WO2023160182A1 - 电化学装置和电子装置 - Google Patents

电化学装置和电子装置 Download PDF

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WO2023160182A1
WO2023160182A1 PCT/CN2022/140583 CN2022140583W WO2023160182A1 WO 2023160182 A1 WO2023160182 A1 WO 2023160182A1 CN 2022140583 W CN2022140583 W CN 2022140583W WO 2023160182 A1 WO2023160182 A1 WO 2023160182A1
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negative electrode
active material
electrode active
material layer
edge
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PCT/CN2022/140583
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English (en)
French (fr)
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陶威
武锐涛
吴飞
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宁德新能源科技有限公司
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Priority to EP22871164.4A priority Critical patent/EP4258404A4/en
Priority to US18/129,360 priority patent/US20230275228A1/en
Publication of WO2023160182A1 publication Critical patent/WO2023160182A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present application relates to the field of electrochemical energy storage, in particular to electrochemical devices and electronic devices.
  • electrochemical energy storage technology With the development of electrochemical energy storage technology, the safety performance and energy density of electrochemical devices (eg, lithium-ion batteries) are increasingly required, and further improvements in this regard are expected.
  • electrochemical devices eg, lithium-ion batteries
  • the positive electrode sheet includes a positive electrode active material layer;
  • the negative electrode sheet includes a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer, and the first negative electrode active material layer is located in the negative electrode collector.
  • the first negative electrode active material layer has a first edge and a second edge in the length direction of the negative pole sheet, and the second negative electrode active material layer has a third edge in the length direction and the fourth edge
  • the positive electrode active material layer has the fifth edge and the sixth edge in the length direction
  • the first edge, the third edge and the fifth edge are on the same side
  • the second edge, the fourth edge and the sixth edge are on the opposite side the other side
  • the third edge protrudes from the first edge and the fifth edge in the length direction
  • the distance between the first edge and the fifth edge in the length direction is less than 2mm.
  • the distance between the first edge and the fifth edge in the length direction is 0.
  • the fourth edge protrudes lengthwise from the second edge and the sixth edge.
  • the distance between the second edge and the sixth edge in the length direction is less than 2 mm.
  • the distance between the second edge and the sixth edge in the length direction is 0.
  • the distance between the third edge and the fifth edge in the length direction is 2 mm to 8 mm.
  • the distance between the fourth edge and the sixth edge in the length direction is 2 mm to 8 mm.
  • the gram capacity of the negative electrode active material in the first negative electrode active material layer is greater than the gram capacity of the negative electrode active material in the second negative electrode active material layer.
  • the resistivity of the second negative electrode active material layer is less than the resistivity of the first negative electrode active material layer; in some embodiments, the mass percentage of the conductive agent in the first negative electrode active material layer is less than that of the second negative electrode active material layer.
  • the mass percentage of conductive agent in the active material layer In some embodiments, the porosity of the first negative electrode active material layer is less than the porosity of the second negative electrode active material layer; In some embodiments, the first negative electrode active material layer And the second negative electrode active material layer includes: a negative electrode active material coated with a modifier, and the coating amount of the negative electrode active material in the first negative electrode active material layer is less than the coating amount of the negative electrode active material in the second negative electrode active material layer; In some embodiments, the average particle diameter of the negative electrode material in the first negative electrode active material layer is greater than the average particle diameter of the negative electrode material in the second negative electrode active material layer; in some embodiments, the first negative electrode active material layer and the second negative electrode The active material layer includes graphite, and the graphite orientation index in the first negative electrode active material layer is greater than the graphite orientation index in the second negative electrode active material layer.
  • the embodiment of the present application also provides an electronic device, including the above-mentioned electrochemical device.
  • the present application protrudes from the first edge and the fifth edge in the length direction by making the third edge, the lithium ions released from the positive electrode sheet can be embedded in the second negative active material layer, because the second negative active material layer has better than
  • the dynamic performance of the first negative electrode active material layer can therefore prevent the lithium precipitation of the negative electrode sheet; in addition, by making the first edge and the fifth edge substantially aligned in the length direction, the capacity loss of the negative electrode is avoided, and the electrochemical performance is ensured.
  • the energy density of the device prevents lithium precipitation and is conducive to cycle performance.
  • Figure 1 shows a cross-sectional view along the length of a negative electrode tab of a portion of an electrochemical device according to some embodiments.
  • FIG. 2 illustrates a cross-sectional view along the length of a negative electrode tab of a portion of an electrochemical device according to some embodiments.
  • FIG. 3 shows a cross-sectional view of part of the electrochemical device of the comparative example along the length direction of the negative electrode tab.
  • FIG. 4 shows a cross-sectional view of part of the electrochemical device of Example 1 along the length direction of the negative electrode sheet.
  • FIG. 5 shows a cross-sectional view of part of the electrochemical device of Example 2 along the length direction of the negative electrode sheet.
  • FIG. 6 shows a cross-sectional view of part of the electrochemical device of Example 3 along the length direction of the negative electrode sheet.
  • FIG. 7 shows a cross-sectional view of part of the electrochemical device of Example 4 along the length direction of the negative electrode sheet.
  • FIG. 8 shows a cross-sectional view of part of the electrochemical device of Example 5 along the length direction of the negative electrode sheet.
  • Positive pole piece 101. Positive current collector; 102. Positive active material layer; 1021. Fifth edge; 11. Separator; 1231. Third edge; 1221. First edge; 1022. Sixth 1232, the fourth edge; 123, the second negative electrode active material layer; 1222, the second edge; 122, the first negative electrode active material layer; 121, the negative electrode current collector; 12, the negative electrode sheet.
  • the negative electrode sheet For the design of electrochemical devices (for example, lithium-ion batteries), it is necessary for the negative electrode sheet to reserve enough space for the lithium extracted from the positive electrode sheet to be fully embedded in the negative electrode active material, so the length and/or width of the negative electrode sheet Usually, the corresponding length and/or width of the positive pole piece will be exceeded, so as to avoid the problem of lithium precipitation or short circuit caused by the positive pole piece exceeding the negative pole piece.
  • the kinetic performance of the part of the negative pole piece beyond the positive pole piece is similar to that of the non-exceeded part, and the path to the excess part of the negative pole piece is longer than the path to the non-exceeded part, so the lithium in the excess part It is not easy to come out, which destroys the balance of coming out and intercalation.
  • the excess lithium is more embedded than the extracted lithium. As time increases, the excess lithium will accumulate, causing the excess part to analyze lithium, which is manifested as the electrode assembly during the cycle. Lithium analysis of the head and tail.
  • asymmetrically narrowed and symmetrically narrowed pole pieces are used to improve the lithium separation at the tail of the negative pole piece, or the method of pasting glue on the tail of the positive pole piece is used to make the lithium ion of the positive pole piece It cannot be pulled out to limit the lithium deposition at the tail of the negative electrode sheet.
  • this method can only allow the excess side length to delay the lithium deposition. It does not fundamentally solve the problem and causes capacity loss.
  • the upper layer of the negative electrode sheet The coating width of the upper layer is greater than the coating width of the lower layer, and the structure of the upper layer covering the lower layer is formed in the width direction of the negative electrode sheet.
  • the dynamics of the upper layer is better than that of the lower layer, and the capacity of the corresponding upper layer will be different from that of the lower layer.
  • the capacity of high-kinetic materials will be low, so the capacity of the part of the upper layer exceeding the lower layer is lower than that of the lower layer, so the corresponding anode-to-cathode capacity ratio (N/P ratio) will change, that is, the excess N /P is small, to a certain extent, it will deteriorate the lithium precipitation.
  • some embodiments of the present application provide an electrochemical device, which includes a positive pole piece 10 and a negative pole piece 12 .
  • the positive electrode tab 10 and the negative electrode tab 12 are separated by a separator 11 disposed therebetween.
  • the positive electrode sheet 10 includes a positive electrode active material layer 102 .
