WO2022193188A1

WO2022193188A1 - Negative electrode plate, electrochemical device, and electronic device

Info

Publication number: WO2022193188A1
Application number: PCT/CN2021/081366
Authority: WO
Inventors: 林小萍; 陈茂华; 谢远森
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-03-17
Filing date: 2021-03-17
Publication date: 2022-09-22
Also published as: CN114127986B; CN114127986A

Abstract

The present application provides a negative electrode plate, an electrochemical device, and a related electronic device. The negative electrode plate comprises a functional layer. The functional layer comprises M conductive layers and N dielectric layers which are provided in a stacked manner, and each conductive layer comprises a lithium wetting material, wherein M≥1 and N≥1. The functional layer of the negative electrode plate of the present application can not only relieve the volume expansion of the negative electrode plate in a charging and discharging cycle, but also inhibit the formation of lithium dendrites; and the electrochemical device comprising the negative electrode plate can have good cycle life and safety performance, and thus can be more widely used in electronic devices.

Description

A kind of negative pole piece, electrochemical device and electronic device

technical field

The present application relates to the technical field of lithium batteries, and in particular, to a negative pole piece, an electrochemical device, and an electronic device.

Background technique

Lithium batteries have the characteristics of high energy density and high power density, and are used more and more widely in electric vehicles and mobile electronic devices. With the continuous development of science and technology, in addition to energy density and power density, people pay more and more attention to the cycle life and safety performance of lithium batteries.

During the charging process of lithium batteries, lithium ions are continuously reduced by electrons at the negative electrode. This process is prone to produce lithium dendrites. Lithium dendrites pierce through the separator, which will lead to a short circuit in the lithium battery and bring safety risks. Moreover, the continuously generated lithium dendrites are prone to fall off, resulting in "dead lithium" that cannot continue to participate in the reaction, resulting in a decrease in the capacity of lithium batteries during cycling. In addition, as the lithium battery is continuously charged and discharged, the volume of lithium continues to expand and shrink, and the negative electrode structure of the lithium battery is easily damaged, resulting in a sharp decrease in the capacity of the lithium battery, and there is a risk of potential safety hazards in severe cases.

Therefore, how to improve the cycle life and safety performance of lithium batteries is an urgent problem to be solved in the field of lithium battery technology.

SUMMARY OF THE INVENTION

In order to solve the above-mentioned technical problems, the present application provides a negative pole piece, by designing the functional layer in the negative pole piece, the volume expansion of the negative pole piece is relieved, and the formation of lithium dendrites is suppressed, so that the battery including the negative pole piece is Chemical units have excellent cycle life and safety performance.

The present application also provides an electrochemical device, the electrochemical device includes the above-mentioned negative electrode plate, so the electrochemical device has excellent cycle life and safety performance.

The present application also provides an electronic device, the electronic device includes the above electrochemical device, so the electronic device has a long service life, strong endurance, high safety performance, and good user experience.

The application provides a negative pole piece, wherein the negative pole piece includes a functional layer; the functional layer includes M conductive layers and N dielectric layers arranged in layers, and the conductive layers include a lithium wetting material;

Among them, M≥1, N≥1.

The functional layer of the negative electrode sheet of the present application includes a dielectric layer and a conductive layer to which a lithium wetting material is attached. On the one hand, the dielectric layer can reduce the electron concentration of the functional layer and prevent lithium ions from forming dendrites at a large current density. Moreover, the dielectric layer can also reduce the electron concentration on the surface of the functional layer, forcing lithium ions to enter the functional layer. deposition, reducing the amount of lithium ion reduction on the surface of the functional layer, thereby inhibiting the formation of lithium dendrites on the surface of the functional layer; on the other hand, the lithium wetting material can induce lithium ions to enter the functional layer for deposition, reducing the formation of lithium dendrites at the negative electrode interface Therefore, the cycle life and safety performance of the electrochemical device can be improved. In addition, the three-dimensional skeleton formed by the stacking of the conductive layer and the dielectric layer can reduce the extrusion and expansion damage of the negative electrode pole piece by the lithium dendrite formed in the functional layer, and relieve the volume expansion of the negative pole piece during the cycle. Therefore, it can further Improve the cycle life and safety performance of electrochemical devices. Moreover, the conductive layer has equipotentiality. When the lithium dendrite contacts the conductive layer, the conductive layer can disperse the electric field at the top of the lithium dendrite, further restrain the continuous growth of the lithium dendrite, and realize the "self-correction" of the dendrite. Thus, the cycle life and safety performance of the electrochemical device are improved.

In the above negative pole piece, the content of the lithium wetting material is distributed in a gradient in the stacking direction.

In the present application, the deposition site of lithium ions is controlled by the distribution of the content of the lithium wetting material, which further induces the deposition of lithium ions at sites far away from the negative electrode interface, and suppresses the formation of lithium dendrites at the interface, thereby improving the safety performance and cycle life of the electrochemical device.

In the above negative pole piece, the negative pole piece further includes a lithium metal layer or a current collector, the functional layer is arranged on the functional surface of the lithium metal layer or the functional surface of the current collector, and the lithium metal layer is The extension direction or the extension direction of the current collector is perpendicular to the lamination direction;

The content of the lithium wetting material is gradually decreasing in a direction away from the lithium metal layer or current collector.

When the negative electrode pole piece is implemented in the above manner, the dielectric layer can more effectively reduce the electron concentration on the surface of the functional layer, forcing lithium ions to enter the functional layer for deposition, reducing the deposition of lithium at the negative electrode interface, thereby suppressing lithium dendrites at the negative electrode interface The formation of electrochemical devices improves the cycle life and safety performance of electrochemical devices. In addition, the lithium wetting material has a high content near the lithium metal layer or current collector, and a low content near the anode interface, which further reduces the deposition of lithium at the anode interface, thereby suppressing the formation of lithium dendrites at the anode interface, enabling electrochemical devices. The safety performance has been further improved.

In the above negative pole piece, the M conductive layers and the N dielectric layers are alternately stacked.

Compared with other stacking methods of M conductive layers and N dielectric layers, the alternate stacking of conductive layers and dielectric layers makes it easier for the lithium dendrites generated in the functional layer to contact the conductive layer, thereby realizing the conductive layer pair. The "self-correction" of lithium dendrites prevents further growth of lithium dendrites in the functional layer, thus improving the cycle life and safety performance of electrochemical devices including the negative electrode.

In the above negative pole piece, the first edge layer and/or the second edge layer of the functional layer is a dielectric layer.

The lithium wetting material is distributed in the conductive layer. Therefore, when the first edge layer and/or the second edge layer of the functional layer is a dielectric layer, lithium ions are more likely to be deposited inside the functional layer, thereby reducing the negative electrode interface. The deposition can inhibit the formation of lithium dendrites at the negative electrode interface, and therefore, the cycle life and safety performance of the electrochemical device including the negative electrode pole piece can be effectively improved.

In the above negative pole piece, the electrical conductivity of the conductive layer is 10 ^-7 S/cm to 10 ⁶ S/cm, and/or,

The electrical conductivity of the dielectric layer is less than 10 ^-8 S/cm.

When the conductivity of the conductive layer and/or the dielectric layer is in the above range, the current density in the functional layer is more conducive to the deposition of lithium ions inside the functional layer, and the formation of lithium dendrites is suppressed. The device has excellent cycle life and safety performance.

In the above negative pole piece, the porosity of the functional layer is 5% to 90%, optionally 50% to 90%.

When the porosity of the functional layer is between 50% and 90%, without affecting the volumetric energy density of the electrochemical device, the functional layer can induce lithium ions to enter its interior and provide deposition sites for lithium ions, thereby suppressing interfacial lithium dendrites. The formation of electrochemical devices improves the cycle life and safety performance of electrochemical devices.

