WO2025199842A1 - 二次电池和电子装置 - Google Patents

二次电池和电子装置

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Publication number
WO2025199842A1
WO2025199842A1 PCT/CN2024/084269 CN2024084269W WO2025199842A1 WO 2025199842 A1 WO2025199842 A1 WO 2025199842A1 CN 2024084269 W CN2024084269 W CN 2024084269W WO 2025199842 A1 WO2025199842 A1 WO 2025199842A1
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WO
WIPO (PCT)
Prior art keywords
active material
negative electrode
secondary battery
electrode active
material layer
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/CN2024/084269
Other languages
English (en)
French (fr)
Inventor
王莉莎
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ningde Amperex Technology Ltd
Original Assignee
Ningde Amperex Technology Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ningde Amperex Technology Ltd filed Critical Ningde Amperex Technology Ltd
Priority to CN202480017200.XA priority Critical patent/CN121039823A/zh
Priority to PCT/CN2024/084269 priority patent/WO2025199842A1/zh
Publication of WO2025199842A1 publication Critical patent/WO2025199842A1/zh
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • 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
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/64—Carriers or collectors
    • H01M4/70—Carriers or collectors characterised by shape or form
    • 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 energy storage technology, and in particular to a secondary battery and an electronic device having the secondary battery.
  • Secondary batteries such as lithium-ion secondary batteries
  • electronic products such as electronic mobile devices, power tools and electric vehicles, and people have increasingly higher requirements for the performance of secondary batteries.
  • the present application provides a secondary battery that can achieve both high energy density and excellent kinetic and cycle performance, and an electronic device having the secondary battery.
  • the secondary battery can maintain a higher energy density, and on the other hand, the negative electrode active particles are in close contact to provide an efficient ion transmission path, reduce impedance, and further improve the kinetic performance of the secondary battery.
  • more pores can be constructed in the negative electrode active material layer to further improve the degree of electrolyte infiltration, thereby reducing the risk of partial loss of negative electrode active material and lithium precipitation in the recess due to the opening of the recess in the negative electrode active material layer, further improving the cycle performance of the secondary battery.
  • 1.3 g/cm 3 ⁇ D ⁇ 1.9 g/cm 3 which allows the secondary battery to have both higher energy density and better kinetic and cycle performance.
  • the electrode assembly has a wound structure, comprising a straight section and a curved section connected along the winding direction.
  • the negative electrode active material layer comprises a first active material region located in the straight section and a second active material region located in the curved section.
  • the compaction density of the first active material region is D1
  • the compaction density of the second active material region is D2 , with 1.3g/ cm3 ⁇ D1 ⁇ 2.0g/cm3, and 1.2g/ cm3 ⁇ D2 ⁇ 1.5g/cm3.
  • the higher compaction density of the first active material region in the straight section allows the first active material region to exert a greater capacity without significantly degrading the kinetic performance and lithium deposition issues in the first active material region, thereby further improving the energy density of the secondary battery.
  • the compaction density of the third active material region located in the center is higher. Without significantly deteriorating the kinetic performance and lithium deposition issues in the third active material region, the third active material region can play a greater capacity role, thereby further improving the energy density of the secondary battery.
  • the width of the recess is 70 ⁇ m to 100 ⁇ m, the depth is 5 ⁇ m to 100 ⁇ m, and the center distance between two adjacent recesses is 1mm to 2mm.
  • Recesses of appropriate size can reduce the risk of excessive loss of negative electrode active material, which is conducive to maintaining a higher energy density and reducing the risk of lithium deposition in the recess. It can also inhibit the aggregation of lithium ions in the recess and maintain the structural stability of the negative electrode to reduce the deformation of the electrode assembly, thereby further improving the problem of easy lithium deposition in the recess after the thick electrode is opened, and improving the efficiency of the secondary battery.
  • Cycle performance; appropriate concave distribution density can improve electrolyte infiltration, reduce ion migration impedance and improve the problem of easy lithium precipitation in the concave part, thereby improving the kinetic performance and cycle performance of the secondary battery.
  • the recess is circular or square when viewed in the thickness direction of the negative electrode sheet.
  • a circular recess facilitates uniform diffusion of lithium ions in the negative electrode active material layer, improves electrolyte wetting and reduces ion migration impedance, thereby improving problems such as poor kinetic performance and low cycle capacity decay caused by increased thickness of the negative electrode active material layer.
  • a square recess can increase the contact area between the electrolyte and the negative electrode active material layer at the boundary, which helps increase the diffusion rate of lithium ions in the negative electrode active material layer, thereby further improving problems such as poor kinetic performance and low cycle capacity decay caused by increased thickness of the negative electrode active material layer.
  • the second aspect of the present application further provides an electronic device comprising a battery compartment and a secondary battery as described above disposed in the battery compartment.
  • the electronic device is powered by the secondary battery, which can achieve both high energy density and excellent dynamic performance and cycle performance.
  • FIG2 is a partial enlarged view of the negative electrode plate of the secondary battery shown in FIG1 at position II.
  • FIG3 is a schematic plan view of the negative electrode plate shown in FIG2 in some embodiments.
  • FIG6 is a schematic structural diagram of an electronic device according to an embodiment of the present application.
  • Electrode assembly 20 Straight section 20A Bend 20B Negative electrode 21 Positive electrode 22 Isolation film 23 Secondary batteries 100 Battery Compartment 101 Positive electrode current collector 220 Positive electrode active material layer 221 Negative electrode current collector 210 Negative electrode active material layer 211 First Area 2100 concavity 2110 First active material area 2111 Second active material area 2112 Third active material area 2113 Fourth active material area 2114 Winding center axis C Winding direction W Thickness T 0 , T 1 Width w Depth h Center distance d Thickness direction X
  • the following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings.
  • Spatial related terms such as “on” etc., can be used herein for convenient description, to describe the relationship between an element or feature and another element (multiple elements) or feature (multiple features) as illustrated in the figure. It should be understood that, in addition to the directions described in the figure, spatial related terms are intended to include different directions of equipment or devices in use or operation. For example, if the equipment in the figure is turned over, the elements described as “above” or “on” other elements or features will be oriented “below” or “below” other elements or features. Therefore, the exemplary term “on” can include the direction above and below. It should be understood that although the terms first, second, third, etc.
  • a secondary battery 100 comprising a housing (not shown), an electrode assembly 20, and an electrolyte (not shown).
  • the electrode assembly 20 and the electrolyte are both located within the housing.
  • the housing may be a packaging bag encapsulated with a packaging film (e.g., an aluminum-plastic film), e.g., if the secondary battery 100 is a soft-pack battery.
  • the secondary battery 100 may also be a steel-shell battery, an aluminum-shell battery, or the like.
  • the electrode assembly 20 includes a negative electrode sheet 21, a positive electrode sheet 22, and a separator 23, wherein the separator 23 is provided between the positive electrode sheet 22 and the negative electrode sheet 21.
  • the electrode assembly 20 may be a wound structure, which is formed by stacking the positive electrode sheet 22, the separator 23, and the negative electrode sheet 21 in sequence and then winding them.
  • the electrode assembly 20 has a winding center axis C perpendicular to the paper surface and a winding direction W wound around the winding center axis C.
  • the winding direction W is the direction of counterclockwise rotation around the winding center axis C as shown in FIG2 . In other embodiments, the winding direction W may also be a clockwise rotation direction.
  • the electrode assembly 20 may also be a laminate structure, which is formed by alternately stacking the positive electrode sheet 22 , the separator 23 , and the negative electrode sheet 21 .
  • the positive electrode sheet 22 includes a positive electrode current collector 220 and a positive electrode active material layer 221 disposed on the surface of the positive electrode current collector 220.
  • the positive electrode current collector 220 can be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, a current collector formed by combining the aforementioned conductive foil and a polymer substrate.
  • the positive electrode active material layer 221 includes an active material, such as at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium-rich manganese-based material, or lithium nickel cobalt aluminum oxide.
  • active material such as at least one of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium-rich manganese-based material, or lithium nickel cobalt aluminum oxide.
  • the positive electrode active material layer 221 may further include a binder to bind the active material particles to facilitate film formation and improve the bonding strength between the positive electrode active material layer 221 and the positive electrode current collector 220.
  • the binder may include, but is not limited to, at least one of polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, polyacrylonitrile, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.
  • the positive electrode active material layer 221 may further include a conductive agent, including but not limited to carbon-based materials, metal-based materials, conductive polymers, or any combination thereof.
  • the carbon-based material may include, but is not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.
