CN111063952A - Lithium iron phosphate lithium ion battery and formation process thereof - Google Patents
Lithium iron phosphate lithium ion battery and formation process thereof Download PDFInfo
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Abstract
The invention provides a lithium iron phosphate lithium ion battery and a formation process thereof, wherein a specially-made lithium ion battery anode material lithium iron phosphate is subjected to processes of coating, baking, rolling, laminating, assembling, baking and the like, and a specific formation process is combined, the steps of injecting liquid, pre-sealing holes, placing, opening the pre-sealed holes, charging at normal temperature with small current and re-sealing holes are specifically included, so that the finally-prepared lithium iron phosphate lithium ion battery can reduce moisture absorption and harm of moisture to the battery, and the lithium iron phosphate battery with high service life and good safety performance is obtained.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium iron phosphate lithium ion battery and a formation process thereof.
Background
In China, new energy automobile science and technology planning is implemented from the fifteen stage, and electric automobiles and hybrid electric automobiles start to enter the visual field of people. Through research and promotion for many years, the electric automobile industry in China has been developed on a large scale at present. Due to the shortage of traditional energy and the requirement of environmental protection, China sets up relevant policies to encourage and support the development of new energy automobiles, and the development of new energy automobiles has important use value.
The battery provides electric energy for a driving motor of the electric automobile, and the electric energy is converted into mechanical energy through the motor. The most widely used power source in the early stage is the lead-acid storage battery, but with the development of the electric automobile technology, the lead-acid storage battery is gradually replaced by the lithium ion battery due to low energy, slow charging speed and short service life. The lithium iron phosphate battery is one of lithium ion batteries, and has longer service life and better safety performance.
In the production process of the lithium ion battery, formation is an important process, a Solid Electrolyte Interface (SEI) film is formed on the surface of a negative electrode during formation, and the quality of the SEI film directly influences the safety, stability, rate, cycle life and other electrochemical properties of the battery. In the prior art, most companies in China are opened to form lithium iron phosphate lithium ion batteries when the batteries are charged, and the lithium iron phosphate lithium ion batteries are easy to absorb water, so that electrolyte is deteriorated, and battery rivets are rusted, so that the problems of overlarge internal pressure, high internal resistance, high self-discharge, low capacity, low cycle life and the like of the batteries are caused.
CN104900930A provides a method for high-efficiency formation of lithium ion batteries, which comprises the steps of firstly carrying out constant-current charging and then carrying out constant-voltage charging until the current is less than 0.01-0.1C, wherein the lithium ion batteries such as lithium iron phosphate, nickel cobalt manganese and the like prepared by the formation process have the battery capacity below 1475mAh, the battery capacity is less than 95 percent after the lithium ion batteries are circularly used for 300 times, the cycle life of the batteries is not high, and the internal resistance of the batteries is necessarily higher.
Disclosure of Invention
In order to solve the problems in the prior art and further optimize the prior art, the invention provides a lithium iron phosphate lithium ion battery and a formation process thereof, so as to realize the following purposes:
1. the lithium iron phosphate lithium ion battery reduces the moisture absorption, reduces the harm of moisture to the battery and prolongs the service life of the battery;
2. the internal resistance of the battery is reduced;
3. the battery capacity is improved;
in order to solve the technical problems, the invention adopts the following technical scheme:
a formation process of a lithium iron phosphate lithium ion battery is characterized by comprising liquid injection, hole pre-sealing, placing, hole opening, normal-temperature low-current charging and hole resealing;
the liquid injection is carried out, wherein the temperature of a battery cell is 25-45 ℃ during liquid injection, and the relative humidity in the glove box is lower than 1%;
