阅读说明：本技术 一种补锂负极片及其制备方法、锂离子电池 (Lithium-supplement negative plate, preparation method thereof and lithium ion battery ) 是由 谭立波 高夜军 阮祝华 苑丁丁 于 2021-08-12 设计创作，主要内容包括：本发明提供一种补锂负极片及其制备方法、锂离子电池,所述补锂负极片包括锂粉复合膜片与负极集流体；单位体积补锂负极片的锂粉复合膜片中锂粉的重量为单位体积正极片中正极主材重量的0.5％-2％。所述制备方法包括以下步骤：(1)混合石墨与硅粉,得到第一负极粉料；(2)混合导电剂、锂粉与步骤(1)所得第一负极粉料,得到第二负极粉料；(3)混合粘结剂与步骤(2)所得第二负极粉料,得到第三负极粉料；(4)将步骤(3)所得第三负极粉料进行辊压,得到锂粉复合膜片；(5)将步骤(4)所得锂粉复合膜片与负极集流体相互层叠并一同辊压,得到补锂负极片。所述补锂负极片弥补了在首次嵌锂过程中所消耗的锂,简化了补锂流程。(The invention provides a lithium-supplementing negative plate, a preparation method thereof and a lithium ion battery, wherein the lithium-supplementing negative plate comprises a lithium powder composite membrane and a negative current collector; the weight of the lithium powder in the lithium powder composite membrane of the unit volume lithium-supplementing negative plate is 0.5-2% of the weight of the main positive material in the unit volume positive plate. The preparation method comprises the following steps: (1) mixing graphite and silicon powder to obtain first negative electrode powder; (2) mixing a conductive agent, lithium powder and the first negative electrode powder obtained in the step (1) to obtain second negative electrode powder; (3) mixing a binder with the second negative electrode powder obtained in the step (2) to obtain third negative electrode powder; (4) rolling the third negative electrode powder obtained in the step (3) to obtain a lithium powder composite membrane; (5) and (4) mutually laminating the lithium powder composite membrane obtained in the step (4) and a negative current collector and rolling together to obtain the lithium-supplement negative plate. The lithium supplement negative plate makes up lithium consumed in the process of lithium intercalation for the first time, and simplifies the lithium supplement process.)

1. The lithium supplement negative plate is characterized by comprising a lithium powder composite membrane and a negative current collector which are stacked;

the weight of the lithium powder in the lithium powder composite membrane of the unit volume lithium-supplementing negative plate is 0.5-2% of the weight of the main positive material in the unit volume positive plate.

2. The lithium-supplementing negative electrode sheet according to claim 1, wherein the negative electrode current collector comprises a carbon-coated copper foil;

preferably, the carbon-coated copper foil is a double-sided carbon-coated copper foil, and comprises a copper foil layer and carbon-coated layers respectively arranged on two sides of the copper foil layer.

3. The lithium-supplementing negative plate according to claim 2, wherein the thickness of the lithium powder composite membrane is 40-80 μm;

preferably, the thickness of the copper foil layer in the double-sided carbon-coated copper foil is 4-5 μm;

preferably, the thickness of the carbon coating layer in the double-sided carbon-coated copper foil is 0.2-0.8 μm.

4. A method for preparing the lithium-supplementing negative electrode sheet according to any one of claims 1 to 3, wherein the method comprises the following steps:

(1) mixing graphite and silicon powder to obtain first negative electrode powder;

(2) mixing a conductive agent, lithium powder and the first negative electrode powder obtained in the step (1) to obtain second negative electrode powder;

(3) mixing a binder with the second negative electrode powder obtained in the step (2) to obtain third negative electrode powder;

(4) rolling the third negative electrode powder obtained in the step (3) to obtain a lithium powder composite membrane;

(5) mutually laminating the lithium powder composite membrane obtained in the step (4) and a negative current collector and rolling together to obtain a lithium-supplement negative plate;

wherein, according to the mass ratio, graphite: silicon powder: conductive agent: the binder (86-87), (9-10), (1-2) and (2-3).

5. The method according to claim 4, wherein the mixing of step (1) is accompanied by stirring;

preferably, the rotation speed of the stirring is 400-800 rpm;

preferably, the stirring time is 40-80 min.

