Negative electrode sheet, battery, and energy storage device

Abstract

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

Description

Negative electrode sheet, battery and energy storage device

[0001] Related Cross-Reference

[0002] The present disclosure claims priority to the Chinese patent application No. 2024113883711, filed on September 30, 2024, entitled "Negative electrode sheet, battery and energy storage device", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, in particular to a negative electrode sheet, a battery and an energy storage device. BACKGROUND

[0004] Hard carbon material is an electrode material with good application prospect, which can be used as negative electrode material of a battery. However, due to the material properties of the precursor used for preparing the hard carbon material, it is difficult for the hard carbon material to simultaneously obtain high capacity and high compaction density. SUMMARY

[0005] To solve the above technical problems, the present disclosure discloses a negative electrode sheet and a preparation method thereof, and an energy storage device, which improves the compaction density of the hard carbon material without affecting the capacity advantage of the hard carbon material, thereby improving the volumetric energy density of the battery and optimizing the performance of the battery.

[0006] In a first aspect, the present disclosure provides a negative electrode sheet, comprising:

[0007] a current collector;

[0008] an active material layer disposed on the current collector, the active material layer comprising a first hard carbon material and a second hard carbon material, the Dv50 of the first hard carbon material being 4 μm to 7 μm, the Dv50 of the second hard carbon material being less than the Dv50 of the first hard carbon material, and the cross-sectional area proportion of the first hard carbon material in the active material layer being 15% to 45%;

[0009] The porosity of the negative electrode sheet is 1% to 10%.

[0010] In a second aspect, the present disclosure provides a battery, comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the separator being disposed between the positive electrode sheet and the negative electrode sheet to form an electrode core, and the electrolyte being injected into the electrode core, wherein the negative electrode sheet is the negative electrode sheet according to the first aspect.

[0011] In a third aspect, the present disclosure provides an energy storage device, comprising the negative electrode sheet according to the first aspect, or the energy storage device comprising the battery according to the second aspect.

[0012] Compared with the prior art, the present disclosure has the following advantages:

[0013] The present disclosure is based on the deep research on the particle size distribution characteristics of hard carbon materials, the proportion of the cross-sectional area in the active material layer, and the corresponding negative electrode tab porosity. It is found that when the first hard carbon material with Dv50 of 4-7 μm is used as the main active material in the active material layer, the proportion of the cross-sectional area in the active material layer is controlled within the range of 15-45%, and the corresponding negative electrode tab porosity is 1-10%, the negative electrode tab has a higher compaction density without affecting the capacity performance of the hard carbon material itself. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative labor.

[0015] Fig. 1 is a structural schematic diagram of a negative electrode tab according to an embodiment of the present disclosure;

[0016] Fig. 2 is an enlarged schematic diagram of the structure at A in Fig. 1;

[0017] Fig. 3 is a schematic diagram corresponding to the method for measuring the first hard carbon material according to an embodiment of the present disclosure;

[0018] Fig. 4 is a schematic diagram corresponding to the method for measuring the second hard carbon material according to an embodiment of the present disclosure;

[0019] Fig. 5 is a structural schematic diagram of a household energy storage system according to an embodiment of the present disclosure;

[0020] Fig. 6 is a structural schematic diagram of an energy storage system according to an embodiment of the present disclosure.

[0021] Reference signs: 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, electric energy conversion device; 30, first user load; 40, second user load; 50, high-voltage cable; 60, first electric energy conversion device; 70, second electric energy conversion device. DETAILED DESCRIPTION

[0022] In the present disclosure, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are mainly used for better description of the present disclosure and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0023] In addition, in addition to indicating the orientation or positional relationship, the above-mentioned partial terms can also be used to indicate other meanings, for example, the term "upper" can also be used to indicate a certain dependent relationship or connection relationship in some cases. For those skilled in the art, the specific meaning of these terms in the present disclosure can be understood according to the specific situation.

[0024] In addition, the terms "mounting", "setting", "provided with", "connection", "connected" should be understood broadly. For example, it can be fixed connection, detachable connection, or integral structure; it can be mechanical connection, or electrical connection; it can be direct connection, or indirect connection through intermediate medium, or internal communication between two devices, elements or components. For those skilled in the art, the specific meaning of the above terms in the present disclosure can be understood according to the specific situation.

[0025] In addition, the terms "first", "second" and the like are mainly used to distinguish different devices, elements or components (the specific types and structures can be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise stated, the meaning of "multiple" is two or more.

