阅读说明：本技术 一种改善软包电芯k值的化成方法 (Formation method for improving K value of soft-package battery cell ) 是由 黄纯洁 张洪旭 谢墨 于 2018-06-26 设计创作，主要内容包括：本发明公开了一种改善软包电芯K值的化成方法,解决了软包电芯常压化成SEI膜成膜不良、电芯主体变形及硬度不够、界面黑斑、析锂等的问题,还解决了软包电芯高温高压夹具化成导致的K值不良率高的问题；本发明在化成工步运行过程中,通过给电芯表面施加一个较小的面压,能够使正、负极与隔膜之间的层间距减小,进一步使化成过程中锂离子的迁移路径减小,从而提高成膜质量,通过控制夹板温度,能够提高电芯的内部活性,从而降低锂离子的迁移难度；本发明具有SEI膜成膜质量高、电芯主体不易变形、电芯K值稳定的优点。(The invention discloses a formation method for improving a K value of a soft-package battery cell, which solves the problems of poor film formation of an SEI film formed by normal pressure formation of the soft-package battery cell, insufficient deformation and hardness of a battery cell main body, black spots on an interface, lithium precipitation and the like, and also solves the problem of high K value reject ratio caused by high-temperature and high-pressure clamp formation of the soft-package battery cell; in the process of the formation process, a smaller surface pressure is applied to the surface of the battery cell, so that the interlayer spacing between the anode and the cathode and the diaphragm can be reduced, the migration path of lithium ions in the formation process is further reduced, the film forming quality is improved, the internal activity of the battery cell can be improved by controlling the temperature of the clamping plate, and the migration difficulty of the lithium ions is reduced; the invention has the advantages of high SEI film forming quality, difficult deformation of the cell main body and stable cell K value.)

1. A formation method for improving a K value of a soft package battery cell is characterized by comprising the following steps:

step 1, placing a soft-packaged battery cell between clamping plates of a clamp formation cabinet, setting a battery cell surface pressure and a clamping plate temperature to control the reduction of interlayer spacing between a positive electrode and a negative electrode of the battery cell and a diaphragm, and obtaining a first battery cell;

step 2, placing the first battery cell obtained in the step 1 in a clamp formation cabinet for standing for 20min, and sequentially performing first-stage charge and discharge, second-stage charge and discharge and third-stage charge and discharge on the first battery cell by adopting currents with different magnitudes to obtain a second battery cell;

and 3, placing the second battery cell obtained in the step 2 into a shaping clamp, adjusting the battery cell surface pressure of the shaping clamp, placing the shaping clamp with the second battery cell in an oven for baking and shaping, and cooling in the environment after shaping to obtain a formed battery cell.

2. The formation method for improving the K value of the soft package cell according to claim 1, wherein the cell surface pressure in the step 1 is 0.01 to 0.05 MPa.

3. The formation method for improving the K value of the soft package core according to claim 2, wherein the temperature of the clamping plate in the step 1 is 45-55 ℃.

4. The formation method for improving the K value of the soft package cell according to any one of claims 1 to 3, wherein the first stage of charging and discharging in the step 2 is charging to 3.3V by using a current constant current of 0.02C, and the charge cut-off time is 80 min.

5. The formation method for improving the K value of the soft package cell according to claim 4, wherein the second stage of charging and discharging in the step 2 is performed by constant current charging to 3.5V with a current of 0.1C, and the charge cut-off time is 40 min.

6. The formation method for improving the K value of the soft package cell according to claim 5, wherein the third stage of charging and discharging in the step 2 is charging to 3.95V by using a current constant current of 0.5C, the charge cut-off time is 80min, and the cut-off current is 0.02C.

7. The formation method for improving the K value of the soft package battery cell according to claim 6, wherein the cell surface pressure in the step 3 is 0.8-1.5 Mpa, the baking temperature is 85 ℃, and the baking time is 2.5 h.

8. The formation method for improving the K value of the soft package core according to claim 7, wherein the cooling temperature in the step 3 is 15 ℃ and the cooling time is 2 h.

Technical Field

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a formation method for improving a K value of a soft package battery cell.

