CN114883525A - Electrochemical device and electronic device - Google Patents
Electrochemical device and electronic device Download PDFInfo
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- CN114883525A CN114883525A CN202210736540.0A CN202210736540A CN114883525A CN 114883525 A CN114883525 A CN 114883525A CN 202210736540 A CN202210736540 A CN 202210736540A CN 114883525 A CN114883525 A CN 114883525A
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Abstract
Embodiments of the present application provide an electrochemical device and an electronic device. The electrochemical device comprises a negative pole piece, wherein the negative pole piece comprises a negative pole current collector, a first layer and a second layer, and the first layer is positioned between the negative pole current collector and the second layer; wherein the first layer comprises a first negative active material and the second layer comprises a second negative active material; the first negative electrode active material contains a first doping element, and the second negative electrode active material contains a second doping element; the mass percentage of the first doping element in the first layer is greater than the mass percentage of the second doping element in the second layer, the first doping element and the second doping element are of the same species, and the first doping element and the second doping element each independently comprise at least one of S, N, P, B, Sn or Sb. Thus, the energy density of the electrochemical device is improved, and the adverse effect on the quick charging performance is reduced.
Description
Technical Field
The present application relates to the field of electrochemical energy storage, in particular to electrochemical devices and electronic devices.
Background
With the development of electrochemical energy storage technology, higher and higher requirements are placed on the energy density and the fast charge performance of electrochemical devices (e.g., lithium ion batteries). However, the energy density and the fast charging performance of the electrochemical device are difficult to be compatible, and generally, the kinetic performance of the electrode sheet is deteriorated to some extent by increasing the energy density, and therefore, further improvement in this respect is expected.
Disclosure of Invention
The application provides an electrochemical device, which comprises a negative pole piece, wherein the negative pole piece comprises a negative pole current collector, a first layer and a second layer, and the first layer is positioned between the negative pole current collector and the second layer; wherein the first layer comprises a first negative active material and the second layer comprises a second negative active material; the first negative electrode active material contains a first doping element, and the second negative electrode active material contains a second doping element; the mass percent of the first doping element in the first layer is greater than the mass percent of the second doping element in the second layer, the first doping element and the second doping element are the same in type, and the first doping element and the second doping element comprise at least one of S, N, P, B, Sn or Sb.
In some embodiments, the mass percentage of the first doping element in the first layer is 0.01% to 1%. In some embodiments, the second doping element in the second layer is 0.001% to 0.01% by mass. In some embodiments, the mass percentage of the first doping element in the first layer is 0.1% to 0.3%. In some embodiments, the first negative active material and the second negative active material each independently comprise at least one of graphite or hard carbon. In some embodiments, the first negative active material and the second negative active material each further independently comprise a silicon-based material. In some embodiments, the mass percentage of the silicon-based material in the first layer is 1% to 30%. In some embodiments, the silicon-based material in the second layer is 0.1 to 4% by mass. In some embodiments, the ratio of the mass of the first layer to the total mass of the first layer and the second layer is 40% to 80%. In some embodiments, the ratio of the mass of the second layer to the total mass of the first and second layers is 20% to 60%.
Embodiments of the present application also provide an electronic device including the electrochemical device described above.
By adopting the double-layer active material layer design in the negative pole piece, the mass percentage of the first doping element in the lower first layer is larger than that of the second doping element in the upper second layer, wherein the first doping element and the second doping element respectively and independently comprise at least one of S, N, P, B, Sn or Sb, so that the high capacity of the negative pole piece is ensured by the higher mass percentage of the first doping element in the first layer, the excellent dynamic performance of the negative pole piece is ensured by the second layer, the quick charge capability is ensured, and the adverse effect on the quick charge performance is reduced while the energy density of the electrochemical device is improved.
Drawings
Fig. 1 shows a schematic cross-sectional view of a negative electrode tab taken along a width direction and a thickness direction according to some embodiments.
Fig. 2 shows schematic cross-sectional views of negative electrode pole pieces taken along the width direction and the thickness direction according to further embodiments.
Detailed Description
The following examples are presented to enable those skilled in the art to more fully understand the present application and are not intended to limit the present application in any way.
