WO2022266797A1 - 负极、电化学装置和电子装置 - Google Patents

负极、电化学装置和电子装置 Download PDF

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WO2022266797A1
WO2022266797A1 PCT/CN2021/101234 CN2021101234W WO2022266797A1 WO 2022266797 A1 WO2022266797 A1 WO 2022266797A1 CN 2021101234 W CN2021101234 W CN 2021101234W WO 2022266797 A1 WO2022266797 A1 WO 2022266797A1
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negative electrode
active material
electrode active
lithium
material particles
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PCT/CN2021/101234
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English (en)
French (fr)
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郑子桂
易政
杜鹏
谢远森
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宁德新能源科技有限公司
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Priority to PCT/CN2021/101234 priority Critical patent/WO2022266797A1/zh
Priority to CN202180005069.1A priority patent/CN114303257A/zh
Priority to EP21946299.1A priority patent/EP4358188A1/en
Publication of WO2022266797A1 publication Critical patent/WO2022266797A1/zh
Priority to US18/390,487 priority patent/US20240162440A1/en

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    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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    • Y02E60/10—Energy storage using batteries

Definitions

  • the application relates to the field of electrochemical energy storage, in particular to negative electrodes, electrochemical devices and electronic devices.
  • Some embodiments of the present application provide a negative electrode, including a negative electrode active material layer, the negative electrode active material layer includes negative electrode active material particles, the negative electrode active material particles include a hole portion and a non-hole portion, and the non-hole portion includes heteroatoms, the heteroatoms include at least one of boron, nitrogen, fluorine, phosphorus or sulfur elements.
  • the presence of pores improves the efficiency of lithium ion intercalation and deintercalation.
  • the negative electrode active material particles are doped with boron, nitrogen, fluorine, phosphorus or sulfur elements, these doping elements can interact with Li + bonds to generate additional capacity, thereby increasing the gram capacity of the negative electrode active material, which is beneficial to increasing the energy density of the corresponding electrochemical device.
  • the non-hole portion has an interface, and the interface is located within a region formed from the junction of the non-hole portion and the hole portion to a distance of 0.5 ⁇ m from the junction.
  • the junction position is the arc where the holes and non-holes intersect. On the arc, use the arc as the endpoint to make a line segment with a minimum distance of 0.5 ⁇ m from the arc, and connect all the endpoints at the other end.
  • the formed area is the interface.
  • the test area is 0.2 ⁇ m ⁇ 0.2 ⁇ m area, based on the total content of element atoms of the heteroatoms, C and O, the atomic content of the heteroatoms is: a%, 1 ⁇ a ⁇ 6. Based on the total content of element atoms of the heteroatoms, C and O, the atomic content of the heteroatoms is a%, 3.3 ⁇ a ⁇ 5.7.
  • the heteroatom content in this range at the interface can improve the lithium storage performance of the carbon negative electrode active material.
  • the atomic content of the heteroatoms is b%, b ⁇ 0.1.
  • the area from 2.8 ⁇ m to 3.2 ⁇ m is the line segment with the shortest distance from the arc of 2.8 ⁇ m and 3.2 ⁇ m to the end point on the arc first, and connects the endpoints of all the line segments at the other end of the line segment to form the longest distance is 3.2 ⁇ m, and the closest distance is 2.8 ⁇ m to form the region.
  • the atomic content of this region less than or equal to 0.1%, it is possible to avoid the adverse effect of heteroatoms inside the negative electrode active material particles on the energy density, and maximize the effect of heteroatoms on the energy density of the electrochemical device to avoid reducing the negative electrode active material.
  • the test area is 50 ⁇ m ⁇ 50 ⁇ m, and the area ratio of the hole portion to the non-hole portion is 0.05 to 0.30.
  • the area ratio of the pore portion to the non-pore portion in this range can not only increase the energy density of the electrochemical device, but also help improve the rate performance of the electrochemical device.
  • the diameter of the holes ranges from 0.1 ⁇ m to 3 ⁇ m.
  • SEM scanning electron microscope images
  • statistics are made on the holes with a pore diameter of 0.1 ⁇ m to 3 ⁇ m on each image, and the average value of the pore diameter is calculated, and then the 50 The average value of the images is the average aperture.
  • the average pore size is 0.6 ⁇ m to 1.5 ⁇ m. In some embodiments, the average pore size is 0.8 ⁇ m to 1.2 ⁇ m.
  • Appropriate size of the pore size is beneficial to promote the transport of lithium ions, and will not have an excessive adverse effect on the energy density of the electrochemical device.
  • the negative electrode active material particles have a specific surface area of 1 m 2 /g to 10 m 2 /g.
  • the specific surface area of the negative electrode active material particles in this range can improve the overall kinetic performance of the electrochemical device, and at the same time, the problem of excessive consumption of the electrolyte will not be caused due to an excessively large specific surface area.
  • the negative electrode has a porosity of 15% to 40%.
  • the porosity in this range achieves a good balance between the promotion of lithium ion transport and the increase of internal resistance.
  • the ratio of ID/ IG of the negative electrode active material particles ranges from 0.8 to 1.4, wherein ID represents the peak intensity at 1350 cm in the Raman spectrum, and IG Indicates the peak intensity at 1580 cm in the Raman spectrum.
  • ID represents the peak intensity at 1350 cm in the Raman spectrum
  • IG Indicates the peak intensity at 1580 cm in the Raman spectrum.
  • the combination of heteroatoms with the carbon atoms of the microcrystalline negative active material will increase the defects of the microcrystalline negative active material.
  • the higher the content of heteroelement atoms the higher the I D / I G value, indicating the defects in the negative active material particles More, the gram capacity of the negative electrode active material particles can be increased.
  • the ID/ IG value is too large, the negative electrode active material particles have too many defects, which is not conducive to the stability of the structure of the negative electrode active material particles.
  • the Dv90 of the negative electrode active material particles is ⁇ 30 ⁇ m.
  • the above particle size of the negative electrode active material particles can improve the kinetic performance of the electrochemical device.
  • the negative active material particles include hard carbon. Compared with graphite, hard carbon has a larger gram capacity and smaller cycle expansion, so that the electrochemical device has excellent rate charge and discharge performance and good charge and discharge cycle performance.
  • the negative active material layer has a compacted density of 0.95 g/cm 3 to 1.40 g/cm 3 . The compacted density in this range achieves a good balance of energy density improvement and impedance increase.
  • the electrochemical device includes the above-mentioned negative electrode and an electrolyte, and the electrolyte includes at least one of fluoroether, fluoroethylene carbonate or ether nitrile.
  • the negative electrode further includes a negative electrode current collector, and the binding force between the negative electrode current collector and the negative electrode active material layer is 3 N/m to 50 N/m. In this way, film stripping and burrs are not likely to occur during slitting, and the internal resistance of the electrochemical device will not be high due to the need for an excessively high content of binder.
  • the electrolyte solution further includes a lithium salt
  • the lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF 6 )
  • the concentration of the lithium salt is 1 mol/L to 2 mol/L
  • the mass ratio of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate is 0.06 to 5.
  • An embodiment of the present application also provides an electronic device, including the above-mentioned electrochemical device.
  • the embodiment of the present application adopts negative electrode active material particles including holes and regions doped with elements such as boron and nitrogen.
  • elements such as boron and nitrogen.
  • the existence of holes improves the efficiency of lithium ion intercalation and deintercalation;
  • the doping of elements such as nitrogen and nitrogen increases the gram capacity of the negative electrode active material, which is conducive to improving the energy density of the corresponding electrochemical device.
  • FIG. 1 shows an example scanning electron microscope image of a negative active material layer.
  • the negative active material layer includes negative active material particles.
  • the negative active material particle includes a pore portion and a non-porous portion having heteroatoms.
  • the pore portion of the negative electrode active material particle refers to a hole with a pore diameter ranging from 0.1 ⁇ m to 3 ⁇ m. In the case that the pore portion is non-circular, the pore diameter refers to any two points in the hole in the scanning electron microscope image the farthest distance. As shown in FIG. 1 , an example scanning electron microscope image of a negative electrode active material layer is shown.
  • the negative electrode active material layer includes a negative electrode active material particle 100.
  • the negative electrode active material particle 100 includes a hole portion 101 and a non-hole portion 102, and the diameter (aperture) of the hole portion is the furthest distance between two points inside the hole (including edge positions). In some embodiments , with a pore size of 0.1 ⁇ m to 3 ⁇ m.
  • Some embodiments of the present application provide a negative electrode, by randomly taking 50 scanning electron microscope images (60 ⁇ m ⁇ 40 ⁇ m), counting the pores with a diameter of 0.1 ⁇ m to 3 ⁇ m on each image, calculating the average value of the aperture, and then calculating The average of 50 images is the average aperture.
  • the average pore size is 0.6 ⁇ m to 1.5 ⁇ m.
  • the heteroatoms include at least one of boron, nitrogen, fluorine, phosphorus, or sulfur and are located at the interface, which is the boundary between the non-hole portion 101 and the non-hole portion 102 in the non-hole portion 102 The area within 0.5 ⁇ m of the position. That is, the interface belongs to the portion of the non-hole portion 102 , which is a region extending from the boundary position between the hole portion 101 and the non-hole portion 102 to the non-hole portion 102 by at most 0.5 ⁇ m. In some embodiments, the interface may extend less than 0.5 ⁇ m (eg, 0.3 ⁇ m) to the other hole when the two holes are relatively close together, when the interface at this location only extends 0.3 ⁇ m from the interface.
  • 0.5 ⁇ m eg, 0.3 ⁇ m
  • the negative electrode active material particles 100 including holes and regions doped with elements such as boron and nitrogen
  • the existence of the holes improves the efficiency of lithium ion intercalation and deintercalation; on the other hand, in the negative electrode active material particles
  • these doping elements can bond with Li + to generate additional capacity, thereby increasing the gram capacity of the negative electrode active material, which is conducive to improving the corresponding electrochemical device. energy density.
