A porous current collector sandwich electrode structure suitable for use in a lithium-ion battery negative electrode

Abstract

The utility model discloses a kind of porous current collector sandwich electrode structures suitable for lithium ion battery negative pole, the electrode structure, by three layers of active material powder coating layer and two layers of porous current collector layer alternate lamination structure, and the uppermost layer and the lowermost layer are active material powder coating layer, the active material powder coating layer evenly covers in the upper and lower surface of porous current collector layer, and reserve tab welding area;The porous current collector layer is porous current collector, and porous structure of through current collector is uniformly arranged on porous current collector, for carrying active material powder;The active material is at least one of graphite powder, silicon-carbon composite particle or other negative active material powder;The porous current collector layer is one of copper foil, stainless steel foil, titanium foil, metal-plastic composite foil material.The utility model is a kind of high gram capacity, high coating amount negative pole, for high energy density lithium secondary battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrode technology, specifically relating to a porous current collector sandwich composite electrode structure. Background Technology

[0002] Lithium-ion batteries have wide applications and are a key technology for transportation electrification and energy modernization. Current lithium battery electrodes generally consist of active material powder coated onto the surface of a metal foil, which is then dried, die-cut into sheets, and finally wound or stacked to assemble the battery. Conventional negative electrode powders have low capacity, low lithium intercalation stress, and minimal volume expansion. For example, if graphite is used as the negative electrode, its thickness expansion after lithium intercalation is less than 20%. This type of active powder coating on the foil surface can balance the requirements of lithium storage capacity and overall electronic / ionic conductivity of the electrode.

[0003] However, with the increasing demand for higher energy density batteries, electrodes are developing in two directions: (1) the specific capacity of active materials is constantly increasing, such as the gradual transition from graphite powder to silicon-carbon powder, which can increase the specific capacity from ~350 mAh / g to 500~600 mAh / g; (2) the areal capacity of electrode active materials is increasing from 3 mAh / cm². 2 Increased to 4~5 mAh / cm 2 Even higher, causing the thickness of the powder coating layer on the electrode to continuously increase.

[0004] Under this development trend, traditional anode structures face two severe challenges: On the one hand, the volume of the electrode expands continuously during the charging and discharging process. For example, after silicon carbon powder is coated on copper foil and lithium is inserted, the thickness expansion is often as high as 50% or more. This can easily lead to the gradual failure of the electrical contact between the active particles and the current collector, resulting in particle deactivation and capacity decay. On the other hand, traditional metal foil current collectors have no ion permeability, and the electrode only allows lithium ions to diffuse on one side. The electrode powder coating is relatively thick, which can easily cause uneven reaction and local lithium plating during fast charging. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a porous current collector sandwich electrode structure suitable for lithium-ion battery anodes, in order to obtain anodes with high specific capacity and high coating amount for use in high energy density lithium secondary batteries.

[0006] In this manual, "lithium-ion battery" means a battery that uses lithium ions as charge carriers to move between the positive and negative electrodes to achieve charging and discharging.

[0007] This utility model provides a porous current collector sandwich electrode structure suitable for the negative electrode of a lithium-ion battery. It consists of three layers of active material powder coating and two layers of porous current collector, stacked alternately. The top and bottom layers are both active material powder coatings, which are negative electrode active material powder coatings uniformly covering the upper and lower surfaces of the porous current collector layers. A tab welding area is reserved to facilitate tab welding via ultrasonic welding or laser welding. The porous current collector layer is a porous current collector with uniformly arranged, interconnected porous structures to support the active material powder. The active material is at least one of graphite powder, silicon-carbon composite particles, or other negative electrode active material powders. The active material coating is formed by uniformly coating the negative electrode active material powder with a conductive agent and a binder into a slurry, then drying it on the porous current collector. The porous current collector layer is one of copper foil, stainless steel foil, titanium foil, or metal-plastic composite foil.

[0008] The aforementioned porous current collector sandwich electrode structure, in which the porous current collector layer and the active material powder coating layer form a five-layer alternating sandwich structure, can significantly reduce the overall weight of the electrode while maintaining a good electron transport network even when the electrode active material repeatedly undergoes large volume changes, thereby improving battery cycle stability and operational reliability. Due to the high permeability of the hollowed-out areas, the weight of the current collector is reduced while simultaneously increasing the overall electrolyte retention and lithium-ion permeability of the electrode, which is of positive significance for improving battery energy density and power / fast-charging performance.