6. The production method according to claim 4 or 5, wherein the conductive agent of step (2) comprises vapor grown carbon fiber;

preferably, the mixing of step (2) is accompanied by stirring;

preferably, the rotation speed of the stirring is 400-800 rpm;

preferably, the stirring time is 40-80 min.

7. The method according to any one of claims 4 to 6, wherein the binder of step (3) comprises polytetrafluoroethylene;

preferably, the mixing of step (3) is accompanied by stirring;

preferably, the rotation speed of the stirring is 400-800 rpm;

preferably, the stirring time is 20-40 min.

8. The method of any one of claims 4 to 7, comprising the steps of:

(1) mixing graphite and silicon powder, and stirring at the rotating speed of 400-800rpm for 40-80min to obtain first cathode powder;

(2) mixing vapor-grown carbon fiber, lithium powder and the first negative electrode powder obtained in the step (1), and stirring at the rotating speed of 400-800rpm for 40-80min to obtain second negative electrode powder;

(3) mixing polytetrafluoroethylene with the second negative electrode powder obtained in the step (2), and stirring at the rotating speed of 400-800rpm for 20-40min to obtain third negative electrode powder;

(4) rolling the third negative electrode powder obtained in the step (3) to obtain a lithium powder composite membrane;

(5) mutually laminating the lithium powder composite membrane obtained in the step (4) and a negative current collector and rolling together to obtain a lithium-supplement negative plate;

wherein, according to the mass ratio, graphite: silicon powder: conductive agent: the binder (86-87), (9-10), (1-2) and (2-3).

9. A lithium ion battery, characterized in that, the lithium ion battery comprises a positive plate, a diaphragm, an electrolyte and the lithium-supplementing negative plate of any one of claims 1 to 3.

10. The lithium ion battery according to claim 9, wherein the lithium ion battery satisfies: the negative electrode active material capacity in the unit area lithium-supplementing negative electrode sheet/the positive electrode active material capacity in the unit area positive electrode sheet is 1.1-1.2.

Technical Field

The invention belongs to the technical field of lithium ion batteries, relates to a lithium supplement negative plate, and particularly relates to a lithium supplement negative plate, a preparation method thereof and a lithium ion battery.

Background

The energy crisis in the world at present leads to the demand and the development of new energy car more and more urgent, and pure electric new energy car replaces traditional gasoline car gradually and becomes the inevitable trend of developing now, and the high requirement of new energy car to power battery is also more and more prominent. In the application of lithium ion batteries at present, the graphite material has irreversible lithium loss of 5-10% in the first charge-discharge process, and the high-capacity silicon negative electrode material has irreversible lithium loss of 15-35% in the first charge-discharge process. At present, the irreversible lithium consumption in the first lithium intercalation process is supplemented in advance by means of a lithium supplementation technology, so that the energy density of the lithium ion battery is improved.

Chemical prelithiation is one of various lithium supplement technologies, and lithium supplement of a negative electrode is realized by utilizing the principle that the activity of a chemical lithiation reagent reacts with an electrode material to introduce lithium ions. The existing chemical pre-lithiation process usually immerses the negative plate in an active lithium solution, but in the process of immersion type pre-lithiation, along with the consumption of lithium ions in the lithium solution, the concentration of the lithium solution contacted with the negative plate is difficult to ensure to be consistent, so that the negative plate is uneven in lithium supplement and poor in lithium supplement effect.

CN 109713215A discloses a lithium-supplement negative plate, a preparation method thereof and a lithium ion battery, wherein the lithium-supplement negative plate comprises a negative plate body and a lithium-supplement composite layer coated on the surface of the negative plate body; the lithium supplement composite layer comprises the following raw materials in percentage by mass: 20-65% of alloy lithium powder, 30-70% of ceramic powder and 5-50% of binder. However, in the invention, the lithium supplement composite layer formed by the alloy lithium powder, the ceramic powder and the binder is coated on the surface of the negative plate, and the method is difficult to ensure uniform coating, so that the consistency of the battery is poor.

