CN110233284B - Low-temperature high-energy-density long-cycle lithium iron phosphate battery - Google Patents

Low-temperature high-energy-density long-cycle lithium iron phosphate battery Download PDF

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CN110233284B
CN110233284B CN201910646876.6A CN201910646876A CN110233284B CN 110233284 B CN110233284 B CN 110233284B CN 201910646876 A CN201910646876 A CN 201910646876A CN 110233284 B CN110233284 B CN 110233284B
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iron phosphate
lithium iron
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CN110233284A (en
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廖宗江
江涛
邹晓兵
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Jiangxi Huiyi New Energy Co ltd
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Abstract

The invention provides a low-temperature high-energy-density long-cycle lithium iron phosphate battery, wherein a doped lithium iron phosphate is adopted as a positive electrode, the average particle size is 1-5 um, D50 is 0.5-5 um, D90 is less than or equal to 8um, and a doping material is boron nitride and carbon fibers or carbon nano tubes; coating nano-grade Al on diaphragm as base film2O3、BaSO4AlN and BN; electrolyte for improving high and low temperature performance is added into the electrolyte. The battery monomer cell of the invention has 0.2C discharge capacity>2200mAh, excellent cycle performance, capacity retention rate of more than 80% after battery core is subjected to 0.5C/0.5C 100% DOD cycle for 1500 times, capacity retention rate of about 80% at-20 ℃, capacity retention rate of about 58% at-40 ℃ and good thermal stability.

Description

Low-temperature high-energy-density long-cycle lithium iron phosphate battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a low-temperature high-energy-density long-cycle lithium iron phosphate battery.
The term of art: CNT means carbon nanotube, PVDF means polyvinylidene fluoride, GR means graphite, CF means carbon fiber, Super P means conductive carbon black, SBR means styrene butadiene rubber, CMC means hydroxymethyl cellulose, PE means polyethylene, EC means ethylene carbonate, PC means propylene carbonate, DEC means diethyl carbonate, DMC means dimethyl carbonate, PTFE means polytetrafluoroethylene, NMP means N-methylpyrrolidone, VC means vinylene carbonate, PAni means polyaniline, PAA means polyacrylic acid, PAALi means lithium polyacrylate, PEAA means polyvinyl acrylic acid.
Background
As each field develops, the performance requirements for batteries are also increasing, and batteries are required to be thinner, lighter, higher in energy density and power density, and higher in safety. Although the existing lithium ion battery can provide higher discharge current, the safety of the used electrode material is lower, so that great potential safety hazard exists when the electric appliance is used, and therefore, the safety performance of the lithium ion battery is further improved by adopting a high-safety material lithium iron phosphate as a positive electrode material.
Lithium cobaltate batteries, ternary material batteries, lithium manganate batteries and lithium iron phosphate batteries are more widely applied in the current market. The lithium iron phosphate battery is superior to other batteries in terms of electrochemical performance including reversible capacity, stability, safety, cyclicity, large-current discharge capacity and price of raw materials. Particularly, the capacity retention rate of the energy type lithium iron phosphate battery in 1C circulation for 2000 times can reach more than 80 percent and is far higher than that of a cobalt acid lithium battery, a ternary material battery and a lithium manganate battery. However, the digital cylindrical battery mainly uses manganese and ternary, and the lithium iron phosphate material uses very little lithium iron phosphate as the anode material in the digital and energy storage cylindrical 18650 battery due to the characteristics of small compaction, low energy density, poor low-temperature performance and the like. Although the ion and electron conductivity properties are improved by various methods, such as doping of lithium sites, iron sites, and even phosphoric acid sites, the low temperature performance of lithium iron phosphate is improved and the energy density thereof is increased by controlling the effective reaction area through improving the particle size and morphology of primary or secondary particles, increasing the electron conductivity through the addition of an additional conductive agent, and the like. When the material is used at low temperature, the performance is poor, the discharge capacity at minus 20 ℃ only accounts for about 30% of that at normal temperature, and the material is also a big obstacle to the popularization and the use, so the improvement of the low-temperature performance is very important. At present, the energy density of a lithium iron phosphate type 18650 lithium ion battery is about 290WH/L, the discharge capacity range is 1000-1500 mAh, researchers do a lot of work in the aspect of improving the performance of the lithium ion battery, for example, Chinese patent with the patent number of CN 2011103954287 discloses 'a low-temperature improved lithium iron phosphate battery', the discharge capacity is 1500mAh, the discharge capacity at-20 ℃ reaches 71.2% of the rated capacity, and the discharge capacity at-40 ℃ reaches 50.6% of the rated capacity. In the previous work of 'high-safety high-energy long-circulation lithium iron phosphate 18650 lithium battery and preparation method thereof' and patent No. 201810889165.7, the battery capacity can reach 2000-2100 mA, the cyclicity and low-temperature discharge performance are excellent, the capacity retention rate is over 80 percent after battery core is cycled for 1000 times by 0.5C/0.5C 100 percent DOD, and the discharge capacity at-20 ℃ reaches 73.6 percent of the rated capacity. However, the capacity of the battery is still limited, and with the development of the field of electric automobiles, batteries with higher specific energy are needed to meet the requirements of digital and energy storage 18650 batteries; therefore, it is necessary to find suitable anode and cathode materials and production processes to prepare lithium iron phosphate type lithium batteries with higher capacity, safety and cycle life.
