Patent Application
20250062316
The present disclosure relates to lithium-ion batteries and related energy storage devices.
Silicon has been proposed for lithium-ion batteries to replace the conventional carbon-based anodes, which have a storage capacity that is limited to ˜370 mAh/g. Silicon readily alloys with lithium and has a much higher theoretical storage capacity (˜3600 to 4200 mAh/g at room temperature) than carbon anodes. However, insertion and extraction of lithium into the silicon matrix causes significant volume expansion (>300%) and contraction. This can result in rapid pulverization of the silicon into small particles and electrical disconnection from the current collector.
The industry has recently turned its attention to nano- or micro-structured silicon to reduce the pulverization problem, i.e., silicon in the form of spaced apart nano- or micro-wires, tubes, pillars, particles, and the like. The theory is that making the structures nano-sized avoids crack propagation and spacing them apart allows more room for volume expansion, thereby enabling the silicon to absorb lithium with reduced stresses and improved stability compared to, for example, macroscopic layers of bulk silicon.
Despite research into various approaches, batteries based primarily on silicon have yet to make a large market impact due to unresolved problems.
There remains a need for anodes for lithium-based energy storage devices such as Li-ion batteries that are easy to manufacture, robust to handling, high in charge capacity amenable to fast charging, for example, at least 1 C, and that are resistant to dimensional changes.
In accordance with an embodiment of this disclosure, an anode for an energy storage device includes a current collector having an electrically conductive layer, a first surface characterized by a first pattern, and a second surface characterized by a complementary second pattern. The anode further includes a patterned lithium storage structure comprising a continuous porous lithium storage layer disposed over the current collector in a pattern corresponding to the first pattern.
In accordance with another embodiment of this disclosure, a method of making an anode for use in an energy storage device includes providing a current collector having an electrically conductive layer, a first surface characterized by a first pattern, and a second surface characterized by a complementary second pattern. A continuous porous lithium storage layer is formed by chemical vapor deposition over the first surface by exposing the current collector to a lithium storage material precursor gas.
The present disclosure provides anodes for energy storage devices that may have one or more of at least the following advantages relative to conventional anodes: improved stability at aggressive ≥1 C charging rates; higher overall areal charge capacity; higher charge capacity per gram of lithium storage material (e.g., silicon); improved physical durability; simplified manufacturing process; more reproducible manufacturing process; or reduced dimensional changes during operation.
It is to be understood that the drawings are for purposes of illustrating the concepts of the disclosure and may not be to scale. Additional details of certain embodiments of the present disclosure may be found in co-pending U.S. patent application Ser. No. 16/991,613 and in U.S. Pat. No. 11,024,842, the entire contents of which are incorporated herein by reference for all purposes. Terms like “overlaying”, “over” or the like include, but do not necessarily require, direct contact (unless such direct contact is noted or clearly required for functionality).
As shown in
In
The properties of the first surface promote adherent formation of the continuous porous lithium storage layer by the CVD deposition method. In some embodiments, different areas of the first pattern and first surface may have differing compositional or physical properties, or the first pattern may even include a sub-pattern, so long as the first surface promotes adherent formation of the continuous porous lithium storage layer. In some embodiments, the properties of the second surface may be selected to i) kinetically or thermodynamically inhibit formation of the continuous porous lithium storage layer in the second pattern, ii) inhibit adhesion of any lithium storage material deposited by the CVD process in the second pattern making such material easy to remove, iii) promote formation of a lithium storage material different than a continuous porous lithium storage layer including, but not limited to, silicon-containing nanowires, or iv) provide a compliant or stress-absorbing interface for a second continuous porous lithium storage layer. In some cases, the properties of the second surface are selected to achieve a combination of effects such effects. In some embodiments, different areas of the second pattern and second surface may have differing compositional or physical properties, or the second pattern may even include a sub-pattern, so long as the second surface displays one or more of properties i) through iv).
In some embodiments, a surface roughening step may be applied to the current collector precursor, for example, to the surface of the electrically conductive layer, so that the first surface may have a roughness higher than the second surface. In some embodiments, the increased roughness may also promote the formation of an adherent continuous porous lithium storage layer in the first pattern. In some embodiments as shown in
In some embodiments, when a roughening process is not easily provided in a pattern, a resist or other roughening-resistant layer may be first applied over the second surface to protect the second surface from roughening step. Such a resist may be applied by printing or by photolithography followed by the roughing, e.g., by treatment with a chemical roughening agent or an electrochemical roughening process. In some embodiments, the resist may be removed, or alternatively, as shown in
In some embodiments as shown in
In some embodiments as shown in
In some embodiments the current collector includes an electrically conductive roughening layer over the electrically conductive layer. For example, as shown in
There are numerous ways to prepare current collector 201e. In some embodiments, an electrically conductive layer precursor composition may be printed and optionally cured. The precursor composition may include, for example, conductive particles such as conductive carbon, copper or silver particles that coalesce or sinter to form particulate structures having high roughness. In some embodiments, the conductive particles may take the form of nanowires or nanotubes.
In some embodiments, the electrically conductive roughening layer 208e may be electroplated onto the electrically conductive layer 203e. Some electroplating solutions and conditions are known to produce a rough electrically conductive surface. To form a pattern, a resist may be first applied to the surface of the electrically conductive layer in the second pattern and electroplating of the roughening layer selectively occurs in the first pattern. Alternatively, the electrically conductive roughening layer may first be electroplated over the entire surface of the electrically conductive layer followed by a patterned etching step. For example, a resist may be applied in a first pattern and the electrically conductive roughening layer is etched in the second pattern.
In some embodiments, the electrically conductive roughening layer includes electrodeposited copper nodules or nanopillars. For instance, an electrically conductive layer (e.g., a copper, nickel, titanium, or stainless-steel foil or mesh) may be provided into a first acid copper plating solution having 50 to 250 g/L of sulfuric acid and less than 10 g/L copper provided as copper sulfate. Copper particles may be deposited at room temperature by cathodic polarization of electrically conductive layer and applying a current density of about 0.1 to 0.3 A/cm2 for a few seconds to a few minutes. In some embodiments, the electrically conductive layer may next be provided into a second acid copper plating solution having 50 to 200 g/L of sulfuric acid and greater than 50 g/L copper provided as copper sulfate. The second acid copper bath may be warmed to temperature of about 30° C. to 50° C. A thin copper layer may be electroplated at over the copper particles to secure the particles to the electrically conductive layer by cathodic polarization and applying a current density of about 0.05 to 0.2 A/cm2 for a few seconds to a few minutes. There are many other methods and conditions useful for electroplating a rough electrically conductive surface.
In some embodiments, the electrically conductive roughening layer 208e may be deposited by electroless plating onto the electrically conductive layer. In some embodiments, electroless plating may employ a catalyst applied to the surface of the electrically conductive layer 203e followed by immersion in an electroless plating bath. Many electroless plating baths are known to deposit a rough electrically conductive layer especially if planarizing additives are removed from the solution. Similar patterning methods that employ a resist may be used as described above for electroplating. In another embodiment, the catalyst may be applied in a pattern corresponding to the first pattern. Immersion in the electroless plating bath will then selectively form the electrically conductive roughening layer 208e in the first pattern.
In some embodiments, as shown in
Throughout this disclosure and unless otherwise noted, the term “electroless plating” includes either or both of i) catalyzed deposition as described above, or ii) so-called immersion plating where a reagent in solution replaces a material at a surface, e.g., the surface of the electrically conducive layer, by a redox exchange process.
