Patent Application
20250140807
The present disclosure relates to a secondary cell containing an anode that comprises a lithium ion storage layer. More particularly, the present disclosure relates to a secondary cell containing an anode comprising a substrate and a lithium ion storage layer, wherein the lithium ion storage layer is deposited on the substrate, a method for manufacturing the secondary cell, as well as a vehicle comprising such secondary cell.
Rechargeable batteries having high energy density and discharge voltage, in particular Li-ion batteries, are a vital component in portable electronic devices and are a key enabler for the electrification of transport and large-scale storage of electricity. To reach higher energy densities, new types of batteries are being developed.
State of the art Li-ion batteries typically consists of stacks of secondary cells, wherein each cell is composed of a cathode comprising a cathode current collector, an electrolyte, an anode comprising an anode current collector, and optionally a separator positioned between the anode and cathode.
In secondary cells where the anodes are made of graphite-based materials and a metal current collector, the cations are extracted from the cathode material and then diffuse from the cathode material through the electrolyte and intercalate into the anode material during charging. During discharge, this process is reversed.
In an effort to increase the energy density, the development has gone towards lithium metal batteries since lithium metal demonstrates a much higher specific capacity and a lower redox potential than graphite. In such batteries, the anode consists of a lithium metal whose corresponding cations carry the current in the electrolyte. However, the use of lithium metal poses several challenges during both manufacturing and cycling of the battery. Lithium metal reacts violently with water and extra precautions are therefore required during assembly of lithium metal battery cells, such as strict dry room conditions, strict waste management and modification of the equipment, to prevent spontaneous ignition. During cycling, lithium metal deposition and dissolution is associated with large volume changes which can reduce the cycling stability of the cell.
Another issue with secondary cells containing lithium metal is the formation of lithium metal dendrites when the corresponding lithium ion is deposited on the anode. That risk increases upon repetition of charging and discharging cycles or during particularly fast charging conditions. This hampers cycling stability, as some of these dendrites can break off and get electronically disconnected, hence reducing access to otherwise useful charge in the battery. Dendrites also increase the risk for short-circuits in the secondary cell, as dendrites can grow through the electrolyte and the separator, thereby putting the anode in contact with the cathode, resulting in serious fire hazards.
Increasing the uniformity of metal plating is thus important to reduce the risk of dendrite formation as well as to alleviate problems related to large volume changes. One way to achieve this is to confine lithium plating within a porous structure. The high surface area of the porous structure reduces the local current density and the risk of dendrites while the available pore volume allows for lithium deposition without further overall volume change in the cell. However, the porous structure adds weight to the battery reducing the advantages of using a lithium metal anode.
Hence, there is a need for more weight and volume efficient secondary cells.
An object of the present invention is to provide a secondary cell with homogenous Li metal deposition growth, wherein the cell contains an anode that comprises a lithium ion storage layer deposited on a substrate. A further object is the provision of a secondary cell that can be assembled without the insertion of any lithium metal.
The present invention thus provides a secondary cell with an improved cell safety level as the cell does not comprise a Li metal foil.
In a first aspect, the present invention relates to a secondary cell comprising an anode, a cathode, an electrolyte, and optionally a separator, characterized in that the anode comprises a substrate and a lithium ion storage layer comprising an active material or a composition of active materials, wherein the lithium ion storage layer is deposited on the substrate.
All aspects and embodiments disclosed herein can be combined with any other aspect and/or embodiment disclosed herein.
In one embodiment the secondary cell is a lithium secondary cell.
The lithium ion storage layer will function as extra lithium ion source for prolonged cycles, and/or increased number of cycles. In one embodiment of the present invention, the lithium ion storage layer comprises metallic lithium.
In one embodiment, the active material or the composition of active materials is selected from any one of non-graphitizing carbon, graphite, silicon, silicon alloy, silicon oxide (SiOx, wherein x is smaller than or equal to 2), silicon-carbon composite, a transition metal dichalcogenide (e.g. titanium disulfide (TiS2)), tin-cobalt alloy, lithium titanate oxide (LTO, Li4Ti5O12), MXenes (e.g. V2CTx, Nb2CTx, Ti2CTx, and Ti3C2Tx, wherein ‘T’ is a functional group, such as O, F, OH or Cl, and x is the number of functional groups and is typically a number from 1 to 4), or a combination of at least two of these.
The term “MXenes”, as used herein, represents two-dimensional inorganic compounds making up a-few-atoms-thick layers of transition metal carbides, nitrides, or carbonitrides. MXenes combine the metallic conductivity of transition metal carbides with a hydrophilic character.
In one embodiment, the lithium-ion storage layer or the anode comprises particles of the active material or composition of active materials.
In one embodiment, the active material or composition of active materials comprises particles, which are at least partially pre-lithiated. The term “pre-lithiated”, as used herein, means that lithium-ions exists in the layer before its first charge cycle.