[0009] In the above-mentioned porous current collector sandwich electrode structure, the porous current collector layer is composed of one or more of square holes, circular holes, rhomboid grid holes, and regular polygonal holes arranged uniformly and periodically, preferably a honeycomb grid in which regular hexagonal holes are arranged in a symmetrical array.

[0010] In the above-mentioned porous current collector sandwich electrode structure, the thickness of the porous current collector layer is 4~20 μm, and the areal density is 2~6 mg / cm³. 2 The number density of pore structures is ≥1 pore / cm². 2 Porosity > 40% (pore volume / total current collector volume), pore size > 10 micrometers. In the above-mentioned porous current collector sandwich electrode structure, the lithium storage capacity (or coating amount) of the active material powder coating layer supported on the surface of the porous current collector layer is 4~20 mAh / cm³. 2 The corresponding coating thickness is 50~200 μm. The active material powder is one of silicon-carbon composite particles and graphite particles or a mixture of the two in a certain proportion (preferably, the mass ratio of graphite particles to silicon-carbon composite particles is 1:0.01~10), and the lithium storage capacity of the active material powder is 300~3000 mAh / g.

[0011] Preferably, the lithium storage capacity of the upper and lower active material powder coating layers is greater than that of the middle active material powder coating layer, and the thickness of the upper and lower layers is also correspondingly greater than that of the middle layer. In the fabrication of the above-mentioned porous current collector sandwich electrode structure, the active material coating is applied to the porous current collector layer via slurry coating, followed by the placement of another porous current collector layer. After the three-layer electrode is fully dried, an active material coating is applied to both the front and back of the electrode. After these layers are firmly bonded and dried, an electrode consisting of three layers of active material powder coating and two layers of porous current collector alternately stacked is obtained.

[0012] This utility model has the following beneficial effects: 1. This utility model uses a porous current collector sandwich active material structure design. The specially made porous current collector structure significantly enhances the contact between the active material and the current collector. In addition, some active material is distributed in the middle of the two porous current collector sandwich layers. The thickness of the active material on one side of the current collector is reduced and the bonding force between the current collector and the active material is enhanced. This enables the electrode volume change to be reduced and the electronic conduction path to be stabilized under high specific capacity and high areal loading conditions, thereby improving the dimensional stability and cycle life of the battery cell.

[0013] 2. In the structure of this utility model, the porous current collector layer has good ion permeability, which can significantly improve the uniformity of electrode reaction and the high current working capacity. At the same time, the porous current collector layer is lighter than conventional copper foil, which can reduce the weight of the electrode and has a positive significance for improving the charging and discharging speed and energy density of the battery.

[0014] 3. The structure of this utility model has excellent cell adaptability, meeting the design needs of different assembly methods such as winding, stacking, and full tabs, as well as different battery types such as cylindrical, soft pack, and square. Attached Figure Description

[0015] Figure 1 The diagram shows the planar structure of the conventional electrode structure and the electrode structure of this utility model. Detailed Implementation

[0016] The present invention will be further illustrated below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above-described invention, and these improvements and adjustments still fall within the scope of protection of the invention.

[0017] Example 1 This practical porous current collector sandwich structure is as follows: Figure 1As shown, it is composed of three layers of active material powder coating and two layers of porous current collector layer, which are stacked alternately. The top and bottom layers are both active material powder coating layers. The active material powder coating layer is a negative electrode active material powder coating layer, which uniformly covers the upper and lower surfaces of the porous current collector layer and reserves a tab welding area to facilitate the tab welding of the porous current collector layer by ultrasonic welding and laser welding. The porous current collector layer has a uniformly distributed porous structure that runs through the current collector, making the current collector whole hollow and transparent, which is used to support the active material powder.

[0018] The porous current collector layer is made of one of the following materials: copper, stainless steel, titanium, or metal-plastic composite material. After pore formation, through-holes are formed on both the upper and lower surfaces. The hexagonal through-holes are tightly arranged to form a honeycomb-like mesh with a pore diameter of 2 mm and a mesh density of 16 pores / cm². 2 Porosity > 40% (pore volume / total current collector volume), areal density ~ 3 mg / cm³ 2 .

