Electrochemical device and electric device

Abstract

The invention provides an electrochemical device and a power utilization device, and belongs to the technical field of secondary batteries, the electrochemical device comprises a negative electrode piece, the negative electrode piece comprises a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is coated on at least one surface of the negative electrode current collector along the thickness direction; the negative electrode active material layer comprises a negative electrode material, and the negative electrode material comprises a silicon-based material; wherein a pore structure exists in the negative electrode active material layer, and when the electrochemical device is in a 40% charge state, the porosity of the negative electrode active material layer is 10%-20%. According to the chemical device provided by the invention, the porosity corresponding to the silicon-containing negative pole piece in the SOC stage with the fastest porosity reduction is limited, and the silicon-containing negative pole piece can still maintain the appropriate porosity after being charged and expanded, so that the energy density and the fast charging performance of the battery are both improved.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to an electrochemical device and an electrical device. Background Art

[0002] With the advancement of lithium-ion battery technology, the market demand for power batteries is not only satisfied with long driving range, but also requires short charging time. In order to solve the range anxiety and improve the energy density of lithium-ion batteries, many power battery manufacturers have introduced silicon negative electrode materials. However, due to the semiconductor properties of silicon negative electrodes, the embedding and extraction rates of lithium ions in silicon negative electrodes are low, resulting in slow charging, which restricts the promotion and application of silicon negative electrodes in secondary batteries.

[0003] The charging process of a battery is a process in which lithium ions are released from the positive electrode, migrate to the negative electrode with the help of the electrolyte, and then embed into the negative electrode. Currently, increasing the porosity of the negative electrode is usually adopted to increase the migration speed of lithium ions on the negative electrode, thereby improving the fast charging capability of the negative electrode. However, in the active material layer of the negative electrode, if the porosity is designed to be too large, the energy density of the battery will be significantly reduced; if the porosity is designed to be too small, the liquid phase diffusion speed of the electrolyte in the battery at the negative electrode will be limited, affecting its fast charging capability.

[0004] Therefore, it is necessary to design an electrochemical device and an electrical device that can take into account both battery energy density and fast charging efficiency when optimizing the negative electrode structure, so as to solve the above problems. Summary of the Invention

[0005] In view of the above shortcomings of the prior art, the present invention provides an electrochemical device and an electrical device to solve the technical problem that the existing electrochemical devices are difficult to balance battery energy density and fast charging performance when using silicon-based negative electrode sheets.

[0006] To achieve the above-mentioned and other related objects, the present invention provides an electrochemical device, comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer being coated on at least one side of the negative electrode current collector along the thickness direction; the negative electrode active material layer comprising a negative electrode material, the negative electrode material comprising a silicon-based material;

[0007] The negative electrode active material layer has a pore structure. When the electrochemical device is at a 40% state of charge, the porosity of the negative electrode active material layer is ε=1-∑(V i ) / V, the porosity ε is 10%-20%, V iis the sum of the volumes of the raw materials of the active material layer when the electrochemical device is at a 40% state of charge, and V is the volume of the negative electrode active material layer when the electrochemical device is at a 40% state of charge.

[0008] In one example of the present invention, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductor, and the negative electrode material further includes a carbon-based material; the porosity ε is ε=1-∑(V i ) / V,V i =V Si +V g +V b +V c , where V Si 、V g 、V b and V c are respectively the volumes of the silicon-based material, the carbon-based material, the negative electrode binder and the negative electrode conductive agent when the electrochemical device is at a 40% state of charge.

[0009] In one example of the present invention, when the electrochemical device is in a 0% state of charge, the porosity of the negative electrode active material layer is ε0, and the porosity ε0 satisfies ε=1-(V Si0 +0.1V g0 +V0(1-ε0)) / V0, where the V Si0 and V g0 are respectively the volumes of the silicon-based material and the carbon-based material when the electrochemical device is in a 0% state of charge, and V0 is the volume of the negative electrode active material layer when the electrochemical device is in a 0% state of charge.

[0010] In an example of the present invention, when the electrochemical device is in a 0% state of charge, the porosity ε0 of the negative electrode active material layer is 21%-30%.

[0011] In one example of the present invention, the mass proportion of the silicon-based material to the sum of the mass of the carbon-based material and the silicon-based material is 8-15wt%; the mass proportion of the carbon-based material to the sum of the mass of the carbon-based material and the silicon-based material is 85-92wt%.

[0012] In an example of the present invention, the carbon-based material includes at least one of graphite, soft carbon, hard carbon, pitch carbide, sintered coke, graphene, and carbon nanotubes.

[0013] In an example of the present invention, the silicon-based material includes at least one of silicon, silicon monoxide and silicon carbide.

[0014] In one embodiment of the present invention, the compaction density of the negative electrode sheet is 1.6-1.7 g / cm 3 .

[0015] In one embodiment of the present invention, the surface density of the negative electrode active material layer is 75-90 g / m 2 .

[0016] In an example of the present invention, the average particle size D50 of the negative electrode material is 10-40 μm.

