Negative plate and lithium ion battery

Abstract

In order to solve the problem of battery performance reduction caused by volume expansion of a silicon-carbon material in a silicon-carbon negative electrode battery in the prior art, the utility model provides a negative electrode plate and a lithium ion battery, the negative electrode plate comprises a current collector, buffer layers and an active substance layer, the buffer layers comprise a first buffer layer and a second buffer layer, the first buffer layer is arranged on the surface of the current collector, and the second buffer layer is arranged on the surface of the active substance layer. The active material layer is arranged on one side of the first buffer layer deviating from the current collector, and the second buffer layer is arranged on one side of the active material layer deviating from the first buffer layer. According to the negative plate provided by the utility model, the first buffer layer and the second buffer layer are used for absorbing stress generated in the expansion process of the active material layer, so that the problems of electrode structure damage and capacity fading caused by silicon-carbon volume change in the cyclic charge-discharge process of the lithium ion battery are improved or relieved, the cycle life of the battery is prolonged, and the use efficiency of the battery is improved; and the overall electrical performance of the lithium ion battery is further improved.

Description

TECHNICAL FIELD

[0001] The utility model belongs to lithium ion battery technical field, concretely relates to a kind of negative pole piece and lithium ion battery. BACKGROUND

[0002] Silicon-carbon negative electrode material has the advantages of high energy density and long cycle life in lithium ion batteries, and is widely used in consumer electronics, electric vehicles and other fields. Its unique physical and chemical properties make it a key material for improving battery performance.

[0003] For consumer batteries, it is crucial to improve battery energy density. Currently, the main method to improve energy density is to increase the content of silicon material in the battery cell. However, the volume expansion of silicon-carbon near 300% makes it difficult to apply high-silicon. SUMMARY

[0004] The utility model solves the technical problems of the prior art, which is the problem of battery performance degradation caused by volume expansion of silicon-carbon material in the application of silicon-carbon negative electrode battery, and provides a negative pole piece and lithium ion battery.

[0005] The utility model solves the above technical problems by adopting the following technical solutions:

[0006] On the one hand, the utility model provides a kind of negative pole piece, including current collector, buffer layer and active material layer, the buffer layer includes first buffer layer and second buffer layer, the first buffer layer is set to the surface of the current collector, the active material layer is set to the side of the first buffer layer away from the current collector, and the second buffer layer is set to the side of the active material layer away from the first buffer layer.

[0007] Optionally, the thickness of the first buffer layer is 2-20 μm, and the thickness of the second buffer layer is 2-20 μm.

[0008] Optionally, the thickness of the active material layer is 20-70 μm.

[0009] Optionally, the active material layer includes a silicon material layer, a silicon-carbon material layer, a silicon-oxygen material layer or a silicon / graphite composite material layer.

[0010] Optionally, the particle size D50 of the active material layer is 5-20 μm.

[0011] Optionally, the porosity of the first buffer layer is 20-70%, and the porosity of the second buffer layer is 20-70%.

[0012] Optionally, the Mohs hardness of the first buffer layer is 1-4, and the Mohs hardness of the second buffer layer is 1-4.

[0013] Optionally, the buffer layer material is a carbon black material layer, a carbon nanotube layer, a graphene layer, a graphite layer, or a ceramic layer.

[0014] Optionally, the negative current collector is selected from a copper foil, a nickel foil, a foamed copper, or a foamed nickel.

[0015] In another aspect, the utility model provides a kind of lithium ion battery, including above-mentioned negative pole piece.

[0016] The utility model has the advantages that:

[0017] The negative pole piece provided by the utility model comprises a current collector, a buffer layer and an active material layer, wherein the buffer layer comprises a first buffer layer and a second buffer layer, the first buffer layer is arranged on the surface of the current collector, the active material layer is arranged on the side of the first buffer layer away from the current collector, and the second buffer layer is arranged on the side of the active material layer away from the first buffer layer. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 FIG. 1 is a structural schematic diagram of the negative pole piece provided by the utility model.

[0019] In the drawings of the specification, the following reference signs are used:

[0020] 1, current collector; 2, buffer layer; 21, first buffer layer; 22, second buffer layer; 3, active material layer. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects solved by the utility model clearer and more understandable, the utility model will be further described in detail below in combination with the drawings and examples.

