CN117650227A - Negative electrode sheet and electrochemical device - Google Patents
Negative electrode sheet and electrochemical device Download PDFInfo
- Publication number
- CN117650227A CN117650227A CN202311790634.7A CN202311790634A CN117650227A CN 117650227 A CN117650227 A CN 117650227A CN 202311790634 A CN202311790634 A CN 202311790634A CN 117650227 A CN117650227 A CN 117650227A
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- Prior art keywords
- negative electrode
- active material
- equal
- lithium
- ion conductor
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- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 55
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- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 52
- 239000011734 sodium Substances 0.000 claims abstract description 48
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- 239000011572 manganese Substances 0.000 description 2
- 229940017219 methyl propionate Drugs 0.000 description 2
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- MBDUIEKYVPVZJH-UHFFFAOYSA-N 1-ethylsulfonylethane Chemical compound CCS(=O)(=O)CC MBDUIEKYVPVZJH-UHFFFAOYSA-N 0.000 description 1
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- NEILRVQRJBVMSK-UHFFFAOYSA-N B(O)(O)O.C[SiH](C)C.C[SiH](C)C.C[SiH](C)C Chemical compound B(O)(O)O.C[SiH](C)C.C[SiH](C)C.C[SiH](C)C NEILRVQRJBVMSK-UHFFFAOYSA-N 0.000 description 1
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- NDPGDHBNXZOBJS-UHFFFAOYSA-N aluminum lithium cobalt(2+) nickel(2+) oxygen(2-) Chemical compound [Li+].[O--].[O--].[O--].[O--].[Al+3].[Co++].[Ni++] NDPGDHBNXZOBJS-UHFFFAOYSA-N 0.000 description 1
- 239000006256 anode slurry Substances 0.000 description 1
- 229910052787 antimony Inorganic materials 0.000 description 1
- WATWJIUSRGPENY-UHFFFAOYSA-N antimony atom Chemical compound [Sb] WATWJIUSRGPENY-UHFFFAOYSA-N 0.000 description 1
- 229910021383 artificial graphite Inorganic materials 0.000 description 1
- 230000002238 attenuated effect Effects 0.000 description 1
- 239000000872 buffer Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
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- 229910052802 copper Inorganic materials 0.000 description 1
- 238000009831 deintercalation Methods 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000003487 electrochemical reaction Methods 0.000 description 1
- 239000011883 electrode binding agent Substances 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 230000001788 irregular Effects 0.000 description 1
- 150000002596 lactones Chemical class 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- 229910002102 lithium manganese oxide Inorganic materials 0.000 description 1
- MHCFAGZWMAWTNR-UHFFFAOYSA-M lithium perchlorate Chemical compound [Li+].[O-]Cl(=O)(=O)=O MHCFAGZWMAWTNR-UHFFFAOYSA-M 0.000 description 1
- 229910001486 lithium perchlorate Inorganic materials 0.000 description 1
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 description 1
- IGILRSKEFZLPKG-UHFFFAOYSA-M lithium;difluorophosphinate Chemical compound [Li+].[O-]P(F)(F)=O IGILRSKEFZLPKG-UHFFFAOYSA-M 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- VLXXBCXTUVRROQ-UHFFFAOYSA-N lithium;oxido-oxo-(oxomanganiooxy)manganese Chemical compound [Li+].[O-][Mn](=O)O[Mn]=O VLXXBCXTUVRROQ-UHFFFAOYSA-N 0.000 description 1
- URIIGZKXFBNRAU-UHFFFAOYSA-N lithium;oxonickel Chemical compound [Li].[Ni]=O URIIGZKXFBNRAU-UHFFFAOYSA-N 0.000 description 1
- MCVFFRWZNYZUIJ-UHFFFAOYSA-M lithium;trifluoromethanesulfonate Chemical compound [Li+].[O-]S(=O)(=O)C(F)(F)F MCVFFRWZNYZUIJ-UHFFFAOYSA-M 0.000 description 1
- 230000003446 memory effect Effects 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 230000005012 migration Effects 0.000 description 1
- 238000013508 migration Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000002429 nitrogen sorption measurement Methods 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- ZRZFJYHYRSRUQV-UHFFFAOYSA-N phosphoric acid trimethylsilane Chemical compound C[SiH](C)C.C[SiH](C)C.C[SiH](C)C.OP(O)(O)=O ZRZFJYHYRSRUQV-UHFFFAOYSA-N 0.000 description 1
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- 238000004513 sizing Methods 0.000 description 1
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 description 1
- BAZAXWOYCMUHIX-UHFFFAOYSA-M sodium perchlorate Chemical compound [Na+].[O-]Cl(=O)(=O)=O BAZAXWOYCMUHIX-UHFFFAOYSA-M 0.000 description 1
- 229910001488 sodium perchlorate Inorganic materials 0.000 description 1
- 159000000000 sodium salts Chemical class 0.000 description 1
- 229910001495 sodium tetrafluoroborate Inorganic materials 0.000 description 1
- XGPOMXSYOKFBHS-UHFFFAOYSA-M sodium;trifluoromethanesulfonate Chemical compound [Na+].[O-]S(=O)(=O)C(F)(F)F XGPOMXSYOKFBHS-UHFFFAOYSA-M 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
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- 239000007858 starting material Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- ZSDSQXJSNMTJDA-UHFFFAOYSA-N trifluralin Chemical compound CCCN(CCC)C1=C([N+]([O-])=O)C=C(C(F)(F)F)C=C1[N+]([O-])=O ZSDSQXJSNMTJDA-UHFFFAOYSA-N 0.000 description 1
- 238000005303 weighing Methods 0.000 description 1
Landscapes
- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
Abstract
The application discloses negative pole piece and electrochemical device, the negative pole piece includes negative pole current collector, negative pole active material layer and fast ion conductor layer, and negative pole active material layer sets up at least one side surface at the negative pole current collector, and fast ion conductor layer sets up at the surface on negative pole active material layer and covers negative pole active material layer, along the thickness direction of negative pole current collector, marks the thickness on negative pole active material layer as L ', marks the thickness on fast ion conductor layer as L, and L/(L' +L) =b, satisfies: b is less than or equal to 0.4. The negative electrode plate can solve the problem of lithium or sodium precipitation of a lithium ion battery or a sodium ion battery during high-current charging.
Description
Technical Field
The application relates to the technical field of batteries, in particular to a negative electrode plate and an electrochemical device.
Background
Since the lithium ion battery enters the market, the lithium ion battery has been widely applied due to the advantages of long service life, large specific capacity, no memory effect and the like. When the lithium ion battery is charged, lithium ions migrate to the negative electrode, and the potential of the negative electrode is more negative due to the too high potential caused by the rapid charging of a large current, the pressure of rapidly receiving lithium by the negative electrode is increased, and the tendency of generating lithium dendrites is increased, so that the negative electrode not only meets the dynamic requirements of lithium ion diffusion but also solves the safety problem caused by the aggravation of the generation tendency of the lithium dendrites during rapid charging. Also, sodium ion batteries can suffer from sodium precipitation during charging, resulting in the formation of sodium dendrites, which present the same problems and risks of lithium dendrites.
At present, quick-filling common solutions: (1) Nano-sizing particles of negative electrode material to make Li + The diffusion path of the anode material is shortened, but the specific surface area of the anode material is increased, so that more side reactions and gas production problems are brought; (2) The cathode is coated in a thin way, but the processing difficulty is high, the consumption of auxiliary materials can be increased, and the energy density of the battery is reduced; (3) Pore-forming or compaction is reduced, dynamics are improved, but the compaction density of the pole piece is reduced, and the energy density of the battery is reduced; (4) The multi-purpose linear ester in the electrolyte reduces the viscosity of the electrolyte and improves the dynamics, but the increase of the linear ester can bring about the problem of gas production.