Generally, the means to increase the energy density will generally affect the dynamic performance of the electrochemical device to varying degrees. When the surface dynamics performance of the negative pole piece is insufficient, lithium precipitation on the surface is easily caused. This application is through adopting double-deck coating technique, and the active material layer of first layer is rich in doping element, and these doping element can improve negative active material's electronic state for negative active material obtains electron more easily, forms new chemical bond, thereby stores more lithium ion, promotes the specific capacity of negative pole piece, is favorable to promoting electrochemical device's energy density. And the active material layer of the second layer contains less doping elements, which is beneficial to ensuring the dynamic performance of the electrochemical device.
Fig. 1 and 2 show schematic cross-sectional views taken along a width direction and a thickness direction of a negative electrode tab according to some embodiments. Some embodiments of the present application provide an electrochemical device including a negative electrode tab. As shown in fig. 1 and 2, in some embodiments, the negative electrode tab includes a negative electrode collector 10, a first layer 11, and a second layer 12, the first layer 11 being located between the negative electrode collector 10 and the second layer 12. It should be understood that although the first and second layers 11 and 12 are illustrated in fig. 1 and 2 as being located on only one side of the negative electrode collector 10, this is merely exemplary, and the first and second layers 11 and 12 may be present on both sides of the negative electrode collector 10.
In some embodiments, the first layer 11 includes a first negative active material 111 and the second layer 12 includes a second negative active material 121. In some embodiments, the mass percentage of the first doping element 112 in the first layer 11 is greater than the mass percentage of the second doping element 122 in the second layer 12. In some embodiments, the first doping element 112 and the second doping element 122 each independently comprise at least one of S, N, P, B, Sn or Sb. S, N, P, B can improve the electronic state of the negative active material (such as graphite), so that the negative active material can obtain electrons more easily to form new chemical bonds, thereby storing more lithium ions, increasing the specific capacity of the negative pole piece, and being beneficial to increasing the energy density of the electrochemical device. In addition, Sn and Sb are beneficial to storing lithium ions, so that the specific capacity of the negative pole piece can be improved. However, these doping elements may affect the lithium affinity of the negative active material, and further affect the dynamic performance of the negative electrode plate.
By having more first doping elements 112 in the first layer 11 close to the negative current collector 10 and less second doping elements 122 in the second layer 12 far from the negative current collector 10, the negative electrode sheet's energy density is improved while minimizing adverse effects on the kinetic performance, thereby achieving high dynamic performance and high energy density of the electrochemical device.
In some embodiments, the doping patterns of the first doping element and the second doping element may include physical doping and chemical doping. Chemical doping includes, for example, solid-phase sintering of an active material and a compound of a corresponding element, or a method of liquid-phase co-precipitation, and a doping element enters a crystal lattice of the active material to affect an electronic structure. Physical doping for example comprises mixing the active material with a corresponding doping element to obtain a new active material. For example, by chemically doping N, the active material is placed in a high temperature environment or a plasma environment, and N is introduced 2 Gas, N 2 The gas can react with the active material, thereby realizing N doping; for example, physical doping, in the case of P doping, P nanoparticles are added to the active material, and then ball milling is performed at high speed, so that physical doping can be achieved by the two. Of course, other suitable doping schemes may also be included.
In some embodiments, the mass percentage of the first doping element 112 in the first layer 11 is 0.01% to 1%. If the mass percentage of the first doping element 112 in the first layer 11 is too small, the effect of the first layer 11 in raising the energy density is relatively limited; if the mass percentage of the first doping element 112 in the first layer 11 is too large, the effect of the first layer 11 in raising the energy density is no longer significantly increased. In some embodiments, the mass percentage of the first doping element 112 in the first layer 11 is 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1%, or other suitable value. In some embodiments, the mass percentage of the first doping element 112 in the first layer 11 is 0.1% to 0.3%. Thus, the negative pole piece can improve the energy density of the negative pole piece and simultaneously minimize the adverse effect on the dynamic performance.
In some embodiments, the second doping element 122 in the second layer 12 is 0.001% to 0.01% by mass. Some doping elements are also inevitably present in the second layer 12. In some embodiments, the kinetic performance of the electrochemical device can be minimally affected by setting the mass percentage of the second doping element 122 in the second layer 12 to 0.01% or less, i.e., without additional doping of the second layer with such elements.