  • the positive electrode sheet 10 may further include a positive electrode current collector 101 , and the positive electrode active material layer 102 may be disposed on one or both sides of the positive electrode current collector 101 .
  • the negative electrode sheet 12 includes a negative electrode current collector 121, a first negative electrode active material layer 122 and a second negative electrode active material layer 123, and the first negative electrode active material layer 122 is positioned between the negative electrode current collector 121 and the second negative electrode active material layer. Between layers 123. It should be understood that although the first negative electrode active material layer 122 and the second negative electrode active material layer 123 are shown as being located on one side of the negative electrode current collector 121 in FIG. The first negative active material layer 122 and the second negative active material layer 123 may exist on both sides.
  • the first negative electrode active material layer 122 has a first edge 1221 and a second edge 1222 in the length direction of the negative electrode sheet 12 (horizontal direction in FIG. 1 ), and the second negative electrode
  • the active material layer 123 has a third edge 1231 and a fourth edge 1232 in the length direction
  • the positive electrode active material layer 102 has a fifth edge 1021 and a sixth edge 1022 in the length direction.
  • the first edge 1221 , the third edge 1231 and the fifth edge 1021 are located on the same side
  • the second edge 1222 , the fourth edge 1232 and the sixth edge 1022 are located on the opposite side.
  • the third edge 1231 protrudes from the first edge 1221 and the fifth edge 1021 in the length direction (horizontal direction in FIG. 1 ).
  • the first edge 1221 is aligned with the fifth edge 1021, but due to process errors, when the distance between the first edge 1221 and the fifth edge 1021 in the length direction is less than 2 mm, the first edge can be considered 1221 is aligned with fifth edge 1021 .
  • the distance between the first edge 1221 and the fifth edge 1021 in the length direction is 0, that is, they are aligned in an ideal state.
  • the kinetic performance of the second negative electrode active material layer 123 is better than that of the first negative electrode active material layer 122 .
  • the kinetic performance of the second negative electrode active material layer 123 is better than that of the first negative electrode active material layer 122, and the part of the negative electrode pole piece 12 that exceeds the positive pole piece 10 in the length direction is basically the second negative electrode active material layer 123, that is, the kinetic performance Better materials, so the part of the negative pole piece 12 that exceeds the positive pole piece 10 in the length direction can well extract lithium ions, which can solve the problem of lithium precipitation, and the structure does not lose active materials, so it will not affect the overall capacity.
  • the kinetic performance of the second negative electrode active material layer 123 is better than that of the first negative electrode active material layer 122, therefore, the gram capacity of the negative electrode active material in the first negative electrode active material layer 122 is higher than that of the negative electrode in the second negative electrode active material layer 123.
  • the gram capacity of the active material if the first edge 1221 obviously does not reach the fifth edge 1021 in the length direction, the negative electrode sheet 12 there will not have enough space to store the lithium ions released from the positive electrode sheet, resulting in lithium precipitation, affecting cycle performance.
  • the dynamic performance of the negative pole piece 12 at the first edge 1221 is the dynamics of the first negative active material layer 122 and the second negative active material layer 123. Due to the superimposed effect of the performance, the kinetic performance will decrease compared with that of only the second negative electrode active material layer 123 , which will lead to lithium precipitation at the edge of the negative electrode sheet 12 and affect the cycle performance.
  • the third edge 1231 protrude from the first edge 1221 and the fifth edge 1021 in the length direction, lithium ions released from the positive electrode active material layer 102 can be embedded in the second negative electrode active material layer 123 and can be well separated out, The lithium analysis on the negative pole piece 12 is avoided; in addition, by making the first edge 1221 and the fifth edge 1021 substantially aligned in the length direction, the first negative electrode active material layer 122 with high capacity is adapted to the positive electrode active material layer 102 , can not only ensure the capacity, but also prevent the first negative electrode active material layer 122 from affecting the dynamic performance of the negative electrode sheet 12 beyond the positive electrode sheet 10, which improves the energy density of the electrochemical device while preventing lithium precipitation, thus ensuring cycle performance. Therefore, the electrochemical device of the present application not only avoids lithium deposition on the negative electrode sheet, but also minimizes adverse effects on the energy density of the electrochemical device, and ensures cycle performance.
  • the lithium ions extracted from the edge region of the positive electrode sheet 10 will not be fully stored in the negative electrode sheet 12. , so that lithium precipitation occurs in the edge region of the negative electrode sheet 12 and reduces the capacity, affects the cycle performance of the electrochemical device, and even causes a short circuit or a safety problem.
  • the first edge 1221 protrudes relative to the fifth edge 1021 of the positive electrode active material layer 102 the dynamic performance of the part of the negative electrode sheet 12 beyond the positive electrode sheet 10 will be reduced, which may lead to lithium precipitation and affect cycle performance.
  • the width direction of the negative electrode sheet it is also possible to use the upper layer coating (the second negative electrode active material layer) width to be greater than the lower layer coating (the first negative electrode active material layer) width, and the edge of the lower layer coating and the edge of the positive electrode active material layer
  • the width of the negative pole piece also exceeds the design of the positive pole piece.
  • the coating of the lower layer on the negative pole piece is aligned with the coating of the positive pole piece, and the coating of the negative pole piece is The upper layer of the cloth exceeds the coating of the positive pole piece, and the dynamic performance of the upper coating is better than that of the lower coating, which can significantly improve the cycle performance.
  • the coating of the upper coating with high dynamic performance improves the dynamic performance, thereby Effectively improve lithium separation and improve cycle performance; compared with fully coating the second negative electrode active material layer, this solution can further increase the energy density.
  • the fourth edge 1232 protrudes from the second edge 1222 and the sixth edge 1022 in the length direction. In this way, the protruding second negative electrode active material layer 123 can better receive the lithium ions released from the positive electrode active material layer 102 , avoiding lithium deposition on the negative electrode sheet 12 .
  • the second edge 1222 is aligned with the sixth edge 1022, but due to the existence of process errors, when the distance between the second edge 1222 and the sixth edge 1022 in the length direction is less than 2mm, it can be considered as the second edge 1222.
  • Edge 1222 is aligned with sixth edge 1022 .
  • the distance between the second edge 1222 and the sixth edge 1022 in the length direction is 0. That is, the alignment in the ideal state.
  • the pole piece 12 protrudes beyond the influence of the dynamic performance of the edge portion of the positive pole piece 10, thereby preventing lithium deposition and ensuring cycle performance. Therefore, the electrochemical device of the present application not only avoids lithium deposition on the negative electrode sheet, ensures cycle performance, but also minimizes adverse effects on the energy density of the electrochemical device.
  • the thickness of the second negative active material layer 123 is smaller than the thickness of the first negative active material layer 122 . In this way, compared with the situation where both the second negative electrode active material layer 123 and the first negative electrode active material layer 122 protrude, the first negative electrode active material layer 122 with a larger thickness is aligned with the edge of the positive electrode active material layer 102, due to the first The gram capacity of the negative electrode active material in the negative electrode active material layer 122 is higher than the gram capacity of the negative electrode active material in the second negative electrode active material layer 123 , so the energy density of the electrochemical device can be improved.
  • the distance between the third edge 1231 and the fifth edge 1021 in the length direction is 2 mm to 8 mm, further 3 mm to 8 mm, and further 3 mm to 5 mm. In some embodiments, the distance between the fourth edge 1232 and the sixth edge 1022 in the length direction is 2 mm to 8 mm, further 3 mm to 8 mm, and further 3 mm to 5 mm.
  • the protruding second negative electrode active material layer 123 cannot sufficiently Receive lithium ions released from the positive electrode active material layer 102; if the distance between the third edge 1231 and the fifth edge 1021 in the length direction or the distance between the fourth edge 1232 and the sixth edge 1022 in the length direction is too large, then The space occupied by the second negative electrode active material layer 123 with a smaller gram capacity may be unnecessarily increased, which will adversely affect the energy density of the electrochemical device.
