Rechargeable lithium ion battery with bendable silicon-graphite composite anode

Abstract

The invention discloses a bendable silicon-graphite composite anode for a lithium ion battery cell. The anode includes a current collector, a lithium accepting host material, and a transition layer sandwiched between the current collector and the lithium accepting host material. The transition layer is in direct contact with the current collector and the lithium-accepting host material. The transition layer includes a graphite active material and a binder. The lithium-accepting main body material is a silicon layer with uniform thickness. The current collector is a metal foil with the thickness smaller than that of a traditional anode current collector.

Description

Technical Field

[0001] This invention relates to rechargeable lithium-ion batteries, specifically to a rechargeable lithium-ion battery having a silicon composite anode, and more specifically, to a flexible silicon-graphite composite anode. Background Technology

[0002] Compared to older rechargeable batteries such as nickel-metal hydride, nickel-cadmium, or lead-acid batteries, rechargeable lithium-ion batteries maintain relatively high energy density, relatively low internal resistance, and a low self-discharge rate when not in use. Because lithium-ion batteries can undergo repeated power cycles throughout their lifespan, they are primarily used as a reliable power source in electric and hybrid vehicles.

[0003] Therefore, while rechargeable lithium batteries have achieved their intended purpose in electric and hybrid vehicles, continuous improvements are still needed to enhance battery performance, lifespan, and manufacturability. Summary of the Invention

[0004] According to several aspects, the present invention discloses a battery cell having a flexible silicon composite electrode. The electrode includes a metal foil, a silicon layer, and an active transition layer sandwiched between the metal foil and the silicon layer. The active transition layer is in direct contact with the metal foil and the silicon layer.

[0005] In another aspect of the invention, the electrode comprises a graphite active material and a binder.

[0006] In another aspect of the invention, the electrode comprises a carbonaceous material, a metal oxide, a metal sulfide, and Li4Ti5O. 12 At least one of the following, and an adhesive.

[0007] In another aspect of the invention, the adhesive comprises at least one selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (PTFE), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and styrene-ethylene-butene-styrene copolymer (SEBS).

[0008] In another aspect of the invention, the electrode further includes a conductive additive, which is at least one of the following: carbon black, graphite, graphene, graphene oxide, conductive carbon black Super P, acetylene black, carbon nanofibers, and carbon nanotubes.

[0009] In another aspect of the invention, the thickness of the metal foil is 1 μm to less than 5 μm, the thickness of the silicon layer is 1 μm to 20 μm, and the thickness of the transition layer is 2 μm to 50 μm.

[0010] In another aspect of the invention, the silicon layer comprises a substantially uniform thickness that conforms to the contour of the transition layer.

[0011] In another aspect of the invention, the electrode is a negative electrode. The areal capacity loading of the graphite transition layer is greater than 0 to 5 mAh / cm². 2 The areal capacity loading of the silicon layer is approximately 4 mAh / cm². 2 .

[0012] In another aspect of the invention, the metal foil includes a non-rough surface in direct contact with the transition layer. An adhesive bonds the transition layer to the non-rough surface.

[0013] In another aspect of the invention, a magnetron sputtering process is used to directly deposit a silicon layer onto a graphite transition layer to achieve a tight bond between the silicon layer and the transition layer.

[0014] According to several aspects, the present invention discloses an electrode for a rechargeable battery. The electrode includes a current collector, a lithium-accepting host material, and a transition layer sandwiched between the current collector and the lithium-accepting host material. The transition layer includes a first surface in direct contact with the current collector and an opposing second surface in direct contact with the lithium-accepting host material.

[0015] In another aspect of the invention, the lithium-receiving host material is a silicon layer.

[0016] In another aspect of the invention, the current collector is a metal foil comprising at least one of copper (Cu), aluminum (Al), nickel (Ni), iron (Fe), titanium (Ti), and any alloy thereof, including stainless steel. In another aspect of the invention, the transition layer comprises a graphite-active material and an adhesive. The adhesive comprises at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and styrene-ethylene-butene-styrene copolymer (SEBS).

