Electrochemical devices and electronic devices

Abstract

The present application provides an electrochemical device and an electronic device. In some embodiments of the present application, an electrochemical device is provided, which includes: a positive electrode, including a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector; a negative electrode, including a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, the negative electrode active material layer includes: an edge region and a main region in a first direction, the edge region is located on one side or both sides of the main region, the first direction is parallel to the width direction of the negative electrode current collector; the capacity per unit area of ​​the edge region to the capacity per unit area of ​​the positive electrode active material layer is CB 1 , 1.05≤CB 1 ≤1.25. This application can improve safety performance and prevent deformation.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical energy storage, and in particular to electrochemical devices and electronic devices. Background Art

[0002] With the development of electrochemical energy storage technology, higher and higher requirements are placed on the safety performance of electrochemical devices (e.g., lithium-ion batteries). Electrochemical devices are prone to lithium deposition at the edge of the negative electrode during charging, resulting in safety hazards, and further improvements in this regard are expected. Summary of the invention

[0003] In some embodiments of the present application, an electrochemical device is proposed, which includes: a positive electrode, including a positive electrode collector and a positive electrode active material layer located on the positive electrode collector; a negative electrode, including a negative electrode collector and a negative electrode active material layer located on the negative electrode collector, the negative electrode active material layer includes in a first direction: an edge region and a main region, the edge region is located on one side or both sides of the main region, and the first direction is parallel to the width direction of the negative electrode collector; the ratio of the capacity per unit area of ​​the edge region to the capacity per unit area of ​​the positive electrode active material layer is CB1, 1.05≤CB1≤1.25.

[0004] In some embodiments of the present application, the ratio of the capacity per unit area of ​​the main region to the capacity per unit area of ​​the positive electrode active material layer is CB2, 1.03≤CB2≤1.045.

[0005] In some embodiments of the present application, the weight per unit area of ​​the edge region is the same as the weight per unit area of ​​the main region, and / or the thickness of the edge region is the same as the thickness of the main region.

[0006] In some embodiments of the present application, the length of the edge region in the first direction is not less than 2 mm; and / or the length of the edge region in the first direction is not greater than 10% of the length of the negative electrode in the first direction.

[0007] In some embodiments of the present application, the negative electrode active material layer includes a negative electrode material, and the gram capacity of the negative electrode material in the main region is smaller than the gram capacity of the negative electrode material in the edge region.

[0008] In some embodiments of the present application, the negative electrode material of the main region includes: graphite; and / or, the negative electrode material of the edge region includes at least one of graphite, silicon, silicon-based materials, silicon-carbon composites or metals.

[0009] In some embodiments of the present application, the negative electrode material in the edge region includes silicon, and the mass ratio of silicon in the negative electrode material in the edge region to the total mass ratio of the negative electrode material is 0.1% to 5%.

[0010] In some embodiments of the present application, the negative electrode active material layer includes a conductive agent, which includes: at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes or metal powder; and / or, the negative electrode active material layer includes a binder, which includes at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene or polyethylene oxide.

[0011] In some embodiments of the present application, the negative electrode active material layer is disposed on the negative electrode current collector by gravure printing and coating.

[0012] An embodiment of the present application further provides an electronic device, comprising the above-mentioned electrochemical device.

[0013] In some embodiments of the present application, an electrochemical device is proposed, which includes: a positive electrode, including a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector; a negative electrode, including a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, the negative electrode active material layer includes: an edge region and a main region in a first direction, the edge region is located on one side or both sides of the main region, and the first direction is parallel to the width direction of the negative electrode current collector; the capacity per unit area of ​​the edge region and the capacity per unit area of ​​the positive electrode active material layer are CB1, 1.05≤CB1≤1.25. The present application can prevent lithium deposition in the edge region, improve safety performance and prevent deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A front view showing the negative electrode of the electrochemical device in some embodiments of the present application

[0015] Figure 2 A top view of a negative electrode of an electrochemical device in some embodiments of the present application is shown.

[0016] Figure 3 A cross-sectional view of an edge region of a negative electrode of an electrochemical device in some embodiments of the present application is shown.

[0017] Figure 4 A cross-sectional view of a main body region of a negative electrode of an electrochemical device in some embodiments of the present application is shown. DETAILED DESCRIPTION

[0018] The following embodiments may enable those skilled in the art to more fully understand the present application, but do not limit the present application in any way.