[0026] Hard carbon materials have the advantages of wide material sources and low temperature rate performance, and are suitable for use as negative active materials of batteries (such as lithium ion batteries, sodium ion batteries, etc.). However, due to the different properties of various precursor materials for preparing hard carbon materials, it is difficult for hard carbon materials to simultaneously have excellent capacity performance and compaction density. Some hard carbon materials prepared from a part of precursors have the characteristics of low capacity but high compaction density; another part of hard carbon materials prepared from precursors have the characteristics of high capacity but low compaction density. It can be seen that if the high capacity advantage of hard carbon materials is to be maintained, it is difficult to obtain a high level of compaction density, which in turn leads to a decrease in the volumetric energy density of the battery, which is not conducive to the industrial application of hard carbon materials in battery products.

[0027] In view of the above problems, the present embodiment 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 improving the volumetric energy density of the battery and optimizing the battery performance.

[0028] In a first aspect, in combination with FIG. 1 and FIG. 2, FIG. 1 is a structural schematic diagram of a negative electrode tab of an embodiment of the present disclosure, in which part of the internal material of the active material layer 2 is shown for the convenience of understanding the technical solutions of the embodiments of the present disclosure; FIG. 2 is an enlarged schematic diagram of the structure at A in FIG. 1. The embodiments of the present disclosure provide a negative electrode tab, which comprises a current collector 1 and an active material layer 2 arranged on the current collector 1. The active material layer 2 comprises first hard carbon material 21 and second hard carbon material 22 as active materials, the Dv50 of the first hard carbon material 21 is 4 μm to 7 μm, the Dv50 of the second hard carbon material 22 is less than the Dv50 of the first hard carbon material 21, the cross-sectional area proportion of the first hard carbon material 21 in the active material layer 2 is 15% to 45%, and the porosity of the negative electrode tab is 1% to 10%.

[0029] It can be understood that the hard carbon material is an active material capable of reversibly embedding and de-embedding lithium ions (or sodium ions, etc.), which can directly participate in electrochemical reactions. Therefore, in the embodiments of the present disclosure, the active material layer 2 comprises the first hard carbon material 21 and the second hard carbon material 22, which means that these hard carbon materials are the main components of the active material layer 2. However, the active material layer 2 can also comprise other auxiliary agents such as conventional amounts of binders, conductive agents, dispersants, etc. in addition to the hard carbon materials. Compared with the hard carbon materials, the influence of these auxiliary agents on the compaction density of the negative electrode tab is relatively low, so the present disclosure does not limit these auxiliary agents. In addition, the active material layer 2 can be arranged on one side or both sides of the current collector 1.

[0030] In addition, the Dv50 of the first hard carbon material 21 is 4 μm to 7 μm, including any point value in the numerical 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 proportion of the first hard carbon material 21 in the active material layer 2 is 15% to 45%, including any point value in the numerical range, for example, the cross-sectional area proportion 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 tab is 1% to 10%, including any point value in the numerical range, for example, the porosity of the negative electrode tab is 1%, 2%, 3%, 5%, 8% or 10%.

[0031] Through in-depth research on the particle size distribution characteristics of the hard carbon material, the proportion of the cross-sectional area of the hard carbon material in the active material layer 2, and the corresponding porosity of the negative electrode tab, the present disclosure has found that when the first hard carbon material 21 with a Dv50 of 4 μm to 7 μm is used as the main active material in the active material layer 2, the cross-sectional area proportion of the first hard carbon material 21 in the active material layer 2 is controlled within the range of 15% to 45%, and the corresponding porosity of the negative electrode tab is 1% to 10%, without affecting the capacity performance of the hard carbon material itself, the negative electrode tab has a higher compaction density.

[0032] The particle size distribution characteristics of the above hard carbon material, its cross-sectional area ratio in the active material layer 2, and the porosity of the negative electrode sheet have important and close effects on optimizing the closest packing mode of the hard carbon material in the active material layer 2 and the utilization degree of the gap space formed between adjacent active materials. According to the cross-sectional area ratio of the first hard carbon material 21 with Dv50 of 4-7 μm in the active material layer 2 being 15-45% and the Dv50 of the second hard carbon material 22 being smaller, it can be known that the first hard carbon material 21 with relatively large size plays a leading role in the active material layer 2, which is based on the capacity performance of the first hard carbon material 21 and effectively packed as large-size particles to be distributed in the active material layer 2 at a certain density.

[0033] At the same time, due to the Dv50 of the second hard carbon material 22 being smaller and the porosity of the negative electrode sheet being 1-10%, the closest packing mode of the hard carbon material in the active material layer 2 is that the first hard carbon material 21 with large size is packed and a certain gap space is formed, and the second hard carbon material 22 with small size is packed in the gap space, thereby improving the utilization of the gap space, optimizing the closest packing mode, and further improving the compaction density. In addition, although the Dv50 of the first hard carbon material 21 is larger than that of the second hard carbon material 22, the Dv50 of the first hard carbon material 21 is 4-7 μm and less than 10 μm, which still belongs to particles with relatively small size as a whole, so that the active material layer 2 can be better filled and the compaction density can be improved.