[0022] In the description of the utility model, need understanding is, the term "longitudinal", "radial", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and so on the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the drawing, just is for the convenience of describing the utility model and simplifying the description, and it is not indicated or implied that the device or element referred to must have a particular orientation, a particular orientation and operation, therefore can not be understood as the limitation to the utility model. In the description of the utility model, unless otherwise specified, the meaning of "a plurality of " is two or more than two.

[0023] In the description of the utility model, it is necessary to explain that, unless otherwise specified and limited, the terms "mounting", "connecting", "connection" should be understood broadly, for example, it can be fixed connection, can also be detachable connection, or integrally connected, can be mechanical connection, can also be electrical connection, can be directly connected, can also be indirectly connected through intermediate medium, can be the communication inside two elements. For ordinary skilled in the art, the specific meaning of the above terms in the utility model can be understood according to specific circumstances.

[0024] Referring to Figure 1 The utility model embodiment provides a kind of negative pole piece, including current collector 1, buffer layer 2 and active material layer 3, the buffer layer 2 includes first buffer layer 21 and second buffer layer 22, the first buffer layer 21 is set to the surface of the current collector 1, the active material layer 3 is set to the side of the first buffer layer 21 away from the current collector 1, the second buffer layer 22 is set to the side of the active material layer 3 away from the first buffer layer 21.

[0025] Specifically, the negative plate provided by the utility model, comprising a current collector 1, a buffer layer 2 and an active material layer 3, wherein the buffer layer 2 further comprises a first buffer layer 21 and a second buffer layer 22, the first buffer layer 21 is arranged on the surface of the current collector 1, the active material layer 3 is arranged on the side of the first buffer layer 21 away from the current collector 1, and the second buffer layer 22 is arranged on the side of the active material layer 3 away from the first buffer layer 21, the active material layer 3 is arranged between the first buffer layer 21 and the second buffer layer 22, that is, the first buffer layer 21 and the second buffer layer 22 absorb the stress generated in the expansion process of the active material layer 3, the first buffer layer 21 and the second buffer layer 22 protect and buffer the active material layer 3 from both sides, absorb and disperse the expansion of the active material layer 3, inhibit the rebound of the negative plate, effectively relieve the volume expansion of silicon carbon, improve the structural stability of the negative plate, and further improve or relieve the electrode structure damage and capacity attenuation problems caused by the volume change of silicon carbon in the lithium ion battery cycle charging and discharging process, so as to ensure that the lithium ion battery can still maintain relatively stable performance after multiple cycles, improve the cycle life and use efficiency of the battery, and further improve the overall electrical performance of the lithium ion battery.

[0026] The first buffer layer 21 is directly arranged on the surface of the current collector 1, and when the silicon carbon material expands in volume during charging and discharging, it can first play a buffering role and absorb part of the expansion stress from the silicon carbon active material. Since it is in close contact with the current collector 1, it can effectively prevent the expansion stress from being directly transmitted to the current collector 1, thereby protecting the structural integrity of the current collector 1 and avoiding deformation or damage of the current collector 1 due to excessive stress, ensuring the stability of electron transmission; the first buffer layer 21 can adapt to the initial volume change of the silicon carbon material to some extent, providing a certain buffer space for the subsequent expansion of the active material layer 3 and reducing the impact on the overall structural stability.

[0027] The second buffer layer 22 is located on the side of the active material layer 3 away from the first buffer layer 21, and when the silicon carbon material expands in volume and expands outward, the second buffer layer 22 acts as a protective barrier on the outer layer, which can further limit the degree of expansion and block the possible rupture, peeling and other situations of the active material due to expansion, prevent the active material from directly contacting the external environment, reduce the loss of active material and the occurrence of side reactions; in addition, the second buffer layer 22 can also buffer the physical pressure or impact force that may be applied from the outside, protect the internal active material layer 3 and the first buffer layer 21, and maintain the relative stability of the entire negative plate structure during the volume expansion process, ensuring the performance and safety of the battery during use.

[0028] In the specific arrangement of the negative plate, the arrangement positions of the first buffer layer 21 and the second buffer layer 22 can be replaced with each other without limitation on the premise that the buffer layer 2 plays a role in relieving the expansion of the active material layer 3.

[0029] In an embodiment, the first buffer layer 21 has a thickness of 2-20 μm, and the second buffer layer 22 has a thickness of 2-20 μm.

