CN216980649U - A lithium battery and a lithium battery pole piece - Google Patents

Abstract

The utility model discloses a lithium battery and a lithium battery pole piece. The lithium battery pole piece comprises a positive pole piece and a negative pole piece. Two or more pole lugs are arranged around each positive pole piece, and each negative pole piece is provided with two or more tabs. The periphery of the pole piece is provided with two or more pole ears. The tabs on each positive pole piece are evenly distributed or centrally symmetric around the periphery of the positive pole piece, and the tabs on each negative pole piece are evenly distributed or centrally symmetric around the periphery of the negative pole piece. The utility model improves the uniformity of the charging and discharging current distribution of the lithium battery by increasing the number of the pole tabs of each layer of battery pole pieces in the lithium battery. The solution provided by the utility model can effectively improve the distribution of the charging and discharging current in the pole piece, make the charging and discharging current distribution more uniform, reduce the polarization during the charging and discharging process, and can effectively improve the discharge power performance of the battery and reduce the charging time.

Description

A lithium battery and a lithium battery pole piece

technical field

The utility model belongs to the field of lithium batteries, in particular to a lithium battery and a lithium battery pole piece.

Background technique

High power density, high energy density Li-ion batteries have this important application in HEV, PHEV, vehicle starter power supply, power tools, drones, etc. The most important issue in all application fields is to reduce the weight of the battery , to increase the energy density of the battery. In order to reduce the overall weight of the battery and obtain a lithium-ion battery with a higher energy density and a higher volume density, it is usually achieved in the following ways: (1) Using a positive and negative electrode material with a higher gram capacity, such as The positive electrode uses a high-nickel positive electrode material or a high-voltage positive electrode material, and the negative electrode uses a silicon carbon negative electrode, etc.; (2) Increasing the capacity of the single cell means reducing the proportion of auxiliary materials and increasing the proportion of positive and negative active materials, thereby Increase the overall energy density of the battery; (3) Improve the surface density of the battery pole piece, which can also reduce the weight ratio of the copper-aluminum foil substrate and increase the battery energy density. The above measures will have certain disadvantages. For example, the use of high-nickel positive electrode materials will make the safety of the battery worse and increase the capacity of the single battery. If the volume of the battery pole piece is increased, the current during the charging and discharging process of the battery will be increased. The uneven distribution affects the overall charge-discharge rate of the battery. Similarly, the third measure will make the current density of the battery unevenly distributed by increasing the surface density of the pole piece, increasing the diffusion resistance of the battery and lithium ions, especially in the case of high current. The current density near the tab will be greater than the current density far away from the tab, thus affecting the battery power performance and charging rate.

In view of the problems caused by the above improvement measures, the industry usually increases the electronic conductivity of the battery pole pieces by introducing more conductive agents in the positive and negative electrode formulations or adding conductive agents with better conductivity such as carbon nanotubes and graphene. performance, reduce the internal resistance of the battery, make the current density distribution of the pole pieces in the battery more uniform, and reduce the polarization problem caused by diffusion, but this method will not only increase the cost of the battery, but also reduce the proportion of active materials due to the increase in the proportion of conductive agents. Thereby reducing the proportion of the energy density increase of the battery.

Utility model content

In view of the above technical problems, the present invention increases the number of battery tabs by designing the battery tabs in different directions, so that the current enters the battery through multiple directions of the poles, so that the battery can be charged and discharged in the process of charging and discharging. The current density distribution is more uniform, reducing the polarization during the charging and discharging process inside the battery, so that a larger charging and discharging current can be used, so that the charging time is shorter, and the discharging power and rate are larger.

The technical scheme of the present utility model is as follows:

On the one hand, the utility model provides a lithium battery and a lithium battery pole piece to improve the method of current distribution inside the lithium battery, the lithium battery pole piece includes a positive pole piece and a negative pole piece, and the periphery of each positive pole piece is There are two or more tabs, and the periphery of each negative pole piece is provided with two or more tabs.

Based on the above solution, preferably, the electrode tabs are formed by extending the positive pole piece or the negative pole piece in a direction away from the pole piece and parallel to the surface of the pole piece.