Background

As the market demands for high energy density increase day by day, the thickness of the separator of the lithium ion battery also needs to be thinner, but the thin separator has the following problems: on one hand, the thinner diaphragm is subjected to mechanical stress, the generated elastic deformation is larger, the internal stress generated by the diaphragm in the cell winding process is larger, and in the formation process, the internal stress of the cell is further increased due to the expansion of the pole piece, and cannot be released, so that the cell deformation is caused, the interlayer spacing of the positive electrode, the negative electrode and the diaphragm of the cell is increased, and the problems of black spots, lithium precipitation, cell body deformation and the like of an interface are caused; on the other hand, thin membranes are prone to puncture by burrs and dust due to poor mechanical strength, resulting in poor K values.

At present, there are two main formation modes for lithium ion soft-package battery cell: ordinary-temperature normal-pressure common formation and high-temperature high-pressure clamp formation; the problems of poor film forming of an SEI film, deformation of a cell main body, insufficient hardness of the cell main body, black spots on an interface, lithium precipitation and the like easily occur in normal temperature and normal pressure general formation; and the problem of poor K value of the battery cell is easily caused by the formation of the high-temperature and high-pressure clamp.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a formation method for improving the K value of a soft-package battery cell.

The invention is realized by the following steps:

step 1, placing a soft-packaged battery cell between clamping plates of a clamp formation cabinet, and setting the surface pressure and the temperature of the battery cell to reduce the interlayer spacing between a positive electrode and a negative electrode of the battery cell and a diaphragm to obtain a first battery cell;

step 2, placing the first battery cell obtained in the step 1 in a clamp formation cabinet for standing for 20min, and sequentially performing first-stage charge and discharge, second-stage charge and discharge and third-stage charge and discharge on the first battery cell by adopting currents with different magnitudes to obtain a second battery cell;

and 3, placing the second battery cell obtained in the step 2 into a shaping clamp, adjusting the battery cell surface pressure of the shaping clamp, placing the shaping clamp with the second battery cell in an oven for baking and shaping, and cooling in the environment after shaping to obtain a formed battery cell.

In the scheme, the cell surface pressure in the step 1 is 0.01-0.05 Mpa.

In the scheme, the temperature of the clamping plate in the step 1 is 45-55 ℃.

In the scheme, the first-stage charging and discharging in the step 2 adopts a current of 0.02C for constant current charging to 3.3V, and the charging cut-off time is 80 min.

In the scheme, the second-stage charging and discharging in the step 2 adopts a current of 0.1C for constant current charging to 3.5V, and the charging cut-off time is 40 min.

In the scheme, the third-stage charging and discharging in the step 2 adopts a current constant current of 0.5C to charge to 3.95V, the charge cut-off time is 80min, and the cut-off current is 0.02C.

In the scheme, the cell surface pressure in the step 3 is 0.8-1.5 Mpa, the baking temperature is 85 ℃, and the baking time is 2.5 hours.

In the scheme, the cooling temperature in the step 3 is 15 ℃, and the cooling time is 2 h.

Compared with the prior art, the invention provides a formation method for improving the K value of a soft package battery cell, which comprises the following steps: step 1, placing a soft-packaged battery cell between clamping plates of a clamp formation cabinet, and controlling interlayer spacing between a positive electrode and a negative electrode of the battery cell and a diaphragm to be reduced to obtain a first battery cell; step 2, placing the first battery cell in a clamp formation cabinet, standing for 20min, and sequentially performing first-stage charge and discharge, second-stage charge and discharge and third-stage charge and discharge on the first battery cell by adopting currents of different magnitudes to obtain a second battery cell; step 3, placing the second battery cell into a shaping fixture, placing the shaping fixture into an oven for baking and shaping, and cooling in the environment after shaping to obtain a formed battery cell; in the formation process, a smaller surface pressure is applied to the surface of the battery cell, so that the interlayer spacing between the positive electrode and the diaphragm, the negative electrode and the diaphragm can be reduced, the migration path of lithium ions in the formation process is further reduced, the film forming quality is improved, the internal activity of the battery cell can be improved by controlling the temperature of the clamping plate, the migration difficulty of the lithium ions is reduced, formation is carried out in three steps, small-current charging is adopted in the early formation stage, namely the first-stage charging and discharging process, a compact SEI film is favorably formed on the surface of a pole piece, the charging current is gradually increased, large-current charging is adopted in the later formation stage, namely the third-stage charging and discharging process, and the formation time can be saved; in addition, by controlling the baking temperature and the cooling temperature, the thickness of the battery cell can be controlled within a specification range while the battery cell is ensured to be smooth in appearance; the invention has the advantages of high SEI film forming quality, difficult deformation of the cell main body and stable cell K value.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The embodiment of the invention provides a formation method for improving a K value of a soft-package battery cell, which is realized by the following steps:

