Negative electrode sheet, battery, and energy storage device

Abstract

The application relates to the technical field of batteries, in particular to a negative electrode sheet, a battery and an energy storage device. The negative electrode sheet comprises a current collector, an active material layer arranged on the current collector, the active material layer comprises first hard carbon material and second hard carbon material, the Dv50 of the first hard carbon material is 4 micrometers to 7 micrometers, the Dv50 of the second hard carbon material is less than the Dv50 of the first hard carbon material, the cross-sectional area proportion of the first hard carbon material in the active material layer is 15% to 45%, and the porosity of the negative electrode sheet is 1% to 10%.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a negative electrode sheet, a battery, and an energy storage device. Background Technology

[0002] Hard carbon materials are promising electrode materials that can be used as negative electrode materials in batteries. However, due to the limitations of the precursors used in the preparation of hard carbon materials, it is difficult to achieve both high capacity and high compaction density simultaneously. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention discloses a negative electrode sheet and its preparation method, as well as an energy storage device. Without affecting the capacity advantages of hard carbon materials, it increases their compaction density, thereby improving the volumetric energy density of the battery and optimizing battery performance.

[0004] In a first aspect, this application provides a negative electrode sheet, the negative electrode sheet comprising:

[0005] current collector;

[0006] An active material layer is disposed on the current collector; the active material layer includes a first hard carbon material and a second hard carbon material, the Dv50 of the first hard carbon material is 4μm to 7μm, the Dv50 of the second hard carbon material is smaller than the Dv50 of the first hard carbon material, and the cross-sectional area of ​​the first hard carbon material in the active material layer accounts for 15% to 45%.

[0007] The porosity of the negative electrode sheet is 1% to 10%.

[0008] Furthermore, the first hard carbon material is at least one of spherical or near-spherical particles, the second hard carbon material is a three-dimensional geometric block particle, and the Dv50 of the second hard carbon material is less than 4 μm.

[0009] Furthermore, the average shape factor F of the first hard carbon material is ≥0.75, and the average shape factor F = 4πA / P 2 Where A is the cross-sectional area of ​​the first hard carbon material and P is the cross-sectional perimeter of the first hard carbon material.

[0010] Further, by mass percentage, the hard carbon material comprises 60wt% to 80wt% of the first hard carbon material and 20wt% to 40wt% of the second hard carbon material; wherein the Dv50 of the second hard carbon material is 1.5μm to 3μm.

[0011] Furthermore, the hard carbon material also includes a third hard carbon material, which is a spherical or near-spherical particle, and the Dv50 of the third hard carbon material is 2μm to 4μm;

[0012] The Dv50 of the second hard carbon material is less than or equal to 2 μm;

[0013] The hard carbon material comprises, by mass percentage, 65 wt% to 75 wt% of the first hard carbon material, 10 wt% to 30 wt% of the second hard carbon material, and 5 wt% to 15 wt% of the third hard carbon material.

[0014] Furthermore, the Dn10 of the first hard carbon material is 0.3 μm to 0.5 μm.

[0015] Furthermore, the Dn10 of the second hard carbon material is 0.3 μm to 0.5 μm.

[0016] Furthermore, the Dn10 of the third hard carbon material is 0.45 μm to 0.55 μm.

[0017] Furthermore, the porosity of the negative electrode sheet is 4% to 6%; and / or,

[0018] The compacted density of the negative electrode sheet is greater than or equal to 0.98 g / cm³. 3 .

[0019] Furthermore, the first hard carbon material and the second hard carbon material are obtained by precursor preparation, wherein the precursor includes one or more of biomass-based precursors, resin-based precursors, pitch-based precursors, and coal-based precursors.

[0020] Secondly, this application provides a battery comprising: a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode to form a cell, and the electrolyte is injected into the cell, wherein the negative electrode is the negative electrode as described in the first aspect.

[0021] Thirdly, this application provides an energy storage device, which includes a negative electrode as described in the first aspect, or the energy storage device includes a battery as described in the second aspect.

[0022] Compared with the prior art, the beneficial effects of this application are as follows:

[0023] This application, through in-depth research on the particle size distribution characteristics of hard carbon materials, their proportion of cross-sectional area in the active material layer, and the corresponding porosity of the negative electrode sheet, creatively discovered that by using a first hard carbon material with a Dv50 of 4μm to 7μm as the main active material in the active material layer, and controlling its proportion of cross-sectional area in the active material layer within the range of 15% to 45%, and the corresponding porosity of the negative electrode sheet being 1% to 10%, the negative electrode sheet can have a higher compaction density without affecting the capacity performance of the hard carbon material itself. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the negative electrode sheet in an embodiment of this application;

[0026] Figure 2 yes Figure 1 Enlarged schematic diagram of the structure at point A;

[0027] Figure 3 This is a schematic diagram corresponding to the method for measuring the first hard carbon material in the embodiments of this application;

[0028] Figure 4 This is a schematic diagram corresponding to the method for measuring the second hard carbon material in the embodiments of this application;

[0029] Figure 5 This is a schematic diagram of the structure of a residential energy storage system according to an embodiment of this application;

[0030] Figure 6 This is a schematic diagram of the structure of an energy storage system according to an embodiment of this application.