[0019] The active coating is a mixed powder of 20 wt% silicon-carbon composite particles and 80 wt% graphite particles (total specific capacity of 600 mAh / g). The mixed active powder is mixed with a certain proportion of binder and conductive agent to form an active layer (layer A), which is then applied to both sides of the porous current collector layer (layer B) using dry or wet coating methods (coating amount on one side is 3 mA / cm²). 2 On the other side, 2 mAh / cm 2 Then, a porous current collector layer (layer B) and an active layer (layer A, coating amount 3 mAh / cm²) are added. 2 This forms a 5-layer sandwich structure with alternating ABABA layers, where the coating amount of the upper and lower A layers is 3 mAh / cm³. 2 The coating amount of the intermediate layer A is 2 mAh / cm². 2 .

[0020] In this battery manufacturing process, layer A has a smaller area than layer B. The uncovered area of ​​layer B is the tab edge, which is used to prepare the electrode through processes such as die-cutting or slitting. During battery manufacturing, the electrodes are cut and die-cut. The tab edge can be welded to the tab using methods such as laser welding, ultrasonic welding, pressure welding, friction welding, or arc welding. The width of the tab edge is adjustable to accommodate different cell designs, such as wound, stacked, multi / full tab, or full tab stacked cells.

[0021] The porous current collector with active material powder coating forms an electrode roll, which can be flexibly cut and die-cut as needed during battery manufacturing.

[0022] The aforementioned porous current collector sandwich electrode structure differs from conventional electrode structures (such as...). Figure 1Compared to the left side, it can reduce the thickness of the active powder coating on one side and enhance the bonding force between the current collector and the active material while keeping the overall weight of the electrode unchanged. It can reduce the volume change of the high areal loading silicon-carbon anode by >50% and improve the fast charging performance (from 1C to 4C) and the cycle life under fast charging conditions (from less than 100 cycles under 1C conditions to 300 cycles, while maintaining >80% capacity).

[0023] Example 2 The porous current collector sandwich structure described in this embodiment is as follows: Figure 1 As shown on the right, the difference from the structure described in Example 1 is that the active material powder used is pure graphite powder (with a gram capacity of 355 mAh / g).

[0024] Example 3 The porous current collector sandwich structure described in this embodiment is as follows: Figure 1 As shown on the right, the difference from the structure described in Example 1 is that in the 5-layer sandwich structure with alternating ABABA layers, the coating amount of layer A is 2 mAh / cm². 2 2mAh / cm 2 and 2 mAh / cm 2 .

Claims

1. A porous current collector sandwich electrode structure suitable for the negative electrode of a lithium-ion battery, characterized in that, The device is composed of three layers of active material powder coating and two layers of porous current collector, which are alternately stacked. The top and bottom layers are both active material powder coating layers. The active material powder coating layer is a negative electrode active material powder coating, which uniformly covers the upper and lower surfaces of the porous current collector layer and reserves a tab welding area to facilitate tab welding of the porous current collector layer by ultrasonic welding or laser welding. The porous current collector layer is a porous current collector with a uniformly arranged porous structure that runs through the current collector to support the active material powder. The negative electrode active material powder is graphite powder or silicon-carbon composite particles. The active material powder coating layer is formed by uniformly coating the negative electrode active material powder with a conductive agent and a binder into a slurry and then drying it on the porous current collector layer. The porous current collector layer is one of copper foil, stainless steel foil, titanium foil, or metal-plastic composite foil.

2. The porous current collector sandwich electrode structure suitable for the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The porous current collector layer has a pore structure consisting of one or more of the following: square pores, circular pores, rhomboid lattice pores, and regular polygonal pores, arranged uniformly and periodically.

3. The porous current collector sandwich electrode structure suitable for the negative electrode of a lithium-ion battery according to claim 2, characterized in that, The porous current collector layer has a pore structure consisting of a honeycomb-like grid formed by symmetrically arranged regular hexagonal pores.

4. The porous current collector sandwich electrode structure suitable for the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The porous current collector layer has a thickness of 4~20μm and an areal density of 2~6 mg / cm³. 2 .

5. The porous current collector sandwich electrode structure suitable for the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The number density of pore structures is ≥1 / cm 2 Porosity > 40%, pore size > 10 micrometers.

6. The porous current collector sandwich electrode structure suitable for the negative electrode of a lithium-ion battery according to claim 1, characterized in that, The lithium storage capacity of the active material powder coating layer supported on the surface of the porous current collector layer is 4~20 mAh / cm³. 2 The corresponding coating thickness is 50~200 μm.

7. The porous current collector sandwich electrode structure suitable for the negative electrode of a lithium-ion battery according to claim 5, characterized in that, The lithium storage capacity of the upper and lower active material powder coating layers is greater than that of the middle active material powder coating layer, and the corresponding thickness of the upper and lower layers is also greater than that of the middle layer.

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