CN 109004304a discloses a soft package lithium ion battery lithium supplement method, a lithium ion battery preparation method and a middle lithium supplement battery, wherein the soft package lithium ion battery lithium supplement method comprises the following steps: A) before the soft package battery is formed, a lithium supplement electrode is arranged in an air bag which is formed after the battery core is packaged and contains electrolyte; B) electrically connecting the negative electrode of the battery cell with the lithium supplement electrode, and discharging the lithium supplement electrode so as to transfer lithium in the lithium supplement electrode to the negative electrode, thereby realizing lithium supplement; C) and cutting to remove the air bag and the lithium supplement electrode. However, the invention needs to redesign the battery structure, and the consistency of the negative electrode after lithium supplement is difficult to ensure, the process is very complex, and the operation is complicated.

Therefore, how to provide a lithium-supplement negative plate and a preparation method thereof can improve the uniformity of lithium supplement and the consistency of a battery, make up irreversible lithium consumed in the process of lithium intercalation for the first time, simplify the lithium supplement process, reduce the operation difficulty and become a problem which needs to be solved by technical personnel in the field at present.

Disclosure of Invention

The invention aims to provide a lithium-supplementing negative plate, a preparation method thereof and a lithium ion battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the invention provides a lithium supplement negative plate, which comprises a lithium powder composite membrane and a negative current collector which are stacked.

The weight of the lithium powder in the lithium powder composite membrane of the lithium-supplementing negative electrode sheet per unit volume is 0.5-2% of the weight of the positive electrode main material per unit volume, and may be, for example, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, or 2%, but is not limited to the values listed, and other values not listed in the range of the values are also applicable.

According to the invention, by adding a proper amount of lithium powder into the negative electrode diaphragm, the irreversible loss caused by the fact that lithium ions form an SEI film on the negative electrode in the first charging process is well compensated, the first coulombic efficiency of the material is improved, and the irreversible capacity loss of the battery cell is reduced. In addition, the content of the lithium powder needs to be controlled within a reasonable range, and when the weight ratio of the lithium powder is lower than 0.5%, the improvement range of the first coulombic efficiency is too small; when the weight ratio of the lithium powder is higher than 2%, excessive lithium powder may form lithium dendrite at the negative electrode, thereby deteriorating the performance of the cell.

Preferably, the negative electrode current collector comprises a carbon-coated copper foil.

Preferably, the carbon-coated copper foil is a double-sided carbon-coated copper foil, and comprises a copper foil layer and carbon-coated layers respectively arranged on two sides of the copper foil layer.

Preferably, the thickness of the lithium powder composite membrane is 40-80 μm, such as 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm or 80 μm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the thickness of the copper foil layer in the double-sided carbon-coated copper foil is 4 to 5 μm, and may be, for example, 4 μm, 4.1 μm, 4.2 μm, 4.3 μm, 4.4 μm, 4.5 μm, 4.6 μm, 4.7 μm, 4.8 μm, 4.9 μm or 5 μm, but is not limited to the values listed, and other values not listed in the range of the values are also applicable.

Preferably, the carbon-coated layer in the double-sided carbon-coated copper foil has a thickness of 0.2 to 0.8 μm, and may be, for example, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm or 0.8 μm, but is not limited to the values listed, and other values not listed in the range of the values are also applicable.

In a second aspect, the present invention provides a method for preparing the lithium-supplementing negative electrode sheet according to the first aspect, wherein the method comprises the following steps:

(1) mixing graphite and silicon powder to obtain first negative electrode powder;

(2) mixing a conductive agent, lithium powder and the first negative electrode powder obtained in the step (1) to obtain second negative electrode powder;

(3) mixing a binder with the second negative electrode powder obtained in the step (2) to obtain third negative electrode powder;

(4) rolling the third negative electrode powder obtained in the step (3) to obtain a lithium powder composite membrane;

(5) and (4) mutually laminating the lithium powder composite membrane obtained in the step (4) and a negative current collector and rolling together to obtain the lithium-supplement negative plate.

Wherein, according to the mass ratio, graphite: silicon powder: conductive agent: the binder (86-87) (9-10) (1-2) (2-3) may be, for example, 86:9:1:2, 86.5:9.5:1.5:2.5, 87:10:2:3, 86:9:2:3, 87:10:1:2, or 86:9:1.5:2.5, but is not limited to the enumerated values, and other values not enumerated within the range of values are equally applicable.