[0017] The present invention also provides an electrical device, which includes the electrochemical device described in any of the above examples.

[0018] The present invention provides an electrochemical device and an electrical device. The electrochemical device limits the porosity of the silicon-containing negative electrode plate corresponding to the SOC stage where the porosity decreases fastest, ensuring that the silicon-containing negative electrode plate can still maintain a suitable porosity after charging and expansion. On the one hand, this avoids the insufficient charging efficiency of the electrochemical device due to the excessively rapid decrease in the negative electrode porosity during the charging process, prevents the problem of lithium plating during the use of the electrochemical device, and improves the fast charging performance of the battery; on the other hand, it can also avoid the decrease in battery energy density due to the excessive porosity of the negative electrode plate in the initial uncharged state, effectively ensuring the capacity of the electrochemical device. In summary, the electrochemical device designs a suitable porosity structure in the silicon negative electrode plate, thereby improving both the energy density and the fast charging performance of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 Schematic diagram of the thickness change of the negative electrode sheet containing silicon material during battery charging. DETAILED DESCRIPTION

[0021] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following examples and the features in the examples can be combined with each other unless they conflict. It should also be understood that the terms used in the examples of the present invention are for the purpose of describing specific embodiments, not for the purpose of limiting the scope of protection of the present invention. The test methods for which specific conditions are not specified in the following examples are generally carried out under conventional conditions or under the conditions recommended by the manufacturers.

[0022] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0023] Compared to carbon-based anode materials, silicon-based anode materials have excellent application prospects in high-capacity fast-charging batteries due to their greater number of lithium insertion and deintercalation sites and higher theoretical specific capacity (up to 4200 mAh / g), and have garnered widespread attention within the industry. However, as semiconductor materials, silicon-based materials suffer from slow internal electron and ion migration, which limits the fast-charging capabilities of batteries assembled with them.

[0024] To improve the conductivity of silicon-containing negative electrode sheets in batteries, the current method of increasing the porosity of the negative electrode sheets is usually adopted. This modification method can reduce the diffusion distance of lithium ions in the electrolyte in silicon particles, thereby increasing the migration speed of lithium ions on the negative electrode sheets and improving the fast charging capability of the negative electrode sheets. However, traditional sheet modification designs usually only focus on the porosity of the negative electrode sheets in the initial state, and do not consider the decrease in the sheet porosity caused by the huge volume expansion of the silicon-based material during the charging process of the silicon-containing negative electrode sheets. As the porosity of the negative electrode sheets decreases, the battery charging rate also drops rapidly in the later stage of the charging process. This results in the design of too small a porosity in the negative electrode sheets failing to achieve the expected effect of improving the fast charging capability of the silicon negative electrode. However, designing too high a porosity in the negative electrode sheets just to improve conductivity will cause the battery to lose a lot of energy density, which is not a good modification method.

[0025] To solve the above problems, the inventors studied the volume change of silicon-containing negative electrode sheets during battery charging. The study found that the volume expansion rate of silicon-containing negative electrode sheets is different in different SOC (State of Charge, also known as remaining capacity) ranges of the battery. Figure 1As shown in the figure, during the battery charging process, the volume expansion of the negative electrode sheet is faster in the battery SOC range of 0%-40%, and the volume expansion rate in the battery SOC range of 40%-80% is slower. The volume expansion rate in the battery SOC range of 80%-100% is further increased compared with the 40%-80% SOC range.

[0026] Based on the above findings, the present application provides an electrochemical device and an electrical device, which limits the porosity of the silicon-containing negative electrode plate corresponding to the SOC stage where the porosity decreases fastest, ensuring that the silicon-containing negative electrode plate can still maintain a suitable porosity after charging and expansion, thereby avoiding insufficient charging efficiency of the electrochemical device due to the rapid decrease in the negative electrode porosity during charging, thereby improving the fast charging capability of the electrochemical device and effectively preventing lithium plating due to insufficient charging efficiency in the electrochemical device.

[0027] The present invention provides an electrochemical device, a specific embodiment of which is a battery comprising one or more "battery cells". The "battery cell" refers to a battery cell that can be independently charged and discharged. The "battery cell" includes a positive electrode plate, a negative electrode plate, an electrolyte, a separator, and corresponding connecting accessories and circuits. The positive electrode plate includes a positive electrode collector and a positive electrode active material layer disposed on the positive electrode collector, and the positive electrode active material layer includes a positive electrode material, a conductive agent, and a binder; the negative electrode plate includes a negative electrode collector and a negative electrode active material layer disposed on the negative electrode collector, and the negative electrode active material layer includes a negative electrode material, a conductive agent, a thickener, and a binder. In the electrochemical device, the positive and negative electrode materials can intercalate and deintercalate lithium ions to achieve energy storage and release. The electrolyte is a carrier for the transmission of lithium ions between the positive electrode plate and the negative electrode plate. The separator can pass lithium ions but is non-conductive, thereby separating the positive electrode plate and the negative electrode plate to prevent short circuits. It should be noted that the type of positive electrode material used in the positive electrode sheet can be any positive electrode active material known in the art, for example, it can be one or more of lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), lithium-rich manganese-based oxide (LRMO) and lithium-containing phosphate; lithium-containing phosphate includes but is not limited to lithium iron manganese phosphate, lithium iron phosphate, lithium manganese phosphate, etc.