In some embodiments, the first anode active material 111 and the second anode active material 121 each independently include at least one of graphite or hard carbon. In some embodiments, the first negative active material 111 and the second negative active material 121 also each independently include a silicon-based material. The silicon-based material can improve the energy density of the electrochemical device. In some embodiments, the silicon-based material comprises at least one of silicon, a silicon oxy material, a silicon carbon material, or a silicon oxy carbon material. In some embodiments, the first anode active material 111 and the second anode active material 121 may be the same or different.
In some embodiments, the mass percentage of the silicon-based material in the first layer 11 is 1% to 30%. If the mass percentage of the silicon-based material in the first layer 11 is too small, the silicon-based material has a relatively small effect of enhancing the energy density of the electrochemical device; if the mass percentage of the silicon-based material in the first layer 11 is too large, the volume expansion of the silicon-based material caused during the cycle is too large, which is disadvantageous to the structural stability of the first layer 11.
In some embodiments, the silicon-based material in the second layer 12 is 0.1 to 4% by mass. If the mass percentage of the silicon-based material in the second layer 12 is too small, the silicon-based material has a relatively small effect of increasing the energy density of the electrochemical device; if the mass percentage of the silicon-based material in the second layer 12 is too large, the volume expansion of the silicon-based material caused during the cycle is too large, which is disadvantageous for the structural stability of the second layer 12. In addition, excess silicon-based material may also adversely affect the conductive properties of second layer 12 due to its relatively weak conductivity.
In some embodiments, the ratio of the mass of the first layer 11 to the total mass of the first layer 11 and the second layer 12 is 40% to 80%. In some embodiments, the ratio of the mass of the second layer 12 to the total mass of the first layer 11 and the second layer 12 is 20% to 60%. In some embodiments, the ratio of the mass of the second layer 12 to the total mass of the first and second layers 11, 12 has less impact on the dynamic performance of the negative electrode tab, however, the impact on the overall capacity of the electrochemical device is greater, which facilitates increasing the overall energy density of the electrochemical device by increasing the ratio of the mass of the first layer 11 to the total mass of the first and second layers 11, 12. For example, the ratio in fig. 2 is larger than that in fig. 1, which is advantageous to improve the overall energy density of the electrochemical device. Of course, if the ratio of the mass of the first layer 11 to the total mass of the first layer 11 and the second layer 12 is too large, it is also not advantageous for the second layer 12 to sufficiently exert the effect of improving the dynamic performance. In some embodiments, the ratio of the mass of the first layer 11 to the total mass of the first layer 11 and the second layer 12 is 40%, 50%, 55%, 60%, 70%, 80%, or other suitable value.
In some embodiments, negative current collector 10 may employ at least one of a copper foil, a nickel foil, or a carbon-based current collector. In some embodiments, the first layer 11 and the second layer 12 may also each independently comprise a binder comprising at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, polyimide, polyamideimide, polyvinylidene fluoride, polytetrafluoroethylene, aqueous acrylic resin, or polyvinyl formal. In some embodiments, the mass ratio of the first negative electrode active material and the binder in the first layer 11 is 90 to 99: 1-10. In some embodiments, the mass ratio of the second anode active material and the binder in the second layer 12 is 90-99: 1-10. It will be appreciated that this is merely exemplary and that other suitable materials or other suitable mass ratios may be included. In some embodiments, the first layer 11 and the second layer 12 may also include a dispersant, such as, for example, carboxymethyl cellulose, sodium carboxymethyl cellulose, and the like.
In some embodiments, the electrochemical device includes an electrode assembly that may include a positive pole piece, a negative pole piece, and a separator disposed between the positive and negative pole pieces. In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. In some embodiments, the positive active material layer may be disposed on one or both sides of the positive current collector.
In some embodiments, the positive electrode current collector may be an aluminum foil, but other positive electrode current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 50 μm. In some embodiments, the positive electrode active material layer may be coated only on a partial area of the positive electrode collector.
In some embodiments, the positive electrode active material layer may include a positive electrode active material, a conductive agent, and a binder. In some embodiments, the positive active material may include at least one of lithium cobaltate, lithium iron phosphate, lithium aluminate, lithium manganate, or lithium nickel cobalt manganate. In some embodiments, the conductive agent of the positive electrode sheet may include at least one of conductive carbon black, flake graphite, graphene, or carbon nanotubes. In some embodiments, the binder in the positive electrode sheet may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, a polyamide, polyacrylonitrile, a polyacrylate, a polyacrylic acid, a polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, a polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer is (80-99): (0.1-10): (0.1-10), but this is merely an example and any other suitable mass ratio may be employed.