Based on the above solution, preferably, the tabs on each positive pole piece are evenly distributed or centrally symmetric around the positive pole piece, and the tabs on each negative pole piece are evenly distributed or centrally symmetric around the negative pole piece.

Based on the above solution, preferably, the number of tabs on each positive pole piece or negative pole piece is 2-6.

On the other hand, the present invention provides a lithium battery, which includes the positive pole piece and the negative pole piece in the above method.

Based on the above solution, preferably, the lithium battery structure includes a square wound structure cell and a laminated structure cell, and the method of adding tabs can be realized by process control in the tab forming process of electrode preparation.

Based on the above solution, preferably, when the lithium battery is in a winding structure, the number of winding turns of the battery is N, where N is an integer greater than or equal to 1, and each turn includes one positive pole piece and one negative pole piece; the The tabs are located on both sides of each pole piece and are centrally symmetric.

Based on the above solution, preferably, when the lithium battery is in a laminated structure, the positive electrode of the battery is N layers, N is an integer greater than or equal to 2, and the negative electrode of the battery is N+1 layers, each layer including one of the positive electrode piece and the negative electrode Pole pieces; the pole tabs are located on both sides of each pole piece and are centrally symmetric.

Based on the above solution, preferably, in a lithium battery with a laminated structure or a winding structure, the tab of each pole piece is located in the diagonal direction of the pole piece. After the battery is assembled, the tab of the negative pole piece and the positive pole The tabs of the sheets do not overlap.

Based on the above solution, preferably, in the square wound battery, polar tabs are designed on both sides of the battery pole pieces, and the pole ears are symmetrical in the center, so that the current flows into the battery bidirectionally through the pole pieces. The pole pieces of the laminated battery can be divided into two designs. One of the designs is consistent with the square wound battery. The pole pieces are designed on both sides of the pole piece, and the pole pieces are symmetrical in the center. The pole piece of the laminated battery is designed as Two pole lugs are designed in the length direction and width direction of the pole piece respectively. The pole lugs in the length direction are center-symmetrical, and the pole lugs in the width direction are also center-symmetrical. By adding battery pole lugs in different directions of the pole piece, the battery It flows into the battery from four directions, reducing the problem of uneven current distribution inside the battery, reducing the internal polarization of the battery, and increasing the overall charge and discharge rate of the battery.

Based on the above solution, preferably, when the lithium battery structure is a winding structure, the number of winding turns of the battery is N turns (N is an integer greater than or equal to 1), and the positive and negative pole pieces in each turn are respectively protruded by 2 tabs, After winding, the number of positive and negative tabs of the whole battery is 2×N, the tabs are located at opposite ends of the battery, and the two positive tabs are respectively distributed on the corresponding positions in the length or width direction of the whole battery. The center is symmetrical, and the two negative electrode tabs are also distributed in the corresponding positions in the length or width direction of the full battery respectively to form a center symmetry. It is 2, and the number of negative poles is 2, that is, the total number of positive and negative poles of the whole battery is 4. As shown in Figure 1, the positive poles are at the 1st and 4th positions, and the negative poles are at 2 Positions No. 3 and No. 3, the distribution of the tabs in this way allows the charging and discharging current of the battery to flow in or out from both sides of the battery, and the current will be more evenly distributed inside the battery.

Based on the above solution, preferably, when the lithium battery structure is a laminated structure, the positive electrode of the battery is N layers (N is an integer greater than or equal to 2), then the negative electrode is N+1 layers, and the positive electrode and the negative electrode pole piece in each layer respectively protrude 2 or 4 tabs, the number of positive pole tabs is 2×N or 4×N, and the number of negative tabs is 2×(N+1) or 4×(N+1) After assembling the full battery, after welding the tabs of each layer of pole pieces, the number of positive tabs is 2 or 4, and the number of negative tabs is also 2 or 4, corresponding to the total number of tabs of the battery. The number is 4 and 8; the tabs on the positive pole piece or the pole piece on the negative pole piece are respectively center-symmetrical.

When the number of positive and negative electrode tabs is 2, the positive electrode tabs are center-symmetrical, and the negative electrode tabs are also center-symmetrical. As shown in Figure 2, the full-battery tab structure is the same as the above-mentioned winding structure. Consistent, as shown in Figure 3, the negative tabs are located at positions 1 and 4, and the positive tabs are at positions 2 and 3, respectively.

