Lithium ion battery with silicon-based active material and negative electrode with water-based binder having good adhesion and cohesion

Abstract

Polymeric binders based on poly(acrylamide-co-acrylate) for negative electrodes with silicon-based active materials are presented. Lithium ion batteries incorporating electrodes formed from the binders achieve longer cycles with suitable performance. Mechanical properties related to the parts of the copolymer are studied to guide the selection of the polymer.

Description

Invention Field

[0001] This invention relates to lithium-ion batteries containing silicon-based anode active materials and exhibiting good cycle performance. The invention further relates to an anode having a binder that provides good cycle performance to the silicon-based active material. Background of the Invention

[0003] Lithium-ion batteries are widely used in consumer electronics due to their relatively high energy density. Furthermore, lithium-ion batteries are becoming increasingly important for hybrid and electric vehicle applications. For some current commercially available batteries, the anode material can be graphite, and the cathode material can include lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel oxide (LiNiO2), lithium nickel cobalt oxide (LiNiCoO2), lithium nickel cobalt manganese oxide (LiNiMnCoO2), and lithium nickel cobalt aluminum oxide (LiNiCoAlO2), etc. For the anode, lithium titanate is a graphite alternative with good cycle performance, but its energy density is lower. Other graphite alternatives, such as tin oxide and silicon, have the potential to provide increased energy density. However, some high-capacity anode materials have been found to be commercially unsuitable due to high irreversible capacity loss and poor discharge and recharge cycles (especially for silicon) associated with structural changes and unusually large volume expansion, which are related to lithium intercalation / alloying. Structural changes and large volume changes can disrupt the structural integrity of the electrodes, thereby reducing cycle efficiency. Invention Overview

[0005] In a first aspect, the present invention relates to a negative electrode for a lithium-ion battery, the negative electrode comprising: an active material containing a silicon-based active material; nanoscale conductive carbon; and a polymer binder comprising poly(acrylamide-co-acrylate) having at least about 5 mol% of an acrylate portion and at least about 5 mol% of an acrylamide portion. The negative electrode may be an element of a negative electrode structure comprising a metal foil current collector and a negative electrode disposed on the current collector, wherein the negative electrode structure has a 180-degree peel adhesion force at a force of at least about 6 psi, and a cohesive force corresponding to maintaining electrode integrity when bent about a mandrel with a diameter of 6 mm. The lithium-ion battery may comprise: a negative electrode structure; a positive electrode structure comprising a current collector and an electrode disposed on the current collector, the electrode comprising lithium metal oxide, conductive carbon, and a polymer binder; a separator disposed between the negative electrode structure and the positive electrode structure; an electrolyte comprising a lithium salt and a non-aqueous solvent; and a container enclosing the electrode structure, the separator, and the electrolyte.

[0006] In another aspect, the present invention relates to a lithium-ion battery cell comprising: a negative electrode comprising a silicon-based active material, nanoscale conductive carbon, and a polymer binder, wherein the polymer binder comprises a copolymer of acrylate and acrylamide; a positive electrode comprising lithium metal oxide, conductive carbon, and the polymer binder; a separator located between the negative and positive electrodes; an electrolyte comprising a lithium salt and a non-aqueous solvent; and a container enclosing the electrodes, the separator, and the electrolyte. In some embodiments, when cycled at a rate of 1C between 2.5 volts and a selected charging voltage from the 10th cycle to the 700th cycle, the capacity of the lithium-ion battery in the 700th cycle is at least about 80% of the capacity in the 5th cycle. Brief description of the attached diagram

[0008] Figure 1 This is a Venn diagram, which shows how the properties of each polymer can be utilized simultaneously when forming the copolymer of the adhesive described herein.

[0009] Figure 2 This is an unfolded diagram of a pouch cell, which has a core that is separate from the pouch casing in two parts.

[0010] Figure 3 for Figure 2 A perspective view of the lower surface of an assembled pouch cell.

[0011] Figure 4 for Figure 3 A schematic diagram of the cross-section of the battery as observed along line 4-4.

[0012] Figure 5 An embodiment of a core comprising an electrode stack is shown.

[0013] Figure 6 The reaction for preparing poly(acrylamide-sodium co-acrylate) copolymer is shown.

[0014] Figure 7 A schematic diagram of the setup for a 180-degree adhesion-peel test.

[0015] Figure 8 The graph shows the adhesion force versus peel distance of a copper foil sample laminated with electrodes formed from eight polymer adhesive compositions.

[0016] Figure 9 The graph shows the adhesion force versus peel distance of a copper foil sample. The copper foil sample is laminated with electrodes formed by an adhesive composition of sodium polyacrylate / polyimide blends and lithium polyacrylate / polyimide blends with different polyacrylate molecular weights.