the injection liquid and the electrolyte comprise the following components: 60-73 parts of solvent, 25-35 parts of lithium salt and 2-5% of additive; the solvent is a mixed solvent of EC, EMC and DMC, and the mass ratio of EC, EMC and DMC is 1:1-1.2: 1-1.4; the additive is one or more of VC, FEC and PS; the lithium salt is LiPO2F2The concentration of lithium salt is 1.05 MOL/L;
the pre-sealing hole is completed within 2 minutes after the liquid injection hole is sealed;
the standing temperature is 20-45 ℃, and the standing time is 18-24 h;
after the pre-sealed hole is opened and the placement is finished, the sealed liquid injection hole is opened after liquid injection;
the normal temperature low current charging comprises the following charging steps:
① left for 2 minutes;
② 0.01.01C for 10-30 min, and limiting voltage to 2.5V;
③ standing for 2-3 min;
④ 0.02.02C for 10-30 minutes, and the voltage is limited to 2.8V;
⑤ standing for 2-3 min;
⑥ 0.05.05C for 30-60 minutes, and limiting the voltage to 3V;
⑦ standing for 2-3 min;
⑧ 0.1.1C for 100-120 min, limiting the voltage to 3.4V;
⑨ standing for 2-3 min;
⑩ 0.12.12C for 350-450 min, the voltage is limited to 3.85V;
the hole is sealed again, and after the charging is finished, the liquid injection hole is sealed again;
the preparation method of the positive electrode material lithium iron phosphate is characterized by comprising the steps of preparing, doping, carbon coating and calcining nanoscale lithium iron phosphate precursor particles;
preparing the nano-scale lithium iron phosphate precursor particles, reacting at the temperature of 180 ℃ and 185 ℃ in a nitrogen atmosphere, and reacting for 8-10h in a heat preservation manner; the addition amount of the anhydrous sodium acetate is 1 to 1.5 times of the total molar amount of the lithium salt, the iron salt and the phosphate; the addition concentration of polyacrylic acid is 10.5-12 g/L;
preparation of the nanoscale lithium iron phosphate precursor particles, lithium salt Li2CO3Iron salt Fe2Cl24H2O and phosphate LiH2PO4In a molar ratio of 1: 0.5-1.5: 1-2;
the doping proportion is 2 to 5 percent; wherein the mixing mass ratio of the sodium-doped zinc oxide to the cobalt-doped manganese oxide is 1: 1.6-2.2; the total amount of the added sodium-doped zinc oxide and cobalt-doped manganese oxide is 11-15% of the mass of the precursor particles;
the adding amount of the N-methyl pyrrolidone is 5-7% of the mass of the precursor particles;
the doping is carried out by taking absolute ethyl alcohol as a medium and carrying out wet ball milling in a ball mill for 3-5h, wherein the rotating speed of the ball mill is 500-;
the carbon coating is carried out, the room temperature liquid phase coating is carried out for 6-12h, the rotating speed of the ball mill is 100-120rad/min, and the mass concentration of the ethylene glycol solution of the corn starch is 15-18%;
and calcining, namely placing in an argon environment for calcining, firstly heating to 400 ℃ at the heating rate of 20 ℃/min, preserving heat for 2h, then heating to 650 ℃ at the heating rate of 10 ℃/min, preserving heat for 2h, finally heating to 750 ℃ at the heating rate of 5 ℃/min, preserving heat for 4h, and then cooling at room temperature to obtain the lithium iron phosphate as the cathode material of the lithium ion battery.
By adopting the technical scheme, the invention has the beneficial effects that:
1. by adopting the lithium iron phosphate lithium ion battery and the formation process thereof, the moisture absorption can be reduced, the harm of moisture to the battery can be reduced, the lithium iron phosphate battery with long service life and good safety performance can be obtained, and the discharge capacity can still reach more than 95 percent of the initial capacity when the lithium iron phosphate battery is recycled for 1000 times;
2. by adopting the lithium iron phosphate lithium ion battery and the formation process thereof, the internal resistance of the prepared battery is reduced to 50-55 milliohms, the nominal voltage of a monomer is increased to 3.33-3.34V, the high-order stop charging voltage is 4.00-4.11V, and the low-order stop discharging voltage is 2.5-3.2V;
3. by adopting the lithium iron phosphate lithium ion battery and the formation process thereof, the battery capacity can reach 1830-;
4. by adopting the lithium iron phosphate lithium ion battery and the formation process thereof, the prepared aluminum shell battery is subjected to a cycle test, the 50-week capacity retention rate is 97.7-98.2%, the battery has a long cycle service life, and the battery has good charge and discharge performance.