  • the porous hard carbon negative electrode active material doped with heteroatoms can well regulate the electronic structure of carbon and improve the conductivity; heteroatoms enter the carbon In the microchip layer, not only the interlayer spacing of carbon is increased, but also more defects and active sites are provided, which can increase the adsorption capacity of lithium ions, thereby improving the gram capacity and rate performance of the electrochemical device; in addition, The large specific surface area and rich pore structure of porous hard carbon negative electrode active materials can not only reduce the resistance of lithium ion transport, but also provide a fast channel for lithium ion and electron transport, reduce the effect of potential hysteresis, and obtain excellent rate performance.
  • the negative electrode active material can be prepared by a resin co-melt blending method, specifically, the second resin containing heteroatom groups with a low carbon residue rate is uniformly blended into the first resin with a high carbon residue rate , where the first resin acts as the matrix resin.
  • the second resin may be a borazine ring-containing polymer, polybenzimidazole, boron phenolic resin, urea-formaldehyde resin, polyaniline, polyimide, melamine resin, polytetrafluoroethylene, polyvinylidene Vinyl fluoride, polychlorotrifluoroethylene, polyperfluoroethylene propylene, phosphoric acid doped epoxy resin, phosphorus-based polyacrylic acid, phosphorus-based polymaleic acid, bisphenol A polysulfone, polyethersulfone, polyarylphenol, poly Polymers such as phenylene sulfide can also be blends of urea-formaldehyde resin and polybenzoborimidazole, blends of boron phenolic resin and polyimide, phosphoric acid doped urea-formaldehyde resin, polyaniline and phosphorus-based polymaleic acid At least one of blends of two or more polymers such as blends
  • the second resin and the first resin are melt blended at 150°C to 270°C at high temperature, then pyrolyzed at 710°C to 1300°C for 2 hours, crushed and screened.
  • the second resin with low carbon residue rate will leave holes in the first resin with high carbon residue rate after pyrolysis, and the benzene series formed after pyrolysis will flow outward in the second resin with low carbon residue rate
  • micropores will be formed in the first resin with high carbon residue rate or continue to dehydrogenate to participate in carbon formation, and heteroelements will be adsorbed on the inner wall of the hole and enter the carbon crystallite interior of the first resin.
  • the distribution of each element of the negative electrode active material layer is analyzed by a scanning electron microscope-energy dispersive analyzer.
  • the hole portion is in a region of 2.8 ⁇ m to 3.2 ⁇ m away from the boundary position between the hole portion and the non-hole portion in the non-hole portion (the direction is perpendicular to the boundary position between the hole portion and the non-hole portion line, the length of the vertical line is 2.8 ⁇ m to 3.2 ⁇ m, connect the endpoints of all the line segments to form the boundary and the area surrounded by the junction between the hole part and the non-hole part), based on the test area of 0.2 ⁇ m ⁇ 0.2
  • the content of heteroatoms in ⁇ m, the atomic content of C and O, the atomic content of heteroatoms is b%, b ⁇ 0.1.
  • changing the type and content of heteroatoms carried by the second resin melt-blended with the first resin can change the doping element of the obtained negative electrode active material particles, which can be a single element (for example, boron, nitrogen , fluorine, phosphorus, sulfur) doping, or double element (for example, boron nitrogen, boron fluorine, boron phosphorus, boron sulfur, nitrogen fluorine, nitrogen phosphorus, nitrogen sulfur, etc.) doping, or three elements (such as , nitrogen phosphorus sulfur, nitrogen fluorine phosphorus, nitrogen fluorine sulfur, etc.) doping.
  • a single element for example, boron, nitrogen , fluorine, phosphorus, sulfur
  • double element for example, boron nitrogen, boron fluorine, boron phosphorus, boron sulfur, nitrogen fluorine, nitrogen phosphorus, nitrogen sulfur, etc.
  • three elements such as , nitrogen phosphorus sulfur, nitrogen fluorine phosphorus, nitrogen fluorine sulfur, etc.
  • the heteroatoms break covalent bonds with the second resin into the first resin during the pyrolysis process, are enriched at the pyrolysis site, and exhibit a gradient decrease in content with increasing distance into the first resin.
  • the introduction of nitrogen doping into carbon materials has the following two advantages: on the one hand, the good bonding between carbon and nitrogen greatly changes the electronic properties of carbon materials and increases more More active sites improve the electrochemical performance of the negative electrode active material; on the other hand, the doping of nitrogen causes a large number of lattice defects in the carbon negative electrode active material, and these defects can be used as lithium storage sites to further improve the carbon density. Lithium storage performance of negative electrode active materials.
  • the content of the doping element at the interface is too little, then its effect of improving the gram capacity of the negative electrode active material is relatively limited; if the content of the doping element at the interface is too large, then it improves the negative electrode active material. The effect of the gram capacity will no longer increase further, and may reduce the energy density of the negative electrode active material layer as a whole.
  • the junction position is at the position of 2.8 ⁇ m to 3.2 ⁇ m in the non-hole portion (this position does not include when passing through a hole portion, and another hole portion passing outside the 2.8 ⁇ m to 3.2 ⁇ m position, only the non-hole portion ) doping elements can play a relatively limited role in improving the gram capacity of the negative electrode active material, therefore, the content of the doping elements at this position should not be too large, so as to avoid reducing the overall energy density of the negative electrode active material layer.
  • the scanning electron microscope analysis is performed on the cross section of the negative electrode active material layer, the test area is 50 ⁇ m ⁇ 50 ⁇ m, the area ratio of the hole part to the non-hole part is 0.05 to 0.30, and the range of the farthest distance between two points in the hole part 0.1 ⁇ m to 3 ⁇ m.
  • the existence state of the second resin in the first resin after melt blending is different, which means that after pyrolysis, it is formed in the first resin with a high carbon residue rate.
  • the pore structure varies in pore size and number of pores. In some embodiments, the large pores (pore diameter > 500nm) in the negative electrode active material particles are difficult to store lithium ions.
  • the pore and non-pore The area ratio of the portion is 0.05 to 0.15, and the diameter of the hole portion is in the range of 0.1 ⁇ m to 0.5 ⁇ m.
  • the pore size is too small or the number of pores is too small, it is not conducive to the lithium ion transport in the negative electrode active material particles, which is not conducive to the improvement of the rate performance of the electrochemical device.
  • the negative electrode active material particles have a specific surface area of 1 m 2 /g to 10 m 2 /g.
  • the specific surface area of the negative electrode active material particles including the pores will increase, and the increased surface area will increase the contact points between the negative electrode active material and the electrolyte, and improve the overall kinetic performance of the electrochemical device.
  • the surface area of the solid electrolyte boundary (SEI) film formed during the first charging process is more, which consumes more lithium ions, resulting in a decrease in the first charge and discharge efficiency of the electrochemical device.
  • the negative electrode active material particles have a specific surface area of 1 m 2 /g to 5 m 2 /g.
  • the negative electrode has a porosity of 15% to 40%.
  • the thickness of the negative electrode active material layer can be continuously changed, that is, the porosity of the active material layer can be adjusted. It can contribute to the electrochemical capacity, which is directly reflected in the improvement of the energy density of the electrochemical device.
  • the porosity is preferably 15% to 30%.
  • the ratio of ID/ IG of the negative electrode active material particles ranges from 0.8 to 1.4, wherein ID represents the peak intensity at 1350cm ⁇ 1 in the Raman spectrum, I G represents the peak intensity at 1580 cm ⁇ 1 in the Raman spectrum.
  • ID represents the peak intensity at 1350cm ⁇ 1 in the Raman spectrum
  • I G represents the peak intensity at 1580 cm ⁇ 1 in the Raman spectrum.
  • the Dv90 of the negative electrode active material particles is ⁇ 30 ⁇ m.
  • the negative electrode active material particles are pulverized and classified sieving is used to control the particle size distribution.
  • Dv10 refers to the particle size corresponding to when the cumulative volume distribution reaches 10% starting from the small side of the particle size distribution of the particles.
  • Dv50 and Dv90 refer to the corresponding particle diameters when the cumulative volume distribution reaches 50% and 90%, respectively, starting from the small side of the particle size distribution of the particles. If the particle size of the negative electrode active material is too large, the intercalation distance of lithium ions will increase, and the contacts between the particles will decrease, so that the kinetics of the electrochemical device will decrease and the impedance will increase.
  • the negative active material particles include hard carbon.
  • hard carbon Compared with graphite, hard carbon has a higher gram capacity, generally 500mAh/g to 710mAh/g, even as high as 1000mAh/g.
  • the microcrystalline carbon layers in the hard carbon particles are roughly arranged in parallel, similar to graphite, but the crystallite size is small and the arrangement is anisotropic.
  • the 002 crystal plane spacing is relatively large, about 0.35nm to 0.40nm, which is larger than the graphite layer spacing, and there is It is conducive to the intercalation of lithium without causing significant structural expansion, and has excellent rate charge-discharge performance and good charge-discharge cycle performance.
  • the interplanar spacing of 002 can be analyzed by BRUKER company model D8ADVANCE XRD equipment.
  • the negative active material layer has a compacted density of 0.95 g/cm 3 to 1.40 g/cm 3 . If the compaction density of the negative electrode active material layer is too small, it is not conducive to the improvement of the overall energy density of the electrochemical device; if the compaction density of the negative electrode active material layer is too large, it will increase the impedance of lithium ion transmission, which is not conducive to the improvement of the energy density of the electrochemical device. Improvement of the rate performance of chemical devices.
  • an electrochemical device includes the above-mentioned negative electrode and 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 negative electrode further includes a negative electrode current collector.