  • the gram capacity of the negative electrode active material in the first negative electrode active material layer 122 is greater than the gram capacity of the negative electrode active material in the second negative electrode active material layer 123 .
  • the resistivity of the second negative electrode active material layer 123 is less than the resistivity of the first negative electrode active material layer 122, therefore, the second negative electrode active material layer 123 can well release the embedded lithium ions, preventing lithium from being separated out. . And it can provide a better channel for lithium ions to transport into the first negative electrode active material layer 122, and promote lithium ions to enter the inner first negative electrode active material layer 122, which is beneficial to the rate performance.
  • the mass percentage of the conductive agent in the first negative electrode active material layer 122 is less than the mass percentage of the conductive agent in the second negative electrode active material layer 123 .
  • the conductive agent can be conductive carbon black, carbon nanotubes, etc., and the kinetic performance of the second negative electrode active material layer 123 can be improved by increasing the content of the conductive agent in the second negative electrode active material layer 123 .
  • the porosity of the first negative electrode active material layer is smaller than that of the second negative electrode active material layer, thereby providing more channels for the transmission of lithium ions.
  • the first negative electrode active material layer 122 and the second negative electrode active material layer 123 include: a negative electrode active material coated with a modifier, and the coating amount of the negative electrode active material in the first negative electrode active material layer 122 is less than The coating amount of the negative electrode active material in the second negative electrode active material layer 123 is such that lithium ions can be more easily intercalated and extracted in the negative electrode active material of the second negative electrode active material layer 123 .
  • the average particle diameter of the negative electrode active material in the first negative electrode active material layer 122 is larger than the average particle diameter of the negative electrode active material in the second negative electrode active material layer 123, so the negative electrode active material in the second negative electrode active material layer 123 The specific surface area of the material is larger, which is conducive to the transmission of lithium ions.
  • the first negative electrode active material layer 122 and the second negative electrode active material layer 123 include graphite, and the orientation index of graphite in the first negative electrode active material layer is greater than that in the second negative electrode active material layer.
  • the positive electrode collector 101 aluminum foil can be used for the positive electrode collector 101 , of course, other positive electrode collectors commonly used in the field can also be used.
  • the positive electrode collector may have a thickness of 1 ⁇ m to 50 ⁇ m.
  • the positive electrode active material layer 102 may be coated only on a partial area of the positive electrode current collector 101 .
  • the positive electrode active material layer 102 may include a positive electrode material, a conductive agent, and a binder.
  • the positive electrode material may include at least one of lithium cobalt oxide, lithium iron phosphate, lithium aluminate, lithium manganate, or lithium nickel cobalt manganese oxide.
  • the conductive agent of the positive electrode sheet 10 may include at least one of conductive carbon black, graphite flakes, graphene or carbon nanotubes.
  • the binder in the positive electrode sheet 10 may include polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, styrene-acrylate copolymer, styrene-butadiene copolymer, Polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene at least one of vinyl fluoride or polyhexafluoropropylene.
  • 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, Any other suitable mass ratio may be used.
  • both the first negative electrode active material layer 122 and the second negative electrode active material layer 123 may include a negative electrode material, a conductive agent, and a binder.
  • the negative electrode material may include at least one of artificial graphite, natural graphite, graphite coated with a modifier, silicon, and silicon-based materials.
  • the silicon-based material includes at least one of silicon, silicon-oxygen material, silicon-carbon material, or silicon-oxygen-carbon material.
  • the conductive agent in the first negative electrode active material layer 122 and the second negative electrode active material layer 123 may include conductive carbon black, Ketjen black, flake graphite, graphene, metal powder, carbon nanotube or carbon fiber at least one of the In some embodiments, the binder in the first negative electrode active material layer 122 and the second negative electrode active material layer 123 may include carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyamide At least one of imine, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin or polyfluorene.
  • CMC carboxymethyl cellulose
  • the mass ratio of the negative electrode material, conductive agent and binder in the first negative electrode active material layer 122 and the second negative electrode active material layer 123 may be (78 to 98.5): (0.1 to 10): ( 0.1 to 10).
  • the above-mentioned negative material can be dissolved in a solvent according to a certain ratio, and mixed uniformly to prepare a slurry.
  • the mass content of the negative electrode material in the second negative electrode active material layer can be 90% to 98%, preferably 97.8%, the mass content of the conductive agent can be 0.2% to 4%, preferably 1.2%, and the binder
  • the mass content of the conductive agent can be 0.6% to 6%, preferably 1.0%, the mass content of the negative electrode material in the first negative electrode active material layer is 98.0%; the mass content of the conductive agent is 1.0%; the mass content of the binding agent can be 0.6% to 6%, preferably 1.0%, the resulting slurry has a viscosity of 2000mPa.s to 7000mPa.s and a solid content of 70% to 80%.
  • the above description is only an example, and any other suitable materials and mass ratios may be used.
  • the types and formulations of the negative electrode materials in the first negative electrode active material layer 122 and the second negative electrode active material layer 123 may be the same or different.
  • the negative electrode current collector 121 may use at least one of copper foil, nickel foil, or carbon-based current collector.
  • the double-layer coating of the negative pole piece is completed by a double-layer coating machine, and the two nozzles are coated at the same time.
  • the width of the coating is realized by the width of the gasket.
  • the width of the upper layer is greater than the width of the lower layer, and the width difference corresponds to the embodiment.
  • the length of coating is determined by the gap valves of the upper and lower layers.
  • the response time of the upper layer is longer than that of the lower layer.
  • the specific time difference is related to the coating speed and the structure of the coating head and tail.
  • the isolation film 11 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid.
  • polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.
  • the thickness of the isolation film 11 is in the range of about 3 ⁇ m to 20 ⁇ m.
  • the surface of the isolation membrane 11 may also include a porous layer, the porous layer is arranged on at least one surface of the isolation membrane, the porous layer includes inorganic particles and a binder, and the inorganic particles are selected from alumina (Al 2 O 3 ), silicon oxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium oxide (HfO 2 ), tin oxide (SnO 2 ), cerium oxide (CeO 2 ), nickel oxide (NiO) , zinc oxide (ZnO), calcium oxide (CaO), zirconia (ZrO 2 ), yttrium oxide (Y 2 O 3 ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or at least one of barium sulfate.
  • alumina Al 2 O 3
  • silicon oxide SiO 2
  • magnesium oxide MgO
  • titanium oxide TiO 2
  • hafnium oxide HfO
  • the pores of the isolation membrane have a diameter in the range of about 0.01 ⁇ m to 1 ⁇ m.
  • the binder of the porous layer is selected from polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, poly At least one of vinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene or polyhexafluoropropylene.
  • the porous layer on the surface of the separator can improve the heat resistance, oxidation resistance and electrolyte wettability of the separator, and enhance the adhesion between the separator and the pole piece.
  • the electrochemical device includes a lithium-ion battery, although the present application is not limited thereto.
  • the electrochemical device further includes an electrolyte, and the electrolyte includes at least one of fluoroether, fluoroethylene carbonate, or ether nitrile.
  • the electrolyte solution also includes a lithium salt, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, the concentration of the lithium salt is 1mol/L to 2mol/L, and the bis(fluorosulfonyl)imide The mass ratio of lithium imide and lithium hexafluorophosphate is 0.06-5.
  • the electrolyte solution may also include a non-aqueous solvent.
  • the non-aqueous solvent can be carbonate compound, carboxylate compound, ether compound, other organic solvent or their combination.
  • the carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound or a combination thereof.
  • chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl carbonate Ethyl Ester (MEC) and combinations thereof.
  • chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl carbonate Ethyl Ester (MEC) and combinations thereof.
  • Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), or combinations thereof.
  • fluorocarbonate compound examples include fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, Fluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-carbonic acid - Difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.
  • FEC fluoroethylene carbonate
  • 1,2-difluoroethylene carbonate 1,1-difluoroethylene carbonate
  • 1,1,2-trifluoroethylene carbonate Fluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-carbonic acid - Difluoro-1-methylethylene carbonate, 1,1,2-trifluor
  • carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone, decanolactone, Valerolactone, mevalonolactone, caprolactone, methyl formate, or combinations thereof.