In the above negative pole piece, the mass of the lithium wetting material is 5% to 95% of the mass of the functional layer, optionally 30% to 60%.

The content of lithium wetting material is too low, the ability to induce lithium ions to enter the internal deposition is low, and the functional pairing has limited ability to improve the cycle life and safety performance of electrochemical devices, and the content of lithium wetting material is too large. It has a negative effect on the energy density of the electrochemical device and the energy density of the electrochemical device; when the content of the lithium wetting material is 30% to 60%, it can induce lithium ions into the functional layer without affecting the energy density of the electrochemical device and the structural stability of the functional layer. The inner layer is deposited, thereby reducing the probability of lithium ions staying at the negative electrode interface, reducing the formation of lithium dendrites at the interface, and improving the cycle life and safety performance of the electrochemical device.

In the above-mentioned negative pole piece, the functional layer further includes lithium metal, and the content of the lithium metal in the functional layer is 0.25 mg/cm ² to 25 mg/cm ² .

The lithium metal in the functional layer can continuously replenish lithium for the negative electrode plate during the cycle, offset the irreversible lithium loss during the charging and discharging process, thereby further improving the cycle life of the electrochemical device including the negative electrode plate.

The present application also provides an electrochemical device, the electrochemical device comprising the above-mentioned negative electrode plate.

The electrochemical device of the present application includes the above-mentioned negative electrode plate, so the electrochemical device has more excellent cycle life and safety performance.

The present application also provides an electronic device, wherein the driving source or energy storage unit of the electronic device is the above-mentioned electrochemical device.

The driving source or energy storage unit of the electronic device of the present application adopts the above-mentioned electrochemical device, so the battery life, cycle life and safety performance are excellent, and the user experience is excellent.

Description of drawings

1 is a schematic diagram of functional layers in an embodiment of the application;

2 is a schematic diagram of a functional layer in another embodiment of the present application;

3 is a schematic structural diagram of a negative pole piece in an embodiment of the application;

4 is a schematic structural diagram of a negative pole piece in another embodiment of the present application;

5 is a schematic structural diagram of a negative pole piece in yet another embodiment of the application;

6 is a scanning electron microscope image of a negative pole piece in Example 8 of the application;

7 is a scanning electron microscope image of the lithium deposition of the negative electrode pole piece in Example 11 of the application;

FIG. 8 is a scanning electron microscope image of the lithium deposition of the negative pole piece in Comparative Example 1 of the present application.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the implementation of the present application. examples, but not all examples. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

A first aspect of the present application provides a negative pole piece, the negative pole piece includes a functional layer; the functional layer includes M conductive layers and N dielectric layers arranged in layers, and the conductive layer includes a lithium wetting material;

Among them, M≥1, N≥1.

FIG. 1 is a schematic diagram of a functional layer in an embodiment of the application. As shown in FIG. 1 , in this embodiment, the functional layer includes a stacked conductive layer a and a dielectric layer b, and the conductive layer a includes a lithium wetting material c; In Figure 1, M=1, N=1.

FIG. 2 is a schematic diagram of a functional layer in another embodiment of the present application. As shown in FIG. 2 , in this embodiment, the functional layer includes a conductive layer a1, a conductive layer a2 and a dielectric layer b that are stacked in layers. The conductive layer a1 and The conductive layer a2 includes a lithium wetting material c; in FIG. 2 , M=2, N=1.

Generally, during the charging process, electrons flow to the negative pole piece, meet with Li ⁺ in the negative pole piece, Li ⁺ gets electrons, thereby depositing lithium metal in the negative pole piece, and the opposite is true during discharge. Therefore, during the continuous charging and discharging process, lithium is continuously deposited and dissolved in the negative pole piece, and the volume of lithium also increases and decreases, so that the volume of the negative pole piece expands and contracts. In addition, during the lithium deposition process, lithium metal tends to form lithium dendrites on the negative pole piece, which creates the risk of piercing the separator and causing a short circuit.

The functional layer of the negative electrode piece of the present application includes a dielectric layer and a conductive layer attached with a lithium wetting material, wherein the dielectric layer can reduce the electron concentration on the surface of the functional layer and prevent lithium ions from forming dendrites at a large electron concentration; Moreover, the dielectric layer can prevent electrons from being transported to the surface of the functional layer, forcing lithium ions into the functional layer for deposition, thereby reducing the amount of lithium ion deposition at the negative electrode interface and inhibiting the formation of lithium dendrites at the negative electrode interface; and, in the induction of lithium wetting materials In this way, lithium ions can quickly enter the functional layer when migrating to the negative electrode, which further reduces the probability of lithium ions staying at the negative electrode interface, thereby maintaining the integrity of the negative electrode interface by further inhibiting the growth of interfacial lithium dendrites, not only avoiding the The potential safety hazard caused by the growth of interfacial lithium dendrites piercing the separator can effectively prevent the deterioration of the cycle performance of electrochemical devices caused by the growth of lithium dendrites and even the formation of "dead lithium".

In addition, the structure of the functional layer of the negative electrode pole piece of the present application corresponds to a skeleton formed by stacking a conductive layer and a dielectric layer, so the functional layer has a certain space inside. When lithium ions enter the interior of the functional layer, even if the lithium ions are reduced to grow into lithium dendrites, the skeleton structure of the functional layer can provide a certain growth space for lithium dendrites, which reduces the volume of lithium dendrites to a certain extent. The extrusion and expansion damage of the negative pole piece maintains the cycle performance and safety performance of the electrochemical device. It is worth mentioning that the conductive layer also has a certain "self-correcting function". Specifically, even if lithium dendrites grow rapidly inside the functional layer, when the growth contacts the conductive layer, due to the equipotentiality of the conductive layer itself, the electric field distribution concentrated on the top of the lithium dendrites can be dispersed and tend to be uniform, thereby preventing The further growth of dendrites realizes the "self-correction" of dendrites, and effectively improves the cycle performance and safety performance of electrochemical devices by further suppressing the volume expansion of the negative electrode.

Therefore, in the negative electrode plate of the present application, the functional layer formed by the conductive layer and the dielectric layer including the lithium-wetting material not only reduces the formation of lithium dendrites in the functional layer, but also inhibits the growth of lithium dendrites at the interface, which is more The volume expansion of the negative electrode plate during long-term application is effectively improved, so it is beneficial to the optimization of the cycle performance and safety performance of the electrochemical device.

In addition, since the negative electrode sheet of the present application can effectively avoid the formation of lithium dendrites and reduce the loss of lithium during cycling, the electrochemical device can also have good Coulomb efficiency.

The present application does not impose strict restrictions on the material of the conductive layer, as long as it can effectively conduct electrons. In the specific implementation process, the conductive layer can be a conductor material, such as copper, nickel, chromium, titanium, tungsten, zirconium, aluminum and its alloys and other metal materials; the material of the conductive layer can also be a semiconductor material, such as solid carbon spheres, hollow Carbon spheres, porous carbon, single-walled carbon nanotubes, multi-layered carbon nanotubes, pure carbon fibers, doped carbon fibers (including carbon fibers doped with oxides, sulfides, carbides, nitrides, metal elements, functional groups, etc.), graphite Carbon-based materials such as graphene cages, doped graphene and doped graphene derivatives. This application can choose, but is not limited to the above-mentioned materials.