Although not shown, any of the current collector embodiments of
Although not shown in
Rather than, or in addition to, patterned roughening treatments, methods of making any of the current collectors of
As shown in
Although not shown in
In some embodiments, the first surface has a higher roughness than the second surface. Herein, surface roughness comparisons and measurements may be made using the Roughness Average (Ra), RMS Roughness (Rq), Maximum Profile Peak Height roughness (Rp), Average Maximum Height of the Profile (Rz), or Peak Density (Pc). The ratio of the second surface roughness to the first surface roughness may be less than 0.8, alternatively less than 0.7, alternatively less than 0.6, alternatively less than 0.5, alternatively less than 0.4, alternatively less than 0.3, alternatively less than 0.2, or alternatively less than 0.1. In some embodiments the first surface is characterized by a roughness Rz in a range of 2.0-2.5 μm, alternatively 2.5-3.0 μm, alternatively 3.0-3.5 μm, alternatively 3.5-4.0 μm, alternatively 4.0-4.5 μm, alternatively 4.5-5.0 μm, alternatively 5.0-5.5 μm, alternatively 5.5-6.0 μm, alternatively 6.0-6.5 μm, alternatively 6.5-7.0 μm, alternatively 7.0-8.0 μm, alternatively 8.0-9.0 μm, alternatively 9.0 to 10.0 μm, or any combination of contiguous ranges thereof. In some embodiments the first surface is characterized by a roughness Ra in a range of 0.20-0.25 μm, alternatively 0.25-0.30 μm, alternatively 0.30-0.35 μm, alternatively 0.35-0.40 μm, alternatively 0.40-0.45 μm, alternatively 0.45-0.50 μm, alternatively 0.50-0.55 μm, alternatively 0.55-0.60 μm, alternatively 0.60-0.65 μm, alternatively 0.65-0.70 μm, alternatively 0.70-0.80 μm, alternatively 0.80-0.90 μm, alternatively 0.90-1.0 μm, or any combination of contiguous ranges thereof. In some embodiments, the first surface may be characterized as having both a surface roughness Rz≥2.5 μm and a surface roughness Ra≥0.25 μm.
In
Electrically Conductive Layer In some embodiments the electrically conductive layer may have a conductivity of at least 103 S/m, or alternatively at least 106 S/m, or alternatively at least 107 S/m, and may include inorganic or organic conductive materials or a combination thereof. In some embodiments, the electrically conductive layer includes a metallic material, e.g., titanium (and its alloys), nickel (and its alloys), copper (and its alloys), or stainless steel. In some embodiments, the electrically conductive layer includes an electrically conductive carbon, such as carbon black, carbon nanotubes, graphene, graphene oxide, reduced graphene oxide, and graphite. In some embodiments the electrically conductive layer may be in the form of a foil, a mesh, or sheet of conductive material. Herein, a “mesh” includes any electrically conductive structure having openings such as found in interwoven wires, foam structures, foils with an array of holes, or the like. In some embodiments, the electrically conductive layer may include multiple layers of different electrically conductive materials. The electrically conductive layer may be in the form of a layer deposited onto an insulating substrate (e.g., a polymer sheet or ceramic substrate coated with a conductive material, including but not limited to, nickel or copper, optionally on both sides). In some embodiments, the electrically conductive layer includes a mesh or sheet of electrically conductive carbon, including but not limited to, those formed from bundled carbon nanotubes or nanofibers. In some embodiments, such carbon-based electrically conductive layers may include a surface layer of a conductive metal, e.g., nickel, copper, zinc, titanium or the like. In some embodiments, the conductive metal surface layer may be applied by electrolytic or electroless plating methods.
The electrically conductive layer may have two sides, each having its own set of first and second surfaces. For example,
Although shown as symmetrical, the patterns, physical properties, or chemical properties, or a combination thereof, of the first and second surfaces on the first and second sides may be different. For example,
In some embodiments, the electrically conductive layer may be characterized as having a yield strength. If the yield strength is too high or too low, it may be difficult to handle in manufacturing such as in roll-to-roll processes. During electrochemical cycling of the anode, deformation of the anode may occur if the yield strength is too low, or alternatively, adhesion of the continuous porous lithium storage layer may be compromised if the yield strength is too high. In some embodiments, methods of the present invention may widen the latitude of acceptable yield strength to meet these various needs. In some cases, the tensile yield strength may be relatively low such as less than about 350 MPa, or relatively high such as greater than 350 MPa. In some embodiments, the tensile yield strength of the electrically conductive layer may be in a range of 25-50 MPa, alternatively 50-100 MPa, alternatively 100-150 MPa, alternatively 150-200 MPa, alternatively 200-250 MPa, alternatively 250-300 MPa, alternatively 300-350 MPa, alternatively 350-400 MPa, alternatively 400-500 MPa, alternatively 500-600 MPa, alternatively 600-700 MPa, alternatively 700-800 MPa, alternatively 800-900 MPa, alternatively 900-1000 MPa, alternatively 1000-1200 MPa, or alternatively 1200-1500 MPa.
Although not shown in
In some embodiments the first surface of the current collector is formed by a surface layer that is patterned in some way to form patterned lithium storage structures of the present disclosure. In some cases, the surface layer is used to provide a chemical composition at the first surface that promotes formation of an adherent continuous porous lithium storage layer, as mentioned earlier. In some embodiments, the surface layer may also be used to increase the surface roughness. In many of the subsequent figures, surface roughness differences between the first surface and second surface are not explicitly shown, but in all cases, such surface roughness differences may optionally exist using methods described above, or in some cases, the surface layer itself may contribute to some or most of the roughness. In some embodiments, at least some or most of the roughness of the first surface may be imparted by the roughness of the electrically conductive layer. In some embodiments, relative to the roughness of the underlying electrically conductive layer, the roughness of the first surface after applying the surface layer may be 5% to 10% higher, alternatively 10% to 25% higher, alternatively 25% to 50% higher, alternatively 50% to 100% higher, alternatively 100% to 150% higher, alternatively 150% to 200% higher, alternatively 200% to 500% higher, alternatively 500% to 1000% higher, alternatively 1000% to 2000% higher, or any combination of contiguous ranges thereof. In some embodiments, the nature of the roughness between the electrically conductive layer and the roughness imparted by the surface layer may be similar with respect to periodicity, magnitude, or pattern, or alternatively, it may be different. In some embodiments, the surface layer may impart an increase in roughness as measured by one type of roughness unit, e.g., measured by Ra, Rq, Rp, Rz, or Pc, that is greater than the increase (if any) in roughness it imparts as measured by a different roughness unit.
In some embodiments, a pattern-modifying layer may be applied in addition to the surface layer. In some embodiments, the pattern-modifying layer may be selected to form a second surface having one or more of properties (i), (ii), (iii), and (iv) described above. Alternatively, or in addition to such properties, the pattern-modifying layer may be electrically insulative to impede charge transfer from the electrically conductive layer to any overlying lithium storage material that may have been deposited on the second surface, thereby deactivating such lithium storage material from participation in electrochemical cycling. Alternatively, or in addition to such properties, the pattern-modifying layer may act as a planarizing or smoothing layer as discussed above with respect to
For example,
In some embodiments, a surface layer may be patterned by applying a pattern-modifying layer overlaying the surface layer. For example,
There are numerous suitable methods to form patterned surface layers and pattern-modifying layers, such methods depending in part on the type of material to be used and resolution. Such methods may include printing of the desired materials or their precursors, lithographic methods which may be additive or subtractive, shadow mask methods for vapor phase patterning, chemical treatments, thermal treatments, electroplating, electroless plating, atomic layer deposition, physical vapor deposition, chemical vapor deposition, plasma treatments, and others. Some non-limiting methods are described in co-pending U.S. patent application Ser. No. 16/909,008 referenced above, which may be used or modified to achieve the desired results of the present disclosure.
Although not shown in
As mentioned, a surface layer may be provided over an electrically conductive layer optionally having a high surface roughness. In some embodiments, a surface layer may include two or more surface sublayers. Each sublayer of the two or more sublayers may have a composition different from the adjacent sublayer(s). The composition in each sublayer may be homogenous or inhomogenous.
The materials and thickness of the surface layer may be selected so that the surface layer is, or may become, sufficiently electrically conductive (i.e., non-insulating) to allow transfer of electrical charge between the electrically conductive layer and the continuous porous lithium storage layer. In addition to the materials discussed below, the surface layer may include dopants or conductive additives such as nanowires, metal particles or the like that promote electrical conductivity. In some embodiments, the surface layer may undergo a reaction during the CVD deposition of the continuous porous lithium storage layer that causes it to become more electrically conductive. For example, the surface layer may include a metal compound and the CVD deposition process may partially reduce a metal compound to its metallic state, i.e., metal at least partly in the (0) oxidation state. In some embodiments, the surface layer material has a conductivity of at least 102 S/m, alternatively at least 103 S/m, alternatively at least 104 S/m, alternatively at least 105 S/m, alternatively at least 106 S/m.
