阅读说明：本技术 一种防止锂离子电池负极析锂的方法 (Method for preventing lithium precipitation of lithium ion battery cathode ) 是由 左美华 王佳 王金锋 余军 于 2019-09-19 设计创作，主要内容包括：本发明公开了一种防止锂离子电池负极析锂的方法,锂离子电池的电芯为方形卷绕电芯,所述卷绕电芯由正极极片、隔膜以及负极极片构成的叠层进行卷绕形成,所述卷绕电芯包括第一表面、第二表面、第一侧面以及第二侧面,所述负极极片涂布时,第一表面、第二表面按照常规面密度涂布,侧面涂布的面密度大于表面的涂布面密度。本发明在极片涂布时,正极极片采用正常的涂布面密度,在负极极片涂布时,极片卷绕时表面的采用常规的面密度涂布,极片卷绕时侧面的面密度高于表面的面密度,即增加了卷绕负极极片侧面的面密度,每一层卷绕侧面只有几毫米,因此在不需要增加电池成本和降低能量密度的情况下,解决了锂离子电池析锂的问题。(The invention discloses a method for preventing lithium precipitation of a lithium ion battery cathode, wherein a battery cell of the lithium ion battery is a square winding battery cell, the winding battery cell is formed by winding a lamination consisting of a positive pole piece, a diaphragm and a negative pole piece, the winding battery cell comprises a first surface, a second surface, a first side surface and a second side surface, when the negative pole piece is coated, the first surface and the second surface are coated according to the conventional surface density, and the surface density of the side surface coating is greater than the coating surface density of the surface. According to the invention, when the pole piece is coated, the normal coating surface density is adopted for the positive pole piece, when the negative pole piece is coated, the conventional surface density coating is adopted for the surface when the pole piece is wound, the surface density of the side surface when the pole piece is wound is higher than that of the surface, namely, the surface density of the side surface of the wound negative pole piece is increased, and the winding side surface of each layer is only several millimeters, so that the problem of lithium precipitation of the lithium ion battery is solved under the condition of not increasing the battery cost and reducing the energy density.)

1. The utility model provides a method for preventing lithium ion battery negative pole from separating out lithium, lithium ion battery's electric core is square coiling electric core, coiling electric core is convoluteed by the stromatolite that positive pole piece, diaphragm and negative pole piece constitute and is formed, coiling electric core includes first surface, second surface, first side and second side, its characterized in that: when the negative pole piece is coated, the first surface and the second surface are coated according to the conventional surface density, and the surface density of the first side surface and the second side surface is greater than that of the first surface and the second surface.

2. The method of claim 1, wherein the method comprises the steps of: the first surface is disposed opposite the second surface, and the first side surface is disposed opposite the second side surface.

3. The method of claim 1, wherein the method comprises the steps of: the positive pole piece is coated by adopting the conventional surface density.

4. The method of claim 1, wherein the method comprises the steps of: the surface density of the negative pole piece coating is greater than that of the positive pole piece coating.

5. The method of claim 1, wherein the method comprises the steps of: when the negative pole piece is coated, the excess coefficient of the first surface and the second surface is 1.02-1.05.

6. The method for preventing lithium evolution from a negative electrode of a lithium ion battery according to claim 1 or 5, wherein: when the negative pole piece is coated, the excess coefficient of the coating of the first side face and the second side face is 1.06-1.09.

7. The method for preventing lithium evolution from a negative electrode of a lithium ion battery according to claim 1 or 2, wherein: the lengths of the first side face and the second side face are smaller than the lengths of the first surface and the second surface.

8. The method of claim 8, wherein the method comprises the steps of: the length of the first side surface and the second side surface is less than 10 mm.

Technical Field

The invention relates to the technical field of electrochemical batteries, in particular to a method for preventing lithium precipitation of a lithium ion battery cathode.

Background

Since lithium ion batteries have the characteristics of high energy density, portability and portability, lithium ion batteries are actively used as energy carriers in the fields of communication, digital cameras, video cameras, notebooks and the like since the commercialization of lithium ion batteries. In recent years, with diversification of electronic digital products, requirements for the appearance of a battery cell tend to be thinned, and users who originally adopt round battery cells such as 18650, 26650 and the like position the shape of the battery cell in a square battery cell according to requirements of product appearance design, so that large-size square battery cells have wide requirements in more and more fields. The square battery cell is mainly classified into a winding type and a lamination type; the laminated square battery has the problems of low production efficiency, poor consistency, low discharge rate, short cycle life and the like, the production efficiency of the wound square battery is high, the conventional square lithium ion secondary battery generally adopts a single-roll core winding structure, namely, a designed positive electrode and a designed negative electrode of the battery are respectively provided with a pole piece after material preparation, coating and slicing, then the positive electrode and the negative electrode are separated by a diaphragm and rotate around a winding die together, the winding core of the battery can be obtained after the winding is finished and is withdrawn, then the winding core is arranged in a shell, the positive electrode and the negative electrode are respectively communicated with a positive electrode and a negative electrode which are positioned on the shell through a positive electrode lug and a negative electrode lug, and the finished lithium ion battery.