The specific implementation mode is as follows:
the invention is further illustrated below with reference to specific examples.
Example 1 lithium iron phosphate lithium ion battery and formation process thereof
The preparation method of the lithium iron phosphate as the positive material of the lithium ion battery comprises the following steps:
1) preparing nanometer lithium iron phosphate precursor particles:
1mmol of lithium salt Li2CO30.5mmol of iron salt Fe2Cl2·4H2O and 1mmol of phosphate LiH2PO4Dissolving in 30ml of ethylene glycol solution, uniformly dissolving by magnetic stirring, adding 3mmol of anhydrous sodium acetate and 0.32g of polyacrylic acid into the mixed solution, and stirring until the mixture is uniformly mixed; then transferring the mixture into a sealed high-pressure reaction kettle, raising the temperature to 180 ℃ in a nitrogen atmosphere, and carrying out heat preservation reaction for 8 hours;
after the reaction is finished, naturally cooling to room temperature, filtering and collecting a solid product, washing the solid product for multiple times by using a deionized water ethanol mixed solvent with the volume fraction of 50% until the solvent is clear and transparent, and putting the solvent into a 50 ℃ oven to be dried for 7 hours to obtain nano-scale lithium iron phosphate precursor particles;
2) doping:
adding sodium-doped zinc oxide and cobalt-doped manganese oxide into nanoscale lithium iron phosphate precursor particles, simultaneously adding N-methyl pyrrolidone, performing wet ball milling in a ball mill for 3 hours by taking absolute ethyl alcohol as a medium, wherein the rotating speed of the ball mill is 550rad/min, and then placing the mixture in a vacuum drying oven at 45 ℃ for drying for 12 hours;
the doping proportion is 2.5%; wherein the mixing mass ratio of the sodium-doped zinc oxide to the cobalt-doped manganese oxide is 1: 1.6;
the total amount of the sodium-doped zinc oxide and the cobalt-doped manganese oxide is 11.5 percent of the mass of the precursor particles;
the adding amount of the N-methyl pyrrolidone is 5.0 percent of the mass of the precursor particles;
3) carbon coating:
grinding the doped precursor particles in a spherical grinder at the rotating speed of 160rad/min for 2h, adding an ethylene glycol solution of corn starch, continuing ball-milling and mixing, carrying out liquid phase coating at room temperature for 8h, and drying to constant weight, wherein the rotating speed of the ball mill is 100 rad/min;
the mass concentration of the ethylene glycol solution of the corn starch is 15%;
4) and (3) calcining:
and placing the lithium iron phosphate in an argon environment for calcination treatment, namely heating to 400 ℃ at a heating rate of 20 ℃/min, preserving heat for 2h, then heating to 650 ℃ at a heating rate of 10 ℃/min, preserving heat for 2h, finally heating to 750 ℃ at a heating rate of 5 ℃/min, preserving heat for 4h, and then cooling at room temperature to obtain the lithium iron phosphate material of the lithium ion battery anode.