[0028] In the aforementioned negative electrode sheet, the negative electrode active material layer includes a negative electrode material, which includes a silicon-based material. The presence of pores in the negative electrode active material layer increases the wettability of the negative electrode sheet in the electrolyte, shortens the distance lithium ions travel within the negative electrode active material layer, and increases the conductive efficiency of the negative electrode sheet.

[0029] In the electrochemical device of the present invention, when the electrochemical device is at 40% SOC, the porosity of the negative electrode active material layer is ε=1-∑(Vi ) / V, the porosity ε is 10%-20%, for example, the porosity can be 10%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%; wherein, V i Where, V is the volume of the negative electrode active material layer when the electrochemical device is at 40% SOC. Alternatively, in one example, when the electrochemical device is at 40% SOC, the porosity ε of the negative electrode active material layer is 10%-15%.

[0030] Traditional electrode structure modification only focuses on the porosity of the electrode in its initial state (i.e., the battery SOC is 0%), and does not consider the different volume increase ratios brought about by different silicon-based material ratios in the negative electrode during the charging process. Therefore, when modifying silicon-containing negative electrode sheets, it is difficult to ensure fast charging performance only by designing the porosity of the electrode in its initial state. It is also necessary to consider the impact of changes in porosity during charging on fast charging performance. Compared to traditional electrode structure modification, the electrochemical device of this application limits the porosity of the negative electrode sheet at the end of the fastest porosity drop stage during charging (i.e., the battery SOC is 40%) to 10%-20%, thereby ensuring both the fast charging capability and energy density of the electrochemical device. On the one hand, this limited porosity range allows the active material layer of the negative electrode plate to maintain an appropriate porosity after rapid expansion during charging to ensure charging efficiency, avoid the insertion and migration rate of lithium ions in the negative electrode plate to decay significantly with the charging process, thereby ensuring the charging rate of the electrochemical device during the charging process, and improving the fast charging capability of the electrochemical device, avoiding lithium deposition in the electrochemical device due to insufficient charging efficiency; on the other hand, it can ensure that the porosity of the negative electrode plate in the uncharged state is not too high, avoiding excessive porosity in the negative electrode active material layer leading to a decrease in the active material content in the negative electrode plate and a decrease in the energy density of the electrochemical device.

[0031] In some embodiments, the negative electrode active material layer further comprises a negative electrode binder and a negative electrode conductor in addition to the negative electrode material, and the negative electrode material further comprises a silicon-based material and a carbon-based material. When the electrochemical device is at 40% SOC, the porosity ε of the negative electrode active material layer is expressed as ε=1-∑(V i ) / V,V i =V Si +V g +V b +V c , where V Si 、V g 、V b and V care the volumes of the silicon-based material, carbon-based material, negative electrode binder and negative electrode conductive agent raw materials when the electrochemical device is at 40% SOC, and V is the volume of the negative electrode active material layer when the electrochemical device is at 40% SOC.

[0032] In this embodiment, when the electrochemical device is at 0% SOC, the porosity ε0 of the negative electrode active material layer is expressed as ε0=1-∑(V i0 ) / V0,V i0 =V Si0 +V g0 +V b0 +V c0 , where V Si0 、V g0 、V b0 and V c0 are the volumes of silicon-based materials, carbon-based materials, negative electrode binders, and negative electrode conductive agents when the electrochemical device is at 0% SOC, V i0 is the initial volume of the raw materials of the negative electrode active material layer, and V0 is the volume of the negative electrode active material layer when the electrochemical device is at 0% SOC. The inventors have found that when the electrochemical device is charged from 0% SOC to 40% SOC, the volume change of each raw material in the negative electrode active material layer satisfies the following relationship: V Si =2V Si0 , V g =1.1V g0 , V b =V b0 , V c =V c0 Therefore, when the mass ratio of each component in the negative electrode active material layer is determined, the porosity ε0 of the electrochemical device at 0% SOC and the porosity ε at 40% SOC satisfy the following relationship: ε=1-(V Si0 +0.1V g0 +V0(1-ε0)) / V0. Based on the above relationship, the porosity ε0 of the negative electrode sheet in the initial state can be designed according to the porosity ε required for 40% SOC.