In one embodiment, the lithium-ion storage layer or anode comprises Li15Si4, LiC6, Li13Sn5, or Li9Al4.
The particles making up the ion storage layer or anode give the layer a certain porosity. Plating of lithium takes place inside the pores, which reduces the overall volume change of the electrode during plating. In addition, a large specific surface area provides for a large reaction area for the plating to occur in comparison with a non-porous anode. This reduces the local current density and thereby the risk of dendrite formation. Preferably, the particles of the lithium ion storage layer have a specific surface area (SSA) of from 0.1 m2/g to 1000 m2/g, preferably from 1 m2/g to 700 m2/g.
In yet another embodiment, the anode has a porosity in the interval of from 10% to 90% of the total volume of the material, preferably from 15% to 75%, more preferably from 25 to 50%. In a preferred porosity interval of from 10% to 30%, lithiation of lithium ions into the active material or composition of active materials is facilitated. In another preferred porosity interval of from 30% to 70%, or from 30% to 60%, plating of lithium metal onto the active material or composition of active materials is facilitated. During lithiation, lithium ions are stored within the anode material or composition of active materials without occupying any of the void volume constituting the pores. Whereas, in accordance with the invention, the lithium plating takes place on the surface of the pores of the active material or composition of active materials, effectively filling the void volume without causing any substantial volume change of the anode. As the lithium ions from lithiation do not occupy the space where plating can occur, an increased areal capacity is reached.
With a conventional anode substrate that only allows for lithium plating, the areal capacity peaks at the maximum level of plating. With an anode of the invention, that capacity level is surpassed, as the anode's maximum plating level is complemented by lithiation. The anode according to the invention also reaches a higher Coulombic Efficiency (CE) as compared to a conventional anode on which only plating occurs, using the same amount of plated lithium (
During continuous cycling, plating of the top surface of the lithium ion storage layer or anode, may result in unfavorable dendritic growth of lithium metal. To prevent dendritic growth, the interfacial activity of the top surface is reduced in accordance with the invention, whereby lithium ion reduction on the top surface is reduced, while at the same time lithium-ions are allowed to migrate deep into the lithium ion storage layer or anode. As a result, lithium metal starts to deposit bottom-up in the lithium ion storage layer or anode, gradually filling the void spaces.
The void space is, in accordance with the present invention, large enough to accommodate the total volume of plated lithium. Hence, the porosity of the layer can be optimized through the choice of active material or composition of active materials, as well as the ratio between lithiated lithium ions and plated lithium metal. The skilled person is well equipped to make such an optimization. By adjusting the porosity, the ratio between lithiated lithium ions and plated lithium metal may be optimized such that the plated lithium can be contained within the porosity of the lithium-ion storage layer rather than being plated on top of the layer surface. The skilled person is well equipped to make such an optimization.
In one embodiment of the present invention, the lithium ion storage layer or anode has a minimum porosity as defined by formula (1),
wherein P is the porosity, r is the N/P ratio, Ca is the anode specific capacity, or in the case of a composition of active materials the weighted average anode specific capacity, [mAh/g], ρa is the anode active material density, or in the case of a composition of active materials the weighted average anode active material density, [g/cm3], CLi is the lithium specific capacity [mAh/g] (3862 mAh/g), and ρLi is the lithium density [g/cm3] (0.53 g/cm3). The term “N/P ratio” is used herein for the capacity ratio between the anode (the negative electrode) and cathode (the positive electrode). Finding the anode specific capacity for the anode material and lithium specific capacity is common knowledge in the field.
In one embodiment the anode loading amount to the cathode loading amount (N/P ratio) is 0.01 to 0.99, preferably 0.25 to 0.75, more preferably 0.3 to 0.5.
In one embodiment the lithium ion storage layer or the anode has a porosity in the range of P to 1.25*P, where P is defined as the porosity according to formula (1).
In one embodiment of the present invention a functional layer is at least partially, optionally fully, coated on the particles of the lithium storage layer. The functional layer is suitable for lithium metal deposition and may promote a homogenous lithium metal deposition growth. Preferably, the functional layer comprises surface functional group, for example, OH, COOH, CSOH, CONH2, CSNH2, NH, NH2, SH, CN, NO2 and triazolium; non-graphitizing carbon; a metal or metalloid, for example Si, Sn, Al, Zn, Ag, In, Mg; a metal or metalloid oxide, for example, Al2O3, LiAlO2, ZnO, MnO2, Co3O4, SnO2, SiOx (x smaller than or equal to 2), V2O5, CuxO (1≤x≤2), TiO2, Li2O, Li2O2, ZrO2, MgO, Ta2O5, Nb2O5, LiAlO2, Li7La3Zr2O12 (LLZO), Li4Ti5O12 (LTO), B2O3, Li3BO3—Li2CO3; a metal fluoride, for example AlF3, LiF; a metal phosphate, for example AlPO4, Li3PO4, Li1.3Al0.3Ti1.7(PO4)3 (LATP); piezoelectric material, such as BaTiO3, or PbZrxTi1-xO3 where x is any number between 1 and 10; a metal hydroxide, such as AlO(OH) (boehmite), Mg(OH)2, Al(OH)3; a metal or metalloid nitride, such as AlN, BN, Si3N4; Al(NO3)3; BaSO4; or a polymer or polymer electrolyte, containing for example polyvinylidene fluoride (PVDF), preferably in its beta phase, PVDF-HFP, PMMA, PEO, polysiloxane for example PDMS, lithium polyacrylate (Li-PAA); and mixtures thereof.