[0019] For the design of electrochemical devices (e.g., lithium-ion batteries), the negative electrode sheet needs to reserve enough space for all the lithium released from the positive electrode sheet to be embedded in the negative electrode material. Therefore, the length and / or width edge of the negative electrode sheet usually exceeds the corresponding length and / or width of the positive electrode sheet, that is, an edge area is formed. The lithium-ion batteries used in mobile electronic devices are basically of narrow and long design. In order to increase the energy density, the coating weight is getting heavier, the compaction density is getting larger, and the charge and discharge current used is getting larger, which leads to more and more obvious edge lithium precipitation phenomenon, which is easy to cause safety hazards.

[0020] Taking lithium-ion batteries as an example, the edge area corresponding to the negative electrode of lithium-ion batteries usually includes non-lithium-embedded areas, transition areas, and lithium-embedded areas in the direction from the edge to the inside. During the battery discharge process, the distribution of lithium ions at the edge of the negative electrode decreases from the lithium-embedded area, transition area to the non-lithium-embedded area. According to the law of free diffusion, the lithium ions in the negative electrode active material will freely diffuse from high concentration to low concentration until the lithium ion concentration equilibrium position in the edge area is reached; during discharge, the lithium-embedded negative electrode will release lithium ions through the electrolyte and the isolation membrane and then embed them into the positive electrode; however, there is no positive electrode corresponding to the edge area of ​​the negative electrode. During the discharge process, the lithium de-lithiation reaction will not occur directly due to the lack of driving force. As the discharge time increases, the lithium ion concentration in the lithium-embedded area of ​​the negative electrode edge decreases, and the lithium ion concentration in the non-lithium-embedded area is high. At this time, according to the law of free diffusion, the lithium ions will diffuse from the non-lithium-embedded area to the lithium-embedded area driven by the concentration difference, and then detach and embed them into the positive electrode. Due to the effect of concentration diffusion, lithium ions are enriched in the edge area, and lithium precipitation is easy to occur in the edge area.

[0021] For the narrow and long structure, the head and tail of the electrode assembly of the electrochemical device store more electrolyte, which causes the head and tail to be immersed in the electrolyte for a long time. Under the long-term immersion of the electrode pieces in the electrolyte, the adhesion between the positive and negative electrode pieces and the separator becomes weaker, the gap between the positive and negative electrode pieces increases, the electron transmission distance increases, and the diffusion distance of the lithium ions of the positive electrode in the liquid phase increases, which will lead to an increase in impedance, making it difficult for lithium ions to be embedded and extracted in the edge area. In order to improve the lithium precipitation in the edge area, on the one hand, the kinetics of the edge area can be improved, and on the other hand, the growth of the internal resistance of the electrode piece during the cycle process in the edge area can be reduced. The greater the state of charge, the faster the aging of the electrode assembly, the greater the growth of the internal resistance, and the easier it is to precipitate lithium; the greater the charging current density, the easier it is to precipitate lithium; the lower the operating temperature, the more negative the potential of the negative electrode will be, and the more likely the lithium deposition side reaction on the surface of the negative electrode will occur.

[0022] In some embodiments of the present application, an electrochemical device is proposed to improve the lithium plating problem by rationally designing the state of charge. In some embodiments of the present application, the electrochemical device includes: a positive electrode and a negative electrode, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, the positive electrode current collector can use copper foil or aluminum foil, and the positive electrode active material layer is located on one side or both sides of the positive electrode current collector; please refer to Figure 1 The negative electrode includes a negative electrode current collector 10 and a negative electrode active material layer 1 located on the negative electrode current collector 10. The negative electrode current collector 10 can use copper foil or aluminum foil. The negative electrode active material layer 1 can be located on one side or both sides of the negative electrode current collector 10. The positive electrode and the negative electrode can be arranged opposite to each other. Please refer to Figure 2 The negative electrode active material layer 1 includes in the first direction: an edge region 11 and a main region 12, the edge region 11 is located on one side or both sides of the main region 12, and the first direction is parallel to the width direction of the negative electrode current collector 10; the capacity per unit area of ​​the edge region and the capacity per unit area of ​​the positive electrode active material layer are CB1, 1.05≤CB1≤1.25.