The application does not impose strict restrictions on the material of the dielectric layer, as long as it can block electron conduction. In the specific implementation process, the dielectric layer can be made of polymer materials, such as polyvinylidene fluoride, polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyphenylene ether, polypropylene carbonate, Polymethyl methacrylate, polyethylene terephthalate, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-chlorotrifluoroethylene, polyvinylidene fluoride-hexafluoropropylene At least one of fluoropropylene and polyvinylidene fluoride; the dielectric layer can also be an inorganic material, such as at least one of sodium silicate and its derivatives, aluminum oxide and its derivatives, silicon oxide and its derivatives. This application can choose, but is not limited to the above-mentioned materials.

This application does not impose strict restrictions on the lithium wetting material, as long as it can have good affinity with lithium. The lithium wetting material can be a metal element, for example, silver, aluminum, gold, barium, calcium, indium, platinum, silicon, tin, zinc, cobalt, gallium; the lithium wetting material can also be a nitride such as molybdenum nitride, sulfide Such as molybdenum sulfide, tin sulfide. In addition, the present application can also modify the conductive layer so that the conductive layer includes hydroxyl (-OH), ester (-COOR), carboxyl (-COOH), amino (-NH ₂ ), sulfo (-SO) ₃ H) and other lithiophilic functional groups to make the conductive layer include lithium wetting materials.

The present application does not strictly limit the manner of obtaining the conductive layer. As an optional embodiment, the present application can obtain the conductive layer by a combination of electrospinning and heat treatment. Specifically, a spinning solution is prepared by using a precursor capable of generating conductive substances and a solvent, electrospinning is performed by an electrospinning device to obtain a fiber film, and then the fiber film is heat-treated in an inert atmosphere to obtain a conductive layer.

As another feasible embodiment, it is also possible to formulate a conductive paste containing a conductive substance and an adhesive, and then select a suitable substrate, and coat the conductive paste on the substrate to obtain a conductive layer.

This application does not strictly limit the method of obtaining the dielectric layer, and the dielectric layer can also be obtained by means of electrospinning or coating, which will not be repeated in this application.

The present application does not impose strict restrictions on the manner of including the lithium wetting material in the conductive layer. As an implementable manner, the present application may adopt the method of preparing the conductive layer by combining the above-mentioned electrospinning and heat treatment. Electrospinning is carried out by adding a precursor of a lithium-wetting material to electrospinning to obtain a fiber membrane including a lithium-wetting material precursor, and then when the fiber membrane is heat-treated, the lithium-wetting material precursor is converted into a lithium-wetting material, thereby making conductive The layer includes a lithium wetting material. As another implementable manner, a certain amount of lithium wetting material may be added to the conductive paste during the process of coating and preparing the conductive layer, so that the obtained conductive layer includes the lithium wetting material.

The present application does not strictly limit the method of stacking conductive layers and dielectric layers to obtain functional layers. As an optional embodiment, the present application can stack M conductive layers and N dielectric layers by means of hot pressing. Get functional layers. As another optional method, the present application can also obtain a functional layer in which a conductive layer and a dielectric layer are stacked by coating. Specifically, a suitable substrate is selected to form M conductive layers and N dielectric layers. The layered pastes are sequentially layered and applied on the surface of the substrate.

On the basis of the aforementioned negative pole piece structure, the present application further limits the content distribution of the lithium wetting material in the conductive layer, which is beneficial to further improve the safety performance and cycle life of the electrochemical device. In some embodiments of the present application, the content of the lithium wetting material in the negative pole piece is distributed in a gradient in the stacking direction.

In this application, the gradient distribution of the content of the lithium wetting material in the stacking direction includes an increasing gradient and a decreasing gradient, wherein the increasing gradient means that the content of the lithium wetting material in the jth conductive layer is less than the (j+1)th The content of the lithium wetting material in the conductive layer, the gradient decreasing means that the content of the lithium wetting material in the jth conductive layer is greater than the content of the lithium wetting material in the (j+1)th conductive layer, 1≤j <M. In the present application, by controlling the content distribution of the lithium wetting material, the location where lithium ions are deposited in the functional layer can be controlled. It can be understood that lithium ions tend to be deposited in parts with a large content of lithium wetting material. Therefore, in the specific implementation process, the content of lithium wetting material in the conductive layer far from the negative electrode interface is controlled to be greater than that in the conductive layer close to the negative electrode interface. The content of lithium wetting material can reduce the deposition of lithium ions near the negative electrode interface, inhibit the formation of lithium dendrites at the negative electrode interface, maintain the integrity of the negative electrode interface, and avoid the formation of interfacial lithium dendrites piercing the diaphragm and causing short circuit. The safety performance of the electrochemical device is further improved.

For example, in the functional layer shown in FIG. 1 , where M=1, the content of the lithium wetting material is distributed in a gradient along the stacking direction inside the conductive layer a. As a possible way, in the process of obtaining the conductive layer a by combining the above-mentioned electrospinning and heat treatment, during spinning, the concentration of the precursor of the lithium wetting material added to the electrospinning device at different time periods changes in a gradient. The spinning solution can make the content of the lithium-wetting material gradient distributed along the thickness direction of the conductive layer a, and then stack the conductive layer a and the dielectric layer b along the thickness direction of the conductive layer a to obtain a functional layer, so that the conductive layer The content of Li-wetting material in a is distributed gradiently in the stacking direction.

When the functional layer includes two or more conductive layers (M≥2), the content of the lithium-wetting material in each conductive layer is distributed in a gradient in the stacking direction, and the content of the lithium-wetting material in each conductive layer is uniformly distributed .

For example, in the functional layer shown in FIG. 2, M=2, the content of the lithium wetting material is uniformly distributed in the conductive layer a1, the content of the lithium wetting material is uniformly distributed in the conductive layer a2, and the lithium wetting material in the conductive layer a1 is uniformly distributed The content of the material is greater than the content of the lithium wetting material in the conductive layer a2, so that in the negative pole piece, the content of the lithium wetting material is distributed in a gradient in the stacking direction.

When two or more conductive layers are included in the functional layer, in the process of preparing M conductive layers by combining electrospinning and heat treatment, the content of the lithium wetting material precursor in the M spinning solutions is changed in a gradient, and then in the lamination process During the process, the conductive layer is laminated with the dielectric layer in the order of increasing or decreasing content of the precursor of the lithium-wetting material in the spinning solution. As another implementable manner, in the process of coating to obtain the conductive layer, the content of the lithium-wetting material in the M conductive pastes in the stacking direction can be changed in a gradient, so that the content of the lithium-wetting material in the stacking direction is changed. upper gradient distribution.

Of course, when the functional layer includes two or more conductive layers, the content of the lithium-wetting material in one conductive layer can also be distributed in a gradient along the stacking direction, and, considering the induced deposition of lithium ions, the lithium-wetting material in one conductive layer The gradient distribution of the content of the wetting material in the stacking direction is the same as the gradient distribution of the content of the lithium wetting material in the different conductive layers in the stacking direction, for example, the gradient is increasing simultaneously or the gradient is decreasing simultaneously.

In some embodiments of the present application, the mass of the lithium-wetting material may be 5% to 95% of the mass of the functional layer, alternatively, 30% to 60%.

Generally, the higher the quality of the lithium-wetting material in the functional layer, the better the lithophilicity of the functional layer, which is more conducive to inducing lithium ions to rapidly enter the functional layer for deposition. However, blindly improving the quality of the lithium-wetting material is not conducive to the improvement of the mass energy density of the electrochemical device and the structural stability of the functional layer. Therefore, the quality of the lithium-wetting material can be controlled in the range of 30% to 60% of the quality of the functional layer. Therefore, without affecting the mass energy density of the electrochemical device, the probability of lithium ions at the negative electrode interface is reduced, the formation of lithium dendrites at the negative electrode interface is suppressed, and the cycle life and safety performance of the electrochemical device are improved. In addition, in the selection of lithium-wetting materials, some materials with good lithiophilic effect and low density can also be selected to further realize the unity of cycle life, safety performance and mass energy density of electrochemical devices.