[0031] Reference numerals: 1. Current collector; 2. Active material layer; 21. First hard carbon material; 22. Second hard carbon material; 100. Energy storage system; 10. Energy storage device; 20. Power conversion device; 30. First user load; 40. Second user load; 50. High-voltage cable; 60. First power conversion device; 70. Second power conversion device. Detailed Implementation

[0032] In this invention, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing the invention and its embodiments, and are not intended to limit the indicated devices, elements, or components to having a specific orientation, or to be constructed and operated in a specific orientation.

[0033] Furthermore, some of the aforementioned terms, besides indicating direction or positional relationships, may also have other meanings. For example, the term "above" may, in certain circumstances, indicate a dependency or connection. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0034] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0035] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, elements, or components (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, elements, or components. Unless otherwise stated, "a plurality of" means two or more.

[0036] Hard carbon materials possess advantages such as wide availability and superior low-temperature rate performance, making them suitable as negative electrode active materials in batteries (e.g., lithium-ion and sodium-ion batteries). However, due to the different properties of various precursor materials used in the preparation of hard carbon materials, it is often difficult for hard carbon materials to simultaneously possess excellent capacity performance and compaction density. Some hard carbon materials prepared from certain precursors exhibit low capacity but high compaction density; others exhibit high capacity but low compaction density. Therefore, maintaining the high capacity advantage of hard carbon materials requires achieving a high compaction density, which leads to a decrease in the volumetric energy density of the battery. This is detrimental to the industrial application of hard carbon materials in battery products.

[0037] To address the aforementioned issues, this application provides a negative electrode sheet, a battery, and an energy storage device, which can effectively improve the compaction density of the negative electrode sheet without affecting the capacity performance of the hard carbon material, thereby increasing the volumetric energy density of the battery and optimizing battery performance.

[0038] The first aspect is the combination Figure 1 and Figure 2 As shown, Figure 1 This is a schematic diagram of the structure of the negative electrode sheet in an embodiment of this application. To facilitate understanding of the technical solution of this application embodiment, a portion of the internal material of the active material layer 2 is shown. Figure 2 yes Figure 1 An enlarged schematic diagram of the structure at point A. This application provides a negative electrode sheet, including a current collector 1 and an active material layer 2 disposed on the current collector 1. The active material layer 2 includes a first hard carbon material 21 and a second hard carbon material 22 as active materials. The first hard carbon material 21 has a diameter (Dv50) of 4 μm to 7 μm, and the second hard carbon material 22 has a smaller Dv50 than the first hard carbon material 21. The cross-sectional area of ​​the first hard carbon material 21 in the active material layer 2 accounts for 15% to 45%, and the porosity of the negative electrode sheet is 1% to 10%.

[0039] It is understood that hard carbon materials are active materials capable of reversibly inserting and deintercalating lithium ions (or sodium ions, etc.) and can directly participate in electrochemical reactions. Therefore, in this embodiment, the active material layer 2 includes a first hard carbon material 21 and a second hard carbon material 22, meaning that these hard carbon materials are the main components of the active material layer 2. However, in addition to hard carbon materials, the active material layer 2 may also include other additives such as binders, conductive agents, and dispersants in conventional amounts. Compared to hard carbon materials, these additives have a lower impact on the compaction density of the negative electrode sheet, therefore this application does not limit the use of these additives. Furthermore, the active material layer 2 can be disposed on one side or both sides of the current collector 1.

[0040] Furthermore, the Dv50 of the first hard carbon material 21 is 4 μm to 7 μm, including any value within this range, for example, the Dv50 of the first hard carbon material 21 is 4 μm, 5 μm, 6 μm, or 7 μm. The cross-sectional area percentage of the first hard carbon material 21 in the active material layer 2 is 15% to 45%, including any value within this range, for example, the cross-sectional area percentage of the first hard carbon material 21 in the active material layer 2 is 15%, 20%, 25%, 30%, 35%, 40%, or 45%. The porosity of the negative electrode sheet is 1% to 10%, including any value within this range, for example, the porosity of the negative electrode sheet is 1%, 2%, 3%, 5%, 8%, or 10%.