According to the invention, a dry electrode mode is adopted, the graphite and the silicon powder are mixed firstly, then the conductive agent and the lithium powder are added, and finally the binder is added, so that the mixing sequence is favorable for fully improving the dispersibility and uniformity of the material, and the performance of the pole piece is obviously improved.

Preferably, the mixing of step (1) is accompanied by stirring.

Preferably, the stirring speed is 400-800rpm, such as 400rpm, 450rpm, 500rpm, 550rpm, 600rpm, 650rpm, 700rpm, 750rpm or 800rpm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the stirring time is 40-80min, for example 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min or 80min, but is not limited to the recited values, and other values not recited in the range of values are equally applicable.

Preferably, the conductive agent of step (2) comprises vapor grown carbon fiber.

Preferably, the mixing of step (2) is accompanied by stirring.

Preferably, the stirring speed is 400-800rpm, such as 400rpm, 450rpm, 500rpm, 550rpm, 600rpm, 650rpm, 700rpm, 750rpm or 800rpm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the stirring time is 40-80min, for example 40min, 45min, 50min, 55min, 60min, 65min, 70min, 75min or 80min, but is not limited to the recited values, and other values not recited in the range of values are equally applicable.

Preferably, the binder of step (3) comprises polytetrafluoroethylene.

Preferably, the mixing of step (3) is accompanied by stirring.

Preferably, the stirring speed is 400-800rpm, such as 400rpm, 450rpm, 500rpm, 550rpm, 600rpm, 650rpm, 700rpm, 750rpm or 800rpm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.

Preferably, the stirring time is 20-40min, for example, 20min, 22min, 24min, 26min, 28min, 30min, 32min, 34min, 36min, 38min or 40min, but is not limited to the values listed, and other values not listed in the range of values are also applicable.

As a preferable technical solution of the second aspect of the present invention, the preparation method comprises the steps of:

(1) mixing graphite and silicon powder, and stirring at the rotating speed of 400-800rpm for 40-80min to obtain first cathode powder;

(2) mixing vapor-grown carbon fiber, lithium powder and the first negative electrode powder obtained in the step (1), and stirring at the rotating speed of 400-800rpm for 40-80min to obtain second negative electrode powder;

(3) mixing polytetrafluoroethylene with the second negative electrode powder obtained in the step (2), and stirring at the rotating speed of 400-800rpm for 20-40min to obtain third negative electrode powder;

(4) rolling the third negative electrode powder obtained in the step (3) to obtain a lithium powder composite membrane;

(5) and (4) mutually laminating the lithium powder composite membrane obtained in the step (4) and a negative current collector and rolling together to obtain the lithium-supplement negative plate.

Wherein, according to the mass ratio, graphite: silicon powder: conductive agent: the binder (86-87), (9-10), (1-2) and (2-3).

In a third aspect, the present invention provides a lithium ion battery, which includes a positive plate, a diaphragm, an electrolyte and the lithium supplement negative plate of the first aspect.

Preferably, the lithium ion battery satisfies: the negative electrode active material capacity per unit area of the lithium-doped negative electrode sheet/the positive electrode active material capacity per unit area of the positive electrode sheet is 1.1 to 1.2, and may be, for example, 1.1, 1.11, 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, or 1.2, but is not limited to the values listed above, and other values not listed in the range of the values are also applicable.

According to the invention, the first coulombic efficiency of the battery cell is improved to more than 89% by controlling the N/P ratio of the lithium ion battery to be 1.1-1.2, so that the battery performance is more excellent.

Compared with the prior art, the invention has the following beneficial effects:

(1) according to the invention, by adding a proper amount of lithium powder into the negative electrode diaphragm and controlling the weight of the lithium powder in the lithium powder composite diaphragm of the unit volume lithium-supplementing negative electrode plate to be 0.5-2% of the weight of the main positive electrode material in the unit volume positive electrode plate, the irreversible loss caused by the SEI (solid electrolyte interphase) film formed by lithium ions at the negative electrode in the first charging process is well compensated, the first coulombic efficiency of the material is improved, and the irreversible capacity loss of the battery cell is reduced;

(2) according to the invention, a dry electrode mode is adopted, the graphite and the silicon powder are mixed firstly, then the conductive agent and the lithium powder are added, and finally the binder is added, so that the mixing sequence is favorable for fully improving the dispersibility and uniformity of the material, and the performance of the pole piece is obviously improved.