When both the positive pole piece and the negative pole piece have four tabs, the structure diagram of the positive and negative pole pieces is shown in Figure 4. The pole tabs have two pole tabs in the length and width directions of the pole piece. The two tabs of the battery are symmetrical in the center, and the two tabs in the width direction are also symmetrical in the center. The positive and negative electrodes are assembled into a full battery by lamination. After the tabs are welded, the whole battery has a total of 4 positive tabs, 4 There are 8 negative tabs in total. The full battery and tab structure are shown in Figure 5. The negative tabs are located at positions 1, 3, 5, and 7, and the positive tabs are located at Positions 2, 3, 5, and 7, as shown in Figure 5, can make the charging and discharging current of the battery flow into or out of the battery from the tab positions in the four directions of the upper, lower, left, and right directions of the battery. It will be more evenly distributed inside the battery, reducing the polarization problem caused by the uneven current part.

Beneficial results of the present invention

The utility model can effectively improve the distribution of the current in the pole pieces during the charging and discharging process by increasing the number of pole tabs of the whole battery after lamination or winding, so that the distribution of the charging and discharging current flowing through the battery is more uniform, and the charging and discharging process is more uniform. The current density of each part of the pole piece tends to be consistent, thereby reducing the reaction polarization caused by the uneven current part. The reduction of polarization can effectively improve the discharge power of the battery and can also use a larger current to charge the battery. to reduce battery charging time.

Description of drawings

Figure 1 is a schematic diagram of a 4-tab wound battery and the distribution of battery tabs, wherein "1" and "4" represent negative electrode tabs; "2" and "3" represent positive electrode tabs.

FIG. 2 is a schematic diagram of the distribution of the tabs of the positive pole piece or the negative pole piece of the two pole tabs.

Figure 3 is a schematic diagram of a 4-pole-tab laminated structure full battery and the distribution of the poles, wherein "1" and "4" represent the negative poles; "2" and "3" represent the positive poles.

FIG. 4 is a schematic diagram of the distribution of the tabs of the positive pole piece or the negative pole piece of the 4-pole tab.

Figure 5 is a schematic diagram of a full battery with an 8-pole-tab laminated structure and the distribution of the poles, wherein "1", "3", "5", and "7" represent the negative poles; "2", "4", "6" , "8" indicates the positive tab.

Fig. 6 is a schematic diagram of the structure of a two-pole-tab laminated battery, wherein "1" represents a positive electrode tab; "2" represents a positive electrode tab.

Detailed ways

The present invention will be further described below through examples. Unless otherwise specified, the raw materials used in the following examples and comparative examples are commercially available conventional raw materials.

Prepare the positive electrode slurry and the negative electrode slurry according to a certain ratio, coat the positive electrode slurry on the aluminum foil, coat the negative electrode slurry on the copper foil foil, and then die-cut the pole piece after drying and cold pressing. If the designed battery is In the winding structure, the positive and negative pole pieces need to be left with tabs on the upper and lower sides, so that the battery after winding has 2 positive electrode tabs and 2 negative electrode tabs. If the designed battery is a laminated structure battery, the mold The cut positive electrode piece has 2 or 4 positive electrode tabs, and the die-cut negative electrode piece has 2 or 4 negative electrode tabs. The die-cut pole pieces are stacked in the order of negative electrode, separator, and positive electrode, and a full battery is assembled. The assembled full battery has 4 or 8 polar ears.

Example 1

The positive electrode uses lithium cobalt oxide material. By mass, the positive electrode formula is 95% lithium cobalt oxide material + 2% polyvinylidene fluoride + 3% (conductive carbon black) SP, the negative electrode uses graphite, and the negative electrode formula is 95% graphite + 2% SBR + 2% sodium hydroxymethyl cellulose + 1% (conductive carbon black) SP, the diaphragm is made of polyethylene (PE) diaphragm, the electrolyte is 1mol/L lithium hexafluorophosphate + EC (ethylene carbonate) + DEC (carbonic acid) Diethyl ester) + DMC (dimethyl carbonate) mixed solvent (volume ratio is 3:4:3), assemble the full battery for testing, the size of the positive pole piece is 85mm*106mm, the size of the negative pole piece is 86mm*108mm, assembled The battery adopts the lamination process. The battery is divided into group A and group B. Group A is the comparison group. The dimensions of the tabs are all 13mm*18mm (length*width). The schematic diagram of the whole battery after assembly is shown in Figure 6. Group B is a battery with a multi-tab battery structure (4-pole battery, each positive pole piece and negative pole piece are set. There are two tabs), the dimensions of the tabs are 13mm*18mm (length*width), as shown in Figure 3, the capacity of the A and B batteries is about 1.2Ah, and the depolarizers of the A and B batteries Except for the structure, other design information is completely consistent.