In some embodiments, the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 3 μm to 20 μm.
In some embodiments, the surface of the separator may further include a porous layer disposed on at least one surface of the separator, the porous layer including inorganic particles selected from alumina (Al) and a binder 2 O 3 ) Silicon oxide (SiO) 2 ) Magnesium oxide (MgO)Titanium oxide (TiO) 2 ) Hafnium oxide (HfO) 2 ) Tin oxide (SnO) 2 ) Cerium oxide (CeO) 2 ) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO) 2 ) Yttrium oxide (Y) 2 O 3 ) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator film have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The porous layer on the surface of the isolating membrane can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the pole piece.
In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not so limited. In some embodiments, the electrochemical device further comprises an electrolyte comprising at least one of fluoroether, fluoroether carbonate, or ether nitrile. In some embodiments, the electrolyte further includes a lithium salt including lithium bis (fluorosulfonyl) imide and lithium hexafluorophosphate, the concentration of the lithium salt is 1 to 2mol/L, and the mass ratio of lithium bis (fluorosulfonyl) imide to lithium hexafluorophosphate is 0.06 to 5. In some embodiments, the electrolyte may further include a non-aqueous solvent. The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.
The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.
Examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), or a combination thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.
Examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, methyl formate, or combinations thereof.
Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.
Examples of other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.
Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an unmanned aerial vehicle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.
In the following, some specific examples and comparative examples are listed to better illustrate the present application, wherein a lithium ion battery is taken as an example.
Comparative example 1
Preparing a negative pole piece: the current collector adopts copper foil, the negative active material adopts artificial graphite, the binder adopts styrene butadiene rubber, and the dispersant adopts carboxymethyl cellulose. Mixing artificial graphite, styrene butadiene rubber and sodium carboxymethylcellulose according to the mass percentage of 98: 1: 1, dispersing the mixture in deionized water to form slurry, uniformly stirring, coating the slurry on a copper foil, drying to form a negative active material layer, and carrying out cold pressing and stripping to obtain a negative pole piece. Wherein the thickness of the anode active material layer is 120 μm.
Preparing a positive pole piece: mixing a positive electrode active material lithium cobaltate, conductive carbon black and a binder polyvinylidene fluoride (PVDF) according to the mass percentage of 94.8: 2.8: and 2.4, fully stirring and uniformly mixing the mixture in an N-methyl pyrrolidone solvent system, and coating the mixture on an aluminum foil to obtain a positive active material layer, wherein the thickness of the positive active material layer is 80 microns. And drying and cold pressing to obtain the positive pole piece.
Preparing an isolating membrane: stirring polyacrylate to form uniform slurry, coating the slurry on the two side surfaces of the porous base material (polyethylene), and drying to form the isolating membrane.
Preparing an electrolyte: under the environment that the water content is less than 10 ppm, lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Propyl Propionate (PP), Vinylene Carbonate (VC) = 20: 30: 20: 28: 2, mass percentage content ratio) are mixed according to the mass percentage content ratio of 8: 92 was formulated to form an electrolyte having a lithium salt concentration of 1 mol/L.
Preparing a lithium ion battery: and sequentially stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the electrode assembly. And (3) placing the electrode assembly in an outer packaging aluminum-plastic film, dehydrating at 80 ℃, injecting the electrolyte, packaging, and carrying out technological processes such as formation, degassing, shaping and the like to obtain the lithium ion battery.
In comparative example 2, only the negative electrode sheet was prepared differently from comparative example 1, specifically, N was doped in the negative active material layer in an amount of 0.1% by weight.
Example 1 preparation of only a negative electrode sheet was different from comparative example 1, specifically, the negative active material layer was double-coated, the thickness of the first layer close to the negative current collector was 60 μm, the thickness of the second layer far from the negative current collector was 60 μm, the first layer was doped with N element, the mass percentage of N element in the first layer was 0.1%, and the mass percentage of N element in the second layer was 0.001%. Examples 2, 6 and 7 differ from example 1 only in that the doping element was changed from the N element to the S element, the P element and the B element. The difference between example 3 and example 1 is that the mass percentage of the N element in the first layer is 0.01%. Example 4 differs from example 3 in that the thickness of the first layer close to the negative electrode current collector was 96 μm and the thickness of the second layer far from the negative electrode current collector was 24 μm. Examples 5, 8, and 9 are different from example 1 in that the mass percentage of the N element in the first layer is 0.2%, 0.5%, and 1%. Examples 10 to 13 differ from example 1 in the ratio of the mass of one layer to the total mass of the first layer and the second layer.
