An ultralow-temperature lithium ion battery with improved energy density and a preparation method thereof

Abstract

The application discloses an ultralow-temperature lithium ion battery with improved energy density and a preparation method thereof, and aims to solve the problem in the battery technology field that the original discharge performance is ensured, and the lithium ion battery can improve the low-temperature tolerance and energy density. The lithium ion battery of the application adds a ternary lithium material with an element ratio of 811 in the positive active coating of lithium cobaltate, and the mass fraction is matched, and adds a silicon material in the negative active coating of graphite. Compared with the prior art, the discharge efficiency can reach 80% in a-40 DEG C environment, the weight energy density is improved by 15.5%, and the volume energy density is improved by 12.2%, thereby providing the industry with a lithium ion battery with more excellent endurance performance in a low-temperature environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to an ultralow-temperature lithium ion battery with improved energy density and a preparation method thereof. BACKGROUND

[0002] The working temperature of a conventional lithium ion battery is between-20 DEG C and 60 DEG C. However, the performance of the lithium ion battery will decrease when the temperature is generally lower than 0 DEG C, and the discharge capacity will decrease accordingly. The performance of the lithium ion battery under a low-temperature condition will decrease, which is manifested as a prolonged charging time, a reduced charging and discharging capacity, a small battery capacity, and a fast power-off speed, thereby affecting the operation of a device configured with the lithium ion battery. However, in special fields such as military industry or in a battery-using device in a northern extremely cold environment, the battery is required to have a high discharge performance and a long service life under an ultralow-temperature condition of-40 DEG C.

[0003] In the prior art, improvements in electrolyte mixed solvents, electrolyte viscosity, positive electrode materials, and separators can widen the working temperature range and improve the discharge performance under a low-temperature condition to a certain extent. In terms of electrodes, the commonly used main material for manufacturing a lithium ion battery under a low-temperature condition is a positive electrode lithium cobalt oxide and a negative electrode graphite. The lithium cobalt oxide has a higher low-temperature resistance than that of lithium iron phosphate. In order to improve the low-temperature performance, CN113517435A discloses a low-temperature lithium battery formula and a tabletting process. The particle size of the lithium cobalt oxide is more suitable for use under a low-temperature condition, and the oil-based formula of the negative electrode is much higher in voltage than that of the water-based formula, so that the electrolyte can also maintain good activity under a low temperature. It can be seen that the lithium cobalt oxide can improve the low-temperature performance through process improvement.

[0004] In addition, Chinese patent CN108539134A discloses an ultralow-temperature lithium ion battery and a preparation method thereof. The positive electrode active material is optimized and controlled, a certain proportion of rare earth elements and alkaline earth metals are doped in the lithium cobalt oxide positive electrode material, the lattice constant c is changed without changing the crystal structure of the raw material, the interlayer spacing of the material is increased, and the electrochemical reversibility and low-temperature resistance of the material are improved. It can be seen that the prior art improves the reversibility of the battery on the basis of low-temperature resistance through doping.

[0005] However, the theoretical gram capacity of the lithium cobalt oxide is 274 mAh / g, and the capacity can only be improved by continuously improving the voltage of the battery through doping and coating. However, the increase in voltage also causes an increase in internal resistance, which is not conducive to discharge under an ultralow-temperature condition. The theoretical gram capacity of the negative electrode graphite is 372 mAh / g, and the capacity of the graphite has reached 355 mAh / g, which is difficult to improve.

[0006] Therefore, the energy density of the lithium cobalt battery has been difficult to improve, resulting in that the endurance of the lithium ion battery of the system cannot be improved, and gradually cannot meet the growing demand of users. SUMMARY

[0007] Therefore, the main purpose of the present application is to provide an ultra-low temperature lithium ion battery with improved energy density and a preparation method thereof, improve the components and preparation methods of the positive lithium cobalt and negative graphite, and realize the improvement of the low temperature resistance and energy density of the lithium ion battery on the basis of ensuring the original discharge performance.