[0034] Therefore, it can be seen that the embodiments of the present disclosure can utilize the first hard carbon material 21 with Dv50 of 4-7 μm in a specific ratio range to exert the capacity performance of the material itself, and fill the second hard carbon material 22 into the gap space between the first hard carbon material 21 by cooperation between the second hard carbon material 22 and the first hard carbon material 21 with specific cross-sectional ratio and particle size distribution characteristics, thereby improving the space utilization of the active material layer 2. In addition, the second hard carbon material 22 provides a shorter channel for lithium ions (or sodium ions) to insert and extract due to the smaller particles, which is beneficial to further improve the kinetic performance of the battery.

[0035] Further, the first hard carbon material 21 is at least one of spherical particles or spheroidal 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.

[0036] The first hard carbon material 21 is a spherical particle, which means that the particle has a spherical shape. The second hard carbon material 22 is a three-dimensional geometric block particle, which means that the particle is composed of multiple polygons or composed of polygons and curved surfaces together. The equivalent diameter of the spherical particle and the three-dimensional geometric block particle can be measured by a scanning electron microscope. For example, as shown in FIG. 3, the one-dimensional width of the spherical particle is measured in a first direction to obtain a first one-dimensional width x1, and the one-dimensional width of the spherical particle is measured in a second direction to obtain a second one-dimensional width x2. The equivalent diameter x is obtained by averaging x1 and x2. As shown in FIG. 4, the one-dimensional width of the three-dimensional geometric block particle is measured in a first direction to obtain a first one-dimensional width y1, and the one-dimensional width of the three-dimensional geometric block particle is measured in a second direction to obtain a second one-dimensional width y2. The equivalent diameter y is obtained by averaging y1 and y2.

[0037] The second hard carbon material 22 is a three-dimensional geometric block particle, which means that the particle is composed of multiple polygons or composed of polygons and curved surfaces together. The equivalent diameter of the spherical particle and the three-dimensional geometric block particle can be measured by a scanning electron microscope. For example, as shown in FIG. 3, the one-dimensional width of the spherical particle is measured in a first direction to obtain a first one-dimensional width x1, and the one-dimensional width of the spherical particle is measured in a second direction to obtain a second one-dimensional width x2. The equivalent diameter x is obtained by averaging x1 and x2. As shown in FIG. 4, the one-dimensional width of the three-dimensional geometric block particle is measured in a first direction to obtain a first one-dimensional width y1, and the one-dimensional width of the three-dimensional geometric block particle is measured in a second direction to obtain a second one-dimensional width y2. The equivalent diameter y is obtained by averaging y1 and y2.

[0038] For example, in an alternative embodiment, the first hard carbon material 21 includes both spherical particles and spherical-like particles; and the second hard carbon material 22 includes irregular cubic, hexahedral, octahedral and other three-dimensional geometric block particles. In another alternative embodiment, the first hard carbon material 21 is a spherical-like particle, and the second hard carbon material 22 includes irregular cubic and hexahedral and other three-dimensional geometric block particles.

[0039] Since the first hard carbon material 21 is spherical or spheroidal, the gap space formed between adjacent first hard carbon materials 21 tends to have a space shape feature of a large middle space and narrow gaps at the edges. The second hard carbon material 22 with a smaller Dv50 is a three-dimensional geometric block particle, which has more edges and angles suitable for narrow spaces, so that the three-dimensional geometric block particle has a higher matching degree with the gap space of the adjacent first hard carbon material 21, can fill more narrow gaps, and the negative electrode sheet has fewer pores and higher compaction density. At the same time, since the contact between the spherical or spheroidal first hard carbon material 21 and the three-dimensional geometric block particle is mostly point and plane contact, which is more stable than the point and point contact between the large size spherical particle and the small size spherical particle, it is beneficial to maintain the structural stability of the active material layer 2 during processing, and reduce the problems such as dislocation deformation of the first hard carbon material 21 and the second hard carbon material 22 caused by processing conditions (such as applying pressure to the active material layer 2).

[0040] Further, the average shape factor F of the first hard carbon material 21 is ≥0.75, and the average shape factor F = 4πA / P 2 That is, F = 4 x π x A / P 2 Wherein A is the cross-sectional area of the first hard carbon material 21, and P is the cross-sectional perimeter of the first hard carbon material 21. Exemplarily, F is 0.75, 0.80, 0.85, 0.90, 0.95, 0.99 or 1. The higher the average shape factor, the closer the first hard carbon material 21 to the spherical shape, the better the isotropy, and the better the particle structure stability, which is beneficial to further improve the structural stability of the negative electrode sheet during processing.