  • the negative active material layer may be located on one side or both sides of the negative current collector.
  • the binding force between the negative electrode current collector and the negative electrode active material layer is 3 N/m to 50 N/m. If the bonding force between the negative electrode active material layer and the negative electrode current collector is too small, the rolling or slitting process will easily cause film release and burrs, resulting in potential safety hazards for electrochemical devices. If the binding force between the negative electrode active material layer and the negative electrode current collector is too large, the mass content of the binder of the negative electrode active material layer is generally required to be high, that is, the binder is excessive, which will lead to internal resistance of the electrochemical device.
  • the binding force between the negative electrode current collector and the negative electrode active material layer is 10 N/m to 20 N/m. At this time, it can ensure that there are fewer potential safety hazards, and it is not necessary to use too much adhesive.
  • a conductive agent and a binder may also be included in the negative electrode active material layer.
  • the conductive agent in the negative electrode active material layer may include at least one of conductive carbon black, Ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers.
  • the binder in the negative active material layer may include carboxymethylcellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysilicon At least one of oxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin or polyfluorene.
  • the mass ratio of the negative active material, the conductive agent and the binder in the negative active material layer may be (78 to 98.5):(0.1 to 10):(0.1 to 10). It should be understood that the above description is only an example, and any other suitable materials and mass ratios may be used.
  • the negative electrode current collector may use at least one of copper foil, nickel foil, or carbon-based current collector.
  • an electrochemical device may include an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.
  • the negative electrode is any one of the above-mentioned negative electrodes.
  • the electrochemical device includes a lithium-ion battery, although the present application is not limited thereto.
  • 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.
  • the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material.
  • the positive electrode active material includes lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadyl phosphate, sodium vanadyl phosphate, lithium vanadate, manganese Lithium oxide, lithium nickelate, lithium nickel cobalt manganese oxide, lithium-rich manganese-based materials or lithium nickel cobalt aluminate.
  • the positive active material layer may further include a conductive agent.
  • the conductive agent in the positive active material layer may include at least one of conductive carbon black, Ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers.
  • the positive electrode active material layer can also include a binder, and the binder in the positive electrode active material layer can include carboxymethylcellulose (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 carboxymethylcellulose
  • the mass ratio of the positive active material, the conductive agent and the binder in the positive active material layer may be (80 to 99):(0.1 to 10):(0.1 to 10).
  • the positive active material layer may have a thickness of 10 ⁇ m to 500 ⁇ m. It should be understood that the above description is only an example, and any other suitable material, thickness and mass ratio may be used for the positive electrode active material layer.
  • Al foil may be used as the positive current collector, and of course, other current collectors commonly used in the art may also be used.
  • the positive electrode collector may have a thickness of 1 ⁇ m to 50 ⁇ m.
  • the positive active material layer may be coated only on a partial area of the current collector of the positive electrode.
  • the isolation film 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 is in the range of about 5 ⁇ m to 50 ⁇ m.
  • the surface of the isolation membrane 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), oxide Zinc (ZnO), calcium oxide (CaO), zirconia (ZrO 2 ), yttrium oxide (Y 2 O 3 ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or sulfuric acid at least one of barium.
  • alumina Al 2 O 3
  • Silicon oxide SiO 2
  • magnesium oxide MgO
  • titanium oxide TiO 2
  • hafnium oxide HfO 2
  • 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, polymethyl methacrylate, 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 electrode assembly of the electrochemical device is a wound electrode assembly, a stacked electrode assembly or a folded electrode assembly.
  • the positive electrode and/or negative electrode of the electrochemical device may be a wound or stacked multi-layer structure, or a single-layer structure in which a single-layer positive electrode, a separator, and a single-layer negative electrode are stacked.
  • the positive electrode, separator, and negative electrode are sequentially wound or stacked into an electrode part, and then packed into an aluminum-plastic film for packaging, injected with an electrolyte, formed, Encapsulation, that is, made of lithium-ion batteries. Then, performance tests were performed on the prepared lithium-ion batteries.
  • 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.
  • Preparation of the positive electrode mix the positive active material lithium cobaltate, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 97:1.4:1.6, and add N-methylpyrrolidone (NMP) as a solvent , stir well.
  • the slurry (solid content is 72wt%) is uniformly coated on the aluminum foil of the positive electrode current collector with a coating thickness of 80 ⁇ m, dried at 85°C, and then cold-pressed, cut into pieces, and slit, and vacuum-coated at 85°C Dry under the same conditions for 4 hours to obtain a positive electrode.
  • negative electrode artificial hard carbon, binder styrene-butadiene rubber and sodium carboxymethylcellulose (CMC) are dissolved in deionized water in a ratio of 97:1.5:1.5 by weight to form negative electrode slurry (solid content is 40wt %). Copper foil with a thickness of 10 ⁇ m was used as the negative electrode current collector, and the negative electrode slurry was coated on the negative electrode current collector with a coating thickness of 50 ⁇ m, dried at 85 ° C, and then cold-pressed, cut into pieces, and cut at 120 °C under vacuum conditions for 12 hours to obtain a negative electrode.
  • CMC carboxymethylcellulose
  • artificial hard carbon is prepared by the following steps: melt blending boron-containing polyethylene and polyphenylene ether with a mass ratio of 1.5:8.5 at 150°C to 300°C, pyrolyze at 710°C for 2 hours, and then Carry out crushing and sieving. After sieving, control Dv90 to be less than or equal to 30 ⁇ m, and Dn10 to range from 0.1 ⁇ m to 0.9 ⁇ m, so that the ratio of the area of the pores to the non-pores is 0.05 to 0.30.
  • the isolation membrane is polyethylene (PE) with a thickness of 7 ⁇ m.
  • EC ethylene carbonate
  • PC propylene carbonate
  • DEC diethyl carbonate
  • Preparation of lithium-ion battery stack the positive electrode, separator, and negative electrode in order, so that the separator is in the middle of the positive electrode and the negative electrode to play the role of isolation, and wind up to obtain the electrode assembly.
  • the electrode assembly is placed in the outer packaging aluminum-plastic film, after dehydration at 80°C, the above electrolyte is injected and packaged, and the lithium-ion battery is obtained through chemical formation, degassing, trimming and other processes.
  • the parameters of the artificial hard carbon preparation process are changed on the basis of the steps in Example 1, and the specific changed parameters are as follows.
  • Examples 2 to 4 are boron element doping (that is, the mass ratio of the first resin polyphenylene ether to the second resin boron-containing polyethylene is 0.85:0.15, 0.85:0.15 and 0.70:0.30), and the pyrolysis temperature 910°C, 1110°C, and 910°C, respectively;
  • Examples 5 to 8 are nitrogen doped (that is, the mass ratios of the first resin polyphenylene ether to the second resin polyaniline are 0.85:0.15, 0.85:0.15, respectively , 0.85:0.15 and 0.70:0.30), its melting temperature is close to that of Examples 1 to 4, and its pyrolysis temperature is shown in Table 4;
  • Examples 9 to 12 are doped with fluorine (that is, the first resin poly The mass ratio of phenylene ether to the second resin polytetrafluoroethylene is respectively 0.85: 0.15, 0.85: 0.15, 0.85: 0.15 and 0.70: 0.30), its melting temperature is close to that of Example 1 to Example 4, and the pyr
  • Scanning Electron Microscope obtains the morphology and structure of the sample through the interaction between the electron beam and the sample, and uses the secondary electron signal imaging.
  • the scanning electron microscope used in this application is the JSM-6360LV type of JEOL company and its supporting X-ray energy spectrometer (scanning electron microscope-energy spectrometer) to analyze the morphology structure and element distribution of the sample.
  • the particle size test method refers to GB/T 19077-2016.
  • the specific process is to weigh 1g of the sample, mix it with 20mL of deionized water and a small amount of dispersant evenly, place it in an ultrasonic device for 5 minutes, and then pour the solution into the sampling system Hydro 2000SM for testing.
  • the testing equipment used is the Mastersizer produced by Malvern. 3000.
  • Particle size measurement is accomplished by measuring the intensity of scattered light as a laser beam passes through a dispersed particle sample during testing. The data is then used analytically to calculate the particle size distribution forming the scatter spectrum.
  • the refractive index of the particles used in the test is 1.8, and one sample is tested three times, and the average value of the particle size of the three tests is finally taken to measure Dv10, Dv50 and Dv90.
  • the surface defect of the sample is tested by laser micro confocal Raman spectrometer, and the ratio of the peak intensity I D at 1350 cm -1 to the peak intensity I G at 1580 cm -1 of the sample is used to characterize the surface defect of the sample . surface imperfections. Multiple potentials are tested for each sample, and the uniformity of surface defectivity in different regions is characterized by its standard deviation.
  • the average value and standard deviation of the I D / I G of the negative electrode active material are obtained by the following method: take the unscreened negative electrode active material, test 100 points, obtain the corresponding I D / I G value, calculate the value of these 100 values Mean and standard deviation values.
  • the specific surface area of the negative electrode active material was measured by nitrogen adsorption/desorption method: the negative electrode active material sample was dried in a vacuum oven, then loaded into a sample tube and measured in the analyzer.
  • the brand of the instrument used for testing the adhesion between the negative electrode active material layer and the negative electrode current collector is Instron, the model is 33652, take the negative electrode (width 30mm ⁇ length (100mm to 160mm)), and use double-sided adhesive tape (model: 3M9448A, width 20mm) ⁇ Length (90mm to 150mm)) is fixed on the steel plate, fix the paper tape with the same width as the negative electrode and the negative electrode side with adhesive tape, adjust the limit block of the tension machine to a suitable position, fold the paper tape upwards and slide 40mm , the slip rate is 50mm/min, and the adhesion force between the negative electrode active material layer and the negative electrode current collector is tested under 180° (that is, stretched in the opposite direction).
