate batteries with artificial graphite as the anode, ternary lithium batteries, lithium manganese oxide batteries, and lithium titanate batteries. Currently, these batteries suffer from the following issues: Lithium iron phosphate batteries with artificial graphite as the anode have good cycle life and safety performance, but low energy density and poor low-temperature discharge performance; ternary lithium batteries with artificial graphite as the anode have high energy density and good low-temperature discharge performance, but poor cycle life and safety performance; lithium manganese oxide batteries with artificial graphite as the anode have high energy density, good low-temperature discharge performance and safety, but poor cycle life; and lithium titanate batteries with lithium titanate as the anode have good cycle life and low-temperature charge and discharge performance, but poor energy density and cost performance. Due to the cold winters in northern my country, the discharge energy of lithium batteries decreases sharply, seriously hindering the promotion and use of new energy vehicles in Northeast and Northwest my country. Currently, conventional lithium iron phosphate batteries discharge energy at -20°C equivalent to 36% of that at 25°C, significantly reducing the range of electric vehicles. Given these challenges, a method for preparing lithium batteries with comprehensive temperature adaptability is urgently needed. Summary of the Invention

[0003] In view of the current disadvantages of poor low-temperature performance of lithium iron phosphate, poor safety performance of ternary lithium batteries that cannot pass the needle penetration test, and poor cycle performance of lithium manganese oxide batteries, the purpose of the present invention is to provide a preparation method for a composite manganese-based lithium battery that is suitable for use in a wide temperature range of -40°C to 55°C and has stable and reliable performance while taking into account safety performance. By composite blending and optimizing the ratio of the positive electrode main materials lithium manganese oxide and lithium iron manganese phosphate, the problems of poor low-temperature performance and low energy density of existing lithium iron phosphate positive electrode materials and poor safety of ternary positive electrode materials are solved.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range is characterized by the following steps:

[0006] Step 1: Positive electrode preparation

[0007] (1) First, according to the mass ratio of lithium manganese oxide (LiMn2O4): lithium iron manganese phosphate (LiMn 0.6 Fe0.4 PO4): conductive agent: binder = 74-78:18-22:2-4:1.6-2, added to the stirring tank; then added organic solvent, kneaded to make the solid content of the slurry in the stirring tank 70-80wt%, while starting the stirring speed of 30-42rad / min and the dispersion speed of 2200-3200rad / min, lasting for 2-3h; continued to add organic solvent to make the solid content of the slurry in the stirring tank 65-75wt%, while starting the stirring speed of 30-42rad / min and the dispersion speed of 2200-3200rad / min, lasting for 0.5-2 hours; finally dispersed evenly to obtain a positive electrode slurry with a viscosity of 7000-8000mPa·s;

[0008] (2) The positive electrode slurry is filtered through a 120-150 mesh filter. After filtering, the surface density of the positive electrode slurry is 18-24.5 mg / cm2 in a continuous coating manner. 2 , double-sided density is 36~49mg / cm 2 The positive electrode coil is uniformly coated on both sides of the positive electrode current collector, the positive electrode current collector is a carbon-coated aluminum foil, and the thickness of the carbon-coated aluminum foil is 12 to 18 μm, to prepare a positive electrode coil;

[0009] (3) The positive electrode coil is rolled using a roller mill at a pressure of 2.6 to 2.9 g / cm 3 The positive electrode coils are rolled to a compaction density of 1000 nm and cut into two equal widths in the middle using a slitting machine. A metal die-cutting machine is used to punch out the positive electrode sheets from each positive electrode coil to obtain positive electrode sheets with appropriate size and shape.