Disclosure of Invention
In view of this, the present application provides a negative electrode tab and an electrochemical device, in which the negative electrode tab is disposed in the electrochemical device, so as to solve the problem of lithium or sodium precipitation during high-current charging (i.e., "fast charging") in which the charging time is shortened.
In a first aspect, the present application provides a negative electrode tab, the negative electrode tab including a negative electrode current collector, a negative electrode active material layer, and a fast ion conductor layer, the negative electrode active material layer being disposed on at least one side surface of the negative electrode current collector, the fast ion conductor layer being disposed on a surface of the negative electrode active material layer and covering the negative electrode active material layer. When the negative electrode plate is configured in the electrochemical device, the fast ion conductor layer of the negative electrode plate is contacted with the isolating film, so that the high-temperature circulation and high-temperature storage performance of the electrochemical device under the condition of high multiplying power are improved, and the long-circulation stability of the electrochemical device is improved.
In some embodiments, the anode active material layer includes an anode active material, the fast ion conductor layer includes a fast ion conductor, a thickness of the anode active material layer is denoted as L 'along a thickness direction of the anode current collector, a thickness of the fast ion conductor layer is denoted as L, and L/(L' +l) =b, satisfying: b is less than or equal to 0.4. When the ratio of the thickness of the fast ion conductor layer to the thickness of the negative electrode active material layer is in the range, the fast ion conductor in the fast ion conductor layer is in contact with the isolating film, so that ions can be embedded into the negative electrode active material layer fast, deposition of the negative electrode active material layer close to the surface of the isolating film in the negative electrode plate is avoided, deposition of the negative electrode active material layer close to the surface of the isolating film is a key problem for causing the fast charging performance of an electrochemical device to be reduced.
In some embodiments, the fast ion conductor comprises a niobium composite metal oxide, the mass percent of the negative electrode active material is noted as W '% based on the mass of the negative electrode active material layer, the mass percent of the niobium composite metal oxide is noted as w% based on the mass of the fast ion conductor layer, and W/(W' +w) =a; the method meets the following conditions: a is less than or equal to 0.5, and W is more than or equal to 80 and less than or equal to 95. The niobium composite metal oxide is an oxide of niobium and is Nb 2 O 5 Based on this, other metal oxides are co-dissolved to form a pure phase M-Nb-O compound, where M is other metal ion. The type and the content of the fast ion conductor are proper, which is more beneficial to the fast receiving of ions on the surface of one side of the negative electrode active material layer close to the isolating film, and the formation of dendrites is avoided.
In some embodiments, the following are satisfied: a/b is more than or equal to 1.3 and less than or equal to 2.3. When the value a, the value b and the value a/b are in the proper ranges, the electrochemical device is beneficial to achieving both high energy density and improvement of quick charge performance.
The technical proposal can be applied to lithium ion batteries and sodium ion batteries, and for lithium ion batteries, li is rapidly transmitted by utilizing the characteristic of a fast ion conductor of niobium composite metal oxide by coating a layer of niobium composite metal oxide on graphite + Avoid Li during fast charging + On the surface of graphite (close to isolationOne side surface of the membrane) to achieve the purpose of improving the quick charge performance of graphite. For sodium ion batteries, the metal is prepared by applying a layer of Na to the surface of, for example, hard carbon + Fast ion conductor for fast Na transmission by utilizing characteristics of fast ion conductor + Avoid Na during fast charging + Sodium precipitation caused by accumulation on the surface of hard carbon (the surface close to one side of the isolating film) can be realized, so that the purpose of improving the quick filling performance of the hard carbon is achieved.
Lithium ion battery
The lithium ion battery comprises a positive pole piece, an isolating film and a negative pole piece, wherein the negative pole piece comprises a negative current collector, a negative active material layer and a fast ion conductor layer, the negative active material layer comprises a negative active material, and the fast ion conductor layer comprises niobium composite metal oxide. The positive pole pieces and the negative pole pieces are stacked in a staggered mode, the isolating film is arranged between two adjacent positive pole pieces and the negative pole pieces, and the fast ion conductor layer of the negative pole piece is in contact with the isolating film.
In some embodiments, the negative electrode active material is a first negative electrode active material for a lithium ion battery, the first negative electrode active material including at least one of graphite, hard carbon, silicon oxygen, or silicon carbon.
In some embodiments, the niobium composite metal oxide includes a compound of formula T x Nb y M z O a′ Wherein T is selected from at least one of K, li, fe, V, W, cr, zr, al, mg, zn, cu, mo, na, ga, P, tc, si, ga, sn, ni, co, mn, sr, Y, in, na or Ti, M is selected from at least one of Al, ti, W, zr, nb, in, ru, sb, sr, Y, ni, co, mn, fe, gr, mo, tc, sn, ga, si, V or Mg, and T and M are different and satisfy: x/(x+y+z) is more than or equal to 0 and less than or equal to 0.6,1 and less than or equal to a'/(x+y+z) is more than or equal to 5, and z/(x+y+z) is more than or equal to 0 and less than or equal to 0.5.
The structures of Compound I are Wadsley-Roth section structure and bronze-like structure, which are favorable for Li + And (5) diffusion. In the charge and discharge process, the volume change of the unit cell is less than or equal to 10%, so that the compound I has good structural stability and good cycle performance. Solid phase diffusion of lithium ions in lithium battery cathodesCoefficient reduction is a main speed control step that causes deterioration of the capacity characteristics of the power battery. When the battery is charged rapidly, the diffusion process of lithium ions in the lithium battery cathode is blocked due to the small diffusion coefficient, so that 'lithium deposition' is easy to generate on the surface of cathode particles, and permanent damage is caused to the battery. The potential of the active material layer close to the surface of the isolating membrane in the negative electrode plate is lower, and the lithium separation risk is larger, so that the safety performance, the cycle performance, the gas production and the like of the lithium ion battery are further influenced. According to the method, the niobium composite metal oxide is introduced into the lithium electrode negative electrode piece, a layer of high-capacity high-adhesion lithium electrode material is coated on the current collector through a double-layer coating technology, and a second layer of niobium composite metal oxide material is coated on the basis, so that the niobium composite metal oxide is in contact with the isolating film, and the quick lithium intercalation and quick lithium ion conduction characteristics of the niobium composite metal oxide are utilized, so that the quick ion accepting capability of the active material layer close to the surface of the isolating film is improved. And further, the high-temperature circulation and high-temperature storage performance of the lithium ion battery under the condition of high multiplying power are improved, the lithium precipitation risk of the lithium electrode negative electrode plate is reduced, and the long-cycle stability of the lithium ion battery is improved. Namely, double-layer coating realizes fast ion transmission of an upper layer (fast ion conductor layer) and high energy density of a lower layer (negative electrode active material layer), and perfectly combines high energy density and fast charge double cores.