The thickness of a surface layer may be as low as a monolayer in some embodiments. In some embodiments, the thickness of the surface layer is in a range of 0.0001 μm to 0.0002 μm, alternatively 0.0002 μm to 0.0005 μm, alternatively 0.0005 μm to 0.001 μm, alternatively 0.001 μm to 0.005 μm, alternatively 0.002 μm to 0.005 μm, alternatively, 0.005 μm to 0.01 μm, alternatively 0.01 μm to 0.02 μm, alternatively 0.02 μm to 0.03 μm, alternatively 0.03 μm to 0.05 μm, alternatively 0.05 μm to 0.1 μm, alternatively 0.1 μm to 0.2 μm, alternatively 0.2 μm to 0.5 μm, alternatively 0.5 μm to 1 μm, alternatively 1 μm to 2 μm, alternatively 2 μm to 5 μm or any combination of contiguous ranges thereof.
In some embodiments the surface layer (or surface sublayer) may include metallic zinc (i.e., Zn (0)) or a zinc alloy such as Zn—Sn or Zn—Ni. In some embodiments, the surface layer may exclude bare metals (valence state of 0). In some embodiments, a surface sublayer that is not the uppermost surface sublayer may include a transition metal in its metallic (zero valent) state.
In some embodiments, the surface layer (or surface sublayer) includes a transition metal compound, e.g., a transition metal oxide, a transition metal sulfide, a transition metal hydroxide, or a transition metallate (e.g., an oxometallate such as chromate), or a mixture thereof. Unless otherwise noted, the term “transition metal” as used anywhere in the present application includes any element in groups 3 through 12 of the periodic table, including lanthanides and actinides. Note that oxometallates may be considered a subset of metal oxides where the metal oxide is anionic in nature and is associated with a cation, which may optionally be an alkali metal, an alkaline earth metal, or another transition metal. In some embodiments, the transition metal of the transition metal compound includes titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, molybdenum, tungsten, or a mixture thereof. In some embodiments, the surface layer includes an oxide of nickel, an oxide of titanium, an oxide of chromium, chromium hydroxide, tungsten hydroxide, molybdenum hydroxide, or a chromate, or a mixture thereof. A surface layer including a transition metal compound may have homogeneous or heterogeneous distribution of elements or stoichiometries through the layer. In some embodiments, the surface layer includes some lithium oxide in addition to the transition metal compound or transition metal.
In some embodiments the surface layer (or surface sublayer) may include a metal silicide. In some embodiments, the metal silicide layer includes a transition metal silicide. In some embodiments the metal silicide has a chemical composition characterized by MxSiy, wherein x is the combined atomic % of one or more transition metals, y is the atomic % of silicon, and the ratio of x to y is in a range of about 0.25 to about 7. The ratio of x to y may vary within a metal silicide surface layer. In some embodiments, a metal silicide surface layer has a gradient in metal content, e.g., where the atomic % of the transition metal(s) decreases in the direction towards the continuous porous lithium storage layer. In some embodiments, M=Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Mo, or W, or a binary or ternary combination thereof. The metal silicide may be stoichiometric or non-stoichiometric. The metal silicide may include a mixture of metal silicides having homogeneously or heterogeneously distributed stoichiometries, mixtures of metals or both. In some embodiments, the metal silicide includes at least some nickel silicide in the form of Ni3Si, Ni31Si12, Ni2Si, Ni3Si2, NiSi, or NiSi2, or a combination thereof. These particular phases may optionally be present as micro- or nano-domains within other metal silicide phases or stoichiometries present in the surface layer. In some embodiments, the metal silicide includes at least some copper silicide in the form of Cu17Si3, Cu56Si11, Cu5Si, Cu33Si7, Cu4Si, Cu19Si6, Cu3Si, or Cu87Si13, or a combination thereof. These particular phases may optionally be present as micro- or nano-domains within other metal silicide phases or stoichiometries present in the surface layer. In some embodiments, the metal silicide includes at least some titanium silicide in the form of Ti5Si3, TiSi, TiSi2, TiSi3, or Ti6Si4, or a combination thereof. These particular phases may optionally be present as micro- or nano-domains within other metal silicide phases or stoichiometries present in the surface layer. In some embodiment, the metal silicide includes at least some chromium silicide in the form of Cr3Si, Cr5Si3, CrSi, or CrSi2, or a combination thereof. These particular phases may optionally be present as micro- or nano-domains within other metal silicide phases or stoichiometries present in the surface layer.
In addition to general patterning and deposition methods mentioned earlier for surface layer, in some embodiments, a metal silicide surface layer may be formed by heating a metal layer that is in contact with a silicon layer to cause interdiffusion and formation of the metal silicide. The necessary heating temperature depends in part on the metal. In some embodiments, the heating step includes heating to a temperature in a range of 200-300° C., alternatively 300-400° C., alternatively 400-500° C., alternatively 500-600° C., alternatively 600-700° C., alternatively 700-800° C., alternatively 800-900° C., or any combination of contiguous ranges thereof. A combination of methods may be used to form a metal silicide surface layer.
In some embodiments, a surface layer or sublayer includes a silicon compound formed by treatment with a silane, a siloxane, or a silazane compound, any of which may be referred to herein as a silicon compound agent. In some embodiments, the silicon compound agent treatment may increase adhesion to an overlying sublayer or to the continuous porous lithium storage layer. In some embodiments, the silicon compound may be a polymer including, but not limited to, a polysiloxane. In some embodiments, a siloxane compound may have a general structure as shown in formula (1)
Si(R)n(OR′)4-n (1)
The silicon compound of the surface layer or sublayer may be derived from a silicon compound agent but have a different chemical structure than the agent used to form it. In some embodiments, the silicon compound may react with the underlying surface to form a bond such as a metal-oxygen-silicon bond, and in doing so, the silicon compound may lose one or more functional groups (e.g., an OR′ group from a siloxane). In some embodiments, the silicon compound agent may include groups that polymerize to form a polymer. In some embodiments, the silicon compound agent may form a matrix of Si—O—Si cross links. In some embodiments, the PECVD deposition of a lithium storage material may alter the chemical structure of the silicon compound agent or even form a secondary derivative chemical species. The silicon compound includes silicon. The silicon compound may be the result of a silicon compound agent reacting with 1, 2, 3, or 4 reactants in 1, 2, 3, or 4 different reactions.
A silicon compound agent may be provided in a solution, e.g., at about 0.3 g/l to 15 g/l in water or an organic solvent. Adsorption methods of a silicon compound agent include an immersion method, a showering method and a spraying method and are not especially limited. In some embodiments a silicon compound agent may be provided as a vapor and adsorbed onto an underlying sublayer. In some embodiments, a silicon compound agent may deposited by initiated chemical vapor deposition (iCVD). In some embodiments, a silicon compound agent may include an olefin-functional silane, an epoxy-functional silane, an acryl-functional silane, an amino-functional silane or a mercapto-functional silane. In some embodiments, a silicon compound agent may be polymerized during deposition or after deposition. Some non-limiting examples of silicon compound agents include hexamethyldisilazane (HMDS), vinyltrimethoxysilane, vinylphenyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 4-glycidylbutyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-3-(4-(3-aminopropoxy)butoxy)propyl-3-aminopropyltrimethoxysilane, imidazolesilane, triazinesilane, 3-mercaptopropyltrimethoxysilane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane, 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane, pentavinylpentamethylcyclopentasiloxane, and octavinyl-T8-silesquioxane. In some embodiments, a layer or sublayer including a silicon compound may include silicon, oxygen, and carbon, and may further include nitrogen or sulfur.
In some embodiments, treatment with a silicon compound agent may be followed by a step to drive off solvent or to initiate polymerization or another chemical transformation, wherein the step may involve heating, contact with a reactive reagent, or both. A surface sublayer formed from a silicon compound agent should not be so thick as to create a significant barrier to charge conduction between the current collector and the continuous porous lithium storage layer. In some embodiments, a sublayer formed from a silicon compound agent has a silicon content in a range of 0.1 to 0.2 mg/m2, alternatively in a range of 0.1-0.25 mg/m2, alternatively in a range of 0.25-0.5 mg/m2, alternatively in a range of 0.5-1 mg/m2, alternatively 1-2 mg/m2, alternatively 2-5 mg/m2, alternatively 5-10 mg/m2, alternatively 10-20 mg/m2, alternatively 20-50 mg/m2, alternatively 50-100 mg/m2, alternatively 100-200 mg/m2, alternatively 200-300 mg/m2, or any combination of ranges thereof. In some embodiments, a surface layer or sublayer formed from a silicon compound agent may include up to one monolayer of the silicon compound agent or its reaction product, alternatively up to 2 monolayers; alternatively up to 4 monolayers, alternatively up to 6 monolayers, alternatively up to 8 monolayers, alternatively up to 10 monolayers, alternatively up to 15 monolayers, alternatively up to 20 monolayers, alternatively up to 50 monolayers, alternatively up to 100 monolayers, alternatively up to 200 monolayers. The surface layer or surface sublayer having the silicon compound may be porous. In some embodiments, the silicon compound may break down or partially breaks down during deposition of the lithium storage layer.