[0017] In another aspect of the invention, the electrode further includes conductive additives, such as carbon black, graphite, graphene, graphene oxide, conductive carbon black Super P, acetylene black, carbon nanofibers, and carbon nanotubes.

[0018] In another aspect of the invention, the silicon layer has a uniform thickness of 1 μm to 20 μm, the transition layer has a thickness of 2 μm to 50 μm, and the current collector has a thickness of 1 μm to less than 5 μm.

[0019] According to several aspects, the present invention discloses an electrode for a rechargeable battery. The electrode includes a current collector, a silicon layer, and a graphite transition layer sandwiched between the current collector and the silicon layer. The graphite transition layer is in direct contact with the current collector and the silicon layer. The graphite transition layer contains an adhesive.

[0020] In another aspect of the invention, the silicon layer comprises a substantially uniform thickness of 1 μm to 20 μm, and the current collector has a thickness of 1 μm to less than 5 μm.

[0021] In another aspect of the invention, the areal capacity loading of the graphite transition layer is greater than 0 to 5 mAh / cm². 2 The areal capacity loading of silicon layer 20 is approximately 4 mAh / cm². 2 .

[0022] Further areas of application will become apparent from the description provided herein. It should be understood that these descriptions and specific examples are for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0023] The accompanying drawings described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way.

[0024] Figure 1 This is a cross-sectional view of a rechargeable lithium-ion battery according to an exemplary embodiment;

[0025] Figure 2 This is a diagram illustrating a cross-section of a flexible silicon composite anode according to an exemplary embodiment;

[0026] Figure 3 This is a microscopic image of a cross-section of a flexible silicon-graphite composite anode according to an exemplary embodiment.

[0027] Figure 4 This is a block diagram of a method for manufacturing a flexible silicon-graphite composite anode according to an exemplary embodiment; and

[0028] Figures 5A-5C This is a graph showing the improved performance of the flexible silicon-graphite composite anode compared to a conventional anode with a silicon layer in direct contact with the current collector. Detailed Implementation

[0029] The following description is merely exemplary in nature and is not intended to limit the invention, application, or use. The illustrated embodiments are disclosed with reference to the accompanying drawings, in which the same reference numerals denote corresponding parts in several figures. The drawings are not necessarily drawn to scale, and some features may be enlarged or minimized to show detail of particular features. The specific structural and functional details disclosed are not intended to be construed as limiting, but rather as a representative basis for instructing those skilled in the art on how to practice the disclosed concepts.

[0030] Figure 1 This is an illustration of a rechargeable lithium-ion battery, generally indicated by reference numeral 100. The rechargeable lithium-ion battery 100 includes at least one battery cell 101. The battery cell 101 includes a negative electrode 102, a positive electrode 104, a porous separator layer 106 separating the negative electrode 102 and the positive electrode 104, and an electrolyte material 108 adapted to conduct lithium ions between the negative electrode 102 and the positive electrode 104 through the porous separator layer 106.

[0031] The negative electrode 102 includes a lithium-receiving host material 103, and the positive electrode 104 includes a lithium-based active material 105, which can store lithium ions at a higher potential than the lithium-receiving host material 103 of the negative electrode 102. The negative electrode 102 is also referred to as the anode 102, and the positive electrode 104 is also referred to as the cathode 104. Each of the negative electrode 102 and the positive electrode 104 is contained by its respective current collectors 112 and 114. The current collectors 112 and 114 can be connected via an interruptible circuit 120, which allows current to flow between the negative electrode 102 and the positive electrode 104 to electrically balance the associated migration of lithium ions between the negative electrode 102 and the positive electrode 104 via the electrolyte material 108.