The negative electrode sheet of the present application also includes a lithium metal layer or a current collector. Generally speaking, the lithium metal layer or current collector is in the form of flakes, and the two larger and opposite faces of the lithium metal layer or current collector are the functional surfaces. When the negative electrode sheet of the present application includes a lithium metal layer or a current collector, the functional layer is provided on the functional surface.

This application does not strictly limit the arrangement of the functional layer on the functional surface. For example, the functional layer can be arranged on the functional surface by hot pressing; or as mentioned above, when the functional layer is obtained by coating, a lithium metal layer or a lithium metal layer can be used. The current collector acts as a substrate. In some embodiments, the functional layer can also be placed directly on the functional surface of the lithium metal layer or current collector without forming a substantial connection between the functional layer and the functional surface. It can be understood that a substantial connection can be formed between the functional layer and the functional surface by means of hot pressing or coating, which is beneficial to further maintain the structural stability of the negative pole piece and the stability of the conductive network during the charging and discharging process.

In a specific implementation process, whether the negative electrode plate includes a lithium metal layer or a current collector can be selected according to the purpose of the negative electrode plate. For example, when the negative pole piece of the present application is used in a button battery, it is possible to choose not to use a lithium metal layer or a current collector, and use the functional layer directly as the negative electrode of the battery, so that the button battery can be lighter in weight. The mass energy density is further improved. When the negative pole piece of the present application is used in a wound type battery, the negative pole piece includes a lithium metal layer or a current collector to facilitate the arrangement of the tabs. In this application, the current collector can be made of but not limited to copper foil.

In order to further improve the inductive effect of the functional layer on lithium ion deposition and the blocking effect of electron transport, as a preferred embodiment, when the negative pole piece includes a lithium metal layer or a current collector, the functional layer is arranged on the lithium metal layer. The surface or the functional surface of the current collector and the extension direction of the lithium metal layer or the extension direction of the current collector is perpendicular to the stacking direction;

The content of the lithium wetting material is gradually decreasing in the direction away from the lithium metal layer or current collector.

FIG. 3 is a schematic structural diagram of a negative pole piece in an embodiment of the application. As shown in FIG. 3 , the negative pole piece includes a lithium metal layer or current collector d and a functional layer e, and the functional layer e is disposed on the lithium metal layer or current collector A functional surface of d. Among them, the functional layer e includes a conductive layer a, a dielectric layer b and a lithium wetting material c, M=1, N=1, and the stacking direction is perpendicular to the extension direction of the lithium metal layer or the extension direction of the current collector and the stacking direction. The direction of the middle arrow is the stacking direction, and the content of the lithium-wetting material gradually decreases in the direction away from the lithium metal layer or the current collector d.

When the negative electrode sheet of the present application is implemented in the above manner, the extending direction of the dielectric layer is parallel to the extending direction of the lithium metal layer or the current collector, and the area of the dielectric layer for blocking electron transfer is large, so the dielectric layer can more effectively reduce the The electron concentration in the functional layer can effectively prevent the combination of lithium ions and electrons, and inhibit the formation of lithium dendrites in the functional layer; and the dielectric layer can more effectively reduce the electron concentration on the surface of the functional layer, forcing lithium ions into the functional layer for deposition. The formation of lithium dendrites at the anode interface is reduced; thus, the cycle life and safety performance of electrochemical devices can be improved. In addition, the content of Li-wetting material is low in the region away from the Li metal layer or current collector and high in the region close to the Li metal layer or current collector, therefore, lithium ions are more inclined to deposit in the region close to the Li metal layer or current collector , thereby reducing the formation of lithium dendrites near the negative electrode interface area, preventing lithium dendrites from piercing the separator and causing safety risks, thereby improving the safety performance of the electrochemical device.

During the research process, the inventor found that the thickness of the functional layer along the stacking direction will have a certain influence on the electrical properties of the electrochemical device. If the thickness of the functional layer along the stacking direction is too large, the energy density of the electrochemical device will decrease. , while the thickness is too small, the improvement of the functional layer on the cycle life and safety performance of the electrochemical device is limited. When the thickness of the functional layer is between 50 μm and 100 μm, the electrochemical device can not only have good energy density, but also have excellent cycle life and safety performance.

In addition, under the condition of a certain thickness of the functional layer, rational control of the number of conductive layers and dielectric layers is beneficial to further improve the cycle life and safety performance of electrochemical devices. Specifically, as the number of conductive layers and dielectric layers increases within a certain range, the cycle life and safety performance of electrochemical devices first show an increasing trend, and then remain basically unchanged. Therefore, for economic considerations, generally The number of layers of the conductive layer M=4 to 6, and/or the number of layers of the dielectric layer N=4 to 6.

In addition to the above-mentioned manner in which the stacking direction is perpendicular to the extending direction of the lithium metal layer or the current collector, the stacking direction and the extending direction of the lithium metal layer or the extending direction of the current collector may be parallel or at any acute angle.

FIG. 4 is a schematic structural diagram of a negative electrode pole piece in another embodiment of the present application. As shown in FIG. 4 , the negative electrode pole piece includes a lithium metal layer or a current collector d and a functional layer e, and the functional layer e is disposed on the lithium metal layer or the current collector. A functional surface of fluid d. The functional layer e includes a conductive layer a1, a conductive layer a2, a dielectric layer b1, a dielectric layer b2 and a lithium wetting material c; M=2, N=2 in FIG. 4, the stacking direction and the extending direction of the lithium metal layer Or the extension direction of the current collector is parallel, and the direction of the arrow in the figure is the lamination direction.

FIG. 5 is a schematic structural diagram of a negative electrode pole piece in another embodiment of the application. As shown in FIG. 5 , the negative electrode pole piece includes a lithium metal layer or a current collector d and a functional layer e, and the functional layer e is disposed on the lithium metal layer or the collector. A functional surface of fluid d. The functional layer e includes a conductive layer a1, a conductive layer a2, a dielectric layer b1, a dielectric layer b2 and a lithium wetting material c; M=2, N=2, the stacking direction and the extending direction of the lithium metal layer or the current collector The direction of extension is an acute angle, and the direction of the arrow in the figure is the stacking direction.

During the research process, the inventors found that, compared with the embodiments shown in FIGS. 4 and 5 , the embodiment shown in FIG. 3 can be more conducive to the functional layer’s ability to inhibit the formation of lithium dendrites at the interface, so that the electrochemical performance can be improved. The cycle life and safety performance of the device are better.

It should be added that no matter the stacking direction is perpendicular, parallel or any acute angle to the extending direction of the lithium metal layer or current collector, the functional layer disposed on the functional surface of the lithium metal layer or current collector includes the functional layer disposed on the lithium metal layer or current collector. One functional surface and two functional surfaces of the fluid. In the specific implementation process, one functional layer is provided on one functional surface of the lithium metal layer or current collector, or two functional layers are provided on two functional surfaces, and the stacking direction of the functional layers provided on different functional surfaces is related to the lithium metal layer or the current collector. The relationship of the fluid extension direction can be selected according to the needs of the negative pole piece.

In this application, the stacking sequence of the M conductive layers and the N dielectric layers has a certain influence on the performance of the functional layer. As a preferred embodiment, the M conductive layers and the N dielectric layers of the present application are alternately stacked.