[0030] Specifically, when the thickness of the first buffer layer 21 is in the range of 2-20 μm, on the one hand, the first buffer layer 21 can have sufficient thickness to effectively absorb the stress generated by the volume expansion of the active material layer 3, and if the thickness is too thin, the stress may not be sufficiently buffered, resulting in direct transmission of stress to the current collector 1. When the first buffer layer 21 is within the range specified in the present application, reliable buffering can be provided at the initial stage of volume expansion of the active material layer 3.

[0031] On the other hand, when the first buffer layer 21 is within the above-mentioned range, the thickness range will not be too thick to hinder the transmission of electrons between the current collector 1 and the active material layer 3. If the first buffer layer 21 is too thick, the distance of electron transmission increases and the resistance increases, which will affect the charge and discharge performance of the battery. That is, when the thickness of the first buffer layer 21 is in the range of 2-20 μm, both the buffering of volume expansion and the maintenance of a good electron transmission channel can be ensured to ensure normal operation of the battery.

[0032] The second buffer layer 22 with a thickness of 2-20 μm can effectively limit the expansion range of the active material layer 3 when it expands outward due to the volume expansion of silicon-carbon. The lower limit of 2 μm can block slight expansion and prevent the active material layer 3 from prematurely contacting the external environment or from local rupture, while the upper limit of 20 μm provides sufficient accommodation and buffering space for more severe volume expansion, avoiding peeling or loss of activity of the active material due to excessive expansion.

[0033] As an interface protection layer of the negative electrode sheet and the external environment, the second buffer layer 22 with a suitable thickness can prevent external factors from affecting the internal active material layer 3 and the first buffer layer 21, and can also better cope with the outward pressure caused by the volume expansion of silicon-carbon, maintain the stability of the overall structure of the negative electrode sheet, and reduce the performance degradation of the battery during use. The thickness of 2-20 μm of the second buffer layer 22 cooperates with the thickness range of the first buffer layer 21, and the two work together to provide suitable buffering and protection from the inside to the outside of the entire negative electrode sheet during the volume expansion of silicon-carbon, ensuring stable operation of the battery under different expansion conditions and improving the reliability and safety of the battery.

[0034] The thickness of the first buffer layer 21 can be 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm.

[0035] The thickness of the second buffer layer 22 can be 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm.

[0036] In an embodiment, the active material layer 3 has a thickness of 20-70 μm.

[0037] Specifically, the thickness of the active material layer 3 in the range of 20-70 μm provides a certain accommodation space for the volume expansion of the silicon-carbon material during the charging and discharging process. When the silicon-carbon volume expands, the active material layer 3 in the above thickness range has a certain margin to adapt to such changes, avoiding the active material from being excessively squeezed or damaged due to insufficient space. In the case of smaller expansion, the thinner active material layer 3 of 20 μm can also withstand a certain degree of volume change, and the upper limit of 70 μm gives more buffering possibilities for the possible larger expansion.

[0038] In addition, the thickness of the active material layer 3 in the above range allows the active material layer 3 itself to disperse the stress generated by the volume expansion of the silicon-carbon to a certain extent. A sufficient thickness can prevent excessive concentration of stress in local areas, thereby reducing the phenomenon of cracking or pulverization of the active material due to excessive local stress, which is conducive to maintaining the structural integrity of the active material layer 3 and ensuring the stable performance of the battery.

[0039] The thickness of the active material layer 3 can be 20 μm, 25 μm, 30 μm, 40 μm, 50 μm, 55 μm, 60 μm, or 70 μm.

[0040] In an embodiment, the active material layer 3 includes a silicon material layer, a silicon-carbon material layer, a silicon-oxygen material layer, or a silicon / graphite composite material layer.

[0041] In an embodiment, the particle size D50 of the active material layer 3 is 5-20 μm.

[0042] Specifically, the particle size of the main material particles in the range of 5-20 μm determines the stress dispersion characteristics of the active material layer 3 when the silicon-carbon volume expands. A smaller particle size (5 μm) means a larger number of particles in a unit volume, and the stress can be dispersed among multiple particles during volume expansion, avoiding stress concentration on a few large particles. A larger particle size (20 μm) is also within a reasonable range and will not cause local stress to be unable to be effectively dispersed due to excessively large particle size. This particle size distribution allows the stress generated by the volume expansion of the silicon-carbon to be more evenly distributed in the active material layer 3, reducing the possibility of damaging the structure of the active material layer 3 due to excessive local stress.