[0008] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0009] In a first aspect, the present application provides an ultra-low temperature lithium ion battery with improved energy density, which comprises a shell, a battery core arranged in the shell and an electrolyte; the battery core comprises a positive electrode sheet, a negative electrode sheet and a separator; the positive electrode sheet comprises a positive electrode active coating, the positive electrode active coating comprises 64-70 parts of ternary lithium, 27.5-30 parts of lithium cobaltate, 1.5-3.5 parts of a positive electrode conductive agent and 1-3 parts of a positive electrode binder by mass fraction; the ratio of nickel element, cobalt element and manganese or aluminum element in the ternary lithium is 8:1:1.

[0010] It should be noted that the ternary lithium can be a nickel-cobalt-manganese ternary lithium material or a nickel-cobalt-aluminum ternary lithium material. In particular, the above technical scheme limits that the ratio of nickel element, cobalt element and manganese element in the nickel-cobalt-manganese ternary lithium material is 8:1:1, and the chemical formula is LiNi 0.8 Co 0.1 Mn 0.1 O2; and limits that the ratio of nickel element, cobalt element and aluminum element in the nickel-cobalt-aluminum ternary material is 8:1:1, and the chemical formula is LiNi 0.8 Co 0.1 Al 0.1 O2.

[0011] Preferably, the negative electrode sheet of the above lithium ion battery comprises a negative electrode active coating, and the negative electrode active coating comprises 89-93 parts of graphite, 4.9-5.1 parts of silicon, 0.5-1.5 parts of a negative electrode conductive agent and 2.5-3.5 parts of a negative electrode binder by mass fraction.

[0012] Preferably, the particle size distribution of the above lithium ion battery is: the particle size distribution is: D50=7.5±1 μm, D10=13.5±1 μm, D90=20±5 μm, and the specific surface area of the graphite is 0.9-1.5 m2 / g.

[0013] Optionally, the negative electrode conductive agent comprises one or more of acetylene black, carbon black conductive agent, conductive graphite, carbon nanotube, graphene and the like, and the negative electrode binder comprises one or more of sodium carboxymethyl cellulose, sodium alginate and styrene butadiene rubber. Preferably, the negative electrode conductive agent comprises 1 part of Super-P conductive carbon black and 0.2 part of nanometer carbon tube (CNT) by mass fraction of the negative electrode active coating; and the negative electrode binder comprises 1 part of carboxymethyl cellulose (CMC) and 2 parts of butadiene rubber (SBR) by mass fraction of the negative electrode active coating.

[0014] Preferably, the ternary lithium is nickel-cobalt-manganese ternary lithium; the particle size distribution of the lithium cobaltate is D50 = 6 ± 1 μm, D10 = 3 ± 2 μm, and D90 = 11 ± 4 μm; the specific surface area of the lithium cobaltate is 0.3-0.7 m2 / g; the particle size distribution of the nickel-cobalt-manganese ternary lithium is D50 = 11 ± 2 μm, D10 ≥ 4.5 μm, and D90 ≤ 30 μm; and the specific surface area of the nickel-cobalt-manganese ternary lithium is 0.3-0.7 m2 / g, which is the same as that of the lithium cobaltate.

[0015] Optionally, the positive electrode conductive agent comprises one or more of acetylene black, carbon black conductive agent, conductive graphite, carbon nanotube, graphene and the like, and the positive electrode binder comprises one or more of epoxy resin, polytetrafluoroethylene, polyvinylidene fluoride and polyacrylate. Preferably, the positive electrode conductive agent comprises 0.6 part of KS-6 graphite conductive agent and 1.4 part of Super-P conductive carbon black by mass fraction of the positive electrode active coating; and the binder comprises 1 part of polyvinylidene fluoride (PVDF) by mass fraction of the positive electrode active coating.

[0016] Preferably, the mass ratio of the lithium cobaltate to the ternary lithium is between 1:2.3 and 1:2.4, and the separator is a ceramic membrane.

[0017] In a second aspect, the present application provides a positive electrode active material, which is a positive electrode active coating of the above-mentioned lithium ion battery.

[0018] It should be noted that the positive electrode active material comprises 64-70 parts of ternary lithium, 27.5-30 parts of lithium cobaltate, 1.5-3.5 parts of positive electrode conductive agent and 1-3 parts of positive electrode binder by mass fraction; and the ratio of nickel element, cobalt element and manganese or aluminum element in the ternary lithium is 8:1:1.