[0010] Step 2: Anode preparation

[0011] (1) First, artificial graphite, thickener, and conductive agent are added to a stirring tank according to the mass ratio of artificial graphite: thickener: conductive agent: binder = 94-95.5:1.2-1.5:1.5-1.9:1.5-2; then solvent is added and mixed to make the solid content of the slurry in the stirring tank 45-50wt%, and at the same time, the stirring speed is turned on at 28-32rad / min and the dispersion speed is turned on at 2200-3200rad / min for 2-3h; the solvent is continued to be added, The solid content of the slurry in the stirred tank is set to 40-46 wt %, and the stirring speed is set to 28-32 rad / min and the dispersion speed is set to 2200-3200 rad / min for 0.5-2 hours. Finally, the binder is added, the stirring speed is adjusted to 10-30 rad / min, and the dispersion speed is adjusted to 1000-2000 rad / min for 0.5-1 hour, and the slurry is uniformly dispersed to obtain a negative electrode slurry with a viscosity of 3000-5000 mPa·s.

[0012] (2) The negative electrode slurry is passed through a 150-200 mesh sieve, filtered, and then coated. The single-side density is 8-10.5 mg / cm 2 , double-sided density is 16~21mg / cm 2 The slurry is evenly coated on both sides of the negative electrode current collector, which is a copper foil with a thickness of 6 to 8 μm, to form a negative electrode coil;

[0013] (3) The above negative electrode coil is rolled by a roller mill to a pressure of 1.4 to 1.5 g / cm 3 The compaction density is rolled and the negative electrode sheet is punched out using a full-page die-cutting laser die to produce negative electrode sheets with suitable size and shape;

[0014] The third step is the preparation of composite manganese-based lithium batteries

[0015] (1) Using a polypropylene diaphragm to insulate and separate the positive and negative electrode sheets, a laminating machine is used to perform a "Z"-shaped lamination and gluing process to form a core package, the positive and negative tabs of the core package are welded together with the positive and negative electrode connecting pieces of the cover plate using an ultrasonic welding machine, a stop frame is installed, and the core package is wrapped and protected with an outer vest, which is then placed in an aluminum shell, and the cover plate is pressed tightly against the upper edge of the aluminum shell to maintain an interference fit between the two, and a laser welding machine is used to melt and weld the cover plate and the upper edge of the aluminum shell into a whole, thereby assembling a non-liquid-injected assembly;

[0016] (2) The unfilled assembly is vacuum baked at a temperature of 80 to 90°C, a vacuum degree of -90 to -98 kPa, and a baking time of 36 to 48 hours. After the baking is completed, the unfilled assembly is filled with liquid using a liquid filling machine at a liquid filling coefficient of 4.6 to 5.2 g / Ah in a dry air atmosphere with a dew point of -35 to -45°C, and allowed to stand at 35 to 45°C for 24 to 48 hours to achieve sufficient infiltration of the electrolyte into the positive and negative electrode sheets and the diaphragm to form a battery cell;

[0017] (3) Using a formation device to charge and activate the battery cell, the formation method is open formation;

[0018] (4) Open circuit aging;

[0019] (5) After the aging is completed, the battery cell is subjected to a capacity test to obtain the capacity and internal resistance performance parameters of the battery cell. After completion, a composite manganese-based lithium battery suitable for use in a wide temperature range is obtained.

[0020] In the preparation method of the composite manganese-based lithium battery suitable for use in a wide temperature range, during the preparation of the positive electrode, the conductive agent selected is one of conductive carbon black, superconducting carbon black, and Ketjen black; the binder selected is polyvinylidene fluoride; and the organic solvent selected is N-methylpyrrolidone.

[0021] In the preparation method of the composite manganese-based lithium battery suitable for use in a wide temperature range, during the preparation of the negative electrode, the conductive agents selected are two of conductive carbon black, superconducting carbon black, Ketjen black, and carbon nanotubes; the thickener selected is sodium carboxymethyl cellulose; the binder selected is styrene-butadiene rubber; and the solvent selected is deionized water.

[0022] The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range, in which the polypropylene diaphragm selected during the preparation of the composite manganese-based lithium battery is a dry-process high-porosity diaphragm with a thickness of 12 to 25 μm and a porosity of 40 to 45%.