[0041] This application, through in-depth research on the particle size distribution characteristics of hard carbon materials, their proportion of cross-sectional area in the active material layer 2, and the corresponding porosity of the negative electrode sheet, creatively discovered that by using a first hard carbon material 21 with a Dv50 of 4μm to 7μm as the main active material in the active material layer 2, and controlling its proportion of cross-sectional area in the active material layer 2 within the range of 15% to 45% and the corresponding porosity of the negative electrode sheet within the range of 1% to 10%, the negative electrode sheet can have a higher compaction density without affecting the capacity performance of the hard carbon material itself.

[0042] The particle size distribution characteristics of the aforementioned hard carbon materials, their proportion of cross-sectional area in the active material layer 2, and the porosity of the negative electrode sheet all have a significant and close influence on optimizing the densest packing of hard carbon materials in the active material layer 2 and the utilization of the gap space formed between adjacent active materials. Given that the first hard carbon material 21, with a Dv50 of 4μm to 7μm, accounts for 15% to 45% of the cross-sectional area in the active material layer 2, and the second hard carbon material 22 has an even smaller Dv50, it can be seen that the relatively larger first hard carbon material 21 plays a dominant role in the active material layer 2. This is due to two factors: firstly, the capacity performance of the first hard carbon material 21 is utilized; and secondly, it is effectively packed as large particles to achieve a certain density distribution in the active material layer 2.

[0043] Simultaneously, because the Dv50 of the second hard carbon material 22 is smaller, and the porosity of the negative electrode sheet is 1% to 10%, the densest packing mode of the hard carbon materials in the active material layer 2 is as follows: large-sized particles of the first hard carbon material 21 are packed together to form certain gap spaces, and small-sized second hard carbon material 22 is packed in these gap spaces, improving the utilization of the gap spaces, optimizing the densest packing mode, and thus increasing the compaction density. Furthermore, although the Dv50 of the first hard carbon material 21 is larger than that of the second hard carbon material 22, the Dv50 level of the first hard carbon material 21 is 4μm to 7μm, less than 10μm, and it is still a relatively small particle size overall. Therefore, it can better fill the active material layer 2 and improve the compaction density.

[0044] Therefore, this embodiment of the application, through the combination of the above-mentioned factors, can both utilize the capacity performance of the first hard carbon material 21 with a Dv50 of 4μm to 7μm within a specific proportion range, and fill the gaps between the first hard carbon materials 21 with the second hard carbon material 22 through the cooperation between the second hard carbon material 22 and the first hard carbon material 21 with specific cross-sectional proportions and particle size distribution characteristics, thereby improving the space utilization of the active material layer 2. In addition, the second hard carbon material 22, due to its smaller particle size, provides shorter channels for the insertion and extraction of lithium ions (or sodium ions), which is beneficial to further improve the kinetic performance of the battery.

[0045] Furthermore, the first hard carbon material 21 is at least one of spherical particles or near-spherical particles, the second hard carbon material 22 is a three-dimensional geometric block particle, and the Dv50 of the second hard carbon material 22 is less than 4 μm.

[0046] Among them, for the first hard carbon material, 21 types of spherical particles are defined as particles with a shape approximately spherical, such as ellipsoidal particles or irregular pebble-like particles. When measuring the equivalent diameter of these spherical particles using a scanning electron microscope, the one-dimensional width of the particles can be measured in different directions, and then the average of the measured one-dimensional widths is calculated to obtain the equivalent diameter. For example... Figure 3 As shown, the one-dimensional width of the quasi-spherical particle is measured in the first direction to obtain the first one-dimensional width x1, and the one-dimensional width of the quasi-spherical particle is measured in the second direction to obtain the second one-dimensional width x2. The equivalent diameter x is obtained by averaging x1 and x2.

[0047] The second hard carbon material 22 is a three-dimensional geometric block particle, which refers to a block particle composed of multiple polygons or a combination of polygons and curved surfaces. These block particles have numerous edges and planes due to the polygonal shape of their outer surface. For example, three-dimensional geometric block particles can be regular or irregular cubes, hexahedrons, octahedrons, or pyramids, etc. When using a scanning electron microscope to measure the equivalent diameter of these three-dimensional geometric block particles, the one-dimensional width of the particle can be measured in different directions, and then the average of the measured one-dimensional widths is calculated to obtain the equivalent diameter. For example... Figure 4 As shown, the one-dimensional width of the three-dimensional geometric block particle is measured in the first direction to obtain the first one-dimensional width y1, and the one-dimensional width of the three-dimensional geometric block particle is measured in the second direction to obtain the second one-dimensional width y2. The equivalent diameter y is obtained by averaging y1 and y2.