  • the metal-based material may include, but is not limited to, metal powder or metal fiber, such as copper, nickel, aluminum, or silver.
  • the conductive polymer may be a polyphenylene derivative.
  • the negative electrode sheet 21 includes a negative electrode current collector 210 and a negative electrode active material layer 211 disposed on the surface of the negative electrode current collector 210 .
  • the negative electrode current collector 210 can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or a carbon-based current collector, or any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate.
  • the negative electrode active material layer 211 includes an active material selected from at least one of a graphite material, an alloy material, lithium metal, and alloys thereof.
  • the graphite material may be selected from at least one of artificial graphite and natural graphite; the alloy material may be selected from at least one of silicon, silicon oxide, tin, and titanium sulfide.
  • the negative electrode active material layer 211 may further include a binder, which is used to bind the negative electrode active particles to facilitate the formation of a film layer and improve the bonding strength between the negative electrode active material layer 211 and the negative electrode current collector 210.
  • the binder may include but is not limited to polyimide, polyvinyl alcohol, sodium carboxymethyl cellulose, hydroxypropyl Cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polymethyl methacrylate, polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, polyacrylonitrile, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.
  • the negative electrode active material layer 211 may further include a dispersant to uniformly disperse the conductive agent and binder, thereby improving the film quality.
  • Dispersants include, but are not limited to, at least one of carboxymethyl cellulose salts, polyacrylates, polyethylene glycol, or polyethylene oxide.
  • the carboxymethyl cellulose salt may include at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.
  • the negative electrode current collector 210 includes a first region 2100 , with a negative electrode active material layer 211 disposed on both opposing surfaces of the first region 2100 .
  • the first region 2100 is a double-sided coating area of the negative electrode current collector 210 .
  • the total thickness of the negative electrode active material layer 211 on the first region 2100 is T, with 0.07 mm ⁇ T ⁇ 0.15 mm.
  • the negative electrode active material layer 211 has a plurality of recesses 2110 , which can be obtained by removing portions of the negative electrode active material layer 211 .
  • the compacted density of the negative electrode active material layer 211 is D, expressed in g/cm 3 , where 3T+1 ⁇ D ⁇ 8T+1.
  • the compaction density D is lower than 3T+1, not only does it significantly reduce the energy density of the secondary battery 100, but it also leads to poor contact between the particles of the negative electrode active material, increasing impedance, hindering the transmission of lithium ions in the negative electrode active material layer 211, and resulting in reduced kinetic performance.
  • the excessive pores in the negative electrode active material layer 211 increase the contact area between the electrolyte and the negative electrode active material, which easily produces side reactions and forms a solid electrolyte membrane (SEI) on the surface of the negative electrode active material, not only increasing impedance but also worsening the lithium precipitation problem, resulting in reduced cycle performance.
  • SEI solid electrolyte membrane
  • the particles of the negative electrode active material are relatively loose, the negative electrode active material is easily detached when the recess 2110 is set, and the sidewalls of the recess 2110 collapse, further reducing the cycle performance and even causing short circuit problems.
  • the compaction density D is higher than 8T+1, although the energy density of the secondary battery 100 is improved, the contact between the particles of the negative electrode active material is too close, the ion channel is blocked, and the dynamic performance of the secondary battery 100 is reduced.
  • the negative electrode active material layer 211 lacks pores for the electrolyte to enter, resulting in poor electrolyte wettability, which also worsens the lithium plating problem and reduces the cycle performance of the secondary battery 100.
  • the particles of the negative electrode active material will produce more fresh surface
  • the electrolyte is consumed, resulting in an increase in side reactions at the sidewalls of the recess 2110 , thereby worsening the lithium deposition problem in the recess 2110 and reducing the cycle performance of the secondary battery 100 .
  • a recess 2110 is provided on the negative electrode active layer.
  • the recess 2110 can accommodate the electrolyte, thereby improving the degree of electrolyte infiltration into the negative electrode sheet 21, reducing the ion migration impedance, and facilitating the transmission and embedding of lithium ions in the entire negative electrode active material layer 211, thereby improving the problems of poor kinetic performance and low cycle capacity attenuation caused by the increase in the thickness of the negative electrode active material layer 211.
  • the secondary battery 100 can maintain a high energy density, and on the other hand, the negative electrode active particles are in close contact to provide an efficient ion transmission path, reducing impedance, thereby further improving the kinetic performance of the secondary battery 100.
  • more pores can be created in the negative electrode active material layer 211 to further improve the degree of electrolyte infiltration, thereby reducing the risk of partial loss of negative electrode active material due to the provision of recesses 2110 in the negative electrode active material layer 211 and causing lithium deposition within the recesses 2110, further improving the cycle performance of the secondary battery 100.
  • the present application provides recesses 2110 in the negative electrode active material layer 211 of the thick electrode sheet and further sets the relationship between the compaction density D and the total thickness T of the negative electrode active material layer 211, thereby achieving a balance between the energy density, kinetic performance, and cycle performance of the secondary battery 100, so that the secondary battery 100 can achieve both high energy density and excellent kinetic performance and cycle performance.
  • setting the compaction density D can also reduce the risk of the negative electrode active material falling off (the side wall of the recess 2110 collapses) when the recess 2110 is set, and at the same time reduce the risk of the particles of the negative electrode active material producing more fresh surfaces and consuming the electrolyte when the recess 2110 is set. Therefore, the risk of increased side reactions at the side wall of the recess 2110 leading to worsening lithium deposition in the recess 2110 can be reduced.
  • 3.5T+1 ⁇ D ⁇ 6.5T+1 can be set, which can further improve the energy density of the secondary battery 100 while maintaining close contact between the negative electrode active particles and creating more pores in the negative electrode active material layer 211 to further improve the electrolyte infiltration degree, thereby further improving the kinetic performance and cycle performance of the secondary battery 100.
  • 4.5T+1 ⁇ D ⁇ 5.5T+1 can be set, thereby further improving the energy density, kinetic performance, and cycle performance of the secondary battery 100.
  • the secondary battery 100 can achieve both a higher energy density and better kinetic and cycling performance.
  • 1.3 g/cm 3 ⁇ D ⁇ 1.9 g/cm 3 can be set, which can achieve both a higher energy density and better kinetic and cycling performance.
  • the compaction density can be 1.3 g/cm 3 , 1.4 g/cm 3 , 1.5 g/cm 3 , 1.6 g/cm 3 , 1.7 g/cm 3 , or any value within the range formed by any two of the above values.
  • the electrode assembly 20 when the electrode assembly 20 is a wound structure, the electrode assembly 20 may include a straight section 20A and a curved section 20B connected along a winding direction W.
  • the negative electrode active material layer 211 includes a first active material region 2111 located in the straight section 20A and a second active material region 2112 located in the curved section 20B.
  • the compaction density of the first active material region 2111 and the compaction density of the second active material region 2112 may be set to D 1 and D 2 , 1.3 g/cm 3 ⁇ D 1 ⁇ 2.0 g/cm 3 , and 1.2 g/cm 3 ⁇ D 2 ⁇ 1.5 g/cm 3 .
  • the first active material region 2111 and the second active material region 2112 may have a compaction density of D 1 , 1.3 g/cm 3 ⁇ D 1 ⁇ 2.0 g/cm 3 , and 1.2 g/cm 3 ⁇ D 2 ⁇ 1.5 g/cm 3 .
  • the specific range of the compaction density of 2112 can improve the problem that the second active material area 2112 at the curved section 20B is squeezed and the stress in the electrode is high, which leads to easy lithium deposition.
  • the compaction density of the first active material area 2111 at the straight section 20A is further improved. Under the premise of not significantly worsening the dynamic performance and lithium deposition problem at the first active material area 2111, the first active material area 2111 can play a greater capacity role, thereby further improving the energy density of the secondary battery 100.
  • the width of the fourth active material region 2114 can be between 2 mm and 10 mm, for example, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, or any specific value between any two adjacent values mentioned above.
  • the width is the distance between any position of the fourth active material region 2114 facing away from the outer periphery of the third active material region 2113 and the inner periphery of the fourth active material region 2114 adjacent to the outer periphery.
  • the circular recess 2110 can facilitate the uniform diffusion of lithium ions in the negative electrode active material layer 211, improve electrolyte infiltration, and reduce ion migration resistance, thereby further improving the problems of poor kinetic performance and low cycle capacity decay caused by the increased thickness of the negative electrode active material layer 211.
  • the electrolyte may be in one or more of a gel state, a solid state, and a liquid state.