A comparative test was carried out on the two groups of batteries A and B. The rate characteristics of the two groups of A and B under different discharge currents were tested respectively. The discharge rates were selected at 10C, 30C, and 50C. As in Table 1. Among them, the capacity retention rate of group B is 3% higher than that of group A at a discharge rate of 10C, the capacity retention rate of group B is 6% higher than that of group A at a discharge rate of 30C, and the capacity retention rate of group B is higher than that of group A at a discharge rate of 50C. The capacity retention rate of group A is 8% higher. Under the same discharge rate, the discharge capacity retention rate of the 4-pole battery (group B) is higher than that of the 2-pole battery (group A). The capacity of the polarization loss is smaller, mainly because the positive and negative electrodes of the B battery are provided with two tabs at both ends of the battery, and the current of the positive and negative electrodes can be diffused inside the battery through the tabs on both sides of the battery at the same time. , the distribution of the current on the internal pole pieces of the battery is more uniform, reducing the polarization inside the battery, while the battery of group A has only one pole lug each for the positive and negative poles, and the current is preferentially distributed at the end close to the pole ear and away from the pole ear. The current has a hysteresis effect, which leads to an increase in the internal reaction polarization of the battery, and with the increase of the discharge rate, the discharge capacity retention rate of group B is also increased compared with that of group A. This is mainly because with the increase of the discharge rate, The discharge current of the battery is also gradually increasing. At this time, the distribution of the current density becomes the main factor affecting the internal reaction of the battery. Because the number of tabs in group B is twice as large as that in group A, and they are distributed at both ends of the battery, making group B The distribution of the current of the battery inside the battery is more uniform than that of the battery of group A, that is, the polarization of the battery of group B caused by the current is much smaller than that of group A, so the battery of group B can release more capacity at high current density.

Table 1. Comparison of battery characteristics of two tab structures under different discharge rates

Item 10C 30C 50C Group A (comparison group) 95% 91% 88% Group B (experimental group) 98% 97% 96%

Claims (7)

1. A lithium battery pole piece comprises a positive pole piece and a negative pole piece, and is characterized in that the periphery of each positive pole piece is provided with two or more tabs, and the periphery of each negative pole piece is provided with two or more tabs; the tab on each positive pole piece is symmetrical to the center of the positive pole piece, and the tab on each negative pole piece is symmetrical to the center of the negative pole piece.

2. The pole piece of lithium battery as claimed in claim 1, wherein the tab is formed by extending the positive pole piece or the negative pole piece away from the pole piece and parallel to the surface of the pole piece.

3. The lithium battery pole piece of claim 1, wherein each positive pole piece or negative pole piece has 2-6 tabs.

4. A lithium battery comprising a lithium battery electrode sheet according to any one of claims 1 to 3.

5. The lithium battery of claim 4, wherein the lithium battery is in a winding structure, the number of winding turns of the battery is N, N is an integer greater than or equal to 1, and each turn comprises one positive pole piece and one negative pole piece; the pole lugs are positioned on two sides of each pole piece and are centrosymmetric.

6. The lithium battery of claim 4, wherein the lithium battery is a laminated structure, the positive electrode of the battery is N layers, N is an integer greater than or equal to 2, the negative electrode of the battery is N +1 layers, and each layer comprises one positive pole piece and one negative pole piece; the pole lugs are positioned on two sides of each pole piece and are centrosymmetric.

7. The lithium battery as claimed in claim 5 or 6, wherein the tab of each pole piece is located in a diagonal direction of the pole piece, and the tab of the negative pole piece is not overlapped with the tab of the positive pole piece after the battery is assembled.

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