[0023] In the method for preparing the composite manganese-based lithium battery suitable for use in a wide temperature range, the polypropylene diaphragm selected during the preparation of the composite manganese-based lithium battery has a size of 20 μm in thickness and 129 mm in width.

[0024] The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range, during the preparation process of the composite manganese-based lithium battery, the electrolyte for liquid injection into the unfilled assembly: the solvent is selected from two of ethylene carbonate, dimethyl carbonate, propylene carbonate, and ethyl methyl carbonate, and the lithium salt is one or two of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(trifluoromethanesulfonyl)imide.

[0025] The preparation method of the composite manganese-based lithium battery suitable for use in a wide temperature range, during the preparation process of the composite manganese-based lithium battery, the formation system is 0.05C constant current charging for 3.33h, 0.1C constant current charging for 4.5h, vacuum exhaust at a vacuum degree of -90kPa for 30min, 0.1C constant current charging to 4.2V, and after the above procedures are completed, sealing is performed.

[0026] The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range comprises the following steps: during the preparation of the composite manganese-based lithium battery, the aging temperature for open circuit aging is 45° C., and the aging time is 72 hours.

[0027] The performance of lithium batteries is closely related to the selected positive electrode material. The design concept of the present invention is as follows:

[0028] In response to the shortcomings of existing lithium-ion battery cathode materials in low-temperature performance, energy density and safety, the present invention proposes an innovative improvement method. Although the existing lithium iron phosphate cathode material has good cycle life and thermal stability, its performance in low-temperature environments is poor and its energy density is low, which limits its use in high-energy density application scenarios. While ternary cathode materials such as lithium nickel cobalt manganese oxide have high energy density and can meet the requirements for battery life, they have defects in safety, especially thermal stability, and are prone to cause safety problems under high temperature or overcharge conditions.

[0029] In order to solve these problems, the present invention proposes to combine lithium manganese oxide (LiMn2O4) and lithium iron manganese phosphate (LiMn 0.6 Fe 0.4 The strategy of composite blending with lithium manganese oxide (LiMn2O4) is adopted. Through this combination, the high energy density and good electrical conductivity of lithium manganese oxide are utilized, while the excellent thermal stability and safety characteristics of lithium manganese iron phosphate are combined to achieve the effect of performance optimization. Lithium manganese iron phosphate has a dual voltage platform of 4.1V and 3.5V, which can well match the voltage of lithium manganese oxide (LiMn2O4). At the same time, lithium manganese oxide (LiMn2O4) has a spinel structure and lithium manganese iron phosphate has an olivine structure, and the two have good lattice compatibility. In the mixing process of the composite material, the focus is on optimizing the ratio of lithium manganese oxide and lithium manganese iron phosphate to ensure that the performance advantages of the two materials can complement each other, thereby maximizing the overall performance of the battery. In addition, the electrochemical performance and stability of the material are further improved through process optimization such as surface modification of the material and particle size control. Ultimately, this design not only significantly improves the discharge performance of the prepared positive electrode material under low temperature conditions, but also increases the energy density of the battery, while enhancing the stability and safety under harsh conditions such as high temperature and overcharge, meeting the needs of high energy density and high safety application scenarios. Through this innovative design, the present invention provides an effective solution for improving the performance of lithium-ion battery positive electrode materials and has broad application prospects.

[0030] The advantages and beneficial effects of the present invention are:

[0031] 1. The preparation method of the composite manganese-based lithium battery of the present invention uses two positive electrode materials, lithium manganese oxide and lithium iron manganese phosphate, for composite blending, while taking advantage of the high platform voltage, high energy density, and low cost of lithium manganese oxide and the good low-temperature performance, good safety performance, and long cycle life of lithium iron manganese phosphate.

[0032] 2. The preparation method of the composite manganese-based lithium battery of the present invention is compatible with the process equipment and process environment standards of conventional lithium iron phosphate system lithium batteries in the past, which greatly improves the adaptability of the preparation method and the feasibility of introducing it into mass production.

