Patent Application
20220302532
None.
The invention relates to the field of Li-ion batteries. More specifically, the invention relates to the field of flexible Li-ion batteries used for flexible electronics.
The advancement of flexible electronics has stimulated intensive efforts to search for corresponding energy storage devices that match their flexibility and bendability. Li-ion batteries are of great interest for development of flexible energy storage devices due to their high energy densities, layered cell structures, and possibly minimal amount of liquid involved.
A plausible approach to flexible energy storage devices is to develop flexible electrodes followed by integration of the electrodes into flexible devices. In this regard, tremendous efforts have been given in this area, including development of flexible electrodes and polymer electrolytes for Li-ion batteries or supercapacitors. The general approach to the development of flexible electrodes is having appropriate nanostructured active electrode materials embedded in or composited with a flexible substrate that may or may not be electrochemically active. For example, carbon nanotubes (CNTs), graphenes, carbon fibers, and carbon cloths have been used as the flexible substrates for making flexible Li-ion anodes and cathodes. These flexible electrodes do improve device flexibility; however, have significant limitations. The flexible electrodes are typically stacked and folded to form a device, which lacks sufficient adhesion between electrode layers to hinder delamination when devices are subject to repeated bending or folding. New approaches to fabrication flexible Li-ion batteries or supercapacitors, including lamination, vacuum infiltration, coating, winding, or printing, have been investigated to form flexible energy storage devices of various configurations; however, none of them seem to be viable for large scale mass production.
In recent years, efforts have been made to improve performances of Li-ion batteries and supercapacitors involving utilization of metal mesh instead of metal foil as current collectors. Shi, et al. reported in a research article (Nano Energy, 2014, 6, 82-91) a flexible supercapacitor, prepared by deposition of carbon materials on stainless steel (SS) mesh, followed by assembly of a pair of mesh electrodes sandwiching a separator that is wetted with an organic electrolyte. Unfortunately, due to lack of sufficient adhesion between electrodes and separator, repeated bending may lead to failure of the supercapacitor due to layer separation. Chen disclosed a 3-D Li battery and a supercapacitor in a US patent (U.S. Pat. No. 9,905,370), where ultrafine metal mesh (UMM) was used as current collector. Thin films of electrode materials and solid state electrolytes were sequentially deposited onto the surfaces of the ultrafine metal mesh wires, forming UMM-based electrodes. The UMM-based anodes and cathodes were alternately stacked and laminated using the electrolyte as adhesive, forming mesh-based 3-D energy storage devices for better electrochemical and mechanical performance characteristics. The metal mesh substrates along with the laminated coating structures of the electrode materials and polymer electrolytes, forming a micro-composite structure, impart certain degrees of flexibility to the 3-D Li-ion batteries and supercapacitors; however, insufficient for substantial folding or bending.
These mesh-based electrodes, compared with conventional foil-based electrodes, allow loading of more electrode materials for improved performance characteristics due to higher porosity of mesh. These include higher energy and power densities. Additionally, a mesh substrate, having pore structures and high surface area, promotes better bonding between electrode materials and the substrate. The novel structures of mesh-based energy storage devices disclosed in the US patent (U.S. Pat. No. 9,905,370) also allow significant improvement over device flexibility, because the energy storage device is a metal wire reinforced composite having a continuous polymer electrolyte matrix. This improves flexibility and reduces risk of delamination upon bending or folding. However, it must be realized that polymer electrolytes are not intended for structural applications, they may not have the mechanical strength to withstand repeated bending or folding of a flexible device. Therefore, additional features of the flexible energy storage devices were introduced to significantly improve flexibility and bendability of the devices as disclosed in a US patent application (US 2020/0321619 A1). Owing to the open structure of the metal mesh, a flexible packaging material was introduced, as a patterned, well distributed matrix phase of the mesh-based energy storage device, which significantly improved device flexibility and bendability.
The flexible energy storage devices disclosed in US patent application (US 2020/0321619 A1), however, have at least one patterned mesh-based anode and one patterned mesh-based cathode that are prepared by depositing of anode and cathode materials respectively onto separate metal mesh current collectors, followed by lamination of the two patterned electrodes that must be aligned well to each other, to ensure the flexible packaging material to bond to themselves through the open pore structures of the anode and the cathode. This, of course, improves resistance to delamination due to the flexibility and mechanical strength of the packaging material; however, it may still delaminate as this is still a two layered structure that some areas of the two coated mesh sheets are still bonded with mechanically weaker polymer electrolyte.