[0019] Further, in the positive electrode active material, the ternary lithium is nickel-cobalt-manganese ternary lithium; the particle size distribution of the lithium cobaltate is: D50=6±1 μm, D10=3±2 μm, D90=11±4 μm, the specific surface area of the lithium cobaltate is 0.3-0.7 m2 / g; the particle size distribution of the nickel-cobalt-manganese ternary lithium is: D50=11±2 μm, D10≥4.5 μm, D90≤30 μm, the specific surface area of the nickel-cobalt-manganese ternary lithium is 0.3-0.7 m2 / g, which is the same as that of the lithium cobaltate.

[0020] Further, in the positive electrode active material, the positive electrode conductive agent includes: 0.6 parts of KS-6 graphite conductive agent and 1.4 parts of Super-P conductive carbon black according to the number of parts by mass of the positive electrode active coating; the binder includes: 1 part of polyvinylidene fluoride (PVDF) according to the number of parts by mass of the positive electrode active coating.

[0021] In a third aspect, the present application provides a preparation method of the above-mentioned ultra-low temperature lithium ion battery with improved energy density, the preparation method comprising the steps of:

[0022] The positive electrode active coating is configured, and 64-70 parts of 811 type ternary lithium, 27.5-30 parts of lithium cobaltate, 1.5-3.5 parts of positive electrode conductive agent and 1-3 parts of positive electrode binder are weighed and screened to obtain slurry;

[0023] The negative electrode active coating is configured, and 89-93 parts of graphite, 4.9-5.1 parts of silicon, 0.5-1.5 parts of negative electrode conductive agent and 2.5-3.5 parts of negative electrode binder are weighed and screened to obtain slurry.

[0024] Further process steps are performed to form a lithium ion battery.

[0025] Preferably, the preparation method further comprises the steps of:

[0026] The positive electrode active coating is coated on both sides of the positive electrode current collector according to a density of 330±3 g / m2, and is dried by passing through an oven;

[0027] The negative electrode active coating is coated on both sides of the negative electrode current collector according to a density of 149±3 g / m2, and is dried by passing through an oven;

[0028] The dried positive electrode is rolled into a film and compacted to 3.42 g / dm 3 ;

[0029] The dried negative electrode is rolled into a film and compacted to 1.58 g / dm 3 .

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] (1) the lithium ion battery of the present application, the ternary lithium material with the element ratio of 811 is added in the positive electrode active coating of lithium cobaltate, and the mass fraction is matched, compared with the existing lithium ion battery with only lithium cobaltate positive material, the discharge efficiency under-40 DEG C environment can reach 80%, and is increased by more than 15%; at the same time, under the same condition, the weight energy density reaches 249.5 Wh / Kg, and is increased by 15.5%, and the volume energy density is 493.4 Wh / L, and is increased by 12.2%; in addition, although the capacity of 0.5C charge and discharge 500 times is reduced, the capacity retention rate can still reach more than 90%, under the condition of super low temperature, the original discharge performance can still be guaranteed, the energy density of the battery is improved, and the cycle life is considered to a certain extent.

[0032] (2) the lithium ion battery of the present application, further adding silicon material in the negative electrode active coating of graphite, realizing the improvement of the battery lithium capacity, cooperating with the positive electrode system of 811 ternary lithium and lithium cobaltate, realizing the reduction of the battery resistivity under the condition of super low temperature, and improving the super low temperature discharge efficiency.

[0033] (3) the lithium ion battery of the present application, further configuring the particle size distribution and specific surface area parameters of 811 ternary lithium and lithium cobaltate, realizing the improvement of the dispersion characteristics and positive electrode interface performance of the two kinds of lithium ion positive electrode active materials.

[0034] (4) the preparation method of the present application, further setting the positive and negative coating density and compaction density, realizing the improvement of the composite effect of the two kinds of lithium ion positive electrode active materials and the two kinds of negative electrode active materials. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 the schematic diagram of each component of the lithium ion battery of the embodiment of the present application;

[0036] Figure 2 the discharge efficiency schematic diagram of the lithium ion battery of the embodiment of the present application under 0.2C discharge at super low temperature;

[0037] Figure 3 the discharge efficiency schematic diagram of the lithium ion battery of the embodiment of the present application under 0.2C discharge at high temperature;

[0038] Figure 4 the 0.5C charge and discharge 500 times capacity retention rate schematic diagram of the lithium ion battery of the embodiment of the present application. DETAILED DESCRIPTION

[0039] In order to better illustrate the purpose, technical scheme and advantages of the present application, the specific embodiments of the present application are further described in detail below. The following examples are used to illustrate the present application, but not as a limitation on the scope of the present application.