  • the liquid electrolyte comprises a lithium salt and an organic solvent.
  • the lithium salt may be selected from, but is not limited to, one or more of lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium tetraphenylborate (LiB(C 6 H 5 ) 4 ), lithium methanesulfonate (LiCH 3 SO 3 ), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(trifluoromethylsulfonyl)imide
  • Examples of carbonate compounds include but are not limited to diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), 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 a combination thereof.
  • DEC diethyl carbonate
  • DMC dimethyl carbonate
  • DPC
  • the concentration of the lithium salt in the electrolyte is 0.5 mol/L to 1.5 mol/L.
  • the lithium salt dissolves in the organic solvent and ionizes, partially forming solvated lithium ions and corresponding anion clusters, which provide ion conductivity. Therefore, increasing the concentration of the lithium salt in the electrolyte can help improve the conductivity of the electrolyte, enhance the kinetic performance of the secondary battery 100, and further reduce the possibility of lithium plating.
  • the concentration of the lithium salt in the electrolyte can be measured using an ion chromatograph.
  • the electronic device 1 may include, but is not limited to, a laptop computer, a pen-type 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 television, 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, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, lighting fixtures, toys, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.
  • the total thickness T of the two layers of negative electrode active material layers 211 is 100 ⁇ m.
  • the negative electrode active material layer 211 is cold pressed.
  • a plurality of recesses 2110 are set on each negative electrode active material layer 211 by laser drilling.
  • the recesses 2110 The width of the recessed portion 2110 is 70 ⁇ m, the depth is 10 ⁇ m, and the center distance between two adjacent recessed portions 2110 is 1 mm.
  • the negative electrode tab is welded to the exposed copper foil.
  • the negative electrode tab is made of copper.
  • Assembly of the secondary battery 100 The positive electrode sheet 22, separator 23, and negative electrode sheet 21 are stacked and wound in sequence to form the electrode assembly 20.
  • a 150 ⁇ m thick aluminum-plastic film with cavities punched and formed is placed in an assembly fixture with the cavities facing upward, and the electrode assembly 20 is placed in the cavities. Electrolyte is injected into the cavities of the aluminum-plastic film, and the positive and negative electrode tabs are led out of the aluminum-plastic film. Then, the battery is formed and packaged to obtain the secondary battery 100 shown in FIG1 .
  • Example 1 The difference from Example 1 lies in the relationship between D and T.
  • Example 1 The difference from Example 1 is that no recess 2110 is provided on the negative electrode active material layer 211 .
  • the positive electrode active material lithium cobalt oxide ( LiCoO2 ), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96.5:1.5:2, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly.
  • the slurry is evenly coated on one surface of a positive electrode current collector 220, i.e., an aluminum foil with a thickness of 12 ⁇ m, leaving an empty foil area at the edge of the aluminum foil, and then dried at 90°C to obtain a positive electrode active material layer 221 with a coating thickness of 74 ⁇ m.
  • the above coating steps are repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode plate 22. Then, the excess empty foil area is removed by laser die-cutting to obtain a positive electrode tab.
  • Assembly of the secondary battery 100 The positive electrode sheet 22, separator 23, and negative electrode sheet 21 are stacked in sequence to form a laminated electrode assembly 20.
  • An aluminum-plastic film (150 ⁇ m thick) with cavities formed therein is placed in an assembly fixture with the cavities facing upward, and the electrode assembly 20 is placed in the cavities. Electrolyte is injected into the cavities of the aluminum-plastic film, and the positive and negative electrode tabs are led out of the aluminum-plastic film. Chemical formation and packaging are then performed to obtain the secondary battery 100 shown in FIG5 .
  • Example 14 The difference from Example 14 lies in the relationship between D and T.
  • the dynamic performance of secondary batteries can be characterized by low-temperature discharge performance.
  • the low-temperature discharge performance test steps are as follows: 1) The secondary battery is allowed to stand at a test temperature of 25°C for 5 minutes, then discharged at a constant current of 0.2C to 3.0V, and allowed to stand for 5 minutes. This discharge capacity is the initial discharge capacity; 2) Charge at a constant current of 0.2C to 4.50V, then charge at a constant voltage of 4.50V to 0.02C, and allow to stand for 5 minutes; 3) Adjust the furnace temperature to -20°C, stand for 60 minutes, then discharge at a constant current of 0.2C to 3.0V, and then allow to stand for 5 minutes. The ratio of the secondary battery's discharge capacity after low-temperature discharge to the initial capacity multiplied by 100% is the low-temperature capacity retention rate. The low-temperature capacity retention rates of 10 samples are averaged.
  • the test steps for the cyclic capacity retention rate of secondary batteries are as follows: 1) The secondary battery is allowed to rest at a test temperature of 25°C for 30 minutes. Then, it is charged to 4.43V at a constant current of 1C. Then, it is charged to 0.05C at a constant voltage. After resting for 5 minutes, it is discharged to 3.0V at a rate of 0.7C. This discharge capacity is the initial discharge capacity and is calculated as 100%. 2) The above charge and discharge steps are repeated for 1000 cycles. The ratio of the discharge capacity after the cycle to the initial capacity of the secondary battery is multiplied by 100% to obtain the capacity retention rate. The capacity retention rates of the 10 samples are averaged.
  • the lithium deposition test procedure for secondary batteries is as follows: 1) Charge the secondary battery after cycle testing at a constant current of 1C to 4.43V, then charge it at a constant voltage of 0.05C. 2) Disassemble the secondary battery and inspect the negative electrode recess for lithium deposition. If the deposited area is greater than or equal to 2 mm2 , the battery is deemed to have deposited lithium and the test fails. The percentage of samples that passed the lithium deposition test out of 10 is the lithium deposition test pass rate. The results are recorded in Table 1.
  • Example 2-8 meets 3.5T+1 ⁇ D ⁇ 6.5T+1, which can further improve the energy density, low-temperature capacity retention rate and cycle capacity retention rate of the secondary battery.
  • Examples 4-6 satisfy 4.5T+1 ⁇ D ⁇ 5.5T+1, which can further improve the energy density, low-temperature capacity retention rate, and cycle capacity retention rate of the secondary battery.
  • Example 14 achieves both a higher energy density and excellent low-temperature and cycle capacity retention by providing recesses while also setting the compaction density D and total thickness T to meet specific conditions.
  • Comparative Example 6 while satisfying the aforementioned relationship in terms of compaction density D and total thickness T, lacks recesses, resulting in poor ion transport and electrolyte wettability, and low low-temperature and cycle capacity retention.
  • the secondary battery can achieve both higher energy density and better low-temperature capacity retention and cycle capacity retention.
  • Example 1 The difference from Example 1 is that in the wound electrode assembly 20 , the compaction density D 1 of the first active material region 2111 located in the straight section 20A is different from the compaction density D 2 of the second active material region 2112 located in the curved section 20B.
  • Example 14 The difference from Example 14 is that the compaction density D 3 of the third active material region 2113 located in the central region is different from the compaction density D 4 of the fourth active material region 2114 located in the edge region.
  • Examples 15-17 had higher compaction densities for the first active material region compared to the second active material region. While the secondary battery's lithium plating pass rate, low-temperature capacity retention, and cycle capacity retention rates did not significantly decrease, the energy density was significantly improved. Compared to Example 18, Examples 15-17 reduced the impact of the compaction density of the first active material region on the lithium plating pass rate, low-temperature capacity retention, and cycle capacity retention rates by limiting the upper limit of the compaction density.
  • Example 19-21 Compared to Example 14, for electrode assemblies with a laminated structure, the third active material region of Examples 19-21 had a higher compaction density than the fourth active material region. The lithium plating pass rate, low-temperature capacity retention rate, and cycle capacity retention rate of the secondary batteries did not significantly decrease, but the energy density was significantly improved. Compared to Example 22, Examples 19-21 reduced the impact of the third active material region's compaction density on the lithium plating pass rate, low-temperature capacity retention rate, and cycle capacity retention rate by limiting its upper limit.
  • Example 1 The difference from Example 1 lies in the relevant dimensions of the recess 2110 .