During charging of a lithium ion battery, lithium ions are extracted from the positive electrode and inserted into the negative electrode. However, when some abnormal condition occurs and lithium ions extracted from the positive electrode cannot be inserted into the negative electrode, lithium ions are precipitated only on the surface of the negative electrode, and a gray substance is formed, which is called lithium extraction. When the negative electrode is excessive and insufficient, lithium ions from the positive electrode after being de-intercalated to the negative electrode do not have enough intercalation space, so that only metallic lithium simple substance can be formed and precipitated on the surface of the negative electrode, the precipitated lithium ions grow up along with the continuous charging and discharging to form lithium crystal branches, and the lithium crystal branches pierce through the diaphragm after growing to a certain degree to cause short circuit of the positive electrode and the negative electrode, thereby generating serious potential safety hazard. Therefore, when the anode and the cathode are matched, a certain excess amount of the cathode needs to be provided so as to prevent the problems of lithium precipitation, low capacity and the like caused by insufficient amount of the cathode in the charging and discharging process, but when the amount of the cathode is excessive, the energy density of the battery is low, the cost is increased, and therefore, a proper amount of the cathode needs to be selected excessively. And for square winding type winding core, the pole piece wound by the next circle is longer than the previous circle, when the positive pole piece is wound by the outer and negative pole pieces, the situation of insufficient negative pole excess can occur, especially, the curvature radius of the winding core of the square winding type is different from part to part, on the side edge with small curvature radius of the winding core, when the positive pole piece is wound by the outer and negative pole pieces, the negative pole is seriously insufficient, and the lithium precipitation is serious. Therefore, it is needed to select an appropriate amount of negative electrode to solve the problem of lithium deposition from the square wound cell without increasing the cost or reducing the energy density.

Disclosure of Invention

The invention aims to solve the technical problem of providing a method for preventing lithium from being separated out from a negative electrode of a lithium ion battery, and the problem of lithium separation from a square winding battery cell is solved by selecting a proper negative electrode in an excessive manner on the premise of not increasing the cost or reducing the energy density.

The technical scheme adopted by the invention for solving the technical problems is as follows: a method for preventing lithium precipitation of a lithium ion battery negative electrode is characterized in that a battery cell of the lithium ion battery is a square winding battery cell, the winding battery cell is formed by winding a lamination composed of a positive electrode pole piece, a diaphragm and a negative electrode pole piece, the winding battery cell comprises a first surface, a second surface, a first side surface and a second side surface, when the negative electrode pole piece is coated, the first surface and the second surface are coated according to a conventional surface density, and the surface densities of the first side surface and the second side surface are greater than the coating surface densities of the first surface and the second surface.

Preferably, the first surface is disposed opposite to the second surface, and the first side surface is disposed opposite to the second side surface.

Preferably, the positive electrode sheet is coated with a conventional areal density.

Preferably, the surface density of the negative pole piece coating is greater than that of the positive pole piece coating.

Preferably, when the negative pole piece is coated, the excess coefficient of the first surface and the second surface is 1.02-1.05.

Preferably, when the negative pole piece is coated, the excess coefficient of the coating on the first side face and the second side face is 1.06-1.09.

Preferably, the lengths of the first side face and the second side face are smaller than the lengths of the first surface and the second surface.

Further preferably, the length of the first side surface and the second side surface is less than 10 mm.

The design capacity of the cell is coating surface density active material ratio active material gram capacity pole piece coating area, therefore, when other parameters are fixed, the size of the surface density determines the design capacity of the cell, therefore, the conventional surface density coating is uniformly coated according to the design capacity; in order to prevent the lithium precipitation of the negative electrode, the capacity of the negative electrode is higher than that of the positive electrode in design, namely the negative electrode is in over-design, therefore, the coating of the first surface and the second surface according to the conventional surface density in the coating of the pole piece also comprises the uniform coating of the over-design and the over-design of the negative electrode.

The excess factor, i.e., actual coated unit area anode capacity/designed unit area anode capacity.