The research on the lithium iron phosphate battery mainly focuses on improving the ion diffusion rate and the ion conductivity, and the ion conductivity and the electron conductivity of the lithium iron phosphate battery are improved by improving the specific surface area of the lithium iron phosphate and coating or doping the lithium iron phosphate battery. The method for improving the low-temperature use performance of the lithium iron phosphate battery mainly focuses on reducing the particle size of the anode and cathode materials, optimizing low-temperature electrolyte and the like, the use environment is difficult to break through minus 20 ℃, and the rate performance is poor. The main method for solving the low-temperature performance of the lithium iron phosphate battery at present comprises the following steps: the low-temperature performance of the lithium iron phosphate battery is improved to a certain extent by adopting the low-melting-point solvent electrolyte and the nanocrystallization of the anode material and the cathode material, but the use temperature of the lithium iron phosphate battery is still difficult to break through-20 ℃, and the popularization and the use of the lithium iron phosphate battery are greatly limited.
Disclosure of Invention
The invention aims to solve the problems and provides a high-energy-density long-cycle lithium iron phosphate 18650 lithium battery, which adopts the following technical scheme:
the utility model provides a long circulation lithium iron phosphate battery of low temperature type high energy density, includes positive plate, negative pole piece, diaphragm, electrolyte and shell, and the positive plate is made at 1~5 mu m's metal aluminium foil both sides with the mixture homogeneous coating that positive pole active material, conductive agent and binder are constituteed, and the negative pole piece is made at 4~8 mu m's metal copper foil both sides with the mixture homogeneous coating that negative pole active material, conductive agent and binder are constituteed, wherein: the anode active material is doped lithium iron phosphate, the average particle size is 1-5 um, D50 is 0.5-5 um, D90 is less than or equal to 8um, and the doped material is boron nitride and element-doped carbon fiber or carbon nano tube.
Boron nitride has a layered structure similar to graphite, and has good lubricity, oxidation resistance, corrosion resistance, thermal conductivity and excellent chemical stability. Boron nitride and carbon fiber or carbon nano tube can form a staggered layered structure with lithium iron phosphate, which is beneficial to the diffusion and conduction of lithium ions; the material has high specific surface area, high dispersibility and compatibility, and the coated material improves the conductivity of the material and reduces the load transmission resistance of electrochemical reaction. The doped lithium iron phosphate material with small particles and uniform distribution is adopted, the particle size composition is reasonable, the filling of pores is realized through the matching of the particle size grade, the compaction density of the lithium iron phosphate material is improved, and finally the energy density of the battery can be improved.
Further, the conductive agent of the positive plate is CNT composite GR or Super P or CF; the diaphragm is a base film coated with a coating layer, the base film is a PE or PP base film, and the coating layer is made of nanoscale Al2O3、BaSO4AlN and BN; the negative active material is graphite, and the conductive agent of the negative plate is conductive carbon black and/or CNT; the electrolyte is LiPF6A solution wherein the solute further comprises LiBF4、LiPO2F2One or more of LiBOB, LiDTI, LiTFSI and LiDFOB, which can improve the high and low temperature performance of the battery; the binder of the positive plate and the negative plate comprises water-soluble lignin.
The novel CNT composite conductive agent is added into the positive and negative electrode slurry, P electrons of carbon atoms on the CNT form a large-range delocalized pi bond, the conjugated effect is obvious, the structure is the same as that of a graphite lamellar structure, the conductive performance is good, and the conductive performance is very excellent when the CNT composite conductive agent is compounded with other materials to be used as the conductive agent. The novel lignin binder is adopted, and the molecular structure of lignin and derivatives thereof contains a large number of polar functional groups such as phenolic hydroxyl, methoxyl, carboxyl and the like, so that strong intermolecular interaction can be generated between the lignin and electrode plates, and the powder binding power is obviously enhanced; the phenolic groups in the lignin and the derivatives thereof can also partially capture free radicals generated by the decomposition of the electrolyte, and reduce the continuous decomposition of the electrolyte under high voltage, thereby forming a compact interfacial film compatible with the anode, preventing the dissolution of transition metals, and improving the stability and the cyclicity of the battery. The insulating properties of diaphragm is good, can improve the self interference killing feature of battery, can carry out the most effectual insulation to negative pole layer and positive pole layer simultaneously and block, unnecessary short circuit or puncture phenomenon can not appear, and wherein the coating material particle size distribution is even, and the diaphragm pore of making is even, and the electrolyte can be fine passes through, and heat resistance and mechanical properties are good, can further promote the overall stability of battery, and the security performance is high. The doped lithium iron phosphate and graphite materials with high specific capacity and high compaction are adopted, and the effective space in the battery is fully utilized, so that the capacity of the battery is improved.
Further, the content of the doping material is 5-15 wt%. The content of the doping material can influence the specific surface area and the conductivity of the lithium iron phosphate material, the content is too high, the specific surface area of the material is increased, particles are easy to be agglomerated together, and the conductivity of the material is poor if the content is too low; the content of the doped material is controlled to be 5-15 wt%, and the conductivity of the material is ensured.
Furthermore, the doping element in the element-doped carbon fiber or the carbon nanotube is one or more of boron, nitrogen, phosphorus and sulfur, so that the defects on the surface of the carbon nanotube are increased to increase holes for receiving electrons, and the conductivity of the carbon nanotube is further improved; meanwhile, the carbon nano tube with excellent conductivity builds a long-range conductive network between the positive active materials, electrons can still be conducted when the positive active materials are cracked in the circulating process, and the long-circulating performance of the battery cell is improved.
Further, the length of the carbon fiber is 0.5-5 μm, and the diameter is 0.5-50 nm;
further, the diameter of the carbon nano tube is 3-6 nm;
further, the boron nitride is hexagonal boron nitride, and the diameter of the hexagonal boron nitride is 0.5-50 nm.
Furthermore, the particle size of the coating layer material is 50-800 nm.
Further, the thickness of the diaphragm is 8-12 μm, the thickness of the base film is 6-10 μm, and the thickness of the coating layer is 2-3 μm. The diaphragm has small thickness, low internal resistance and high porosity, thereby improving the rate capability and the cycle performance of the battery.