Mixing the prepared lithium iron phosphate with auxiliary materials, coating the mixture on an aluminum foil to obtain a positive electrode material, coating a graphite material on a copper foil to obtain a negative electrode material, and performing a series of processes such as baking, rolling, laminating, assembling, baking, liquid injection, formation, capacity grading and the like to complete the preparation of the lithium iron phosphate lithium ion battery;
the formation process comprises the following specific steps:
(1) liquid injection
Injecting liquid into the baked battery cell in a glove box in a nitrogen atmosphere, wherein the temperature of the battery cell is 30 ℃ and the relative humidity in the glove box is lower than 1% during liquid injection, vacuumizing is performed before liquid injection, the electrolyte is ensured to be completely injected, and redundant gas is discharged;
the electrolyte comprises the following components in parts by weight: 60 parts of solvent, 25 parts of lithium salt and 5% of additive;
the solvent is a mixed solvent of EC, EMC and DMC, and the mass ratio of EC, EMC and DMC is 1:1: 1;
the additive is FEC;
the lithium salt is LiPO2F2The concentration of lithium salt is 1.05 MOL/L;
(2) pre-sealing holes
After the liquid injection is finished, screwing the cap, sealing the liquid injection hole, and finishing the pre-sealing within 2 minutes;
(3) lay aside
The electrolyte is effectively absorbed, the pole piece is well soaked, the standing temperature is 25 ℃, and the standing time is 24 hours;
(4) opening pre-sealed holes
After the placement is finished, opening the sealed liquid injection hole after liquid injection;
(5) normal temperature small current charging
The charging process comprises the following steps:
① laying aside for 2 min
② 0.01.01C for 15 min, and 2.5V for limiting voltage
③ laying aside for 2 min
④ 0.02.02C for 10 min, and 2.8V for limiting voltage
⑤ laying aside for 2 min
⑥ 0.05.05C for 30 min, and limiting voltage to 3V
⑦ laying aside for 2 min
⑧ 0.1.1C for 100 min, and 3.4V for limiting voltage
⑨ laying aside for 2 min
⑩ 0.12.12C for 350 min, and limiting voltage to 3.85V
(6) Resealing
And after the charging is finished, sealing the liquid injection hole again.
The lithium iron phosphate lithium ion battery prepared by the process of example 1 has an internal resistance of 50 milliohms, a nominal voltage of the monomer of 3.336V, a high-end charging voltage of 4.008V, and a low-end discharging voltage of 2.51V; the battery capacity is 1830mAh, and the gram capacity of the lithium iron phosphate can reach 150 mAh; the prepared aluminum-shell battery is subjected to a cycle test, the capacity retention rate of 50 weeks is 97.7%, the battery has a long cycle service life, and the battery has good charge and discharge performance.
Embodiment 2 lithium iron phosphate lithium ion battery and formation process thereof
The preparation method of the lithium iron phosphate as the positive material of the lithium ion battery comprises the following steps:
1) preparing nanometer lithium iron phosphate precursor particles:
1mmol of lithium salt Li2CO31.5mmol of iron salt Fe2Cl2·4H2O and 1.5mmol of phosphate LiH2PO4Dissolving in 30ml of glycol solution, uniformly dissolving by magnetic stirring, adding 5mmol of anhydrous sodium acetate and 0.35g of polyacrylic acid into the mixed solution, and stirring until the mixture is uniformly mixed; then transferring the mixture into a sealed high-pressure reaction kettle, raising the temperature to 185 ℃ in a nitrogen atmosphere, and carrying out heat preservation reaction for 10 hours;
after the reaction is finished, naturally cooling to room temperature, filtering and collecting a solid product, washing the solid product for multiple times by using a deionized water ethanol mixed solvent with the volume fraction of 50% until the solvent is clear and transparent, and putting the solvent into a 50 ℃ oven to be dried for 8 hours to obtain nano-scale lithium iron phosphate precursor particles;
2) doping:
adding sodium-doped zinc oxide and cobalt-doped manganese oxide into nanoscale lithium iron phosphate precursor particles, simultaneously adding N-methyl pyrrolidone, carrying out wet ball milling for 5 hours in a ball mill by taking absolute ethyl alcohol as a medium, wherein the rotating speed of the ball mill is 500rad/min, and then placing the mixture in a vacuum drying oven at 45 ℃ for drying for 12 hours;
the doping proportion is 4 percent; wherein the mixing mass ratio of the sodium-doped zinc oxide to the cobalt-doped manganese oxide is 1: 2.0;
the total amount of the sodium-doped zinc oxide and the cobalt-doped manganese oxide is 13.0 percent of the mass of the precursor particles;
the adding amount of the N-methyl pyrrolidone is 6.2 percent of the mass of the precursor particles;
3) carbon coating:
grinding the doped precursor particles in a spherical grinder at the rotating speed of 160rad/min for 2.5h, adding an ethylene glycol solution of corn starch, continuing ball-milling and mixing, carrying out liquid phase coating at room temperature for 10h, and drying to constant weight after the rotating speed of the ball mill is 120 rad/min;
the mass concentration of the ethylene glycol solution of the corn starch is 16.6%;
4) and (3) calcining:
and placing the lithium iron phosphate in an argon environment for calcination treatment, namely heating to 400 ℃ at a heating rate of 20 ℃/min, preserving heat for 2h, then heating to 650 ℃ at a heating rate of 10 ℃/min, preserving heat for 2h, finally heating to 750 ℃ at a heating rate of 5 ℃/min, preserving heat for 4h, and then cooling at room temperature to obtain the lithium iron phosphate material of the lithium ion battery anode.