The surface layer or surface sublayers in the first surface may include materials and methods as described in co-pending PCT Application No. PCT/US2021/039426, the entire contents of which are incorporated by reference for all purposes.
In the present disclosure, the continuous porous lithium storage layer 107 is substantially free of nanostructures in the form of spaced-apart wires, pillars, tubes or the like, or in the form of ordered linear vertical channels extending through the lithium storage layer.
The continuous porous lithium storage layer includes a porous material capable of reversibly incorporating lithium. In some embodiments, the continuous porous lithium storage layer includes silicon, germanium, antimony, tin, or a mixture of two or more of these elements. In some embodiments, the continuous porous lithium storage layer is substantially amorphous. In some embodiments, the continuous porous lithium storage layer includes substantially amorphous silicon. Such substantially amorphous storage layers may include a small amount (e.g., less than 20 atomic %) of crystalline material dispersed therein. The continuous porous lithium storage layer may include dopants such as hydrogen, boron, phosphorous, sulfur, fluorine, aluminum, gallium, indium, arsenic, antimony, bismuth, nitrogen, or metallic elements. In some embodiments the continuous porous lithium storage layer may include porous substantially amorphous hydrogenated silicon (a-Si:H), having, e.g., a hydrogen content of from 0.1 to 20 atomic %, or alternatively higher. In some embodiments, the continuous porous lithium storage layer may include methylated amorphous silicon. Note that, unless referring specifically to hydrogen content, any atomic % metric used herein for a lithium storage material or layer refers to all atoms other than hydrogen.
In some embodiments, the continuous porous lithium storage layer includes at least 40 atomic % silicon, germanium or a combination thereof, alternatively at least 50 atomic %, alternatively at least 60 atomic %, alternatively at least 70 atomic %, alternatively, at least 80 atomic %, alternatively at least 90 atomic %. In some embodiments, the continuous porous lithium storage layer includes at least 40 atomic % silicon, alternatively at least 50 atomic %, alternatively at least 60 atomic %, alternatively at least 70 atomic %, alternatively, at least 80 atomic %, alternatively at least 90 atomic %, alternatively at least 95 atomic %, alternatively at least 97 atomic %. Note that in the case of prelithiated anodes as discussed below, the lithium content is excluded from this atomic % characterization.
In some embodiments, the continuous porous lithium storage layer includes less than 10 atomic % carbon, alternatively less than 5 atomic %, alternatively less than 2 atomic %, alternatively less than 1 atomic %, alternatively less than 0.5 atomic %. In some embodiments, the continuous porous lithium storage layer includes less than 1% by weight of carbon-based binders, graphitic carbon, graphene, graphene oxide, reduced graphene oxide, carbon black and conductive carbon.
The continuous porous lithium storage layer includes voids or interstices (pores), which may be random or non-uniform with respect to size, shape, and distribution. Such porosity does not result in, or a result from, the formation of any recognizable lithium storage nanostructures such as nanowires, nanopillars, nanotubes, ordered nanochannels or the like. In some embodiments, the pores are polydisperse. In some embodiments, the continuous porous lithium storage layer may be characterized as nanoporous. In some embodiments the continuous porous lithium storage layer has an average density in a range of 1.0-1.1 g/cm3, alternatively 1.1-1.2 g/cm3, alternatively 1.2-1.3 g/cm3, alternatively 1.3-1.4 g/cm3, alternatively 1.4-1.5 g/cm3, alternatively 1.5-1.6 g/cm3, alternatively 1.6-1.7 g/cm3, alternatively 1.7-1.8 g/cm3, alternatively 1.8-1.9 g/cm3, alternatively 1.9-2.0 g/cm3, alternatively 2.0-2.1 g/cm3, alternatively 2.1-2.2 g/cm3, alternatively 2.2-2.25 g/cm3, or any combination of contiguous ranges thereof, and includes at least 80 atomic % silicon, alternatively at least 85 atomic % silicon, alternatively at least 90 atomic % silicon, alternatively at least 95 atomic % silicon. Note that a density of less than 2.3 g/cm3 is evidence of the porous nature of a-Si containing lithium storage layers. In some embodiments, the majority of active material (e.g., silicon, germanium or alloys thereof) of the continuous porous lithium storage layer has substantial lateral connectivity across portions of the current collector creating, such connectivity extending around random pores and interstices (as discussed later). Referring to
In some embodiments, the continuous porous lithium storage layer includes a substoichiometric oxide of silicon (SiOx), germanium (GeOx) or tin (SnOx) wherein the ratio of oxygen atoms to silicon, germanium or tin atoms is less than 2:1, i.e., x<2, alternatively less than 1:1, i.e., x<1. In some embodiments, x is in a range of 0.02 to 0.95, alternatively 0.02 to 0.10, alternatively 0.10 to 0.50, or alternatively 0.50 to 0.95, alternatively 0.95 to 1.25, alternatively 1.25 to 1.50, or any combination of contiguous ranges thereof.
In some embodiments, the continuous porous lithium storage layer includes a substoichiometric nitride of silicon (SiNy), germanium (GeNy) or tin (SnNy) wherein the ratio of nitrogen atoms to silicon, germanium or tin atoms is less than 1.25:1, i.e., y<1.25. In some embodiments, y is in a range of 0.02 to 0.95, alternatively 0.02 to 0.10, alternatively 0.10 to 0.50, or alternatively 0.50 to 0.95, alternatively 0.95 to 1.20, or any combination of contiguous ranges thereof. Lithium storage layer having a substoichiometric nitride of silicon may also be referred to as nitrogen-doped silicon or a silicon-nitrogen alloy.
In some embodiments, the continuous porous lithium storage layer includes a substoichiometric oxynitride of silicon (SiOxNy), germanium (GeOxNy), or tin (SnOxNy) wherein the ratio of total oxygen and nitrogen atoms to silicon, germanium or tin atoms is less than 1:1, i.e., (x+y)<1. In some embodiments, (x+y) is in a range of 0.02 to 0.95, alternatively 0.02 to 0.10, alternatively 0.10 to 0.50, or alternatively 0.50 to 0.95, or any combination of contiguous ranges thereof.
In some embodiments, the above sub-stoichiometric oxides, nitrides or oxynitrides are provided by a CVD process, including but not limited to, a PECVD process. The oxygen and nitrogen may be provided uniformly within the continuous porous lithium storage layer, or alternatively the oxygen or nitrogen content may be varied as a function of storage layer thickness.
CVD generally involves flowing a precursor gas, a gasified liquid in terms of direct liquid injection CVD or gases and liquids into a chamber containing one or more objects, typically heated, to be coated. Chemical reactions may occur on and near the hot surfaces, resulting in the deposition of a thin film on the surface. This is accompanied by the production of chemical by-products that are exhausted out of the chamber along with unreacted precursor gases. As would be expected with the large variety of materials deposited and the wide range of applications, there are many variants of CVD that may be used to form the lithium storage layer, the surface layer or sublayer, a supplemental layer (see below) or other layers. It may be done in hot-wall reactors or cold-wall reactors, at sub-torr total pressures to above-atmospheric pressures, with and without carrier gases, and at temperatures typically ranging from 100-1600° C. in some embodiments. There are also a variety of enhanced CVD processes, which involve the use of plasmas, ions, photons, lasers, hot filaments, or combustion reactions to increase deposition rates and/or lower deposition temperatures. Various process conditions may be used to control the deposition, including but not limited to, temperature, precursor material, gas flow rate, pressure, substrate voltage bias (if applicable), and plasma energy (if applicable).
As mentioned, the continuous porous lithium storage layer, e.g., a layer of silicon or germanium or both, may be provided by plasma-enhanced chemical vapor deposition (PECVD). Relative to conventional CVD, deposition by PECVD can often be done at lower temperatures and higher rates, which can be advantageous for higher manufacturing throughput. In some embodiments, the PECVD is used to deposit a substantially amorphous silicon layer (optionally doped) over the surface layer. In some embodiments, PECVD is used to deposit a substantially amorphous continuous porous silicon layer over the surface layer.
