CN102646812A - Structure of cathode material of lithium ion battery - Google Patents

Abstract

The invention discloses a structure of a lithium ion battery negative electrode material, which comprises an active material layer, a loose conductive layer and a hard shell conductive layer distributed radially in sequence, and the active material layer communicates with the hard shell conductive layer through the loose conductive layer , the structure of the loose conductive layer is an elastic memory structure, and the volume of the loose conductive layer changes with the volume of the active material layer. The present invention adopts a radially distributed three-layer structure, and uses the loose conductive layer as the middle layer, whose volume can change with the active material layer, so the structure can effectively reduce the volume effect in the process of charging and discharging, alleviate or even eliminate the dusting of the negative electrode material. Melting and shedding phenomena, thereby improving the specific capacity and cycle stability of the battery.

Description

A kind of structure of negative electrode material of lithium ion battery

technical field

The invention relates to the technical field of batteries, in particular to a structure of a negative electrode material of a lithium ion battery.

Background technique

With the rapid development of the microelectronics industry and the automobile industry, and the popularization of various portable communication devices, personal computers, and small electronic devices, human requirements for lithium-ion batteries are also moving towards high energy density, high power density, high safety, Development in the direction of long life, fast charging and discharging, and light and thin. At present, commercial lithium-ion batteries use graphite as the negative electrode and lithium-containing compounds as the positive electrode. Among them, the theoretical specific capacity of graphite is only 372mAh/g, which has become a huge obstacle to improving the performance of lithium-ion batteries. Therefore, in recent years, the development of new anode materials with high capacity has become the research focus in the field of lithium-ion batteries.

At present, metal alloys and metal oxides with high specific capacity have attracted the attention of researchers. Compared with traditional carbon anode materials, they have extremely high lithium storage capacity, such as silicon (4200mAh/g), tin (994mAh/g), tin oxide (781mAh/g). But they also have big problems as lithium-ion battery negative electrode materials: in the process of battery charging and discharging, the negative electrode materials produce serious volume expansion effect (silicon is as high as 300%), which will cause electrode pulverization, thereby reducing battery life; Secondary charging and discharging will cause agglomeration of negative electrode materials and affect the cycle stability of the battery. At present, the main ways to solve these problems are: ① prepare nano-sized negative electrode materials to alleviate the volume expansion during charging and discharging; ② compound inactive materials and active lithium storage materials to reduce the volume expansion of negative electrode materials and prevent active materials Agglomeration; ③Prepare negative electrode materials with special structure, and use structural advantages to alleviate the volume expansion of negative electrode materials.

In the existing research, many people have solved the above problems to some extent. Chinese patent CN1402366A discloses a Si-C-X composite negative electrode material with a core-shell structure, which can alleviate the agglomeration of active materials and volume expansion during charge and discharge to a certain extent. The researchers first dissolved the carbon-containing precursor in an organic solvent, and then slowly added silicon alloy powder to form a uniform solution. The organic solution was volatilized at 80° C. to obtain a silicon alloy-carbon precursor mixture. The mixture is then calcined in an inert atmosphere to obtain a silicon alloy-carbon composite material. However, the thickness of the carbon coating layer of the composite material prepared by this method is uneven, and the bonding force between the carbon layer and the silicon alloy is weak. During the rapid charge and discharge process, the carbon layer is easy to separate and peel off from the silicon alloy, which seriously affects the cycle of the battery. stable performance.

Contents of the invention

The problem to be solved by the present invention is to provide a negative electrode structure of a battery with a three-layer structure that can keep the overall volume constant, so as to overcome the above-mentioned problems in the prior art.

The structure of a lithium ion battery negative electrode material according to the present invention comprises an active material layer, a loose conductive layer and a hard shell conductive layer radially distributed in sequence, the active material layer and the hard shell conductive layer communicate through the loose conductive layer, The structure of the loose conductive layer is an elastic memory structure, and the volume of the loose conductive layer changes with the volume of the active material layer. The present invention adopts a radially distributed three-layer structure, and the loose conductive layer is used as the middle layer, and its volume changes with the change of the active material layer, so the structure can effectively reduce the volume effect in the charging and discharging process, alleviate or even eliminate the negative electrode material. Powdering and shedding phenomenon, thereby improving the specific capacity and cycle stability of the battery.