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Abstract

提供一种二次电池和电子装置。二次电池包括电极组件，电极组件包括负极极片。负极极片包括负极集流体和设于负极集流体表面的负极活性材料层。负极集流体包括第一区域，第一区域的相对两表面均设有负极活性材料层。第一区域上负极活性材料层的总厚度为T，0.07mm≤T≤0.15mm。负极活性材料层设有多个凹部。负极活性材料层的压实密度为D(g/cm 3)，3T+1≤D≤8T+1。

Description

二次电池和电子装置 技术领域
本申请涉及储能技术领域，尤其涉及一种二次电池和具有所述二次电池的电子装置。
背景技术
二次电池(如锂离子二次电池)在电子移动设备、电动工具及电动汽车等电子产品中有着广泛使用，人们对二次电池的性能要求也越来越高。
相关技术中通过提高极片的活性材料层的厚度来提升二次电池的能量密度。然而，厚极片的设计延长了锂离子的迁移路径且迁移阻抗增加，循环过程中锂离子难以快速地到达临近集流体的部分活性材料层，浓差极化增大，引起动力学性能降低、循环容量衰减等问题。因此对具有厚极片的二次电池而言，如何使二次电池兼顾较高的能量密度以及较优的动力学性能和循环性能成为亟待解决的问题。
发明内容
本申请提供一种能够兼顾较高的能量密度以及较优的动力学性能和循环性能的二次电池以及具有上述二次电池的电子装置。
本申请第一方面提供一种二次电池，包括电极组件。电极组件包括负极极片。负极极片包括负极集流体和设于负极集流体表面的负极活性材料层。负极集流体包括第一区域，第一区域的相对两表面均设有负极活性材料层。第一区域上负极活性材料层的总厚度为T，0.07mm≤T≤0.15mm。负极活性材料层设有多个凹部，负极活性材料层的压实密度为D，单位为g/cm3，3T+1≤D≤8T+1。
本申请针对具有较厚负极活性材料层的负极极片，通过在负极活性层上设置凹部，改善电解液对负极极片的浸润程度，降低离子迁移阻抗，利于锂离子在负极活性材料层中的的传输和嵌入，从而改善由于负极活性材料层厚度增加导致的动力学性能差、循环容量衰减低等问题。同时，通过设置压实密度和总厚度之间的关系，一方面，使得二次电池可维持较高的能量密度，另一方面，使得负极活性颗粒接触紧密以提供高效的离子传输路径，降低阻抗，进而进一步提高二次电池的动力学性能的同时，还可在负极活性材料层中构建较多的孔隙以进一步提高电解液浸润程度，从而减小由于负极活性材料层开设凹部导致部分负极活性材料缺失并引起凹部内析锂的风险，进一步提高二次电池的循环性能。因此，本申请在厚极片中设置凹部并进一步设置压实密度与总厚度的关系，可实现二次电池的能量密度、动力学性能和循环性能之间的平衡，使二次电池兼顾较高的能量密度以及较优的动力学性能和循环性能。另外，通过设置 压实密度和总厚度之间的关系，还可减小当设置凹部时负极活性材料脱落(凹部侧壁坍塌)的风险，同时减小当设置凹部时负极活性材料的颗粒产生较多的新鲜表面并消耗电解液的风险，进而减小凹部侧壁处副反应增多恶化凹部内析锂问题的风险。
基于第一方面，在一些可能的实现方式中，3.5T+1≤D≤6.5T+1。可在进一步提高二次电池的能量密度的同时，使得负极活性颗粒保持接触紧密并在负极活性材料层中构建更多的孔隙以进一步提高电解液浸润程度，从而进一步改善二次电池的动力学性能和循环性能。
基于第一方面，在一些可能的实现方式中，4.5T+1≤D≤5.5T+1。可在进一步提高二次电池的能量密度的同时，使得负极活性颗粒保持接触紧密并在负极活性材料层中构建更多的孔隙以进一步提高电解液浸润程度，从而进一步改善二次电池的动力学性能和循环性能。
基于第一方面，在一些可能的实现方式中，1.2g/cm3≤D≤2.2g/cm3。可使得二次电池兼顾较高的能量密度以及较优的动力学性能和循环性能。
基于第一方面，在一些可能的实现方式中，1.3g/cm3≤D≤1.9g/cm3。可使得二次电池兼顾更高的能量密度以及较优的动力学性能和循环性能。
基于第一方面，在一些可能的实现方式中，电极组件为卷绕结构，电极组件包括沿卷绕方向相连接的平直段和弯曲段。负极活性材料层包括位于平直段的第一活性材料区和位于弯曲段的第二活性材料区。第一活性材料区的压实密度为D1，第二活性材料区的压实密度为D2,1.3g/cm3≤D1≤2.0g/cm3，1.2g/cm3≤D2≤1.5g/cm3。可改善弯曲段处的第二活性材料区受到挤压、极片内应力较高导致容易析锂的问题，同时平直段处的第一活性材料区的压实密度较高，在不显著恶化第一活性材料区处的动力学性能和析锂问题的前提下，第一活性材料区可发挥更大的容量作用，因此二次电池的能量密度进一步提高。
基于第一方面，在一些可能的实现方式中，电极组件为叠片结构。负极活性材料层包括第三活性材料区和围绕第三活性材料区的外周缘设置的第四活性材料区。第三活性材料区的压实密度为D3，第四活性材料区的压实密度为D4，1.2g/cm3≤D3≤2.0g/cm3，1.2g/cm3≤D4≤1.7g/cm3。可改善位于边缘处的第四活性材料区由于厚度相对较薄、负极活性材料相对较少导致容易析锂的问题，同时位于中心的第三活性材料区的压实密度较高，在不显著恶化第三活性材料区处的动力学性能和析锂问题的前提下，第三活性材料区可发挥更大的容量作用，因此二次电池的能量密度进一步提高。
基于第一方面，在一些可能的实现方式中，凹部的宽度为70μm至100μm，深度为5μm至100μm，相邻两个凹部的中心间距为1mm至2mm。适当尺寸的凹部可减少过多负极活性材料缺失的风险，利于维持较高的能量密度并减小凹部内析锂恶化的风险，也可抑制锂离子在凹部内聚集，并维持负极极片的结构稳定性以减小电极组件变形，进而进一步改善厚极片开设凹部后凹部内容易析锂的问题，提高二次电池的 循环性能；适当的凹部分布密度可改善电解液浸润，降低离子迁移阻抗并改善凹部内容易析锂的问题，提高二次电池的动力学性能和循环性能。
基于第一方面，在一些可能的实现方式中，从负极极片的厚度方向观察，凹部为圆形或方形。圆形的凹部利于锂离子在负极活性材料层中均匀扩散，提高电解液浸润并降低离子迁移阻抗，改善由于负极活性材料层厚度增加导致的动力学性能差、循环容量衰减低等问题。方形的凹部可增加电解液和负极活性材料层在边界处的接触面积，利于提高锂离子在负极活性材料层的扩散速度，从而进一步改善由于负极活性材料层厚度增加导致的动力学性能差、循环容量衰减低等问题。
基于第一方面，在一些可能的实现方式中，二次电池的CB值为1至1.05，从而进一步减小负极活性材料层的析锂风险，提高二次电池的循环性能。
基于第一方面，在一些可能的实现方式中，凹部为移除部分负极活性材料层得到。
本申请第二方面还提供一种电子装置，其包括电池仓和设于电池仓内的如上二次电池。电子装置通过上述二次电池供电，且二次电池能够兼顾较高的能量密度和较优的动力学性能与循环性能。
附图说明
本申请的上述和/或附加的方面和优点从结合下面附图对实施例的描述中将变得明显和容易理解，其中：
图1为本申请一实施方式提供的二次电池的结构示意图。
图2为图1所示的二次电池的负极极片于II处的局部放大图。
图3为图2所示的负极极片于一些实施例中的平面示意图。
图4为图2所示的负极极片于另一些实施例中的平面示意图。
图5为本申请另一实施方式提供的二次电池的结构示意图。
图6为本申请一实施方式的电子装置的结构示意图。
主要元件符号说明
电子装置            1
电极组件            20
平直段              20A
弯曲段              20B
负极极片            21
正极极片            22
隔离膜              23
二次电池            100
电池仓              101
正极集流体          220
正极活性材料层      221
负极集流体          210
负极活性材料层      211
第一区域            2100
凹部                2110
第一活性材料区      2111
第二活性材料区      2112
第三活性材料区      2113
第四活性材料区      2114
卷绕中心轴         C
卷绕方向           W
厚度               T0、T1
宽度               w
深度               h