Compared with the way in which i (2≤i≤M) conductive layers are stacked and then k (2≤k≤N) dielectric layers are stacked, the cross-stacking arrangement of conductive layers and dielectric layers can make the generation of noise generated in the functional layer. Lithium dendrites are easier to contact the conductive layer, which is more conducive to the "self-correction" of lithium dendrites by the conductive layer, thereby inhibiting the further growth of lithium dendrites, reducing the risk of lithium dendrites puncturing the separator and causing short circuits, and lithium dendrites. The energy density loss caused by crystals can be improved, and the safety performance and cycle life of electrochemical devices can be improved.

In a preferred embodiment, the first edge layer and/or the second edge layer of the functional layer is a dielectric layer.

In this application, the first edge layer and/or the second edge layer of the functional layer respectively refers to the first layer and/or the last layer of the functional layer in the stacking direction.

It can be understood that when M=1, no matter how the conductive layer and the dielectric layer are stacked, the first edge layer and/or the second edge layer of the functional layer must be a dielectric layer. When M≧2, the first edge layer and/or the second edge layer of the functional layer in the present application is a dielectric layer.

Since the lithium wetting material is distributed in the conductive layer, when the first edge layer and/or the second edge layer is a dielectric layer, lithium ions are more likely to be deposited inside the functional layer, so the amount of lithium deposition at the negative electrode interface In this way, the formation of lithium dendrites at the negative electrode interface is suppressed, so that the cycle life and safety of the electrochemical device can be further improved.

During the research, the inventors found that when the conductivity of the conductive layer is 10 ^-7 S/cm to 10 ⁶ S/cm, and/or, when the conductivity of the dielectric layer is less than 10 ^-8 S/cm, the electrochemical device has Better energy density, cycle life and safety performance.

The present application can optimize the current density in the functional layer by controlling the conductivity of the conductive layer and/or the conductivity of the dielectric layer, which is more conducive to the deposition of lithium ions inside the functional layer and inhibits the formation of lithium dendrites. When the conductivity of the conductive layer and/or the conductivity of the dielectric layer is within the above range, the current density in the functional layer will neither be too high, thereby increasing the risk of lithium dendrite formation in the functional layer, nor will the current density in the functional layer be too high. Therefore, the organic unity of safety performance, cycle performance and capacity of electrochemical devices can be realized.

When the material of the conductive layer is a conductor material, the conductivity of the conductive layer is 10 ^-3 S/cm to 10 ⁶ S/cm; when the material of the conductive layer is a semiconductor material, the conductivity of the conductive layer is 10 ^-7 to 10 ³ . In the specific implementation process, the selection of conductive layer materials or dielectric layer materials, the selection of appropriate parameters in the preparation process of the conductive layer and/or the dielectric layer, the selection of the conductive layer and/or the dielectric layer preparation process The conductivity of the conductive layer and/or the dielectric layer is adjusted by adding a certain amount of conductive agent or insulating material, etc., so that the conductivity of the conductive layer and/or the dielectric layer is within the above range.

The porosity of the functional layer has a certain influence on the deposition of lithium metal in the functional layer. The inventor found in the research process that the porosity of the functional layer is 5% to 90%, and can be further selected to be 50% to 90%.

It can be understood that the larger the porosity of the functional layer, the more favorable it is for the shuttle of lithium ions in the functional layer, inducing lithium ions to enter the functional layer more quickly for deposition, and the functional layer can have a larger specific surface area for the deposition of lithium ions. Provide more sites. However, the large porosity of the functional layer often means that the functional layer has a large volume, which is not conducive to the improvement of the volumetric energy density of electrochemical devices. Therefore, the porosity of the functional layer is controlled in the range of 50% to 90%, so that lithium ions can be induced to enter the functional layer and deposited without affecting the volume energy density of the electrochemical device, and the interfacial lithium dendrite can be suppressed. formed to improve the cycle life and safety performance of electrochemical devices.

In the specific implementation process, the materials of the conductive layer and the dielectric layer with suitable porosity, the thickness of the conductive layer and the dielectric layer, and the appropriate preparation process of the conductive layer and the dielectric layer (for example, the temperature of electrospinning) can be selected. , spinning solution concentration), and the lamination process (eg, pressure and temperature of hot pressing) of the conductive layer and the dielectric layer make the porosity of the functional layer between 50% and 90%.

The good mechanical strength of the functional layer can realize the stability of the structure of the functional layer during the charge-discharge cycle, prevent the functional layer from being broken during the cycle, so that the functional layer can continue to function, and ensure the stable structure of the negative pole piece. In the specific implementation process, the mechanical strength of the functional layer can be adjusted by selecting the materials of the conductive layer and the dielectric layer with appropriate strength, combining the preparation process of the conductive layer and the dielectric layer, and the stacking process of the conductive layer and the dielectric layer.

On the basis of the above negative pole piece, the functional layer of the negative pole piece of the present application further includes lithium metal, and the content of lithium metal in the functional layer is 0.25 mg/cm ² to 25 mg/cm ² , that is, per square centimeter of the functional layer The area includes 0.25mg to 25mg lithium metal. The area of the functional layer refers to the area of the surface of the functional layer closest to the functional surface of the current collector.

By including a certain content of lithium metal in the functional layer, the lithium lost in the discharge cycle can be supplemented, and the cycle life of the electrochemical device including the negative electrode plate can be further improved.

In a specific implementation process, the functional layer may include the above-mentioned content of lithium metal by means of a melting method, a physical vapor deposition method, an electrochemical method, or the like.

A second aspect of the present application further provides an electrochemical device, the electrochemical device comprising the above-mentioned negative electrode plate. It can be understood that an electrochemical device generally includes a positive electrode, an electrolyte (electrolyte), a separator, and the like in addition to the negative electrode.

The present application does not impose strict limitations on the electrochemical device, for example, the electrochemical device may be a wound battery, a laminated battery, a solid-state battery, and the like. In the specific implementation process, a suitable electrochemical device can be constructed by using the negative electrode plate of the present application, matched with a suitable positive electrode plate, electrolyte (electrolyte), separator, etc., as required.

In some embodiments of the present application, the negative pole piece may only have a functional layer. In this case, the extending direction of the functional layer may be parallel to the extending direction of the positive pole piece, so that the negative pole piece and the positive pole piece of the electrochemical device are opposite to each other. , and cooperate with the diaphragm and electrolyte (quality) to obtain an electrochemical device with excellent cycle life and safety performance.

In other embodiments of the present application, the negative pole piece includes a functional layer and a current collector, and the functional layer is arranged on the functional surface of the current collector. Cooperate with diaphragm and electrolyte (quality) to obtain electrochemical devices with excellent cycle life and safety performance.

In the electrochemical device of the present application, the functional layer included in the negative electrode plate can effectively reduce the volume expansion of the negative electrode plate and the formation of lithium dendrites during charge-discharge cycles, so that the electrochemical device has excellent cycle life and safety performance.

A third aspect of the present application further provides an electronic device, which includes the above electrochemical device. An electrochemical device can be used as a driving source or an energy storage unit for the electronic device. The electronic devices in this application can be, but are not limited to, mobile devices (eg, smart watches, mobile phones, notebook computers, etc.), electric vehicles (eg, electric bicycles, hybrid electric vehicles, power-assisted bicycles, etc.), and the like.

Since the electronic device of the present application includes the aforementioned electrochemical device, it has excellent endurance, service life and safety performance, and has a good user experience.

The present application will be further described below with reference to the embodiments. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. In the following examples, the raw materials used were all commercially available unless otherwise stated.

The button cells of Examples 1-17 were all prepared according to the following methods.