In one embodiment of the present invention the substrate is a current collector.
The substrate may be selected from any one of metal foil or metal mesh, such as copper foil or copper mesh; a polymer coated with a conducting material, preferably a metal; a graphite sheet, carbon nanotubes (CNT), graphene, graphene oxide, carbon nanofibers, and carbon paper.
In one embodiment of the present invention the anode does not comprise any lithium metal when the secondary cell is in its uncharged state. Preferably, the secondary cell does not comprise any lithium metal when the secondary cell is in its uncharged state.
In one embodiment of the present invention, the electrolyte is a liquid electrolyte comprising at least one lithium salt and at least one or more solvents selected from the group consisting of carbonate solvents and their fluorinated equivalents, diC1-4 ethers and their fluorinated equivalents and ionic liquids. The lithium salt is preferably one or more selected from the group consisting of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (fluorosulfonyl) (trifluoromethanesulfonyl) imide (LiFTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium (pentafluoroethanesulfonyl)(trifluoromethanesulfonyl)imide (LiPTFSI), lithium trifluoromethanesulfonate (LiOTf), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorobis(oxalato)phosphate (LiDFOP), lithium tetrafluoro(oxalato)phosphate (LiTFOP), lithium tetrafluoroborate (LiBF4), lithium nitrate (LiNO3) lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI). The solvent is preferably selected from the group consisting of 1,2-dimethoxyethane (DME), N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR13-FSI), N-propyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13-TFSI), 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14-FSI), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14-TFSI), 1-ethyl-3-methylimidazolium 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM-FSI), bis(trifluoromethanesulfonyl)imide (EMIM-TFSI), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), and propylene carbonate (PC), and their fluorinated equivalents.
In an alternative embodiment of the present invention, the electrolyte is a solid electrolyte comprising Li2S—P2S5; Li3PS4; Li7P3S11; LLZO-based materials, for example Li7La3Zr2O12, Li6.24La3Zr2Al0.24O11.98, and Li6.4La3Zr1.4Ta0.6O12; Li0.34La0.56TiO3 (LLTO); Li1.3Al0.3 Ti1.7 (PO4)3 (LATP); thio-LISICON for example Li10MP2X12 (M=Si or Ge; X═S or Se); lithium argyrodite Li6+yMyIVM1-yVS5X (X═Cl, Br, or I; MIV is a group IV element for example Si, Ge, or Sn; MV is a group V element for example P or Sb, and 0≤y≤1); polymer-based solid electrolytes, for example PEO-LiTFSI mixtures; lithium hydrido-borates LixByHz (x=1 or 2, 1≤y≤12, 4≤z≤14) and lithium hydrido-carba-borates LiCxByHz (x=1 or 2, 9≤y≤11, 12≤z≤14).
In a second aspect, the present invention relates to a vehicle comprising a secondary cell according to the first aspect of the present invention.
In a third aspect, the present invention relates to a method for manufacturing a secondary cell according to the first aspect of the present invention, comprising assembling the cell without inserting any lithium metal. This means that you do not have to handle any lithium metal during manufacture, which simplifies the manufacturing process. For example, no special equipment modification or dry room conditions will be required to avoid ignition. This also entails an improved production speed as well as a reduced cost for manufacturing.
In a fourth aspect, the present invention relates to a secondary cell comprising an anode, a cathode, optionally a separator, and an electrolyte, characterized in that the anode comprises an active material or a composition of active materials in multiple layers.
In one embodiment, the anode comprises at least two different layers, wherein the layers have different exchange current densities of lithium plating. In one embodiment, the anode comprises from 3 to 5 layers. Each layer of the 3 to 5 layers may have a different exchange current density of lithium plating.
In one embodiment, the anode does not include a separate current collector layer.
In one embodiment, the anode layer closest to the separator has a surface with lower exchange current density of lithium plating compared to the other anode layer(s).
In one embodiment, each layer of the anode has a different coating, or wherein one layer is not coated and the remainder of the layers each has a different coating. The coating may be selected from the list of functional layers hereinabove.