中心间距           d
厚度方向           X
如下具体实施方式将结合上述附图进一步说明本申请。
具体实施方式
下面对本申请实施例中的技术方案进行清楚、详细地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。除非另有定义，本文所使用的所有的技术和科学术语与属于本申请的技术领域的技术人员通常理解的含义相同。在本申请的说明书中所使用的术语只是为了描述具体的实施例的目的，不是旨在于限制本申请。
下文，将详细地描述本申请的实施方式。但是，本申请可体现为许多不同的形式，并且不应解释为限于本文阐释的示例性实施方式。而是，提供这些示例性实施方式，从而使本申请透彻的和详细的向本领域技术人员传达。
另外，为了简洁和清楚，在附图中，各种组件、层的尺寸或厚度可被放大。遍及全文，相同的数值指相同的要素。如本文所使用，术语“及/或”、“以及/或者”包括一个或多个相关列举项目的任何和所有组合。另外，应当理解，当要素A被称为“连 接”要素B时，要素A可直接连接至要素B，或可能存在中间要素C并且要素A和要素B可彼此间接连接。
进一步，当描述本申请的实施方式时使用“可”指“本申请的一个或多个实施方式”。
本文使用的专业术语是为了描述具体实施方式的目的并且不旨在限制本申请。如本文所使用，单数形式旨在也包括复数形式，除非上下文另外明确指出。应进一步理解，术语“包括”，当在本说明书中使用时，指存在叙述的特征、数值、步骤、操作、要素和/或组分，但是不排除存在或增加一个或多个其他特征、数值、步骤、操作、要素、组分和/或其组合。
空间相关术语，比如“上”等可在本文用于方便描述，以描述如图中阐释的一个要素或特征与另一要素(多个要素)或特征(多个特征)的关系。应理解，除了图中描述的方向之外，空间相关术语旨在包括设备或装置在使用或操作中的不同方向。例如，如果将图中的设备翻转，则描述为在其他要素或特征“上方”或“上”的要素将定向在其他要素或特征的“下方”或“下面”。因此，示例性术语“上”可包括上面和下面的方向。应理解，尽管术语第一、第二、第三等可在本文用于描述各种要素、组分、区域、层和/或部分，但是这些要素、组分、区域、层和/或部分不应受这些术语的限制。这些术语用于区分一个要素、组分、区域、层或部分与另一要素、组分、区域、层或部分。因此，下面讨论的第一要素、组分、区域、层或部分可称为第二要素、组分、区域、层或部分，而不背离示例性实施方式的教导。
在本申请中，参数数值之间的大于、小于或不等于设计关系，需要排除测量设备的合理误差。
请参阅图1，本申请一实施方式提供一种二次电池100，包括外壳(图未示)、电极组件20和电解液(图未示)。电极组件20和电解液均位于外壳内。其中，外壳可以是采用封装膜(如铝塑膜)封装得到的包装袋，如二次电池100为软包电池。在另一些实施例中，二次电池100也可以是钢壳电池、铝壳电池等。
电极组件20包括负极极片21、正极极片22以及隔离膜23，隔离膜23设于正极极片22和负极极片21之间。如图1所示，电极组件20可以是卷绕结构，其由正极极片22、隔离膜23和负极极片21依次层叠后卷绕形成。其中，如图1所示，电极组件20具有垂直于纸面的卷绕中心轴C和绕卷绕中心轴C进行卷绕的卷绕方向W。卷绕方向W为图2所示绕着卷绕中心轴C进行逆时针转动的方向。在另一些实施例中，卷绕方向W也可以为顺时针转动的方向。
如图5所示，在另一些实施例中，电极组件20还可以是叠片结构，其由正极极片22、隔离膜23和负极极片21依次交替层叠形成。
正极极片
正极极片22包括正极集流体220和设于正极集流体220表面的正极活性材料层221。正极集流体220可以使用铝箔或镍箔等，也可为任何现有技术中公开的复合集流体，例如但不仅限于前述导电箔和聚合物基底结合形成的集流体。
正极活性材料层221包含活性材料，如包含钴酸锂、锰酸锂、镍酸锂、镍钴锰酸锂、磷酸铁锂、磷酸锰铁锂、磷酸钒锂、磷酸钒氧锂、富锂锰基材料或镍钴铝酸锂中的至少一种。
正极活性材料层221还可包括粘结剂，用以粘结活性材料颗粒从而便于形成膜层，同时还能够提高正极活性材料层221与正极集流体220之间的结合力。在一些实施例中，粘结剂可包括但不仅限于聚酰亚胺、聚乙烯醇、羧甲基纤维素钠、羟丙基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、聚氧化乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚甲基丙烯酸甲酯、聚偏氟乙烯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、聚丙烯腈、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙等中的至少一种。
正极活性材料层221还可包含导电剂，导电剂包括但不限于基于碳的材料、基于金属的材料、导电聚合物或其任意组合。在一些实施例中，基于碳的材料可包括但不仅限于自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。在一些实施例中，基于金属的材料可包括但不仅限于金属粉或金属纤维，例如铜、镍、铝或银。在一些实施例中，导电聚合物可为聚亚苯基衍生物。
负极极片
负极极片21包括负极集流体210和设于负极集流体210表面的负极活性材料层211。
负极集流体210可以采用铜箔、镍箔、不锈钢箔、钛箔或碳基集流体等中的至少一种，也可为任何现有技术中公开的复合集流体，例如但不仅限于前述导电箔和聚合物基底结合形成的集流体。
负极活性材料层211包含活性物质，其可选自石墨类材料、合金类材料、锂金属及其合金中的至少一种。石墨类材料可选自人造石墨、天然石墨中的至少一种；合金类材料可选自硅、氧化硅、锡、硫化钛中的至少一种。
负极活性材料层211还可包括导电剂，导电剂包括但不限于基于碳的材料、基于金属的材料、导电聚合物或其任意组合。在一些实施例中，基于碳的材料可包括但不仅限于自天然石墨、人造石墨、碳黑、乙炔黑、科琴黑、碳纤维或其任意组合。基于金属的材料可包括但不仅限于金属粉或金属纤维，例如铜、镍、铝或银。导电聚合物可为聚亚苯基衍生物。
负极活性材料层211还可包括粘结剂，粘结剂用以粘结负极活性颗粒从而便于形成膜层，同时还能够提高负极活性材料层211与负极集流体210之间的结合力。在一些实施例中，粘结剂可包括但不仅限于聚酰亚胺、聚乙烯醇、羧甲基纤维素钠、羟丙 基纤维素、二乙酰基纤维素、聚氯乙烯、羧化的聚氯乙烯、聚氟乙烯、聚氧化乙烯、含亚乙基氧的聚合物、聚乙烯吡咯烷酮、聚氨酯、聚甲基丙烯酸甲酯、聚偏氟乙烯、聚四氟乙烯、聚偏1,1-二氟乙烯、聚乙烯、聚丙烯、聚丙烯腈、丁苯橡胶、丙烯酸(酯)化的丁苯橡胶、环氧树脂或尼龙等。
负极活性材料层211还可包括分散剂，分散剂用于使导电剂和粘结剂分散均匀，提高膜层质量。分散剂包括但不限于羧甲基纤维素盐、聚丙烯酸盐、聚乙二醇或聚环氧乙烷的至少一种。在一些实施例中，羧甲基纤维素盐可以包括羧甲基纤维素钠或羧甲基纤维素锂中的至少一种。
请参照图2，负极集流体210包括第一区域2100，第一区域2100的相对两表面均设有负极活性材料层211。即，第一区域2100为负极集流体210的双面涂覆区。第一区域2100上负极活性材料层211的总厚度为T，0.07mm≤T≤0.15mm。负极活性材料层211设有多个凹部2110，凹部2110可为移除部分负极活性材料层211得到。其中，总厚度T的测量方法可以包括如下步骤：将二次电池100放电至3.0V，拆解二次电池100，清洗、烘干；使用万分尺测得负极极片21的厚度T0；使用溶剂洗掉负极活性材料层211，烘干，并使用万分尺测得负极集流体210的厚度T1；然后，通过下式计算总厚度T：T＝T0-T1。
而且，负极活性材料层211的压实密度为D，单位为g/cm3，3T+1≤D≤8T+1。其中，压实密度D的测量方法可以包括如下步骤：将二次电池100放电至3.0V，拆解二次电池100，清洗、烘干；使用天平对一定面积A的负极极片21进行称重，重量记为W0；使用万分尺测得负极极片21的厚度T0；使用溶剂洗掉负极活性材料层211，烘干，测量负极集流体210的重量，记为W1；使用万分尺测得负极集流体210的厚度T1；然后，通过下式计算压实密度D：D＝(W0-W1)/[(T0-T1)×A]。