  • T0 (T1-T2)/2
  • the compacted density of the negative electrode active material layer W0/(T0 ⁇ S).
  • the negative electrode active material layer samples were prepared as complete discs. Thirty samples were tested for each example or comparative example, each sample having a volume of about 0.35 cm 3 . According to the "GB/T24586-2009 Determination of Apparent Density, True Density and Porosity of Iron Ore" standard, the negative electrode porosity was tested.
  • the negative electrode active material was mixed, coated, and dried to make a negative electrode, and a lithium sheet was used as the positive electrode, which was assembled into a button battery for testing.
  • the button cell was discharged at 0.05C to 5.0mV, at 50 ⁇ A to 5.0mV, at 10 ⁇ A to 5.0mV, and at 0.1C to 2.0V, and the capacity of the button cell at this time was recorded as gram capacity.
  • 0.05C refers to the current value at 0.05 times the design gram capacity
  • 0.1C refers to the current value at 0.1 times the design gram capacity.
  • the first-time efficiency CE of the lithium-ion battery is calculated by the following formula: first-time discharge capacity/first-time charge capacity ⁇ 100%.
  • Lithium-ion batteries prepared by adopting all the comparative examples and the examples were taken, and the average value was taken. Lithium-ion batteries were charged and discharged repeatedly through the following steps, and the discharge capacity retention and thickness expansion of the lithium-ion batteries were calculated.
  • Cycle capacity retention (discharge capacity of the 400th cycle/discharge capacity of the first cycle) ⁇ 100%;
  • Cycle thickness expansion (thickness of fully charged lithium-ion battery at the 400th cycle/thickness of fully charged lithium-ion battery at the first cycle) ⁇ 100%
  • Judgment of the degree of lithium precipitation is based on the state of contamination of the separator in contact with the negative electrode after full charging and dismantling.
  • the separator in contact with the negative electrode is white as a whole and the gray area is less than 2%, it is judged as no lithium precipitation ;
  • the gray area is between 2% and 20%, it is judged as slight lithium precipitation;
  • the separator in contact with the negative electrode is white , but part of the gray can still be clearly observed, and the gray area is 20% to 60%, it is judged as lithium precipitation; when most of the separator in contact with the negative electrode is gray, and the gray area > 60%, it is judged as serious lithium precipitation lithium.
  • Tables 1 to 4 show the respective parameters and evaluation results of the corresponding Examples 1 to 28 and Comparative Examples 1 to 6. Wherein, boron, nitrogen, fluorine, phosphorus or sulfur elements are collectively referred to as heteroatoms.
  • Example 1 By comparing Example 1, Example 5, Example 9, Example 13, Example 17, Example 21, Example 25 and the comparative example, it can be known that by selecting the second resin with different heteroelements, different heteroelements can be obtained.
  • Element-doped hard carbon active material comparative example 1 to example 3, as the pyrolysis temperature increases from 710 ° C to 1110 ° C, the hetero The atomic content decreases significantly with the increase of the pyrolysis temperature; comparing Example 2 and Example 4, the second resin with the same heteroelement and heat treatment process are selected, and different heteroatoms can be obtained easily by changing the amount of the second resin added.
  • Example 9 Example 10, and Example 11 doped with fluorine, and Comparative Example 1, Comparative Example 2, and Comparative Example 3 without element doping exhibited similar laws as those described above.
  • Example 6 and Example 8 and Comparative Example 2 and Comparative Example 4 it can be seen that by changing the amount of the second resin added, the area ratio of the pores and non-pores of the obtained hard carbon active material is also correspondingly increased.
  • the rich pore structure of the hard carbon negative electrode active material makes the corresponding negative electrode active material layer have a high porosity, and the high porosity and d002 interplanar spacing much higher than that of the graphite negative electrode active material make the hard carbon negative electrode active material have excellent fast Charging performance, under the same charging and discharging conditions, the lithium analysis of all examples is better than the comparative example 6 in which the negative electrode active material is graphite.
  • the pore structure helps to increase the contact between the active material particles and the electrolyte and increase the lithium ion deintercalation rate, but the larger specific surface area and porosity will lead to the formation of more SEI films during the first charging process, resulting in irreversible capacity loss.
  • Example 14 and Example 16 doped with phosphorus, and Comparative Example 2 and Comparative Example 4 without element doping it can be seen that the negative electrode active material particles have a close particle size, and the corresponding negative electrode active material layer and the current collector.
  • the bonding force is close; comparing the compacted densities of the negative electrode active material layers, the compacted densities of the negative electrode active material layers of Example 16 and Comparative Example 4 are all low, which is due to the increase in the content of the second resin added in the matrix resin.
  • the pore content of the hard carbon negative electrode active material increases, so the compaction density of the negative electrode active material layer decreases.
  • the comparison between Example 14 and Example 16 shows that a higher compaction density can obtain a higher energy density increase.
  • the defects can increase the lithium storage sites of the active materials and increase the lithium ion deintercalation rate, but the defects also lead to a large irreversible capacity of the hard carbon active materials. Comparing the examples and comparative examples, it can be known that the first charge and discharge efficiency of the lithium ion battery containing the hard carbon negative active material in all embodiments is lower than that of the comparative example 6 containing the graphite negative active material, wherein the fluorine element doping example 11
  • the first charge-discharge efficiency of the hard carbon negative active material lithium-ion battery is relatively high as 76.7%; compared with comparative example 1 to comparative example 5, the first charge-discharge efficiency of the embodiment doped with heteroelement is relatively high, this This is due to the fact that the heteroelement-doped active material has more lithium storage sites.
  • the lithium-ion batteries containing hard carbon negative electrode active materials can obtain higher energy density. Comparing Examples 1 to 28 with Comparative Examples 1 to 5, containing The energy densities obtained in the examples doped with elements are all higher than those in the comparative examples, and the example 5 doped with nitrogen has the highest energy density improvement. Moreover, the cycle performance and expansion performance of the examples are also better than those of the comparative examples without heteroelement doping, and the comprehensive electrochemical performance is better.
  • the low expansion characteristics of the hard carbon negative electrode active material in the process of charging and discharging make it possible for the assembled lithium-ion battery to maintain the thickness change of the lithium-ion battery at a level below about 3% after 400 cycles, and the thickness change level of the lithium-ion battery is far Lower than Comparative Example 6 containing graphite negative active material, while the capacity retention rate of the lithium ion battery assembled in all embodiments after 400 cycles is maintained at a comparable level with Comparative Example 6 containing graphite negative active material.
  • the molar mass of LiFSI is 187.07 g/mol, and the molar mass of LiPF 6 is 151.91 g/mol.
  • Example 5 the only difference between Examples 26 to 28 and Example 12 is that the lithium salt bis(fluorosulfonyl)imide lithium (LiFSI) was added, and its cycle was improved by regulating the mass ratio of LiFSI to LiPF 6 This is mainly because the negative electrode active material doped with heteroatoms can interact with the lithium salt in the electrolyte to improve the interface between the negative electrode and the electrolyte.