[0033] 3. The preparation method of the composite manganese-based lithium battery of the present invention achieves a significant improvement in the energy output efficiency of the lithium battery in a low-temperature environment or working condition of -20°C (from 36% to 80.8%) while maintaining substantially unchanged safety performance and cost consumption. The energy output efficiency can reach 69.3% in a low-temperature environment of -40°C and operate stably. At the same time, the energy output efficiency remains unchanged (approximately 100%) at a high temperature of 55°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram of the shape and size of the positive electrode sheet of the present invention.

[0035] Figure 2 This is a diagram of the shape and size of the negative electrode sheet of the present invention.

[0036] Figure 3 Schematic diagram of the cross section of the core package structure of the present invention, wherein (a) is the front view, (b) is the top view, and (c) is the side view.

[0037] Figure 4 This is a schematic diagram of ultrasonic welding of the positive and negative electrode tabs of the core package with the positive and negative electrode connecting pieces of the cover plate of the present invention.

[0038] Figure 5 Schematic diagram of the internal structure of the non-liquid-filled assembly of the present invention, wherein (a) is a front view, (b) is a side view, and (c) is a cross-sectional view.

[0039] Figure 1-Figure 5 In the figure, the reference numerals are: 1 positive electrode sheet (11 positive electrode ear), 2 negative electrode sheet (21 negative electrode ear), 3 diaphragm, 4 core pack, 5 cover plate, 6 pole column, 7 cover plate connecting piece, 8 pole ear, 9 ultrasonic welding head, 10 aluminum shell.

[0040] Figure 6 Schematic diagram comparing the normal temperature (25°C) vs. high temperature (55°C) 0.5C discharge performance curves of the present invention.

[0041] Figure 7-Figure 8 This is a schematic diagram comparing the normal temperature vs. low temperature 0.5C discharge performance curves of the present invention. Figure 7 It is a composite manganese-based lithium battery. Figure 8 It is a conventional lithium iron phosphate battery.

[0042] Figure 9-10 This is a schematic diagram comparing the discharge energy at room temperature vs. low temperature 0.5C of the present invention. Figure 7 It is a composite manganese-based lithium battery. Figure 8 It is a conventional lithium iron phosphate battery. DETAILED DESCRIPTION

[0043] In order to better understand the structure and performance of the present invention, the present invention is further described in detail through embodiments and drawings.

[0044] Example 1

[0045] In this embodiment, a method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range includes the following steps:

[0046] 1. Cathode preparation

[0047] First, according to the mass ratio of lithium manganese oxide (LiMn2O4): lithium manganese iron phosphate (LiMn 0.6 Fe 0.4PO4): conductive agent: binder = 76.8:19.2:2.2:1.8, take 6.4kg of lithium manganese oxide, 1.6kg of lithium iron manganese phosphate, 0.183kg of conductive carbon black, and 0.15kg of polyvinylidene fluoride (PVDF) and add them into a stirring tank; then add 2.08kg of organic solvent N-methyl pyrrolidone to make the solid content of the slurry in the stirring tank be 80wt%, and at the same time start the stirring speed of 30rad / min and the dispersion speed of 2500rad / min for 2.5h; continue to add 1.49kg of organic solvent N-methyl pyrrolidone to make the solid content of the slurry in the stirring tank be 70wt%, and at the same time start the stirring speed of 35rad / min and the dispersion speed of 2500rad / min for 2 hours; finally disperse evenly to obtain a positive electrode slurry with a viscosity of 7600mPa·s;

[0048] The positive electrode slurry was filtered through a 150-mesh filter. After filtering, the surface density of the single surface was 24.25 mg / cm 2 , double-sided density 48.5mg / cm 2 The positive electrode coil is evenly coated on both sides of the positive electrode current collector, the positive electrode current collector is a carbon-coated aluminum foil, the carbon coating layer thickness is 1 μm, and the total thickness of the carbon-coated aluminum foil is 15 μm, to prepare a positive electrode coil;

[0049] The positive electrode coil was rolled using a roller mill at 2.89 g / cm 3 The compaction density is rolled and the slitting machine is used to cut the positive electrode coils into two equal widths in the middle. The hardware die-cutting machine is used to punch out the positive electrode sheets for each positive electrode coil to obtain positive electrode sheets with the shape and size as shown in the figure. Figure 1 .