[0041] Wherein, the longitudinal cross-sectional area of the first hard carbon material along the thickness direction of the active material layer is measured and calculated, and the transverse cross-sectional area of the first hard carbon material perpendicular to the thickness direction of the active material layer is measured and calculated. The average of the above longitudinal cross-sectional area and transverse cross-sectional area is the cross-sectional area. The longitudinal cross-sectional perimeter of the first hard carbon material along the thickness direction of the active material layer is measured and calculated, and the transverse cross-sectional perimeter of the first hard carbon material perpendicular to the thickness direction of the active material layer is measured and calculated. The average of the above longitudinal cross-sectional perimeter and transverse cross-sectional perimeter is the cross-sectional perimeter.

[0042] In an alternative embodiment, the hard carbon material comprises 60wt% to 80wt% of the first hard carbon material 21 and 20wt% to 40wt% of the second hard carbon material 22, in terms of mass percentage; wherein the Dv50 of the second hard carbon material 22 is 1.5μm to 3μm. For example, the hard carbon material comprises 60wt% of the first hard carbon material 21 and 40wt% of the second hard carbon material 22, or the hard carbon material comprises 70wt% of the first hard carbon material 21 and 30wt% of the second hard carbon material 22, or the hard carbon material comprises 75wt% of the first hard carbon material 21 and 25wt% of the second hard carbon material 22. In addition, the Dv50 of the second hard carbon material 22 is 1.5μm to 3μm, including any point value within the numerical range, for example, the Dv50 of the second hard carbon material 22 is 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.5μm, 2.8μm or 3.0μm.

[0043] In the embodiments of the present disclosure, the proportion of the first hard carbon material 21 with a Dv50 of 4μm to 7μm is higher than the proportion of the second hard carbon material 22 with a Dv50 of 1.5μm to 3μm. On the one hand, whether it is the first hard carbon material 21 with a relatively large particle size or the second hard carbon material 22 with a relatively small particle size, the overall particle size of both is less than 10μm, so it can be seen that the hard carbon material in the active material layer 2 of the embodiments of the present disclosure generally uses small particle hard carbon material to better improve the compaction density; especially the particle size of the second hard carbon material 22 is less than or equal to 3μm, and the three-dimensional geometric block-shaped particles in this particle size range can help to more significantly improve the compaction density. On the other hand, the proportion of the spherical or spherical-like first hard carbon material 21 is higher than that of the three-dimensional geometric block-shaped second hard carbon material 22, which indicates that the active material layer 2 as a whole still uses the isotropic first hard carbon material 21 as the main hard carbon material component, and the anisotropic second hard carbon material 22 is filled in the gap space of the first hard carbon material 21, which does not affect the capacity performance of the negative electrode sheet, can maintain good structural stability, and can also provide better compaction density.

[0044] In another alternative embodiment, the hard carbon material further comprises a third hard carbon material, the third hard carbon material is a spherical or spherical-like particle, the Dv50 of the third hard carbon material is 2μm to 4μm, and the Dv50 of the second hard carbon material 22 is less than or equal to 2μm. In terms of mass percentage, the hard carbon material comprises 65wt% to 75wt% of the first hard carbon material 21, 10wt% to 30wt% of the second hard carbon material 22, and 5wt% to 15wt% of the third hard carbon material.

[0045] The Dv50 of the third hard carbon material is 2-4 μm, including any point value within the range, for example, the Dv50 of the third hard carbon material is 2 μm, 2.5 μm, 3 μm, 3.5 μm or 4 μm. The Dv50 of the second hard carbon material 22 is less than or equal to 2 μm, including any point value within the range, for example, the Dv50 of the second hard carbon material 22 is 1 μm, 1.2 μm, 1.5 μm, 1.8 μm or 2 μm. In addition, the composition of the hard carbon material can be, for example, 65 wt% of the first hard carbon material 21, 30 wt% of the second hard carbon material 22 and 5 wt% of the third hard carbon material, or 70 wt% of the first hard carbon material 21, 25 wt% of the second hard carbon material 22 and 5 wt% of the third hard carbon material, or 75 wt% of the first hard carbon material 21, 10 wt% of the second hard carbon material 22 and 15 wt% of the third hard carbon material, and so on.

[0046] Compared with the hard carbon material only including the first hard carbon material 21 and the second hard carbon material 22, by adding the third hard carbon material with the Dv50 between the first hard carbon material 21 and the second hard carbon material 22, a more grading gradient can be provided, thereby further improving the filling effect on the gap space between the adjacent first hard carbon materials 21 to ensure a higher filling degree of the gap space.