In PECVD processes, according to various implementations, a plasma may be generated in a chamber in which the substrate is disposed or upstream of the chamber and fed into the chamber. Various types of plasmas may be used including, but not limited to, capacitively-coupled plasmas, inductively-coupled plasmas, and conductive coupled plasmas. Any appropriate plasma source may be used, including DC, AC, RF, VHF, combinatorial PECVD and microwave sources may be used. In some embodiments, magnetron assisted RF PECVD may be used.
PECVD process conditions (temperatures, pressures, precursor gases, carrier gasses, dopant gases, flow rates, energies, and the like) can vary according to the particular process and tool used, as is well known in the art.
In some implementations, the PECVD process is an expanding thermal plasma chemical vapor deposition (ETP-PECVD) process. In such a process, a plasma generating gas is passed through a direct current arc plasma generator to form a plasma, with a web or other substrate including the current collector optionally in an adjoining vacuum chamber. A silicon source gas is injected into the plasma, with radicals generated. The plasma is expanded via a diverging nozzle and injected into the vacuum chamber and toward the substrate. An example of a plasma generating gas is argon (Ar). In some embodiments, the ionized argon species in the plasma collide with silicon source molecules to form radical species of the silicon source, resulting in deposition onto the current collector. Example ranges for voltages and currents for the DC plasma source are 60 to 80 volts and 40 to 70 amperes, respectively.
Any appropriate silicon source may be used to deposit silicon, including silane (SiH4), dichlorosilane (H2SiCl2), monochlorosilane (H3SiCl), trichlorosilane (HSiCl3), silicon tetrachloride (SiCl4), and diethylsilane. Depending on the gas(es) used, the silicon layer may be formed by decomposition or reaction with another compound, such as by hydrogen reduction. In some embodiments, the gases may include a silicon source such as silane, a noble gas such as helium, argon, neon, or xenon, optionally one or more dopant gases, and substantially no hydrogen. In some embodiments, the gases may include argon, silane, and hydrogen, and optionally some dopant gases. In some embodiments the gas flow ratio of argon relative to the combined gas flows for silane and hydrogen is at least 3.0, alternatively at least 4.0. In some embodiments, the gas flow ratio of argon relative to the combined gas flows for silane and hydrogen is in a range of 3-5, alternatively 5-10, alternatively 10-15, alternatively 15-20, or any combination of contiguous ranges thereof. In some embodiments, the gas flow ratio of hydrogen gas to silane is in a range of 0-0.1, alternatively 0.1-0.2, alternatively 0.2-0.5, alternatively 0.5-1, alternatively 1-2, alternatively 2-5, or any combination of contiguous ranges thereof. In some embodiments, higher porosity silicon may be formed and/or the rate of silicon deposition may be increased when the gas flow ratio of silane relative to the combined gas flows of silane and hydrogen increases. In some embodiments a dopant gas is borane or phosphine, which may be optionally mixed with a carrier gas. In some embodiments, the gas flow ratio of dopant gas (e.g., borane or phosphine) to silicon source gas (e.g., silane) is in a range of 0.0001-0.0002, alternatively 0.0002-0.0005, alternatively 0.0005-0.001, alternatively 0.001-0.002, alternatively 0.002-0.005, alternatively 0.005-0.01, alternatively 0.01-0.02, alternatively 0.02-0.05, alternatively 0.05-0.10, or any combination of contiguous ranges thereof. Such gas flow ratios described above may refer to the relative gas flow, e.g., in standard cubic centimeter per minute (SCCM). In some embodiments, the PECVD deposition conditions and gases may be changed over the course of the deposition.
In some embodiments, the temperature at the current collector during at least a portion of the time of PECVD deposition is in a range of 20° C. to 50° C., 50° C. to 100° C., alternatively 100° C. to 200° C., alternatively 200° C. to 300° C., alternatively 300° C. to 400° C., alternatively 400° C. to 500° C., alternatively 500° C. to 600° C., or any combination of ranges thereof. In some embodiments, the temperature may vary during the time of PECVD deposition. For example, the temperature during early times of the PECVD may be higher than at later times. Alternatively, the temperature during later times of the PECVD may be higher than at earlier times.
The thickness or mass per unit area of the continuous porous lithium storage layer depends on the storage material, desired charge capacity and other operational and lifetime considerations. Increasing the thickness typically provides more capacity. If the continuous porous lithium storage layer becomes too thick, electrical resistance may increase and the stability may decrease. In some embodiments, the anode may be characterized as having an active silicon areal density of at least 1.0 mg/cm2, alternatively at least 1.5 mg/cm2, alternatively at least 3 mg/cm2, alternatively at least 5 mg/cm2. In some embodiments, the lithium storage structure may be characterized as having an active silicon areal density in a range of 1.5-2 mg/cm2, alternatively in a range of 2-3 mg/cm2, alternatively in a range of 3-5 mg/cm2, alternatively in a range of 5-10 mg/cm2, alternatively in a range of 10-15 mg/cm2, alternatively in a range of 15-20 mg/cm2, or any combination of contiguous ranges thereof “Active silicon” refers to the silicon in electrical communication with the current collector that is available for reversible lithium storage at the beginning of cell cycling, e.g., after anode “electrochemical formation” discussed later. “Areal density” refers to the surface area of the electrically conductive layer over which active silicon is provided. In some embodiments, not all of the silicon content is active silicon, i.e., some may be tied up in the form of non-active silicides or electrically isolated from the current collector.
In some embodiments the continuous porous lithium storage has an average thickness of at least 1 μm, alternatively at least 2.5 μm, alternatively at least 6.5 μm. In some embodiments, the continuous porous lithium storage layer has an average thickness in a range of about 0.5 μm to about 50 μm. In some embodiments, the continuous porous lithium storage layer comprises at least 80 atomic % amorphous silicon and/or has a thickness in a range of 1-1.5 μm, alternatively 1.5-2.0 μm, alternatively 2.0-2.5 μm, alternatively 2.5-3.0 μm, alternatively 3.0-3.5 μm, alternatively 3.5-4.0 μm, alternatively 4.0-4.5 μm, alternatively 4.5-5.0 μm, alternatively 5.0-5.5 μm, alternatively 5.5-6.0 μm, alternatively 6.0-6.5 μm, alternatively 6.5-7.0 μm, alternatively 7.0-8.0 μm, alternatively 8.0-9.0 μm, alternatively 9.0-10 μm, alternatively 10-15 μm, alternatively 15-20 μm, alternatively 20-25 μm, alternatively 25-30 μm, alternatively 30-40 μm, alternatively 40-50 μm, or any combination of ranges thereof.
In some embodiments, the second surface includes a transition metal or a transition metal layer capable of forming metal silicide structures when subjected to a vaporized silicon source and elevated temperatures. In some embodiments, the second surface includes nickel and PECVD silicon deposition conditions are selected to form nickel silicide structures such as nanowires or microwires in the second pattern, for example, by subjecting the nickel-containing electrically conductive layer to a temperature in a range of 450-550° C. As discussed below, the continuous porous lithium storage layer of silicon may concurrently deposit over the first surface in the first pattern along with the metal silicide structures over the second surface in the second pattern. However, to avoid substantial growth of such metal silicide structures in the second pattern, the temperature may be lower, for example, to a range of 150 to 375° C., sufficient to deposit the silicon of the continuous porous lithium storage layer.
In some embodiments, after deposition of the continuous porous lithium storage layer, there may optionally be a cleaning step to remove unwanted material that may have been deposited on the second surface. Such cleaning may include sonication, contact with a brush or wipe, contact with a fluid jet (liquid or gas), flexure of the anode, or transfer to a delamination substrate that may include an adhesion layer (e.g., adhesive tape).
According to various embodiments of the present disclosure, the one or more first regions of the continuous porous lithium storage layer may readily be provided in almost any pattern desired, enabling a multitude of potential functionalities.
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It should be noted that both sides of the current collector may optionally include a patterned lithium storage structure, and the two sides may have the same or a different pattern, e.g., to account for differences in stresses when winding. In some embodiments, one side of the current collector includes a patterned lithium storage structure and the other side includes a non-patterned lithium storage layer.