当压实密度D低于3T+1时，不仅会导致二次电池100的能量密度大幅降低，而且使得负极活性材料的颗粒之间接触性差，阻抗增大，阻碍了锂离子在负极活性材料层211中的传输，导致动力学性能降低，同时负极活性材料层211中过多的孔隙使得电解液与负极活性材料之间的接触面积增大，容易产生副反应并在负极活性材料表面生成固态电解质膜(SEI)，不仅提高阻抗，而且也恶化了析锂问题，导致循环性能降低。另外，由于负极活性材料的颗粒之间较为松散，当设置凹部2110时负极活性材料容易脱落，凹部2110侧壁坍塌，从而进一步降低了循环性能甚至引发短路问题。
当压实密度D高于8T+1时，虽然二次电池100的能量密度提高，然而由于负极活性材料的颗粒之间接触过于紧密，离子通道受阻，降低了二次电池100的动力学性能。而且负极活性材料层211中缺少供电解液进入的孔隙，导致电解液浸润性变差，因此也恶化了析锂问题，导致二次电池100循环性能降低。另外，由于负极活性材料的颗粒之间接触过于紧密，当设置凹部2110时负极活性材料的颗粒会产生较多的新鲜表面 并消耗电解液，导致凹部2110侧壁处副反应增多，从而恶化了凹部2110内的析锂问题，降低了二次电池100的循环性能。
本申请中，针对具有较厚负极活性材料层211的负极极片21，通过在负极活性层上设置凹部2110，凹部2110可容纳电解液，改善电解液对负极极片21的浸润程度，降低离子迁移阻抗，利于锂离子在整个负极活性材料层211中的传输和嵌入，从而改善由于负极活性材料层211厚度增加导致的动力学性能差、循环容量衰减低等问题。同时，通过设置负极活性材料层211的压实密度D和负极活性材料层211的总厚度T之间的关系，一方面，使得二次电池100可维持较高的能量密度，另一方面，使得负极活性颗粒接触紧密以提供高效的离子传输路径，降低阻抗，进而进一步提高二次电池100的动力学性能的同时，还可在负极活性材料层211中构建较多的孔隙以进一步提高电解液浸润程度，从而减小由于负极活性材料层211开设凹部2110导致部分负极活性材料缺失并引起凹部2110内析锂的风险，进一步提高二次电池100的循环性能。因此，本申请在厚极片的负极活性材料层211中设置凹部2110并进一步设置压实密度D与负极活性材料层211总厚度T的关系，可实现二次电池100的能量密度、动力学性能和循环性能之间的平衡，使二次电池100可兼顾较高的能量密度以及较优的动力学性能和循环性能。另外，设置压实密度D还可减小当设置凹部2110时负极活性材料脱落(凹部2110侧壁坍塌)的风险，同时减小当设置凹部2110时负极活性材料的颗粒产生较多的新鲜表面并消耗电解液的风险，因此可减小凹部2110侧壁处副反应增多导致凹部2110内析锂恶化的风险。
进一步地，可设置3.5T+1≤D≤6.5T+1，可在进一步提高二次电池100的能量密度的同时，使得负极活性颗粒保持接触紧密并在负极活性材料层211中构建更多的孔隙以进一步提高电解液浸润程度，从而进一步改善二次电池100的动力学性能和循环性能。更进一步地，可设置4.5T+1≤D≤5.5T+1，从而进一步提高二次电池100的能量密度、动力学性能和循环性能。
在一些实施例中，1.2g/cm3≤D≤2.2g/cm3。通过进一步设置压实密度D的具体范围，可使得二次电池100兼顾较高的能量密度以及较优的动力学性能和循环性能。进一步地，可设置1.3g/cm3≤D≤1.9g/cm3，可使得二次电池100兼顾更高的能量密度以及较优的动力学性能和循环性能。作为示例，压实密度可以为1.3g/cm3、1.4g/cm3、1.5g/cm3、1.6g/cm3、1.7g/cm3或在上述任意两个数值所组成的范围内的任一值。
如图1所示，当电极组件20为卷绕结构时，电极组件20可包括沿卷绕方向W相连接的平直段20A和弯曲段20B。负极活性材料层211包括位于平直段20A的第一活性材料区2111和位于弯曲段20B的第二活性材料区2112。可设置第一活性材料区2111的压实密度为D1，第二活性材料区2112的压实密度为D2,1.3g/cm3≤D1≤2.0g/cm3，1.2g/cm3≤D2≤1.5g/cm3。通过进一步设置第一活性材料区2111和第二活性材料区 2112的压实密度的具体范围，可改善弯曲段20B处的第二活性材料区2112受到挤压、极片内应力较高导致容易析锂的问题，同时平直段20A处的第一活性材料区2111的压实密度进一步提高，在不显著恶化第一活性材料区2111处的动力学性能和析锂问题的前提下，第一活性材料区2111可发挥更大的容量作用，从而使二次电池100的能量密度进一步提高。
如图5所示，当另一些实施例的电极组件20为叠片结构时，负极活性材料层211包括第三活性材料区2113和围绕第三活性材料区2113的外周缘设置的第四活性材料区2114。由于负极极片21制作时需要经过压合工序，压合时第四活性材料区2114可向远离第三活性材料区2113的方向延展，而第三活性材料区2113被第四活性材料区2114环绕使得可活动空间被限制，因此，第三活性材料区2113的厚度可大于第四活性材料区2114的厚度。因此，可设置第三活性材料区2113的压实密度为D3，第四活性材料区2114的压实密度为D4,1.3g/cm3≤D3≤2.2g/cm3，1.2g/cm3≤D4≤1.7g/cm3。通过进一步设置第三活性材料区2113和第四活性材料区2114的压实密度的具体范围，可改善位于边缘处的第四活性材料区2114由于厚度相对较薄、负极活性材料相对较少导致容易析锂的问题，同时位于中心的第三活性材料区2113的压实密度进一步提高，在不显著恶化第三活性材料区2113处的动力学性能和析锂问题的前提下，第三活性材料区2113可发挥更大的容量作用，从而使二次电池100的能量密度进一步提高。其中，第四活性材料区2114的宽度可为2mm至10mm，例如可为2mm、3mm、4mm、5mm、6mm、7mm、8mm、9mm、10mm或前述任意两个相邻数值之间的任意具体数值。该宽度为第四活性材料区2114背离第三活性材料区2113的外周缘的任意一位置处至该第四活性材料区2114与该外周缘相邻的内周缘之间的距离。
在一些实施例中，二次电池100的CB值为1至1.05，从而进一步减小负极活性材料层211的析锂风险。其中，CB值为负极活性材料层211的单位面积的容量与正极活性材料层221的单位面积容量的比值。其中，CB值的测量方法可以包括如下步骤：1)将二次电池100在25℃的测试温度下静置30分钟；2)以0.2C恒流充电至4.5V，再恒压放电至0.02C；3)静置5分钟；4)以0.2C DC至3V并记录0.2C下的放电容量Q1；5)静置五分钟；6)以0.2C恒流充电至4.5V，再恒压放电至0.02C容量截止；7)静置5分钟；8)以0.2C DC至3V；9)针对第6步充电容量做dv/dq曲线，于截止电压处做水平切线并读取对应的横坐标，记为容量值Q，然后，通过下式计算CB值：CB＝Q/Q1。
如图3和图4所示，在一些实施例中，凹部2110的宽度w为70μm至100μm，深度h为5μm至100μm，相邻两个凹部2110的中心间距d为1mm至2mm。适当尺寸的凹部2110可减少过多负极活性材料缺失的风险，利于维持较高的能量密度并减小凹部2110内析锂恶化的风险，也可抑制锂离子在凹部2110内聚集，并维持负极极片21的结构稳定性以减小电极组件20变形，进而进一步改善厚极片开设凹部2110 后凹部2110内容易析锂的问题，提高二次电池100的循环性能。另外，适当的凹部2110分布密度可改善电解液的浸润，降低离子迁移阻抗并改善厚极片开设凹部2110后凹部2110内容易析锂的问题，提高二次电池100的循环性能和动力学性能。凹部2110之间均匀分布还可减小负极极片21局部温度过高的风险，当二次电池100内部产气时也利于将气体快速排出电极组件20以减小电极组件20内部压力积聚的风险，这同样可改善凹部2110内析锂的问题，提高二次电池100的循环性能。另外，本申请通过设置压实密度D和总厚度T之间的关系，即便当凹部2110尺寸较小或分布密度较小时，也可减小当设置凹部2110时凹部2110侧壁坍塌的风险。其中，可采用激光打孔的方式形成凹部2110，激光打孔具有较高的精度，有利于得到尺寸较小且均匀分布的凹部2110。
请参阅图3，在一些实施例中，从负极极片21的厚度方向X(即图3中垂直纸面的方向)观察，凹部2110为方形。方形的凹部2110可增加电解液和负极活性材料层211在边界处的接触面积，利于提高锂离子在负极活性材料层211的扩散速度，从而进一步改善由于负极活性材料层211厚度增加导致的动力学性能差、循环容量衰减低等问题。请参阅图4，从负极极片21的厚度方向X观察，凹部2110还可以为圆形。圆形的凹部2110可利于锂离子在负极活性材料层211中均匀扩散，提高电解液浸润并降低离子迁移阻抗，从而进一步改善由于负极活性材料层211厚度增加导致的动力学性能差、循环容量衰减低等问题。