[0047] Further, the Dn10 of the first hard carbon material 21 is 0.3-0.5 μm.

[0048] Further, the Dn10 of the second hard carbon material 22 is 0.3-0.5 μm.

[0049] Further, the Dn10 of the third hard carbon material is 0.45-0.55 μm.

[0050] When the Dn of each hard carbon material is preferably controlled within the above range, it is beneficial to further control the porosity of the negative electrode sheet within the range claimed, and reduce the impact of the increased porosity on the compaction density of the negative electrode sheet.

[0051] It should be noted that in the embodiments of the present disclosure, the Dv50, Dn10, cross-sectional area ratio and average shape factor of each hard carbon material in the active material layer 2, and the porosity and compaction density of the negative electrode sheet can be determined by testing or calculation through methods or devices known in the art.

[0052] For example, the particle size and morphology of the hard carbon material can be analyzed by a particle size and shape analyzer to obtain the particle size of the hard carbon material, and then the Dv50 and Dn10 and other indicators can be obtained; the cross-sectional area and cross-sectional perimeter of the hard carbon material can also be calculated, and the average shape factor and the porosity of the negative electrode sheet and other indicators can be further calculated.

[0053] Preferably, the porosity of the negative electrode tab is 4% to 6%. When the porosity of the negative electrode tab is optimized in the range of 4% to 6%, especially further optimized at 5%, the improvement effect of the compaction density and the infiltration rate of the electrolyte to the active material layer 2 can be well balanced.

[0054] Further, the compaction density of the negative electrode tab is greater than or equal to 0.98 g / cm 3 The present disclosure finds that with the effective improvement of the compaction density, not only the volumetric energy density of the battery is improved, but also the capacity retention rate is improved to a certain extent. In addition, it should be noted that for the negative electrode tab with graphite as the negative electrode active material, the interlayer interaction force of the graphite is stronger, and it is more likely to have a higher compaction density. However, for the scheme of the embodiment of the present disclosure, the negative electrode tab with hard carbon material as the main active material is adopted, and the particle size, cross-sectional proportion and porosity of different hard carbon materials are comprehensively regulated to make the negative electrode tab reach 0.98 g / cm 3 The above compaction density is not easy to achieve.

[0055] Optionally, the first hard carbon material 21 and the second hard carbon material 22 are respectively prepared by a precursor, and the precursor includes one or more of a biomass-based precursor, a resin-based precursor, a pitch-based precursor and a coal-based precursor.

[0056] The pitch-based precursor or the coal-based precursor is beneficial to improve the compaction density of the prepared hard carbon material due to the higher carbonization metamorphic degree, but at the same time, the prepared hard carbon material has excessively low capacity characteristics. The biomass-based precursor or the resin-based precursor is used to prepare the hard carbon material with high capacity characteristics, but the compaction density is low, which will lead to the decrease of the volumetric energy density of the finally prepared battery.

[0057] In the embodiment of the present disclosure, the precursor of the first hard carbon material 21 preferably adopts the biomass-based precursor or the resin-based precursor to obtain higher capacity characteristics from the material properties; especially in the embodiment of the present disclosure, the proportion of the first hard carbon material 21 is relatively high, which is more beneficial to play the advantage of high capacity. As for the compaction density, since the cross-sectional area proportion of the first hard carbon material 21 with Dv50 of 4 μm to 7 μm in the active material layer 2 is 15% to 45% in the embodiment of the present disclosure, and the second hard carbon material 22 with smaller Dv50 is used to fill the gap space between adjacent first hard carbon materials 21, the compaction density can be improved without affecting the capacity, and then the volumetric energy density of the battery is improved.

[0058] In a second aspect, the embodiment of the present disclosure provides a battery, which comprises: a positive electrode tab, a negative electrode tab, a separator and an electrolyte, the separator is arranged between the positive electrode tab and the negative electrode tab to form an electrode core, and the electrolyte is injected into the electrode core, wherein the negative electrode tab is the negative electrode tab of the first aspect.

[0059] In a third aspect, the embodiments of the present disclosure further provide a storage device 10, which comprises the battery separator film according to the first aspect or the second aspect.

[0060] Taking electrochemical storage as an example, the embodiments of the present disclosure provide a storage device 10, which is provided with a group of chemical batteries, mainly using chemical elements in the batteries as energy storage medium. The charging and discharging process is accompanied by chemical reaction or change of the energy storage medium. In simple terms, the wind energy and solar energy generated by the electric energy are stored in the chemical batteries. When the use of external electric energy reaches the peak, the stored electric quantity is released for use, or transferred to the place where the electric quantity is in short supply for use.