Compared with the traditional battery, the battery has the advantages that the diaphragm, the aluminum foil current collector and the copper foil current collector which are thinner are adopted, the thickness can be reduced by about 50%, and finally, the content of active substances is improved by increasing the length of a battery roll core, so that the battery capacity is improved.
Further, the water-soluble lignin comprises one or more of lignosulfonate, sulfonated alkali lignin, sulfonated enzymatic hydrolysis lignin, carboxylated alkali lignin, carboxylated enzymatic hydrolysis lignin, ammonium alkali lignin, ammonium enzymatic hydrolysis lignin, aminated alkali lignin and aminated enzymatic hydrolysis lignin.
Further, the material of the coating layer also comprises polyacrylamide grafted graphene oxide or porous polyimide, and the material contains a large number of micropores through which an electrolyte can freely pass.
Furthermore, the adding amount of the positive electrode active material, the conductive agent and the binder is 93.5-97.5 parts, 1-2 parts and 2.5-5.5 parts respectively.
Furthermore, the adding amount of the negative electrode active material, the conductive agent and the binder is 92-95 parts, 2-5 parts and 3-6 parts respectively.
Further, the total concentration of solute in the electrolyte is 1-1.5 mol/L.
Furthermore, the electrolyte also comprises one or more additives of methyl benzoate, ethyl acetate, pyrophosphate, phosphorous acid triacrylate and (pentafluorophenyl) diphenylphosphorus (PFPDPP), and the additives can be used as an electrolyte stabilizer to form a protective layer on a positive electrode and a negative electrode, prevent overcharge, improve the cyclicity of the battery and prolong the service life of the battery.
Further, the solvent of the electrolyte is: EC. Two or more of PC, DMC, DEC, EMC and VC can effectively improve the low-temperature performance and the cycle performance of the battery.
Further, the conductive carbon black is Super P, KS-6 and C45One or more of (a).
Further, the binder further comprises one or more of PVDF, PTFE, CMC, SBR, PAni, PAA, PAALi, PEAA.
Further, the rolling thickness of the positive plate is 146-150 mu m, and the rolling compaction density is 2.2-2.5 g/c m3The slitting width is 58-61 mm; the rolling thickness of the negative plate is 148-152 mu m, and the rolling compaction density is 2.0-2.4 g/c m3And the slitting width is 58-61 mm.
The preparation method of the low-temperature high-energy-density long-cycle lithium iron phosphate battery comprises the following steps of:
s1, preparing anode and cathode slurry: adding a deionized water solvent into water-soluble lignin, and stirring for 0.5-1.5 hours in a planetary dispersion vacuum stirrer; adding a positive electrode conductive agent or a negative electrode conductive agent into the stirred solution, and stirring for 0.5-1 h to obtain a conductive adhesive solution;
taking a half of the positive electrode active material or the negative electrode active material, adding the conductive adhesive solution, adding other binders, stirring for 0.5-1.5 h, adding the other half of the positive electrode active material or the negative electrode active material, stirring for 1-3 h at the rotating speed of 5000-6000 r/min, adjusting the adding amount of deionized water, and adjusting the viscosity to be 5000-8000 mPa & s;
s2, coating: respectively coating the positive electrode slurry and the negative electrode slurry on a metal aluminum foil and a metal copper foil, controlling the single-side coating temperature to be 80-115 ℃, controlling the double-side coating temperature to be 80-130 ℃, and drying to obtain a positive electrode plate and a negative electrode plate;
s3, rolling: placing the positive plate and the negative plate on a roller press for rolling, wherein the rolling thickness of the obtained positive plate is 146-150 mu m, and the rolling compaction density is 2.2-2.5 g/cm3(ii) a The thickness of the negative plate is 148-152 mu m, and the rolling compaction is 2.0-2.4 g/c m3；
S4, preparing a diaphragm: adding a lignin and/or lignin derivative binder into NMP (N-methyl pyrrolidone) serving as a solvent, stirring at a rotating speed of 5000-6000 r/min for 3-4 hours, then adding a coating layer material and deionized water, and stirring at a rotating speed of 5000-6000 r/min for 5-6 hours to prepare coating layer slurry; coating layer slurry with the same thickness on two sides of the base film by using a coating machine, and drying;
s5, manufacturing a laminated core: cutting the positive and negative pole pieces into strips with the width of 58-61 mm, and winding the diaphragm and the positive and negative pole pieces into a roll core on a winding machine at the temperature of 20-25 ℃ and the humidity of 20-40% RH; baking at 90-100 ℃ under vacuum after shell assembly;
s6, injection: injecting electrolyte with the relative humidity of more than 5.5 g under the RH of 1-5% in a vacuum environment, vacuumizing, sealing after no floating liquid exists, cleaning and oiling;
s7, formation: and charging the battery cell, controlling the voltage to enable the battery cell to be formed, and activating the battery.
The invention prepares the slurry by adopting the novel positive and negative electrode active substances, the conductive agent and the binder, optimizes the proportion of the positive and negative electrode slurry, develops the novel positive and negative electrode homogenate process, and improves the preparation process of the lithium battery to prepare the lithium iron phosphate 18650 lithium battery with the energy density of 450Wh/L and the capacity of more than 2250 mAh.
The invention can obtain the following beneficial effects:
1. compared with other anode materials, LiFePO4The price of the material is relatively low, and the material cost is low; the positive active substance adopts doped lithium iron phosphate, has the advantages of small particles, uniform distribution, high specific capacity and high compaction, and does not need to add a positive active supplementary lithium material; boron nitride and carbon fiber or carbon nano tube can form a staggered layered structure with lithium iron phosphate, which is beneficial to the diffusion and conduction of lithium ions; the coating has high specific surface area and high dispersibility and compatibility, improves the conductivity of the material after coating, reduces the charge transfer resistance of electrochemical reaction, and greatly improves the cyclicity and the capacity of the battery.