Patterning resolution, i.e., the minimum practical lateral dimension or feature width of the first or second region, may be a function of patterning method, a surface layer thickness and target lithium storage layer thickness. In some embodiments, the feature width is at least 1 μm, alternatively at least 2 μm, alternatively at least 5 μm, alternatively at least 10 μm. In some embodiments, the feature width is in a range of 1 μm-2 μm, alternatively 2 μm-5 μm, alternatively 5 μm-10 μm, alternatively 10 μm-20 μm, alternatively 20-50 μm, alternatively 50 μm-100 μm, alternatively 100 μm to 200 μm, alternatively 200-500 μm, alternatively 500 μm-1 mm, alternatively 1 mm-2 mm, alternatively 2 mm-5 mm, alternatively 5 mm to 10 mm, or any combination of ranges thereof.
In some embodiments the patterned lithium storage structure includes one or more first regions characterized by a critical dimension which represents the maximum radial distance between any point within the first region to a second region not having the continuous porous lithium storage layer of the first region.
In some embodiments, the one or more first regions (e.g., 113 in
As mentioned, the one or more second regions (e.g., 114) or the second pattern (e.g., 109) may in some cases provide areas of stress relief when bending or winding the anode and/or contact areas for making electrical connection to the battery cell. In some cases, it has been found that when the first surface forms a strong bond with a continuous porous lithium storage layer and there are no second regions, large stresses are placed on the electrically conductor during electrochemical cycling of the anode. This may lead to deformations and buckling of the current collector and anode. Although the anode may still be functional, such deformations and buckling may in some cases cause unacceptable geometrical changes to the battery, e.g., an apparent increase in thickness. Most of this expansion is not due to silicon itself, but to the deformations caused in the anode overall including the current collector. A cross-sectional view of such buckling is shown in
By patterning the anode according to some embodiments of the present disclosure, the stresses applied to the current collector may be substantially reduced thereby lessening physical deformations and buckling. As such, the apparent thickness after cycling may be made closer to the actual thickness.
In some embodiments, the pattern is chosen to induce a controlled deformation that may be managed. That is, without a patterned lithium storage structure, the anode deformations may be mostly random in nature. However, by applying a pattern, some deformations may still occur, but their shapes can in part be predetermined by the first pattern. In this way, the rest of the cell components may be appropriately adjusted in advance to account for the change in shape.
In some embodiments, the current collector may have high tensile strength and be more resistant to deformations during cycling. In such cases, the stresses caused by cycling of a non-patterned continuous porous lithium storage layer cannot be transferred to the current collector and may instead cause catastrophic delamination of the continuous porous lithium storage layer. By patterning an anode having a high tensile strength current collector according to some embodiments of the present disclosure, the stresses of electrochemical cycling may be substantially reduced and result in an anode that undergoes low buckling with a continuous porous lithium storage layer that remains adhered.
In some embodiments, the second surfaces and second regions primarily provide space to allow for more robust handling of the anode or for the continuous porous lithium storage layer to expand, as described above. However, in some embodiments, the second regions may be designed to provide additional functionality or benefits to the anode. In some embodiments, the second surface may be recessed relative to the first surface. For example,
In some other embodiments, the first surface of the current collector may be recessed relative to the second surface. For example,
In some embodiments, the second surface may include a compliant material that allows for moderately adherent deposition of a second lithium storage material, but that may flex during electrochemical cycling. For example,
In some embodiments of the present disclosure, anodes of the present disclosure may include a second lithium storage material overlaying at least a portion of the second surface in second regions, wherein either or both the chemical composition or physical structure of the second lithium storage material are different than the continuous porous lithium storage layer.
In some embodiments, the second regions may include a plurality of lithium storage structures such as nanostructures, e.g., nanowires, formed on the current collector over the second surface. Methods of growing lithium storage nanowires are well known in the art, including but not limited to CVD and PECVD methods described in U.S. Pat. Nos. 9,325,014 and 8,257,866, the entire contents of which are incorporated by reference for all purposes.
In some embodiments (not shown), most of the continuous porous lithium storage layer 1507 is deposited under a first set of conditions and then followed by a change in conditions to form alloyed nanowires, and optionally lithium storage nanowires, in the second region.
Prior art lithium storage nanowires may have certain disadvantages, one of which is physical robustness to handling (e.g. rubbing) causing nanowires to break off. On the other hand, nanowire structures may be more robust to bending stresses induced during winding than continuous layers of lithium storage material. According to some embodiments of the present disclosure, the first regions may help physically protect the nanowires in the second regions. By providing lithium storage nanowires in the one or more second region, the loss in surface area capacity caused by patterning the continuous porous lithium storage layer can be partially or entirely recovered. Further, the combination of two types of lithium storage structures may provide the anode with a broader range of charging and discharging capabilities and/or increased lifetime. In addition, the plurality of lithium storage structures such as nanowires have been found not to apply lower stresses to the current collector resulting in less anode deformation.
In some embodiments, the patterned lithium storage structure includes a functional composition in second regions deposited over the second surface. As shown in
In some embodiments the functional composition may be deposited by wet coating or printing method, including but not limited to, screen printing, inkjet printing, gravure printing, offset printing, flexographic printing, curtain coating, spray coating, spin coating and slot die coating. For example, the functional composition may be coated over the entire anode and substantially removed from the top surface of the continuous porous lithium storage layer 1607a by a doctor blade or squeegee (
In some embodiments, the functional composition may act as a supplemental active lithium storage layer for the anode and may be provided, for example, by coating a slurry containing an active lithium storage material (e.g., graphite or silicon-containing particles), a binder matrix and a solvent. Many other coatable, binder-based lithium storage layers are known in the art and may be used. Such binder-based lithium storage layers generally have lower areal lithium storage capacity than the continuous porous lithium storage layer. However, some may more easily withstand bending stresses during winding or the like and will at least partially offset the loss in surface area capacity caused by patterning the continuous porous lithium storage layer.
In some embodiments where the one or more second regions include active lithium storage materials, e.g., as lithium storage nanowires, a binder-based lithium storage material or the like, the ratio of the total area of first region(s) of continuous porous lithium storage layer (e.g., 1513, 1613a, 1613b) relative to the total area of the second region(s) (e.g., 1514, 1614a, 1614b) may be in range of 50:1 to 20:1, alternatively 20:1 to 10:1, alternatively 10:1 to 5:1, alternatively 5:1 to 2:1, alternatively 2:1 to 1:1, alternatively 1:1 to 1:2, alternatively 1:2 to 1:5, alternatively 1:5 to 1:10, alternatively 1:10 to 1:20, alternatively 1:20 to 1:50, or any combination of contiguous ranges thereof.
In some embodiments, the functional composition includes a polymer comprising a source of lithium ion, e.g., as lithium sulfonate or lithium carboxylate groups or the like. This may be used to supplement the lithium ion present in the electrolyte and reduce possible lithium ion starvation effects due to irreversible losses of lithium in the anode over time.
In some embodiments, the functional composition may act to partially confine expansion of the continuous porous lithium storage layer (1607a, 1607b) that may occur during lithiation. Such confinement may help increase lifetime. In some embodiments, the expansion confinement composition may include a polymer or a mixture of a polymer and inorganic particles. In some embodiments, the expansion confinement primarily directed to a lateral expansion (as in
In some embodiments, the functional composition (1632a, 1632b) may include an electrically conductive material, e.g., silver (or other metal) nanowires, metallic particles, a conductive polymer, a conductive metal oxide, carbon nanofibers, carbon nanotubes, or a combination. In some embodiments, the presence of such electrically conductive materials may help enable electrical continuity of the anode after electrochemical cycling and some possible breakdown of the continuous porous lithium storage layer structure. In some embodiments the functional composition may include an electrically conductive material mentioned above, but the conductive materials are sufficiently dilute in a binder or matrix so that the functional composition itself does not readily conduct electrical current at normal battery operating voltages.
In some embodiments, functional composition (1632a, 1632b) may be conductive to lithium ions. In the case where the functional composition 1632b is over continuous porous lithium storage layer 1607b (
In some embodiments, the functional composition may act as a solid-state electrolyte or separator.
In some embodiments, the functional composition may include any combination of materials or functions described above.
In some embodiments, the second region may include lithium storage nanowires grown on the current collector and one or more functional composition according to any of the embodiments described above.
Although not shown, in some embodiments, the second continuous porous lithium storage layer, the plurality of second lithium storage structures, or the functional material may be provided over the second surface in a third pattern that constitutes a subset of the second pattern, but spaced away from the first pattern, thereby leaving some open space adjacent to the first regions.