These and other objectives are achieved in the present invention by 1) utilization of a metal mesh as substrate and current collector, and 2) sequentially deposition of patterned coatings on metal mesh wires of a first electrode, an electrolyte, a second electrode, a metal coating as second current collector, and a flexible packaging material, to produce a single mesh based Li-ion battery.
Accordingly, it is an object of the present invention to claim a flexible, foldable Li-ion battery by sequential deposition of a patterned electrode material, an electrolyte, a second electrode material, a second metal current collector and a flexible packaging material on a flexible metal mesh substrate. It is another objective of the invention to further disclose the flexible Li-ion battery with features for folding and flexing functionalities. The coatings of the electrode, the electrolyte, the second electrode, and the second current collector are cylindrical in nature around metal mesh wire, which improve resistance to delamination between the layers upon repeated bending. There is at least one primary linear strip of flexible packaging material phase in the device, where only metal mesh is embedded, which facilitates folding of the claimed energy storage device along the strip axis. The primary strip or strips may divide the claimed Li-ion battery into two or more sub cells, which may be considered being connected in parallel.
The principle of the present invention may be understood with reference to the detailed description, in conjunction with the accompanying drawings, in which:
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Like in previously disclosed 3-D mesh-based energy storage devices (Chen, U.S. Pat. No. 9,905,370 and US 2020/0321619 A1), the electrode coatings adhere more strongly to metal wire surfaces than they do to metal foil. This is because cylindrical coatings on mesh wires have a closed structure and mesh has higher surface area than foil. Likewise, subsequent electrolyte coatings are bonded more strongly on the cylindrical electrode coatings. This is a great attribute for flexible electrodes, as the strong adhesions of the coatings significantly hinder delamination between these layers from repeated bending or folding.
Contrary to previously disclosed mesh-based flexible Li-ion batteries (Chen, U.S. Pat. No. 9,905,370 and US 2020/0321619 A1) that the first electrode (12) and second electrode (16) are deposited on separate metal mesh and aligned and laminated subsequently, the present invention has the first electrode (12) and second electrode (16) on the same metal mesh wire, which may lead to a thinner battery with more structural flexibility and eliminate possibility of delamination between two coated metal meshes. It is worth noting that battery 30 is essentially a metal wire/fiber reinforced inorganic/organic/metal composite, which may provide the battery with significantly improved overall electrochemical and structural performance.
Li-ion batteries, as energy storage devices, commonly use a metal oxide as cathode and a carbon material as anode. In the present invention, the first electrode may be a Li-ion anode and the second a cathode, or vice versa. In one embodiment of the invention, the first electrode may not be present initially, instead, upon initial charge, it is formed as a thin layer of Li metal deposited at the interface of the metal wire and the electrolyte, when the second electrode is a Li-ion cathode.
In another embodiment where the first electrode is a cathode, the second electrode may not be present initially and is formed at the interface of the electrolyte and the metal film current collector upon initial charge. This and the previous embodiments are preferred in the invention as they may exemplify a reduced total thickness and simplified fabrications of the device.
While in other embodiments of the invention, both first and second electrodes are required to be present in the beginning. Any suitable Li-ion battery cathode materials may be used in the first or second electrode layer, with LiCoO2, LiNiO2, LiMn2O4, LiFePO4, or LiNixCoyMnz, as an example. Any suitable Li-ion anode material may be used in the first or second electrode layer in the invention, with graphite, Si, or LiTiO (Li4Ti5O12, spinel) as an example. Any suitable polymer or ceramic electrolytes may be used in the electrolyte layer in the invention. Any suitable metal may be used in the second electrode current collector layer, with Al, Cu, Ni, Pt, or Au, as an example.
A flexible polymeric packaging materials may be used to enclose and/or infiltrate the multilayer coated mesh. Any suitable flexible polymeric materials may be used to enclose the device, with polysiloxane, polyurethane, polyester (PET), polyimide (PI), polyethylene naphthalate (PEN), polyetherimide (PEI), and fluropolymers or copolymers as an example. The thickness of the flexible polymer packaging layer (T) may range, for example, from 1 to 100 microns. It is worth noting that the packaging material fills all of the porous structures of the primary folding strip (20A), the unblocked mesh holes (20B), and the edges of the coated mesh wires, which transforms the energy storage device into a flexible, metal mesh/fiber reinforced ceramic/polymer composite.