In some embodiments, the mass percentage of the niobium composite metal oxide is 88wt% to 92wt% based on the mass of the fast ion conductor layer, at which time the loss of energy density due to the use of the fast ion conductor can be reduced and satisfied: a is more than or equal to 0.1 and less than or equal to 0.3,0.05, b is more than or equal to 0.2, and a/b is more than or equal to 1.3 and less than or equal to 1.6. The lithium is separated out when the value a is too small (for example, less than 0.1) and the high-temperature cycle and the high-temperature storage performance under the high multiplying power are poor, because the smaller the value a is, the smaller the dosage of the fast ion conductor is, the exposed negative electrode active material layer is caused, and the improvement of the fast charging performance is not facilitated.
an excessively large value of a (e.g., greater than 0.3) reduces the energy density. Because the lithium intercalation voltage platform of the fast ion conductor is higher than that of graphite, the energy density of the battery can be reduced to a certain extent, and therefore, the fast ion conductor is used in a relatively small amount while the purpose of ion transmission is achieved. When the value a, the value b and the value a/b are all in the above ranges, the improvement of the quick charge performance of the lithium ion battery and the realization of high energy density are both facilitated.
In some embodiments, the negative electrode sheet has a compacted density of 1.79g/cm 3 To 2.4g/cm 3 . The magnitude of the compacted density is a synergistically adapted relationship with compound I, the larger the ratio of compound I in the fast ion conductor layer, the higher the compacted density, but the lower the energy density. For the fast ion conductor of the compound I, the compaction density is in the range, so that the energy density of the electrochemical device is improved. Preferably, the compacted density of the negative electrode plate is 1.79g/cm 3 To 2.28g/cm 3 。
In some embodiments, compound I has a specific surface area of 0.8m 2 /g to 20m 2 And/g. At this time, it is advantageous to further improve the high temperature cycle and the high temperature storage performance at a large magnification. Preferably, the specific surface area of the compound I is 0.8m 2 /g to 1.2m 2 /g。
In some embodiments, the plateau voltage of the negative electrode tab to lithium is 0.1V to 1.0V. Preferably, the plateau voltage of the negative electrode tab to lithium is 0.4V to 0.8V.
In some embodiments, the gram capacity of the negative electrode sheet per unit area in the lithium ion battery is 350-2000 mAh/g.
Sodium ion battery
The sodium ion battery comprises a positive pole piece, an isolating film and a negative pole piece, wherein the negative pole piece comprises a negative pole current collector, a negative pole active material layer and a fast ion conductor layer, the negative pole active material layer comprises a negative pole active material, and the fast ion conductor layer comprises niobium composite metal oxide. The positive pole pieces and the negative pole pieces are stacked in a staggered mode, the isolating film is arranged between two adjacent positive pole pieces and the negative pole pieces, and the fast ion conductor layer of the negative pole piece is in contact with the isolating film.
In some embodiments, the negative electrode active material is a second negative electrode active material for a sodium ion battery, the second negative electrode active material comprising at least one of hard carbon, antimony, and mixtures thereof.
In some embodiments, the niobium composite metal oxide includes a compound of the formula Na x′ A y′ Ti z′ O 2 At least one of the compounds II of (c), wherein a is selected from at least one of Ni, co, li, gr and satisfies: 0.6 < x ' < 0.7, y ' +z ' =1. The structure of the compound II is a P2 phase, and the structure can improve the transmission rate of sodium ions and maintain the integrity of a layered structure, and has excellent rate performance and cycle performance.
In some embodiments, the combined gram capacity of the negative electrode sheet per unit area in the sodium ion battery is 240 to 300mAh/g.
The application introduces Na into the sodium electrode negative electrode plate + The fast ion conductor of (2) is prepared by coating a layer of high-capacity high-adhesion sodium-electricity negative electrode material on a current collector by a double-layer coating technology, and then coating a second layer of Na + Fast ion conductor material, na + The fast ion conductor material contacts with the diaphragm by Na + The characteristics of rapid sodium intercalation and rapid sodium ion conduction of the rapid ion conductor improve the high-temperature circulation and high-temperature storage performance of the sodium ion battery under the condition of high multiplying power, reduce the risk of sodium precipitation of the negative plate, and improve the long-cycle stability of the sodium ion battery. The double-layer coating realizes the upper layer fast ion transmission, the lower layer high energy density, and perfectly combines the high energy density and the fast charge double cores.
In some embodiments, the mass percentage of the niobium composite metal oxide is 80wt% to 88wt% based on the mass of the fast ion conductor layer, at which time the loss of energy density due to the use of the fast ion conductor can be reduced and satisfied: a is more than or equal to 0.1 and less than or equal to 0.3,0.05, b is more than or equal to 0.2,2 and a/b is more than or equal to 2.3. and when the value a, the value b and the value a/b are in proper ranges, the improvement of high energy density and quick charge performance is realized.
In some embodiments, the negative electrode sheet has a compacted density of 1.2g/cm 3 To 2.1g/cm 3 . The magnitude of the compacted density is a synergistically adapted relationship with compound II, the larger the ratio of compound II in the fast ion conductor layer, the higher the compacted density, but the lower the energy density. For compoundsAnd II, the compacting density of the fast ion conductor is in the range, so that the energy density of the electrochemical device is improved. Preferably, the compacted density of the negative electrode plate is 1.6g/cm 3 To 1.7g/cm 3 。
In some embodiments, the specific surface area of compound II is 0.5m 2 /g to 10m 2 And/g. In order to realize better effect of rapidly transferring ions, the smaller the particles of the rapid ion conductor material are, the better the particles are, so that the migration path of the ions is short, but the particles are too small to bring about larger specific surface area, so that more side reactions are brought about, and the high-temperature cycle performance and the high-temperature storage performance are deteriorated. Preferably, the specific surface area of the compound II is 0.5m 2 /g to 5m 2 /g。
In some embodiments, the plateau voltage of the negative pole piece to sodium is 0.28V to 0.5V. Preferably, the plateau voltage of the negative pole piece to sodium is 0.36V to 0.4V.
In a second aspect, the application provides an electrochemical device, the electrochemical device includes an anode plate, an isolating film and the anode plate, the anode plate and the anode plate are stacked in a staggered manner, the isolating film is arranged between two adjacent anode plates and the anode plate, and a fast ion conductor layer of the anode plate is in contact with the isolating film.
According to the quick-charge type electrochemical device, the quick-ion conductor layer is arranged on the surface of the negative electrode active material layer, when the negative electrode plate is configured in the electrochemical device, the quick-ion conductor layer in the negative electrode plate is in contact with the isolating membrane, so that the capacity of the negative electrode active material layer for receiving ions (such as lithium ions and sodium ions) on one side, close to the isolating membrane, of the negative electrode active material layer is improved, and the quick-charge performance of the electrochemical device is further improved.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
When the lithium ion battery is charged, lithium migrates to the negative electrode, and the too high potential caused by the fast charging high current can lead to more negative potential of the negative electrode, at the moment, the pressure of rapidly receiving lithium by the negative electrode can become larger, and the tendency of generating lithium dendrites can become larger, so that the negative electrode not only needs to meet the dynamic requirement of lithium diffusion during fast charging, but also needs to solve the safety problem caused by the aggravation of the generation tendency of the lithium dendrites, and the main technical difficulty in the fact of the fast charging lithium ion battery is the intercalation of lithium ions in the negative electrode, especially the intercalation of lithium ions on the surface of the negative electrode close to one side of the isolating film.