The thickness of the loose conductive layer in the present invention is 0.05-2um.

The loose conductive layer in the present invention is a dendritic structure layer composed of carbon fiber, carbon nanotube, pyrolytic carbon, graphene or graphite.

The loose conductive layer in the present invention is a fibrous structure layer composed of carbon fiber, carbon nanotube, pyrolytic carbon, graphene or graphite.

The loose conductive layer of the present invention is a cage structure layer composed of carbon fiber, carbon nanotube, pyrolytic carbon, graphene or graphite.

The loose conductive layer in the present invention is a network structure layer composed of carbon fiber, carbon nanotube, pyrolytic carbon, graphene or graphite.

The loose conductive layer in the present invention is a foam-like structural layer made of carbon fiber, carbon nanotube, pyrolytic carbon, graphene or graphite.

The loose conductive layer in the present invention is a granular structure layer or a sheet structure layer composed of carbon fiber, carbon nanotube, pyrolytic carbon, graphene or graphite.

The hard shell conductive layer of the present invention is made of dense carbon or silicon carbide, and its density is 1.8-2.0 g/cm ³ .

The thickness of the hard shell conductive layer in the present invention is 0.05-0.5um.

Through the above technical solutions, the structure of a negative electrode material for a lithium ion battery of the present invention has a three-layer structure, and its active material layer has a relatively high lithium storage capacity, but the volume will be very large during the intercalation ^/ extraction process. Changes in the body produce a lot of pressure on the external substances. Since the loose conductive layer has a loose elastic memory structure, it can buffer the volume effect of the active material layer by changing its own structure and volume when subjected to the pressure of the inner active material layer. At the same time, the loose conductive layer has good conductivity, which can ensure the communication between the active material layer and the outside. The hard-shell conductive layer has a high density, a hard texture, and good electrical conductivity, which can not only ensure the rapid insertion/extraction of Li ⁺ , but also ensure the integrity of the material. At the same time, because the outer layer of the active material layer is coated with carbon material, it can effectively prevent the aggregation of the central material during the charging and discharging process of the battery, so the battery cycle stability of the negative electrode structure of the lithium ion battery of the present invention is excellent.

Description of drawings

Fig. 1 is a schematic structural diagram of a negative electrode material for a lithium ion battery according to the present invention.

Fig. 2 is a schematic diagram of the principle of intercalation/desorption of Li ⁺ in a negative electrode material of a lithium ion battery according to the present invention.

Fig. 3 is the battery negative electrode structure of the dendritic loose conductive layer.

Fig. 4 is the battery negative electrode structure of the fibrous loose conductive layer.

Fig. 5 is a battery negative electrode structure with a mesh-shaped loose conductive layer.

Fig. 6 is the negative electrode structure of the battery with cage-shaped loose conductive layer.

Fig. 7 is the negative electrode structure of the battery with granular loose conductive layer.

Fig. 8 is the battery negative electrode structure with lamellar loose conductive layer.

Fig. 9 is a battery negative electrode structure with a foamy loose conductive layer.

In the figure, 1, the active material layer; 2, the loose conductive layer; 3, the hard shell conductive layer.

Detailed ways

As shown in Figure 1, the structure of a kind of negative electrode material of lithium-ion battery of the present invention comprises active material layer 1, loose conductive layer 2 and hard shell conductive layer 3 radially distributed successively, active material layer 1 and hard shell conductive layer 3 are communicated through the loose conductive layer 2, the structure of the loose conductive layer 2 is an elastic memory structure, and the volume of the loose conductive layer 2 changes with the volume of the active material layer 1. . The present invention adopts a radially distributed three-layer structure, and uses the loose conductive layer as the middle layer, whose volume changes with the change of the active material layer, so the structure can effectively reduce the volume effect in the charging and discharging process, alleviate or even eliminate the negative electrode material. Powdering and shedding phenomenon, thereby improving the specific capacity and cycle stability of the battery.

The above-mentioned active material layer 1 is silicon, silicon monoxide, silicon dioxide, tin, tin monoxide, tin dioxide, copper, nickel, manganese, cobalt, antimony or lead of submicron or nanometer scale, or a composite of the above substances have a high lithium storage capacity.