In addition, in the present application, the following method may be employed to measure the corresponding parameters.
And (3) testing the efficiency for the first time:
charging the lithium ion battery at a constant current of 1C at 45 ℃ until the voltage rises to a rated voltage of 4.45V, then charging at the constant voltage until the current is reduced to 0.02C, and recording the charging capacity Qc; laying aside for 5 min, then carrying out 0.2C constant current discharge on the lithium ion battery, and stopping and recording the discharge capacity Qd when the voltage is reduced to 3V; wherein first efficiency = Qc/Qd.
And (3) energy density testing:
the test conditions are 25 ℃, 3C is charged to 4.45V, then the battery is placed for 30 min, then 1C is discharged to 3V, the battery is placed for 10 min, the test is cycled, and after the last cycle is 1000 times, the volume = length × width × thickness of the lithium ion battery, and the energy density = capacity/volume of the lithium ion battery is calculated by using the capacity and volume of the lithium ion battery.
The capacity of the lithium ion battery means that the lithium ion battery is directly charged to rated voltage of 4.48V at constant current of 0.5C at 25 ℃, then constant voltage charging is carried out until the current is reduced to 0.02C, and at the moment, the lithium ion battery is placed for 30 min; then, discharging the lithium ion battery at 0.2C until the discharge voltage reaches 3V; wherein capacity = current time; capacity = t × ⅆ of the lithium ion battery; volume =5.0mm 80mm 61mm of the lithium ion battery.
Lithium separation test:
and under the test condition of 25 ℃, carrying out 3C constant current charging on the lithium ion battery until the voltage is increased to the rated voltage of 4.45V, then transferring to constant voltage for charging until the current is reduced to 0.02C, standing for 20 min, and observing a fully charged negative electrode interface after the lithium ion battery is disassembled.
Definition of the negative first and second layers: and cutting the negative pole piece by using a plasma laser beam to obtain a section. EDS scanning is carried out on different areas of the cross section, distribution diagrams of element types and content of the areas with different thicknesses can be obtained, a straight line parallel to the current collector is drawn along the position of color mutation on the distribution diagrams, a first layer is arranged below the straight line along the thickness direction of the pole piece, and a second layer is arranged above the straight line.
Testing of doping elements:
qualitative analysis of doping elements: 1) carrying out X-ray diffraction (XRD) and Raman (Raman) spectrum tests on a sample material to be tested at normal temperature, and judging the types and bonding modes of doping elements by comparing the three-intensity peak positions and intensities of a standard spectrum; 2) and (3) scanning the material by an energy spectrometer (EDS), and judging the element types contained in the material according to the energy wavelength of the backscattered electrons.
Quantitative analysis of doping elements; 1) and performing EDS scanning on the sample material to be detected, and analyzing the content of the elements according to the energy intensity of the backscattered electrons.
Table 1 shows the respective parameters and evaluation results of examples 1 to 13 and comparative examples 1 to 2.