In order to solve the technical problems, the application provides a negative electrode plate and an electrochemical device, wherein Li is achieved by coating a layer of fast ionic conductor material on a graphite electrode plate + Thereby solving the problem of lithium precipitation during graphite charging. The technology can be applied to lithium ion batteries and plays a great role in lithium battery application terminals. The method is also suitable for solving the sodium precipitation problem of the sodium ion battery, the global reserve of lithium resources is limited, and the content of lithium elements in the crust is only 0.0065%. With the development of new energy automobiles, the demand of batteries is greatly increased, the bottleneck of a resource end is gradually displayed, and the large-scale application of the lithium ion batteries is limited due to higher cost. Sodium resources are very abundant, crust abundance is 2.64%, which is 440 times of lithium resources, and sodium resources are widely distributed and are simple to refine. The role of sodium as a substitute for lithium has emerged and has gained increasing attention in the battery field. The sodium ion battery works similarly to the lithium ion battery, and the sodium ion battery also follows the operation principle of deintercalation (in the charging process, sodium ions are deintercalated from the positive electrode and intercalated into the negative electrode, and the discharging process is opposite). Thus, sodium precipitation also occurs in sodium ion batteries resulting in the formation of sodium dendrites. Dendrite problems in sodium ion batteries mean that sodium ions move between electrodes during charge and discharge of the battery, and dendritic sodium deposits are easily formed, resulting in internal short circuits or damage of the battery, thereby affecting the performance and life of the battery. The root cause of this problem is that the sodium ions move between the electrodes at a slow rate, and irregular deposits are easily formed on the electrode surfaces, thereby forming dendrites. The formation of sodium dendrites presents the same problems and risks of lithium dendrites.
The 'quick charge' for shortening the charge time must be charged by a large current, and the ions are required to be quickly chargedTo move to the anode, it is necessary to rapidly insert into the anode material (rapidly insert into the active material layer), otherwise, problems of sodium or lithium precipitation easily occur, and safety problems easily occur. The application uses the characteristic of the fast ion conductor of the niobium composite metal oxide to rapidly transfer Li mainly by coating a layer of niobium composite metal oxide on the outer surface (the surface on the side facing away from the current collector) of the anode active material layer + Or Na (or) + Avoid Li during fast charging + Or Na (or) + The lithium or sodium precipitation problem is caused by stacking on the surface layer of the anode active material layer, so that the purpose of improving the quick charge performance of the electrochemical device is achieved.
Electrochemical device
The application provides an electrochemical device, the electrochemical device includes positive pole piece, negative pole piece, barrier film and electrolyte, and the barrier film sets up between positive pole piece and negative pole piece.
Negative pole piece
The negative electrode pole piece comprises a negative electrode current collector, a negative electrode active material layer and a fast ion conductor layer, wherein the negative electrode active material layer is arranged on at least one side surface of the negative electrode current collector, the fast ion conductor layer is arranged on the surface of the negative electrode active material layer and covers the negative electrode active material layer, the thickness of the negative electrode active material layer is marked as L 'along the thickness direction of the negative electrode current collector, the thickness of the fast ion conductor layer is marked as L, and L/(L' +L) =b, so that the following conditions are satisfied: b is less than or equal to 0.4. Illustratively, the value of b ranges from 0.001, 0.005, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, or any two of the above ranges.
In some embodiments, the negative electrode active material layer comprises a negative electrode active material, the fast ion conductor layer comprises a fast ion conductor comprising a niobium composite metal oxide, the mass percent of the negative electrode active material is noted as W '% based on the mass of the negative electrode active material layer, the mass percent of the niobium composite metal oxide is noted as w% based on the mass of the fast ion conductor layer, and W/(W' +w) =a, satisfies: a is less than or equal to 0.5, and W is more than or equal to 80 and less than or equal to 95. Illustratively, the value of a ranges from 0.001, 0.005, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, or a range of any two of the foregoing values. Illustratively, the value of W ranges from 80, 82, 84, 85, 86, 88, 90, 92, 94, 95 or any two of the values recited above.
In some embodiments, the following are satisfied: a/b is more than or equal to 1.3 and less than or equal to 2.3. Illustratively, the value range of a/b is 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.1, 2.3 or a range of any two of the above values.
Others
Positive electrode plate
The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material in the positive electrode active material layer can be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate and compounds obtained by adding other transition metals or non-transition metals into the compounds.
For example, a metal foil or a porous metal plate, for example, a foil or a porous plate of a metal such as aluminum, copper, nickel, titanium, or iron, or an alloy thereof, such as Al (aluminum) foil, may be used as the positive electrode current collector.
The positive electrode sheet may be prepared according to a conventional method in the art.
Isolation film
The type of the above-mentioned separator is not particularly limited, and may be selected according to actual demands. For example, the separator film may be a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, and a multilayer composite film thereof, but is not limited to these materials.
Electrolyte solution
The electrolyte comprises an organic solvent, electrolyte lithium salt and an additive. The type of the material is not particularly limited, and the material can be selected according to actual requirements.
The above organic solvent is exemplified by one or more of Ethylene Carbonate (EC), propylene Carbonate (PC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), butylene Carbonate (BC), fluoroethylene carbonate (FEC), methyl Formate (MF), methyl Acetate (MA), ethyl Acetate (EA), propyl Acetate (PA), methyl Propionate (MP), ethyl Propionate (EP), propyl Propionate (PP), methyl Butyrate (MB), ethyl Butyrate (EB), 1, 4-butyrolactone (GBL), sulfolane (SF), dimethylsulfone (MSM), methylsulfone (EMS) or diethylsulfone (ESE), and preferably two or more.
Illustratively, the electrolyte lithium salt includes LiPF 6 Lithium hexafluorophosphate, liBF 4 Lithium tetrafluoroborate, liClO 4 (lithium perchlorate), liAsF 6 (lithium hexafluoroarsenate), liFeSI (lithium bis-fluorosulfonyl imide), liTFSI (lithium bis-trifluoromethanesulfonyl imide), liTFS (lithium trifluoromethanesulfonate), liDFOB (lithium difluorooxalato borate), liBOB (lithium bisoxalato borate), liPO 2 F 2 (lithium difluorophosphate), liDFOP (lithium difluorodioxalate phosphate) or LiTFOP (lithium tetrafluorooxalate phosphate). Exemplary electrolyte sodium salts include, naPF 6 Sodium hexafluorophosphate, naOTF (sodium trifluoromethanesulfonate), naTFSI (sodium bistrifluoro-methanesulfonimide), naBF 4 (sodium tetrafluoroborate), naBOB (sodium dioxaborate), naDFOB (sodium difluorooxaloborate) or NaClO 4 (sodium perchlorate) one or more of the following.
The above electrolyte may optionally further include other additives, which may be any additives that can be used as a lithium ion secondary battery, and the present invention is not particularly limited and may be selected according to actual needs. As an example, the additive may be one or more of Vinylene Carbonate (VC), ethylene carbonate (VEC), succinonitrile (SN), adiponitrile (ADN), 1, 3-propenesulfonic acid lactone (PST), tris (trimethylsilane) phosphate (TMSP), trimethyl borate (TMB), or tris (trimethylsilane) borate (TMSB).
The electrochemical device may be prepared according to a conventional method in the art. The positive electrode plate, the isolating film and the negative electrode plate are stacked in sequence, so that the isolating film is positioned between the positive electrode plate and the negative electrode plate to play a role in isolation, and an electrode assembly is obtained, or the electrode assembly can be obtained after winding; and placing the electrode assembly in a packaging shell, injecting electrolyte and sealing to obtain the electrochemical device.
The electrochemical device of the present application may include any device in which an electrochemical reaction occurs, and specific examples thereof include all kinds of primary or secondary batteries.
Example 1
Lithium ion battery
The lithium ion battery comprises a positive pole piece, an isolating film and a negative pole piece, wherein the negative pole piece comprises a negative current collector, a negative active material layer and a fast ion conductor layer, the negative active material layer comprises a negative active material, and the fast ion conductor layer comprises niobium composite metal oxide. The positive pole pieces and the negative pole pieces are stacked in a staggered mode, the isolating film is arranged between two adjacent positive pole pieces and the negative pole pieces, and the fast ion conductor layer of the negative pole piece is in contact with the isolating film.