[0023] In some embodiments of the present application, the capacity per unit area of ​​the edge region is greater than the capacity per unit area of ​​the positive electrode active material layer, so that the edge region can ensure that the lithium ions released by the positive electrode are accommodated, and lithium precipitation is avoided because the negative electrode does not have enough space to receive lithium ions. At the same time, CB1 needs to be greater than 1.05. In addition to ensuring that the edge region of the negative electrode can accommodate the lithium ions released by the positive electrode, by setting a sufficiently large negative electrode capacity in the edge region, the state of charge of the edge region of the negative electrode can be limited to a lower level. Compared with the negative electrode in the fully embedded state, the potential will be higher, so that the potential of the edge region of the negative electrode is far away from the lithium precipitation potential. On the other hand, the edge region is controlled at a lower state of charge to reduce the aging rate of the electrochemical device, so that the impedance increase rate of the electrochemical device is slowed down, and the kinetic performance of the negative electrode is maintained at a good level, making lithium insertion easier, and further preventing lithium precipitation. At the same time, in this embodiment, CB1 is controlled not to be greater than 1.25, so as to avoid the problem of excessive excess capacity leading to cost increases and increased lithium ion transmission paths. More importantly, it has been found through experiments that when CB>1.25, the electrochemical device will have a problem of pole piece deformation after full charge.

[0024] In some embodiments of the present application, the capacity per unit area of ​​the main region 12 and the capacity per unit area of ​​the positive electrode active material layer are CB2, 1.03≤CB2≤1.045. In some embodiments of the present application, 1.03≤CB2, that is, the capacity per unit area of ​​the main region 11 is greater than the capacity per unit area of ​​the positive electrode active material layer, so as to ensure that the lithium released by the positive electrode can be fully embedded in the negative electrode. At the same time, CB2≤1.045, that is, the capacity per unit area of ​​the main region 11 is less than the capacity per unit area of ​​the edge region 11. This is because for the negative electrode, the edge region is in contact with the electrolyte, so the main region has a strong adhesion force compared to the edge region, and the edge region has a poor adhesion force. On the other hand, the immersion of the edge electrolyte causes the cohesion to deteriorate, making it easier for the main region to embed lithium. Therefore, in the design of the electrochemical device in the embodiment of the present application, the difference between the main region and the edge region is eliminated, and the lithium embedding capacity of the negative electrode in the edge region is improved, so that the edge region of the negative electrode and the main body The lithium embedding capacity reaches the same level, thereby solving the lithium precipitation problem.

[0025] In some embodiments of the present application, the weight per unit area of ​​the edge region is the same as the weight per unit area of ​​the main region. In some embodiments, the thickness of the edge region is the same as the thickness of the main region. In some embodiments of the present application, the weight and thickness of the edge region and the main region can be the same, which avoids the unevenness of the negative electrode and avoids the problem of wrinkles and curling during lamination or winding due to uneven weight or uneven thickness.

[0026] In some embodiments of the present application, the length of the edge region 11 in the first direction is not less than 2 mm. In some embodiments, the edge region 11 may be an edge region or include an edge region, and the length of the edge region 11 in the first direction may be the width of the edge region, and the width is not less than 2 mm. This ensures that the edge region 11 has sufficient width so that the negative electrode has sufficient margin when the positive electrode and the negative electrode are stacked or wound. If the edge region is too narrow, it will be difficult to control the negative electrode active material layer to exceed the positive electrode active material layer when the positive electrode and the negative electrode are stacked together, resulting in processing difficulties, and its improvement effect on lithium precipitation will also be reduced.

[0027] In some embodiments, the length of the edge region 11 in the first direction is not greater than 10% of the length of the negative electrode in the first direction. In some embodiments, the length of the edge region 11 in the direction cannot be too large. If the length of the edge region 11 in the first direction is too large, the manufacturing cost will be significantly increased.

[0028] In some embodiments of the present application, the negative electrode active material layer includes a negative electrode material, and the gram capacity of the negative electrode material in the main region is less than the gram capacity of the negative electrode material in the edge region. A negative electrode material with a larger gram capacity is used in the edge region, thereby increasing the gram capacity of the edge region and inhibiting lithium precipitation. In some embodiments of the present application, the negative electrode material in the main region includes: graphite; in some embodiments, the negative electrode material in the edge region includes at least one of graphite, silicon, silicon-based materials, silicon-carbon composites, or metals. In some embodiments, the gram capacity of the graphite used in the edge region may be higher than the gram capacity of the graphite used in the main region. In some embodiments, Figure 3 The cross-sectional view of the edge region is schematically shown. The negative electrode active material layer on the negative electrode current collector 10 in the edge region may include a conductive layer 13 and a mixed negative electrode material 15. Figure 4 The cross-sectional view of the main body region is schematically shown, and it can be seen that the negative electrode active material layer on the negative electrode current collector 10 in the main body region may include a conductive layer 13 and graphite 14 .