[0061] At present, the application scenarios of storage (i.e. energy storage) are relatively wide, including power generation side storage, power grid side storage and power consumption side storage, and the corresponding types of storage devices 10 include:

[0062] (1) Large-scale storage power station applied in wind power and photovoltaic power station, which can assist renewable energy power generation to meet the grid connection requirements, and improve the utilization rate of renewable energy. The storage power station is a high-quality active / reactive power regulation power source in the power supply side, which realizes the load matching of electric energy in time and space, enhances the renewable energy consumption capacity, reduces the instantaneous power change, reduces the impact on the power grid, improves the new energy power generation consumption problem, and has great significance in power grid system backup, relieving peak load power supply pressure and peak regulation;

[0063] (2) Storage container applied in the power grid side, the main functions of which are peak regulation, frequency regulation and relieving power grid congestion, which can realize the peak clipping and valley filling of power consumption load, i.e. charging the storage battery when the power consumption load is low, and releasing the stored electric quantity when the power consumption load is high, so as to realize the balance between power production and consumption;

[0064] (3) Small energy storage cabinet applied to power consumption side, the main functions are power self-generation and self-use, peak-valley price difference arbitrage, capacity cost management and improvement of power supply reliability. According to different application scenarios, the energy storage on the power consumption side can be divided into industrial and commercial energy storage cabinets, household energy storage devices 10, energy storage charging piles, etc., which are generally used with distributed photovoltaic power. Industrial and commercial users can use energy storage for valley-peak price difference arbitrage and capacity cost management. In the electricity market implementing peak-valley electricity price, through charging the energy storage system 100 at low electricity price and discharging the energy storage system 100 at high electricity price, peak-valley price difference arbitrage is realized, and the electricity cost is reduced. In addition, industrial enterprises suitable for two-part electricity price can use the energy storage system 100 to store energy at low electricity consumption and discharge at peak load, thereby reducing the maximum demand amount of the reported peak power and achieving the purpose of reducing capacity electricity cost. Household photovoltaic power storage can improve the level of power self-generation and self-use. Due to high electricity price and poor power supply stability, household photovoltaic power demand is driven. Considering that photovoltaic power is generated during the day and users generally have high load at night, by configuring energy storage, photovoltaic power can be better utilized, the level of self-generation and self-use is improved, and the electricity cost is reduced. In addition, communication base stations, data centers and other fields need to configure energy storage for backup power supply.

[0065] Please refer to FIG. 5, which is a structural schematic diagram of a household energy storage system 100 according to an embodiment of the present disclosure. The present disclosure provides a household energy storage system 100, which includes an electric energy conversion device 20 (photovoltaic panel), a first user load 30 (street lamp), a second user load 40 (for example, household appliances such as air conditioner, etc.), and an energy storage device 10. The energy storage device 10 is a small energy storage cabinet, which can be installed on an outdoor wall by wall hanging. Specifically, the photovoltaic panel can convert solar energy into electric energy during the electricity price valley period, and the energy storage device 10 is used to store the electric energy and supply the street lamp and household appliances for use during the electricity price peak period, or supply power during power grid outage.

[0066] Please refer to FIG. 6, which is a structural schematic diagram of an energy storage system 100 according to an embodiment of the present disclosure. The embodiment of FIG. 5 is used as an example to illustrate the scenario of shared energy storage on the generation / distribution side, and the energy storage device 10 of the present disclosure is not limited to the scenario of shared energy storage on the generation / distribution side.

[0067] The energy storage system 100 provided by the present disclosure comprises a high-voltage cable 50, a first electric energy conversion device 60, a second electric energy conversion device 70, and an energy storage device 10 provided by the present disclosure. In the power generation condition, the first electric energy conversion device 60 and the second electric energy conversion device 70 are used to convert other forms of energy into electric energy, are connected with the high-voltage cable, and supply the power distribution network for use. When the power load is low, the first electric energy conversion device 60 and the second electric energy conversion device 70 generate excess power, and the excess power is stored in the energy storage device 10, so as to reduce the wind and light curtailment rate and improve the new energy power generation consumption problem. When the power load is high, the power grid issues an instruction, the energy storage device 10 stores the electric energy, and the high-voltage cable 50 transmits the electric energy in the grid-connected mode to supply the power consumption side, so as to provide peak shaving, frequency modulation, backup and other services for the power grid operation, fully play the role of the power grid peak shaving, promote the power grid peak shaving and valley filling, and relieve the power supply pressure of the power grid.

[0068] Optionally, the first electric energy conversion device 60 and the second electric energy conversion device 70 can convert at least one of solar energy, light energy, wind energy, heat energy, tidal energy, biomass energy and mechanical energy into electric energy.