TABLE 1
| First of all Doping Element(s) | First doping element Mass of essence Ratio of ratios | Second doping Element(s) | Second doping element Mass of essence Ratio of division | Quality of the first layer With the first layer and the second layer Total mass of two layers Ratio of (2) | Separating lithium | First effect Rate of change | Energy density | |
| Comparative example 1 | 100% | Whether or not | 91.0% | 700 | ||||
| Comparative example 2 | N | 0.1% | N | 0.1% | 100% | Is that | 92.5% | 715 |
| Example 1 | N | 0.1% | N | 0.001% | 50% | Whether or not | 92.0% | 710 |
| Example 2 | S | 0.1% | S | 0.001% | 50% | Whether or not | 91.5% | 705 |
| Example 3 | N | 0.01% | N | 0.001% | 50% | Whether or not | 91.5% | 705 |
| Example 4 | N | 0.01% | N | 0.001% | 80% | Whether or not | 92.2% | 712 |
| Example 5 | N | 0.2% | N | 0.001% | 50% | Whether or not | 92.8% | 725 |
| Example 6 | P | 0.1% | P | 0.001% | 50% | Whether or not | 92.1% | 710 |
| Examples7 | B | 0.1% | B | 0.001% | 50% | Whether or not | 91.7% | 708 |
| Example 8 | N | 0.5% | N | 0.001% | 50% | Is that | 92.8% | 725 |
| Example 9 | N | 1% | N | 0.001% | 50% | Is that | 92.8% | 725 |
| Example 10 | N | 0.1% | N | 0.001% | 60% | Whether or not | 92.3% | 723 |
| Example 11 | N | 0.1% | N | 0.001% | 70% | Whether or not | 92.4% | 724 |
| Example 12 | N | 0.1% | N | 0.001% | 80% | Whether or not | 92.5% | 725 |
| Example 13 | N | 0.1% | N | 0.001% | 85% | Is that | 92.5% | 725 |
As can be seen from comparing examples 1 to 13 and comparative example 1, the energy density of the electrochemical device can be improved by employing a two-layer anode active material layer design in which a specific doping element is contained in the first layer, relative to a general anode active material layer.
As can be seen from comparing examples 1 to 13 and comparative example 2, by adopting a two-layer negative active material layer design in which the first layer contains the doping element and the second layer contains no or less doping element, the kinetic performance of the electrochemical device can be improved and the surface lithium deposition of the negative electrode sheet can be improved, relative to a negative active material layer containing the doping element as a whole.
As can be seen from comparing examples 1,3, 5, 8, and 9, when the mass percentage of the doping element in the first layer is decreased, the energy density of the electrochemical device is decreased accordingly, and when the mass percentage of the first doping element exceeds 0.5%, lithium deposition occurs more easily.
As can be seen from comparing example 1 and examples 10 to 13, the energy density of the electrochemical device increases as the ratio of the mass of the first layer to the total mass of the first layer and the second layer increases.
As can be seen from comparing examples 1,2, 6 and 7, doping the first layer with different doping elements can correspondingly improve the kinetic performance of the lithium ion battery.
As can be seen from comparing examples 3 and 4, the energy density of the lithium ion battery increases as the ratio of the mass of the first layer to the total mass of the first layer and the second layer increases.
The foregoing description is only exemplary of the preferred embodiments of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the disclosure herein is not limited to the particular combination of features described above, but also encompasses other combinations of features described above or equivalents thereof. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.
Claims (10)
1. An electrochemical device, comprising:
the negative pole piece comprises a negative pole current collector, a first layer and a second layer, wherein the first layer is positioned between the negative pole current collector and the second layer;
wherein the first layer comprises a first negative active material and the second layer comprises a second negative active material; the first negative electrode active material contains a first doping element, and the second negative electrode active material contains a second doping element;
a mass percentage of a first doping element in the first layer is greater than a mass percentage of a second doping element in the second layer, the first and second doping elements being the same, the first and second doping elements including at least one of S, N, P, B, Sn or Sb.
2. The electrochemical device according to claim 1, wherein the mass percentage of the first doping element in the first layer is 0.01% to 1%.
3. The electrochemical device according to claim 1, wherein the second doping element in the second layer is 0.001 to 0.01% by mass.
4. The electrochemical device according to claim 1, wherein the mass percentage of the first doping element in the first layer is 0.1% to 0.3%.
5. The electrochemical device of claim 1, wherein the first negative active material and the second negative active material each independently comprise at least one of graphite or hard carbon.
6. The electrochemical device according to claim 5, wherein the first negative active material and the second negative active material further each independently comprise a silicon-based material.
7. The electrochemical device according to claim 6, wherein the silicon-based material in the first layer is 1 to 30% by mass.
8. The electrochemical device according to claim 6, wherein the silicon-based material in the second layer is 0.1 to 4% by mass.
9. The electrochemical device according to claim 1, wherein a ratio of a mass of the first layer to a total mass of the first layer and the second layer is 40% to 80%, and a ratio of a mass of the second layer to a total mass of the first layer and the second layer is 20% to 60%.
10. An electronic device comprising the electrochemical device according to any one of claims 1 to 9.
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