[0032] Rechargeable lithium-ion batteries 100 can be manufactured by stacking multiple battery cells 101 or by folding or rolling up continuous lengths of battery cells 101 to achieve desired battery voltage, energy storage, and power output. Roll-to-roll (R2R) manufacturing processes, also known as roll-to-roll or roll-to-roll processes, are efficient methods for mass-producing rechargeable lithium-ion batteries by continuously folding or rolling predetermined lengths of battery cells 101 into a complete battery. Components of the battery cell 101, such as the negative electrode 102 or the anode 102, need to be sufficiently flexible or bendable for R2R manufacturing processes.

[0033] A typical anode current collector 112 is formed from a conductive material, such as a metal foil with a thickness of approximately 5 to 24 micrometers (μm). Silicon (Si) is chosen due to its abundant reserves, high room-temperature specific capacity, and relative performance compared to Li / Li. +A moderate lithiation potential of approximately 0.3V makes it a suitable host material for lithium-ion anodes. Typically, the silicon layer is deposited directly onto a pre-roughened surface of a metal foil using a scalable and controllable physical vapor deposition method. The roughness (Rz) of the pre-roughened surface is approximately 8 μm.

[0034] It has been found that during the R2R process, by continuously folding or rolling the battery cells 101 of a predetermined length into a complete battery 100, the silicon layer is bent at a different radius than the metal foil, which may cause the silicon layer to be pulled off the rough surface of the metal foil. The flexible silicon composite anode 200 of the present invention solves the problem of the silicon anode layer being pulled off and detached from the metal foil in the R2R manufacturing process by employing an active transition layer, preferably a graphite transition layer, sandwiched between the silicon layer and the planar metal foil, which is thinner than the rough metal foil used for directly depositing the silicon layer. The active transition layer provides additional area capacity to the battery cell 101, and the relatively thin metal foil enables greater flexibility than conventional thicker metal foils used as anode current collectors.

[0035] Figure 2 This is a cross-sectional view of a flexible silicon composite anode 200. The flexible silicon composite anode 200 includes a metal foil 202, a silicon layer 204, and an active transition layer 206 sandwiched between the metal foil 202 and the silicon layer 204. The active transition layer 206 is in direct contact with the metal foil 202 and the silicon layer 204.

[0036] The metal foil 202 can be formed from elemental copper (Cu), aluminum (Al), copper (Cu), nickel (Ni), iron (Fe), titanium (Ti), and any alloy thereof, including stainless steel and other suitable conductive metals. The metal foil 202 includes an inner surface 202A and an opposing outer surface 202B. Both surfaces 202A and 202B are substantially flat and do not require pre-roughening. Measured between the inner surface 202A and the outer surface 202B, the thickness (T1) of the metal foil 202 is about 1 μm to 20 μm, preferably 3 μm to 12 μm. It should be understood that the thickness of the metal foil 202 is thinner than the 5 μm thickness of the metal foil in a conventional negative electrode. Compared to typical electrodes with thicker metal foils, the relatively thin metal foil 202 enables more flexible electrodes and battery cells 101 with higher energy densities. Using a relatively thin metal foil also saves on cost and materials.

[0037] The active transition layer 206 comprises greater than 0 wt% to about 98 wt% of an active material (e.g., graphite), greater than 0 wt% to about 98 wt% of a carbon conductive additive, and greater than 0 wt% to about 20 wt% of a binder. The active transition layer 206, containing graphite as the active material, is also referred to as the graphite transition layer 206. The natural surface roughness of the graphite transition layer 206 allows for strong adhesion to the silicon layer 204, while the binder facilitates strong adhesion to the metal foil 202. Measured between the inner surface 202A of the metal foil 202 and the inner surface 204A of the silicon layer 204, the thickness (T2) of the active transition layer 206 is about 1 μm to 60 μm, preferably about 2 μm to 50 μm. The areal capacity loading of the graphite transition layer 206 is greater than 0 to 5 mAh / cm². 2 .