隔离膜
隔离膜23包括具有多孔结构的膜层，其材质包括但不仅限于聚乙烯、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，隔离膜23可为聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜等。
电解液
电解液的状态可以是凝胶态、固态和液态中的一种或多种。在一些实施例中，液态电解液包括锂盐和有机溶剂。锂盐可选自但不仅限于六氟磷酸锂(LiPF6)、四氟硼酸锂(LiBF4)、六氟砷酸锂(LiAsF6)、高氯酸锂(LiClO4)、四苯硼酸锂(LiB(C6H5)4)、甲磺酸锂(LiCH3SO3)、双氟磺酰亚胺锂(LiFSI)、双三氟甲烷磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiCF3SO3)、双(三氟甲基磺酰)亚胺锂(LiN(SO2CF3)2、三(三氟甲基磺酰)甲基锂(LiC(SO2CF3)3)、二草酸硼酸锂(LiBOB)和二氟磷酸锂(LiPO2F2)中的一种或多种。例如，锂盐选用LiPF6，因为它可以给出高的离子导电率并改善循环特性。有机溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、腈化合物、其它有机溶剂或它们的组合。碳酸酯化合物的实例包括但不仅限于碳酸二乙酯(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)、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)、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其组合。
在一些实施例中，锂盐在电解液中的浓度0.5mol/L至1.5mol/L。锂盐溶解于有机溶剂中并电离，部分形成溶剂化的锂离子和对应阴离子团，提供离子导通能力。因此通过提高锂盐在电解液中的浓度，有利于提高电解液的电导率，提升二次电池100的动力学性能，进一步降低了析锂的可能性。锂盐在电解液中的浓度可采用离子色谱仪测定。
请参阅图6，本申请一实施方式还提供一种电子装置1，其包括电池仓101和上述二次电池100。电子装置1可包括但不仅限于笔记本电脑、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、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。
以下通过具体实施例和对比例对本申请进行说明。本领域技术人员应理解，本申请中描述的制备方法仅是实施例，其他任何合适的制备方法均在本申请的范围内。
实施例1
(1)正极极片22的制备：将正极活性材料钴酸锂(LiCoO2)、导电炭黑(Super P)、聚偏二氟乙烯(PVDF)按照重量比96.5:1.5:2进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成固含量为75wt％的浆料，并搅拌均匀。预先在厚度为12μm的正极集流体220即铝箔的部分表面贴发泡胶，将浆料均匀涂覆在铝箔的一个表面上，加热以使得发泡胶脱落以使铝箔的部分表面显露出来，然后90℃条件下烘干，得到涂层厚度为74μm的正极活性材料层221，在铝箔的另一个表面上重复以上涂覆步骤，得到双面涂覆的正极极片22。然后，对正极极片22进行冷压，并在显露出来的铝箔上焊接正极极耳，正极极耳的材质为铝。
(2)负极极片21的制备：将负极活性材料人造石墨、导电炭黑(Super P)、丁苯橡胶(SBR)按照重量比96:1.5:2.5进行混合，加入去离子水作为溶剂，调配成重量百分比为70wt％的浆料，并搅拌均匀。预先在8μm的负极集流体210即铜箔的部分表面贴发泡胶，将浆料均匀涂覆在铜箔的一个表面上，加热以使得发泡胶脱落以使铝箔的部分表面显露出来，然后110℃条件下烘干，得到涂层厚度为50μm的负极活性材料层211，在铜箔的另一个表面上重复以上涂覆步骤，得到双面涂覆的负极极片21，即两层负极活性材料层211的总厚度T为100μm。然后，将负极活性材料层211冷压。再采用激光打孔的方式在每一负极活性材料层211上设置多个凹部2110，凹部2110 的宽度为70μm，深度为10μm，相邻两个凹部2110的中心间距为1mm。然后，在显露出来的铜箔上焊接负极极耳，负极极耳的材质为铜。
(3)电解液的制备：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)以质量比EC:EMC:DEC＝30:50:20混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF6)溶解并混合均匀，得到锂盐的浓度为1.15mol/L的电解液。
(4)隔离膜23的制备：选用厚度为9μm的聚乙烯(PE)膜。
(5)二次电池100的组装：将正极极片22、隔离膜23和负极极片21依次层叠卷绕后得到电极组件20，将冲坑成型的铝塑膜(厚度为150μm)置于组装夹具内，坑面朝上，并将电极组件20置于坑内。向铝塑膜的坑内注入电解液，并将正极极耳和负极极耳引出铝塑膜外。然后进行化成，封装，得到图1所示出的二次电池100。
实施例2-13和对比例1-2
与实施例1不同之处在于D与T的关系。
对比例3
与实施例1不同之处在于负极活性材料层211上未设置凹部2110。
实施例14
(1)正极极片22的制备：将正极活性材料钴酸锂(LiCoO2)、导电炭黑(Super P)、聚偏二氟乙烯(PVDF)按照重量比96.5:1.5:2进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成固含量为75wt％的浆料，并搅拌均匀。将浆料均匀涂覆在厚度为12μm的正极集流体220即铝箔的一个表面上，在铝箔的边缘预留空箔区，然后90℃条件下烘干，得到涂层厚度为74μm的正极活性材料层221，在铝箔的另一个表面上重复以上涂覆步骤，得到双面涂覆的正极极片22。然后，通过激光模切成型切除多余的空箔区，得到正极极耳。
(2)负极极片21的制备：将负极活性材料人造石墨、导电炭黑(Super P)、丁苯橡胶(SBR)按照重量比96:1.5:2.5进行混合，加入去离子水作为溶剂，调配成重量百分比为70wt％的浆料，并搅拌均匀。将浆料均匀涂覆在8μm的负极集流体210即铜箔的一个表面上，在铜箔的边缘预留空箔区，然后110℃条件下烘干，得到涂层厚度为65μm的负极活性材料层211，在铜箔的另一个表面上重复以上涂覆步骤，得到双面涂覆的负极极片21。然后，即两层负极活性材料层211的总厚度T为130μm。然后，将负极活性材料层211冷压。再采用激光打孔的方式在每一负极活性材料层211上设置多个凹部2110，凹部2110的宽度为70μm，深度为10μm，相邻两个凹部2110的中心间距为1mm。然后，通过激光模切成型切除多余的空箔区，得到负极极耳。
(3)电解液的制备：在干燥氩气气氛中，首先将有机溶剂碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)以质量比EC:EMC:DEC＝30:50:20混合，然后向有机溶剂 中加入锂盐六氟磷酸锂(LiPF6)溶解并混合均匀，得到锂盐的浓度为1.15mol/L的电解液。
(4)隔离膜23的制备：选用厚度为9μm的聚乙烯(PE)膜。
(5)二次电池100的组装：将正极极片22、隔离膜23和负极极片21依次层叠得到叠片结构的电极组件20，将冲坑成型的铝塑膜(厚度为150μm)置于组装夹具内，坑面朝上，并将电极组件20置于坑内。向铝塑膜的坑内注入电解液，并将正极极耳和负极极耳引出铝塑膜外。然后进行化成，封装，得到图5所示出的二次电池100。
对比例4-6
与实施例14不同之处在于D与T的关系。
对各对比例和实施例的二次电池各取10个进行能量密度、动力学性能和循环性能测试，测试结果记录于表1中。