[0029] In some embodiments of the present application, the negative electrode material in the edge region includes silicon, and the mass of silicon in the negative electrode material in the edge region accounts for 0.1% to 5% of the total mass of the negative electrode material. In some embodiments, the edge region uses a mixture of silicon and graphite, or a mixture of silicon and other negative electrode materials. Silicon produces a large volume change when lithium is inserted and removed, so the mass content of the controller needs to be controlled to avoid excessive volume change that causes damage to the negative electrode active material layer.

[0030] In some embodiments of the present application, the negative electrode active material layer includes a conductive agent, which includes: at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes or metal powder; in some embodiments, the negative electrode active material layer includes a binder, which includes at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene or polyethylene oxide.

[0031] In some embodiments of the present application, the negative electrode active material layer is disposed on the negative electrode current collector by gravure printing and coating. In some embodiments, gravure printing is used to increase the adhesion between the negative electrode current collector and the negative electrode active material layer and increase conductivity.

[0032] In some embodiments of the present application, the positive electrode active material layer corresponding to the main area has the same composition and coating weight as the positive electrode active material layer corresponding to the edge area, that is, the present application may only improve the negative electrode active material layer without improving the positive electrode, thereby inhibiting lithium precipitation.

[0033] In some embodiments, the positive electrode active material layer may include a positive electrode material, a conductive agent, and a binder. In some embodiments, the positive electrode material may include at least one of lithium cobaltate, lithium iron phosphate, lithium aluminum oxide, lithium manganate, or nickel cobalt manganate. In some embodiments, the conductive agent of the positive electrode plate may include at least one of carbon black, lamellar graphite, graphene, or carbon nanotubes. In some embodiments, the binder in the positive electrode plate may include polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, a polyamide, a polyacrylonitrile, a polyacrylate, a polyacrylic acid, a polyacrylate, a carboxymethyl cellulose sodium, polyvinyl acetate, polyvinylpyrrolidone, a polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. In some embodiments, the mass ratio of the positive electrode material, the conductive agent, and the binder in the positive electrode active material layer 102 is (80-99): (0.1-10): (0.1-10), but this is only an example, and any other suitable mass ratio may be used.

[0034] In some embodiments, the electrochemical device includes a separator between the positive electrode and the negative electrode, and the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene or ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a good effect on preventing short circuits and can improve the stability of the battery through the shutdown effect. In some embodiments, the thickness of the separator 11 is in the range of about 3 μm to 20 μm.

[0035] In some embodiments, the surface of the isolation membrane may further include a porous layer, the porous layer being disposed on at least one surface of the isolation membrane, the porous layer including inorganic particles and a binder, the inorganic particles being selected from at least one of aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the isolation membrane have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is selected from at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The porous layer on the surface of the separator can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the separator, and enhance the adhesion between the separator and the pole piece.

[0036] In some embodiments, the electrochemical device includes a lithium ion battery, but the present application is not limited thereto. In some embodiments, the electrochemical device also includes an electrolyte, and the electrolyte includes at least one of a fluoroether, a fluoroethylene carbonate, or an ether nitrile. In some embodiments, the electrolyte also includes a lithium salt, and the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, and the concentration of the lithium salt is 1 mol / L to 2 mol / L, and the mass ratio of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate is 0.06 to 5. In some embodiments, the electrolyte may also include a non-aqueous solvent. The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.

[0037] The carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound or a combination thereof.

[0038] Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC) or combinations thereof. Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate or combinations thereof.

[0039] Examples of the carboxylic acid ester compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

[0040] Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0041] Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid esters or combinations thereof.

[0042] Embodiments of the present application also provide an electronic device including the above-mentioned electrochemical device. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a drone, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0043] Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein a lithium-ion battery is used as an example.