[0033] It should be noted that, in the present invention, the porosity test method of the negative electrode sheet can be: (1) for the negative electrode sheet in the initial state, the initial volume V of the raw material of the negative electrode active material layer is weighed before coating the active material layer. i0 Then, after the negative electrode sheet is made, the volume of the active material layer V0 is measured, and finally the porosity of the negative electrode sheet when the electrochemical device is at 0% SOC is calculated as ε0 = 1-∑(V i0) / V0. (2) For the negative electrode sheet charged to 40% SOC, after the electrochemical device is charged to 40% SOC, the negative electrode sheet can be removed from the electrochemical device and the volume V of the active material layer on the negative electrode sheet when charged to 40% SOC can be measured; then the active material layer on the negative electrode sheet can be scraped off and the volume of the active material layer raw material powder can be measured to obtain the volume V of the negative electrode active material layer raw material when charged to 40% SOC. i Finally, the porosity of the negative electrode sheet is calculated when the electrochemical device is at 40% SOC: ε = 1-∑(V i ) / V.

[0034] In some embodiments, the mass ratio of the silicon-based material to the combined mass of the carbon-based material and the silicon-based material is 8-15 wt %, and the mass ratio of the carbon-based material to the combined mass of the carbon-based material and the silicon-based material is 85-92 wt %. The porosity ε0 of the negative electrode sheet at 0% SOC of the electrochemical device is 21%-30%, and the porosity ε of the negative electrode sheet at 40% SOC of the electrochemical device is controlled to be between 10% and 20%.

[0035] In some embodiments, the surface density of the negative electrode active material layer coated on the negative electrode sheet is 75-90 g / m 2 For example, the surface density of the negative electrode active material layer can be 75g / m 2 , 80g / m 2 , 85g / m 2 or 90g / m 2 In the present invention, the method for testing the surface density of the negative electrode sheet can be to cut the negative electrode sheet to be tested into a round sample of a fixed area, weigh the sample mass and the mass of the sample empty current collector, and calculate the surface density according to the following formula: Surface density = (sample mass - sample empty current collector mass) / sample area.

[0036] In some embodiments, the compaction density of the negative electrode sheet is 1.6-1.7 g / cm 3 For example, the compaction density of the negative electrode sheet can be 1.60g / cm 3 , 1.61g / cm 3 , 1.62g / cm 3 , 1.63g / cm 3 , 1.65g / cm 3 , 1.66g / cm 3 , 1.67g / cm 3 、1.68g / cm 3 , 1.69g / cm 3 or 1.70g / cm 3In the present invention, the compaction density of the negative electrode sheet can be tested by cutting the negative electrode sheet to be tested into a round sample of a fixed area, weighing the sample mass and the mass and thickness of the empty sample current collector, and calculating the compaction density according to the following formula: compaction density = (sample mass - sample empty current collector mass) / (area × (sample thickness - sample empty current collector thickness)).

[0037] In addition, it should be noted that, under the premise of confirming the content of each component in the negative electrode active material layer, the surface density and compaction density of the negative electrode sheet will also affect the energy density and fast charging capability of the electrochemical device. If the surface density and compaction density of the negative electrode sheet are high, the fast charging capability of the electrochemical device will be reduced. If the surface density and compaction density of the negative electrode sheet are low, the energy density of the electrochemical device will be reduced. When the surface density and compaction density of the negative electrode sheet are within the numerical range of the above embodiment, it is possible to further improve the energy density and fast charging capability of the electrochemical device on the basis of the effect brought by the porosity.

[0038] In some embodiments, the silicon-based material is selected from at least one of silicon, silicon monoxide, and silicon carbide. That is, the silicon-based material can be any one of the materials listed above, for example, silicon, silicon monoxide, or silicon carbide; the silicon-based material can also be any two or more combinations of the materials listed above, for example, the silicon-based material can be a combination of silicon and silicon monoxide, or a combination of silicon and silicon carbide, or a combination of silicon monoxide and silicon carbide, or a combination of silicon, silicon monoxide, and silicon carbide, etc., which are not listed here one by one. When the silicon-based material is a combination of two or more materials, there is no restriction on the proportion of each material in the combination, and they can be mixed in any proportion. In other embodiments, the silicon-based material can also be a material not listed above.

[0039] In some embodiments, the carbon-based material is selected from at least one of graphite, soft carbon, hard carbon, pitch carbide, sintered coke, graphene and carbon nanotubes. That is, the carbon-based material can be any one of the materials listed above, for example, graphite, soft carbon, hard carbon, pitch carbide, sintered coke, graphene or carbon nanotubes, etc.; the carbon-based material can also be any two or more combinations of the materials listed above, for example, the carbon-based material can be a combination of graphite and graphene, or a combination of graphite and hard carbon, or a combination of graphite and pitch carbide, or a combination of graphite, graphene and hard carbon, etc., which are not listed one by one here. When the carbon-based material is a combination of two or more materials, there is no restriction on the proportion of each material in the combination, and they can be mixed in any proportion. In other embodiments, the carbon-based material can also be a material not listed above.

[0040] In some embodiments, the average particle size D50 of the negative electrode material is 10-40 μm. For example, the average particle size of the negative electrode material can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, or 40 μm. It should be noted that the average particle size D50 can be defined as the particle size corresponding to 50% of the volume accumulation in the particle size distribution curve of the particles; D50 can be measured by, for example, laser diffraction method. Laser diffraction method is generally capable of measuring particle sizes from the submicron range to several millimeters, thereby obtaining highly reproducible and high-resolution results.