  • ether compounds are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxy ethyl ethane, 2-methyltetrahydrofuran, tetrahydrofuran or a combination thereof.
  • organic solvents examples include dimethylsulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, methyl Amides, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.
  • Embodiments of the present application also provide an electronic device including the above electrochemical device.
  • the electronic device in the embodiment of the present application is not particularly limited, and it may be used in any electronic device known in the prior art.
  • electronic devices may include, but are not limited to, notebook computers, pen-based computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, Unmanned aerial vehicles, lighting equipment, toys, game consoles, clocks, electric tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.
  • the negative pole piece copper foil is used for the current collector, artificial graphite is used as the negative active material, conductive carbon black is used as the conductive agent material, and styrene-butadiene rubber and carboxymethyl cellulose are used as the binder.
  • Positive electrode sheet preparation The positive electrode material lithium cobaltate, conductive carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in the N-methylpyrrolidone solvent system according to the mass percentage ratio of 94.8:2.8:2.4 After being uniform, it is coated on an aluminum foil to obtain a positive electrode active material layer, and the thickness of the positive electrode active material layer is 80 ⁇ m. After drying and cold pressing, the positive electrode sheet is obtained.
  • PVDF polyvinylidene fluoride
  • Preparation of the isolation film Stir the polyacrylate to form a uniform slurry, apply the slurry to both surfaces of the porous substrate (polyethylene), and form the isolation film after drying.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • PC propylene carbonate
  • PP propyl propionate
  • VC vinylene carbonate
  • Lithium-ion battery preparation stack the positive pole piece, the separator, and the negative pole piece in order, so that the separator is in the middle of the positive pole piece and the negative pole piece to play the role of isolation, and wind up to obtain the electrode assembly. Place the electrode assembly in the aluminum-plastic film of the outer packaging. After dehydration at 80°C, inject the above electrolyte and package it. After chemical formation, degassing, shaping and other processes, a lithium-ion battery is obtained. Wherein, as shown in FIG. 3 , the head and tail of the negative electrode active material layer in the length direction exceed the positive electrode active material layer by 8 mm.
  • the current collector is made of copper foil
  • the negative electrode active material is made of artificial graphite
  • the conductive agent is made of conductive carbon black
  • the binder is made of styrene-butadiene rubber and carboxymethyl cellulose. Mix the negative electrode active material, conductive agent and binder in a mass percentage ratio of 98:1:1 and disperse them in deionized water to form a lower layer slurry.
  • the negative electrode active material, conductive agent and binder in the mass percentage ratio Mix 97.8:1.2:1 and disperse in deionized water to form an upper layer slurry, stir evenly, coat on copper foil, and dry to form the first negative electrode active material layer and the second negative electrode active material layer respectively, the first negative electrode active material layer layer and the second negative electrode active material layer have the same thickness, the head and tail ends of the second negative electrode active material layer in the length direction all exceed the first negative electrode active material layer by 8mm, and the second negative electrode active material layer completely covers the first negative electrode The active material layer is cold-pressed and slitting to obtain the negative electrode sheet.
  • the positive electrode active material layer is aligned with the first negative electrode active material layer, and the head and tail ends of the second negative electrode active material layer in the length direction all exceed the positive electrode active material layer by 8mm .
  • the difference between the preparation of the lithium ion battery of Example 3 and that of Example 1 lies in the structure of the finally obtained lithium ion battery. Specifically, as shown in Figure 6, after the lithium-ion battery is obtained, at the head in the length direction of the negative electrode sheet, one end of the positive electrode active material layer exceeds the corresponding end of the first negative electrode active material layer, and the end of the second negative electrode active material layer The corresponding end exceeds one end of the positive electrode active material layer, and the structure of the tail portion in the length direction of the negative electrode sheet is the same as that of Example 1.
  • the structure of the head in the length direction of the negative electrode sheet is the same as that of Example 1.
  • one end of the positive electrode active material layer exceeds the corresponding end of the first negative electrode active material layer
  • the corresponding end of the second negative electrode active material layer exceeds one end of the positive electrode active material layer by 8mm.
  • Cycle capacity retention discharge capacity of 1000 cycles/initial discharge capacity.
  • Table 1 shows various parameters and evaluation results of Examples 1 to 5 and Comparative Example 1.
  • Lithium analysis in the head Lithium analysis at the tail cycle capacity retention Comparative example 1 Lithium analysis Lithium analysis 70%
  • Example 1 Lithium free Lithium free 85% Example 2
  • Example 3 Lithium analysis Lithium free 75%
  • Example 4 Lithium free Lithium analysis 80%
  • Example 5 Lithium free Lithium analysis 75%
  • the two ends of the second negative electrode active material layer exceed the first negative electrode active material layer, the two ends of the first negative electrode active material layer are aligned with the two ends of the positive electrode active material layer, and the two ends of the second negative electrode active material layer
  • the kinetic performance is better than that of the first negative electrode active material layer, therefore, lithium ions can be better intercalated and extracted at the head and tail of the negative electrode sheet, and the first negative electrode active material layer is aligned with the positive electrode active material layer, so preventing While analyzing lithium, the cycle performance of lithium-ion batteries is improved.
  • the heads of the first negative electrode active material layer and the second negative electrode active material layer are all beyond one end of the positive electrode active material layer, and the first negative electrode active material layer reduces the dynamic performance of the whole at the head, thus causing Lithium ions cannot be extracted well, resulting in lithium precipitation and affecting the cycle capacity retention rate.
  • the negative electrode active material layer is double-layer coating, but the positive electrode active material layer protrudes beyond the end of the first negative electrode active material layer at the head, so the second negative electrode active material layer is basically responsible for containing the negative electrode active material layer at the head. Lithium ions, causing the negative electrode sheet to not provide enough space to accommodate lithium ions in the head, which will cause lithium precipitation and affect cycle performance.
  • the tails of the first negative electrode active material layer and the second negative electrode active material layer are all beyond one end of the positive electrode active material layer, and the tail of the first negative electrode active material layer reduces the overall kinetic performance, thus causing lithium ion It cannot be removed well, resulting in lithium precipitation at the tail, and affecting the cycle capacity retention rate.
  • the positive electrode active material layer protrudes from the end of the first negative electrode active material layer at the tail, so the second negative electrode active material layer is basically responsible for accommodating lithium ions at the tail, causing the negative pole piece to fail to provide sufficient accommodation at the tail. Space for lithium ions, which in turn causes lithium precipitation and affects cycle performance.

