CN112751098A - Formation method of lithium iron phosphate battery - Google Patents

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a formation method of a lithium iron phosphate battery. A lithium iron phosphate battery formation method, after 24 hours of normal temperature standing after battery liquid injection, clamping the battery by two clamping plates larger than a battery body, and leaking a tab and an air bag part; charging the treated battery for 10h-16.7h by using a current of 0.03C-0.05C; placing the charged battery into a 40-60 ℃ oven for standing and aging, recovering the room temperature, fixing the battery by using a clamp, charging the battery to 3.65V by using 0.1-0.3C current, continuing to discharge the battery to 2.5V by using 0.1-0.3C current, charging and discharging the battery once by using 0.5-1C current, and finally keeping 30% of electric quantity; and (4) carrying out air-exhaust sealing on the prepared battery under the vacuum condition. The lithium iron phosphate battery obtained by the formation method has obviously long cycle life and obviously reduced bulging proportion.

Description

Formation method of lithium iron phosphate battery

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a formation method of a lithium iron phosphate battery.

Background

The lithium ion battery has the advantages of high energy density, quick charge and discharge, environmental protection and the like, is widely applied to a plurality of occasions such as electric vehicles, hybrid electric vehicles, digital products, mobile communication base stations and the like, and has great market demand. Particularly, the lithium iron phosphate battery has long cycle life, stable and non-decomposed anode material, incomparable safety with other anode materials, rich lithium iron phosphate resource and high environmental protection.

In the lithium ion battery manufacturing process, formation is an important process, and the formation is that a layer of Solid Electrolyte Interface (SEI) film is generated on the surface of a negative electrode in the first charging process of the lithium ion battery, and the electrical property, the safety performance and the cycle function of the battery are directly influenced by the compactness formed by the SEI film. The conventional low current formation method contributes to stable SEI film formation, but a long formation process due to a long low current leads to low production efficiency and increases the production cost of the battery.

The invention patent with publication number CN109167112A discloses a high-temperature clamp formation method of a lithium titanate battery, which adopts high-temperature sectional charging to form a stable SEI film, but has higher requirements on formation equipment; the invention patent with publication number CN109346776A discloses a formation method of a soft package lithium ion battery, which can reduce the accumulation of gas in the battery in the formation process, effectively reduce the influence of gas generation on the formation of a solid electrolyte membrane, and avoid the occurrence of black spots on a pole piece. However, the battery is directly formed after liquid injection, the pole piece is not fully soaked, and the performance of the battery is influenced to a certain extent.

Disclosure of Invention

The invention aims to provide a better formation method for a lithium iron phosphate battery, which can improve the swelling phenomenon of the battery in the using process and prolong the cycle performance of the battery.

In order to achieve the above purpose, the invention adopts the following technical scheme (the following contents are as the claims):

the invention provides a formation method of a lithium iron phosphate battery, which comprises the following steps:

s1 after the battery is injected with liquid and is stood for 24 hours at normal temperature, the battery is clamped by two clamping plates which are larger than the battery body, the lug and the air bag part are leaked, and the thickness of the clamping plates is 3-5 mm.

S2, charging the battery for 10h-16.7h by using current of 0.03C-0.05C;

s3, placing the battery after charging into an oven with the temperature of 40-60 ℃, standing and aging, recovering the room temperature for 5h, fixing the battery by using a clamp, charging to 3.65V by using a current of 0.1-0.3C, continuing to discharge to 2.5V by using a current of 0.1-0.3C, charging and discharging for one week by using a current of 0.5-1C, and finally keeping 30% of electric quantity;

s4, performing air extraction and sealing under the vacuum degree of-0.08 MPa to-0.09 MPa;

further, the positive electrode material of the battery is lithium iron phosphate, and the negative electrode material of the battery is graphite;

further, step S4 is to stand for 1min to 3min under the vacuum degree of-0.08 MPa to-0.09 MPa, to carry out air extraction and sealing, wherein the air temperature is 25 +/-2 ℃, the dew point is lower than-45 ℃, and the sealing temperature is 170 ℃ to 190 ℃;

further, in step S1, the clamping plate is one or more of a tempered glass plate, an acrylic plate and a PP plate;

further, in step S3, the aging time is 24-60 h.

Advantageous effects

The invention has the advantages of prolonging the service life of the battery and improving the bulging phenomenon of the battery in the use process. The electrolyte is formed at normal temperature, the requirement on formation equipment is low, and after the battery is injected with liquid, the battery is kept stand for 24 hours at normal temperature, so that the electrolyte is fully contacted with active substances, the infiltration effect of the electrolyte is improved, and the precondition is provided for forming an even and compact SEI film.

Drawings

Fig. 1 is a cycle curve diagram of lithium iron phosphate batteries corresponding to example 1 and example 2 of the present invention, and comparative example 1 and comparative example 2.