The invention has the beneficial effects that: according to the invention, when the pole piece is coated, the normal coating surface density is adopted for the positive pole piece, the coating surface density is intermittently increased when the negative pole piece is coated, the surface when the pole piece is wound is coated by adopting the conventional surface density, the surface density of the side surface when the pole piece is wound is higher than that of the surface, namely the surface density of the side surface of the wound negative pole piece is increased, and the winding side surface of each layer is only several millimeters, so that the problem of lithium precipitation of the negative pole of the lithium ion battery is solved under the condition of not increasing the battery cost and reducing the energy density.

Drawings

FIG. 1 is a schematic view of a positive electrode sheet prior to winding;

FIG. 2 is a schematic view of the negative pole piece before winding;

fig. 3 is a schematic structural diagram of a square cell;

FIG. 4 is a disassembled view of the negative electrode of the battery of comparative example 1 after being fully charged;

FIG. 5 is a disassembled view of the negative electrode of the battery of comparative example 2 after being fully charged;

FIG. 6 is a disassembled view of the negative electrode of the battery of the embodiment after being fully charged;

fig. 7 is a schematic diagram of a pole piece after disassembly of a square cell.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

In the embodiment and the comparative example, a 374258-and 980mAh lithium ion battery is selected, the battery cell is a square battery cell, the anode of the battery cell is 523 anode material, and the anode pole piece substrate is aluminum foil with the thickness of 12-20 mu m; the negative electrode is graphite, the copper foil with the thickness of 8-14um is selected as the base material of the negative electrode pole piece, the structure of the manufactured lithium ion battery is shown in figure 3, the dotted line in figure 3 marks the side surface of the battery cell, and the other two surfaces are surfaces. As shown in FIG. 7, the width of the pole piece is d, the length of the pole piece surface is m, and the length of the pole piece side surface is n. The surfaces comprise a first surface and a second surface which are oppositely arranged, and the side surfaces comprise a first side surface and a second side surface which are oppositely arranged. When the pole piece is wound, the lengths of the first surface and the second surface which are oppositely arranged on the same layer are the same, and the lengths of the first side surface and the second side surface which are oppositely arranged on the same layer are the same, and the lengths of the surfaces and the side surfaces are gradually increased along with the winding, namely the surface of the outer layer is larger than the surface of the inner layer, and the length of the side surface of the outer layer is larger than the length of the side surface of the inner layer.

Other materials also comprise solvent N-methyl pyrrolidone, deionized water, a water lug and a diaphragm aluminum plastic film, wherein the binder and the thickening agent in the positive electrode stirring process adopt Styrene Butadiene Rubber (SBR) and sodium carboxymethyl cellulose (CMC), and the binder in the negative electrode stirring process adopts polyvinylidene fluoride. The lithium salt in the electrolyte is lithium hexafluorophosphate, the organic solvent is ethylene carbonate, dimethyl carbonate and diethyl carbonate, and the additive is vinylene carbonate.

The assembly process of the lithium ion battery comprises the following steps:

pulping: mixing the powder-shaped positive and negative electrode active substances with a solvent and a bonding agent respectively, and stirring the mixture uniformly at a high speed to prepare slurry-shaped positive and negative electrode substances;

coating: uniformly coating the prepared slurry on the surface of a metal foil, drying, slitting and rolling to respectively prepare a positive pole piece and a negative pole piece;

assembling: placing the positive plate, the diaphragm, the negative plate and the diaphragm from top to bottom in sequence, winding to prepare a battery pole core, injecting electrolyte, sealing and other technological processes to finish the assembly process of the battery, and preparing a finished battery;

formation: and (4) carrying out charge and discharge tests on the finished product battery by using special battery charge and discharge equipment.

The design value of the surface density of the positive electrode sheet is 19.70mg/cm²The designed surface density value of the negative pole piece is 8.98mg/cm²。

Comparative example 1:

the materials are selected as raw materials, the anode plate is coated according to a normal process, and the surface density of the coating is uniform and is 19.70mg/cm²(ii) a When the negative pole piece is coated, the negative pole excess coefficient is 1.05, and the coating surface density is 9.67mg/cm²And after coating, slitting, rolling, flaking, winding, packaging, injecting liquid, forming and grading to obtain the lithium ion battery.

Comparative example 2:

the materials are selected as raw materials, the positive pole piece is coated according to a normal process, the surface density of the coating is consistent, and the surface density is 19.70mg/cm²The cathode excess coefficient when coating the cathode pole piece is 1.08, and the coating surface density is 9.70mg/cm²And after coating, slitting, rolling, flaking, winding, packaging, injecting liquid, forming and grading to obtain the lithium ion battery.