2. The positive electrode and the negative electrode adopt novel lignin binders, and phenolic groups in the lignin and derivatives thereof can partially capture free radicals generated by decomposition of the electrolyte, so that a compact interface film compatible with the positive electrode and the negative electrode is formed, continuous decomposition of the electrolyte under high voltage is reduced, and the cyclicity and the rate capability of the lithium battery are effectively improved.
3. Thinner ceramic diaphragm, aluminum foil current collector and copper foil current collector are adopted, the thickness of the pole piece and the diaphragm is reduced, the length of the roll core is finally increased, the content of active substances is improved, the effective space in the battery is fully utilized, and therefore the capacity of the battery is improved; the diaphragm is made of a nano coating layer material, so that the grain size is small, the pore distribution is uniform, the resistivity is high, the prepared ceramic diaphragm has more and uniform pores, the electrolyte can freely pass through the ceramic diaphragm, and the battery has high overall stability and safety performance and good cyclicity.
4. The novel electrolyte and the solvent are adopted, so that the low-temperature performance and the cycle performance of the battery can be effectively improved, a protective layer can be formed on a positive electrode and a negative electrode, overcharge is prevented, the cycle performance of the battery is improved, and the service life of the battery is prolonged; the doped lithium iron phosphate material, the doped conductive agent and the diaphragm adopted by the invention act synergistically, so that the ion diffusion rate and the ion and electron conductivity are improved, the specific surface area of the anode material is improved, and the particle size of the anode material is reduced, so that the internal resistance of the anode material and the cathode material is reduced, the low-temperature service performance of the battery is effectively improved, the capacity retention rate at minus 20 ℃ is about 80%, and the capacity retention rate at minus 40 ℃ is about 58%.
5. The energy density of the battery reaches 450Wh/L, the 0.2C discharge capacity of the monomer battery cell is more than 2200mAh, the cycle performance is excellent, and the capacity retention rate is more than 80 percent after the battery cell is subjected to 0.5C/0.5C 100 percent DOD (dot over D) cycle for 1500 times.
6. The battery of the invention has the advantages of environmental protection, long cycle service life, high safety and the like. The lithium battery has small mass and large capacity, reduces the weight of the equipment while providing high electric quantity, and has very wide application prospect.
Drawings
Fig. 1 is a discharge curve diagram of a low-temperature type high-energy-density long-cycle lithium iron phosphate battery according to the present invention at 0.2C, 0.5C, and 1C discharge rates;
fig. 2 is a cycle curve diagram of the low-temperature type high-energy-density long-cycle lithium iron phosphate battery of the invention at a charge-discharge rate of 0.5C/0.5C.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1:
a low-temperature high-energy-density long-cycle lithium iron phosphate battery comprises a positive plate, a negative plate, a diaphragm, electrolyte and a shell; wherein, the positive plate is prepared by uniformly coating a mixture consisting of a positive active material, a conductive agent and a binder on two sides of a 1.5 μm metal aluminum foil, the rolling thickness is 148 μm, and the rolling compaction density is 2.35g/c m3The slitting width is 58 mm; the negative plate is prepared by uniformly coating a mixture consisting of a negative active material, a conductive agent and a binder on two sides of a metal copper foil with the thickness of 5 mu m, the rolling thickness is 148 mu m, and the rolling compaction density is 2.2g/c m3The slitting width was 58 mm. The mass of the obtained battery was 40.16 g.
The anode active material adopts doped lithium iron phosphate with the average particle size of 1.5um, wherein D50 is 1.5um, D90 is 5um, and the doped material comprises 10 wt% of hexagonal boron nitride with the diameter of 5-30 nm and 5 wt% of phosphorus-doped carbon fiber with the length of 1-4.5 mu m and the diameter of 3-50 nm; the conductive agent is CNT composite GR, and the binder is lignosulfonate. The negative electrode active material is graphite, the conductive agent is CNT, and the binder is ammonium enzymatic hydrolysis lignin, sulfonated alkali lignin and PEAA. The adding amounts of the positive electrode active material, the conductive agent and the binder in the positive electrode coating mixture are 93.8 wt%, 1.2 wt% and 5 wt% respectively, and the adding amounts of the negative electrode active material, the conductive agent and the binder in the negative electrode coating mixture are 92.2 wt%, 2.5 wt% and 5.3 wt% respectively, wherein the adding amount of the ammonification enzymolysis lignin is 2wt%, the adding amount of the sulfonated alkali lignin is 1.5 wt%, and the adding amount of the PEAA is 1.8 wt%.
The diaphragm is a PE basal membrane coated with a coating layer, and the coating layer is made of nanoscale Al2O3And BaSO4(mass ratio 1: 1) and the particle size is 50-800 nm. LiPF with electrolyte of 1mol/L6Solution, 0.2mol/L LiBF4Solution and 0.1mol/L LiPO2F2The solvent of the solution is EC, PC and VC (volume ratio is 1: 1: 1).
Example 2:
a low-temperature high-energy-density long-cycle lithium iron phosphate battery comprises a positive plate, a negative plate, a diaphragm, electrolyte and a shell; wherein the positive plate is formed by activating the positive electrodeThe mixture of the material, the conductive agent and the adhesive is evenly coated on two sides of a metal aluminum foil with the thickness of 2 mu m, the rolling thickness is 147 mu m, and the rolling compaction density is 2.3g/c m3The slitting width is 59 mm; the negative plate is prepared by uniformly coating a mixture consisting of a negative active material, a conductive agent and a binder on two sides of a 6.5-micron metal copper foil, wherein the rolling thickness is 149 microns, and the rolling compaction density is 2.3g/c m3The slitting width was 59 mm. The obtained battery had a mass of 40.43 g.