[0038] Active materials can also include carbonaceous materials (such as hard carbon, soft carbon, etc.) and Li4Ti5O. 12 The materials used include one or more of the following: metal oxides / sulfides (e.g., TiO2, FeS, etc.) and other lithium-accepting anode materials that replace graphite. Carbon conductive additives include one or more of the following: carbon black, graphite, graphene, graphene oxide, conductive carbon black Super P, acetylene black, carbon nanofibers, carbon nanotubes, and other conductive additives. Binders include one or more of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and styrene-ethylene-butene-styrene copolymer (SEBS).

[0039] The silicon layer 204 includes an inner surface 204A in direct contact with the active transition layer 206 and an opposing outer surface 204B. Measured between the inner surface 204A and the outer surface 204B, the thickness (T3) of the silicon layer 204 is approximately 0.001 μm to 30 μm, preferably 1 μm to 20 μm. The areal capacity loading of the silicon layer 20 is approximately 0.5 to 20 mAh / cm². 2 The preferred capacity is 4mAh / cm³. 2 The silicon layer 204 has a uniform thickness because it conforms to the contour of the active transition layer 206 to provide area capacity. Uniform thickness means a substantially consistent thickness with a variation of about 2% to 20%.

[0040] Figure 3This is a microscopic image 300 of a cross-section of a flexible silicon composite anode 200 (also referred to as a silicon-graphite composite anode 200) having a graphite transition layer 206. The microscopic image shows the graphite transition layer 206 sandwiched between a silicon layer 204 and a planar metal foil 202. The graphite transition layer 206 includes a natural roughness sufficient to achieve a tight bond with the silicon layer 204, while the adhesive in the graphite transition layer 206 facilitates a tight bond with the planar metal foil 202.

[0041] Figure 4 This is a block diagram 400 illustrating a method for manufacturing a flexible silicon-graphite composite anode 200. At block 402, a planar metal foil is coated with a slurry of a graphite-active material. At block 404, the slurry coating on the metal foil is dried and rolled to form a graphite transition layer 206. At block 406, a silicon layer 204 is directly deposited onto the graphite transition layer 206 using magnetron sputtering. Magnetron sputtering is a technique used for thin film deposition. The deposition process involves jetting material from a target onto the natural contour surface of the graphite transition layer 206.

[0042] Return to reference Figure 1 The cathode comprises about 30 wt% to 98 wt% of cathode active material, more than 0 wt% to about 50 wt% of solid electrolyte, more than 0 wt% to about 30 wt% of conductive additives and more than 0 wt% to about 20 wt% of binder.

[0043] The cathode active material includes at least one of the following: layered oxides represented by the formula LiMeO2; olivine-type oxides represented by the formula LiMePO4; monoclinic oxides represented by the formula Li3Me2(PO4)3; spinel-type oxides represented by the formula LiMe2O4; or Lonfoss represented by one or both of the formulas LiMeSO4F or LiMePO4F, wherein Me is a transition metal (e.g., Co, Ni, Mn, Fe, Al, V, or combinations thereof).

[0044] The cathode solid electrolyte includes at least one oxide-based solid electrolyte. For example, garnet-type (e.g., Li7La3Zr2O) 12 ), perovskite type (e.g., Li), 3x La 2 / 3-x TiO3), NASICON type (e.g., Li) 1.4 Al 0.4 Ti 1.6 (PO4)3 and Li 1+x Al x Ge 2-x (PO4)3), LISICON type (e.g., Li 2+2x Zn 1-xGeO4), metal-doped or anisovalent substituted oxide solid electrolytes, such as Al (or Nb)-doped Li7La3Zr2O 12 Sb-doped Li7La3Zr2O 12 Ga-substituted Li7La3Zr2O 12 LiSn2P3O substituted with Cr and V 12 Al-substituted perovskite Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 .