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Abstract

本申请提供了电化学装置和电子装置。电化学装置包括：正极极片和负极极片；正极极片包括正极活性材料层；负极极片包括负极集流体、第一负极活性材料层和第二负极活性材料层；第一负极活性材料层在负极极片的长度方向上具有第一边缘和第二边缘，第二负极活性材料层在长度方向上具有第三边缘和第四边缘，正极活性材料层在长度方向上具有第五边缘和第六边缘；第三边缘在长度方向突出于第一边缘和第五边缘；第一边缘与第五边缘在负极极片的长度方向上的间隔距离小于2mm，第二负极活性材料层的动力学性能优于第一负极活性材料层的动力学性能。本申请在防止析锂的同时保证了容量。

Description

电化学装置和电子装置
相关申请的交叉引用
本申请基于申请号为202210189708.0、申请日为2022年02月28日，名称为“电化学装置和电子装置”的中国专利申请提出，并要求该中国专利申请的优先权，上述中国专利申请的公开内容全文以引入方式并入本文。
技术领域
本申请涉及电化学储能领域，具体地涉及电化学装置和电子装置。
背景技术
伴随电化学储能技术的发展，对电化学装置(例如，锂离子电池)的安全性能和能量密度提出了越来越高的要求，期望这方面的进一步改进。
发明内容
本申请提供了一种电化学装置，正极极片包括正极活性材料层；负极极片包括负极集流体、第一负极活性材料层和第二负极活性材料层，第一负极活性材料层位于负极集流体和第二负极活性材料层之间；其中，第一负极活性材料层在负极极片的长度方向上具有第一边缘和第二边缘，第二负极活性材料层在长度方向上具有第三边缘和第四边缘，正极活性材料层在长度方向上具有第五边缘和第六边缘，第一边缘、第三边缘和第五边缘位于同一侧，第二边缘、第四边缘和第六边缘位于相对的另一侧；第三边缘在长度方向上突出于第一边缘和五边缘；第一边缘与第五边缘在长度方向上的间隔距离小于2mm。
在一些实施例中，第一边缘与第五边缘在长度方向上的间隔距离为0。在一些实施例中，第四边缘在长度方向上突出于第二边缘和第六边缘。在一些实施例中，第二边缘与第六边缘在长度方向上的间隔距离小于2mm。在一些实施例中，第二边缘与第六边缘在 长度方向上的间隔距离为0。在一些实施例中，第三边缘与第五边缘在长度方向上的间隔距离为2mm至8mm。在一些实施例中，第四边缘与第六边缘在长度方向上的间隔距离为2mm至8mm。
在一些实施例中，第一负极活性材料层中的负极活性材料的克容量大于第二负极活性材料层中的负极活性材料的克容量。在一些实施例中，第二负极活性材料层的电阻率小于第一负极活性材料层的电阻率；在一些实施例中，第一负极活性材料层中导电剂的质量百分含量小于第二负极活性材料层中导电剂的质量百分含量；在一些实施例中，第一负极活性材料层的孔隙率小于第二负极活性材料层的孔隙率；在一些实施例中，第一负极活性材料层和第二负极活性材料层中包括：包覆改性剂的负极活性材料，第一负极活性材料层中负极活性材料的包覆量小于第二负极活性材料层中负极活性材料的包覆量；在一些实施例中，第一负极活性材料层中负极材料的平均粒径大于第二负极活性材料层中负极材料的平均粒径；在一些实施例中，第一负极活性材料层和第二负极活性材料层中包括石墨，第一负极活性材料层中石墨取向指数大于第二负极活性材料层中石墨取向指数。
本申请的实施例还提供了一种电子装置，包括上述的电化学装置。
本申请通过使第三边缘在长度方向上突出于第一边缘和第五边缘，从正极极片释放的锂离子可以嵌入在第二负极活性材料层中，由于第二负极活性材料层具有优于第一负极活性材料层的动力学性能，因此可以防止负极极片的析锂；另外，通过使第一边缘与第五边缘在长度方向上基本对齐，避免了负极的容量损失，保证了电化学装置的能量密度，防止析锂并有利于循环性能。
附图说明
图1示出了根据一些实施例的电化学装置的部分的沿着负极极片的长度方向的截面图。
图2示出了根据一些实施例的电化学装置的部分的沿着负极极片的长度方向的截面图。
图3示出了对比例的电化学装置的部分的沿着负极极片的长度方向的截面图。
图4示出了实施例1的电化学装置的部分的沿着负极极片的长度方向的截面图。
图5示出了实施例2的电化学装置的部分的沿着负极极片的长度方向的截面图。
图6示出了实施例3的电化学装置的部分的沿着负极极片的长度方向的截面图。
图7示出了实施例4的电化学装置的部分的沿着负极极片的长度方向的截面图。
图8示出了实施例5的电化学装置的部分的沿着负极极片的长度方向的截面图。
附图说明：10、正极极片；101、正极集流体；102、正极活性材料层；1021、第五边缘；11、隔离膜；1231、第三边缘；1221、第一边缘；1022、第六边缘；1232、第四边缘；123、第二负极活性材料层；1222、第二边缘；122、第一负极活性材料层；121、负极集流体；12、负极极片。
具体实施方式
下面的实施例可以使本领域技术人员更全面地理解本申请，但不以任何方式限制本申请。
对于电化学装置(例如，锂离子电池)的设计而言，需要负极极片预留出足够的空间供正极极片脱出的锂全部嵌入负极活性材料中，因此负极极片的长度和/或宽度通常会超出正极极片的相应长度和/或宽度，以避免出现正极极片超出负极极片而引起析锂或者短路的问题。然而，负极极片超出正极极片的部分的动力学性能和未超出部分的动力学性能相近，传输到负极极片超出部分的路径比传输到未超出部分的路径要长，因此超出部分的锂不易脱出，破坏了脱出和嵌入的平衡，超出部分嵌入的锂比脱出的锂要多，随着时间增加超出部分的锂就出现了累积，造成超出部分析锂，表现为循环过程中电极组件的头部和尾部的析锂。一些技术中，采用非对称式收窄和对称式收窄的极片，来改善负极极片尾部出现的析锂，或者是采用在正极极片尾部贴胶的方式，使得正极极片的锂离子无法脱出来限制负极极片尾部析锂，然而这种方法只能让超出部分边长，延缓析锂，没有从本质上解决问题，并且造成了容量损失，一些技术中，在负极极片的上层的涂布宽度大于下层的涂布宽度，在负极极片宽度方向上形成上层包覆下层的结构，上层的动力学优于下层的动力学，对应的上层的容量和下层的容量会有一定差异，一般来说，高动力学的材料容量会偏 低，因此在上层超出下层的部分的容量低于下层，因此对应的阳阴极容量比(N/P比)会发生变化，即超出部分的N/P较小，一定程度上会恶化析锂。
如图1所示，本申请的一些实施例提供了一种电化学装置，电化学装置包括正极极片10和负极极片12。在一些实施例中，正极极片10和负极极片12由设置在它们之间的隔离膜11间隔开。在一些实施例中，正极极片10包括正极活性材料层102。在一些实施例中，正极极片10还可以包括正极集流体101，正极活性材料层102可以设置在正极集流体101的一侧或两侧上。
在一些实施例中，负极极片12包括负极集流体121、第一负极活性材料层122和第二负极活性材料层123，第一负极活性材料层122位于负极集流体121和第二负极活性材料层123之间。应该理解，虽然图1中将第一负极活性材料层122和第二负极活性材料层123示出为位于负极集流体121的一侧上，但是这仅是示例性地，在负极集流体121的两侧上可以均存在第一负极活性材料层122和第二负极活性材料层123。
在一些实施例中，如图1所示，第一负极活性材料层122在负极极片12的长度方向(图1中左右水平方向)上具有第一边缘1221和第二边缘1222，第二负极活性材料层123具有在长度方向上具有第三边缘1231和第四边缘1232，正极活性材料层102在长度方向上具有第五边缘1021和第六边缘1022。在一些实施例中，第一边缘1221、第三边缘1231和第五边缘1021位于同一侧，第二边缘1222、第四边缘1232和第六边缘1022位于相对的另一侧。
在一些实施例中，如图1所示，第三边缘1231在长度方向(图1中左右水平方向)上突出于第一边缘1221和第五边缘1021。在一些实施例中，第一边缘1221与第五边缘1021对齐，但是由于工艺误差的存在，第一边缘1221与第五边缘1021在长度方向上的间隔距离小于2mm时，即可以认为第一边缘1221与第五边缘1021对齐。在一些实施例中，第一边缘1221与第五边缘1021在长度方向上的间隔距离为0，即处于理想状态的对齐。并且，第二负极活性材料层123的动力学性能优于第一负极活性材料层122的动力学性能。