The anode active material adopts doped lithium iron phosphate with the average particle size of 2.5um, wherein D50 is 3um, D90 is 7um, and the doped material comprises 12wt% of hexagonal boron nitride with the diameter of 10-30 nm and 3 wt% of nitrogen and phosphorus doped carbon fiber with the length of 2-5 mu m and the diameter of 15-40 nm; the conductive agent is CNT composite CF, and the binder is sulfonated enzymatic hydrolysis lignin, carboxylated alkali lignin and PTFE. The negative electrode active material is graphite, the conductive agent is CNT, and the binder is lignosulfonate, carboxylated enzymatic lignin, CMC, PANi and PAA. The adding amounts of the positive electrode active material, the conductive agent and the binder in the positive electrode coating mixture are respectively 95.5 wt%, 2wt% and 2.5 wt%, wherein the adding amounts of the sulfonated enzymatic hydrolysis lignin are 0.8 wt%, the carboxylated alkali lignin is 1.2 wt% and the PTFE is 0.5 wt%, the adding amounts of the negative electrode active material, the conductive agent and the binder in the negative electrode coating mixture are respectively 92.5 wt%, 4.5 wt% and 3 wt%, wherein the adding amount of the CMC is 0.5 wt%, the adding amount of the lignosulfonate is 0.7 wt%, the adding amount of the carboxylated enzymatic hydrolysis lignin is 0.8 wt%, the adding amount of the PANi is 0.5 wt%, and the adding amount of the PAA is 0.5 wt%.
The diaphragm is a PE basal membrane coated with a coating layer, and the coating layer is made of nano-scale BaSO4And AlN (in a mass ratio of 3: 2) with a particle diameter of 100 to 500 nm. LiPF electrolyte of 0.8mol/L6The solution, 0.25mol/L LiBOB solution and 0.3mol/L LiDTI solution, and the solvents are EC, DMC, DEC and VC (volume ratio is 1: 1: 1: 1).
Example 3:
a low-temperature high-energy-density long-cycle lithium iron phosphate battery comprises a positive plate, a negative plate, a diaphragm, electrolyte and a shell; wherein the positive plate is prepared from positive active material, conductive agent and binderThe mixture was uniformly coated on both sides of a 3.5 μm metal aluminum foil, rolled to a thickness of 150 μm, and rolled to a compact density of 2.45g/c m3The slitting width is 58.5 mm; the negative plate is prepared by uniformly coating a mixture consisting of a negative active material, a conductive agent and a binder on two sides of a 6-micron metal copper foil, wherein the rolling thickness is 150 microns, and the rolling compaction density is 2.33g/c m3The slitting width was 58.5 mm. The mass of the obtained battery was 39.81 g.
The anode active material adopts doped lithium iron phosphate with the average particle size of 3.5um, wherein D50 is 4um, D90 is 6um, the doped material is 8 wt% of hexagonal boron nitride with the diameter of 10-30 nm, 3.5 wt% of sulfur and phosphorus doped carbon nano tubes with the diameter of 3-5 nm and 3.5 wt% of boron and nitrogen doped carbon fibers with the length of 1-4.5 mu m and the diameter of 6-50 nm; the conductive agent is CNT composite GR, and the binder is aminated alkali lignin, ammonified enzymatic hydrolysis lignin and PVDF. The negative active material is graphite, and the conductive agents are Super P and C45The binder is sulfonated alkali lignin, carboxylated alkali lignin, CMC and PANi. The adding amounts of the positive electrode active material, the conductive agent and the binder in the positive electrode coating mixture are respectively 95.5 wt%, 1.5 wt% and 3 wt%, wherein the adding amounts of the aminated alkali lignin are 1.5 wt%, the aminated enzymatic lignin is 1.0 wt% and the PVDF is 0.5 wt%, the adding amounts of the negative electrode active material, the conductive agent and the binder in the negative electrode coating mixture are respectively 93.2 wt%, 3.5 wt% and 3.3 wt%, wherein the adding amount of the sulfonated alkali lignin is 0.8 wt%, the adding amount of the carboxylated alkali lignin is 0.8 wt%, the adding amount of the CMC is 1 wt%, and the adding amount of the PANi is 0.7 wt%.
The diaphragm is a PE basal membrane coated with a coating layer, and the coating layer is made of nanoscale Al2O3BN and polyacrylamide grafted graphene oxide (the mass ratio is 10: 8: 3), and the particle size is 80-600 nm. LiPF electrolyte of 0.9mol/L6The solution, 0.2mol/L LiBOB solution, 0.2mol/L LiDFOB solution and 0.2mol/L LiTFSI solution, the solvents are EC, DMC, DEC and VC (the volume ratio is 1: 1: 1: 1), and additives of methyl benzoate, pyrophosphate and phosphorous acid triacrylate (the addition amount is 0.0025mol/L) are also added, so that the stability and the cyclicity of the battery are improved.
Example 4:
a low-temperature high-energy-density long-cycle lithium iron phosphate battery comprises a positive plate, a negative plate, a diaphragm, electrolyte and a shell; wherein, the positive plate is prepared by uniformly coating a mixture consisting of a positive active material, a conductive agent and a binder on two sides of a metal aluminum foil with the thickness of 150 mu m, and the rolling compaction density is 2.5g/c m3The slitting width is 59.5 mm; the negative plate is prepared by uniformly coating a mixture consisting of a negative active material, a conductive agent and a binder on two sides of a metal copper foil with the thickness of 5 mu m, the rolling thickness is 150 mu m, and the rolling compaction density is 2.4g/c m3The slitting width was 59.5 mm. The mass of the obtained battery was 40.21 g.