Mixing the prepared lithium iron phosphate with auxiliary materials, coating the mixture on an aluminum foil to obtain a positive electrode material, coating a graphite material on a copper foil to obtain a negative electrode material, and performing a series of processes such as baking, rolling, laminating, assembling, baking, liquid injection, formation, capacity grading and the like to complete the preparation of the lithium iron phosphate lithium ion battery;
the formation process comprises the following specific steps:
(1) liquid injection
Injecting liquid into the baked battery cell in a glove box in a nitrogen atmosphere, wherein the temperature of the battery cell is 40 ℃ and the relative humidity in the glove box is lower than 1% during liquid injection, vacuumizing is performed before liquid injection, the electrolyte is ensured to be completely injected, and redundant gas is discharged;
the electrolyte comprises the following components in parts by weight: 66 parts of solvent, 35 parts of lithium salt and 5% of additive;
the solvent is a mixed solvent of EC, EMC and DMC, and the mass ratio of EC, EMC and DMC is 1: 1.2: 1.2;
the additive is VC;
the above-mentionedLithium salt of LiPO2F2The concentration of lithium salt is 1.05 MOL/L;
(2) pre-sealing holes
After the liquid injection is finished, screwing the cap, sealing the liquid injection hole, and finishing the pre-sealing within 2 minutes;
(3) lay aside
The electrolyte is effectively absorbed, the pole piece is well soaked, the standing temperature is 20 ℃, and the standing time is 18 h;
(4) opening pre-sealed holes
After the placement is finished, opening the sealed liquid injection hole after liquid injection;
(5) normal temperature small current charging
The charging process comprises the following steps:
① laying aside for 2 min
② 0.01.01C for 20 min, and 2.5V for limiting voltage
③ laying aside for 2 min
④ 0.02.02C for 20 min, and 2.8V for limiting voltage
⑤ laying aside for 2 min
⑥ 0.05.05C for 45 min, and limiting voltage to 3V
⑦ laying aside for 2 min
⑧ 0.1.1C for 120 min, and 3.4V for limiting voltage
⑨ laying aside for 2 min
⑩ 0.12.12C for 350 min, and limiting voltage to 3.85V
(6) Resealing
And after the charging is finished, sealing the liquid injection hole again.
The lithium iron phosphate lithium ion battery prepared by the process of example 2 has an internal resistance of 50 milliohms, a nominal voltage of the monomer of 3.338V, a high-end charging voltage of 4.009V, and a low-end discharging voltage of 2.85V; the battery capacity is 1885mAh, and the gram capacity of the lithium iron phosphate can reach 152 mAh; the prepared aluminum-shell battery is subjected to a cycle test, the capacity retention rate of 50 weeks is 98.2%, the battery has a long cycle service life, and the battery has good charge and discharge performance.