第二负极活性材料层123的动力学性能优于第一负极活性材料层122，负极极片12在长度方向上超过正极极片10的部分基本为第二负极活性材料层123，即动力学性能较好的材料，因此负极极片12在长度方向上超过正极极片10的部分能够很好的脱出锂离子，可以解决析锂问题，并且该结构并未损失活性物质，因此不会影响到整体的容量。第二负极活性材料层123的动力学性能优于第一负极活性材料层122，因此，第一负极活性材料 层122中的负极活性材料的克容量高于第二负极活性材料层123中的负极活性材料的克容量，第一边缘1221如果明显在长度方向上未达到第五边缘1021，该处的负极极片12就会无足够的空间存储正极极片脱出的锂离子，造成析锂，影响循环性能。第一边缘1221如果在长度方向上明显超出第五边缘1021，则负极极片12在第一边缘1221处的动力学性能为第一负极活性材料层122和第二负极活性材料层123的动力学性能叠加后的效果，因此动力学性能会相比于只有第二负极活性材料层123时下降，从而导致负极极片12边缘处析锂，影响循环性能。通过使第三边缘1231在长度方向上突出于第一边缘1221和第五边缘1021，从正极活性材料层102释放的锂离子可以嵌入在第二负极活性材料层123中并可以很好的析出，避免了负极极片12上的析锂；另外，通过使第一边缘1221与第五边缘1021在长度方向上基本对齐，使得高容量的第一负极活性材料层122与正极活性材料层102适配，既能保证容量，又能防止第一负极活性材料层122影响负极极片12超出正极极片10部分的动力学性能，提升了电化学装置的能量密度的同时防止析锂，从而保证了循环性能。因此，本申请的电化学装置既避免了负极极片上的析锂，又可以最小化对电化学装置的能量密度的不利影响，并保证循环性能。
如果第二负极活性材料层123的第一边缘1221相对于正极活性材料层102的第五边缘1021缩进，则会出现正极极片10的边缘区域脱出的锂离子在负极极片12无法完全存储，使得负极极片12边缘区域会出现析锂并降低了容量，影响电化学装置的循环性能，甚至造成短路或者安全问题。另一方面，如果第一边缘1221相对于正极活性材料层102的第五边缘1021突出，则负极极片12超出正极极片10的部分动力学性能降低，可能会导致析锂，影响循环性能。
在负极极片的宽度方向，也可使用上层涂布(第二负极活性材料层)宽度大于下层涂布(第一负极活性材料层)宽度，并且下层涂布的边缘与正极活性材料层的边缘对齐，另外在负极极片的宽度方向上也有负极极片的宽度超过正极极片的设计，在本技术方案中，负极极片上的下层涂布与正极极片的涂布对齐，负极极片涂布的上层则超出正极极片的涂布，且上层涂布的动力学性能优于下层涂布，能明显的改善循环性能，上层的高动力学性能的涂布，提升了动力学性能，从而有效的改善析锂，提升循环性能；相较于全部涂布第二负极活性材料层，此种方案可以进一步提升能量密度。
在一些实施例中，如图2所示，第四边缘1232在长度方向上突出于第二边缘1222和第六边缘1022。如此，突出的第二负极活性材料层123可以更好地接收从正极活性材料层102释放的锂离子，避免引起负极极片12上的析锂。
在一些实施例中，第二边缘1222与第六边缘1022对齐，但是由于工艺误差的存在，当第二边缘1222与第六边缘1022在长度方向上的间隔距离小于2mm时，即可以认为第二边缘1222与第六边缘1022对齐。在一些实施例中，第二边缘1222与第六边缘1022在长度方向上的间隔距离为0。即处于理想状态的对齐。通过使第二边缘1222与第六边缘1022在长度方向上基本对齐，保证第一负极活性材料层122的量，从而提升了电化学装置的能量密度，并且防止第一负极活性材料层122对于负极极片12突出于正极极片10的边缘部分的动力学性能的影响，从而防止析锂并保证循环性能。因此，本申请的电化学装置既避免了负极极片上的析锂，保证循环性能，又可以最小化对电化学装置的能量密度的不利影响。
在一些实施例中，第二负极活性材料层123的厚度小于第一负极活性材料层122的厚度。如此，相较于第二负极活性材料层123和第一负极活性材料层122均突出的情况，厚度较大的第一负极活性材料层122由于与正极活性材料层102的边缘对齐，由于第一负极活性材料层122中的负极活性材料的克容量高于第二负极活性材料层123中的负极活性材料的克容量，因此能够提升电化学装置的能量密度。
在一些实施例中，第三边缘1231与第五边缘1021在长度方向上的间隔距离为2mm至8mm，进一步的为3mm至8mm，更进一步的为3mm至5mm。在一些实施例中，第四边缘1232与第六边缘1022在长度方向上的间隔距离为2mm至8mm，进一步的为3mm至8mm，更进一步的为3mm至5mm。如果第三边缘1231与第五边缘1021在长度方向上的间隔距离或第四边缘1232与第六边缘1022在长度方向上的间隔距离太小，则突出的第二负极活性材料层123不能充分地接收从正极活性材料层102释放的锂离子；如果第三边缘1231与第五边缘1021在长度方向上的间隔距离或第四边缘1232与第六边缘1022在长度方向上的间隔距离太大，则可能不必要地增加克容量较小的第二负极活性材料层123所占用的空间，对电化学装置的能量密度造成不利影响。一些实施例中，第一负极活性材料层122中的负极活性材料的克容量大于第二负极活性材料层123中的负极活性材料的克容量。
在一些实施例中，第二负极活性材料层123的电阻率小于第一负极活性材料层122的电阻率，因此，第二负极活性材料层123能够很好的释放嵌入的锂离子，防止析锂。并且能够为锂离子传输进入第一负极活性材料层122提供较好的同道，促使锂离子进入更靠内部的第一负极活性材料层122，有利于倍率性能。在一些实施例中，第一负极活性材料层122中导电剂的质量百分含量小于第二负极活性材料层123中导电剂的 质量百分含量。导电剂可以是导电炭黑、碳纳米管等，通过提高第二负极活性材料层123中导电剂的含量从而提高第二负极活性材料层123的动力学性能。在一些实施例中，第一负极活性材料层的孔隙率小于第二负极活性材料层的孔隙率，从而为锂离子的传输提供更多的通道。在一些实施例中，第一负极活性材料层122和第二负极活性材料层123中包括：包覆改性剂的负极活性材料，第一负极活性材料层122中负极活性材料的包覆量小于第二负极活性材料层123中负极活性材料的包覆量，这样锂离子在第二负极活性材料层123的负极活性材料中能够更容易的嵌入和脱出。在一些实施例中，第一负极活性材料层122中负极活性材料的平均粒径大于第二负极活性材料层123中负极活性材料的平均粒径，因此第二负极活性材料层123中的负极活性材料的比表面积更大，有利于锂离子的传输。在一些实施例中，第一负极活性材料层122和第二负极活性材料层123中包括石墨，第一负极活性材料层中石墨取向指数大于第二负极活性材料层中石墨取向指数。
在一些实施例中，正极集流体101可以采用铝箔，当然，也可以采用本领域常用的其他正极集流体。在一些实施例中，正极集流体的厚度可以为1μm至50μm。在一些实施例中，正极活性材料层102可以仅涂覆在正极集流体101的部分区域上。
在一些实施例中，正极活性材料层102可以包括正极材料、导电剂和粘结剂。在一些实施例中，正极材料可以包括钴酸锂、磷酸铁锂、铝酸锂、锰酸锂或镍钴锰酸锂中的至少一种。在一些实施例中，正极极片10的导电剂可以包括导电炭黑、片层石墨、石墨烯或碳纳米管中的至少一种。在一些实施例中，正极极片10中的粘结剂可以包括聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、苯乙烯-丙烯酸酯共聚物、苯乙烯-丁二烯共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素纳、聚醋酸乙烯酯、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。在一些实施例中，正极活性材料层102中的正极材料、导电剂和粘结剂的质量比为(80-99)：(0.1-10)：(0.1-10)，但是这仅是示例，可以采用任何其他合适的质量比。