(1) Preparation of negative pole piece

A: Preparation of conductive layer: 0.8 parts by mass of polyacrylonitrile was dissolved in 10 parts by mass of N,N-dimethylformamide and then tin tetrachloride was added to obtain a spinning solution containing a certain concentration of tin tetrachloride ; The spinning solution is injected into the electrospinning device for electrospinning to obtain a polyacrylonitrile fiber film. During the spinning process, the working state of the electrospinning device is set to control the thickness of the polyacrylonitrile fiber film; The fiber membrane was placed in a muffle furnace, and the muffle furnace was heated to 230 °C at a heating rate of 1 °C per minute in an air atmosphere, and then kept for 2 hours. The polyacrylonitrile fiber membrane was pre-oxidized, and the pre-oxidized polypropylene was The nitrile fiber film is heated to 800°C at a heating rate of 5°C per minute under an argon atmosphere in a tube furnace for 4 hours, and tin dioxide (lithium wetting material) is distributed in the obtained carbon fiber film to obtain a conductive layer;

In the process of injecting the spinning solution into the electrospinning device, when the concentration of tin tetrachloride in the spinning solution does not change (that is, when the concentration of tin tetrachloride is not adjusted), a polyacrylonitrile fiber membrane can be obtained along the A polyacrylonitrile fiber film with a uniform distribution of tin tetrachloride content in the thickness direction;

During the process of injecting the spinning solution into the electrospinning device, the concentration of tin tetrachloride in the spinning solution was adjusted at different time periods so that the concentration of tin tetrachloride showed a gradient change, which could be obtained along the thickness direction of the polyacrylonitrile fiber film. The polyacrylonitrile fiber membrane with the content gradient distribution of tin tetrachloride;

B: Preparation of dielectric layer: 0.8 parts by mass of polyvinylidene fluoride was dissolved in 10 parts by mass of N,N-dimethyl amide to obtain a spinning solution, and the spinning solution was injected into an electrospinning device for electrospinning The polyvinylidene fluoride fiber membrane was obtained, the working state of the electrospinning device was set, and the thickness of the polyvinylidene fluoride fiber membrane was controlled; electric layer;

C: Preparation of functional layers: The M conductive layers and the N dielectric layers are punched into a disc with a diameter of 18 mm, and the M conductive layers and the N dielectric layers are alternately stacked by means of hot pressing to obtain the functional layer. Using an electrochemical method, lithium is pre-supplemented in the functional layer, so that the content of lithium metal in the functional layer is 4.1 mg/cm ² ;

D: the functional layer obtained in step C is arranged on a functional surface of the negative electrode current collector copper foil by means of hot pressing to obtain a negative electrode pole piece;

Wherein, the stacking direction of the conductive layer and the dielectric layer is perpendicular to the extending direction of the copper foil current collector.

(2) Preparation of positive electrode sheet

The positive electrode active material lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride are mixed in a mass ratio of 97.5:1.0:1.5 and added to N-methylpyrrolidone to prepare a positive electrode slurry with a solid content of 0.75, and stir evenly. The positive electrode slurry is uniformly coated on the functional surface of the current collector aluminum foil, the aluminum foil is dried at 90°C to obtain a positive electrode piece, and the positive electrode piece is punched into a sheet with a diameter of 14 mm;

The loading amount of the positive electrode active material on the positive electrode sheet is 1 mg/cm ² .

(3) Preparation of electrolyte

In a dry argon atmosphere, firstly, dioxolane and dimethyl ether were mixed in a volume ratio of 1:1 to obtain a mixed solution, and then lithium bistrifluoromethanesulfonimide was added to the mixed solution and mixed uniformly to obtain The electrolyte solution with lithium bistrifluoromethanesulfonimide concentration of 1M.

(4) Button battery assembly

Choose CR2032 battery case, the diameter of the battery case is 20mm, the height is 3.2mm, and the thickness is 0.25mm; the above-mentioned negative pole piece, positive pole piece, and separator are assembled according to the button battery assembly method commonly used in the field, and the side is assembled after assembly. Sealing - top sealing - liquid injection - packaging, and finally a button battery is obtained;

The separator is a polyethylene film with a thickness of 15 μm.

Example 18

The preparation of the button battery in this example is basically the same as that in Example 1. The only difference is that this example does not pre-supplement lithium after obtaining the functional layer in step C of (1) preparing the negative pole piece.

Example 19

The preparation of the button battery in this example is basically the same as that in Example 1. The only difference is that in this example, in the step D of (1) preparing the negative pole piece, the functional layer obtained in the step C is formed by hot pressing. When a negative electrode pole piece is obtained on a functional surface of the negative electrode current collector copper foil, the stacking direction of the dielectric layer and the conductive layer is parallel to the extending direction of the current collector.

Example 20

The preparation steps of the button battery in this example are basically the same as those in Example 1. The only difference is that in (1) the preparation step D of the negative pole piece in this example, the functional layer is arranged before the negative electrode current collector copper foil. , using a 1.5T roller machine to roll the functional layer, and the rolling speed is 1m/min.

Comparative Example 1

The preparation process of the button battery of this comparative example is as follows:

(1) Preparation of negative pole piece

Dissolve 0.8 parts by mass of polyacrylonitrile in 10 parts by mass of a solvent to obtain a spinning solution, inject the spinning solution into an electrospinning device for electrospinning to obtain a polyacrylonitrile fiber film, and set the working state of the electrospinning device so that The thickness of the polyacrylonitrile fiber film was 60 μm; after that, the polyacrylonitrile fiber film was placed in a muffle furnace, and the muffle furnace was heated to 230 °C at a heating rate of 1 °C per minute in an air atmosphere and kept for 2 hours. The polyacrylonitrile fiber film is pre-oxidized, and then the pre-oxidized polyacrylonitrile fiber film is heated to 800° C. at a heating rate of 5° C. per minute under an argon atmosphere in a tube furnace for 4 hours to obtain a carbon fiber film. The carbon fiber film is punched into thin sheets with a diameter of 18 mm to obtain a conductive layer, which is placed on a functional surface of the negative electrode current collector copper foil by hot pressing, and lithium is pre-supplemented in the functional layer by an electrochemical method, so that lithium metal is functional. The content in the layer is 4.1 mg/cm ² to obtain a negative pole piece;

In this comparative example, the preparation of the positive pole piece, the preparation of the electrolyte, and the process of button-type assembly are the same as those in Example 1.

Comparative Example 2

The preparation process of the button battery in this comparative example is as follows:

(1) Preparation of negative pole piece

Dissolve 0.8 parts by mass of polyvinylidene fluoride in 10 parts by mass of a solvent to obtain a spinning solution, inject the spinning solution into an electrospinning device for electrospinning to obtain a polyvinylidene fluoride fiber film, and set the working state of the electrospinning device , so that the thickness of the polyvinylidene fluoride fiber film is 60 μm; the polyvinylidene fluoride fiber film is placed in a vacuum drying oven at 80 ° C for 12 hours, and then the polyvinylidene fluoride fiber film is punched into pieces with a diameter of 18mm. , obtain a dielectric layer, and set the dielectric layer on a functional surface of the negative electrode current collector copper foil by hot pressing to obtain a negative electrode pole piece;

In this comparative example, the preparation of the positive pole piece, the preparation of the electrolyte, and the assembly of the button battery are the same as those in Example 1.