Drawings

Fig. 1 is a graph showing the cycle performance test of the lithium ion batteries obtained in application examples 1 to 3 and comparative application examples 1 to 3.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

The embodiment provides a lithium-supplement negative plate and a preparation method thereof, and the preparation method comprises the following steps:

(1) mixing graphite and silicon powder, and stirring at the rotating speed of 600rpm for 60min to obtain first negative electrode powder;

(2) mixing vapor-grown carbon fiber and lithium powder with the first negative electrode powder obtained in the step (1), and stirring at the rotating speed of 600rpm for 60min to obtain second negative electrode powder;

(3) mixing polytetrafluoroethylene with the second negative electrode powder obtained in the step (2), and stirring at the rotating speed of 600rpm for 30min to obtain third negative electrode powder;

(4) rolling the third negative electrode powder obtained in the step (3) to obtain a lithium powder composite membrane;

(5) and (4) mutually laminating the lithium powder composite membrane obtained in the step (4) and the double-sided carbon-coated copper foil, and rolling together to obtain the lithium-supplement negative plate.

Wherein, according to the mass ratio, graphite: silicon powder: conductive agent: the binder is 86.5:9.5:1.2:2.3, and the weight of the lithium powder in the lithium powder composite membrane of the unit volume lithium-supplementing negative plate is 0.5% of the weight of the positive electrode main material in the unit volume positive plate.

The thickness of the lithium powder composite membrane in the lithium-supplement negative plate obtained in the embodiment is 60 μm, the thickness of the copper foil layer in the double-sided carbon-coated copper foil is 4.5 μm, and the thickness of the carbon-coated layer is 0.5 μm.

Example 2

The present embodiment provides a lithium supplement negative electrode sheet and a preparation method thereof, where except that the weight of lithium powder in a lithium powder composite membrane of a lithium supplement negative electrode sheet per unit volume is controlled to be 1% of the weight of a positive electrode main material in a positive electrode sheet per unit volume, the other conditions are the same as those in embodiment 1, and thus, details are not repeated here.

Example 3

The present embodiment provides a lithium supplement negative electrode sheet and a preparation method thereof, where except that the weight of lithium powder in a lithium powder composite membrane of a lithium supplement negative electrode sheet per unit volume is controlled to be 2% of the weight of a positive electrode main material in a positive electrode sheet per unit volume, the other conditions are the same as those in embodiment 1, and thus, details are not repeated here.

Example 4

The embodiment provides a lithium-supplement negative plate and a preparation method thereof, and the preparation method comprises the following steps:

(1) mixing graphite and silicon powder, and stirring for 80min at the rotating speed of 400rpm to obtain first negative electrode powder;

(2) mixing vapor-grown carbon fiber and lithium powder with the first negative electrode powder obtained in the step (1), and stirring at the rotating speed of 400rpm for 80min to obtain second negative electrode powder;

(3) mixing polytetrafluoroethylene with the second negative electrode powder obtained in the step (2), and stirring at the rotating speed of 400rpm for 40min to obtain third negative electrode powder;

(4) rolling the third negative electrode powder obtained in the step (3) to obtain a lithium powder composite membrane;

(5) and (4) mutually laminating the lithium powder composite membrane obtained in the step (4) and the double-sided carbon-coated copper foil, and rolling together to obtain the lithium-supplement negative plate.

Wherein, according to the mass ratio, graphite: silicon powder: conductive agent: the binder is 86:9:1:2, and the weight of the lithium powder in the lithium powder composite membrane of the unit volume lithium-supplementing negative plate is 0.5 percent of the weight of the positive electrode main material in the unit volume positive plate.

The thickness of the lithium powder composite membrane in the lithium-supplement negative plate obtained in the embodiment is 40 μm, the thickness of the copper foil layer in the double-sided carbon-coated copper foil is 4 μm, and the thickness of the carbon-coated layer is 0.2 μm.