The first electrode material layer may be deposited in a number of ways, including wet chemical, vapor, or electrochemical techniques. The first electrode layer on mesh wire surface may not cover the mesh holes fully, and the thickness of first electrode may range, for example, from 1 micron to 25 microns. The electrolyte material layer may be deposited in a number of ways, including wet chemical, vapor, or electrochemical techniques and it may not cover the mesh holes fully, and the thickness of electrolyte may range, for example, from 0.5 micron to 25 microns. The second electrode material layer may be deposited in a number of ways, including wet chemical, vapor, or electrochemical techniques and it may not cover the mesh holes fully, and the thickness of the layer may range, for example, from 1 micron to 25 microns. The current collector layer for the second electrode may be deposited in a number of ways, including wet chemical, vapor, or electrochemical techniques and it may or may not cover the mesh holes fully, and the thickness may range, for example, from 0.1 micron to 10 microns.
Having generally described the invention, the following examples serve to illustrate the preferred embodiments of the present invention and should not be construed as limiting the scope of the invention:
A Ni mesh (3×6 cm2, opening 5 microns, wire diameter 2 microns) was first soaked in a NaOH solution (1.0 M) at 60° C. for 16 hrs, then cleaned by repeated soaking and sonicating in 50% isopropyl alcohol (IPA) for 16 hrs, and dried in an oven at 120° C. for 1 hr. The mesh sample was clamped with four Al spacer bars (0.5 cm×0.5 cm×5 cm) at the two ends of the rectangular mesh and suspended on top of an Al plate (5×5 cm2) using 4 small screws at each of the four corners of the square Al plate. The suspended mesh on Al plate was placed on a spin coater.
A LixPOyNz (LiPON-like) ceramic electrolyte precursor solution was prepared as follows: A solution of lithium acetate, (Li(CH3COO)2.2H2O, 5.10 g, 0.05 mol, in 100 mL of 50% IPA) was mixed with a solution of H3PO4 (49.5%, 0.017 mol) and ethylenediamine (15.0 g, 0.25 mol) in a 250-mL flask at room temperature. The resulting solution was heated under reflux for 6 hrs and cooled to room temperature, ready for subsequent spin-coating.
The precursor solution was added onto the surface of the mesh that was suspended on top of the Al plate and placed on a spin-coater. The precursor solution was allowed to conditioning for 30 seconds, permitting complete wetting on both sides of the mesh, followed by spinning at 1200 rpm for 15 seconds. The coating was first dried in air at 160° C. for 16 hrs followed by heating at 400° C. in air for 4 hrs and 850° C. in N2 for 8 hrs, forming thin films of LixPOyNz ceramic electrolyte. X-ray diffraction (XRD) confirmed formation of an amorphous phase of the and SEM study revealed formation of uniform coating with a thickness of ˜0.5 micron.
The Ni mesh coated with LixPOyNz was further coated with a LiCoO2 cathode. The preparation and processing of the cathode film were described as follows:
A LiCoO2 precursor solution was prepared as follows: A solution of lithium acetate, (Li(CH3COO)2.2H2O, 5.10 g, 0.05 mol, in 50 mL 50%) was mixed with a solution of cobalt acetate, (Co(CH3COO)2.4H2O, 12.55 g, 0.05 mol in 50 mL 50% IPA) and poly(ethylene glycol) (8.80 g, 0.2 mol) in a 250-mL flask at room temperature. The resulting pink-colored solution was heated under reflux for 6 hrs and cooled to room temperature, ready for subsequent spin-coating.
With the peripheries of the electrolyte coated Ni mesh being covered with a polyimide (PI) tape on both sides, a small portion of the LiCoO2 precursor solution was added on the surface of the ceramic electrolyte coating on the Ni mesh and conditioned for 30 seconds, permitting complete wetting on both sides of the coated mesh, followed by spinning at 1200 rpm for 10 seconds. The coating was first dried in air at 160° C. for 16 hrs, followed by removing polyimide tapes and heating at 400° C. in air for 4 hrs and 850° C. in N2 for 8 hrs, forming thin films of LiCoO2. X-ray diffraction (XRD) confirmed formation of crystalline LiCoO2 and SEM study revealed formation of uniform coating. This process was repeated until the thickness of LiCoO2 layer became ˜2 microns.
With the peripheries of the electrolyte and LiCoO2 coated Ni mesh being covered with polyimide tape once again, the LiCoO2 surface was metalized with aluminum by vacuum deposition with an Al film thickness of ˜0.5 micron. During the deposition process, the coated mesh was rotated along X- and Y-axes to ensure a uniform Al deposition round coated metal mesh wires. An aluminum foil tab (18A) was glued onto the aluminum film using an electrically conductive adhesive.