[0048] For example, in one optional embodiment, the first hard carbon material 21 includes both spherical particles and near-spherical particles; the second hard carbon material 22 includes irregular cubic, hexahedral, and octahedral block particles. In another optional embodiment, the first hard carbon material 21 is near-spherical particles, and the second hard carbon material 22 includes irregular cubic and hexahedral block particles.

[0049] Since the first hard carbon material 21 is spherical or near-spherical, the gaps between adjacent first hard carbon materials 21 often have a shape characterized by a large central space and narrow gaps at the edges. The second hard carbon material 22, with a smaller Dv50, is a three-dimensional geometric block particle with more edges and angles suitable for narrow spaces. Therefore, these three-dimensional geometric block particles have a higher degree of matching with the gaps between adjacent first hard carbon materials 21, filling more narrow gaps, resulting in fewer pores and higher compaction density in the negative electrode sheet. Simultaneously, since the contact between the spherical or near-spherical first hard carbon material 21 and the three-dimensional geometric block particles is mostly point-to-plane contact, it is more stable than the point-to-point contact between large spherical particles and small spherical particles. This helps maintain the structural stability of the active material layer 2 during processing and reduces problems such as misalignment and deformation of the first hard carbon material 21 and the second hard carbon material 22 caused by processing conditions (e.g., applying pressure to the active material layer 2).

[0050] Furthermore, the average shape factor F of the first hard carbon material 21 is ≥0.75, and the average shape factor F = 4πA / P 2 Where A is the cross-sectional area of ​​the first hard carbon material 21, and P is the perimeter of the cross-section of the first hard carbon material 21. For example, F can be 0.75, 0.80, 0.85, 0.90, 0.95, 0.99, or 1. A higher average shape factor indicates that the first hard carbon material 21 is closer to a sphere, has better isotropy, and better particle structure stability, which is beneficial for further improving the structural stability of the negative electrode sheet during processing.

[0051] Specifically, the longitudinal cross-sectional area of ​​the first hard carbon material along the thickness direction of the active material layer and the transverse cross-sectional area of ​​the first hard carbon material along the thickness direction perpendicular to the active material layer are measured and calculated, and the average of the longitudinal and transverse cross-sectional areas is used to obtain the cross-sectional area. Similarly, the perimeter of the longitudinal cross-section of the first hard carbon material along the thickness direction of the active material layer and the perimeter of the transverse cross-section of the first hard carbon material along the thickness direction perpendicular to the active material layer are measured and calculated, and the average of the longitudinal and transverse cross-sectional perimeters is used to obtain the cross-sectional perimeter.

[0052] In one optional embodiment, the hard carbon material comprises, by mass percentage, 60 wt% to 80 wt% of a first hard carbon material 21 and 20 wt% to 40 wt% of a second hard carbon material 22; wherein the Dv50 of the second hard carbon material 22 is 1.5 μm to 3 μm. For example, the hard carbon material comprises 60 wt% of the first hard carbon material 21 and 40 wt% of the second hard carbon material 22, or the hard carbon material comprises 70 wt% of the first hard carbon material 21 and 30 wt% of the second hard carbon material 22, or the hard carbon material comprises 75 wt% of the first hard carbon material 21 and 25 wt% of the second hard carbon material 22. Furthermore, the Dv50 of the second hard carbon material 22 being 1.5 μm to 3 μm includes any value within this range, for example, the Dv50 of the second hard carbon material 22 being 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, or 3.0 μm.

[0053] In this embodiment, the proportion of the first hard carbon material 21 with a Dv50 of 4μm to 7μm is higher than that of the second hard carbon material 22 with a Dv50 of 1.5μm to 3μm. On the one hand, both the relatively large particle size of the first hard carbon material 21 and the relatively small particle size of the second hard carbon material 22 result in an overall particle size of less than 10μm. This indicates that the active material layer 2 in this embodiment generally uses small-particle hard carbon material to better improve compaction density. In particular, the particle size of the second hard carbon material 22 is less than or equal to 3μm; these three-dimensional geometric block particles within this particle size range contribute significantly to improving compaction density. On the other hand, the spherical or near-spherical first hard carbon material 21 is used in greater quantities than the three-dimensional geometric block-shaped second hard carbon material 22, indicating that the active material layer 2 as a whole still uses the first hard carbon material 21 with better isotropy as the main hard carbon material component, and the second hard carbon material 22 with better anisotropy is used to fill the gap space of the first hard carbon material 21. This does not affect the capacity performance of the negative electrode sheet, can maintain good structural stability, and can also provide better compaction density.