[0069] The number of the energy storage device 10 can be multiple, the multiple energy storage devices 10 are connected in series or in parallel with each other, and the multiple energy storage devices 10 are supported and electrically connected by an isolation plate (not shown in the figure). In the embodiment, “multiple” means two or more than two. The energy storage device 10 can further be provided with an energy storage box outside for accommodating the energy storage device 10.

[0070] Optionally, the energy storage device 10 can include but is not limited to a battery module, a battery pack, a battery system and the like. The actual application form of the energy storage device 10 provided by the embodiment of the present disclosure can be but is not limited to the listed products, and can also be other application forms. The embodiment of the present disclosure does not strictly limit the application form of the energy storage device 10. The embodiment of the present disclosure only takes the energy storage device 10 as a multi-core battery as an example for description. When the energy storage device 10 is a single battery, the energy storage device 10 can be at least one of a cylindrical battery and a square battery.

[0071] The scheme of the present disclosure will be further introduced in combination with specific embodiments and experimental data.

[0072] Embodiment 1

[0073] The embodiment provides a negative electrode sheet, and a preparation method thereof comprises the following steps.

[0074] The first hard carbon material in spherical and spheroid shape and the second hard carbon material in three-dimensional geometric block shape are weighed according to the mass ratio, and then put into a VC mixer for physical mixing, for example, running at 500 r / min for 2 h, until the above-mentioned hard carbon materials are completely mixed, thereby obtaining a negative electrode active material. The physical property parameters of the above-mentioned negative electrode active material are shown in Table 1.

[0075] The above-mentioned negative electrode active material, thickening agent carboxymethyl cellulose, conductive agent conductive carbon black, and binder styrene-butadiene rubber are mixed according to the mass ratio of 95:2:1.5:1.5, deionized water is added, and stirred uniformly to obtain a negative electrode slurry with a solid content of 30%. The negative electrode slurry is uniformly coated on one surface of a copper foil, and then vacuum dried, rolled, punched, and a circular negative electrode sheet is obtained.

[0076] Examples 2-3

[0077] Except that the first hard carbon material and the second hard carbon material are adjusted according to the physical property parameters of the negative electrode active material in Table 1, the rest is the same as Example 1.

[0078] Examples 4-6

[0079] Except that a third hard carbon material in spherical and spheroid shape is added, and the first hard carbon material and the second hard carbon material are adjusted according to the physical property parameters of the negative electrode active material in Table 1, the rest is the same as Example 1.

[0080] Comparative Example 1

[0081] Except that the second hard carbon material is not used, and the first hard carbon material and the second hard carbon material are adjusted according to the physical property parameters of the negative electrode active material in Table 1, the rest is the same as Example 1.

[0082] Comparative Example 2

[0083] Except that the first hard carbon material and the second hard carbon material are adjusted according to the physical property parameters of the negative electrode active material in Table 1, the rest is the same as Example 1.

[0084] Comparative Examples 3-4

[0085] Except that the first hard carbon material and the second hard carbon material are adjusted according to the physical property parameters of the negative electrode active material in Table 1, the rest is the same as Example 4.

[0086] <Battery assembly>

[0087] Preparation of electrolyte: In an argon atmosphere glove box with water content ≤1 ppm, ethylene carbonate and diethyl carbonate are mixed according to the volume ratio of 1:1, then sodium salt NaPF6 is added and dissolved into the above-mentioned organic solvent, and the electrolyte is obtained after mixing uniformly. The molar concentration of NaPF6 in the electrolyte is 1 mol / L.

[0088] Assembling of button cell: circular sodium sheet, separator (glass fiber membrane with thickness of 260 μm), circular negative electrode sheet of the above examples and comparative examples were stacked in order with the separator in the middle between the circular sodium sheet and the negative electrode sheet to play the role of isolation, and then the prepared electrolyte was injected to assemble a 2032 type button cell.

[0089] After the assembled button cell was placed for 12 h, the charge-discharge test and other electrical performance tests were carried out.

[0090] <Performance test>

[0091] Hard carbon negative electrode material sheet resistance test: four-probe method was used, and the current and voltage of the negative electrode sheet were measured by using a resistivity tester, and then the resistivity at different pressures was calculated, with the unit of Ω. The resistance data in Table 3 are the test results at a pressure of 25 MPa.

[0092] Cycle performance test: the test temperature was 25℃, the button cells of the examples and comparative examples were discharged at 0.2C to 0.005V, and then charged at 0.2C to 2V after standing for 10 min. The capacity obtained in this step was the initial discharge capacity CO, and the cycle test of 0.2C charge / 0.2C discharge was carried out for 200 times (cycles), and the discharge capacity of the 200th cycle was recorded. Cycle capacity retention rate = (discharge capacity of the 200th cycle / initial discharge capacity CO) x 100%.