[0040] The working principle of the super-low-temperature lithium ion battery with improved energy density is that high-nickel ternary lithium material is added in the positive electrode active material of lithium cobaltate,

[0041] Reference Figure 1 According to the embodiment of the present application, a super-low-temperature lithium ion battery with improved energy density is provided. The lithium ion battery comprises a shell, a battery core arranged in the shell, and an electrolyte; the battery core comprises a positive electrode sheet, a negative electrode sheet, and a separator.

[0042] To achieve the purpose of the application, the main features of the embodiment are that the positive electrode sheet comprises positive electrode active coating, and the positive electrode active coating comprises 64-70 parts of ternary lithium, 27.5-30 parts of lithium cobaltate, 1.5-3.5 parts of positive electrode conductive agent, and 1-3 parts of positive electrode binder by mass fraction. In particular, the ratio of nickel element, cobalt element and manganese element in the ternary lithium is 8:1:1, and the chemical formula is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0043] To achieve the purpose of the application, the secondary features of the embodiment are that the negative electrode sheet comprises negative electrode active coating, and the negative electrode active coating comprises 89-93 parts of graphite, 4.9-5.1 parts of silicon, 0.5-1.5 parts of negative electrode conductive agent, and 2.5-3.5 parts of negative electrode binder by mass fraction.

[0044] To achieve the purpose of the application, preferably, the separator is a ceramic membrane.

[0045] The working principle of the embodiment is that the nickel element is one of the main active materials in the ternary lithium material, which can improve the capacity; the cobalt element is also an active material, which stabilizes the layered structure of the material, reduces the mixing of cations, facilitates deep discharge of the material, and thus improves the discharge capacity of the material; and the manganese element improves the structural stability of the material. The ternary lithium battery with high nickel content is used in the embodiment, and the mass fraction is 64-70 parts, and the lithium cobaltate is dispersed in an amount of 27.5-30 parts, so that the energy density of the lithium ion battery is greatly improved, the discharge performance and energy density are realized, the influence of the low stability of the nickel element on the whole battery is reduced, and the lithium cobaltate can form a stable layered structure with the ternary lithium, thereby reducing the influence of the ternary lithium material with high nickel content on the overall safety of the lithium ion battery, so that the lithium ion battery has high voltage platform, good discharge performance, high energy density, good safety and excellent low-temperature adaptability under super-low temperature condition. It can be understood that the ternary lithium battery with high nickel content will easily cause the irreversible thickening of the SEI layer (solid electrolyte interface) of the positive electrode, so the lithium ion battery of the embodiment will sacrifice the cycle life. However, due to the compounding of lithium cobaltate and other factors, the decrease of the cycle life of the lithium ion battery will be within an acceptable range. At the same time, the negative active coating uses 89-93 parts of graphite and 4.9-5.1 parts of silicon, so that the negative electrode can accommodate the increased energy density of the positive active material. The silicon material has a polyhedral structure and is mixed in the layered structure of the graphite, which can achieve excellent low-temperature performance and reduce the low-temperature resistance of the lithium ion battery.

[0046] In addition, the ceramic film is coated with ceramic particles. Specifically, a layer of Al203, SiO2, Mg(OH)2 or other inorganic ceramic particles with good heat resistance is coated on the surface of a PP, PE or multi-layer composite separator as a substrate, and the substrate is tightly bonded together after special process treatment. The high and low temperature resistance of the separator is improved to ensure the stability of the ternary lithium at high and low temperatures.

[0047] Compared with the existing lithium ion battery, the embodiment uses 64-70 parts of 811 type ternary lithium and 27.5-30 parts of lithium cobaltate as the positive active coating, and uses 89-93 parts of graphite and 4.9-5.1 parts of silicon, which can realize the improvement of the energy density of the battery under super-low temperature condition while ensuring the original discharge performance, and to a certain extent, the cycle life is also taken into account.