[0054] In another optional embodiment, the hard carbon material further includes a third hard carbon material, which is a spherical or near-spherical particle with a Dv50 of 2 μm to 4 μm, and the second hard carbon material 22 has a Dv50 less than or equal to 2 μm. By mass percentage, the hard carbon material comprises 65 wt% to 75 wt% of the first hard carbon material 21, 10 wt% to 30 wt% of the second hard carbon material 22, and 5 wt% to 15 wt% of the third hard carbon material.

[0055] The Dv50 of the third hard carbon material is 2μm to 4μm, including any value within this range. For example, the Dv50 of the third hard carbon material is 2μm, 2.5μm, 3μm, 3.5μm, or 4μm. The Dv50 of the second hard carbon material 22 is less than or equal to 2μm, including any value within this range. For example, the Dv50 of the second hard carbon material 22 is 1μm, 1.2μm, 1.5μm, 1.8μm, or 2μm. Furthermore, the composition of the hard carbon material can be, for example, 65wt% of the first hard carbon material 21, 30wt% of the second hard carbon material 22, and 5wt% of the third hard carbon material; or 70wt% of the first hard carbon material 21, 25wt% of the second hard carbon material 22, and 5wt% of the third hard carbon material; or 75wt% of the first hard carbon material 21, 10wt% of the second hard carbon material 22, and 15wt% of the third hard carbon material, and so on.

[0056] Compared to hard carbon materials that only include first hard carbon material 21 and second hard carbon material 22, the addition of Dv50 to the third hard carbon material between the first hard carbon material 21 and the second hard carbon material 22 can provide a greater gradation gradient, thereby further improving the filling effect on the gap space between adjacent first hard carbon materials 21, and ensuring a higher degree of filling of the gap space.

[0057] Furthermore, the Dn10 of the first hard carbon material 21 is 0.3 μm to 0.5 μm.

[0058] Furthermore, the Dn10 of the second hard carbon material 22 is 0.3 μm to 0.5 μm.

[0059] Furthermore, the Dn10 of the third hard carbon material is 0.45 μm to 0.55 μm.

[0060] When the Dn of each hard carbon material is preferably controlled within the above-mentioned range, it is beneficial to further control the porosity of the negative electrode sheet within the range of the application, and reduce the impact on the compaction density of the negative electrode sheet caused by the increase in porosity.

[0061] It should be noted that, in the embodiments of this application, the Dv50, Dn10, cross-sectional area ratio in the active material layer 2, and average shape factor of each hard carbon material, as well as the porosity and compaction density of the negative electrode sheet, can be determined by testing and calculation using methods or equipment known in the art.

[0062] For example, the microstructure and morphology of hard carbon materials can be analyzed using a particle size and shape analyzer to obtain the particle size of the hard carbon materials, and then obtain indicators such as Dv50 and Dn10; the cross-sectional area and cross-sectional perimeter of the hard carbon materials can also be calculated, and further calculated to obtain indicators such as the average shape factor and the porosity of the negative electrode sheet.

[0063] Preferably, the porosity of the negative electrode sheet is 4% to 6%. When the porosity of the negative electrode sheet is optimized within the range of 4% to 6%, especially when it is further optimized to 5%, the effect of increasing the compaction density and the wetting rate of the electrolyte on the active material layer 2 can be better balanced.

[0064] Furthermore, the compaction density of the negative electrode sheet is greater than or equal to 0.98 g / cm³. 3 This application finds that with the effective increase of compaction density, not only is the volumetric energy density of the battery improved, but the capacity retention rate is also improved to a certain extent. It should also be noted that for negative electrode sheets using graphite as the negative electrode active material, the interlayer interaction force of graphite is stronger, making it easier to achieve a higher compaction density. However, the solution in this application uses a negative electrode sheet with hard carbon material as the main active material, comprehensively controlling factors such as the particle size, cross-sectional area ratio, and porosity of different hard carbon materials to achieve a negative electrode sheet density of 0.98 g / cm³. 3 The above compaction density is not easy to achieve.

[0065] Optionally, the first hard carbon material 21 and the second hard carbon material 22 are obtained by a precursor preparation, wherein the precursor includes one or more of biomass-based precursors, resin-based precursors, pitch-based precursors, and coal-based precursors.

[0066] Pitch-based or coal-based precursors, due to their high degree of carbonization and alteration, are beneficial for increasing the compaction density of the resulting hard carbon materials. However, this also results in hard carbon materials with excessively low capacity. On the other hand, biomass-based or resin-based precursors produce hard carbon materials with high capacity, but their compaction density is relatively low, which leads to a decrease in the volumetric energy density of the final battery.