在一些实施例中，第一负极活性材料层122和第二负极活性材料层123均可以包括负极材料、导电剂和粘结剂。在一些实施例，负极材料可以包括人造石墨、天然石墨、包覆改性剂的石墨、硅、硅基材料中的至少一种。在一些实施例中，硅基材料包括硅、硅氧材料、硅碳材料或硅氧碳材料中的至少一种。在一些实施例中，第一负极活性材料层122和第二负极活性材料层123中的导电剂可以包括导电炭黑、科琴黑、片层石墨、石墨烯、 金属粉、碳纳米管或碳纤维中的至少一种。在一些实施例中，第一负极活性材料层122和第二负极活性材料层123中的粘结剂可以包括羧甲基纤维素(CMC)、聚丙烯酸、聚乙烯基吡咯烷酮、聚苯胺、聚酰亚胺、聚酰胺酰亚胺、聚硅氧烷、丁苯橡胶、环氧树脂、聚酯树脂、聚氨酯树脂或聚芴中的至少一种。在一些实施例中，第一负极活性材料层122和第二负极活性材料层123中的负极材料、导电剂和粘结剂的质量比可以为(78至98.5)：(0.1至10)：(0.1至10)。一些实施例中，可以将上述负材料按照一定的比例溶于溶剂中，混合均匀后制备得到浆料。具体地，第二负极活性材料层中负极材料的质量含量可以90％至98％，优选的为97.8％，导电剂的质量含量可以为0.2％至4％，优选的为1.2％，粘结剂的质量含量可以为0.6％至6％，优选的为1.0％，第一负极活性材料层中负极材料的质量含量为98.0％；导电剂的质量含量为1.0％；粘结剂的质量含量可以为0.6％至6％，优选为1.0％，得到的浆料的粘度为2000mPa.s至7000mPa.s，固含量为70％至80％。应该理解，以上所述仅是示例，可以采用任何其他合适的材料和质量比。在一些实施例中，第一负极活性材料层122和第二负极活性材料层123中的负极材料的种类和配方可以相同也可以不同。在一些实施例中，负极集流体121可以采用铜箔、镍箔或碳基集流体中的至少一种。
负极极片双层涂布是通过双层涂布机完成的，两个喷嘴同时进行涂布，涂布的宽度通过垫片宽度实现，上层的宽度大于下层的宽度，宽度差与实施例对应。涂布的长度由上下层的间隙阀决定，其中上层响应时间长，下层短，具体时间差与涂布速度相关，也与涂布头尾的结构相关。
在一些实施例中，隔离膜11包括聚乙烯、聚丙烯、聚偏氟乙烯、聚对苯二甲酸乙二醇酯、聚酰亚胺或芳纶中的至少一种。例如，聚乙烯包括选自高密度聚乙烯、低密度聚乙烯或超高分子量聚乙烯中的至少一种。尤其是聚乙烯和聚丙烯，它们对防止短路具有良好的作用，并可以通过关断效应改善电池的稳定性。在一些实施例中，隔离膜11的厚度在约3μm至20μm的范围内。
在一些实施例中，隔离膜11的表面还可以包括多孔层，多孔层设置在隔离膜的至少一个表面上，多孔层包括无机颗粒和粘结剂，无机颗粒选自氧化铝(Al 2O 3)、氧化硅(SiO 2)、氧化镁(MgO)、氧化钛(TiO 2)、二氧化铪(HfO 2)、氧化锡(SnO 2)、二氧化铈(CeO 2)、氧化镍(NiO)、氧化锌(ZnO)、氧化钙(CaO)、氧化锆(ZrO 2)、氧化钇(Y 2O 3)、碳化硅(SiC)、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙或硫酸钡中的至少一种。在一些实施例中，隔离膜的孔具有在约0.01μm至1μm的范围的直 径。多孔层的粘结剂选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、羧甲基纤维素钠、聚乙烯呲咯烷酮、聚乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯或聚六氟丙烯中的至少一种。隔离膜表面的多孔层可以提升隔离膜的耐热性能、抗氧化性能和电解质浸润性能，增强隔离膜与极片之间的粘结性。
在一些实施例中，电化学装置包括锂离子电池，但是本申请不限于此。在一些实施例中，电化学装置还包括电解液，电解液包括氟醚、氟代碳酸乙烯酯或醚腈中至少一种。在一些实施例中，电解液还包括锂盐，锂盐包括双(氟磺酰基)酰亚胺锂和六氟磷酸锂，锂盐的浓度为1mol/L至2mol/L，且双(氟磺酰基)酰亚胺锂和六氟磷酸锂的质量比为0.06至5。在一些实施例中，电解液还可以包括非水溶剂。非水溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、其它有机溶剂或它们的组合。
碳酸酯化合物可为链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或其组合。
链状碳酸酯化合物的实例为碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸甲乙酯(MEC)及其组合。所述环状碳酸酯化合物的实例为碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)、碳酸乙烯基亚乙酯(VEC)或者其组合。所述氟代碳酸酯化合物的实例为碳酸氟代亚乙酯(FEC)、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯、碳酸三氟甲基亚乙酯或者其组合。
羧酸酯化合物的实例为乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯、甲瓦龙酸内酯、己内酯、甲酸甲酯或者其组合。
醚化合物的实例为二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、乙氧基甲氧基乙烷、2-甲基四氢呋喃、四氢呋喃或者其组合。
其它有机溶剂的实例为二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、甲酰胺、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯、磷酸三辛酯、和磷酸酯或者其组合。
本申请的实施例还提供了包括上述电化学装置的电子装置。本申请实施例的电子装置没有特别限定，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括，但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、无人机、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
下面列举了一些具体实施例和对比例以更好地对本申请进行说明，其中，采用锂离子电池作为示例。
对比例1
负极极片的制备：集流体采用铜箔，负极活性材料采用人造石墨，导电剂材料导电炭黑、粘结剂采用丁苯橡胶和羧甲基纤维素。将负极活性材料、导电剂和粘结剂按质量百分含量比98：1：1混合后分散于去离子水中形成浆料，搅拌均匀后涂布于铜箔上，干燥，形成负极活性材料层，负极活性材料层的厚度为120μm，冷压、分条后得到负极极片。
正极极片制备：将正极材料钴酸锂、导电炭黑、粘结剂聚偏二氟乙烯(PVDF)按质量百分含量比94.8：2.8：2.4在N-甲基吡咯烷酮溶剂体系中充分搅拌混合均匀后，涂覆于铝箔上，得到正极活性材料层，正极活性材料层的厚度为80μm。再经烘干、冷压，得到正极极片。
隔离膜的制备：将聚丙烯酸酯搅拌形成均匀浆料，将浆料涂布到多孔基材(聚乙烯)的两侧表面上，烘干后形成隔离膜。
电解液的制备：在含水量小于10ppm的环境下，将六氟磷酸锂与非水有机溶剂(碳酸乙烯酯(EC)：碳酸二乙酯(DEC)：碳酸亚丙酯(PC)：丙酸丙酯(PP)：碳酸亚乙烯酯(VC)＝20：30：20：28：2，质量百分含量比)按质量百分含量比8：92配制以形成锂盐浓度为1mol/L的电解液。
锂离子电池的制备：将正极极片、隔离膜、负极极片按顺序依次叠好，使隔离膜处于正极极片和负极极片中间起到隔离的作用，并卷绕得到电极组件。将电极组件置于外包装铝塑膜中，在80℃下脱去水分后，注入上述电解液并封装，经过化成、脱气、整形等 工艺流程得到锂离子电池。其中，如图3所示，负极活性材料层在长度方向上的头部和尾部超出正极活性材料层8mm。