In some embodiments, the negative electrode active material is a first negative electrode active material for a lithium ion battery, the first negative electrode active material including at least one of graphite, hard carbon, silicon oxygen, or silicon carbon.
In some embodiments, the niobium composite metal oxide includes a compound of formula T x Nb y M z O a′ Wherein T is selected from at least one of K, li, fe, V, W, cr, zr, al, mg, zn, cu, mo, na, ga, P, tc, si, ga, sn, ni, co, mn, sr, Y, in, na or Ti, M is selected from at least one of Al, ti, W, zr, nb, in, ru, sb, sr, Y, ni, co, mn, fe, gr, mo, tc, sn, ga, si, V or Mg, and T and M are different and satisfy: x/(x+y+z) is more than or equal to 0 and less than or equal to 0.6,1 and less than or equal to a'/(x+y+z) is more than or equal to 5, and z/(x+y+z) is more than or equal to 0 and less than or equal to 0.5. Preferably, compound I is selected from Nb 16 W 5 O 55 、Nb 18 W 16 O 93 、TiNb 2 O 7 、Nb 16 W 5 O 93 、Cr 0.5 Nb 24.5 O 62 、Ti 2 Nb 14 O 39 、TiNb 24 O 62 、TiNb 6 O 17 、Ni 2 Nb 34 O 87 、Cu 2 Nb 34 O 87 、Cr 0.5 Nb 24.5 O 62 、V 3 Nb 17 O 50 、Zn 2 Nb 34 O 87 、Al 0.5 Nb 24.5 O 62 、MoNb 12 O 33 、ZrNb 24 O 62 、AlNb 11 O 29 、Mg 2 Nb 34 O 87 、GaNb 11 O 29 、Mo 3 Nb 14 O 44 、CrNb 11 O 29 、HfNb 24 O 62 、FeNb 11 O 28 、GaNb 49 O 124 、NaNb 13 O 33 、Ni 2 Nb 34 O 87 、TiNb 6 O 17 、WNb 12 O 33 、LiNbO 3 、Li 3 NbO 4 、TiCr 0.5 Nb 10.5 O 2 、VNb 9 O 25 、KNb 5 O 13 、K 6 Nb 10.8 O 30 、PNb 9 O 25 、Nb 18 W 8 O 69 、Ti 2 Nb 10 O 29 、Cr 0.2 Fe 0.8 Nb 11 O 29 、Fe 0.8 Mn 0.2 Nb 11 O 29 、Fe 0.8 V 0.2 Nb 11 O 29 Or Cu 0.02 Ti 0.94 Nb 2.04 O 7 At least one of them. More preferably, compound I is selected from TiNb 2 O 7 、Nb 16 W 5 O 93 Or Nb (Nb) 16 W 5 O 55 At least one of them.
In some embodiments, the following are satisfied: a is more than or equal to 0.1 and less than or equal to 0.3. Illustratively, the value of a ranges from 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, or any two of the above values.
In some embodiments, the following are satisfied: b is more than or equal to 0.05 and less than or equal to 0.2. Illustratively, the value of b ranges from 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, or any two of the above values.
In some embodiments, the following are satisfied: a/b is more than or equal to 1.3 and less than or equal to 1.6. Illustratively, the value range of a/b is 1.3, 1.4, 1.5, 1.6 or a range of any two of the values recited above.
In some embodiments, the following are satisfied: w is more than or equal to 88 and less than or equal to 92. The value range of W is illustratively 88, 89, 90, 91, 92 or a range of any two of the values described above.
In some embodiments, compound I has a specific surface area of 0.8m 2 /g to 20m 2 And/g. Exemplary, the specific surface area of Compound I is 0.8m 2 /g、1m 2 /g、1.1m 2 /g、1.2m 2 /g、2m 2 /g、5m 2 /g、8m 2 /g、10m 2 /g、15m 2 /g、20m 2 /g or any two values above.
In some embodiments, the negative electrode sheet has a compacted density of 1.79g/cm 3 To 2.4g/cm 3 . Illustratively, the negative electrode sheet has a compacted density of 1.79g/cm 3 、1.8g/cm 3 、1.9g/cm 3 、2g/cm 3 、2.1g/cm 3 、2.28g/cm 3 、2.4g/cm 3 Or a range of any two values recited above.
In some embodiments, the plateau voltage of the negative pole piece to lithium is 0.1V to 1.0V. Illustratively, the plateau voltage of the negative pole piece to lithium is 0.1V, 0.2V, 0.4V, 0.6V, 0.8V, 1.0V, or a range of any two of the above values.
Example 2
Sodium ion battery
The sodium ion battery comprises a positive pole piece, an isolating film and a negative pole piece, wherein the negative pole piece comprises a negative pole current collector, a negative pole active material layer and a fast ion conductor layer, the negative pole active material layer comprises a negative pole active material, and the fast ion conductor layer comprises niobium composite metal oxide. The positive pole pieces and the negative pole pieces are stacked in a staggered mode, the isolating film is arranged between two adjacent positive pole pieces and the negative pole pieces, and the fast ion conductor layer of the negative pole piece is in contact with the isolating film.
In some embodiments, the negative electrode active material is a second negative electrode active material for a sodium ion battery, the second negative electrode active material comprising at least one of hard carbon, sb, and mixtures thereof.
In some embodiments, the niobium composite metal oxide includes a compound of the formula Na x′ A y′ Ti z′ O 2 At least one of the compounds II of (c), wherein a is selected from at least one of Ni, co, li, gr and satisfies: 0.6 < x ' < 0.7, y ' +z ' =1. Preferably, compound II is selected from Na 0.66 Ni 0.17 Co 0.17 Ti 0.66 O 2 、Na 2/3 Co 1/3 Ti 2/3 O 2 、Na 0.66 Li 0.22 Ti 0.78 O 2 、P2-Na 0.66 Li 0.22 Ti 0.78 O 2 、P2-Na 0.62 Cr 0.63 Ti 0.37 O 2 Or P3-Na 0.63 Cr 0.63 Ti 0.37 O 2 At least one of them.
In some embodiments, the following are satisfied: a is more than or equal to 0.1 and less than or equal to 0.3. Illustratively, the value of a ranges from 0.1, 0.13, 0.15, 0.18, 0.2, 0.23, 0.25, 0.28, 0.3, or any two of the above values.
In some embodiments, the following are satisfied: b is more than or equal to 0.05 and less than or equal to 0.2. Illustratively, the value of b ranges from 0.05, 0.08, 0.1, 0.13, 0.15, 0.18, 0.2, or any two of the above values.
In some embodiments, the following are satisfied: a/b is more than or equal to 2 and less than or equal to 2.3. Illustratively, the value range of a/b is 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3 or a range of any two of the foregoing values.
In some embodiments, the following are satisfied: w is more than or equal to 80 and less than or equal to 88. Illustratively, the range of values for W is 80, 82, 84, 86, 88 or a range of any two of the values described above.
In some embodiments, the specific surface area of compound II is 0.5m 2 /g to 10m 2 And/g. Exemplary, the specific surface area of Compound II is 0.5m 2 /g、0.8m 2 /g、1m 2 /g、3m 2 /g、5m 2 /g、8m 2 /g、10m 2 /g or any two values above.