  • LiFSI lithium salt bis(fluorosulfonyl)imide lithium

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Abstract

本申请提供了负极、电化学装置和电子装置。负极包括负极活性材料层，负极活性材料层包括负极活性材料颗粒，负极活性材料颗粒包括孔部以及具有杂原子的非孔部，所述杂原子包括硼、氮、氟、磷或硫元素中的至少一种并且位于界面处，界面为非孔部中距离孔部和非孔部之间的交界位置0.5μm以内的区域。本申请的实施例通过采用包括孔部和具有硼、氮等元素掺杂的非孔部的负极活性材料颗粒，一方面，孔部的存在改善了锂离子嵌入和脱嵌的效率，另一方面，硼、氮等元素的掺杂提升了负极活性材料的克容量，有利于提升相应的电化学装置的能量密度。

Description

负极、电化学装置和电子装置 技术领域
本申请涉及电化学储能领域，尤其涉及负极、电化学装置和电子装置。
背景技术
随着电化学装置(例如，锂离子电池)的发展和进步，对其循环性能和能量密度提出了越来越高的要求。目前，为了提升电化学装置的循环性能和能量密度，负极活性材料的改进是重要的方面。
发明内容
本申请的一些实施例提供了一种负极，包括负极活性材料层，所述负极活性材料层包括负极活性材料颗粒，所述负极活性材料颗粒包括孔部和非孔部，所述非孔部包括杂原子，所述杂原子包括硼、氮、氟、磷或硫元素中的至少一种。一方面，孔部的存在改善了锂离子嵌入和脱嵌的效率，另一方面，在负极活性材料颗粒中掺杂有硼、氮、氟、磷或硫元素时，这些掺杂元素可以与Li +发生键合，产生额外的容量，从而提升负极活性材料的克容量，有利于提升相应的电化学装置的能量密度。
在一些实施例中，所述非孔部具有界面，所述界面位于所述非孔部和孔部交界位置至距离所述交界位置0.5μm形成的区域内。交界位置为孔部和非孔部相交的弧线，在弧线上以弧线为端点作距离弧线距离最短为0.5μm的线段，将另一端所有的端点连接，所形成的区域为界面。通过扫描电子显微镜-能谱仪分析，在所述界面位置，测试面积为0.2μm×0.2μm区域内，基于所述杂原子、C和O的元素原子总含量，所述杂原子的原子含量为a％，1≤a≤6。基于所述杂原子、C和O的元素原子总含量，所述杂原子的原子含量为a％，3.3≤a≤5.7。界面处的该范围内的杂原子含量，可以提高碳负极活性材料的储锂性能。在一些实施例中，通过扫描电子显微镜-能谱仪分析，在所述非孔部内且距离所述交界位置2.8μm至3.2μm的区域，在测试面积为0.2μm×0.2μm区域内，基于所述杂原子、C和O的元素原子总含量，所述杂原子的原子含 量为b％，b≤0.1。具体的，2.8μm至3.2μm的区域为首先在弧线上选端点作距离弧线距离最短为2.8μm和3.2μm的线段，将线段的另一端所有线段的端点连接，所形成的最远距离为3.2μm，最近距离为2.8μm形成的区域。通过使该区域的原子含量小于等于0.1％，可以避免负极活性材料颗粒内部的杂原子对能量密度的不利影响，最大化杂原子对电化学装置的能量密度的提升作用，以避免降低负极活性材料层整体的能量密度，因此本申请中，b≤0.1。在一些实施例中，通过扫描电子显微镜-能谱仪分析，测试面积为50μm×50μm，孔部与非孔部的面积比值为0.05至0.30。孔部与非孔部的处于该范围的面积比值不仅可以提升电化学装置的能量密度，而且还有利于改善电化学装置的倍率性能。
在一些实施例中，所述孔部的孔径取值范围为0.1μm至3μm。在一些实施例中，通过随机拍50张扫描式电子显微镜图像(SEM)(60μm×40μm)，对每张图像上孔径为0.1μm至3μm的孔进行统计，计算孔径的平均值，然后计算50张图像的平均值，即为平均孔径。在本申请中，平均孔径为0.6μm至1.5μm。在一些实施例中，平均孔径为0.8μm至1.2μm。
适当大小的孔径有利于促进锂离子的传输，而且不会对电化学装置的能量密度产生过大的不利影响。
在一些实施例中，负极活性材料颗粒的比表面积为1m 2/g至10m 2/g。负极活性材料颗粒的处于该范围的比表面积可以提升电化学装置整体的动力学性能，同时也不会由于比表面积过大而引起电解液消耗过快的问题。
在一些实施例中，负极孔隙率为15％至40％。处于该范围的孔隙率，取得了促进锂离子传输和内阻电阻增大两者之间的良好平衡。
在一些实施例中，在拉曼光谱测试下，负极活性材料颗粒的I D/I G的比值范围为0.8至1.4，其中，I D表示拉曼光谱中1350cm -1处的峰值强度，I G表示拉曼光谱中1580cm -1处的峰值强度。杂原子在与微晶负极活性材料的碳原子结合会增加微晶负极活性材料的缺陷，杂元素原子含量越高，测试到更高的I D/I G值，表明负极活性材料颗粒中的缺陷更多，可以提升负极活性材料颗粒的克容量。另一方面，如果I D/I G值太大，则负极活性材料颗粒的缺陷太多，不利于负极活性材料颗粒的结构的稳定。
在一些实施例中，负极活性材料颗粒的Dv10＜6μm，Dv50＜15μm。在一些实施例中，负极活性材料颗粒的Dv90＜30μm。负极活性材料颗粒的以上粒径可以改善电化学装置的动力学性能。在一些实施例中，负极活性材料颗粒包括硬碳。硬碳相对于石墨具有更大的克容量和更小的循环膨胀，使得电化学装置具有优异的倍率充放电性能和很好的充放电循环性能。在一些实施例中，负极活性材料层的压实密度为0.95g/cm 3至1.40g/cm 3。该范围的压实密度取得了能量密度提升和阻抗增大这两者的良好的平衡。
本申请的另一些实施例提供了一种电化学装置，电化学装置包括上述负极和电解液，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，负极还包括负极集流体，负极集流体和负极活性材料层之间的粘结力为3N/m至50N/m。如此，在分条时不易发生脱膜、毛刺，也不会由于需要过高含量的粘结剂而导致电化学装置的内阻偏高。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(LiFSI)和六氟磷酸锂(LiPF 6)，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。通过调控与LiFSI与LiPF 6的质量比，改善了其循环性能和膨胀性能，因为掺杂了杂原子的负极活性材料能和电解液中锂盐相互作用，改善了负极和电解液之间的界面。
本申请的实施例还提供了一种电子装置，包括上述电化学装置。
本申请的实施例通过采用包括孔部和具有硼、氮等元素掺杂的区域的负极活性材料颗粒，一方面，孔部的存在改善了锂离子嵌入和脱嵌的效率，另一方面，硼、氮等元素的掺杂提升了负极活性材料的克容量，有利于提升相应的电化学装置的能量密度。
附图说明
图1示出了负极活性材料层的示例扫描电镜图像。
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。
本申请的一些实施例提供了一种负极，该负极包括负极活性材料层。在一些实施例中，负极活性材料层包括负极活性材料颗粒。在一些实施例中，负极活性材料颗粒包括孔部以及具有杂原子的非孔部。在一些实施例中，负极活性材料颗粒的孔部是指孔径范围为0.1μm至3μm的孔，在孔部为非圆形的情况下，孔径指的是扫描电镜图像中孔中任意的两点的最远距离。如图1所示，示出了负极活性材料层的示例扫描电镜图像，负极活性材料层包括负极活性材料颗粒100，为了简单的目的，在图1中仅标出了其中一个负极活性材料颗粒100。在一些实施例中，负极活性材料颗粒100包括孔部101和非孔部102，孔部的直径(孔径)为孔内部(包括边缘位置)两点之间最远的距离，在一些实施例中，孔径为0.1μm至3μm。
本申请的一些实施例提供了一种负极，通过随机拍50张扫描电镜图像(60μm×40μm)，对每张图像上孔径为0.1μm至3μm的孔进行统计，计算孔径的平均值，然后计算50张图像的平均值，即为平均孔径。在本申请中，平均孔径为0.6μm至1.5μm。
在一些实施例中，杂原子包括硼、氮、氟、磷或硫元素中的至少一种并且位于界面处，该界面为非孔部102中距离孔部101和非孔部102之间的交界位置0.5μm以内的区域。即，该界面属于非孔部102的部分，该部分为从孔部101和非孔部102之间的交界位置出发，往非孔部102延伸最多0.5μm的区域。在一些实施例中，在两个孔部相距较近时，可能延伸不到0.5μm(例如0.3μm)即到达另一孔部，此时界面在该位置处仅从交界位置延伸0.3μm。
通过采用包括孔部和具有硼、氮等元素掺杂的区域的负极活性材料颗粒100，一方面，孔部的存在改善了锂离子嵌入和脱嵌的效率，另一方面，在负极活性材料颗粒中掺杂有硼、氮、氟、磷或硫元素时，这些掺杂元素可以与Li +发生键合，产生额外的容量，从而提升负极活性材料的克容量，有利于提升相应的电化学装置的能量密度。在一些实施例中，以硬碳作为负极活性材料为例，掺杂有杂原子的多孔硬碳负极活性材料，杂元素能很好地调控碳的电子结构，提升了导电性；杂原子进入碳微晶片层内，不仅增大了碳的层间距，还提供了更多的缺陷和活性位点，可以增加对锂离子的吸附能力，从而提升了电化学装置的克容量和倍率性能；另外，多孔硬碳负极活性材料的大 比表面积和丰富的孔道结构，不仅可以降低锂离子传输阻力，还可以提供锂离子和电子传输的快速通道，降低了电位滞后的效应，获得优异的倍率性能。