[0093] Volume energy density calculation: battery volume energy density = battery capacity x discharge platform / volume, basic unit is Wh / L (watt-hour / L), wherein the battery capacity is 2.0V-4V capacity.

[0094] Table 1 Physical property parameters of negative electrode active material

[0095] Table 2 Related parameters of negative electrode sheet

[0096] Table 3 Performance test results

[0097] As can be seen from the above Tables 1 to 3, the compaction density and cycle stability of the negative electrode plate of the examples 1 to 6 are all better than those of the comparative example 1, which shows that the negative electrode plate of the examples of the present disclosure can effectively improve the compaction density, and further improve the volumetric energy density, and the cycle stability of the battery is also improved. As can be seen from the comparison of the examples 1 to 6 and the comparative example 2, although the cross-sectional area ratio of the first hard carbon material in the comparative example 2 is appropriate, the porosity of the negative electrode plate of the comparative example 2 is too high, which still leads to the reduction of the compaction density, the volumetric energy density and the cycle stability. As can be seen from the comparison of the examples 1 to 6 and the comparative example 4, although the porosity of the negative electrode plate of the comparative example 4 is small, the cross-sectional area ratio of the first hard carbon material is too high, which still leads to the reduction of the compaction density, the volumetric energy density and the cycle stability.

[0098] As can be seen from the comparison of the examples 1 to 3 and the examples 4 to 6, the compaction density and the cycle stability of the examples 4 to 6 are better, which shows that the use of the first hard carbon material, the second hard carbon material and the third hard carbon material with the above-mentioned Dv50 for the negative electrode active material can further improve the compaction density to 1.02 g / cm 3 The above-mentioned volumetric energy density and cycle stability are also improved more obviously. Especially for the example 5, the compaction density is improved to 1.05 g / cm 3 , which is at a higher level.

[0099] The above-mentioned technical solutions of the examples of the present disclosure are introduced in detail, and the principles and implementation manners of the present disclosure are described by using specific examples. The above-mentioned examples are only used to help understand the technical solutions and the core ideas of the present disclosure. Meanwhile, for the general skilled in the art, the specific implementation manners and application ranges will be changed according to the ideas of the present disclosure. In summary, the content of the present disclosure should not be understood as a limitation.

Claims

1. A negative electrode sheet, wherein, The negative electrode plate comprises: a current collector; an active material layer provided on the current collector; the active material layer comprises a first hard carbon material and a second hard carbon material, the Dv50 of the first hard carbon material is 4 μm to 7 μm, the Dv50 of the second hard carbon material is less than the Dv50 of the first hard carbon material, and the cross-sectional area proportion of the first hard carbon material in the active material layer is 15% to 45%; The porosity of the negative electrode plate is 1% to 10%.

2. The negative electrode sheet according to claim 1, wherein The first hard carbon material is at least one of spherical or spheroid particles, and 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, wherein The first hard carbon material has an average shape factor F ≥ 0.75, the average shape factor F = 4πA / P 2 wherein the A is a cross-sectional area of the first hard carbon material, and the P is a cross-sectional perimeter of the first hard carbon material.

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

5. The negative electrode sheet according to claim 2, wherein The hard carbon material further comprises a third hard carbon material, the third hard carbon material is spherical or spheroid particles, 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 65wt% to 75wt% of the first hard carbon material, 10wt% to 30wt% of the second hard carbon material, and 5wt% to 15wt% of the third hard carbon material in terms of mass percentage.

6. The negative electrode sheet according to claim 1, wherein 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 further comprises a third hard carbon material, and the Dn10 of the third hard carbon material is 0.45 μm to 0.55 μm.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein The porosity of the negative electrode plate is 4% to 6%; and / or, The compacted density of the negative electrode sheet is greater than or equal to 0.98 g / cm 3 .

8. The negative electrode sheet according to any one of claims 1 to 6, wherein The first hard carbon material and the second hard carbon material are respectively prepared from a precursor, and the precursor comprises one or more of a biomass-based precursor, a resin-based precursor, a pitch-based precursor, and a coal-based precursor.

9. A battery, wherein, The battery comprises a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, the separator is arranged between the positive electrode plate and the negative electrode plate to form an electric core, and the electrolyte is injected into the electric core, wherein the negative electrode plate is the negative electrode plate according to any one of claims 1 to 8.

10. An energy storage device, wherein, The energy storage device comprises the negative electrode plate according to any one of claims 1 to 8, or the energy storage device comprises the battery according to claim 9.

Images