In some embodiments, the negative electrode sheet is compactedThe degree of the reaction was 1.2g/cm 3 To 2.1g/cm 3 . Illustratively, the negative electrode sheet has a compacted density of 1.2g/cm 3 、1.4g/cm 3 、1.6g/cm 3 、1.7g/cm 3 、1.8g/cm 3 、2.0g/cm 3 、2.1g/cm 3 Or a range of any two values recited above.
In some embodiments, the plateau voltage of the negative pole piece to sodium is 0.28V to 0.5V. Illustratively, the plateau voltage of the negative pole piece to sodium is 0.28V, 0.3V, 0.33V, 0.36V, 0.38V, 0.4V, 0.45V, 0.5V, or a range of any two of the above values.
Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Unless otherwise indicated, the parts, percentages and ratios listed below are based on weight, and the starting materials used are either commercially available or synthetically obtained according to conventional methods.
(one)Preparation of lithium ion batteries
Example 1
(1) Preparation of positive electrode plate
The positive electrode active material nickel cobalt lithium manganate (molecular formula LiNi 0.5 Co 0.2 Mn 0.3 O 2 Abbreviated as NCM 523), an anode conductive agent acetylene black, an anode binder polyvinylidene fluoride (PVDF, weight average molecular weight of 2 x 10) 5 Up to 10X 10 5 ) Mixing according to the mass ratio of 94:3:3, adding N-methyl pyrrolidone (NMP) as a solvent, and stirring under the action of a vacuum stirrer to obtain the anode slurry with the solid content of 75wt% and uniform system. And uniformly coating the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with the thickness of 6 mu m, and drying at the temperature of 110 ℃ to obtain a positive electrode plate with a single-sided coated positive electrode active material layer. And repeating the steps on the other surface of the aluminum foil to obtain the positive electrode plate with the double-sided coating positive electrode active material layer. And cold pressing, cutting and welding the tab to obtain the anode plate with the specification of 74mm x 8511 mm for later use.
(2) Preparation of negative electrode plate
(2.1) preparation of first negative electrode slurry
A first negative electrode active material(artificial graphite), negative electrode conductive agent acetylene black, negative electrode binder styrene butadiene rubber (SBR, weight average molecular weight of 1×10) 5 Up to 1.1X10 5 ) Mixing thickener sodium carboxymethylcellulose (CMCNa) according to a mass ratio of 95:2:2:1, adding deionized water as a solvent, and stirring under the action of a stirrer until the solid content is 50wt% and the system is uniform to obtain a first negative electrode slurry.
(2.2) preparation of second negative electrode slurry
A second negative electrode active material (TiNb 2 O 7 BET of 1.2m 2 Per g), anode conductive agent acetylene black, anode binder styrene butadiene rubber (SBR, weight average molecular weight 1×10) 5 Up to 1.1X10 5 ) Mixing thickener sodium carboxymethylcellulose (CMCNa) according to a mass ratio of 95:2:2:1, adding deionized water as a solvent, and stirring under the action of a stirrer until the solid content is 70wt% and the system is uniform to obtain second negative electrode slurry.
(2.3) preparation of negative electrode sheet
And simultaneously coating the prepared first negative electrode slurry and second negative electrode slurry on one surface of a copper foil with the thickness of 8um by adopting a double coating process, and drying at 100 ℃ to obtain the negative electrode plate with the single-sided coating negative electrode active material layer. And repeating the steps on the other surface of the copper foil to obtain the negative electrode plate with the double-sided coating negative electrode active material layer. And cold pressing, cutting and welding the electrode lugs to obtain the negative electrode plate with the specification of 76mm x 867mm for standby.
(3) Preparation of a separator film
A Polyethylene (PE) porous film with the thickness of 8 mu m is used as a separation film, and the separation film is cut according to the sizes of the positive pole piece and the negative pole piece before use to obtain proper widths.
(4) Preparation of electrolyte
Lithium hexafluorophosphate as a lithium salt and a nonaqueous organic solvent (ethylene carbonate (EC): propylene Carbonate (PC): polypropylene (PP): diethyl carbonate (DEC) =1:1:1:1, mass ratio) were prepared into an electrolyte having a lithium salt concentration of 1.0mol/L under an environment having a water content of less than 10 ppm.
(5) Preparation of lithium ion batteries
Sequentially stacking the positive pole piece, the isolating film and the negative pole piece, enabling the isolating film to be positioned between the positive pole piece and the negative pole piece to play a role of isolation, and winding to obtain the electrode assembly. And placing the electrode assembly in an aluminum plastic film of a packaging bag, dehydrating at 80 ℃, injecting the electrolyte, packaging, and performing technological processes such as formation, degassing, shaping and the like to obtain the lithium ion battery.
Examples 2 to 15 the same as example 1 was carried out, except that the relevant preparation parameters were adjusted according to table 1.
Comparative examples 1 to 4 each have no fast ion conductor layer, and are the same as example 1 except that the relevant parameters were adjusted according to table 1.
(II)Preparation of sodium ion batteries
Example 16
(1) Preparation of positive electrode plate
In a drying room with the temperature of 25 ℃ and the relative humidity of less than or equal to 2 percent, the anode material NaNi is prepared 0.316 Fe 0.332 Mn 0.352 O 2 Mixing polyvinylidene fluoride as a binder and acetylene black as a conductive agent according to a mass ratio of 80:10:10, adding an N-methyl pyrrolidone (NMP) solvent, and fully stirring and mixing to form positive electrode slurry with a solid content of 72%; coating 200 μm (here thickness refers to the sum of the coating thicknesses coated on one or both sides of the aluminum foil) on an aluminum foil having a thickness of 10 μm using a doctor blade, followed by drying at 70 ℃ for 12 hours, followed by cold pressing; then, a small wafer having a diameter of 14mm was punched out to be used as a positive electrode sheet in an original state. (2) Preparation of negative electrode plate
(2.1) preparation of first negative electrode slurry
Mixing the first negative electrode active material hard carbon, the binder polyvinylidene fluoride and the conductive agent acetylene black according to the mass ratio of 94:3:3, adding the N-methyl pyrrolidone (NMP) solvent, and fully stirring and mixing to obtain the first negative electrode slurry.
(2.2) preparation of second negative electrode slurry
A second anode active material (P2-Na 0.66 Li 0.22 Ti 0.78 O 2 BET of 0.6m 2 /g) binder polyvinylidene fluorideEthylene and acetylene black serving as a conductive agent are mixed according to a mass ratio of 94:3:3, an N-methyl pyrrolidone (NMP) solvent is added, and the mixture is fully stirred and mixed to form positive electrode slurry with a solid content of 72%, so that second negative electrode slurry is obtained.
(2.3) preparation of negative electrode sheet
And simultaneously coating the prepared first negative electrode slurry and second negative electrode slurry on one surface of a copper foil with the thickness of 8um by adopting a double coating process, and drying at 100 ℃ to obtain the negative electrode plate with the single-sided coating negative electrode active material layer. And repeating the steps on the other surface of the copper foil to obtain the negative electrode plate with the double-sided coating negative electrode active material layer. And cold pressing, cutting and welding the electrode lugs to obtain the negative electrode plate with the specification of 76mm x 867mm for standby.
(3) Preparation of a separator film
A Polyethylene (PE) porous film with the thickness of 8 mu m is used as a separation film, and the separation film is cut according to the sizes of the positive pole piece and the negative pole piece before use to obtain proper widths.
(4) Preparation of electrolyte
Sodium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC): propylene Carbonate (PC): polypropylene (PP): diethyl carbonate (DEC) =1:1:1:1, mass ratio) are prepared into an electrolyte with a lithium salt concentration of 1.0mol/L under an environment with a water content of less than 10 ppm.