As shown in FIGS. 3-9 , the above-mentioned loose conductive layer 2 has a thickness of 0.05-2 μm, and covers the surface of the active material layer 1 with a high degree of uniformity. It can be composed of conductive carbon materials such as carbon fiber, carbon nanotube, pyrolytic carbon, graphene or graphite, and its shape can be dendritic, fibrous, cage, mesh, granular, sheet or foam, etc. It has elasticity The structure of the memory can change with the change of the active material layer.

The above-mentioned hard shell conductive layer 3 is made of dense carbon or silicon carbide, its density is 1.8-2.0g/cm ³ ; its thickness is 0.05-0.5um; it covers the surface of the loose conductive layer 2 with a high degree of uniformity; it has good Conductivity and the ability to transport lithium ions, while having a certain stiffness and being able to withstand a certain pressure.

As shown in Figure 2, the charging and discharging process of the lithium ion battery with the battery negative electrode structure of the present invention is: lithium ion ^Li is intercalated during discharge, and at this time due to the intercalation of lithium ions, the volume of the active material layer 1 in the negative electrode of the lithium ion battery increases , while the volume of the hard-shell conductive layer 3 remains unchanged, the volume of the loose conductive layer 2 increases to ensure that the entire volume remains unchanged; when lithium ions are deintercalated during charging, the volume of the active material layer 1 decreases due to the detachment of lithium ions, and the loose conductive layer 2 is now loose and conductive The volume of layer 2 is reduced to keep the entire volume constant, which improves the cycle stability of the battery. According to experiments, the structure of the loose conductive layer 2 can be made into dendritic, fibrous, cage-like, net-like or foam-like structures capable of shrinking and deforming with memory rebound. In the present invention, the loose conductive layer 2 is used as the middle layer, and its volume can change with the active material layer 1, so this structure can effectively reduce the volume effect in the charging and discharging process, alleviate or even eliminate the pulverization and falling off of the negative electrode material, thereby improving the performance of the battery. specific capacity and cycle stability.

Claims (10)

1. the structure of a lithium ion battery negative material; It is characterized in that: comprise radially-arranged successively active material layer, loose conductive layer and duricrust conductive layer; Said active material layer and duricrust conductive layer are through said loose conductive layer UNICOM; The structure of said loose conductive layer is the elastic memory structure, and the volume of said loose conductive layer changes with the change in volume of said active material layer.

2. the structure of a kind of lithium ion battery negative material according to claim 1 is characterized in that, the thickness of said loose conductive layer is 0.05～2um.

3. the structure of a kind of lithium ion battery negative material according to claim 1 is characterized in that, the dendritic structure layer of said loose conductive layer for being made up of carbon fiber, CNT, RESEARCH OF PYROCARBON, Graphene or graphite.

4. the structure of a kind of lithium ion battery negative material according to claim 1 is characterized in that, the filamentary structure layer of said loose conductive layer for being made up of carbon fiber, CNT, RESEARCH OF PYROCARBON, Graphene or graphite.

5. the structure of a kind of lithium ion battery negative material according to claim 1 is characterized in that, the cage structure layer of said loose conductive layer for being made up of carbon fiber, CNT, RESEARCH OF PYROCARBON, Graphene or graphite.

6. the structure of a kind of lithium ion battery negative material according to claim 1 is characterized in that, the network structure layer of said loose conductive layer for being made up of carbon fiber, CNT, RESEARCH OF PYROCARBON, Graphene or graphite.

7. the structure of a kind of lithium ion battery negative material according to claim 1 is characterized in that, the pumiceous texture layer of said loose conductive layer for being made up of carbon fiber, CNT, RESEARCH OF PYROCARBON, Graphene or graphite.

8. the structure of a kind of lithium ion battery negative material according to claim 1 is characterized in that, nutty structure layer or the laminated structure layer of said loose conductive layer for being made up of carbon fiber, CNT, RESEARCH OF PYROCARBON, Graphene or graphite.

9. the structure of a kind of lithium ion battery negative material according to claim 1 is characterized in that, said duricrust conductive layer is made up of dense carbon or carborundum, and density is 1.8～2.0g/cm ³

10. according to the structure of claim 1 or 8 described a kind of lithium ion battery negative materials, it is characterized in that the thickness of said duricrust conductive layer is 0.05～0.5um.

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