[0043] When the particle size D50 of the main material particles in the active material layer 3 is in the range of 5-20 μm, there is a certain gap between the particles, which can serve as a buffer space when the silicon-carbon volume expands. When the particles expand, these gaps can be partially filled, thereby relieving the mutual squeezing of the particles and further reducing the phenomenon of particle breakage or pulverization due to excessive squeezing, which helps to maintain the structural stability of the active material layer 3.

[0044] In an embodiment, the porosity of the first buffer layer 21 is 20-70%, and the porosity of the second buffer layer 22 is 20-70%.

[0045] The porosity of the first buffer layer 21 and the second buffer layer 22 in the range of 20-70% provides sufficient storage space for the electrolyte, which can be filled in the pores, and the pores can accommodate the electrolyte. As the porosity increases, the space for storing the electrolyte also increases, which improves the liquid retention of the pole piece, thereby effectively improving the cycle life of the battery cell.

[0046] The buffer layer 2 with a porosity of 20-70% can effectively buffer the expansion stress. When the silicon-carbon material expands in volume during charging and discharging, the active material layer 3 will be extruded in all directions. The pores of the first buffer layer 21 and the second buffer layer 22 can act as a buffer space to absorb part of the stress generated by the expansion.

[0047] In an embodiment, the Mohs hardness of the first buffer layer 21 is 1-4, and the Mohs hardness of the second buffer layer 22 is 1-4.

[0048] The material with a Mohs hardness of 1-4 has a relatively soft texture. When the silicon-carbon material expands in volume during charging and discharging, the softer buffer layer 2 can better withstand and disperse the stress generated by the expansion. Compared with materials with higher hardness, when the active material layer 3 is extruded due to the volume expansion of the silicon-carbon, the buffer layer 2 can absorb stress by its own deformation, avoiding stress concentration in local areas, thereby protecting the structural integrity of the current collector 1 and the active material layer 3.

[0049] Specifically, in the preferred embodiment, the Mohs hardness of the first buffer layer 21 can be 1-2, and the Mohs hardness of the second buffer layer 22 can be 1-2.

[0050] In an embodiment, the buffer layer 2 is made of a carbon black material layer, a carbon nanotube layer, a graphene layer, a graphite layer, or a ceramic layer.

[0051] The carbon black of the carbon black material layer is composed of tiny carbon particles, and there are certain gaps between the particles. When the silicon-carbon negative electrode expands in volume during charging and discharging, the gaps are compressed, thereby absorbing the stress generated by the expansion. At the same time, the carbon black particles can move relatively to a certain extent and rearrange to adapt to the volume change, effectively preventing the stress from being transmitted to the current collector 1 and causing excessive extrusion on the active material layer 3.

[0052] Carbon nanotubes have extremely high strength and modulus, and bear pressure when the silicon-carbon expands in volume. The interweaving and connection between carbon nanotubes form a network structure with elasticity. When subjected to expansion stress, the network can deform to a certain extent to absorb energy while maintaining the overall structural stability, thereby protecting the current collector 1 and the active material layer 3.

[0053] Graphene, as a two-dimensional carbon material, has good flexibility. When the silicon-carbon material expands, the graphene layer in the buffer layer can adapt to the volume change by stretching and bending itself, and at the same time, exert a uniform restraining force on the active material layer 3 to prevent it from expanding excessively and breaking.

[0054] The graphite in the graphite layer has a layered structure. When the silicon-carbon expands in volume, the graphite layers can slide relative to each other. This sliding mechanism can effectively absorb and disperse the stress generated by expansion, and the interlayer sliding can adapt to the volume change without damaging the overall structure, thereby protecting the current collector 1 and the active material layer 3 from excessive stress impact.

[0055] Ceramic materials generally have high hardness and chemical stability. In the buffer layer 2, the ceramic layer can protect the internal active material and current collector 1. When the silicon-carbon expands in volume, it can prevent external physical damage such as collision, extrusion, etc. from affecting the negative electrode sheet, and its chemical stability can avoid unnecessary chemical reactions with electrolyte, etc., thereby maintaining the stability of the chemical environment inside the battery.

[0056] In summary, when the material of the buffer layer 2 is selected from the above-mentioned materials, it can have corresponding beneficial effects on the volume expansion of silicon-carbon and the stability of the negative electrode sheet.

[0057] In an embodiment, the negative current collector 1 is selected from copper foil, nickel foil, foamed copper, or foamed nickel.

[0058] In an embodiment, the resistance of the active material layer 3 is 5-100 mΩ.