[0041] The composition and preparation method of the electrochemical device provided by the present invention are described in detail below:

[0042] Preparation of positive electrode sheets: The positive electrode material, positive electrode conductive agent, and positive electrode binder are mixed in a weight ratio of (90 to 99):(1 to 10):(1 to 10), optionally in a weight ratio of 93:3:4. N-methylpyrrolidone (NMP) solvent is added and thoroughly stirred to obtain a positive electrode slurry. The mixture is stirred in a vacuum mixer until the mixture becomes uniform and transparent. The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil. The positive electrode current collector aluminum foil is then air-dried at room temperature and then transferred to an oven for drying. The positive electrode sheets are then cold-pressed and slit. Among them, the positive electrode conductive agent can be selected from: at least one of conductive materials such as carbon black (SuperP), acetylene black, carbon nanotubes (CNT), graphene, nanofibers (VGCF), for example, the positive electrode conductive agent is SP and CNT, and the mass ratio of SP and CNT is 2:1; the positive electrode binder can be selected from: at least one of polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), for example, the binder can be PVDF.

[0043] Preparation of negative electrode sheets: After mixing the negative electrode material, negative electrode conductive agent, negative electrode binder and negative electrode thickener in a mass ratio of (90 to 99): (1 to 10): (1 to 10): (1 to 10), the weight ratio can optionally be 96:1:2:1, deionized water is added to adjust the solid content of the slurry to 55%, and then under the action of a vacuum mixer, the mixture is fully stirred and mixed to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on both sides of the negative electrode current collector copper foil; after drying at room temperature, it is transferred to an oven for drying, and then cold pressed, cut and other processes are performed to obtain a negative electrode sheet. Among them, the negative electrode conductive agent can be selected from at least one conductive material such as carbon black (Super P), acetylene black, carbon nanotubes (CNT), graphene, nanofibers (VGCF); the negative electrode binder is selected from at least one binding material such as polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR); the negative electrode thickener is selected from carboxymethyl cellulose, which can be sodium carboxymethyl cellulose (CMC-Na) or lithium carboxymethyl cellulose (CMC-Li).

[0044] Diaphragm preparation: The diaphragm is made of PE or PP porous membrane, and PP / PE / PP porous membrane can be selected, with a thickness of 9μm to 18μm, such as 9μm, 12μm, 16μm or 18μm; the air permeability is 180s / 100mL to 380s / 100mL, such as 180s / 100mL, 280s / 100mL or 380s / 100mL; the porosity is 30% to 50%, such as 30%, 40% or 50%.

[0045] Preparation of electrolyte: Ethylene carbonate (EC), diethylhexanoate (DEC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 1:2:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0046] Assembling an electrochemical device (secondary battery): The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets to act as a barrier. The sheet is then wrapped with aluminum plastic film, dried, and filled with the prepared electrolyte. After packaging, resting, and forming, a 1Ah battery (i.e., a lithium-ion secondary battery) is finally produced.

[0047] The specific steps and conditions for electrolyte formation are as follows: after the electrolyte is injected, maintain a hot press environment of 0.1MPa, charge at 0.02C for 17 minutes at 45°C in a static state, stand for 5 minutes and then charge to 0.3Ah at 0.02C, then cut off the air bag and vacuum seal, and stand at room temperature for 48 hours to complete the electrolyte formation.

[0048] In addition, the present invention further provides an electrical device, comprising the electrochemical device described in any of the above embodiments, wherein the electrochemical device can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc.

[0049] The technical solutions of the present invention are described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art.

[0050] Example 1

[0051] This embodiment provides a secondary battery, in which the porosity ε of the negative electrode plate is 20% when the battery is in a state of 40% SOC. The preparation process of the secondary battery is as follows:

[0052] (1) Preparation of positive electrode sheet: positive electrode material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 The prepared lithium supplement (O2) was mixed with the lithium supplement agent, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) in a weight ratio of 97:2:1. N-methylpyrrolidone (NMP) was added as a solvent and the mixture was thoroughly stirred to obtain a positive electrode slurry. The mixture was stirred in a vacuum mixer until the mixture became homogeneous and transparent. The positive electrode slurry was evenly coated on a 16μm aluminum foil current collector. The aluminum foil current collector was then air-dried at room temperature and then transferred to an oven at 80°C to 120°C for 6 hours. The positive electrode sheets were then cold-pressed and slit.

[0053] (2) Preparation of negative electrode sheet: The negative electrode material, conductive agent acetylene black, thickener sodium carboxymethyl cellulose (CMC) and binder styrene butadiene rubber (SBR) are mixed in a mass ratio of 96:1:1:2. The negative electrode material includes graphite and silicon dioxide (SiO), the mass content of silicon dioxide relative to the negative electrode material is 12%, and the mass content of graphite relative to the negative electrode material is 92%. After the raw materials are mixed, deionized water is added to adjust the solid content of the slurry to 55%. After stirring and dispersing evenly, the slurry is coated on both sides of the negative electrode current collector copper foil and dried at 75°C. The coated single side surface density is 85g / cm 2 , the dried negative electrode sheet is rolled to 1.65g / cm 3 The compaction density is then cut into negative electrode sheets.