[0050] 2. Anode preparation

[0051] According to the mass ratio of artificial graphite: thickener: conductive agent: binder = 95.05:1.4:1.85:1.7, 5 kg of artificial graphite, 0.074 kg of sodium carboxymethyl cellulose, and 0.097 kg of conductive agent were taken and added to the stirring tank; then 5.4 kg of deionized water was added and mixed to make the solid content of the slurry in the stirring tank 47.4 wt%, and the stirring speed was turned on at 28 rad / min and the dispersion speed was turned on at 2800 rad / min for 2.5 hours; 0.56 kg of deionized water was continued to be added to make the solid content of the slurry in the stirring tank 45.1 wt%, and the stirring speed was turned on at 28 rad / min and the dispersion speed was turned on at 2800 rad / min for 1 hour to achieve uniform dispersion of the slurry; finally, 0.179 kg of styrene-butadiene rubber with a solid content of 50 wt% was added, the stirring speed was adjusted to 20 rad / min, the dispersion speed was adjusted to 1500 rad / min, and the duration was 0.5 hour to obtain a negative electrode slurry with a viscosity of 3500 mPa·s.

[0052] The negative electrode slurry was passed through a 200-mesh sieve and filtered before coating. The single-side density was 8.3 mg / cm 2 , double-sided density is 16.6mg / cm 2 The slurry is evenly coated on both sides of the negative electrode current collector, which is a copper foil with a thickness of 6 μm, to make a negative electrode coil;

[0053] The above negative electrode coil is rolled by a roller mill at a pressure of 1.5g / cm 3 The compaction density is rolled and the negative electrode sheet is punched using a full-page die-cutting laser die to produce the negative electrode sheet with a shape and size such as Figure 2 .

[0054] 3. Preparation of composite manganese-based lithium batteries

[0055] The positive and negative electrodes are insulated and separated using a conventional polypropylene diaphragm (diaphragm thickness 20 μm, width 129 mm), and a laminating machine is used to perform a "Z"-shaped lamination and gluing process to form a core package ( Figure 3 ), then weld the positive and negative tabs of the core package and the positive and negative connecting pieces of the cover together using an ultrasonic welding machine ( Figure 4 ), then install the stop frame, use the outer vest to wrap the core package as a whole for protection, install it into the aluminum shell, press the cover plate and the upper edge of the aluminum shell tightly to keep the two in an interference fit state, and use a laser welding machine to melt and weld the cover plate and the upper edge of the aluminum shell into a whole, thus assembling the non-liquid-injected assembly ( Figure 5 );

[0056] like Figure 3 As shown, the core package 4 structure includes a positive electrode sheet 1, a negative electrode sheet 2 and a separator 3. The positive electrode sheets 1 and the negative electrode sheets 2 are arranged alternately in sequence and are insulated and separated by the separator 3. A positive electrode ear 11 is provided at one end of the positive electrode sheet 1, and a negative electrode ear 21 is provided at one end of the negative electrode sheet 2.

[0057] like Figure 4 As shown, when the two core packages 4 are connected, a cover connecting piece 7 and a pole 6 are respectively provided on the upper and lower parts of the cover 5, and the pole ears 8 of the positive and negative pole connecting pieces on the two core packages 4 are arranged relative to each other and overlapped with the cover connecting piece 7. The ultrasonic welding head 9 of the ultrasonic welding machine moves in the vertical direction to weld the pole ears 8 and the cover connecting piece 7, so that continuous ultrasonic welding of the two core packages 4 can be realized.

[0058] like Figure 5 As shown, the structure of the assembly is as follows: two core packages 4 are connected and folded in half and then placed in the aluminum shell 10, the pole tabs 8 of the two core packages 4 and the cover connecting pieces 7 connected to the pole tabs 8 are bent separately, the cover 5 is located on the inner side of the top of the aluminum shell 10, and the pole 6 is located on the outer side of the top of the aluminum shell 10.