Example 3 lithium iron phosphate lithium ion battery and formation process thereof
The preparation method of the lithium iron phosphate as the positive material of the lithium ion battery comprises the following steps:
1) preparing nanometer lithium iron phosphate precursor particles:
1mmol of lithium salt Li2CO31.5mmol of iron salt Fe2Cl2·4H2O and 2mmol of phosphate LiH2PO4Dissolving in 30ml of glycol solution, uniformly dissolving by magnetic stirring, adding 6.5mmol of anhydrous sodium acetate and 0.36g of polyacrylic acid into the mixed solution, and stirring until the mixture is uniformly mixed; then transferring the mixture into a sealed high-pressure reaction kettle, raising the temperature to 185 ℃ in a nitrogen atmosphere, and carrying out heat preservation reaction for 10 hours;
after the reaction is finished, naturally cooling to room temperature, filtering and collecting a solid product, washing the solid product for multiple times by using a deionized water ethanol mixed solvent with the volume fraction of 50% until the solvent is clear and transparent, and putting the solvent into a 50 ℃ oven to be dried for 7 hours to obtain nano-scale lithium iron phosphate precursor particles;
2) doping:
adding sodium-doped zinc oxide and cobalt-doped manganese oxide into nanoscale lithium iron phosphate precursor particles, simultaneously adding N-methyl pyrrolidone, carrying out wet ball milling for 5 hours in a ball mill by taking absolute ethyl alcohol as a medium, wherein the rotating speed of the ball mill is 550rad/min, and then placing the mixture in a vacuum drying oven at 45 ℃ for drying for 10 hours;
the sodium-doped zinc oxide and the cobalt-doped manganese oxide are doped in a proportion of 5%; wherein the mixing mass ratio of the sodium-doped zinc oxide to the cobalt-doped manganese oxide is 1: 2.2;
the total amount of the sodium-doped zinc oxide and the cobalt-doped manganese oxide is 15.0 percent of the mass of the precursor particles;
the adding amount of the N-methyl pyrrolidone is 7.0 percent of the mass of the precursor particles;
3) carbon coating:
grinding the doped precursor particles in a spherical grinder at the rotating speed of 160rad/min for 2.5h, adding an ethylene glycol solution of corn starch, continuing ball-milling and mixing, carrying out liquid phase coating at room temperature for 6h, and drying to constant weight, wherein the rotating speed of the ball mill is 120 rad/min;
the mass concentration of the ethylene glycol solution of the corn starch is 17.5%;
4) and (3) calcining:
and placing the lithium iron phosphate in an argon environment for calcination treatment, namely heating to 400 ℃ at a heating rate of 20 ℃/min, preserving heat for 2h, then heating to 650 ℃ at a heating rate of 10 ℃/min, preserving heat for 2h, finally heating to 750 ℃ at a heating rate of 5 ℃/min, preserving heat for 4h, and then cooling at room temperature to obtain the lithium iron phosphate material of the lithium ion battery anode.
Mixing the prepared lithium iron phosphate with auxiliary materials, coating the mixture on an aluminum foil to obtain a positive electrode material, coating a graphite material on a copper foil to obtain a negative electrode material, and performing a series of processes such as baking, rolling, laminating, assembling, baking, liquid injection, formation, capacity grading and the like to complete the preparation of the lithium iron phosphate lithium ion battery;
the formation process comprises the following specific steps:
(1) liquid injection
Injecting liquid into the baked battery cell in a glove box in a nitrogen atmosphere, wherein the temperature of the battery cell is 45 ℃ and the relative humidity in the glove box is lower than 1% during liquid injection, vacuumizing is performed before liquid injection, the electrolyte is ensured to be completely injected, and redundant gas is discharged;
the electrolyte comprises the following components in parts by weight: 73 parts of solvent, 25 parts of lithium salt and 2% of additive;
the solvent is a mixed solvent of EC, EMC and DMC, and the mass ratio of EC, EMC and DMC is 1: 1.2: 1.4;
the additive is FEC;
the lithium salt is LiPO2F2The concentration of lithium salt is 1.05 MOL/L;
(2) pre-sealing holes
After the liquid injection is finished, screwing the cap, sealing the liquid injection hole, and finishing the pre-sealing within 2 minutes;
(3) lay aside
The electrolyte is effectively absorbed, the pole piece is well soaked, the standing temperature is 45 ℃, and the standing time is 18 h;
(4) opening pre-sealed holes
After the placement is finished, opening the sealed liquid injection hole after liquid injection;
(5) normal temperature small current charging
The charging process comprises the following steps:
① laying aside for 2 min
② 0.01.01C for 30 min, and 2.5V for limiting voltage
③ resting for 3 minutes
④ 0.02.02C for 30 min, and 2.8V for limiting voltage
⑤ resting for 3 minutes
⑥ 0.05.05C for 60 min, and limiting voltage to 3V
⑦ resting for 3 minutes
⑧ 0.1.1C for 120 min, and 3.4V for limiting voltage
⑨ resting for 3 minutes
⑩ 0.12.12C for 450 min, and has a limit voltage of 3.85V
(6) Resealing
And after the charging is finished, sealing the liquid injection hole again.