[0067] In this embodiment, the precursor of the first hard carbon material 21 is preferably a biomass-based precursor or a resin-based precursor to obtain higher capacity characteristics from the material properties. In particular, in this embodiment, the proportion of the first hard carbon material 21 is relatively high, which is more conducive to giving full play to its high capacity advantage. As for the compaction density, since the cross-sectional area of ​​the first hard carbon material 21 with a Dv50 of 4μm to 7μm in this embodiment accounts for 15% to 45% in the active material layer 2, and the gap space between adjacent first hard carbon materials 21 is filled by the second hard carbon material 22 with a smaller Dv50, the compaction density can be increased without affecting the capacity, thereby improving the volumetric energy density of the battery.

[0068] Secondly, embodiments of this application provide a battery, including: a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is disposed between the positive electrode and the negative electrode to form a battery cell, and the electrolyte is injected into the battery cell. The negative electrode is the same as the negative electrode in the first aspect.

[0069] Thirdly, embodiments of this application also provide an energy storage device 10, which includes the battery separator membrane described in the first or second aspect.

[0070] Taking electrochemical energy storage as an example, this application provides an energy storage device 10. The energy storage device 10 is equipped with a set of chemical batteries. It mainly uses the chemical elements in the batteries as energy storage medium. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage medium. Simply put, the electrical energy generated by wind and solar energy is stored in the chemical batteries. When the use of external electrical energy reaches its peak, the stored electricity is released for use, or transferred to places with a shortage of electricity for use.

[0071] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding types of energy storage devices 10 include:

[0072] (1) Large-scale energy storage power stations applied to wind power and photovoltaic power stations can assist renewable energy power generation in meeting grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power regulation power source on the power supply side, energy storage power stations can achieve load matching of power in time and space, enhance the absorption capacity of renewable energy, reduce instantaneous power changes, reduce the impact on the power grid, improve the absorption of new energy power generation, and are of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation.

[0073] (2) Energy storage containers applied on the grid side mainly function as peak shaving, frequency regulation and grid congestion relief. In terms of peak shaving, they can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption.

[0074] (3) Small energy storage cabinets applied to the electricity consumption side mainly function as self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improvement of power supply reliability. Depending on the application scenario, electricity consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices 10, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley pricing, by charging the energy storage system 100 when the electricity price is low and discharging the energy storage system 100 when the electricity price is high, peak-valley price arbitrage can be achieved, reducing electricity costs. In addition, industrial enterprises subject to two-part tariffs can use the energy storage system 100 to store energy during off-peak hours and discharge during peak loads, thereby reducing peak power and the maximum demand declared, achieving the goal of reducing capacity electricity costs. Household photovoltaics with energy storage can improve the level of self-consumption of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations is driven. Given that photovoltaic power generation occurs during the day, while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0075] Please see Figure 5 , Figure 5 This is a schematic diagram of a residential energy storage system 100 according to an embodiment of this application. The residential energy storage system 100 includes a power conversion device 20 (photovoltaic panel), a first user load 30 (streetlight), a second user load 40 (e.g., household appliances such as air conditioners), and an energy storage device 10. The energy storage device 10 is a small energy storage box that can be wall-mounted to an outdoor wall. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 10 stores this electrical energy and supplies it to streetlights and household appliances during peak electricity prices, or provides power during power outages / power interruptions.

[0076] Please see Figure 6 , Figure 6 This is a schematic diagram of the structure of an energy storage system 100 according to an embodiment of this application, and this application Figure 5 The embodiments are illustrated using a shared energy storage scenario on the generation / distribution side as an example. The energy storage device 10 of this application is not limited to the energy storage scenario on the generation / distribution side.

[0077] This application provides an energy storage system 100, which includes a high-voltage cable 50, a first power conversion device 60, a second power conversion device 70, and the energy storage device 10 provided in this application. During power generation, the first power conversion device 60 and the second power conversion device 70 convert other forms of energy into electrical energy, which is then connected to the high-voltage cable and supplied to the power consumption side of the distribution network. When the power load is low and the first power conversion device 60 and the second power conversion device 70 generate excess power, the excess electricity is stored in the energy storage device 10, reducing wind and solar curtailment rates and improving the absorption of new energy power generation. When the power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 10, along with the high-voltage cable 50, in a grid-connected mode to supply power to the power consumption side. This provides various services for power grid operation, such as peak shaving, frequency regulation, and backup, fully leveraging the peak shaving function of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure on the power grid.