在一些实施例中，该负极活性材料可以采用树脂共熔融混法制备，具体地，将低残炭率的含杂原子基团的第二树脂均匀地掺混入高残炭率的第一树脂内，其中第一树脂作为基体树脂。在一些实施例中，第二树脂可以是含硼嗪环类聚合物、聚苯并硼咪唑、硼酚醛树脂、脲醛树脂、聚苯胺、聚酰亚胺、三聚氰胺树脂、聚四氟乙烯、聚偏氟乙烯、聚三氟氯乙烯、聚全氟乙丙烯、磷酸掺杂环氧树脂、磷基聚丙烯酸、磷基聚马来酸、双酚A型聚砜、聚醚砜、聚芳酚、聚苯硫醚等聚合物，也可以是脲醛树脂与聚苯并硼咪唑共混物、硼酚醛树脂与聚酰亚胺共混物、磷酸掺杂脲醛树脂、聚苯胺与磷基聚马来酸共混物等两种或多种聚合物的共混物的至少一种，第一树脂可以包括聚氯乙烯、聚甲基丙烯酸甲酯、聚醚醚酮、聚苯醚、聚碳酸酯、聚乙二醇、聚酯纤维、聚对苯二甲酸乙二醇脂、聚苯乙烯等的一种聚合物或多种聚合物的共混聚合物。在一些实施例中，将第二树脂与第一树脂在150℃至270℃下经高温熔融共混后，经710℃至1300℃热解2小时，破碎筛分后得到。在热解过程中，低残炭率组分第二树脂热解后在高残炭率第一树脂内留下孔洞，同时热解后形成的苯系物在低残炭率第二树脂内向外溢出过程中会在高残炭率第一树脂内形成微孔或继续脱氢参与成碳，在杂元素吸附在孔洞内壁进入第一树脂的碳微晶内部。应该理解，上述制备方法仅是示例性的，还可以采用其他合适的制备方法来制备负极活性材料。
在一些实施例中，由扫描电子显微镜-能谱仪对负极活性材料层的各元素分布进行分析，在界面处，基于测试面积为0.2μm×0.2μm的杂原子(即，硼、氮、氟、磷和硫元素原子)、C和O的元素原子含量，界面处的杂原子的原子含量为a％，1≤a≤6。即，界面处的杂原子的原子含量a％＝杂原子个数/(杂原子个数+C原子个数+O原子个数)。孔部在一些实施例中，在非孔部中距离孔部和非孔部之间的交界位置2.8μm至3.2μm的区域处(方向为从孔部和非孔部之间的交界位置做垂线，垂线为2.8μm至3.2μm的长度，将所有的线段的端点连接，形成的边界与孔部和非孔部之间的交界位置所围绕的区域)，基于测试面积为0.2μm×0.2μm的杂原子、C和O的元素原子含量，杂原子的原子含量为b％，b≤0.1。即，该区域处的杂原子的原子含量b％＝杂原 子个数/(杂原子个数+C原子个数+O原子个数)。在一些实施例中，改变与第一树脂熔融共混的第二树脂所携带的杂原子的种类以及含量，可以改变所得负极活性材料颗粒的掺杂元素，可以是单一元素(例如，硼、氮、氟、磷、硫)掺杂，也可以是双元素(例如，硼氮、硼氟、硼磷、硼硫、氮氟、氮磷、氮硫等)掺杂，也可以是三元素(例如，氮磷硫、氮氟磷、氮氟硫等)掺杂。在一些实施例中，在热解过程中杂原子与第二树脂共价键断裂进入第一树脂，在热解处富集并且向第一树脂内随距离增大而呈现含量梯度降低。在一些实施例中，在碳材料中引入氮掺杂有以下两方面的优点：一方面，碳与氮之间良好的键合作用，极大的改变了碳材料中的电子性能，增加了更多的活性位点，提高了负极活性材料的电化学性能；另一方面，氮元素的掺杂使得碳负极活性材料中出现大量晶格缺陷，这些缺陷可以作为储锂的位点，进一步提高碳负极活性材料的储锂性能。在一些实施例中，如果界面处的掺杂元素的含量太少，则其改善负极活性材料的克容量的作用相对有限；如果界面处的掺杂元素的含量太大，则其改善负极活性材料的克容量的作用不再进一步增大，而且可能降低负极活性材料层整体的能量密度。在一些实施例中，交界位置向非孔部内2.8μm至3.2μm位置处(该位置不包括当经过一个孔部，向外2.8μm至3.2μm位置经过的另一个孔部，仅为非孔部)的掺杂元素能够起到改善负极活性材料的克容量的作用相对受限，因此，该位置处的掺杂元素的含量不宜过大，以避免降低负极活性材料层整体的能量密度。
在一些实施例中，对负极活性材料层的截面进行扫描电子显微镜分析，测试面积为50μm×50μm，孔部与非孔部的面积比值为0.05至0.30，孔部内两点的最远距离的范围为0.1μm至3μm。在一些实施例中，由于不同树脂间的相容性不一，熔融共混后第二树脂在第一树脂内的存在状态不同，表现在热解之后在高残炭率的第一树脂内形成孔结构的孔径与孔数量有所差异。在一些实施例中，负极活性材料颗粒中的大孔(孔径＞500nm)难以存储锂离子，过大的孔径及孔数量会使活性材料的能量密度降低，因此，优选地，孔部与非孔部的面积比值为0.05至0.15，孔部的孔径范围为0.1μm至0.5μm。另一方面，如果孔径太小或孔数量太少则不利于负极活性材料颗粒中的锂离子传输，从而不利于电化学装置的倍率性能的提升。
在一些实施例中，负极活性材料颗粒的比表面积为1m 2/g至10m 2/g。包括孔部的负极活性材料颗粒的比表面积会有所增大，增大的表面积增加了负极活性材料与电解液的接触位点，提升了电化学装置整体的动力学性能，但是过大的比表面积在首次充电过程中形成的固体电解质界相(SEI)膜更多，消耗更多的锂离子，导致电化学装置的首次充放电效率下降。在一些实施例中，负极活性材料颗粒的比表面积为1m 2/g至5m 2/g。
在一些实施例中，负极孔隙率为15％至40％。随辊压压力的控制，可实现负极活性材料层的厚度的连续变化，即实现活性材料层孔隙率的调控，该孔隙率与存在于颗粒内部的孔洞、孔道作用相似，孔隙率一定程度上亦可对电化学容量作出贡献，直接反映为电化学装置的能量密度的提升。而孔隙率过大，负极活性材料颗粒间的接触点减少，电化学装置的内阻增大并且能量密度也有所损失。因此，负极孔隙率优选为15％至30％。
在一些实施例中，在拉曼光谱测试下，所述负极活性材料颗粒的I D/I G的比值范围为0.8至1.4，其中，I D表示拉曼光谱中1350cm -1处的峰值强度，I G表示拉曼光谱中1580cm -1处的峰值强度。杂原子在与微晶负极活性材料的碳原子结合会增加微晶负极活性材料的缺陷，杂元素原子含量越高，测试到更高的I D/I G值，表明负极活性材料颗粒中的缺陷更多，可以提升负极活性材料颗粒的克容量。另一方面，如果I D/I G值太大，则负极活性材料颗粒的缺陷太多，不利于负极活性材料颗粒的结构的稳定。
在一些实施例中，负极活性材料颗粒的Dv10＜6μm，Dv50＜15μm。在一些实施例中，负极活性材料颗粒的Dv90＜30μm。将负极活性材料颗粒粉碎，使用分级筛分以控制粒度分布。在一些实施例中，Dv10指的是从颗粒的粒径分布的小的那侧开始，体积累积分布达到10％时对应的粒径。同理地，Dv50和Dv90分别指的是从颗粒的粒径分布的小的那侧开始，体积累积分布达到50％和90％时对应的粒径。负极活性材料颗粒的粒度过大，锂离子脱嵌距离增大，颗粒间接触点减少，使电化学装置的动力学下降，阻抗增加。
在一些实施例中，负极活性材料颗粒包括硬碳。与石墨相比，硬碳具有较高的克容量，一般为500mAh/g至710mAh/g，甚至可高达1000mAh/g。硬碳颗粒内的微晶碳层大致平行排列，类似于石墨，但微晶尺寸小且排列各向异性，002晶面间距较大，约为0.35nm至0.40nm，大于石墨的层间距，有利 于锂的嵌入而不会引起结构显著膨胀，具有优异的倍率充放电性能和很好的充放电循环性能。002晶面间距可以通过BRUKER公司型号为D8ADVANCE的XRD设备进行分析。
在一些实施例中，负极活性材料层的压实密度为0.95g/cm 3至1.40g/cm 3。如果负极活性材料层的压实密度太小，则不利于电化学装置整体的能量密度的提升；如果负极活性材料层的压实密度太大，则会增大锂离子传输的阻抗，不利于电化学装置的倍率性能的提升。
在一些实施例中，提供了一种电化学装置，该电化学装置包括上述负极和电解液，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，负极还包括负极集流体。在一些实施例中，负极活性材料层可以位于负极集流体的一侧或两侧上。在一些实施例中，负极集流体和负极活性材料层之间的粘结力为3N/m至50N/m。如果负极活性材料层与负极集流体之间的粘结力太小，则辊压或分条工序极易发生脱膜、毛刺，导致电化学装置的安全隐患。如果负极活性材料层与负极集流体之间的粘结力太大，则通常要求负极活性材料层的粘结剂的质量含量较高，即粘结剂过量，这会导致电化学装置的内阻偏高，动力学损失严重，长循环性能衰减加速。在一些实施例中，负极集流体和负极活性材料层之间的粘结力为10N/m至20N/m。此时，既能确保安全隐患较少，又不至于需要采用过多的粘结剂。
在一些实施例中，负极活性材料层中还可以包括导电剂和粘结剂。在一些实施例中，负极活性材料层中的导电剂可以包括导电炭黑、科琴黑、片层石墨、石墨烯、碳纳米管或碳纤维中的至少一种。在一些实施例中，负极活性材料层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，负极活性材料层中的负极活性材料、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)。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，负极集流体可以采用铜箔、镍箔或碳基集流体中的至少一种。
在一些实施例中，电化学装置可以包括电极组件，电极组件包括正极、负极、设置在正极和负极之间的隔离膜。在一些实施例中，负极为上述任一种负极。
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。
在一些实施例中，正极包括正极集流体和设置在正极集流体上的正极活性材料层，正极活性材料层可以包括正极活性材料。在一些实施例中，正极活性材料包括钴酸锂、磷酸铁锂、磷酸锰铁锂、磷酸铁钠、磷酸钒锂、磷酸钒钠、磷酸钒氧锂、磷酸钒氧钠、钒酸锂、锰酸锂、镍酸锂、镍钴锰酸锂、富锂锰基材料或镍钴铝酸锂中的至少一种。在一些实施例中，正极活性材料层还可以包括导电剂。在一些实施例中，正极活性材料层中的导电剂可以包括导电炭黑、科琴黑、片层石墨、石墨烯、碳纳米管或碳纤维中的至少一种。在一些实施例中，正极活性材料层还可以包括粘结剂，正极活性材料层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，正极活性材料层中的正极活性材料、导电剂和粘结剂的质量比可以为(80至99)：(0.1至10)：(0.1至10)。在一些实施例中，正极活性材料层的厚度可以为10μm至500μm。应该理解，以上所述仅是示例，正极活性材料层可以采用任何其他合适的材料、厚度和质量比。