[0054] (3) Preparation of electrolyte: In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), diethylhexanoate (DEC), and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 1:2:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0055] (4) Diaphragm preparation: The diaphragm is a 9 μm polyethylene diaphragm coated on both sides with a ceramic coating with a thickness of 2 μm.

[0056] (5) Battery Assembly: The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in sequence, with the separator placed between the positive and negative electrode sheets to act as an insulator. The sheet is then wrapped with aluminum plastic film and transferred to a vacuum oven for drying at 120°C. 3.0 g / Ah of electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, and capacity separation, a secondary battery (i.e., lithium-ion battery) with a capacity of 1 Ah is finally prepared.

[0057] Example 2

[0058] This embodiment provides a secondary battery of the same system as that of Example 1. The difference between this embodiment and Example 1 is that when preparing the negative electrode plate, the mass content of silicon monoxide in the negative electrode material used is 8%, and the porosity ε of the negative electrode plate when the battery is in a 40% SOC state is 15%.

[0059] Example 3

[0060] This embodiment provides a secondary battery of the same system as that of Example 1. The difference between this embodiment and Example 1 is that when preparing the negative electrode plate, the mass content of silicon monoxide in the negative electrode material used is 10%, and the porosity ε of the negative electrode plate when the battery is in a state of 40% SOC is 13%.

[0061] Example 4

[0062] This embodiment provides a secondary battery of the same system as that of Example 1. The difference between this embodiment and Example 1 is that when preparing the negative electrode plate, the mass content of silicon monoxide in the negative electrode material used is 13%, and the porosity ε of the negative electrode plate when the battery is in a state of 40% SOC is 10%.

[0063] Example 5

[0064] This embodiment provides a secondary battery with the same system as that of embodiment 3. The difference between this embodiment and embodiment 3 is that when preparing the negative electrode sheet, the surface density of the negative electrode current collector coated with the negative electrode slurry is 75g / cm 2 After drying, the negative electrode sheet is rolled to 1.65g / cm 3The compaction density of the negative electrode sheet is 13% at a battery SOC of 40%.

[0065] Example 6

[0066] This embodiment provides a secondary battery with the same system as that of embodiment 3. The difference between this embodiment and embodiment 3 is that when preparing the negative electrode sheet, the surface density of the negative electrode current collector coated with the negative electrode slurry is 80g / cm 2 After drying, the negative electrode sheet is rolled to 1.65g / cm 3 The compaction density of the negative electrode sheet is 13% at a battery SOC of 40%.

[0067] Example 7

[0068] This embodiment provides a secondary battery with the same system as that of embodiment 4. The difference between this embodiment and embodiment 4 is that when preparing the negative electrode sheet, the surface density of the negative electrode current collector coated with the negative electrode slurry is 90g / cm 2 After drying, the negative electrode sheet is rolled to 1.65g / cm 3 The compaction density of the negative electrode sheet is 13% at a battery SOC of 40%.

[0069] Example 8

[0070] This embodiment provides a secondary battery with the same system as that of embodiment 3. The difference between this embodiment and embodiment 3 is that when preparing the negative electrode sheet, the negative electrode sheet is rolled to 1.6 g / cm after the slurry is applied and dried. 3 The compaction density of the negative electrode is 15%, while the porosity ε of the negative electrode sheet is 15% when the battery is in a 40% SOC state.

[0071] Example 9

[0072] This embodiment provides a secondary battery with the same system as that of embodiment 3. The difference between this embodiment and embodiment 3 is that when preparing the negative electrode sheet, the negative electrode sheet is rolled to 1.63g / cm after the slurry is applied and dried. 3 The compaction density of the negative electrode sheet is 14% at a battery SOC of 40%.

[0073] Example 10

[0074] This example provides a secondary battery with the same system as Example 8. The difference between this example and Example 8 is that when preparing the negative electrode sheet, the surface density of the negative electrode current collector coated with the negative electrode slurry is 70g / cm 2 After drying, the negative electrode sheet is rolled to 1.58g / cm 3 The compaction density of the prepared negative electrode sheet is 16% in the state of 40% SOC of the battery.

[0075] Example 11

[0076] This example provides a secondary battery with the same system as Example 8. The difference between this example and Example 8 is that when preparing the negative electrode sheet, the surface density of the negative electrode current collector coated with the negative electrode slurry is 70g / cm 2 , while the porosity ε of the negative electrode sheet is 15% when the battery is in the 40% SOC state.

[0077] Example 12

[0078] This example provides a secondary battery with the same system as Example 7. The difference between this example and Example 7 is that when preparing the negative electrode sheet, the surface density of the negative electrode current collector coated with the negative electrode slurry is 100g / cm 2 The porosity ε of the prepared negative electrode sheet is 10% when the battery is in a 40% SOC state.