The anode may optionally include various additional layers and features. The current collector may include one or more features to ensure that a reliable electrical connection can be made in the energy storage device. In some embodiments, a supplemental layer is provided over the patterned lithium storage structure. In some embodiments, the supplemental layer is a protection layer to enhance lifetime or physical durability. The supplemental layer may be an oxide formed from the lithium storage material itself, e.g., silicon dioxide in the case of silicon, or some other suitable material. A supplemental layer may be deposited, for example, by ALD, CVD, PECVD, evaporation, sputtering, solution coating, ink jet or any method that is compatible with the anode. In some embodiments the supplemental layer may conformally coat the patterned lithium storage structure. In some embodiments, the top surface of the supplemental layer corresponds to a top surface of the anode.
A supplemental layer should be reasonably conductive to lithium ions and permit lithium ions to move into and out of the patterned lithium storage structure during charging and discharging. In some embodiments, the lithium ion conductivity of a supplemental layer is at least 10−9 S/cm, alternatively at least 10−8 S/cm, alternatively at least 10−7 S/cm, alternatively at least 10−6 S/cm. In some embodiments, the supplemental layer acts as a solid-state electrolyte.
Some non-limiting examples of materials used in a supplemental layer include metal oxides, nitrides, or oxynitrides, e.g., those containing aluminum, titanium, vanadium, zirconium or tin, or mixtures thereof. The metal oxide, metal nitride or metal oxynitride may include other components such as phosphorous or silicon. The supplemental layer may include a lithium-containing material such as lithium phosphorous oxynitride (LIPON), lithium phosphate, lithium aluminum oxide, (Li,La)xTiyOz, or LixSiyAl2O3. In some embodiments, the supplemental layer includes a metal oxide, metal nitride, or metal oxynitride, and has an average thickness of less than about 100 nm, for example, in a range of about 0.1 to about 10 nm, or alternatively in a range of about 0.2 nm to about 5 nm. UPON or other solid-state electrolyte materials having superior lithium transport properties may have a thickness of more than 100 nm, but may alternatively, be in a range of about 1 to about 50 nm.
In some embodiments, the continuous porous lithium storage layer may be at least partially prelithiated prior to a first electrochemical cycle after battery assembly, or alternatively prior to battery assembly. That is, some lithium may be incorporated into the continuous porous lithium storage layer to form a lithiated storage layer even prior to a first battery cycle. In some embodiments, the lithiated storage layer may break into smaller structures, including but not limited to platelets, that remain electrochemically active and continue to reversibly store lithium. Note that “lithiated storage layer” simply means that at least some of the potential storage capacity of the lithium storage layer is filled, but not necessarily all. In some embodiments, the lithiated storage layer may include lithium in a range of 1% to 5% of the theoretical lithium storage capacity of the continuous porous lithium storage layer, alternatively 5% to 10%, alternatively 10% to 15%, alternatively 15% to 20%, alternatively, 20% to 30%, alternatively 30% to 40%, alternatively 40% to 50%, alternatively 50% to 60%, alternatively 60% to 70%, alternatively 70% to 80%, alternatively 80% to 90%, alternatively 90% to 100%, or any combination of ranges thereof. In some embodiments, a surface layer may capture some of the lithium, and one may need to account for such capture to achieve the desired lithium range in the lithiated storage layer.
In some embodiments prelithiation may include depositing lithium metal over the continuous porous lithium storage layer, alternatively between one or more lithium storage sublayers, or both, e.g., by evaporation, e-beam or sputtering. Alternatively, prelithiation may include contacting the anode with a reductive lithium organic compound, e.g., lithium naphthalene, n-butyllithium or the like. In some embodiments, prelithiation may include incorporating lithium by electrochemical reduction of lithium ion in prelithiation solution. In some embodiments, prelithiation may include a thermal treatment to aid the diffusion of lithium into the lithium storage layer.
In some embodiments the anode may be thermally treated prior to battery assembly. In some embodiments, thermally treating the anode may improve adhesion of the various layers or electrical conductivity, e.g., by inducing migration of metal from the current collector or atoms from the optional supplemental layer into the continuous porous lithium storage layer. In some embodiments, the continuous porous lithium storage layer includes at least 80 atomic % amorphous silicon and at least 0.05 atomic % copper, alternatively at least 0.1 atomic % copper, alternatively at least 0.2 atomic % copper, alternatively at least 0.5 atomic % copper, alternatively at least 1 atomic % copper. In some embodiments, the continuous porous lithium storage layer may include at least 80 atomic % amorphous silicon and also include copper in an atomic % range of 0.05-0.1%, alternatively 0.1-0.2%, alternatively 0.2-0.5%, alternatively 0.5-1%, alternatively 1-2%, alternatively 2-3%, alternatively 3-5%, alternatively 5-7%, or any contiguous combination of ranges thereof. In some embodiments, the aforementioned ranges of atomic % copper may correspond to a cross-sectional area of the continuous porous lithium storage layer of at least 1 μm2, which may be measured, e.g., by energy dispersive x-ray spectroscopy (EDS). In some embodiments, there is a gradient where the concentration of copper in portions of the continuous porous lithium storage layer near the current collector is higher than portions further from the current collector. In some embodiments, instead of copper or in addition to copper, the continuous porous lithium storage layer may include another transition metal such as zinc, chromium or titanium, e.g., when the surface layer includes a metal oxide layer of TiO2. The atomic % of such transition metals (Zn, Cr, or Ti) may be present in the continuous porous lithium storage layer in any of the atomic % ranges mentioned above with respect to copper. In some embodiments, the continuous porous lithium storage layer may include more copper than other transition metals. Special thermal treatments are not always necessary to achieve migration of transition metals into the lithium storage layer.
In some embodiments, thermally treating the anode may be done in a controlled environment having a low oxygen and water (e.g., less than 10 ppm or partial pressure of less than 0.1 Torr, alternatively less than 0.01 Torr content to prevent degradation). In some embodiments, anode thermal treatment may be carried out using an oven, infrared heating elements, contact with a hot plate or exposure to a flash lamp. The anode thermal treatment temperature and time depend on the materials of the anode. In some embodiments, anode thermal treatment includes heating the anode to a temperature of at least 50° C., optionally in a range of 50° C. to 950° C., alternatively 100° C. to 250° C., alternatively 250° C. to 350° C., alternatively 350° C. to 450° C., alternatively 450° C. to 550° C., alternatively 550° C. to 650° C., alternatively 650° C. to 750° C., alternatively 750° C. to 850° C., alternatively 850° C. to 950° C., or a combination of these ranges. In some embodiments, the thermal treatment may be applied for a time period of 0.1 to 120 minutes.
In some embodiments one or more processing steps described above may be performed using roll-to-roll methods wherein the electrically conductive layer or current collector is in the form of a rolled film, e.g., a roll of metal foil, mesh, or fabric.
The preceding description relates primarily to the anode/negative electrode of a lithium-ion battery (LIB). The LIB typically includes a cathode/positive electrode, an electrolyte and a separator (if not using a solid-state electrolyte). As is well known, batteries can be formed into multilayer stacks of anodes and cathodes with an intervening separator. Alternatively, anode/cathode stacks can be formed into a so-called jelly-roll. Such structures are provided into an appropriate housing having desired electrical contacts.
Positive electrode (cathode) materials include, but are not limited to, lithium metal oxides or compounds (e.g., LiCoO2, LiFePO4, LiMnO2, LiNiO2, LiMn2O4, LiCoPO4, LiNixCoyMnzO2, LiNixCoyAlzO2, LiFe2(SO4)3, or Li2FeSiO4), carbon fluoride, metal fluorides such as iron fluoride (FeF3), metal oxide, sulfur, selenium and combinations thereof. Cathode active materials are typically provided on, or in electrical communication with, an electrically conductive cathode current collector.
The current separator allows ions to flow between the anode and cathode but prevents direct electrical contact. Such separators are typically porous sheets. Non-aqueous lithium-ion separators are single layer or multilayer polymer sheets, typically made of polyolefins, especially for small batteries. Most commonly, these are based on polyethylene or polypropylene, but polyethylene terephthalate (PET) and polyvinylidene fluoride (PVdF) can also be used. For example, a separator can have >30% porosity, low ionic resistivity, a thickness of ˜10 to 50 μm and high bulk puncture strengths. Separators may alternatively include glass materials, ceramic materials, a ceramic material embedded in a polymer, a polymer coated with a ceramic, or some other composite or multilayer structure, e.g., to provide higher mechanical and thermal stability.