Example 5

The embodiment provides a lithium-supplement negative plate and a preparation method thereof, and the preparation method comprises the following steps:

(1) mixing graphite and silicon powder, and stirring at the rotating speed of 800rpm for 40min to obtain first negative electrode powder;

(2) mixing vapor-grown carbon fiber and lithium powder with the first negative electrode powder obtained in the step (1), and stirring at the rotating speed of 800rpm for 40min to obtain second negative electrode powder;

(3) mixing polytetrafluoroethylene with the second negative electrode powder obtained in the step (2), and stirring at the rotating speed of 800rpm for 20min to obtain third negative electrode powder;

(4) rolling the third negative electrode powder obtained in the step (3) to obtain a lithium powder composite membrane;

(5) and (4) mutually laminating the lithium powder composite membrane obtained in the step (4) and the double-sided carbon-coated copper foil, and rolling together to obtain the lithium-supplement negative plate.

Wherein, according to the mass ratio, graphite: silicon powder: conductive agent: the binder is 87:10:2:3, and the weight of the lithium powder in the lithium powder composite membrane of the unit volume lithium-supplementing negative plate is 0.5 percent of the weight of the positive electrode main material in the unit volume positive plate.

The thickness of the lithium powder composite membrane in the lithium-supplement negative plate obtained in the embodiment is 80 μm, the thickness of the copper foil layer in the double-sided carbon-coated copper foil is 5 μm, and the thickness of the carbon-coated layer is 0.8 μm.

Comparative example 1

The present comparative example provides a negative electrode sheet and a method for preparing the same, wherein the conditions are the same as those in example 1 except that no lithium powder is added, and thus, the details are not repeated herein.

Comparative example 2

The preparation method is the same as that of example 1 except that the weight of the lithium powder in the lithium powder composite membrane of the lithium supplement negative plate in unit volume is controlled to be 3% of the weight of the positive electrode main material in the positive plate in unit volume, and therefore, the details are not repeated herein.

Comparative example 3

The comparative example provides a lithium-supplement negative electrode sheet and a preparation method thereof, and the preparation method comprises the following steps:

(1) mixing graphite, silicon powder, vapor-grown carbon fiber, lithium powder and polytetrafluoroethylene, and stirring at the rotating speed of 600rpm for 150min to obtain negative electrode powder;

(2) rolling the negative electrode powder obtained in the step (1) to obtain a lithium powder composite membrane;

(3) and (3) mutually laminating the lithium powder composite membrane obtained in the step (2) and the double-sided carbon-coated copper foil, and rolling together to obtain the lithium-supplement negative plate.

Wherein, according to the mass ratio, graphite: silicon powder: conductive agent: the binder is 86.5:9.5:1.2:2.3, and the weight of the lithium powder in the lithium powder composite membrane of the unit volume lithium-supplementing negative plate is 0.5% of the weight of the positive electrode main material in the unit volume positive plate.

The thickness of the lithium powder composite membrane in the lithium-supplementing negative plate obtained in the comparative example is 60 micrometers, the thickness of the copper foil layer in the double-sided carbon-coated copper foil is 4.5 micrometers, and the thickness of the carbon-coated layer is 0.5 micrometers.

Application example 1

In the application example, the lithium ion battery is prepared by applying the lithium-supplement negative plate provided in example 1, and the specific preparation process is as follows:

1. preparing a positive plate:

firstly, LiFePO is put in a stirring kettle₄Mixing SP, PVDF and CNT in a mass ratio of 96:1.8:1.7:0.5 to obtain anode slurry with solid content of 54 wt%;

secondly, the positive pole slurry is evenly coated on a double-sided carbon-coated aluminum foil with the thickness of 12 mu m by adopting extrusion coating, and is dried at the temperature of 120 ℃ to prepare a dry positive pole piece, and the single-sided surface density of the positive pole piece is controlled to be 105g/m²。

Wherein, the specification of the double-sided carbon-coated aluminum foil is (10+0.5+0.5) mu m multiplied by 257mm, the thickness of one side of the carbon-coated layer is 0.5 mu m, and the thickness of the double sides is 1 mu m.