[0059] The uninjected assembly was vacuum baked at 85°C, with a relative vacuum of -98 kPa and a baking time of 36 hours. After the baking, the uninjected assembly was injected with 156 g of liquid using an injection machine in a dry air atmosphere with a dew point of -45°C. The assembly was left to stand at 45°C for 24 hours to ensure that the electrolyte fully infiltrated the positive and negative electrodes and the separator to form a battery cell.

[0060] In this embodiment, the electrolyte has the following composition: the solvent is selected from ethylene carbonate and dimethyl carbonate (volume ratio is 1:1), the lithium salt is lithium hexafluorophosphate, and the lithium salt concentration is 1 mol / L.

[0061] The battery cells were charged and activated using a formation device. The formation method was open-cell formation. The formation regimes were 0.05C constant current charging for 3.33 h, 0.1C constant current charging for 4.5 h, vacuum exhaust (relative vacuum degree -90 kPa, time 30 min), and 0.1C constant current charging to 4.2 V. After the above procedures were completed, the cells were sealed.

[0062] Open circuit aging, aging temperature is 45℃, aging time is 72h;

[0063] The capacity test showed that the capacity was 28.84Ah and the internal resistance was 0.65mΩ, and a composite manganese-based lithium battery suitable for use in a wide temperature range was produced.

[0064] This preparation method achieves a significant improvement in the energy output efficiency of lithium batteries (from 36% to 80.8%) in a low-temperature environment or working condition of -20°C, while maintaining basically unchanged safety performance and cost consumption. The energy output efficiency can reach 69.3% in a low-temperature environment of -40°C and operate stably. At the same time, the energy output efficiency remains unchanged (approximately 100%) at a high temperature of 55°C.

[0065] like Figure 6 As shown, the above-mentioned composite manganese-based lithium battery was subjected to 0.5C normal temperature 25℃ and high temperature 55℃ discharge performance tests. The test results show that the composite manganese-based lithium battery has good discharge performance at a high temperature of 55℃, and its discharge capacity ratio is about 100% compared with that at normal temperature, and the discharge platform voltage is not reduced compared with that at normal temperature.

[0066] like Figure 7-Figure 8As shown, the discharge performance test of the composite manganese-based lithium battery of the present invention is carried out at 0.5C room temperature 25℃, low temperature -20℃ and -40℃, and the discharge performance test of the conventional lithium iron phosphate battery is carried out at 0.5C room temperature 25℃ and low temperature -20℃. By comparing the test results, it can be seen that the discharge capacity ratio of the conventional lithium iron phosphate battery at a low temperature of -20℃ is about 45% of the discharge capacity at a normal temperature of 25℃, and the initial discharge voltage at a low temperature of -20℃ is about 2.85V. The discharge capacity ratio of the composite manganese-based lithium battery at -20℃ and -40℃ is about 98% and 93% of the discharge capacity at a normal temperature of 25℃, and the initial discharge voltage at low temperatures of -20℃ and -40℃ is about 3.4V and 2.4V. Compared with the embarrassing situation that conventional lithium iron phosphate cannot discharge at a low temperature of -40℃, its low temperature discharge resistance is significantly enhanced.

[0067] like Figure 9-10 As shown, the battery cells of the composite manganese-based lithium battery of the present invention are subjected to 0.5C discharge energy tests at room temperature 25°C, low temperatures -20°C and -40°C, and the battery cells of the conventional lithium iron phosphate battery are subjected to 0.5C discharge energy tests at room temperature 25°C and low temperature -20°C. By comparing the test results, it can be seen that the discharge energy of the conventional lithium iron phosphate battery at a low temperature of -20°C is about 36% of the discharge energy at a normal temperature of 25°C, while the discharge energy of the composite manganese-based lithium battery at -20°C and -40°C is about 80.8% and 69.3% of the discharge energy at a normal temperature of 25°C. At low temperatures of -20°C and -40°C, the energy output efficiency of the composite manganese-based lithium battery is significantly stronger than that of the conventional lithium iron phosphate battery.