[0078] Optionally, the first power conversion device 60 and the second power conversion device 70 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electrical energy.

[0079] The number of energy storage devices 10 can be multiple, and the multiple energy storage devices 10 can be connected in series or in parallel. The multiple energy storage devices 10 are supported and electrically connected by an isolation plate (not shown). In this embodiment, "multiple" means two or more. An energy storage box can also be provided on the outside of the energy storage device 10 to house the energy storage device 10.

[0080] Optionally, the energy storage device 10 may include, but is not limited to, battery modules, battery packs, battery systems, etc. The actual application form of the energy storage device 10 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 10. This application embodiment only uses a multi-cell battery as an example for illustration. When the energy storage device 10 is a single battery, the energy storage device 10 may be at least one of cylindrical batteries, prismatic batteries, etc.

[0081] The solution of this application will be further described below with reference to specific embodiments and experimental data.

[0082] Example 1

[0083] This embodiment provides a negative electrode sheet, the preparation method of which includes the following steps:

[0084] Spherical and near-spherical first hard carbon materials and three-dimensional geometric block-shaped second hard carbon materials are weighed according to a mass ratio and then placed into a VC mixer for physical mixing, for example, running at 500 r / min for 2 hours until the hard carbon materials are completely mixed, thereby obtaining the negative electrode active material. The physical properties of the above negative electrode active material are shown in Table 1 below.

[0085] The above-mentioned negative electrode active material, thickener carboxymethyl cellulose, conductive agent conductive carbon black, and binder styrene-butadiene rubber were mixed in a mass ratio of 95:2:1.5:1.5. Deionized water was added, and the mixture was stirred evenly to obtain a negative electrode slurry with a solid content of 30%. The negative electrode slurry was uniformly coated on one surface of a copper foil, and then vacuum dried. After rolling and stamping, a circular negative electrode sheet was obtained.

[0086] Examples 2-3

[0087] Except for adjusting the first and second hard carbon materials according to the physical properties of the negative electrode active materials in Table 1, the rest is the same as in Example 1.

[0088] Examples 4-6

[0089] Except for adding spherical and near-spherical third hard carbon materials, and adjusting the first and second hard carbon materials according to the physical property parameters of the negative electrode active materials in Table 1, the rest is the same as in Example 1.

[0090] Comparative Example 1

[0091] Except for the absence of a second hard carbon material and the adjustment of the first and second hard carbon materials according to the physical property parameters of the negative electrode active material in Table 1, everything else is the same as in Example 1.

[0092] Comparative Example 2

[0093] Except for adjusting the first and second hard carbon materials according to the physical properties of the negative electrode active materials in Table 1, the rest is the same as in Example 1.

[0094] Comparative Examples 3-4

[0095] Except for adjusting the first and second hard carbon materials according to the physical properties of the negative electrode active materials in Table 1, the rest is the same as in Example 4.

[0096] <Battery Assembly>

[0097] Preparation of electrolyte: In an argon-atmospheric glove box with a moisture content ≤1ppm, ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1:1. Then, sodium salt NaPF6 was added and dissolved in the organic solvent. After thorough mixing, the electrolyte was obtained. The molar concentration of NaPF6 in the electrolyte was 1 mol / L.

[0098] Assembly of coin cell: The circular sodium sheet, the separator (glass fiber membrane with a thickness of 260 μm), and the circular negative electrode sheet of the above embodiments and comparative examples are stacked in sequence, so that the separator is placed between the circular sodium sheet and the negative electrode sheet to play a role in isolation. Then the prepared electrolyte is injected to assemble a 2032 type coin cell.

[0099] After the assembled button cells were left to stand for 12 hours, charge-discharge and other electrical performance tests were conducted.

[0100] Performance Testing

[0101] Resistance testing of hard carbon negative electrode material: The four-probe method was used, and a resistivity meter was used to measure the current and voltage of the negative electrode. The resistivity under different pressures was then calculated, with the unit being Ω. The resistance data in Table 3 are all test results at a pressure of 25 MPa.

[0102] Cyclic performance test: The test temperature was 25℃. The coin cells of the examples and comparative examples were discharged to 0.005V at 0.2C, allowed to stand for 10 minutes, and then charged to 2V at a constant current of 0.2C. The capacity obtained in this step was taken as the initial discharge capacity C0. A 200-cycle test of 0.2C charge / discharge was performed, and the discharge capacity of the 200th cycle was recorded. Cyclic capacity retention rate = (Discharge capacity of the 200th cycle / Initial discharge capacity C0) × 100%.

[0103] Volumetric energy density calculation: Battery volumetric energy density = battery capacity × discharge plateau / volume, the basic unit is Wh / L (watt-hours per liter), where the battery capacity is 2.0V-4V capacity.