[0048] It can be understood that the conductive agent includes one or more of acetylene black, carbon black conductive agent, conductive graphite, carbon nanotube, graphene and other materials, the positive electrode binder includes one or more of epoxy resin, polytetrafluoroethylene, polyvinylidene fluoride and polyacrylate, and the negative electrode binder includes one or more of sodium carboxymethyl cellulose, sodium alginate and butadiene rubber.

[0049] In a more specific embodiment, the positive active coating includes, by mass parts, 64-70 parts of ternary lithium, 27.5-30 parts of lithium cobaltate, 0.6 parts of KS-6 graphite conductive agent, 1.4 parts of Super-P conductive carbon black, and 1 part of polyvinylidene fluoride (PVDF); the negative active coating includes, by mass parts, 89-93 parts of graphite, 4.9-5.1 parts of silicon, 1 part of Super-P conductive carbon black, 0.2 parts of carbon nanotube (CNT), 1 part of carboxymethyl cellulose (CMC), and 2 parts of butadiene styrene latex (SBR).

[0050] Compared with the existing lithium ion battery, the embodiment improves the energy density, discharge performance, and low-temperature resistance by configuring KS-6 graphite conductive agent and Super-P conductive carbon black in the positive active coating to ensure the dispersion of the two active materials and improve the conductivity of the positive electrode. The embodiment improves the conductivity of the positive electrode by doping Super-P conductive carbon black and carbon nanotube (CNT) in the extrusion of graphite doped with silicon, and reduces the resistance value in the ultra-low temperature state.

[0051] It can be understood that the 811 ternary lithium material of the embodiment can be doped with boron elements for modification, so as to improve the stability of the material structure by changing the lattice constant of the material or the valence of part of the elements in the material, improve the electronic conductivity and ionic conductivity of the material, reduce the cationic disordering of the high-nickel ternary 811 material, and increase the output power density of the battery.

[0052] In a specific embodiment of the lithium ion battery, in the lithium ion battery, the positive active coating of the positive electrode sheet contains, by percentage, the following components: 67.2% of 811 nickel-cobalt-manganese ternary lithium, 28.8% of lithium cobaltate, 0.6% of KS-6 graphite conductive agent, 1.4% of Super-P conductive carbon black, and 1% of polyvinylidene fluoride (PVDF). The negative active coating of the positive electrode sheet contains, by percentage, the following components: 90.8% of graphite, 5% of silicon, 1% of Super-P conductive carbon black, 1% of carboxymethyl cellulose (CMC), 2% of butadiene styrene latex water-based (SBR), and 0.2% of carbon nanotube (CNT). The separator is a ceramic separator.

[0053] Specifically, the 67.2% of 811 nickel cobalt manganese ternary lithium has a particle size distribution of D50 = 11 ± 2 pm, D10 ≥ 4.5 pm, D90 ≤ 30 pm, and a specific surface area of 0.3-0.7 m2 / g. The 28.8% of lithium cobaltate has a particle size distribution of D50 = 6 ± 1 pm, D10 = 3 ± 2 pm, D90 = 11 ± 4 pm, and a specific surface area of 0.3-0.7 m2 / g. The parameters can realize the formation of the structure of the two positive electrode active materials in the forming process, which is easy for lithium ion to be deintercalated at low temperature. The 90.8% of graphite has a particle size distribution of D50 = 7.5 ± 1 pm, D10 = 13.5 ± 1 pm, D90 = 20 ± 5 pm, and a specific surface area of 0.9-1.5 m2 / g. The parameters can realize good mixing of the silicon material.

[0054] The lithium ion battery of the specific embodiment is configured as a soft pack battery with a size of length 198 mm, width 59 mm * thickness 5.2 mm. The manufacturing steps of the lithium ion battery of the embodiment include.