The anode active material adopts doped lithium iron phosphate with the average particle size of 5um, wherein D50 is 5um, D90 is 8um, the doped material is 3 wt% of hexagonal boron nitride with the diameter of 0.5-50 nm, 1.5 wt% of phosphorus-doped carbon nano tubes with the diameter of 3-6 nm and 0.5 wt% of sulfur-and phosphorus-doped carbon fibers with the length of 0.5-4.5 mu m and the diameter of 6-50 nm; the conductive agent is CNT composite Super P, and the binder is carboxylated enzymatic hydrolysis lignin, ammonium alkali lignin and PTFE. The negative active material is graphite, the conductive agents are Super P and KS-6, and the binders are CMC, SBR and sulfonated enzymatic hydrolysis lignin. The adding amounts of the positive electrode active material, the conductive agent and the binder in the positive electrode coating mixture are respectively 94.2 wt%, 1 wt% and 4.8 wt%, wherein the adding amounts of the carboxylated enzymatic hydrolysis lignin are 1.0 wt%, the ammonium alkali lignin is 1.8 wt% and the PTFE is 2wt%, and the adding amounts of the negative electrode active material, the conductive agent and the binder in the negative electrode coating mixture are respectively 94.5 wt%, 2.2 wt% and 3.3 wt%, wherein the adding amount of the sulfonated enzymatic hydrolysis lignin is 1.5 wt%, the adding amount of the SBR is 0.8 wt%, and the adding amount of the CMC is 0.7 wt%.
The diaphragm is a PE basal membrane coated with a coating layer, and the coating layer is made of nano-scale BaSO4AlN and BN (in a mass ratio of 1: 1: 1.5) and having a particle diameter of 80 to 800 nm. LiPF electrolyte of 1.1mol/L6The solution, 0.05mol/L LiDFOB solution and 0.1mol/L LiTFSI solution, and the solvents are EC, DEC, EMC and VC (volume ratio is 1: 1: 1: 1).
Example 5:
low-temperature high-energyThe long-cycle lithium iron phosphate battery with the density comprises a positive plate, a negative plate, a diaphragm, electrolyte and a shell; wherein the positive plate is prepared by uniformly coating a mixture consisting of a positive active material, a conductive agent and a binder on two sides of a 3.5-micron metal aluminum foil, the rolling thickness is 150 microns, and the rolling compaction density is 2.5g/c m3The slitting width is 59.5 mm; the negative plate is prepared by uniformly coating a mixture consisting of a negative active material, a conductive agent and a binder on two sides of a 6-micron metal copper foil, wherein the rolling thickness is 150 microns, and the rolling compaction density is 2.4g/c m3The slitting width was 59.5 mm. The mass of the obtained battery was 41.07 g.
The anode active material adopts doped lithium iron phosphate with the average particle size of 5um, wherein D50 is 5um, D90 is 8um, the doped material is 3 wt% of hexagonal boron nitride with the diameter of 0.5-50 nm, 1.5 wt% of boron, nitrogen and sulfur doped carbon nano tubes with the diameter of 3-6 nm and 0.5 wt% of phosphorus doped carbon fibers with the length of 0.5-4.5 mu m and the diameter of 6-50 nm; the conductive agent is CNT composite Super P, and the binder is aminated enzymatic hydrolysis lignin and PAALi. The negative active material is graphite, and the conductive agents are Super P, KS-6 and C45The binder is aminated enzymatic hydrolysis lignin, SBR, PANi and PVDF. The adding amounts of the positive electrode active material, the conductive agent and the binder in the positive electrode coating mixture are respectively 95.5 wt%, 1.5 wt% and 3 wt%, wherein the adding amounts of the aminated enzymatic lignin are 2.5 wt% and the PAALi is 0.5 wt%, the adding amounts of the negative electrode active material, the conductive agent and the binder in the negative electrode coating mixture are respectively 93.2 wt%, 3.5 wt% and 3.3 wt%, wherein the adding amount of the aminated enzymatic lignin is 1 wt%, the adding amount of the SBR is 0.8 wt%, the adding amount of the PANi is 0.7 wt%, and the adding amount of the PVDF is 0.8 wt%.
The diaphragm is a PE basal membrane coated with a coating layer, and the coating layer is made of nanoscale Al2O3、BaSO4AlN and porous polyimide (in a mass ratio of 10: 8: 5: 1) with a particle size of 200 to 800 nm. LiPF electrolyte of 0.8mol/L6The solution, 0.2mol/L LiDFOB solution and 0.1mol/L LiTFSI solution, and the solvents are EC, DMC and VC (volume ratio is 1: 1: 1: 1).