在一些实施例中，正极集流体可以采用Al箔，当然，也可以采用本领域常用的其他集流体。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，正极活性材料层可以仅涂覆在正极的集流体的部分区域上。
在一些实施例中，隔离膜包括聚乙烯、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，隔离膜的厚度在约5μm至50μm的范围内。
在一些实施例中，隔离膜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。
在本申请的一些实施例中，电化学装置的电极组件为卷绕式电极组件、堆叠式电极组件或折叠式电极组件。在一些实施例中，电化学装置的正极和/或负极可以是卷绕或堆叠式形成的多层结构，也可以是单层正极、隔离膜、单层负极叠加的单层结构。
在本申请的一些实施例中，以锂离子电池为例，将正极、隔离膜、负极按顺序卷绕或堆叠成电极件，之后装入例如铝塑膜中进行封装，注入电解液，化成、封装，即制成锂离子电池。然后，对制备的锂离子电池进行性能测试。
本领域的技术人员将理解，以上描述的电化学装置(例如，锂离子电池)的制备方法仅是实施例。在不背离本申请公开的内容的基础上，可以采用本领域常用的其他方法。
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。
实施例1
正极的制备：将正极活性材料钴酸锂、导电炭黑(Super P)、聚偏二氟乙烯(PVDF)按照重量比97：1.4：1.6进行混合，加入N-甲基吡咯烷酮(NMP)作为溶剂，搅拌均匀。将浆料(固含量为72wt％)均匀涂覆在正极集流体铝箔上，涂覆厚度为80μm，在85℃下烘干，然后经过冷压、裁片、分切后，在85℃的真空条件下干燥4小时，得到正极。
负极的制备：将人造硬碳、粘结剂丁苯橡胶和羧甲基纤维素钠(CMC)按重量比97：1.5：1.5的比例溶于去离子水中，形成负极浆料(固含量为40wt％)。采用10μm厚度铜箔作为负极集流体，将负极浆料涂覆于负极的集流体上，涂覆厚度为50μm，在85℃下烘干，然后经过冷压、裁片、分切后，在120℃的真空条件下干燥12小时，得到负极。
其中，人造硬碳通过以下步骤制备：将含硼原子基团的含硼聚乙烯与聚苯醚以质量比1.5：8.5在150℃至300℃下熔融共混，经710℃热解2h，然后进行破碎筛分，筛分后控制Dv90小于或等于30μm，Dn10的取值范围为0.1μm至0.9μm，从而得到孔部与非孔部的面积比值为0.05至0.30。
隔离膜的制备：隔离膜为7μm厚的聚乙烯(PE)。
电解液的制备：在干燥的氩气气氛手套箱中，将碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二乙酯(DEC)按照质量比为EC：PC：DEC＝1：1：1进行混合，溶解并充分搅拌后加入锂盐LiPF 6，混合均匀后获得基础电解液，其中LiPF 6的浓度为1mol/L，接着加入2wt％的1,3-丙烷磺内酯，2wt％的氟代碳酸乙烯酯，2wt％的丁二腈，混合均匀后即为电解液。
锂离子电池的制备：将正极、隔离膜、负极按顺序依次叠好，使隔离膜处于正极和负极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，切边等工艺流程得到锂离子电池。
其他实施例和对比例是在实施例1的步骤的基础上将人造硬碳制备过程进行参数变更，具体变更的参数如下所述。
实施例2至实施例4为硼元素掺杂(即，第一树脂聚苯醚与第二树脂含硼聚乙烯的质量比分别为0.85：0.15、0.85：0.15和0.70：0.30)，热解温度 分别为910℃、1110℃和910℃；实施例5至实施例8为氮元素掺杂(即，第一树脂聚苯醚与第二树脂聚苯胺的质量比分别为0.85：0.15、0.85：0.15、0.85：0.15和0.70：0.30)，其熔融温度与实施例1至实施例4相接近，热解温度见表4；实施例9至实施例12为氟元素掺杂(即，第一树脂聚苯醚与第二树脂聚四氟乙烯的质量比分别为0.85：0.15、0.85：0.15、0.85：0.15和0.70：0.30)，其熔融温度与实施例1至实施例4相接近，热解温度见表4；实施例13至实施例16为磷元素掺杂(即，第一树脂聚苯醚与第二树脂磷基聚丙烯酸的质量比分别为0.85：0.15、0.85：0.15、0.85：0.15和0.70：0.30)，其熔融温度与热解温度分别与实施例1至实施例4相似；实施例17至实施例20为硫元素掺杂(即，第一树脂聚苯醚与第二树脂聚醚砜的质量比分别为0.85：0.15、0.85：0.15、0.85：0.15和0.70：0.30)，其熔融温度与热解温度分别与实施例1至实施例4相似；实施例21至实施例24为硼氮元素掺杂(即，第一树脂聚苯醚与第二树脂的质量比分别为0.85：0.15、0.85：0.15、0.85：0.15和0.70：0.30)，第二树脂为脲醛树脂和聚苯并硼咪唑的共混物，且脲醛树脂和聚苯并硼咪唑质量比为2：3，其熔融温度与热解温度分别与实施例1至实施例4相似；实施例25至实施例28为氮磷元素掺杂(即，第一树脂聚苯醚与第二树脂的质量比分别为0.85：0.15、0.85：0.15、0.85：0.15和0.70：0.30)，第二树脂为脲醛树脂与磷酸掺杂脲醛树脂质量比为2：3的共混物，其熔融温度与热解温度分别与实施例1至实施例4相似；对比例1至对比例4中使用的第二树脂不含杂元素(即，第一树脂聚苯醚与第二树脂聚醚醚酮的质量比分别为0.85：0.15、0.85：0.15、0.85：0.15和0.70：0.30)，其熔融温度与实施例1至实施例4相似，热解温度见表4；对比例5为第一树脂聚苯醚在910℃下热解得到的硬碳活性材料，不含孔结构与杂元素，对比例6为人造石墨材料。
下面描述本申请的各个参数的测试方法。
1.SEM测试：
扫描式电子显微镜(SEM)是通过电子束与样品的相互作用，并利用二次电子信号成像得到样品的形貌结构。本申请中使用的扫描电镜为JEOL公 司的JSM-6360LV型及其配套的X射线能谱仪(扫描电子显微镜-能谱仪)对样品的形貌结构和元素分布进行分析。
2.负极活性材料颗粒的粒径测试：
颗粒粒度测试方法参照GB/T 19077-2016。具体流程为称量样品1g与20mL去离子水和微量分散剂混合均匀，置于超声设备中超声5min后将溶液倒入进样系统Hydro 2000SM中进行测试，所用测试设备为马尔文公司生产的Mastersizer 3000。测试过程中当激光束穿过分散的颗粒样品时，通过测量散射光的强度来完成粒度测量。然后数据用于分析计算形成该散射光谱图的颗粒粒度分布。测试所用颗粒折射率为1.8，一个样品测试三次，颗粒粒度最终取三次测试的平均值测得Dv10，Dv50和Dv90。
3.I D/I G的比值测试：
利用激光显微共聚焦拉曼光谱仪测试样品的表面缺陷度，采用样品在1350cm -1处的峰值强度I D与在1580cm -1处的峰值强度I G的比值I D/I G值表征样品的表面缺陷度。每个样品测试多个电位，通过其标准差值表征不同区域的表面缺陷度的均匀性。负极活性材料的I D/I G的平均值和标准差采取如下方法得到：取未筛分的负极活性材料，测试100个点，得到对应的I D/I G值，计算这100个值的平均值和标准差值。
4.负极活性材料颗粒的比表面积测试：
使用比表面积分析仪(TristarⅡ3020M)，通过氮吸附/脱附法测量负极活性材料的比表面积：将负极活性材料样品在真空干燥箱中烘干，然后装入样品管中在分析仪中测量。
5.负极活性材料层与负极集流体粘结力测试：
负极活性材料层与负极集流体的粘结力测试所用仪器的品牌为Instron，型号为33652，取负极(宽30mm×长度(100mm至160mm))，用双面胶纸(型号：3M9448A，宽度20mm×长度(90mm至150mm))固定于钢板上，将与负极等宽的纸带与负极一侧用胶纸固定，调整拉力机限位块至合适位置，将纸带向上翻折及滑移40mm，滑移速率为50mm/min，测试180°下(即反方向拉伸)负极活性材料层与负极集流体之间的粘结力。
6.负极活性材料层的压实密度的测试：
取完全放电的锂离子电池，拆解出负极，清洗，烘干，使用电子天平对一定面积S的负极(负极集流体的双面涂覆有负极活性材料层)进行称重，重量记为W1，并使用万分尺测得负极的厚度T1。使用溶剂洗掉负极活性材料层，烘干，测量负极集流体的重量，记为W2，并使用万分尺测得负极集流体的厚度T2。通过下式计算设置在负极集流体一侧的负极活性材料层的重量W0和厚度T0以及负极活性材料层的压实密度：
W0＝(W1-W2)/2
T0＝(T1-T2)/2
负极活性材料层的压实密度＝W0/(T0×S)。
7.负极孔隙率的测试：
将负极活性材料层样品制备成完整圆片。每个实施例或对比例测试30个样品，每个样品体积为约0.35cm 3。根据《GB/T24586-2009铁矿石表观密度真密度和孔隙率的测定》标准进行测试负极孔隙率。
8.负极活性材料的克容量测试：
将负极活性材料通过混料、涂布、烘干后制成负，使用锂片做正极，组装成扣式电池进行测试。扣式电池以0.05C放电至5.0mV，以50μA放电至5.0mV，以10μA放电至5.0mV，以0.1C充电至2.0V，记录此时扣式电池的容量，记为克容量。0.05C指的是0.05倍设计克容量下的电流值，0.1C指的是0.1倍设计克容量下的电流值。
9.锂离子电池的首次充放电效率的测试：
将锂离子电池以0.5C充电至4.48V，记录首次充电容量，然后以0.5C放电至3.0V，记录其首次放电容量。通过下式计算锂离子电池的首次效率CE＝首次放电容量/首次充电容量×100％。
10.能量密度测试：