In one embodiment, the particles, and/or coating(s), have been functionalized with a moiety chosen from the group consisting of OH, COOH, CSOH, CONH2, CSNH2, NH, NH2, SH, CN, NO2 and triazolium.
In one embodiment, there is a different active material or composition of active materials in each layer of the anode.
In one embodiment, the active material or composition of active materials of at least one layer comprises metallic lithium.
In one embodiment, the active material or composition of active materials of each individual layer has been chosen from the group consisting of non-graphitizing carbon, graphite, silicon, silicon oxide (SiOx, x smaller than or equal to 2), silicon-carbon composite, a transition metal dichalcogenide (e.g. titanium disulfide (TiS2)), tin-cobalt alloy, lithium titanate oxide (LTO, Li4Ti5O12), Mxenes (e.g. V2CTx, Nb2CTx, Ti2CTx, and Ti3C2Tx), or a combination of at least two of these.
In one embodiment, the anode comprises an electronically insulating film coating the layer closest to the separator.
In one embodiment, the electronically insulating film comprises a material that has been chosen from the group consisting of Al2O3, Piezoelectric materials (e.g. BaTiO3, PbZrxTi1-xO3 where x is any number between 1 and 10), Li2O, LiF, a fluoropolymer for example polyvinylidene fluoride (PVDF), preferentially in its beta phase, PVDF-HFP, PMMA, PEO, polysiloxane, for example PDMS, lithium polyacrylate (Li-PAA), and mixtures thereof.
In one embodiment, one of the layers of the anode is a current collector. Alternatively, the anode comprises a separate current collector. The separate current collector may be in the form of a foil, or in the form of a mesh.
In one embodiment, the foil is coated with a material that has been chosen from the group consisting of C, Si, Sn, Al, Zn, Ag, In, Mg.
In a fifth aspect, the present invention relates to a secondary cell comprising an anode, a cathode, optionally a separator, and an electrolyte, characterized in that the anode comprises particles of an active material or a composition of active materials, and a current collector, in one single structure, wherein the structure comprises carbon, silicon, and/or metal oxide(s), and that the anode does not comprise any additional current collector.
In one embodiment, the structure consists of a material selected from the group consisting of carbon, silicon, and/or metal oxide(s).
In one embodiment, the anode constitutes one layer.
In one embodiment, the anode comprises at least two anode layers, at least one anode layer comprising an active electrode material or composition of active materials, and a current collector, in one single structure, and wherein the layers have different exchange current densities of lithium plating.
In one embodiment, the anode layer closest to the separator has a surface with lower exchange current density of lithium plating compared to the other anode layer(s).
An anode comprising >96% commercial grade artificial graphite with a reversible intercalation capacity of >350 mAh/g, or 2 mAh/cm2, was used. The anode was coated, after which it was left uncalendared, giving a porosity of from 45% to 55%. As the anode was charged to 4 mAh/cm2, the deposition of lithium metal was 2 mAh/cm2, giving a N/P ratio of 0.5. A two-electrode half-cell was created using the above-mentioned anode as the working electrode and lithium metal in large excess as the counter electrode. The electrolyte used was constituted LiFSI:Dimethoxyethane (DME): 1,1,2,2-Tetrafluoroethyl 2,2,3,3-Tetrafluoropropyl Ether (TTE) in a 1:1.2:3 molar ratio.
A 2nd cycle charge and discharge curve of the above-mentioned anode under galvanostatic cycling conditions is shown in
Coulombic Efficiency (CE) for lithium metal plating and stripping on a bare copper foil was compared with CE for lithiation and plating, and de-lithiation and stripping on the anode described in Example 1. The total amount of plated lithium, 2 mAh/cm2, was the same for both electrodes. For the bare copper foil, the total capacity was 2 mAh/cm2, while the anode described in Example 1 had a total capacity of 4 mAh/cm2. This higher capacity is due to the additional 2 mAh/cm2 being available through lithiation.
A cell was assembled with a lithium nickel manganese cobalt oxide cathode (NMC) with a high nickel content (>80% Ni), an anode as described in Example 1, and an electrolyte consisting of LiFSI:DME:TTE in a 1:1.2:3 molar ratio. The cathode had an areal capacity of 4 mAh/cm2, and the anode had an areal capacity of 2 mAh/cm2, giving a N/P ratio of 0.5. Half the charge capacity of the anode was in the form of plated lithium onto lithiated graphite.
The cell was cycled at a charge rate of 4 mA/cm2 and discharged at 2 mA/cm2. Slower cycling was performed every 50th cycle for assessment of the cell capacity at lower discharge rates. The capacity as a function of the cycle number is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2250160-5 | Feb 2022 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/053897 | 2/16/2023 | WO |