Detailed Description

The following is a detailed description of embodiments of the invention, but the invention can be implemented in many different ways, as defined and covered by the claims. 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

After the lithium iron phosphate battery is injected with liquid, the lithium iron phosphate battery stands for 24 hours at normal temperature, and the battery is clamped by two toughened glass plates with the thickness of about 4mm larger than that of the battery body, so that the lug and the air bag part are exposed. Charging for 16.7h by using 0.03C current on a formation cabinet, removing a clamping plate, enabling a battery air bag to face upwards, standing for 48h in a 45 ℃ oven, taking out, cooling to the normal temperature, recovering for 5h, clamping by using the clamping plate, charging to 3.65V by using 0.1C current, then continuously discharging to 2.5V by using 0.1C current, charging and discharging for one week by using 0.5C current, and finally keeping 30% of electric quantity. The battery clamp plate is removed, and air extraction and sealing are carried out under the condition that the vacuum degree is-0.09 MPa.

Example 2

After the lithium iron phosphate battery is injected with liquid, the lithium iron phosphate battery stands for 24 hours at normal temperature, and the battery is clamped by two toughened glass plates with the thickness of about 4mm larger than that of the battery body, so that the lug and the air bag part are exposed. Charging for 10h by using 0.05C current on a formation cabinet, removing a clamping plate, enabling a battery air bag to face upwards, standing for 48h in a 45 ℃ oven, taking out, cooling to normal temperature, clamping by using the clamping plate, charging to 3.65V by using 0.3C current, continuing to discharge to 2.5V by using 0.3C current, charging and discharging for one week by using 1C current, and finally keeping 30% of electric quantity. The battery clamp plate is removed, and air extraction and sealing are carried out under the condition that the vacuum degree is-0.09 MPa.

Comparative example 1

After the lithium iron phosphate battery is injected with liquid, the lithium iron phosphate battery stands for 24 hours at normal temperature, and the battery is clamped by two toughened glass plates with the thickness of about 4mm larger than that of the battery body, so that the lug and the air bag part are exposed. Charging the battery for 25 hours on a formation cabinet by using 0.02C current, removing a clamping plate, enabling the air bag of the battery to face upwards, standing the battery for 48 hours in a baking oven at 45 ℃, taking the battery out, cooling the battery to the normal temperature, performing air suction and sealing under the condition that the vacuum degree is minus 0.09MPa, charging the battery to 3.65V by using 0.2C current, then continuing discharging the battery to 2.5V by using 0.2C current, charging and discharging the battery for one week by using 1C current, and finally keeping 30% of electric quantity. The battery clamp plate is removed, and air extraction and sealing are carried out under the condition that the vacuum degree is-0.09 MPa.

Comparative example 2

After the lithium iron phosphate battery is injected with liquid, the lithium iron phosphate battery is kept stand for 24 hours at normal temperature, and the battery is clamped by two toughened glass plates with the thickness of about 4mm larger than that of the battery body, so that the lug and the air bag part are exposed. Charging 50% by 0.2C current on a formation cabinet, removing a clamp plate, enabling a battery air bag to face upwards, standing in a 45 ℃ oven for 48 hours, taking out the battery air bag, cooling to normal temperature, clamping by the clamp plate, charging to 3.65V by 1C current, continuing to discharge to 2.5V by normal working current, and finally keeping 30% of electric quantity. The battery clamp plate is removed, and air extraction and sealing are carried out under the condition that the vacuum degree is-0.09 MPa.

Fig. 1 is a cycle curve diagram of lithium iron phosphate batteries corresponding to example 1 and example 2 of the present invention, and comparative example 1 and comparative example 2. It is understood from the graph that the cycle lives of examples 1 and 2 are significantly longer than those of comparative examples 1 and 2, and the swelling ratio of the batteries is significantly reduced.

Claims (7)

1. A formation method of a lithium iron phosphate battery is characterized by comprising the following steps:

s1 standing the battery for 24h at normal temperature after the battery is injected with liquid, clamping the battery by two clamping plates larger than the battery body, and leaking the lug and the air bag part;

s2, charging the battery processed by the S1 for 10h-16.7h by using current of 0.03C-0.05C;

s3, placing the battery after the charging of S2 in an oven with the temperature of 40-60 ℃, standing and aging, recovering the room temperature, fixing the battery by using a clamp, charging the battery to 3.65V by using a current of 0.1-0.3C, continuing to discharge the battery to 2.5V by using a current of 0.1-0.3C, then charging and discharging for one week by using a current of 0.5-1C, and finally keeping the electric quantity of 30%;

s4 the battery prepared in S3 was sealed under vacuum by evacuation.

2. The chemical conversion method according to claim 1, wherein the step S4 of sealing by pumping under vacuum is performed by standing under a vacuum degree of-0.08 MPa to-0.09 MPa for 1min to 3min, and sealing by pumping under an air temperature of 25 ℃ ± 2, a dew point of less than-45 ℃ and a sealing temperature of 170 ℃ to 190 ℃.

3. The method as claimed in claim 1, wherein in step S1, the clamping plate is a tempered glass plate, an acrylic plate or a PP plate.

4. The method for forming the lithium iron phosphate battery according to claim 1, wherein in step S3, the aging time is 24-60 h; the room temperature recovery time was 5 h.

5. The method as claimed in claim 1, wherein the positive electrode material of the lithium iron phosphate battery is lithium iron phosphate, and the negative electrode material of the lithium iron phosphate battery is graphite.

6. The method as claimed in claim 1, wherein in step S3, the thickness of the sandwich plate is 3-5 mm.

7. The method as claimed in claim 1, wherein the air bag of the battery is kept upward when the battery is placed in an oven for standing.

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