将采用所有对比例和实施例的锂离子电池各组取5支，取平均值。首先，在25℃的环境中，进行第一次充电和放电，在0.5C的充电电流下进行恒流和恒压充电，直到上限电压为4.48V，然后在0.2C的放电电流下进行恒流放电，放电截止电压为3V，计算各实施例和对比例相对于对比例6的能量密度提高百分比，即能量密度占对比例6的百分比。
11.锂离子电池循环性能测试：
将采用所有对比例和实施例制备的锂离子电池各取5支，取平均值。通过以下步骤对锂离子电池重复进行充电和放电，并计算锂离子电池的放电容量保持率和厚度膨胀。
首先，在25℃的环境中，进行第一次充电和放电，在0.7C的充电电流下进行恒流充电，直到达到上限电压4.48V后转为恒压充电，然后在1.0C的放电电流下进行恒流放电，直到最终电压为3V，记录首次循环的放电容量和满充锂离子电池厚度；而后进行400次的充电和放电循环，记录第400次循环的放电容量和满充锂离子电池厚度。
循环容量保持率＝(第400次循环的放电容量/首次循环的放电容量)×100％；
循环厚度膨胀＝(第400次循环的满充锂离子电池厚度/首次循环的满充锂离子电池厚度)×100％
12.析锂测试
取被测锂离子电池在25℃测试温度下，静止5分钟，以3C的电流将锂离子电池恒流充电至4.48V，再以4.48V的恒压充电至0.05C；静置5分钟，再以0.5C的电流恒流放电至2.0V，静止5分钟。重复上述充放电流程10次后，将锂离子电池满充，于干燥房内拆解，拍照记录负极以及与负极相接触的隔离膜的状态。
析锂程度判定：根据满充拆解负极相接触的隔离膜被污染的状态来判定，当负极相接触的隔离膜整体显示为白色且显示为灰色的面积<2％，则判定为不析锂；当负极相接触的隔离膜大部分为白色，但有部分位置可观察到灰色，灰色面积在2％至20％之间，则判定为轻微析锂；当负极相接触的隔离膜部分为白色，但仍可明显观察到部分灰色，灰色面积在20％至60％，则判定为析锂；当负极相接触的隔离膜大部分显示为灰色，灰色面积＞60％时，则判定为严重析锂。
表1至表4示出了相应实施例1至28和对比例1至6的各个参数和评估结果。其中，将硼、氮、氟、磷或硫元素统称为杂原子。
表1
Figure PCTCN2021101234-appb-000001
注：“/”表示未添加。
通过比较实施例1、实施例5、实施例9、实施例13、实施例17、实施例21、实施例25及对比例可知，通过选择带有不同杂元素的第二树脂，能够获得不同杂元素掺杂的硬碳活性材料；对比实施例1至实施例3，随着热解温度从710℃提升至1110℃，相同杂元素原子含量的实施例1、实施例2、实施例3的杂原子含量随着热解温度的提高明显降低；对比实施例2与实施例4，选择带有相同杂元素的第二树脂和热处理工艺，通过改变第二树脂添加量，可以简便地获得不同杂原子含总含量的硬碳活性材料；不同杂元素掺杂的硬碳活性材料的I D/I G均高于对比例组的无杂元素掺杂硬碳活性材料，远高于对比例6的石墨活性材料；不同杂元素掺杂的硬碳活性材料的克容量均高于对比例组的无杂元素掺杂硬碳活性材料及石墨 活性材料，其中，实施例5为在710℃下热处理的氮掺杂硬碳负极活性材料，具有最高的克容量。
表2
Figure PCTCN2021101234-appb-000002
通过比较氮掺杂的实施例5、实施例6、实施例7的负极活性材料的002晶面间距随着热处理温度的提升而下降；硬碳活性材料具有相近的比表面积；负极具有相近的孔隙率。同时，氟掺杂的实施例9、实施例10和实施例11，以及无元素掺杂的对比例1、对比例2和对比例3呈现出与上述说明类似的规律。通过比较实施例6与实施例8及对比例2与对比例4，可知通过的改变第二树脂添加量，获得的硬碳活性材料的孔部与非孔部的面积比也相应提升。
硬碳负极活性材料丰富的孔结构使其相应的负极活性材料层具有较高的孔隙率，高空隙率和远高于石墨负极活性材料的d002晶面间距使硬碳负极活性材料具有优异的快充性能，在相同充放电条件下，所有实施例的析锂情况均优于负极活性材料为石墨的对比例6。孔结构有助于增加活性材料颗粒与电解液的接触，提升锂离子脱嵌速度，但较大的比表面积及孔隙率会导致首次充电过程形成更多SEI膜，造成不可逆容量损失。对比实施例6与对比例2及实施例8与对比例4的锂离子电池的首次充放电效 率可知，更多的孔含量的实施例8与对比例4的锂离子电池的首次充放电效率更低。
表3
Figure PCTCN2021101234-appb-000003
对比磷掺杂的实施例14和实施例16，以及无元素掺杂的对比例2和对比例4，可知，负极活性材料颗粒具有接近的颗粒度，相应负极活性材料层与集流体之间的粘结力接近；比较负极活性材料层的压实密度可知，实施例16及对比例4的负极活性材料层的压实密度均较低，这是由于在基体树脂内添加第二树脂含量的提升，热解后硬碳负极活性材料的孔部含量增加，故负极活性材料层的压实密度有所下降。实施例14和实施例16对比可以表明，更高的压实密度可以获得更高的能量密度提升。
表4
Figure PCTCN2021101234-appb-000004
Figure PCTCN2021101234-appb-000005
硬碳负极活性材料存在较多缺陷，缺陷可以增加活性材料的储锂位点，提升锂离子脱嵌速率，但缺陷同时也导致硬碳活性材料较大的不可逆容量。对比实施例以及对比例，可知，所有实施例中含硬碳负极活性材料的锂离子电池的首次充放电效率均比含石墨负极活性材料的对比例6低，其中，氟元素掺杂实施例11的硬碳负极活性材料锂离子电池的首次充放电效率相对较高为76.7％；与对比例1至对比例5相比，掺杂有杂元素的实施例的首次充放电效率相对较高，这是由于杂元素掺杂活性材料具备更多的储锂位点所致。
得益于杂元素掺杂获得的更多储锂容量，含硬碳负极活性材料的锂离子电池可以获得更高的能量密度，对比实施例1至实施例28与对比例1至5，含杂元素掺杂的实施例获得的能量密度均高于对比例，其中，氮元素掺杂的实施例5具有最高的能量密度提升。且实施例的循环性能和膨胀性能也相比于无杂元素掺杂的对比例效果更优，综合电化学性能更佳。
同时，硬碳负极活性材料在充放电过程中的低膨胀特性，使其组装的锂离子电池在循环400圈后锂离子电池厚度变化维持在约3％以下的水平，锂离子电池厚度变化水平远低于含石墨负极活性材料的对比例6，同时所 有实施例组装的锂离子电池在循环400圈后锂离子电池的容量保持率与含石墨负极活性材料的对比例6保持在相当的水平。
表5
Figure PCTCN2021101234-appb-000006
注：LiFSI摩尔质量为187.07g/mol，LiPF 6摩尔质量为151.91g/mol。
表5中，实施例26至28与实施例12不同的仅仅是加入了锂盐双(氟磺酰基)酰亚胺锂(LiFSI)，通过调控与LiFSI与LiPF 6的质量比，改善了其循环性能和膨胀性能，这主要是因为，掺杂了杂原子的负极活性材料能和电解液中锂盐相互作用，改善负极和电解液之间的界面。
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. 一种负极，其包括：负极活性材料层，所述负极活性材料层包括负极活性材料颗粒，所述负极活性材料颗粒包括孔部和非孔部，所述非孔部包括杂原子，所述杂原子包括硼、氮、氟、磷或硫元素中的至少一种。
  2. 根据权利要求1所述的负极，所述非孔部具有界面，所述界面为所述非孔部和孔部交界位置至距离所述交界位置0.5μm形成的区域，其中，通过扫描电子显微镜-能谱仪分析，满足以下条件(a)至(c)中的至少一者：
    (a)在所述界面位置，测试面积为0.2μm×0.2μm区域内，基于所述杂原子、C和O的元素原子总含量，所述杂原子的原子含量为a％，1≤a≤6；
    (b)在所述非孔部内且距离所述交界位置2.8μm至3.2μm的区域，在测试面积为0.2μm×0.2μm区域内，基于所述杂原子、C和O的元素原子总含量，所述杂原子的原子含量为b％，b≤0.1；
    (c)在测试面积为50μm×50μm区域内，所述孔部与所述非孔部的面积比值为0.05至0.30。
  3. 根据权利要求1所述的负极，其中，所述孔部的孔径取值范围为0.1μm至3μm。
  4. 根据权利要求1所述的负极，其中，所述负极活性材料颗粒的比表面积为1m 2/g至10m 2/g。
  5. 根据权利要求1所述的负极，其中，所述负极孔隙率为15％至40％。
  6. 根据权利要求1所述的负极，其中，在拉曼光谱测试下，所述负极活性材料颗粒的I D/I G的比值范围为0.8至1.4，
    其中，I D表示拉曼光谱中1350cm -1处的峰值强度，I G表示拉曼光谱中1580cm -1处的峰值强度。
  7. 根据权利要求1所述的负极，其中，满足以下条件(d)至(g)中的至少一者：
    (d)所述负极活性材料颗粒的Dv10＜6μm，Dv50＜15μm；
    (e)所述负极活性材料颗粒的Dv90＜30μm；
    (f)所述负极活性材料颗粒包括硬碳；
    (g)所述负极活性材料层的压实密度为0.95g/cm 3至1.40g/cm 3。
  8. 一种电化学装置，包括根据权利要求1至7中任一项所述的负极和电解液，所述电解液包括氟醚、氟代碳酸乙烯酯或醚腈中的至少一种。
  9. 根据权利要求8所述的电化学装置，其中，满足以下条件(h)至(i)中至少一种：
    (h)所述负极还包括负极集流体，所述负极集流体和所述负极活性材料层之间的粘结力为3N/m至50N/m；
    (i)所述电解液还包括锂盐，所述锂盐包括双(氟磺酰基)酰亚胺锂和六氟磷酸锂，所述锂盐的浓度为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。
  10. 一种电子装置，包括根据权利要求8或9所述的电化学装置。
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