[0055] In a third aspect, the present application provides a preparation method of the above-mentioned ultra-low temperature lithium ion battery with improved energy density, which comprises the steps of:

[0056] Step (1) batching: 67.2% of 811 nickel cobalt manganese ternary lithium, 28.8% of lithium cobaltate, 0.6% of KS-6 graphite conductive agent, 1.4% of Super-P conductive carbon black and 1% of polyvinylidene fluoride (PVDF) are weighed according to the percentage as the positive electrode active material, and the slurry is sieved for standby; 90.8% of graphite, 5% of silicon, 1% of Super-P conductive carbon black, 1% of carboxymethyl cellulose (CMC), 2% of styrene butadiene latex water-based (SBR) and 0.2% of carbon nanotube (CNT) are weighed according to the percentage as the negative electrode active material, and the slurry is sieved for standby.

[0057] Step (2) coating: the positive electrode active slurry is coated on both sides of the positive electrode current collector according to the density of 330 ± 3 g / m2, and is dried through the oven; the negative electrode active slurry is coated on both sides of the negative electrode current collector according to the density of 149 ± 3 g / m2, and the negative electrode active coating is dried through the oven.

[0058] Step (3) film rolling: the dried positive electrode is film-rolled and compacted to 3.42 g / dm 3 ; the dried negative electrode is film-rolled and compacted to 1.58 g / dm 3 .

[0059] Step (4) sheet making: the film-rolled electrode sheet is sheeted using a rubber plate knife mold, the negative electrode sheet is 1.2 mm wider than the positive electrode sheet, and the negative electrode sheet is 3 mm longer than the positive electrode sheet.

[0060] Step (5) laminated packaging: before lamination, the workshop humidity is controlled below 2% RH, and the laminated body is made by lamination process, with one more layer of negative electrode than positive electrode, and the outer layer is negative electrode sheet. In this way, high-nickel 811 ternary lithium can be prevented from absorbing water vapor.

[0061] Step (6) tab welding: the positive tab is 0.1*8*26mm aluminum tab, and the negative tab is 0.1*8*26mm nickel tab, and the tabs are welded firmly with the tab handle of the laminated body by using ultrasonic welding machine.

[0062] Step (7) packaging: 151 hot method aluminum-plastic film is used for packaging.

[0063] Step (8) baking: 90℃ high vacuum oven baking for 12h.

[0064] Step (9) liquid injection: electrolyte is injected according to the amount of 3.5g / Ah.

[0065] Step (10) formation: high-temperature and pressure formation, temperature is 80℃, pressure is 0.8Mpa,

[0066] Step (11) forming: first, the excess electrolyte and the gas generated during formation are pumped out, then the excess edge is cut off and the edge folding is completed.

[0067] The preparation method of the embodiment sets the positive and negative electrode coating density and compaction density, and can realize the improvement of the composite effect of two kinds of lithium ion positive electrode active materials and two kinds of negative electrode active materials.

[0068] As shown in Figures 2 to 4 , the lithium ion battery obtained by the above preparation method. In the ultra-low temperature environment of-40℃, discharge from 0.2C capacity until the voltage drops to 2.8V.

[0069] The original lithium cobaltate positive electrode and graphite negative electrode battery has a discharge efficiency of about 70%. As shown in Figure 2 , the lithium ion battery of the embodiment adopts lithium cobaltate and 811 ternary lithium positive electrode and graphite and silicon negative electrode, and can realize a discharge efficiency of more than 80%. As shown in Figure 3 , the lithium ion battery obtained by the above preparation method can realize a discharge efficiency of 100% in a high-temperature environment of 55℃, and has a wide temperature adaptation range.

[0070] The original lithium cobaltate positive electrode and graphite negative electrode battery has an energy density of 216.1 Wh / Kg and a volume energy density of 438.5 Wh / L. Under the same parameters and process conditions, the lithium ion battery of the embodiment uses lithium cobaltate and 811 ternary lithium positive electrode and graphite and silicon negative electrode, and can realize a weight energy density of 249.5 Wh / Kg, which is increased by 15.5% compared with the original, and a volume energy density of 493.4 Wh / L, which is increased by 12.2% compared with the original.

[0071] As shown in Figure 4 The capacity retention rate of the lithium ion battery of the embodiment after 500 cycles of 0.5C charging and discharging can reach more than 90%, and the cycle life is limitedly reduced compared with the original scheme.

[0072] The above embodiments mainly describe the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application.