2. Preparing an electrolyte:

the electrolyte was prepared in an argon-filled glove box with less than 10ppm water and less than 1ppm oxygen. The preparation of the electrolyte comprises the following steps: ethylene Carbonate (EC) in volume ratio: dimethyl carbonate (DMC): diethyl carbonate (DEC) 30:40:30 configuration 1.2mol/L LiPF₆And LFSI (LiPF)₆: LFSI ═ 1.1:0.1) electrolyte, then 0.5 wt% additive VC, 1.5 wt% FEC, 0.5 wt% DTD and 0.5 wt% LiPO were added₂F₂And mixing uniformly for later use.

3. Assembling the lithium ion battery:

and (2) winding the positive plate, the diaphragm and the negative plate provided by the embodiment 1 to form a winding core, then placing the winding core in an aluminum shell, welding a cover plate, baking the winding core in a baking oven at 100 ℃ for 12 hours, injecting the electrolyte into the aluminum shell, standing at high temperature, forming, then carrying out secondary injection, and standing and grading to obtain the corresponding lithium ion battery. Wherein the diaphragm is a polyethylene diaphragm with the thickness of (7+2+1+1) mu m, the lithium ion battery has the thickness of 20mm, the width of 150mm and the height of 120mm, the rated capacity of the lithium ion battery is 20Ah (1C-20A), and the lithium ion battery satisfies the following conditions: the negative electrode active material capacity per unit area of the lithium-supplemented negative electrode sheet/the positive electrode active material capacity per unit area of the positive electrode sheet was 1.15.

Application example 2

In this application example, the lithium ion battery is prepared by using the lithium supplement negative electrode sheet provided in example 2, and the specific preparation process is the same as that in application example 1, and therefore, the detailed description is omitted here.

Application example 3

In this application example, the lithium ion battery is prepared by using the lithium supplement negative electrode sheet provided in example 3, and the specific preparation process is the same as that in application example 1, and therefore, the detailed description is omitted here.

Comparative application example 1

In the comparative application example, the lithium-ion battery is prepared by using the lithium-supplement negative electrode sheet provided in comparative example 1, and the specific preparation process is the same as that in application example 1, and therefore, the detailed description is omitted here.

Comparative application example 2

In the comparative application example, the lithium-ion battery is prepared by using the lithium-supplement negative electrode sheet provided in the comparative example 2, and the specific preparation process is the same as that in the application example 1, so that details are not described herein.

Comparative application example 3

In the comparative application example, the lithium-ion battery is prepared by using the lithium-supplement negative electrode sheet provided in comparative example 3, and the specific preparation process is the same as that in application example 1, and therefore, the details are not described herein.

The lithium ion batteries obtained in application examples 1-3 and comparative application examples 1-3 were assembled into 12pcs cells, and the median of the cell performance of each group was taken as the electrical performance data of the group, including the first stock efficiency (see table 1) and the cycle performance test (charge and discharge test at 25 ℃ under 1C) (see fig. 1).

TABLE 1

As can be seen from table 1, the battery cell after the lithium powder is added in the negative electrode stirring process is higher in the first stock efficiency, which is related to the loss of lithium ions in the negative electrode plate making up for the lithium powder in the first charging process, and the application example 3 and the comparative application example 2 are the largest in the first discharge capacity.

As can be seen from fig. 1: the cycle performance of application example 3 is the best, wherein compared with application example 2, as the number of cycles increases, excessive lithium powder can form lithium dendrite on the negative electrode due to excessive addition of the lithium powder, so that the performance of the battery cell is damaged; in contrast to application example 3, the subsequent stirring and dispersing are not uniform enough due to the adoption of the one-step charging mode, and finally, the cycle performance of the obtained battery is poor.

Therefore, according to the invention, by adding a proper amount of lithium powder into the negative electrode diaphragm and controlling the weight of the lithium powder in the lithium powder composite diaphragm of the unit volume lithium-supplementing negative electrode plate to be 0.5-2% of the weight of the main positive electrode material in the unit volume positive electrode plate, the irreversible loss caused by the SEI film formed by lithium ions at the negative electrode in the primary charging process is well compensated, the primary coulombic efficiency of the material is improved, and the irreversible capacity loss of the battery cell is reduced; in addition, the invention adopts a dry electrode mode, firstly graphite and silicon powder are mixed, then the conductive agent and lithium powder are added, and finally the binder is added, and the mixing sequence is favorable for fully improving the dispersibility and uniformity of the material, thereby obviously improving the performance of the pole piece.

The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.