step 1, placing a soft-packaged battery cell between clamping plates of a clamp formation cabinet, setting the temperature of the clamping plates to be 45-55 ℃, applying a battery cell surface pressure of 0.01-0.05 Mpa to the surface of the battery cell, and controlling the interlayer spacing between a positive electrode and a negative electrode of the battery cell and a diaphragm to be reduced to obtain a first battery cell;

the small cell surface pressure is adopted for processing, so that the interlayer spacing of the anode, the cathode and the diaphragm can be reduced, and the migration path of lithium ions in the formation process is further shortened, thereby improving the film forming quality; moreover, the smaller interlayer spacing can ensure that the diaphragm is well bonded with the pole piece, so that the hardness and the flatness of the cell body are improved; in addition, the small cell surface pressure can prevent the phenomenon that the K value is bad due to the fact that burrs, particles and the like are extruded by the expansion of the positive pole and the negative pole in the formation process of the cell because the pressure of the clamping plate is too large; the temperature of the clamping plate is 45-55 ℃, the surface temperature of the battery cell can be increased, so that the internal activity of the battery cell is improved, and the migration difficulty of lithium ions is further reduced;

step 2, placing the first battery cell obtained in the step 1 in a clamp formation cabinet for standing for 20min, and sequentially performing first-stage charge and discharge, second-stage charge and discharge and third-stage charge and discharge on the first battery cell by adopting currents with different magnitudes to obtain a second battery cell;

specifically, placing the first battery cell in a clamp formation cabinet and standing for 20 min; the formation process specifically comprises the following steps: firstly, in the first stage of charging and discharging, the constant current charging is carried out to 3.3V by adopting the current with the capacity value of 0.02 time of the battery, and the charging cut-off time is 80 min; then, in the second stage of charging and discharging, the constant current charging is carried out to 3.5V by adopting the current with the capacity value of 0.1 time of the battery, and the charging cut-off time is 40 min; finally, in the third stage, the charging and discharging are carried out by adopting the constant current charging of the current with the capacity value of 0.5 time of the battery to 3.95V, the charging cut-off time is 80min, and the cut-off current is 0.02C;

the formation early stage, namely the first-stage charging and discharging process, adopts low-current charging, which is beneficial to forming a compact SEI film on the surface of the pole piece, and the formation later stage, namely the third-stage charging and discharging process, adopts high-current charging, which can save the formation time;

step 3, placing the second battery cell obtained in the step 2 into a shaping clamp, adjusting the battery cell surface pressure of the shaping clamp to be 0.8-1.5 Mpa, placing the shaping clamp with the second battery cell in an oven, baking for 2.5 hours at the baking temperature of 85 ℃, cooling for 2 hours at the environment of 15 ℃ after shaping, and obtaining a formed battery cell;

through control baking temperature and cooling temperature, can be when guaranteeing that electric core outward appearance is smooth, with electric core thickness control in specification range.

Compared with the prior art, the invention provides a formation method for improving the K value of the soft-package battery cell, solves the problems of poor film formation of an SEI film formed by normal pressure formation of the soft-package battery cell, insufficient deformation and hardness of a battery cell main body, black spots on an interface, lithium precipitation and the like, and also solves the problem of high K value reject ratio caused by formation of a high-temperature high-pressure clamp of the soft-package battery cell; in the process of operation of the formation process, a smaller surface pressure is applied to the surface of the battery cell, so that the interlayer spacing between the anode and the cathode and the diaphragm can be reduced, the migration path of lithium ions in the formation process is further reduced, the film forming quality is improved, the internal activity of the battery cell can be improved by controlling the temperature of the clamping plate, the migration difficulty of the lithium ions is reduced, formation is carried out in three steps, small-current charging is adopted in the early formation stage, namely the first-stage charging and discharging process, a compact SEI film is formed on the surface of a pole piece, the charging current is gradually increased, large-current charging is adopted in the later formation stage, namely the third-stage charging and discharging process, and the formation time can be saved; in addition, by controlling the baking temperature and the cooling temperature, the thickness of the battery cell can be controlled within a specification range while the battery cell is ensured to be smooth in appearance; the invention has the advantages of high SEI film forming quality, difficult deformation of the cell main body and stable cell K value.