The metalized mesh based battery was immersed in a 18 wt % polyimide solution in DMAc (N,N-Dimethylacetamide) for 5 min. and slowly lifted out of the solution. The coated mesh was then heated in dry air at 100° C. for 30 min and 300° C. for another 30 min. The thickness of the packaging polymer film was ˜2 microns and most of the pores (20B) left prior to the packaging were filled completely. The well packaged mesh-based Li-ion battery showed excellent flexibility and can be cycled repeatedly following initial charge.
A Ni mesh (3×6 cm2, opening 5 microns, wire diameter 2 microns) was first soaked in a NaOH solution (1.0 M) at 60° C. for 16 hrs, then cleaned by repeated soaking and sonicating in 50% isopropyl alcohol (IPA) for 16 hrs, and dried in an oven at 120° C. for 1 hr. The surface treated Ni mesh was marked/covered with a polyimide tape on strip 20A, with a width of 100 microns. The PI marked mesh sample was clamped with four Al spacer bars (0.5 cm×0.5 cm×5 cm) at the two ends of the rectangular mesh and suspended on top of an Al plate (5×5 cm2) using 4 small screws at each of the four corners of the square Al plate. The suspended mesh on Al plate was placed on a spin coater.
The LixPOyNz (LiPON-like) ceramic electrolyte precursor prepared as described in Example 1, was added onto the surface of the mesh that was suspended on top of the Al plate and placed on a spin-coater. The precursor solution was allowed to conditioning for 30 seconds, permitting complete wetting on both sides of the mesh, followed by spinning at 1200 rpm for 15 seconds. The coating was dried in air at 160° C. for 16 hrs first followed by heating at 400° C. in air for 4 hrs, and 850° C. in N2 for 8 hrs after PI tape was removed, forming patterned thin films of LixPOyNz ceramic electrolyte. X-ray diffraction (XRD) confirmed formation of an amorphous phase of the electrolyte and SEM study revealed uniform coating with a thickness of ˜0.5 micron.
With the peripheries and strip of 20A of the electrolyte coated Ni mesh being covered with polyimide (PI) tape on both sides, a small portion of the LiCoO2 precursor solution prepared as described in Example 1, was added on the surface of the coating on the Ni mesh and conditioned for 30 seconds, permitting complete wetting on both sides of the coated mesh, followed by spin at 1200 rpm for 10 seconds. The coating was first dried in air at 160° C. for 16 hrs, followed by removing polyimide tapes and heating at 400° C. in air for 4 hrs and 850° C. in N2 for 8 hrs, forming thin films of LiCoO2. X-ray diffraction (XRD) confirmed formation of crystalline LiCoO2 and SEM study revealed formation of uniform coating. This process was repeated until the thickness of LiCoO2 layer was ˜2 microns.
With the peripheries of the electrolyte and LiCoO2 coated Ni mesh being covered with polyimide tape once again, the LiCoO2 surface was metalized with aluminum by vacuum deposition with a film thickness of ˜0.5 micron. During the deposition process, the coated mesh was rotated along X- and Y-axes for a uniform Al deposition round coated metal wires. A couple of aluminum foil tabs (18A) were glued onto the aluminum film current collector using an electrically conductive adhesive.
The metalized mesh-based battery without any PI tape strips attached was lowered into a 18 wt % polyimide solution in DMAc (N,N-Dimethylacetamide) for 5 min. and slowly lifted out of the solution. The coated mesh was then heated in dry air at 100° C. for 30 min and 300° C. for another 30 min. The thickness of the packaging polymer film was 2 microns and most of the unfilled pores (20B) and strip of 20A were filled completely. The well packaged mesh-based Li-ion battery showed excellent flexibility and foldability around primary axis 20A. It can be cycled repeatedly following initial charge.
In conclusion, the invention discloses a solid-state, flexible Li-ion battery that is built on a sheet of ultrafine metal mesh wires by sequential deposition of patterned films of first electrode, electrolyte, second electrode, second electrode current collector, and flexible packaging material. The claimed solid-state, flexible Li-ion battery shows improved electrochemical and mechanical properties that are crucial to the development of new advanced mobile and portable electronics.
The embodiments of the present invention described above are exemplary. Many changes and modifications may be made to the disclosures recited above, while remaining within the scope of the invention. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims, along with their full equivalents.