The electrolyte in lithium ion cells may be a liquid, a solid, or a gel. A typical liquid electrolyte comprises one or more solvents and one or more salts, at least one of which includes lithium. During the first few charge cycles (sometimes referred to as formation cycles), the organic solvent and/or the electrolyte may partially decompose on the negative electrode surface to form an SEI (Solid-Electrolyte-Interphase) layer. The SEI is generally electrically insulating but ionically conductive, thereby allowing lithium ions to pass through. The SEI may lessen decomposition of the electrolyte in the later charging cycles.
Some non-limiting examples of non-aqueous solvents suitable for some lithium ion cells include the following: cyclic carbonates (e.g., ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), butylene carbonate (BC) and vinylethylene carbonate (VEC)), vinylene carbonate (VC), lactones (e.g., gamma-butyrolactone (GBL), gamma-valerolactone (GVL) and alpha-angelica lactone (AGL)), linear carbonates (e.g., dimethyl carbonate (DMC), methyl ethyl carbonate (MEC, also commonly abbreviated EMC), diethyl carbonate (DEC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), methyl butyl carbonate (NBC) and dibutyl carbonate (DBC)), ethers (e.g., tetrahydrofuran (THF), 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane (DME), 1,2-diethoxyethane and 1,2-dibutoxyethane), nitriles (e.g., acetonitrile and adiponitrile) linear esters (e.g., methyl propionate, methyl pivalate, butyl pivalate and octyl pivalate), amides (e.g., dimethyl formamide), organic phosphates (e.g., trimethyl phosphate and trioctyl phosphate), organic compounds containing an S═O group (e.g., dimethyl sulfone and divinyl sulfone), and combinations thereof.
Non-aqueous liquid solvents can be employed in combination. Examples of these combinations include combinations of cyclic carbonate-linear carbonate, cyclic carbonate-lactone, cyclic carbonate-lactone-linear carbonate, cyclic carbonate-linear carbonate-lactone, cyclic carbonate-linear carbonate-ether, and cyclic carbonate-linear carbonate-linear ester. In some embodiments, a cyclic carbonate may be combined with a linear ester. Moreover, a cyclic carbonate may be combined with a lactone and a linear ester. In some embodiments, the weight ratio, or alternatively the volume ratio, of a cyclic carbonate to a linear ester is in a range of 1:9 to 10:1, alternatively 2:8 to 7:3.
A salt for liquid electrolytes may include one or more of the following non-limiting examples: LiPF6, LiBF4, LiClO4 LiAsF6, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiCF3SO3, LiC(CF3SO2)3, LiPF4(CF3)2, LiPF3(C2F5)3, LiPF3(CF3)3, LiPF3 (iso-C3F7)3, LiPF5(iso-C3F7), lithium salts having cyclic alkyl groups (e.g., (CF2)2(SO2)2xLi and (CF2)3(SO2)2xLi), LiFSI (lithium bis(fluorosulfonyl)imide), LiTDI (lithium 4,5-dicyano-2-(trifluoromethyl)imidazole), and combinations thereof.
In some embodiments, the total concentration of salt in a liquid non-aqueous solvent (or combination of solvents) is at least 0.3 M, alternatively at least 0.7M. The upper concentration limit may be driven by a solubility limit and operational temperature range. In some embodiments, the concentration of salt is no greater than about 2.5 M, alternatively no more than about 1.5 M. In some embodiments, the electrolyte may include a saturated solution of a lithium salt and excess solid lithium salt.
In some embodiments, the battery electrolyte includes a non-aqueous ionic liquid and a lithium salt. Additives may be included in the electrolyte to serve various functions such as stabilizing the battery. For example, additives such as polymerizable compounds having an unsaturated double bond may be added to stabilize or modify the SEI. Certain amines or borate compounds may act as cathode protection agents. Lewis acids can be added to stabilize fluorine-containing anion such as PF6. Safety protection agents include those to protect overcharge, e.g., anisoles, or act as fire retardants, e.g., alkyl phosphates.
A solid electrolyte may be used without the separator because it serves as the separator itself. It is electrically insulating, ionically conductive, and electrochemically stable. In the solid electrolyte configuration, a lithium containing salt, which could be the same as for the liquid electrolyte cells described above, is employed but rather than being dissolved in an organic solvent, it is held in a solid polymer composite. Examples of solid polymer electrolytes may be ionically conductive polymers prepared from monomers containing atoms having lone pairs of electrons available for the lithium ions of electrolyte salts to attach to and move between during conduction, such as polyvinylidene fluoride (PVDF) or chloride or copolymer of their derivatives, poly(chlorotrifluoroethylene), poly(ethylene-chlorotrifluoroethylene), or poly(fluorinated ethylene-propylene), polyethylene oxide (PEO) and oxymethylene linked PEO, PEO-PPO-PEO crosslinked with trifunctional urethane, poly(bis(methoxy-ethoxy-ethoxide))-phosphazene (MEEP), triol-type PEO crosslinked with difunctional urethane, poly((oligo)oxyethylene)methacrylate-co-alkali metal methacrylate, polyacrylonitrile (PAN), polymethylmethacrylate (PMMA), polymethylacrylonitrile (PMAN), polysiloxanes and their copolymers and derivatives, acrylate-based polymer, other similar solvent-free polymers, combinations of the foregoing polymers either condensed or crosslinked to form a different polymer, and physical mixtures of any of the foregoing polymers. Other less conductive polymers that may be used in combination with the above polymers to improve the strength of thin laminates include: polyester (PET), polypropylene (PP), polyethylene naphthalate (PEN), polyvinylidene fluoride (PVDF), polycarbonate (PC), polyphenylene sulfide (PPS), and polytetrafluoroethylene (PTFE). Such solid polymer electrolytes may further include a small amount of organic solvent such as those listed above. The polymer electrolyte may be an ionic liquid polymer. Such polymer-based electrolytes can be coated using any number of conventional methods such as curtain coating, slot coating, spin coating, inkjet coating, spray coating or other suitable method.
In some embodiments, the original, non-cycled anode may undergo structural or chemical changes during electrochemical charging/discharging, for example, from normal battery usage or from an earlier “electrochemical formation step”. As is known in the art, an electrochemical formation step is commonly used to form an initial SEI layer and involves relatively gentle conditions of low current and limited voltages. The modified anode prepared in part from such electrochemical charging/discharging cycles may still have excellent performance properties, despite such structural and/or chemical changes relative to the original, non-cycled anode. In some embodiments, the lithium storage layer of the cycled anode may no longer appear as a continuous layer, and instead, appear as separated pillars or islands, generally with a height-to-width aspect ratio of less than 2. While not being bound by theory, in the case of amorphous silicon, it may be that small amounts delaminate upon cycling at high stress areas. Alternatively, or in addition, it may be that structural changes upon lithiation and delithiation are non-symmetrical resulting in such islands or pillars.
In some embodiments, electrochemical cycling conditions may be set to utilize only a portion of the theoretical charge/discharge capacity of silicon (3600 mAh/g). In some embodiments, electrochemical charging/discharging cycles may be set to utilize 400-600 mAh/g, alternatively 600-800 mAh/g, alternatively 800-1000 mAh/g, alternatively 1000-1200 mAh/g, alternatively 1200-1400 mAh/g, alternatively 1400-1600 mAh/g, alternatively 1600-1800 mAh/g, alternatively 1800-2000 mAh/g, alternatively 2000-2200 mAh/g, alternatively 2200-2400 mAh/g, alternatively 2400-2600 mAh/g, alternatively 2600-2800 mAh/g, alternatively 2800-3000 mAh/g, alternatively 3000-3200 mAh/g, alternatively 3200-3400 mAh/g, or any combination of ranges thereof.
Although the present anodes have been discussed with reference to batteries, in some embodiments the present anodes may be used in hybrid lithium ion capacitor devices.
Still further embodiments herein include the following enumerated embodiments.
The specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of embodiments of the invention. However, other embodiments of the invention may be directed to specific embodiments relating to each individual aspect, or specific combinations of these individual aspects.
The above description of example embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above.
In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present technology. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.
Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Additionally, details of any specific embodiment may not always be present in variations of that embodiment or may be added to other embodiments.
Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.
As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a method” includes a plurality of such methods and reference to “the anode” includes reference to one or more anodes and equivalents thereof known to those skilled in the art, and so forth. The invention has now been described in detail for the purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practice within the scope of the appended claims.
All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes. None is admitted to be prior art.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/064018 | 12/17/2021 | WO |