Claims

1. An ultralow temperature lithium ion battery with improved energy density, the lithium ion battery comprising a housing, a battery core disposed within the housing, and an electrolyte; the battery core comprising a positive electrode sheet, a negative electrode sheet, and a separator; characterized in that, The positive electrode sheet comprises positive electrode active coating, the positive electrode active coating comprises 64-70 parts of ternary lithium, 27.5-30 parts of lithium cobaltate, 1.5-3.5 parts of positive electrode conductive agent and 1-3 parts of positive electrode binder by mass fraction; the ratio of nickel element, cobalt element and manganese or aluminum element in the ternary lithium is 8:1:1; The negative electrode sheet comprises negative electrode active coating, the negative electrode active coating comprises 89-93 parts of graphite, 4.9-5.1 parts of silicon, 0.5-1.5 parts of negative electrode conductive agent and 2.5-3.5 parts of negative electrode binder by mass fraction.

2. The ultra-low temperature lithium-ion battery with improved energy density of claim 1, wherein, The particle size distribution of the graphite is: D50=7.5±1μm, D10=13.5±1μm, D90=20±5μm, and the specific surface area of the graphite is 0.9~1.5㎡ / g.

3. The ultralow temperature lithium-ion battery with improved energy density of claim 2, wherein, The negative electrode conductive agent comprises 1 part of Super-P conductive carbon black and 0.2 part of nano carbon tube (CNT) by mass fraction of negative electrode active coating; the negative electrode binder comprises 1 part of carboxymethyl cellulose (CMC) and 2 parts of styrene butadiene latex (SBR) by mass fraction of negative electrode active coating.

4. The ultralow temperature lithium-ion battery with improved energy density of claim 1, wherein, The ternary lithium is nickel-cobalt-manganese ternary lithium; the particle size distribution of the lithium cobaltate is: D50=6±1μm, D10=3±2μm, D90=11±4μm, and the specific surface area of the lithium cobaltate is 0.3-0.7㎡ / g; the particle size distribution of the nickel-cobalt-manganese ternary lithium is: D50=11±2μm, D10≥4.5μm, D90≤30μm, and the specific surface area of the nickel-cobalt-manganese ternary lithium is 0.3-0.7㎡ / g, which is the same as that of the lithium cobaltate.

5. The ultralow temperature lithium-ion battery with improved energy density of claim 1, wherein, The positive electrode conductive agent comprises 0.6 part of KS-6 graphite conductive agent and 1.4 part of Super-P conductive carbon black by mass fraction of positive electrode active coating; the binder comprises 1 part of polyvinylidene fluoride (PVDF) by mass fraction of positive electrode active coating.

6. The ultra-low temperature lithium ion battery with improved energy density according to claim 1, wherein the mass ratio of the lithium cobaltate to the ternary lithium is between 1:2.3 and 1:2.4, and the separator is a ceramic membrane.

7. A positive electrode active material, characterized by, The positive electrode active coating of the ultra-low temperature lithium ion battery with improved energy density according to any one of claims 1 to 6.

8. A method of producing an energy density-improved ultralow-temperature lithium-ion battery according to any one of claims 1 to 6, characterized by, The preparation method comprises the steps of: Preparation of positive electrode active coating: 64-70 parts of 811 type ternary lithium, 27.5-30 parts of lithium cobaltate, 1.5-3.5 parts of positive electrode conductive agent and 1-3 parts of positive electrode binder are weighed and screened to obtain slurry; Preparation of negative electrode active coating: 89-93 parts of graphite, 4.9-5.1 parts of silicon, 0.5-1.5 parts of negative electrode conductive agent and 2.5-3.5 parts of negative electrode binder are weighed and screened to obtain slurry; Further process steps are performed to form the lithium ion battery.

9. The production method according to claim 8, wherein The preparation method further comprises the steps of: The positive electrode active coating is coated on both sides of the positive electrode current collector at a density of 330±3g / m2, and then dried in an oven; The negative electrode active coating is coated on both sides of the negative electrode current collector at a density of 149±3g / m2, and then dried in an oven; The dried positive electrode was calendered and compacted to 3.42 g / dm3; The dried negative electrode was calendered and compacted to 1.58 g / dm3.

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