[0079] Example 13

[0080] This embodiment provides a secondary battery of the same system as that of Example 3. The difference between this embodiment and Example 3 is that when preparing the negative electrode plate, silicon carbide is used instead of silicon 2 oxide in the negative electrode material; the porosity ε of the prepared negative electrode plate is 13% when the battery is in a 40% SOC state.

[0081] Comparative Example 1

[0082] This comparative example provides a secondary battery of the same system as Example 4. The difference between this comparative example and Example 4 is that when preparing the negative electrode plate, the mass content of silicon monoxide in the negative electrode material used is 15%, so that the porosity ε of the negative electrode plate is 6% when the battery is in a 40% SOC state.

[0083] Comparative Example 2

[0084] This comparative example provides a secondary battery of the same system as Example 4. The difference between this comparative example and Example 4 is that when preparing the negative electrode plate, the mass content of silicon monoxide in the negative electrode material used is 11%, so that the porosity ε of the negative electrode plate is 25% when the battery is in a 40% SOC state.

[0085] Porosity testing was performed on the negative electrode sheets prepared in Examples 1 to 13 and Comparative Examples 1 to 2. Initial energy density testing and cycle capacity retention testing were also performed on the electrochemical devices prepared in Examples 1 to 13 and Comparative Examples 1 to 2 to verify the superior capacity and fast-charging performance of the electrochemical devices corresponding to the different Examples and Comparative Examples. The test results are shown in Table 1. The test methods are as follows:

[0086] (1) Porosity ε test of negative electrode sheet: 1. For the negative electrode sheet in the initial state, weigh the volume of the negative electrode material, negative electrode binder and negative electrode conductive agent powder before coating the active material layer to obtain the initial volume V of the negative electrode active material layer raw material. i0 Then, after the negative electrode sheet is made, the volume of the active material layer V0 is measured, and finally the porosity of the negative electrode sheet when the electrochemical device is at 0% SOC is calculated as ε0 = 1-∑(V i0 ) / V0. 2. For the negative electrode sheet charged to 40% SOC, after the electrochemical device is charged to 40% SOC, the negative electrode sheet can be removed from the electrochemical device and the volume V of the active material layer on the negative electrode sheet charged to 40% SOC can be measured; then the active material layer on the negative electrode sheet can be scraped off and the volume V of the raw material powder of the active material layer charged to 40% SOC can be measured. i Finally, the porosity of the negative electrode sheet is calculated when the electrochemical device is at 40% SOC: ε = 1-∑(V i ) / V.

[0087] (2) Battery energy density test: At room temperature of 25°C, in the test voltage range of 2.8V (discharge cut-off voltage) to 4.3V (charge cut-off voltage), the battery is first charged at a current rate of 0.33C. After standing for 30 minutes, the battery is discharged at a current rate of 0.33C. After discharge, the discharge capacity of 0.33C / 0.33C is measured. Repeat three times, take the average of the three discharge capacities and divide it by the battery volume to obtain the battery energy density.

[0088] (3) Capacity retention rate test of battery fast charging cycle: At room temperature of 25℃, in the test voltage range of 2.8V (discharge cut-off voltage) to 4.3V (charge cut-off voltage), the battery is first charged to full charge at a current rate of 0.33C; after standing for 30 minutes, the battery is discharged to 10% SOC at a current rate of 0.33C; then, the battery is charged to 61% SOC at a current rate of 2.5C, the battery is charged to 65% SOC at a current rate of 2.4C, the battery is charged to 69% SOC at a current rate of 2.2C, the battery is charged to 73% SOC at a current rate of 2.0C, the battery is charged to 76% SOC at a current rate of 1.8C, and the battery is charged to 80% SOC at a current rate of 1.6C; finally, the battery is left to stand for 30 minutes and discharged to the discharge cut-off voltage at a current rate of 0.33C to complete a battery fast charging process. Repeat the above battery fast charging process 50 times, record the initial discharge capacity and 50cls discharge capacity of the battery, and calculate the capacity retention rate of 50cls fast charging cycle (50cls capacity retention rate = 50cls discharge capacity / initial discharge capacity).

[0089] Table 1: Parameter test results of negative electrode sheets prepared in Examples 1 to 13 and Comparative Examples 1 to 2, as well as the energy density and fast charge cycle capacity retention test results of the corresponding secondary batteries

[0090]

[0091] Comparing the test results of Examples 1 to 4 and Comparative Examples 1 to 2, it can be seen that controlling the porosity ε of the negative electrode sheet at 40% SOC of the battery to 10%-20% can optimize both the energy density and fast charging performance of the battery. If the porosity ε is higher than 20%, although the fast charging performance of the battery is improved, it is easy to lose active materials due to the excessive porosity ε0 of the negative electrode sheet when not charged, resulting in a decrease in the battery energy density; if the porosity ε is lower than 10%, although the energy density of the battery is guaranteed, the porosity is too low due to the expansion of the negative electrode sheet during charging, resulting in limited fast charging performance of the battery, and lithium plating is likely to occur during charging, causing the fast charging cycle capacity to decrease too quickly, and even causing safety problems;

[0092] By comparing the test results of Examples 4 and 7 and Examples 5 and 6, it can be seen that under the same compaction density and negative electrode material component ratio of the negative electrode sheet, only adjusting the surface density of the active material slurry coated on the negative electrode sheet does not affect the porosity ε of the negative electrode sheet at 40% SOC of the battery.