(5) Preparation of sodium ion batteries
Sequentially stacking the positive pole piece, the isolating film and the negative pole piece, enabling the isolating film to be positioned between the positive pole piece and the negative pole piece to play a role of isolation, and winding to obtain the electrode assembly. And placing the electrode assembly in an aluminum plastic film of a packaging bag, dehydrating at 80 ℃, injecting the electrolyte, packaging, and performing technological processes such as formation, degassing, shaping and the like to obtain the lithium ion battery.
Examples 17 to 26 the same as in example 1, except that the relevant preparation parameters were adjusted according to table 2.
Comparative example 5 was conducted in the same manner as in example 1 except that the relevant parameters were adjusted in accordance with table 2 without the fast ion conductor layer.
(III) test section
1. Gram Capacity test
The negative electrode sheets of each example and comparative example were taken, dried, punched into small disks with a diameter of 14mm, weighed, and the mass M of the active material was calculated from the duty ratio of the active material in the sheet, and then assembled with a Li sheet into a button half cell (coin cell), and then the half cell was subjected to a charge and discharge test on a blue cell test system (LAND CT 2001A). The charge and discharge test is carried out at a current density of 10mA/g, and the specific discharge flow is as follows: the capacity C of the half-cell was recorded at this time, gram capacity=c/M, with 10mA/g discharged to 5.0mV and after 5 minutes of resting, charged to 3.0V at 10 mA/g. And similarly, gram capacity test in the sodium ion battery is carried out by only replacing the lithium sheet with the sodium sheet.
2. Active material vs. Li+/Li operating Voltage test
The negative electrode sheets of each example and comparative example were taken, dried, punched into small disks with a diameter of 14mm, weighed, and the mass M of the active material was calculated from the duty ratio of the active material in the sheet, and then assembled with a Li sheet into a button half cell (coin cell), and then the half cell was subjected to a charge and discharge test on a blue cell test system (LAND CT 2001A). The charge and discharge test is carried out at a current density of 10mA/g, and the specific discharge flow is as follows: charging energy N and charging capacity C were read on a blue cell test system at 10mA/g to 5.0mV, after 5 minutes of rest at 10mA/g to 3.0V, active material vs li+/Li operating voltage=n/C. Active substance vs. Na+/Na operating voltage test: and the sodium ion battery is tested by only replacing the lithium sheet with the sodium sheet.
3. Specific surface area BET test
The graphite and niobium composite metal oxides in the negative electrode active materials of each example and comparative example were subjected to specific surface area test by nitrogen adsorption measurement using a specific surface area analyzer (Tristar ii 3020M). Wherein, the specific test is carried out according to the national standard GB/T19587-2017 'determination of specific surface area of solid substance by gas adsorption BET method'.
4. High temperature storage test at high magnification
The lithium ion batteries of each example and comparative example were subjected to constant current and constant voltage charging at a current of 4C under an environment of 25 ℃ until the upper limit voltage was 4.3V, and then stored at 85 ℃ for 12 hours, and the thickness change before and after storage of the lithium ion battery was recorded, and the thickness expansion ratio t= (thickness after storage-thickness before storage)/thickness before storage×100%. The storage performance is characterized by T, and the smaller the T value is, the better the storage performance is. When the lithium ion battery is charged at a high rate, if lithium is separated from the lithium ion battery, the gas yield of the lithium ion battery can be obviously increased. And (3) sodium ion battery testing, wherein the charging upper limit voltage is only adjusted to 4.0V, and the discharging cut-off voltage is only adjusted to 2.0V.
5. Energy density testing at high magnification
The test temperature was 25 ℃, the lithium ion batteries prepared in each example and comparative example were first charged to 4.3V at a constant current of 0.2C magnification, then charged to 0.05C at a constant voltage, left standing for 5 minutes, then discharged to 2.8V at 0.2C, the discharge energy thereof was recorded, and then the discharge energy density of 0.2C was calculated according to the formula, energy density (Wh/L) =discharge energy (Wh)/electrochemical device volume. The higher the energy density, the better. And (3) sodium ion battery testing, wherein the charging upper limit voltage is only adjusted to 4.0V, and the discharging cut-off voltage is only adjusted to 2.0V.
6. High temperature cycle test at high magnification:
the lithium ion batteries in comparative examples and examples of the present application were charged and discharged by the following procedure, and the cyclic capacity retention rate of the lithium ion batteries was calculated. First, in an environment of 45 ℃, a first charge-discharge cycle was performed. Constant-current and constant-voltage charging is carried out on the lithium ion battery by using the current of 4C until the upper limit voltage is 4.3V; then, the lithium ion battery was subjected to constant current discharge at a current of 0.5C until the cutoff voltage was 2.8V, and the discharge capacity C0 of the first cycle was recorded. Subsequently, 300 charge and discharge cycles were performed according to the charge and discharge flow described above, and the discharge capacity C300 at the 300 th cycle was recorded. The cyclic capacity retention of the lithium ion battery was calculated using the following formula: (C300/C0). Times.100%. When the lithium is separated during high-rate charging, the cycle of the battery can be remarkably and rapidly attenuated. In the sodium ion battery, the testing method is consistent, and the charging upper limit voltage is only required to be adjusted to be 4.0V, and the discharging cut-off voltage is only required to be adjusted to be 2.0V.
7. Pole piece compaction density test
Obtained by using active material per unit mass per unit volume. Weighing a current collector with the unit area of A and a negative electrode plate by using an electronic scale, wherein the weights of the current collector and the negative electrode plate are respectively recorded as M1 and M2; the thickness of the current collector and the positive plate was measured using a ten-thousandth ruler, and the thicknesses were recorded as C1 and C2, respectively. The compacted density of the positive electrode= [ (M2-M1)/(C2-C1) ]/a.
TABLE 1
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Note that: the "/" in Table 1 indicates no relevant preparation parameters.
In combination with table 1, the comparison between examples 1 to 3 shows that, when three compounds I of different molecular formulas are used, it can be seen that, when three niobium composite metal oxides of the same content but different molecular formulas are disposed on the surface of the negative electrode active material layer, the improvement of the fast charge performance and the compromise of the high energy density of the lithium ion battery can be achieved on the premise that the parameters a, b and a/b are all suitable. The values of a are further changed from the examples 4 to 6, and it can be seen that when the value of a is 0.05, both the high-temperature cycle and the high-temperature storage performance under a large multiplying power are obviously reduced, i.e. the too small value of a is not beneficial to the improvement of the quick charge performance of the lithium ion battery. When the value a is 0.5, the energy density of the lithium ion battery is obviously reduced, namely, the value a is too large, which is unfavorable for realizing high energy density. Examples 7 to 8 change the types of the anode active materials in the anode active material layer, and it can be seen that the technical scheme of the application is not only suitable for graphite anodes but also suitable for silicon-containing anodes, and the lithium ion battery with the silicon-containing anodes has the energy density of 800 at the highest multiplying power on the premise that the type of the compound I, the parameter a, the parameter b and the parameter a/b are all suitable, and the capacity retention rate of 300 circles at 4C 45 ℃ is also 87%, and the expansion rate of 12 hours stored at 4C 85 ℃ is only 8.6%. The specific surface area of the compound I is further adjusted in examples 10 to 12, and it can be seen that the comparative area is suitable, which is beneficial to further improving the quick charge performance of the lithium ion battery.