[0068] The implementation results show that the present invention adjusts the component ratio of the battery positive electrode material and optimizes the surface density design parameters, so that the performance advantages of the positive electrode active material such as low temperature resistance, good safety, low cost and high energy density can be fully utilized. The selection of an adapted wide-temperature electrolyte allows it to stably exert its performance in a wide temperature range, so that the battery can operate safely and stably in different temperature environments. The preparation method of the present invention is compatible with the conventional lithium iron phosphate system lithium battery process equipment and process environment standards in the past, which greatly improves the adaptability of the preparation method and the feasibility of introducing mass production. The composite manganese-based lithium battery prepared by the present invention can continue to work stably in a wide temperature range of -40°C to 55°C, and has excellent performance.

[0069] As described above, the present invention is described by way of some embodiments. It will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. A method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range, characterized in that: Proceed as follows: Step 1: Positive electrode preparation (1) First, according to the mass ratio of lithium manganese oxide (LiMn2O4): lithium iron manganese phosphate (LiMn 0.6 Fe 0.4 PO4): conductive agent: binder = 74-78:18-22:2-4:1.6-2, added to the stirring tank; then added organic solvent, kneaded to make the solid content of the slurry in the stirring tank 70-80wt%, while starting the stirring speed of 30-42rad / min and the dispersion speed of 2200-3200rad / min, lasting for 2-3h; continued to add organic solvent to make the solid content of the slurry in the stirring tank 65-75wt%, while starting the stirring speed of 30-42rad / min and the dispersion speed of 2200-3200rad / min, lasting for 0.5-2 hours; finally dispersed evenly to obtain a positive electrode slurry with a viscosity of 7000-8000mPa·s; (2) The positive electrode slurry is filtered through a 120-150 mesh filter. After filtering, the surface density of the positive electrode slurry is 18-24.5 mg / cm2 in a continuous coating manner. 2 , double-sided density is 36~49mg / cm 2 The positive electrode coil is uniformly coated on both sides of the positive electrode current collector, the positive electrode current collector is a carbon-coated aluminum foil, and the thickness of the carbon-coated aluminum foil is 12 to 18 μm, to prepare a positive electrode coil; (3) The positive electrode coil is rolled using a roller mill at a pressure of 2.6 to 2.9 g / cm 3 The positive electrode coils are rolled to a compaction density of 1000 nm and cut into two equal widths in the middle using a slitting machine. A metal die-cutting machine is used to punch out the positive electrode sheets from each positive electrode coil to obtain positive electrode sheets with appropriate size and shape. Step 2: Anode preparation (1) First, artificial graphite, thickener, and conductive agent are added to a stirring tank according to the mass ratio of artificial graphite: thickener: conductive agent: binder = 94-95.5:1.2-1.5:1.5-1.9:1.5-2; then solvent is added and mixed to make the solid content of the slurry in the stirring tank 45-50wt%, and at the same time, the stirring speed is turned on at 28-32rad / min and the dispersion speed is turned on at 2200-3200rad / min for 2-3h; the solvent is continued to be added, The solid content of the slurry in the stirred tank is set to 40-46 wt %, and the stirring speed is set to 28-32 rad / min and the dispersion speed is set to 2200-3200 rad / min for 0.5-2 hours. Finally, the binder is added, the stirring speed is adjusted to 10-30 rad / min, and the dispersion speed is adjusted to 1000-2000 rad / min for 0.5-1 hour, and the slurry is uniformly dispersed to obtain a negative electrode slurry with a viscosity of 3000-5000 mPa·s. (2) The negative electrode slurry is passed through a 150-200 mesh sieve, filtered, and then coated. The single-side density is 8-10.5 mg / cm 2 , double-sided density is 16~21mg / cm 2 The slurry is evenly coated on both sides of the negative electrode current collector, which is a copper foil with a thickness of 6 to 8 μm, to form a negative electrode coil; (3) The above negative electrode coil is rolled by a roller mill to a pressure of 1.4 to 1.5 g / cm 3 The compaction density is rolled and the negative electrode sheet is punched out using a full-page die-cutting laser die to produce negative electrode sheets with suitable size and shape; The third step is the preparation of composite manganese-based lithium batteries (1) Using a polypropylene diaphragm to insulate and separate the positive and negative electrode sheets, a laminating machine is used to perform a "Z"-shaped lamination and gluing process to form a core package, the positive and negative tabs of the core package are welded together with the positive and negative electrode connecting pieces of the cover plate using an ultrasonic welding machine, a stop frame is installed, and the core package is wrapped and protected with an outer vest, which is then placed in an aluminum shell, and the cover plate is pressed tightly against the upper edge of the aluminum shell to maintain an interference fit between the two, and a laser welding machine is used to melt and weld the cover plate and the upper edge of the aluminum shell into a whole, thereby assembling a non-liquid-injected assembly; (2) The unfilled assembly is vacuum baked at a temperature of 80 to 90°C, a vacuum degree of -90 to -98 kPa, and a baking time of 36 to 48 hours. After the baking is completed, the unfilled assembly is filled with liquid using a liquid filling machine at a liquid filling coefficient of 4.6 to 5.2 g / Ah in a dry air atmosphere with a dew point of -35 to -45°C, and allowed to stand at 35 to 45°C for 24 to 48 hours to achieve sufficient infiltration of the electrolyte into the positive and negative electrode sheets and the diaphragm to form a battery cell; (3) Using a formation device to charge and activate the battery cell, the formation method is open formation; (4) Open circuit aging; (5) After the aging is completed, the battery cell is subjected to a capacity test to obtain the capacity and internal resistance performance parameters of the battery cell. After completion, a composite manganese-based lithium battery suitable for use in a wide temperature range is obtained.