[0044] Example 1

[0045] Preparation of negative electrode: The current collector uses copper foil, the edge area uses a mixture of graphite and silicon as the negative electrode material, the conductive material carbon black, and the binder use styrene-butadiene rubber and carboxymethyl cellulose. The mixed negative electrode material, conductive agent and binder are mixed at a mass percentage ratio of 98:1:1 and dispersed in deionized water to form a slurry in the edge area. Graphite is used as the negative electrode material in the main area, and the conductive material carbon black and the binder use styrene-butadiene rubber and carboxymethyl cellulose. The negative electrode material, conductive agent and binder are mixed at a mass percentage ratio of 98:1:1 and dispersed in deionized water to form a slurry in the main area. The slurry in the main area is coated on copper foil to form the main area, and the slurry in the edge area is coated on one side of the main area to form the edge area. In order to ensure consistent compaction density, the coating weight of the edge area is consistent with the coating weight of the main area. After coating, it is dried in a vacuum oven, and a negative electrode with consistent thickness and compaction density in the edge area and the main area is prepared by three cold pressings and stripping.

[0046] Preparation of positive electrode: The positive electrode materials of lithium cobalt oxide, carbon nanotubes (CNT), Super P and polyvinylidene fluoride (PVDF) are fully stirred and mixed in an N-methylpyrrolidone solvent system at a mass percentage ratio of 96.2:0.5:0.3:3, and then coated on aluminum foil to obtain a positive electrode active material layer. After drying and cold pressing, the positive electrode is obtained.

[0047] Preparation of isolation film: polyacrylate is stirred to form a uniform slurry, the slurry is coated on both sides of the porous substrate (polyethylene), and the isolation film is formed after drying.

[0048] Preparation of electrolyte: In an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): vinylene carbonate (VC) = 20:30:20:28:2, mass percentage ratio) are prepared in a mass percentage ratio of 8:92 to form an electrolyte with a lithium salt concentration of 1 mol / L.

[0049] Preparation of lithium-ion battery: stack the positive electrode, separator and negative electrode in order, so that the separator is between the positive electrode and the negative electrode to play a role of isolation, and wind them to obtain the electrode assembly. Place the electrode assembly in the outer packaging aluminum plastic film, remove moisture at 80°C, inject the above electrolyte and package, and obtain the lithium-ion battery through the process of formation, degassing, shaping, etc.

[0050] The difference between each embodiment and comparative example is only the negative electrode. The specific differences are shown in the table below.

[0051] The test methods of the present application are described below.

[0052] Lithium deposition on negative electrode: At 25°C, charge the lithium-ion battery to 4.3V at a constant current of 1C, then charge to 4.5V at a constant current of 0.5C, and finally charge to 0.05C at a constant voltage of 4.5V, let stand for 2 minutes, and then discharge to 3.0V at a constant current of 1C, let stand for 2 minutes. This is a cycle. After repeating 800 cycles, disassemble the lithium-ion battery to obtain the electrode assembly, spread the electrode assembly flat, and if any part of the negative electrode edge area is larger than 2mm 2 If lithium deposition occurs in the edge area, it is judged as edge lithium deposition. The battery thickness can be monitored during the test. If any abnormality is found, the battery can be disassembled to confirm whether lithium deposition occurs in the edge area.

[0053] Expansion during the cycle: An important parameter that reflects the changes in the internal structure of the battery during the cycle. Generally, interface abnormalities such as purple spots, black spots, lithium deposition, etc. occur during the battery cycle process, which will lead to abnormalities. During the above-mentioned cycle test of lithium deposition on the negative electrode sheet, the cycle expansion rate = thickness increased during the cycle / initial thickness. If the expansion during the cycle is abnormal, the battery will generally be disassembled to confirm the interface problem.

[0054] Table 1

[0055]

[0056] The preparation parameters and performance test results of Examples 1 to 7 and Comparative Example 1 are shown in the table above. In Comparative Example 1, graphite is used in both the edge area and the main area, and the mixed material is graphite and silicon. In different embodiments, CB1 is controlled by controlling the silicon content in the mixed material.

[0057] As can be seen from Table 1, the CB1 of Comparative Example 1 is less than 1.05, the CB1 of Example 7 is greater than 1.25, and the CB1 of Examples 1 to 6 satisfies 1.05≤CB1≤1.25. It can be seen that the cycle expansion rate of Comparative Example 1 is relatively high, and serious lithium deposition in the edge area occurs, and the battery is deformed. After the CB1 is increased, no lithium deposition in the edge area occurs in the battery. It can be seen that the problem of lithium deposition in the edge area can be solved by controlling CB1 to be greater than 1.05. It can be seen from Examples 1 to 7 that when CB1 is within the range defined in the present application, the cycle expansion rate is small, lithium deposition in the edge area does not occur, and the battery does not deform. When CB1 is greater than 1.25, the cycle expansion rate increases, and battery deformation occurs. It can be seen that when CB1 is too large, it is not conducive to the overall performance of the battery.