[0093] Comparing the test results of Examples 7 to 10, it can be seen that under the same negative electrode material component ratio, adjusting the compaction density of the negative electrode sheet will overall change the porosity of the negative electrode sheet at 0% SOC and 40% SOC of the battery. When the compaction density of the negative electrode sheet is between 1.6-1.7 g / cm 3 When the porosity is within the appropriate range, the energy density and fast charging capability of the secondary battery can be further improved on the basis of the effect brought by the limited porosity ε. 3 ) will lead to an overall decrease in the porosity of the electrode, resulting in a decrease in the fast charge cycle capacity retention rate, affecting the fast charge performance of the battery; if the compaction density of the negative electrode is too low (such as less than 1.6g / cm 3 ), although it will increase the porosity of the negative electrode sheet, it will also lead to a decrease in the energy density of the negative electrode sheet at the same thickness, resulting in a decrease in the energy density of the secondary battery.

[0094] Comparing the test results of Examples 5 to 8 and Examples 11 to 12, it can be seen that although the surface density of the negative electrode sheet has little effect on the porosity of the electrode sheet, it still has some impact on the energy density and fast charging performance of the secondary battery. When the compaction density of the negative electrode sheet is between 75-90g / m 2When the porosity is within the appropriate range, it is possible to further improve the energy density and fast charging capability of the secondary battery on the basis of the effect brought by the limited porosity ε. Comparing the test results of Examples 8 and 11, it can be seen that if the surface density of the negative electrode sheet is too low (less than 75g / m 2 ), it will cause the battery energy density to decrease; Comparing the test results of Examples 7 and 12, it can be seen that if the surface density of the negative electrode sheet is too high (higher than 90g / m 2 ), it will cause the battery fast charge cycle capacity retention rate to decrease, affecting the fast charge performance of the secondary battery.

[0095] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. An electrochemical device, characterized in that The electrochemical device includes a negative electrode plate, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer is coated on at least one side of the negative electrode current collector along the thickness direction; The negative electrode active material layer includes a negative electrode material, and the negative electrode material includes a silicon-based material; The negative electrode active material layer has a pore structure. When the electrochemical device is at a 40% state of charge, the porosity of the negative electrode active material layer is ε=1-∑(V i ) / V, the porosity ε is 10%-20%, V i is the sum of the volumes of the raw materials of the active material layer when the electrochemical device is at a 40% state of charge, and V is the volume of the negative electrode active material layer when the electrochemical device is at a 40% state of charge.

2. The electrochemical device according to claim 1, characterized in that The negative electrode active material layer further comprises a negative electrode binder and a negative electrode conductor, and the negative electrode material further comprises a carbon-based material; the porosity ε is ε=1-∑(V i ) / V,V i =V Si +V g +V b +V c , where V Si 、V g 、V b and V c are respectively the volumes of the silicon-based material, the carbon-based material, the negative electrode binder and the negative electrode conductive agent when the electrochemical device is at a 40% state of charge.

3. The electrochemical device according to claim 2, characterized in that: When the electrochemical device is in a 0% state of charge, the porosity of the negative electrode active material layer is ε0, and the porosity ε0 satisfies ε=1-(V Si0 +0.1V g0 +V0(1-ε0)) / V0, where the V Si0 and V g0 are respectively the volumes of the silicon-based material and the carbon-based material when the electrochemical device is in a 0% state of charge, and V0 is the volume of the negative electrode active material layer when the electrochemical device is in a 0% state of charge.

4. The electrochemical device according to claim 1 or 3, characterized in that: When the electrochemical device is in a 0% state of charge, the porosity ε0 of the negative electrode active material layer is 21%-30%.

5. The electrochemical device according to claim 2, characterized in that: The mass proportion of the silicon-based material to the sum of the mass of the carbon-based material and the silicon-based material is 8-15 wt %; the mass proportion of the carbon-based material to the sum of the mass of the carbon-based material and the silicon-based material is 85-92 wt %.

6. The electrochemical device according to claim 2, characterized in that: The carbon-based material includes at least one of graphite, soft carbon, hard carbon, pitch carbide, sintered coke, graphene and carbon nanotubes.

7. The electrochemical device according to claim 1, characterized in that: The silicon-based material includes at least one of silicon, silicon monoxide and silicon carbide.

8. The electrochemical device according to claim 1, characterized in that The compaction density of the negative electrode sheet is 1.6-1.7 g / cm 3 .

9. The electrochemical device according to claim 1, characterized in that: The surface density of the negative electrode active material layer is 75-90 g / m 2 .

10. An electrical device, characterized in that: The electrical device comprises the electrochemical device according to any one of claims 1 to 9.

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