The lithium iron phosphate lithium ion battery prepared by the process of example 3 had an internal resistance of 52 milliohms, a nominal cell voltage of 3.340V, a high-end charging voltage of 4.011V, and a low-end discharging voltage of 3.22V; the battery capacity is 1862mAh, and the gram capacity of the lithium iron phosphate can reach 155 mAh; the prepared aluminum-shell battery is subjected to a cycle test, the capacity retention rate of 50 weeks is 98.0%, the battery has a long cycle service life, and the battery has good charge and discharge performance.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art will understand that various changes, modifications and substitutions can be made without departing from the spirit and scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. A formation process of a lithium iron phosphate lithium ion battery is characterized by comprising liquid injection, hole pre-sealing, placing, hole opening, normal-temperature low-current charging and hole resealing.
2. The chemical synthesis process according to claim 1, wherein the charging is carried out at normal temperature and low current, and the charging steps are as follows:
① left for 2 minutes;
② 0.01.01C for 10-30 min, and limiting voltage to 2.5V;
③ standing for 2-3 min;
④ 0.02.02C for 10-30 minutes, and the voltage is limited to 2.8V;
⑤ standing for 2-3 min;
⑥ 0.05.05C for 30-60 minutes, and limiting the voltage to 3V;
⑦ standing for 2-3 min;
⑧ 0.1.1C for 100-120 min, limiting the voltage to 3.4V;
⑨ standing for 2-3 min;
⑩ 0.12.12C for 350-450 min, the voltage is limited to 3.85V.
3. The chemical synthesis process according to claim 1, wherein the liquid is injected, the temperature of a cell during liquid injection is 25-45 ℃, and the relative humidity in a glove box is lower than 1%.
4. The formation process according to claim 3, wherein the components of the injection liquid and the electrolyte comprise: 60-73 parts of solvent, 25-35 parts of lithium salt and 2-5% of additive; the solvent is a mixed solvent of EC, EMC and DMC, and the mass ratio of EC, EMC and DMC is 1:1-1.2: 1-1.4; the additive is one or more of VC, FEC and PS; the lithium salt is LiPO2F2The concentration of lithium salt was 1.05 MOL/L.
5. The chemical synthesis process according to claim 1, wherein the standing temperature is 20-45 ℃ and the standing time is 18-24 h.
6. The formation process according to claim 1, wherein the preparation method of the positive electrode material lithium iron phosphate comprises preparation, doping, carbon coating and calcination of nanoscale lithium iron phosphate precursor particles.
7. The formation process as claimed in claim 6, wherein the preparation of the nano-scale lithium iron phosphate precursor particles is carried out at a reaction temperature of 180 ℃ and 185 ℃ in a nitrogen atmosphere, and the reaction is carried out for 8-10h under heat preservation; the addition amount of the anhydrous sodium acetate is 1 to 1.5 times of the total molar amount of the lithium salt, the iron salt and the phosphate; the addition concentration of polyacrylic acid is 10.5-12 g/L.
8. The formation process according to claim 7, wherein the preparation of the nanoscale lithium iron phosphate precursor particles is a lithium salt Li2CO3Iron salt Fe2Cl24H2O and phosphate LiH2PO4In a molar ratio of 1: 0.5-1.5: 1-2.
9. The formation process according to claim 6, wherein the doping is performed in a proportion of 2% to 5%; wherein the mixing mass ratio of the sodium-doped zinc oxide to the cobalt-doped manganese oxide is 1: 1.6-2.2; the total amount of the added sodium-doped zinc oxide and cobalt-doped manganese oxide is 11-15% of the mass of the precursor particles.
10. The formation process as claimed in claim 6, wherein the carbon coating is performed at room temperature for 6-12h, the rotation speed of the ball mill is 100-120rad/min, and the mass concentration of the ethylene glycol solution of the corn starch is 15-18%.
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