Example 6:
the method for preparing the low-temperature type high-energy-density long-cycle lithium iron phosphate battery of the embodiment 1 to the embodiment 5 includes the following steps:
s1, preparing anode and cathode slurry: adding a deionized water solvent into water-soluble lignin, and stirring for 0.5-1.5 hours in a planetary dispersion vacuum stirrer; adding a positive electrode conductive agent or a negative electrode conductive agent into the stirred solution, and stirring for 0.5-1 h to obtain a conductive adhesive solution;
taking a half of the positive electrode active material or the negative electrode active material, adding the conductive adhesive solution, adding other binders, stirring for 0.5-1.5 h, adding the other half of the positive electrode active material or the negative electrode active material, stirring for 1-3 h at the rotating speed of 5000-6000 r/min, adjusting the adding amount of deionized water, and adjusting the viscosity to be 5000-8000 mPa & s;
s2, coating: respectively coating the positive electrode slurry and the negative electrode slurry on a metal aluminum foil and a metal copper foil, controlling the single-side coating temperature to be 80-115 ℃, controlling the double-side coating temperature to be 80-130 ℃, and drying to obtain a positive electrode plate and a negative electrode plate;
s3, rolling: placing the positive plate and the negative plate on a roller press for rolling, wherein the rolling thickness of the obtained positive plate is 146-150 mu m, and the rolling compaction density is 2.2-2.5 g/cm3(ii) a The thickness of the negative plate is 148-152 mu m, and the rolling compaction is 2.0-2.4 g/c m3；
S4, preparing a diaphragm: adding a lignin and/or lignin derivative binder into NMP (N-methyl pyrrolidone) serving as a solvent, stirring at a rotating speed of 5000-6000 r/min for 3-4 hours, then adding a coating layer material and deionized water, and stirring at a rotating speed of 5000-6000 r/min for 5-6 hours to prepare coating layer slurry; coating layer slurry with the same thickness on two sides of the base film by using a coating machine, and drying;
s5, manufacturing a laminated core: cutting the positive and negative pole pieces into strips with the width of 58-61 mm, and winding the diaphragm and the positive and negative pole pieces into a roll core on a winding machine at the temperature of 20-25 ℃ and the humidity of 20-40% RH; baking at 90-100 ℃ under vacuum after shell assembly;
s6, injection: injecting electrolyte into the liquid injection environment under the conditions that the vacuum degree is more than or equal to-0.085 Pa and the relative humidity is 1-5% RH, sealing after no floating liquid exists, cleaning and oiling;
s7, formation: and charging the battery cell, controlling the voltage to enable the battery cell to be formed, and activating the battery.
Among them, the element-doped carbon nanotube and/or carbon fiber is prepared according to CN 108963256 a.
The preparation method of the doped lithium iron phosphate comprises the following steps:
(1) mixing lithium hydroxide, lithium carbonate or lithium acetate, a composite iron source consisting of ferric orthophosphate and metal iron powder and lithium dihydrogen phosphate according to a certain proportion, then putting into a dispersion kettle, adding a solvent serving as a dispersing agent for dispersion, coarse grinding and fine grinding to obtain uniformly mixed slurry, and performing spray drying to obtain spherical precursor powder;
(2) adding boron nitride into the spherical precursor powder, finally adding carbon-doped carbon nanotubes and/or carbon fibers, and placing the mixture in a mortar for grinding for 2.5 hours to obtain a doped lithium iron phosphate precursor;
(3) the method comprises the following steps of (1) heating a doped lithium iron phosphate precursor to 550 ℃ at a heating rate of 30 ℃/min in a nitrogen atmosphere at room temperature as an initial temperature, and keeping for 3 hours; raising the temperature to 700 ℃ at the temperature rise rate of 20 ℃/min, and keeping the temperature for 8 hours; and cooling to below 50 ℃ to obtain black powder, namely the doped lithium iron phosphate.
Comparative example 1:
the same procedure as in example 3 was repeated except that the positive electrode active material used was gold lithium technology K24 type lithium iron phosphate.
Comparative example 2:
the positive active material adopts gold lithium scientific K24 type lithium iron phosphate, the positive conductive agent adopts carbon nano tube, the diaphragm adopts nano Al on PE basal membrane2O3Otherwise, the same procedure as in example 3 was repeated.
Comparative example 3:
the positive active material adopts gold lithium scientific K24 type lithium iron phosphate, the positive binder adopts PVDF, the negative binders CMC and SBR, the diaphragm adopts nanometer Al on PE basal membrane2O3Otherwise, the same procedure as in example 3 was repeated.
And (4) testing results:
the performance tests of the lithium iron phosphate 18650 lithium battery cells of examples 1-5 and comparative examples 1-3 showed the following results:
1. the discharge capacity of the lithium iron phosphate type 18650 lithium batteries of examples 1 to 5 and comparative examples 1 to 3 at a discharge rate of 0.2C and the cyclicity of the battery cell at a charge-discharge rate of 0.5C/0.5C were tested under the following test conditions:
and (3) testing discharge capacity: the battery cell is charged to 3.65V at 0.2C, and then discharged to 2.5V at 0.2C, 0.5C and 1C, and the test result is shown in figure 1;
and (3) testing the cyclicity: the cut-off voltage was 3.65V at 0.5C, and after standing and discharging at 0.5C, the cut-off voltage was 2.5V for one charge-discharge cycle, and the results are shown in Table 1, and the test results of example 3 are shown in FIG. 2.
TABLE 1
Figure BDA0002133721460000151
Figure BDA0002133721460000161
As can be seen from Table 1, the discharge capacity of the lithium iron phosphate 18650 lithium battery is more than or equal to 2250mAh of 0.2C of the single battery cell, and the maximum discharge capacity of the lithium iron phosphate 18650 lithium battery in the prior art is 2000mAh (CN201810889165.7), compared with the prior art, the discharge capacity of the lithium iron phosphate 18650 lithium battery is improved by more than 10%; as shown in fig. 1 and table 1, after the battery cell is subjected to 0.5C/0.5C 100% DOD cycling for 1500 times, the capacity retention rate is all over 80%, the cyclicity is improved by over 1/3, and the battery cell has excellent cycling performance.
2. The capacity retention rates of the lithium iron phosphate 18650 lithium batteries of examples 1-5 and comparative examples 1-3 at different temperatures were tested, and the results are shown in table 2, and the test results of examples 1 and 2 are shown in fig. 2.
TABLE 2
Figure BDA0002133721460000162
As can be seen from fig. 2 and table 2, the lithium iron phosphate 18650 lithium battery of the present invention has high discharge capacity and good thermal stability, the capacity retention rate at 55 ℃ is above 99%, the capacity retention rate at 0 ℃ is above 91%, the capacity retention rate at-20 ℃ is about 80%, the capacity retention rate at-40 ℃ is about 58%, which indicates that the lithium iron phosphate positive electrode is doped with BN, carbon-doped carbon nanotube or carbon fiber, the separator material is made of a nano-porous material, and the positive and negative binders are made of water-soluble cellulose, so that the low-temperature service performance of the battery is improved; the capacity retention rate at the maximum temperature of-20 ℃ reaches 81.5 percent, the capacity retention rate at the temperature of-40 ℃ reaches 59.4 percent, and the capacity retention rate is improved by more than 15 percent.