[0058] Table 2

[0059]

[0060] The preparation parameters and performance test results of Examples 2, 8 to 9 are shown in the table above. The mixed material is graphite and silicon. In different embodiments, CB1 is controlled by controlling the silicon content in the mixed material, and CB2 is controlled by controlling the type of graphite used in the main region.

[0061] It can be seen from Table 2 that for Examples 2, 8 and 9, 1.03≤CB2≤1.045 is satisfied, the cycle expansion rate is small, lithium plating does not occur, and there is no deformation. However, in Example 10, the gram capacity per unit area of ​​the main region is too low, resulting in CB2 being too small, less than 1.03, so the main region does not have sufficient capacity to accommodate lithium ions, resulting in lithium plating, which in turn causes battery deformation and an increase in the cycle expansion rate.

[0062] Table 3

[0063]

[0064] The preparation parameters and performance test results of Examples 2, 8, 10 to 11 are shown in the table above. The mixed material is graphite and silicon. In different embodiments, CB1 is controlled by controlling the silicon content in the mixed material, and CB2 is controlled by controlling the type of graphite used in the main region.

[0065] It can be seen from Table 3 that when the width of the negative electrode is constant, changing the width of the edge area and the main area has an impact on the battery. It can be seen from Table 3 that no lithium deposition occurred in the edge area in the above embodiments, and the batteries were not deformed, and the cycle expansion rates were small. It can be seen that when the width of the edge area is not more than 10% of the width of the negative electrode, the safety performance and cycle performance of the battery can be guaranteed.

[0066] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of disclosure involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features. For example, the above features are replaced with the technical features with similar functions disclosed in the present application.

Claims

1. An electrochemical device comprising: A positive electrode, comprising a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector; A negative electrode, comprising a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, wherein the negative electrode active material layer comprises: an edge region and a main region in a first direction, wherein the edge region is located on one side or both sides of the main region, and the first direction is parallel to a width direction of the negative electrode current collector; The ratio of the capacity per unit area of ​​the edge region to the capacity per unit area of ​​the positive electrode active material layer is CB1, 1.05≤CB1≤1.25; The capacity ratio of the main body region per unit area to the positive electrode active material layer per unit area is CB2, 1.03≤CB2≤1.045; The edge region is the negative electrode active material layer on the region where the width edge of the negative electrode exceeds the corresponding width of the positive electrode.

2. The electrochemical device according to claim 1, wherein: The weight per unit area of ​​the edge region is the same as the weight per unit area of ​​the main region, and / or the thickness of the edge region is the same as the thickness of the main region.

3. The electrochemical device according to claim 1, wherein The length of the edge area in the first direction is not less than 2 mm; and / or, A length of the edge region in the first direction is not greater than 10% of a length of the negative electrode in the first direction.

4. The electrochemical device according to claim 1, wherein The negative electrode active material layer includes a negative electrode material, and the gram capacity of the negative electrode material in the main region is smaller than the gram capacity of the negative electrode material in the edge region.

5. The electrochemical device according to claim 1, wherein The negative electrode material of the main body region includes: graphite; And / or, the negative electrode material of the edge region includes at least one of graphite, silicon, a silicon-carbon composite or a metal.

6. The electrochemical device according to claim 4, wherein: The negative electrode material in the edge region includes silicon, and the mass ratio of silicon in the negative electrode material in the edge region to the total mass ratio of the negative electrode material is 0.1% to 5%.

7. The electrochemical device according to claim 1, wherein: The negative electrode active material layer includes a conductive agent, and the conductive agent includes at least one of carbon black, carbon fiber, carbon nanotube, or metal powder; and / or, The negative electrode active material layer includes a binder, and the binder includes at least one of polyvinyl alcohol, sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene or polyethylene oxide.

8. The electrochemical device according to claim 1, wherein The negative electrode active material layer is disposed on the negative electrode current collector by gravure printing and coating.

9. An electronic device comprising the electrochemical device according to any one of claims 1 to 8.

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