As is apparent from the fact that no fast ion conductor layer was provided on the surface of the negative electrode active material layer in each of comparative examples 1 to 3, the capacity retention rate of each of comparative examples 1 to 3 at 4c 45 ℃ for 300 cycles was not more than 55%, and the expansion rate thereof at 4c 85 ℃ for 12 hours was as high as 25% or more. Therefore, the quick charge performance of the lithium ion battery can be remarkably improved by arranging the quick ion conductor layers on the surfaces of the anode active material layers.
In comparative example 4, since the negative electrode active material layer contains both the negative electrode active material and the fast ion conductor, at this time, the fast ion conductor can improve the fast charge performance of the lithium ion battery, but the problem of the pole piece surface layer chromatography lithium cannot be well solved. The possible reasons are: the mixing mode leads to the fact that the cathode materials (graphite, silicon and the like) with poor dynamics are also on the surface layer of the pole piece, and when the pole piece is charged at a high rate, a great amount of lithium is not embedded into the cathode materials with poor dynamics, and is enriched on the surfaces of the cathode materials, so that the problem of lithium precipitation still exists. When the fast ion conductor is placed on the upper layer of the negative electrode material with poor dynamics, a large amount of lithium is quickly intercalated into the fast ion conductor material at first, so that the problem of lithium precipitation caused by the fact that lithium is not intercalated is avoided, and the fast ion conductor is transferred to the negative electrode material with poor dynamics (graphite, silicon and the like), so that the buffer time is provided for lithium intercalation of the negative electrode material on the lower layer.
TABLE 2
Note that: the "/" in Table 2 indicates no relevant preparation parameters.
In combination with table 2, the comparison between examples 16 to 18 shows that, when three compounds II of different molecular formulas are used, it can be seen that, when three niobium composite metal oxides of the same content but different molecular formulas are disposed on the surface of the negative electrode active material layer, the rapid charging performance of the sodium-ion battery can be improved and the high energy density can be achieved on the premise that the parameters a, b and a/b are all suitable. The values of a in examples 19 to 21 are further changed, and it can be seen that when the value of a is 0.05, the energy density of the sodium ion battery is obviously reduced, and the high-temperature cycle and the high-temperature storage performance under a large multiplying power are also obviously reduced, i.e. the small value of a is not beneficial to the improvement of the quick charge performance and the energy density of the sodium ion battery. When the value a is 0.5, the energy density of the sodium ion battery is obviously reduced, namely, the value a is too large, which is unfavorable for realizing high energy density. The specific surface area of the compound II is further adjusted in examples 22 to 24, and it can be seen that the comparative area is suitable, which is beneficial to further improving the fast charge performance of the sodium ion battery. The surface of comparative example 5 was not provided with a fast ion conductor layer, and it is apparent that the capacity retention rate of comparative example 1 at 4c 45 ℃ for 300 cycles was only 65%, and the expansion rate thereof at 4c 85 ℃ for 12 hours was as high as 30%. Therefore, the fast ion conductor layers are arranged on the surfaces of the anode active material layers, so that the fast charge performance of the sodium ion battery can be obviously improved.
The foregoing description of the preferred embodiment of the present invention is not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Claims (10)
1. The negative electrode plate is characterized by comprising a negative electrode current collector, a negative electrode active material layer and a fast ion conductor layer;
the fast ion conductor layer is arranged on the surface of the negative electrode active material layer and covers the negative electrode active material layer;
in the thickness direction of the negative electrode current collector, the thickness of the negative electrode active material layer is denoted as L ', the thickness of the fast ion conductor layer is denoted as L, and L/(L' +l) =b, satisfies: b is less than or equal to 0.4.
2. The negative electrode tab of claim 1, wherein the negative electrode active material layer comprises a negative electrode active material, the fast ion conductor layer comprises a fast ion conductor comprising a niobium composite metal oxide;
the mass percentage content of the anode active material is recorded as W'% based on the mass of the anode active material layer;
The mass percentage content of the niobium composite metal oxide is noted as W% based on the mass of the fast ion conductor layer, and W/(W' +w) =a;
the method meets the following conditions: a is less than or equal to 0.5, and W is more than or equal to 80 and less than or equal to 95.
3. The negative electrode tab of claim 2, wherein: a/b is more than or equal to 1.3 and less than or equal to 2.3.
4. The negative electrode tab of claim 3, wherein when the negative electrode active material is a first negative electrode active material for a lithium ion battery, at least one of the following conditions is satisfied:
(1) The niobium composite metal oxide comprises a compound having a molecular formula of T x Nb y M z O a′ Wherein T is selected from at least one of K, li, fe, V, W, cr, zr, al, mg, zn, cu, mo, na, ga, P, tc, si, ga, sn, ni, co, mn, sr, Y, in, na or Ti, M is selected from at least one of Al, ti, W, zr, nb, in, ru, sb, sr, Y, ni, co, mn, fe, gr, mo, tc, sn, ga, si, V or Mg, and T and M are different and satisfy: x/(x+y+z) is more than or equal to 0 and less than or equal to 0.6,1 and less than or equal to a'/(x+y+z) is more than or equal to 5, and z/(x+y+z) is more than or equal to 0 and less than or equal to 0.5;
(2)0.1≤a≤0.3；
(3)0.05≤b≤0.2；
(4)1.3≤a/b≤1.6；
(5)88≤W≤92。
5. the negative electrode tab of claim 4, wherein,the specific surface area of the compound I is 0.8m 2 /g to 20m 2 /g；
Preferably, the specific surface area of the compound I is 0.8m 2 /g to 1.2m 2 /g。
6. The negative electrode tab of claim 5, wherein at least one of the following conditions is satisfied:
(1) The compaction density of the negative electrode plate is 1.79g/cm 3 To 2.4g/cm 3 ；
Preferably, the compacted density of the negative electrode plate is 1.79g/cm 3 To 2.28g/cm 3 ；
(2) The platform voltage of the negative electrode plate to lithium is 0.1V to 1.0V;
preferably, the platform voltage of the negative electrode plate to lithium is 0.4V to 0.8V.
7. The negative electrode tab of claim 3, wherein when the negative electrode active material is a second negative electrode active material for a sodium ion battery, at least one of the following conditions is satisfied:
(1) The niobium composite metal oxide comprises Na with molecular formula x′ A y′ Ti z′ O 2 At least one of the compounds II of (c), wherein a is selected from at least one of Ni, co, li, gr and satisfies: 0.6 < x ' < 0.7, y ' +z ' =1;
(2)0.1≤a≤0.3；
(3)0.05≤b≤0.2；
(4)2≤a/b≤2.3；
(5)80≤W≤88。
8. the negative electrode tab of claim 7 wherein the specific surface area of compound II is 0.5m 2 /g to 10m 2 /g；
Preferably, the specific surface area of the compound II is 0.5m 2 /g to 5m 2 /g。
9. The negative electrode tab of claim 8, characterized by at least one of the following conditions being satisfied:
(1) The compaction density of the negative electrode plate is 1.2g/cm 3 To 2.1g/cm 3 ；
Preferably, the compacted density of the negative electrode plate is 1.6g/cm 3 To 1.7g/cm 3 ；
(2) The platform voltage of the negative electrode plate to sodium is 0.28V to 0.5V;
preferably, the platform voltage of the negative pole piece to sodium is 0.36V to 0.4V.
10. An electrochemical device comprising a positive electrode sheet, a separator, and the negative electrode sheet of any one of claims 1 to 9;
the positive pole pieces and the negative pole pieces are stacked in a staggered mode, the isolating film is arranged between two adjacent positive pole pieces and the negative pole pieces, and the fast ion conductor layer of the negative pole piece is in contact with the isolating film.
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