实施例1
实施例1与对比例1的锂离子电池的制备的不同仅在于负极极片的制备，下面仅描述不同之处。集流体采用铜箔，负极活性材料采用人造石墨，导电剂采用导电炭黑、粘结剂采用丁苯橡胶和羧甲基纤维素。将负极活性材料、导电剂和粘结剂质量百分含量比98：1：1混合后分散于去离子水中形成下层浆料，将负极活性材料、导电剂和粘结剂按质量百分含量比97.8：1.2：1混合后分散于去离子水中形成上层浆料，搅拌均匀后涂布在铜箔上，干燥，分别形成第一负极活性材料层和第二负极活性材料层，第一负极活性材料层和第二负极活性材料层的厚度相同，第二负极活性材料层在长度方向上的头部和尾部两端均超出第一负极活性材料层8mm，第二负极活性材料层完全覆盖第一负极活性材料层，冷压、分条后得到负极极片。在得到锂离子电池之后，如图4所示，正极活性材料层与第一负极活性材料层对齐，第二负极活性材料层在长度方向上的头部和尾部两端均超出正极活性材料层8mm。
实施例2
实施例2的锂离子电池的制备与实施例1的不同在于最后得到的锂离子电池的结构。具体地，如图5所示，在得到锂离子电池之后，在负极极片长度方向的头部，第一负极活性材料层的一端与第二负极活性材料层的相应端对齐，且均超过正极活性材料层同一侧的相应端8mm，在负极极片长度方向的尾部的结构与实施例1相同。
实施例3
实施例3的锂离子电池的制备与实施例1的不同在于最后得到的锂离子电池的结构。具体地，如图6所示，在得到锂离子电池之后，在负极极片长度方向的头部，正极活性材料层的一端超出第一负极活性材料层的相应端，第二负极活性材料层的相应端超过正极活性材料层的一端，在负极极片长度方向的尾部的结构与实施例1相同。
实施例4
实施例4的锂离子电池的制备与实施例1的不同在于最后得到的锂离子电池的结构。具体地，如图7所示，在得到锂离子电池之后，在负极极片长度方向的头部的结构与实施例1相同。在负极极片长度方向的尾部，第一负极活性材料层的一端与第二负极活性材料层的相应端对齐，且均超过正极活性材料层的相应端8mm。
实施例5
实施例5的锂离子电池的制备与实施例1的不同在于最后得到的锂离子电池的结构。具体地，如图8所示，在得到锂离子电池之后，在负极极片长度方向的头部的结构与实施例1相同。在负极极片长度方向的尾部，正极活性材料层的一端超出第一负极活性材料层的相应端，第二负极活性材料层的相应端超过正极活性材料层的一端8mm。
另外，在本申请中，采用如下方法测量相应的参数。
能量密度测试：测试条件为25℃，3C充电至4.45V，然后搁置30min，随后1C放电至3V，搁置10min，如此循环测试，最后循环至1000次之后，将锂离子电池按上述过程充满电并拆解，观察负极极片的析锂情况。
循环容量保持率＝1000次循环的放电容量/初始放电容量。
表1示出了实施例1至5和对比例1的各项参数和评估结果。
表1
组别 头部析锂情况 尾部析锂情况 循环容量保持率
对比例1 析锂 析锂 70％
实施例1 不析锂 不析锂 85％
实施例2 析锂 不析锂 80％
实施例3 析锂 不析锂 75％
实施例4 不析锂 析锂 80％
实施例5 不析锂 析锂 75％
在对比例1中，单层负极活性材料层的两端超出正极活性材料层，此超出的负极活性材料层部分动力学性能不好，因此导致头部和尾部出现析锂。
在实施例1中，第二负极活性材料层的两端超出第一负极活性材料层，第一负极活性材料层的两端与正极活性材料层的两端对齐，且第二负极活性材料层的动力学性能优于第一负极活性材料层，因此，锂离子在负极极片的头部和尾部能够较好的嵌入和脱出，并且第一负极活性材料层与正极活性材料层对齐，因此在防止析锂的同时提升了锂离子电池的循环性能。在实施例2中，第一负极活性材料层和第二负极活性材料层的头部均超出正极活性材料层的一端，第一负极活性材料层在头部降低了整体的动力学性能，因此导致锂离 子无法很好的脱出，导致析锂，并影响循环容量保持率。在实施例3中，负极活性材料层是双层涂布，但是在头部正极活性材料层突出于第一负极活性材料层的端部，因此在头部基本由第二负极活性材料层负责容纳锂离子，导致负极极片在头部无法提供足够的容纳锂离子的空间，进而造成析锂并影响循环性能。在实施例4中，第一负极活性材料层和第二负极活性材料层的尾部均超出正极活性材料层的一端，第一负极活性材料层在尾部降低了整体的动力学性能，因此导致锂离子无法很好的脱出，导致尾部析锂，并影响循环容量保持率。在实施例5中在尾部正极活性材料层突出于第一负极活性材料层的端部，因此在尾部基本由第二负极活性材料层负责容纳锂离子，导致负极极片在尾部无法提供足够的容纳锂离子的空间，进而造成析锂并影响循环性能。
以上描述仅为本申请的较佳实施例以及对所运用技术原理的说明。本领域技术人员应当理解，本申请中所涉及的公开范围，并不限于上述技术特征的特定组合而成的技术方案，同时也应涵盖由上述技术特征或其等同特征进行任意组合而形成的其它技术方案。例如上述特征与本申请中公开的具有类似功能的技术特征进行互相替换而形成的技术方案。

Claims (10)

  1. 一种电化学装置，其中，包括：正极极片和负极极片；
    所述正极极片包括正极活性材料层；
    所述负极极片包括负极集流体、第一负极活性材料层和第二负极活性材料层，所述第一负极活性材料层位于所述负极集流体和所述第二负极活性材料层之间；
    其中，所述第一负极活性材料层在所述负极极片的长度方向上具有第一边缘和第二边缘，所述第二负极活性材料层在所述长度方向上具有第三边缘和第四边缘，所述正极活性材料层在所述长度方向上具有第五边缘和第六边缘，所述第一边缘、所述第三边缘和所述第五边缘位于同一侧，所述第二边缘、所述第四边缘和所述第六边缘位于相对的另一侧；
    所述第三边缘在所述长度方向上突出于所述第一边缘和所述第五边缘；
    所述第一边缘与所述第五边缘在所述长度方向上的间隔距离小于2mm。
  2. 根据权利要求1所述的电化学装置，其中，
    所述第一边缘与所述第五边缘在所述长度方向上的间隔距离为0。
  3. 根据权利要求1所述的电化学装置，其中，所述第四边缘在所述长度方向上突出于所述第二边缘和所述第六边缘。
  4. 根据权利要求3所述的电化学装置，其中，所述第二边缘与所述第六边缘在所述长度方向上的间隔距离小于2mm。
  5. 根据权利要求4所述的电化学装置，其中，所述第二边缘与所述第六边缘在所述长度方向上的间隔距离为0。
  6. 根据权利要求1所述的电化学装置，其中，所述第三边缘与所述第五边缘在所述长度方向上的间隔距离为2mm至8mm。
  7. 根据权利要求3所述的电化学装置，其中，所述第四边缘与所述第六边缘在所述长度方向上的间隔距离为2mm至8mm。
  8. 根据权利要求1所述的电化学装置，其中，
    所述第一负极活性材料层中的负极活性材料的克容量大于所述第二负极活性材料层中的负极活性材料的克容量。
  9. 根据权利要求1所述的电化学装置，其中，满足如下的至少一项：
    (a)所述第二负极活性材料层的电阻率小于所述第一负极活性材料层的电阻率；
    (b)所述第一负极活性材料层中导电剂的质量百分含量小于所述第二负极活性材料层中导电剂的质量百分含量；
    (c)所述第一负极活性材料层的孔隙率小于所述第二负极活性材料层的孔隙率；
    (d)所述第一负极活性材料层和所述第二负极活性材料层中包括：包覆改性剂的负极活性材料，所述第一负极活性材料层中负极活性材料的包覆量小于所述第二负极活性材料层中负极活性材料的包覆量；
    (e)所述第一负极活性材料层中负极活性材料的平均粒径大于所述第二负极活性材料层中负极活性材料的平均粒径；
    (f)所述第一负极活性材料层和所述第二负极活性材料层中包括石墨，所述第一负极活性材料层中石墨取向指数大于所述第二负极活性材料层中石墨取向指数。
  10. 一种电子装置，包括根据权利要求1至9中任一项所述的电化学装置。
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