2. The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range according to claim 1, characterized in that: During the preparation of the positive electrode, the conductive agent selected is one of conductive carbon black, superconducting carbon black, and Ketjen black; the binder selected is polyvinylidene fluoride; and the organic solvent selected is N-methylpyrrolidone.

3. The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range according to claim 1, characterized in that: During the preparation of the negative electrode, the conductive agents selected are two of conductive carbon black, superconducting carbon black, Ketjen black, and carbon nanotubes; the thickener selected is sodium carboxymethyl cellulose, the binder selected is styrene-butadiene rubber; and the solvent selected is deionized water.

4. The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range according to claim 1, characterized in that: In the preparation process of composite manganese-based lithium batteries, the polypropylene diaphragm selected is a dry-process high-porosity diaphragm with a thickness of 12 to 25 μm and a porosity of 40 to 45%.

5. The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range according to claim 1, characterized in that: During the preparation of composite manganese-based lithium batteries, the polypropylene diaphragm size selected is: thickness 20μm, width 129mm.

6. The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range according to claim 1, characterized in that: During the preparation of the composite manganese-based lithium battery, the electrolyte for liquid injection into the uninjected assembly: the solvent is selected from two of ethylene carbonate, dimethyl carbonate, propylene carbonate, and ethyl methyl carbonate, and the lithium salt is one or two of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bis(trifluoromethanesulfonyl)imide.

7. The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range according to claim 1, characterized in that: During the preparation process of the composite manganese-based lithium battery, the formation system is 0.05C constant current charging for 3.33h, 0.1C constant current charging for 4.5h, vacuum exhaust at a vacuum degree of -90kPa for 30min, and 0.1C constant current charging to 4.2V. After the above procedures are completed, sealing is carried out.

8. The method for preparing a composite manganese-based lithium battery suitable for use in a wide temperature range according to claim 1, characterized in that: During the preparation of the composite manganese-based lithium battery, the aging temperature of the open circuit aging was 45°C and the aging time was 72h.

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