Comparative Example 3

(1) Preparation of negative pole piece

Dissolve 0.8 parts by mass of polyacrylonitrile in 10 parts by mass of N,N-dimethyl amide solvent, and then add tin tetrachloride, so that the concentration of tin tetrachloride in the spinning solution is 0.4M; The liquid was injected into the electrospinning device for electrospinning to obtain a polyacrylonitrile fiber membrane, and the working state of the electrospinning device was set so that the thickness of the polyacrylonitrile fiber membrane was 60 μm; after that, the polyacrylonitrile fiber membrane was placed in a muffle furnace , in the air atmosphere at a heating rate of 1 ℃ per minute, the muffle furnace is heated to 230 ℃ and kept for 2 hours, the polyacrylonitrile fiber film is pre-oxidized, and the pre-oxidized polyacrylonitrile fiber film is placed in the tube furnace. In a medium argon atmosphere, the temperature was raised to 800°C at a heating rate of 5°C per minute and held for 4 hours. In the obtained carbon fiber film, tin dioxide was uniformly distributed along the thickness direction of the carbon fiber film, and the carbon fiber film was punched into pieces with a diameter of 18 mm. , obtain a conductive layer, and set the conductive layer on a functional surface of the negative electrode current collector copper foil by hot pressing to obtain a negative electrode pole piece;

Comparative Example 4

In this comparative example, a copper foil with a diameter of 18mm was used as the negative pole piece;

In the specific examples and comparative examples, the number of conductive layers (M), the number of dielectric layers (N), the thickness of the conductive layer before hot pressing, the thickness of the dielectric layer before hot pressing, the thickness of the functional layer along the stacking direction, The composition of the negative pole piece, the concentration of tin tetrachloride in the spinning solution added to the electrospinning device at different spinning time periods when preparing each conductive layer, and the content of the lithium wetting material in the conductive layer in the direction away from the current collector The distribution and other parameters are shown in Table 1.

Table 1

The thickness of the functional layer in the stacking direction in Table 1 was obtained by using the argon ion polishing CP method to prepare a sample of the negative pole piece and then observing it with a scanning electron microscope.

The electrical conductivity of the conductive layer and the dielectric layer, the porosity of the functional layer, and the quality of the lithium-wetting material based on the quality of the functional layer in each Example and Comparative Example are shown in Table 2.

Table 2

In Table 2, the detection methods of relevant parameters are as follows:

1. Conductivity:

A. Turn on the resistivity of the four probes, and calibrate the instrument with the standard resistance method to confirm that the instrument can be used normally;

B. Set the thickness of the film according to the thickness of the sample, select the shape of the probe as square, and select the voltage gear and probe spacing according to the thickness and material of the sample;

C. Connect the test probe, and make the probe contact with the sample by adjusting the probe platform up and down slightly.

D. After the resistance data displayed by the four-probe resistance meter is stable, the conductivity data is read as the conductivity of the sample;

2. The porosity of the functional layer:

According to the national standard method GB/T 21650.1-2008, the porosity of the functional layer is tested by mercury intrusion method;

3. Content of lithium wetting material:

According to the national standard method GB/T 27761-2011, the content of tin dioxide in the material was tested by thermogravimetric analyzer.

Test example

The following parameters were tested for the negative pole pieces and laminated button batteries of the above embodiments and comparative examples.

1. The composition of the negative pole piece:

The microscopic morphology of the negative pole piece obtained in Example 8 was observed using a scanning electron microscope, and the results are shown in Figure 6;

It can be seen from Figure 6 that:

6 includes copper foil 101, lithium metal layer 201, dielectric layer 301, conductive layer 401, dielectric layer 501, and conductive layer 601. Therefore, the functional layer of the present application is formed by stacking a dielectric layer and a conductive layer, and has three-dimensional structure;

2. Lithium deposition state in the negative pole piece:

The negative pole pieces obtained in Example 11 and Comparative Example 1 were charged to 3.7V with a constant current of 0.2C, then charged to 0.025C with a constant voltage, left for 5 minutes, and discharged to 2.55V with a constant current of 0.5C; cycle 10 times After that, let it stand for 5 minutes, and charge it with a constant current of 0.1C to a full charge state of 3.7V; the sample of the negative electrode piece was prepared by the argon ion polishing CP method, and then the sample was observed by scanning electron microscope. The results are shown in Figures 7 and 7, respectively. 8;

From the comparison of Figure 7 and Figure 8, it can be seen that:

In the negative pole piece of Fig. 7, the deposition of lithium in the functional layer is very dense, and the deposition amount is large; while in the negative pole piece of Fig. 8, the deposition of lithium ions is very loose, and the deposition amount is also less; The comparison shows that the negative electrode plate of the present application can effectively induce lithium deposition inside the functional layer, and the lithium deposition is very dense; moreover, as can be seen from Figure 7, lithium is not easily deposited in the area close to the negative electrode interface, therefore, the negative electrode interface The formation of lithium dendrites is suppressed; therefore, it can be shown that when the stacking direction is perpendicular to the extension direction of the current collector, and the gradient of the lithium-wetting material decreases in the stacking direction, the negative electrode plate can induce the deposition of lithium ions in the region close to the current collector, reducing the The probability of lithium ions depositing on the negative electrode interface suppresses the formation of lithium dendrites on the negative electrode interface; thus the electrochemical device including the negative electrode pole piece can show better cycle life and safety performance; In Table 3, Example 11 and Comparative Example 1 This can also be confirmed by the comparison of the cycle number and volume expansion rate of the coin cell battery;

3. Cycle performance:

At 20°C, using a blue-electric electrochemical workstation, charge to 3.7V at a rate of 0.2C with constant current, then charge with constant voltage to 0.025C, let stand for 5 minutes, and then discharge to 2.55V with a constant current of 0.5C; let stand for 5 minutes , this is one cycle, and the cycle performance is the number of cycles when the discharge capacity decays to 80% of the discharge capacity of the first cycle. The results are shown in Table 3;

4. Volume expansion rate:

At 20°C, use a blue-electric electrochemical workstation to charge to 3.7V with a constant current of 0.2C, then charge to 0.025C with a constant voltage, let stand for 5 minutes, and discharge to 2.55V with a constant current of 0.5C; For one cycle, when the discharge capacity of the battery decayed to 80% of the discharge capacity of the first cycle, the test was stopped, the battery was disassembled, and the negative pole piece was taken out, soaked in dimethyl carbonate solution, and prepared by argon ion polishing CP method For the sample of the negative pole piece, use a scanning electron microscope to observe the cross section of the negative pole piece (perpendicular to the functional surface of the current collector), and obtain the thickness T of the cross section of the negative pole piece after the cycle. The thickness of the cross section of the negative pole piece before the cycle is t, the capacity Retention rate=(T-t)/T, the results are shown in Table 3;

5. Coulomb efficiency:

At 20°C, using a blue-electric electrochemical workstation, charged to 3.7V with a constant current rate of 0.2C, then charged to 0.025C with a constant voltage, let stand for 5 minutes, and then discharged to 2.55V with a constant current of 0.5C, let stand for 5 minutes, This is a cycle, and the Coulomb efficiency is the average value of the ratio of the discharge capacity to the charge capacity in each cycle when the capacity decays to 80% of the discharge capacity of the first cycle. The results are shown in Table 3.

table 3

类别category	循环性能(圈)Cycling performance (lap)	体积膨胀率(％)Volume expansion rate (%)	库伦效率Coulomb efficiency
实施例1Example 1	9090	8080	98.8％98.8%
实施例2Example 2	9393	8585	98.78％98.78%
实施例3Example 3	100100	7575	99.54％99.54%
实施例4Example 4	9090	8080	98.87％98.87%
实施例5Example 5	100100	8080	99.36％99.36%