[0059] In an embodiment, the active material layer 3 further includes a binder and a conductive agent, wherein the content of the binder accounts for 0.5-5% of the total content of the active material layer 3.

[0060] In an embodiment, the buffer layer 2 includes a binder, and the content of the binder accounts for 20-60% of the total content of the buffer layer 2.

[0061] In another embodiment of the utility model, a lithium ion battery is provided, which comprises the above-mentioned negative electrode sheet.

[0062] The negative sheet in the lithium ion battery comprises a current collector 1, an active material layer 3, and first and second buffer layers 22 arranged at different positions, when the silicon-carbon material in the negative sheet expands in volume during the charging and discharging of the battery, the buffer layer 2 can effectively relieve the stress caused by the expansion, specifically, the first buffer layer 21 protects the current collector 1 from the direct impact of the expansion stress, and the second buffer layer 22 prevents the active material layer 3 from excessive expansion and rupture, thereby maintaining the structural stability of the negative sheet, and the stable negative sheet structure further guarantees the structural integrity of the entire lithium ion battery, reduces the problems of battery bulging, short circuit and the like caused by the structural change of the negative sheet, and improves the safety and reliability of the battery; meanwhile, as the number of cycles increases, the buffer layer 2 continuously plays its buffering role, so that the active material of the negative sheet can maintain a good state, reduces the peeling and pulverization of the active material, and ensures the normal embedding and extraction of lithium ions in the negative sheet, therefore, the capacity retention rate of the battery is improved, and the cycle life of the battery is effectively prolonged.

[0063] In the specific operation, the preparation of the lithium ion battery comprises the following operations:

[0064] The active material (graphite), the dispersant (CMC) and the binder (SBR) are stirred according to the proportion, then water is added to adjust the solid content, and secondary dispersion and coating are performed;

[0065] The active material (graphite), the dispersant (CMC) and the binder (SBR) are stirred according to the proportion, then water is added to adjust the solid content, and secondary dispersion and coating are performed;

[0066] The active material (graphite), the dispersant (CMC) and the binder (SBR) are stirred according to the proportion, then water is added to adjust the solid content, and secondary dispersion and coating are performed;

[0067] The above negative sheet is dried, the corresponding positive sheet and the separator are assembled and injected with liquid to obtain the lithium ion battery.

[0068] The above only describes the preferred embodiments of the present application and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A negative electrode sheet characterized by comprising: The negative electrode sheet comprises a current collector (1), a buffer layer (2) and an active material layer (3), the buffer layer (2) comprises a first buffer layer (21) and a second buffer layer (22), the first buffer layer (21) is arranged on the surface of the current collector (1), the active material layer (3) is arranged on the side of the first buffer layer (21) away from the current collector (1), and the second buffer layer (22) is arranged on the side of the active material layer (3) away from the first buffer layer (21); The thickness of the active material layer (3) is 20-70 μm; The active material layer (3) comprises a silicon material layer, a silicon-carbon material layer, a silicon-oxygen material layer or a silicon / graphite composite material layer; The particle size D50 of the active material layer (3) is 5-20 μm.

2. The negative electrode sheet according to claim 1, wherein The thickness of the first buffer layer (21) is 2-20 μm, and the thickness of the second buffer layer (22) is 2-20 μm.

3. The negative electrode sheet according to claim 1, wherein The porosity of the first buffer layer (21) is 20-70%, and the porosity of the second buffer layer (22) is 20-70%.

4. The negative electrode sheet according to claim 1, wherein The Mohs hardness of the first buffer layer (21) is 1-4, and the Mohs hardness of the second buffer layer (22) is 1-4.

5. The negative electrode sheet according to claim 1, wherein The buffer layer (2) is a carbon black material layer, a carbon nanotube layer, a graphene layer, a graphite layer or a ceramic layer.

6. The negative electrode sheet according to claim 1, wherein The current collector (1) is selected from a copper foil, a nickel foil, a foamed copper or a foamed nickel.

7. A lithium-ion battery, characterized by The negative electrode sheet comprises a current collector (1), a buffer layer (2) and an active material layer (3), the buffer layer (2) comprises a first buffer layer (21) and a second buffer layer (22), the first buffer layer (21) is arranged on the surface of the current collector (1), the active material layer (3) is arranged on the side of the first buffer layer (21) away from the current collector (1), and the second buffer layer (22) is arranged on the side of the active material layer (3) away from the first buffer layer (21);

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