二次电池的能量密度测试步骤如下：1)将二次电池在25℃的测试温度下静置30分钟，以0.7C恒流充电至4.50V，再以4.50V恒压充电至0.05C，静置5min，以0.2C恒流放电至3.0V，静置5min，得出二次电池的放电容量C；2)上述二次电池以0.7C恒流充电至3.95V后，再以3.95V恒压充电至0.05C，然后用激光测厚仪测试二次电池的长L、宽W、高H，能量密度(ED)＝C/(L×W×H)，单位为Wh/L。对10个样品的能量密度取平均值。
二次电池的动力学性能可用低温放电性能表征，低温放电性能测试步骤如下：1)将二次电池在25℃的测试温度下静置5分钟，以0.2C恒流放电至3.0V，静置5分钟，此放电容量作为首次放电容量；2)以0.2C恒流充电至4.50V，再以4.50V恒压充电至0.02C，静置5min；3)调节炉内温度为-20℃，静置60分钟，以0.2C恒流放电至3.0V，而后静置5分钟，低温放电后二次电池的放电容量与首次容量的比值乘以100％即为低温容量保持率。对10个样品的低温容量保持率取平均值。
二次电池的循环容量保持率测试步骤如下：1)将二次电池在25℃的测试温度下静置30分钟，以1C恒定电流将二次电池充电至4.43V，然后恒压充电至0.05C，接着静置5min，再采用0.7C放电至3.0V，此放电容量为首次放电容量，计为100％；2)按以上充放电步骤依次循环1000圈，循环后二次电池的放电容量与首次容量的比值乘以100％即为容量保持率。对10个样品的容量保持率取平均值。
二次电池的析锂测试步骤如下：1)将循环测试后的二次电池以1C恒定电流将二次电池充电至4.43V，然后恒压充电至0.05C；2)将以上二次电池拆解，检查负极极片凹部区域是否产生析锂，若析锂面积大于或等于2mm2，则判定为析锂，测试不通过。10个样品中通过析锂测试的样品所占的比例即为析锂测试通过率。结果记录于表1中。
表1
从表1数据可知，针对卷绕结构的电极组件，相较于对比例1-2中设置凹部的厚极片，实施例1-11在设置凹部的同时设置压实密度D和总厚度T满足3T+1≤D≤8T+1，使得二次电池可维持较高的能量密度的同时，改善了离子传输路径使得二次电池的低温容量保持率提高，而且也改善了电解液的浸润程度，从而提高了析锂测试通过率以及二次电池的循环容量保持率，因此实施例1-11的二次电池可兼顾较高的能量密度以及较优的低温容量保持率和循环容量保持率。对比例3的压实密度D和总厚度T虽满足上述关系但未设置凹部，因此离子传输路径和电解液浸润性差，二次电池的低温容量保持率和循环容量保持率较低。进一步地，实施例2-8满足3.5T+1≤D≤6.5T+1，可进一步提高二次电池的能量密度、低温容量保持率和循环容量保持率。更进一步地，实施例4-6满足4.5T+1≤D≤5.5T+1，可进一步提高二次电池的能量密度、低温容量保持率和循环容量保持率。
同理，针对叠片结构的电极组件，相较于对比例4-5中设置凹部的厚极片，实施例14通过设置凹部的同时设置压实密度D和总厚度T满足特定条件，二次电池可兼顾较高的能量密度以及较优的低温容量保持率和循环容量保持率。对比例6的压实密度D和总厚度T虽满足上述关系但未设置凹部，因此离子传输路径和电解液浸润性差，二次电池的低温容量保持率和循环容量保持率较低。
而且实施例1-14的压实密度满足1.2g/cm3≤D≤2.2g/cm3时，二次电池可兼顾较高的能量密度以及较优的低温容量保持率和循环容量保持率。
实施例15-18
与实施例1不同之处在于，卷绕结构的电极组件20中，位于平直段20A的第一活性材料区2111的压实密度D1与位于弯曲段20B的第二活性材料区2112的压实密度为D2不同。
实施例19-22
与实施例14不同之处在于，位于中心区域的第三活性材料区2113的压实密度D3与位于边缘区域的第四活性材料区2114的压实密度D4不同。
表2
从表2数据可知，针对卷绕结构的电极组件，相较于实施例1，实施例15-17的第一活性材料区相较于第二活性材料区的压实密度更高，二次电池的析锂通过率、低温容量保持率和循环容量保持率未显著降低，但能量密度的提升较明显。相较于实施例18，实施例15-17通过限制第一活性材料区的压实密度的上限值，减小了其对析锂通过率、低温容量保持率和循环容量保持率的影响。
相较于实施例14，针对叠片结构的电极组件，实施例19-21的第三活性材料区相较于第四活性材料区的压实密度更高，二次电池的析锂通过率、低温容量保持率和循环容量保持率未显著降低，但能量密度的提升较明显。相较于实施例22，实施例19-21通过限制第三活性材料区的压实密度的上限值，减小了其对析锂通过率、低温容量保持率和循环容量保持率的影响。
实施例23-37
与实施例1不同之处在于凹部2110的相关尺寸。
表3
从表3数据可知，相较于实施例26和32，实施例1、23-25、28-31中凹部的尺寸适当增大，可提高电解液在整个负极活性材料层中的浸润程度并降低离子迁移阻抗，因此二次电池的析锂通过率提高，二次电池的循环容量保持率和低温循环保持率也提高。相较于实施例27和33，实施例1、23-25、28-31中限制了凹部尺寸的上限，避免了更多负极活性材料的缺失，且可减小电解液负极活性材料之间的接触面积增大引发副反应的风险，降低阻抗，因此二次电池可维持较高的能量密度，且析锂通过率和循环容量保持率也提高。
相较于实施例36，实施例1、34-35中凹部的分布密度适当增大，避免了更多负极活性材料的缺失，且可减小电解液负极活性材料之间的接触面积增大引发副反应的风险，降低阻抗，因此二次电池可维持较高的能量密度，且析锂通过率和循环容量保持率也提高。相较于实施例37，实施例1、34-35中限制了凹部分布密度的上限，因此可提高电解液在整个负极活性材料层中的浸润程度并降低离子迁移阻抗，因此二次电池的析锂通过率提高，二次电池的循环容量保持率和低温循环保持率也提高。
以上所揭露的仅为本申请较佳实施方式而已，当然不能以此来限定本申请，因此依本申请所作的等同变化，仍属本申请所涵盖的范围。

Claims (12)

  1. 一种二次电池，包括电极组件，所述电极组件包括负极极片，其中，
    所述负极极片包括负极集流体和设于所述负极集流体表面的负极活性材料层，所述负极集流体包括第一区域，所述第一区域的相对两表面均设有所述负极活性材料层，所述第一区域上所述负极活性材料层的总厚度为T，0.07mm≤T≤0.15mm；
    所述负极活性材料层设有多个凹部，所述负极活性材料层的压实密度为D，单位为g/cm3，3T+1≤D≤8T+1。
  2. 如权利要求1所述的二次电池，其中，3.5T+1≤D≤6.5T+1。
  3. 如权利要求2所述的二次电池，其中，4.5T+1≤D≤5.5T+1。
  4. 如权利要求1至3项中任一项所述的二次电池，其中，1.2g/cm3≤D≤2.2g/cm3。
  5. 如权利要求4所述的二次电池，其中，1.3g/cm3≤D≤1.9g/cm3。
  6. 如权利要求1至3项中任一项所述的二次电池，其中，所述电极组件为卷绕结构，所述电极组件包括沿卷绕方向相连接的平直段和弯曲段，所述负极活性材料层包括位于所述平直段的第一活性材料区和位于所述弯曲段的第二活性材料区，所述第一活性材料区的压实密度为D1，所述第二活性材料区的压实密度为D2,1.3g/cm3≤D1≤2.0g/cm3，1.2g/cm3≤D2≤1.5g/cm3。
  7. 如权利要求1至3项中任一项所述的二次电池，其中，所述电极组件为叠片结构，所述负极活性材料层包括第三活性材料区和围绕所述第三活性材料区的外周缘设置的第四活性材料区，所述第三活性材料区的压实密度为D3，所述第四活性材料区的压实密度为D4,1.3g/cm3≤D3≤2.2g/cm3，1.2g/cm3≤D4≤1.7g/cm3。
  8. 如权利要求1至7项中任一项所述的二次电池，其中，所述凹部的宽度为70μm至100μm，深度为5μm至100μm，相邻两个所述凹部的中心间距为1mm至2mm。
  9. 如权利要求1至8项中任一项所述的二次电池，其中，从所述负极极片的厚度方向观察，所述凹部为圆形或方形。
  10. 如权利要求1至9项中任一项所述的二次电池，其中，所述二次电池的CB值为1至1.05。
  11. 如权利要求1至9项中任一项所述的二次电池，其中，所述凹部为移除部分所述负极活性材料层得到。
  12. 一种电子装置，其中，包括电池仓以及设于所述电池仓内的如权利要求1至11中任一项所述的二次电池。
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