The results of the temperature rise experiments are shown in table 3.
TABLE 3
Figure BDA0002133721460000171
As shown in Table 3, the lithium iron phosphate 18650 lithium battery of the invention has a temperature rise of about 1.5 ℃ at 55 ℃, a temperature rise of about 10 ℃ at 0 ℃, a temperature rise of about 15 ℃ at-20 ℃ and a temperature rise of about 21 ℃ at-40 ℃, and further proves that the lithium battery of the invention has good thermal stability.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments or portions thereof without departing from the spirit and scope of the invention.

Claims (8)

1. The utility model provides a long circulation lithium iron phosphate battery of low temperature type high energy density which characterized in that, includes positive plate, negative pole piece, diaphragm, electrolyte and shell, and the positive plate is made at 1~5 mu m's metal aluminium foil both sides with the mixture homogeneous coating that positive active material, conductive agent and binder are constituteed, and the negative pole piece is made at 4~8 mu m's metal copper foil both sides with the mixture homogeneous coating that negative active material, conductive agent and binder are constituteed, wherein: the cathode active material is doped lithium iron phosphate, the average particle size is 1-5 um, D50 is 0.5-5 um, D90 is less than or equal to 8um, the doped material is boron nitride, and element-doped carbon fiber or carbon nano tube, the boron nitride is hexagonal boron nitride, the doped elements in the element-doped carbon fiber or carbon nano tube are one or more of boron, nitrogen, phosphorus and sulfur, the content of the doped material is 5-15 wt%, wherein: the content of boron nitride is 10 wt%, the diameter is 5-30 nm, the content of element-doped carbon fiber is 5 wt%, or the content of boron nitride is 12wt%, the diameter is 10-30 nm, the content of element-doped carbon fiber is 3 wt%, or the content of boron nitride is 8 wt%, the diameter is 10-30 nm, the content of element-doped carbon fiber is 3.5 wt%, the content of element-doped carbon nanotube is 3.5 wt%, or the content of boron nitride is 3 wt%, the diameter is 0.5-50 nm, the content of element-doped carbon fiber is 0.5 wt%, and the content of element-doped carbon nanotube is 1.5 wt%.
2. The low-temperature type high-energy-density long-cycle lithium iron phosphate battery as claimed in claim 1, wherein the conductive agent of the positive plate is CNT composite GR, CNT composite Super P or CNT composite CF; the diaphragm is a base film coated with a coating layer, the base film is a PE or PP base film, and the coating layer is made of nanoscale Al2O3、BaSO4AlN and BN; the negative active material is graphite, and the conductive agent of the negative plate is conductive carbon black and/or CNT; the electrolyte is LiPF6A solution wherein the solute further comprises LiBF4、LiPO2F2One or more of LiBOB, LiDTI, LiTFSI and LiDFOB, wherein the binder of the positive plate and the negative plate comprises water-soluble lignin.
3. The low-temperature type high-energy-density long-cycle lithium iron phosphate battery according to claim 1, further comprising at least one of the following technical features:
the length of the carbon fiber is 0.5-5 mu m, and the diameter of the carbon fiber is 0.5-50 nm;
the diameter of the carbon nano tube is 3-6 nm.
4. The low-temperature type high-energy-density long-cycle lithium iron phosphate battery according to claim 2, further comprising at least one of the following technical features:
the water-soluble lignin comprises one or more of lignosulfonate, sulfonated alkali lignin, sulfonated enzymatic lignin, carboxylated alkali lignin, carboxylated enzymatic lignin, ammonium alkali lignin, ammonium enzymatic lignin, aminated alkali lignin and aminated enzymatic lignin;
the particle size of the coating layer material is 50-800 nm;
the diaphragm is 8-12 mu m in thickness, the base film is 6-10 mu m in thickness, and the coating layer is 2-3 mu m in thickness.
5. The low-temperature high-energy-density long-cycle lithium iron phosphate battery as claimed in any one of claims 1 to 4, wherein the positive electrode active material, the conductive agent and the binder are added in an amount of 93.5 to 97.5 parts, 1 to 2 parts and 2.5 to 5.5 parts by mass, respectively;
the adding amount of the active material, the conductive agent and the binder in the negative coating mixture is respectively 92-95 parts, 2-5 parts and 3-6 parts.
6. The low-temperature type high-energy-density long-cycle lithium iron phosphate battery according to claim 5, further comprising at least one of the following technical features:
the conductive carbon black is Super P, KS-6 and C45One or more of;
the binder further comprises one or more of PVDF, PTFE, CMC, SBR, PANi, PAA, PAALi, PEAA;
the total concentration of solute in the electrolyte is 1-1.5 mol/L, and the solvent of the electrolyte is as follows: EC. Two or more of PC, DMC, DEC, EMC, VC.
7. The low-temperature type high-energy-density long-cycle lithium iron phosphate battery as claimed in claim 6, wherein the electrolyte further comprises one or more additives selected from methyl benzoate, ethyl acetate, pyrophosphate, phosphorous acid triacrylate and (pentafluorophenyl) diphenylphosphorus.
8. The low-temperature type high-energy-density long-cycle lithium iron phosphate battery as claimed in claim 1, wherein the rolled thickness of the positive plate is 146-150 μm, and the rolled compaction density is 2.2-2.5 g/c m3The slitting width is 58-61 mm; the rolling thickness of the negative plate is 148-152 mu m, and the rolling compaction density is 2.0-2.4 g/c m3And the slitting width is 58-61 mm.
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