[0104]

[0105] Table 1 Physical properties of the negative electrode active material

[0106]

[0107] Table 2. Relevant parameters of the negative electrode sheet.

[0108]

[0109] Table 3 Performance Test Results

[0110] As shown in Tables 1 to 3 above, the compaction density and cycle stability of Examples 1 to 6 are superior to those of Comparative Example 1. This demonstrates that the negative electrode sheet of the present application can effectively improve the compaction density, thereby increasing the volumetric energy density and improving the cycle stability of the battery. Comparing Examples 1 to 6 with Comparative Example 2, it can be seen that although the cross-sectional area of ​​the first hard carbon material in Comparative Example 2 is relatively suitable, the porosity of the negative electrode sheet in Comparative Example 2 is too high, which still leads to a decrease in compaction density, volumetric energy density, and cycle stability. Comparing Examples 1 to 6 with Comparative Example 4, it can be seen that although the porosity of the negative electrode sheet in Comparative Example 4 is relatively small, the cross-sectional area of ​​the first hard carbon material is too high, which still leads to a decrease in compaction density, volumetric energy density, and cycle stability.

[0111] Comparing Examples 1-3 and Examples 4-6, it can be seen that Examples 4-6 exhibit better compaction density and cycle stability, indicating that using the aforementioned first, second, and third hard carbon materials of Dv50 as the negative electrode active material can further improve the compaction density to 1.02 g / cm³. 3 The improvements in volumetric energy density and cycle stability are also more pronounced. In particular, in Example 5, the compaction density increased to 1.05 g / cm³. 3 The level is relatively high.

[0112] The battery separator and its preparation method, as well as the energy storage device disclosed in the embodiments of the present invention, have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the technical solution and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes: current collector; An active material layer is disposed on the current collector; the active material layer includes a first hard carbon material and a second hard carbon material, the first hard carbon material has a Dv50 of 4 μm to 7 μm, the second hard carbon material has a smaller Dv50 than the first hard carbon material, and the cross-sectional area of ​​the first hard carbon material in the active material layer accounts for 15% to 45%; The porosity of the negative electrode sheet is 1%~10%; The average shape factor F of the first hard carbon material is ≥0.75, and the average shape factor F = 4πA / P2, where A is the cross-sectional area of ​​the first hard carbon material and P is the cross-sectional perimeter of the first hard carbon material.

2. The negative electrode sheet according to claim 1, characterized in that, The first hard carbon material is at least one of spherical or near-spherical particles, the second hard carbon material is a three-dimensional geometric block particle, and the Dv50 of the second hard carbon material is less than 4 μm.

3. The negative electrode sheet according to claim 2, characterized in that, The hard carbon material comprises, by mass percentage, 60 wt% to 80 wt% of the first hard carbon material and 20 wt% to 40 wt% of the second hard carbon material; wherein the Dv50 of the second hard carbon material is 1.5 μm to 3 μm.

4. The negative electrode sheet according to claim 2, characterized in that, The hard carbon material also includes a third hard carbon material, which is a spherical or near-spherical particle, and the Dv50 of the third hard carbon material is 2 μm to 4 μm. The Dv50 of the second hard carbon material is less than or equal to 2 μm; The hard carbon material comprises, by mass percentage, 65 wt% to 75 wt% of the first hard carbon material, 10 wt% to 30 wt% of the second hard carbon material, and 5 wt% to 15 wt% of the third hard carbon material.

5. The negative electrode sheet according to claim 1, characterized in that, The Dn10 of the first hard carbon material is 0.3 μm to 0.5 μm; and / or, The Dn10 of the second hard carbon material is 0.3 μm to 0.5 μm; and / or, The active material layer also includes a third hard carbon material, wherein the Dn10 of the third hard carbon material is 0.45 μm to 0.55 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The porosity of the negative electrode sheet is 4%~6%; and / or, The compacted density of the negative electrode sheet is greater than or equal to 0.98 g / cm³. 3 .

7. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, The first hard carbon material and the second hard carbon material are obtained by precursor preparation, and the precursor includes one or more of the following: biomass-based precursor, resin-based precursor, pitch-based precursor, and coal-based precursor.

8. A battery, characterized in that, The battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is disposed between the positive electrode and the negative electrode to form a cell. The electrolyte is injected into the cell. The negative electrode is the negative electrode as described in any one of claims 1 to 7.

9. An energy storage device, characterized in that, The energy storage device includes a negative electrode as described in any one of claims 1 to 7, or the energy storage device includes a battery as described in claim 8.

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