实施例6Example 6	100100	8080	99.48％99.48%
实施例7Example 7	150150	6060	99.67％99.67%
实施例8Example 8	130130	8080	99.64％99.64%
实施例9Example 9	200200	3535	99.86％99.86%
实施例10Example 10	180180	4040	99.78％99.78%
实施例11Example 11	200200	3030	99.87％99.87%
实施例12Example 12	180180	3535	99.81％99.81%
实施例13Example 13	205205	2525	99.9％99.9%
实施例14Example 14	180180	3030	99.84％99.84%
实施例15Example 15	220220	2020	99.92％99.92%
实施例16Example 16	180180	5050	99.7％99.7%
实施例17Example 17	152152	4040	99.69％99.69%
实施例18Example 18	5050	3030	97％97%
实施例19Example 19	8080	9090	97.8％97.8%
实施例20Example 20	128128	9090	99.63％99.63%
对比例1Comparative Example 1	6060	300300	97.1％97.1%
对比例2Comparative Example 2	7070	100100	97.5％97.5%
对比例3Comparative Example 3	8080	180180	97.96％97.96%
对比例4Comparative Example 4	5050	500500	96％96%

It can be seen from Table 3 that:

1. Compared with the comparative examples in Examples 1 to 17 and Example 19, the batteries of the examples have a larger number of cycles and a smaller volume expansion rate, indicating that the negative pole piece of the electrochemical device satisfies the requirements of the present application. In the technical solution, the cycle performance and safety performance of the electrochemical device can be improved because: on the one hand, the dielectric layer can reduce the electron concentration of the functional layer, prevent lithium ions from forming dendrites at high current density, thereby inhibiting lithium dendrites In addition, the dielectric layer can also reduce the electron concentration on the surface of the functional layer, forcing lithium ions to deposit inside the functional layer, thus reducing the formation of lithium dendrites at the negative interface; on the other hand, the lithium wetting material can also induce lithium The ions are deposited inside the functional layer to reduce the formation of lithium dendrites at the negative electrode interface; in addition, the three-dimensional skeleton formed by the stacking of the conductive layer and the dielectric layer can reduce the extrusion and expansion damage of the negative electrode pole pieces by the lithium dendrites formed in the functional layer. Alleviate the volume expansion of the negative pole piece during the cycle; although the cycle life of Example 18 is poor compared with the comparative examples with pre-supplementation of lithium, the coulomb of Example 18 without pre-supplementation of lithium Compared with Comparative Example 1 and Comparative Example 2, the efficiency is not much different, so it shows that the functional layer of the present application can inhibit the formation of lithium dendrites, thereby reducing the consumption of lithium ions, thereby helping to improve the Coulomb efficiency of the electrochemical device; Compared with Comparative Example 1 and Comparative Example 2, Comparative Example 3 includes a lithium wetting material, and the presence of the lithium wetting material can further inhibit the formation of lithium dendrites and further reduce the consumption of lithium ions. The Coulombic efficiency of chemical devices has been improved;

2. Compared with Example 1 and 3, the battery of Example 3 has a larger number of cycles and a smaller volume expansion. When the content of the lithium wetting material is gradually decreased in the stacking direction, the cycle life of the electrochemical device is affected. The improvement of safety performance and safety performance is better, because the higher content of lithium wetting material in the region near the current collector can more effectively induce lithium ions to enter the functional layer to deposit, inhibit the formation of lithium dendrites at the negative electrode interface, so the electrochemical device It has better cycle life and safety performance; the same conclusion can also be drawn from the comparison of Example 4 and Example 6;

3. Compared with Example 11, the battery of Example 9 shows a smaller volume expansion rate, and the safety performance of the electrochemical device is better. The reason is that the lithium wetting material is distributed in the conductive layer, so the functional When the first edge layer and/or the second edge layer of the layer is a dielectric layer, lithium ions are more inclined to be deposited in the inner conductive layer, thereby inhibiting the formation of lithium branches at the negative electrode interface and improving the safety performance of the electrochemical device;

4. Compared with Example 9 and Example 10, the battery of Example 9 has better cycle life and safety performance. The reason is that when the layer of the functional layer closest to the negative electrode interface is a dielectric layer, the dielectric layer can Effectively inhibit the formation of interfacial lithium dendrites;

5. Compared with Example 15, the cycle number of the battery obtained in Example 18 is significantly larger than that in Example 15. This is because when lithium metal is included in the functional layer of the negative pole piece, lithium metal can supplement the cycle process. Therefore, the cycle life of electrochemical devices can be significantly improved;

6. Compared with the other examples, Example 19 shows that the battery obtained in Example 19 has a small number of cycles and a large volume expansion rate, which shows that the cycle performance and safety performance of the battery are worse. This is because the functional layer in the other examples is The stacking direction is perpendicular to the extension direction of the current collector, and the dielectric layer can more effectively reduce the electron concentration of the functional layer and inhibit the formation of lithium dendrites at the anode interface, thereby improving the cycle life and safety performance of the electrochemical device.

7. Compared with Example 13, Example 16 and Example 17 have worse cycle performance and safety performance than Example 13, because the content of lithium wetting material is too high (Example 13). 17), the structural stability of the functional layer is reduced, which is not conducive to the improvement of the cycle life and safety performance of the electrochemical device, and the energy density of the electrochemical device will also be affected; Therefore, when the quality of the lithium-wetting material is controlled to be 30% to 60% of the quality of the functional layer, it is more beneficial to improve the cycle life and safety of electrochemical devices. performance;

8. Compared with Example 13, Example 20 has poor cycle performance and safety performance of the electrochemical device obtained in Example 20. The reason is that the porosity of the functional layer is low, and lithium cannot smoothly enter the functional layer for deposition. Therefore, lithium tends to be deposited on the negative electrode interface, and it is easy to form interfacial lithium dendrites, which is not conducive to the cycle performance and safety performance of electrochemical devices.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: The technical solutions described in the foregoing embodiments can still be modified, or some or all of the technical features thereof can be equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present application. scope.

Claims

A negative pole piece, wherein the negative pole piece comprises a functional layer; the functional layer comprises M conductive layers and N dielectric layers arranged in layers, and the conductive layers comprise a lithium wetting material;

Among them, M≥1, N≥1.
The negative electrode sheet according to claim 1, wherein the content of the lithium wetting material is distributed in a gradient in the stacking direction.
The negative pole piece according to claim 1 or 2, wherein the negative pole piece further comprises a lithium metal layer or a current collector, the functional layer is provided on the functional surface of the lithium metal layer or the functional surface of the current collector and The extending direction of the lithium metal layer or the extending direction of the current collector is perpendicular to the stacking direction;

The content of the lithium wetting material is gradually decreasing in a direction away from the lithium metal layer or current collector.
The negative pole piece according to any one of claims 1-3, wherein the M conductive layers and the N dielectric layers are alternately stacked.
The negative pole piece according to any one of claims 1-4, wherein the first edge layer and/or the second edge layer of the functional layer is a dielectric layer.
The negative pole piece according to claim 1, wherein the electrical conductivity of the conductive layer is 10 -7 to 10 6 S/cm, and/or,

The electrical conductivity of the dielectric layer is less than 10 -8 S/cm.
The negative pole piece according to any one of claims 1-6, wherein the porosity of the functional layer is 5% to 90%, optionally 50% to 90%.
The negative pole piece according to any one of claims 1-7, wherein the mass of the lithium wetting material is 5% to 95% of the mass of the functional layer, and optionally 30% to 60%.
The negative pole piece according to any one of claims 1-8, wherein the functional layer further comprises lithium metal, and the content of the lithium metal in the functional layer is 0.25 mg/cm 2 to 25 mg/cm 2 .
An electrochemical device, wherein the electrochemical device comprises the negative electrode plate of any one of claims 1-9.
An electronic device, wherein the driving source or energy storage unit of the electronic device is the electrochemical device of claim 10 .