[0045] The cathode conductive additives include at least one of carbon black, graphite, graphene, graphene oxide, conductive carbon black Super P, acetylene black, carbon nanofibers, carbon nanotubes, and other conductive additives.

[0046] The cathode binder material includes at least one of the following: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and styrene-ethylene-butene-styrene copolymer (SEBS).

[0047] The membrane layer 106 comprises at least one of the following materials, and the liquid electrolyte will wet 5% to 100% (e.g., 90%) of the porosity of the layer: Polyolefin-based membranes, such as polyacetylene: polypropylene (PP), polyethylene (PE), bilayer type: PP-PE, trilayer type: PP-PE-PP. Cellulose membranes, polyvinylidene fluoride (PVDF) membranes, and porous polyimide membranes. Ceramic-coated membranes, such as SiO2-coated PE. High-temperature stable membranes, such as polyimide (PI) nanofiber-based nonwoven fabrics, polyethylene membranes coated with nano-Al2O3 and poly(lithium 4-styrene sulfonate), SiO2-coated polyethylene (PE) membranes, copolyimide-coated polyethylene membranes, polyetherimide (PEI) (bisphenol A acetone phthalic anhydride (BPADA) and p-phenylenediamine) membranes, expanded polytetrafluoroethylene reinforced polyvinylidene fluoride-hexafluoropropylene membranes, and sandwich-structured PVDF / PMIA / PVDF nanofiber membranes.

[0048] The solid electrolyte in the solid electrolyte layer 108 includes at least one oxide-based solid electrolyte, such as garnet-type (e.g., Li7La3Zr2O). 12 ), perovskite type (e.g., Li), 3x La 2 / 3-x TiO3), NASICON type (e.g., Li)1.4 Al 0.4 Ti 1.6 (PO4)3 and Li 1+x Al x Ge 2-x (PO4)3), LISICON type (e.g., Li 2+2x Zn 1-x GeO4) and metal-doped or anisovalent substituted oxide solid electrolytes, such as Al (or Nb)-doped Li7La3Zr2O 12 Sb-doped Li7La3Zr2O 12 Ga-substituted Li7La3Zr2O 12 LiSn2P3O substituted with Cr and V 12 Al-substituted perovskite Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 The solid electrolyte in the solid electrolyte layer 108 may include a sulfide-based solid electrolyte, such as a Li₂S-P₂S₅ system or a Li₂S-P₂S₅-MO system. X System, Li2S-P2S5–MS x System, LGPS (Li 10 GeP2S 12 ), thio-LISICON (Li 3.25 Ge 0.25 P 0.75 S4), Li 3.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.3 Lithium amalgam Li6PS5X (X = Cl, Br, or I), Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 (25mS / cm), Li 9.6 P3S 12 Li7P3S 11 Li9P3S9O3, Li 10.35 Ge 1.35 P 1.65 S 12 Li 10.35 Si 1.35 P 1.65 S 12 Li 9.81 Sn 0.81P 2.19 S 12 Li 10 (Si 0.5 Ge 0.5 P2S 12 Li 10 (Ge 0.5 Sn 0.5 P2S 12 Li 10 (Si 0.5 Sn 0.5 P2S 12 Li 3.833 Sn 0.833 As 0.166 S4, LiI-Li4SnS4, and Li4SnS4. The solid electrolyte in the solid electrolyte layer may include: nitride-based solid electrolytes, such as Li3N, Li7PN4, and LiSi2N3; hydride-based SEs, such as LiBH4, LiBH4–LiX (X = Cl, Br, or I), LiNH2, Li2NH, LiBH4–LiNH2, and Li3AlH6; halide-based SEs, such as LiI, Li3InCl6, Li2CdCl4, Li2MgCl4, Li2CdI4, Li2ZnI4, and Li3OCl; and borate-based SEs, such as Li2B4O7 and Li2O–B2O3–P2O5.

[0049] Figures 5A-5C This is a graph illustrating the improved performance of the flexible silicon-graphite composite anode (shown by dashed lines) compared to a conventional anode (shown by solid lines) having a silicon layer in direct contact with the current collector. Figures 5A-5C As shown, the flexible silicon-graphite composite anode exhibits high discharge capacity and reduced voltage polarization potential at current rates of 0.05℃, 0.1℃ and 0.2℃.

[0050] The flexible silicon-graphite composite anode 200 for R2R battery manufacturing is achieved by employing a graphite transition layer 206 to ensure good bonding with both the silicon layer 204 and the thinner planar metal foil 202; the planar metal foil 202 is thinner compared to the thickness of conventional metal foils used for directly depositing silicon layers. The graphite transition layer 206 ensures good bonding with both the silicon anode layer 204 and the thinner metal foil 202. The natural surface roughness of the graphite transition layer 206 allows for tight adhesion to the silicon layer 204, while the binder in the graphite transition layer 206 bonds tightly to the flat surface of the metal foil 202. The graphite transition layer 206 provides additional area capacity to the battery cell 101 and ensures good electronic conduction of the silicon layer 204. Therefore, the silicon-graphite composite anode 200 design provides higher capacity compared to anodes with a silicon layer directly disposed on a relatively thick, rough metal foil.

[0051] Numerical data are presented in range format herein. The term "about" as used herein is known to those skilled in the art. Alternatively, the term "about" may include + / - 0.5% of a given value. It should be understood that this range format is used merely for convenience and brevity and should be flexibly interpreted to include not only the numerical values ​​explicitly listed as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly stated. While embodiments have been described in detail, those skilled in the art to which this invention pertains will recognize various alternative designs and embodiments for practicing the disclosed methods within the scope of the appended claims.

[0052] The description of this invention is merely exemplary in nature, and variations that do not depart from the spirit of the invention are intended to fall within its scope. These variations should not be considered as departing from the spirit and scope of the invention.

Claims

1. A battery cell, comprising: Electrode, the electrode comprising: metal foil; Silicon layer; and An active transition layer is sandwiched between the metal foil and the silicon layer, wherein the active transition layer is in direct contact with the metal foil and the silicon layer.

2. The battery cell according to claim 1, wherein the active transition layer comprises: Graphite active materials; as well as An adhesive comprising at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and styrene-ethylene-butene-styrene copolymer (SEBS).

3. The battery cell according to claim 1, wherein the active transition layer comprises: Carbonaceous materials, metal oxides, metal sulfides and Li4Ti5O 12 At least one of them; and An adhesive comprising at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and styrene-ethylene-butene-styrene copolymer (SEBS).

4. The battery cell according to claim 2 further includes a carbon conductive additive, wherein the carbon conductive additive includes at least one of the following: carbon black, graphite, graphene, graphene oxide, conductive carbon black Super P, acetylene black, carbon nanofibers, and carbon nanotubes.

5. The battery cell according to claim 2, wherein: The thickness of the metal foil is from 1 μm to less than 5 μm; The thickness of the silicon layer is 1 μm to 20 μm; as well as The thickness of the active transition layer is 2 μm to 50 μm.

6. The battery cell of claim 5, wherein the silicon layer comprises a substantially uniform thickness consistent with the contour of the active transition layer.

7. The battery cell according to claim 5, wherein the electrode is a negative electrode.

8. The battery cell according to claim 5, wherein: The areal capacity loading of the active transition layer is greater than 0 to 5 mAh / cm². 2 ;as well as The areal capacity loading of the silicon layer 20 is approximately 4 mAh / cm². 2 .

9. The battery cell of claim 5, wherein the metal foil includes a non-rough surface in direct contact with the active transition layer, wherein the adhesive bonds the transition layer to the non-rough surface.

10. The battery cell of claim 5, wherein the silicon layer is directly deposited onto the active transition layer using a magnetron sputtering process to achieve a tight bond with the transition layer.

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