[0017] Figure 10 The graph shows the adhesion force versus peel distance of a copper foil sample. The copper foil sample is laminated with electrodes formed by poly(acrylamide-co-sodium acrylate) adhesive compositions in which each monomer unit has a different weight percentage, and electrodes formed by a contrasting adhesive composition.

[0018] Figure 11 This is a schematic diagram of the spindle test.

[0019] Figure 12 The graph shows the normalized capacity versus cycle life of a semi-coin cell with a SiOx anode, which is formed from poly(acrylamide-sodium co-acrylate) binder with different ratios of individual monomer units (from 100:0 to 0:100).

[0020] Figure 13 The graph shows the standardized capacity versus cycle life of a semi-button cell with a SiOx anode, which is formed from a binder composition of sodium polyacrylate / polyimide blends with different molecular weights of polyacrylate and lithium polyacrylate / polyimide blends.

[0021] Figure 14 A graph showing the normalized capacity versus cycle life of a button cell with a SiOx anode formed from eight polymer binder compositions.

[0022] Figure 15 A normalized capacity versus cycle life curve for a button cell with a SiOx anode formed by a poly(acrylamide-co-sodium acrylate) binder and an electrode formed by a contrasting binder composition.

[0023] Detailed description of the invention

[0024] Improved lithium-ion battery cycling is achieved by assembling silicon-based active materials into electrodes using a polymer binder, which is an acrylate monomer (S-PAA) (where the cation can be a metal cation, such as Na). + A copolymer of S-PAA and acrylamide monomers was developed. A desirable polymeric adhesive was found to exhibit good adhesion to the current collector and good interparticle cohesion. The S-PAA monomer provides good cohesion, while the acrylamide comonomer provides good adhesion. An adhesive based on an S-PAA-acrylamide copolymer with an appropriate monomer ratio is described to achieve excellent cycling performance with silicon-based anode active materials. As described herein, cycling performance has been significantly improved compared to other polymeric adhesives. This copolymer adhesive is also water-processable, providing processing advantages. The improved cycling performance is particularly advantageous for vehicle applications where cycling performance is an important criterion for commercial applicability.

[0025] Lithium is used in both primary and secondary batteries. An attractive feature of lithium for use in batteries or accumulators is its light weight and the fact that it is the most positively charged metal; aspects of these characteristics are advantageously available in lithium-based batteries. Certain forms of metals, metal oxides, and carbon materials are known to incorporate lithium ions from the electrolyte into their structure through intercalation, alloying, or similar mechanisms. The positive electrode of a lithium-based battery generally comprises an active material reversibly intercalated with lithium / alloyed with lithium. A lithium-ion battery generally refers to a battery in which the negative electrode active material is also an intercalated / alloyed lithium material. As used herein and for convenience, the terms battery and accumulator, and their variants, are used interchangeably unless some explicit distinctions are given.

[0026] The batteries described herein are lithium-ion batteries that use a non-aqueous electrolyte solution containing lithium cations and suitable anions. For rechargeable lithium-ion batteries, during charging, the cathode (positive electrode) undergoes oxidation, extracting lithium ions and releasing electrons. During discharging, the cathode undergoes reduction, inserting lithium ions and consuming electrons. Similarly, during charging, the anode (negative electrode) undergoes reduction, absorbing lithium ions and consuming electrons, and during discharging, the anode undergoes oxidation, releasing lithium ions and electrons. Unless otherwise stated, the performance values ​​mentioned herein are obtained at room temperature (i.e., approximately 23 ± 2 °C). As described below, some tests were performed on electrodes with silicon-based active materials in lithium batteries with lithium metal electrodes (referred to as half-cells) or lithium-ion batteries with a positive electrode containing lithium metal oxide (referred to as full-cells). In half-cells with silicon-based electrodes, the lithium electrode acts as the negative electrode, and the silicon electrode acts as the positive electrode, which is the opposite of its usual role as the negative electrode in lithium-ion batteries.

[0027] The term “element” is used in its conventional sense here to refer to a member of the periodic table, wherein if the element is in a composition, the element has a suitable oxidation state, and wherein, when expressed in elemental form, the element is in its elemental form M. 0 Therefore, metallic elements are generally only in their elemental form or in suitable alloys of metallic elements in the metallic state. In other words, apart from metal alloys, metal oxides or other metal compositions are generally not metallic.

[0028] When lithium-ion batteries are in use, the absorption and release of lithium from both the positive and negative electrodes causes structural changes in the electroactive materials. As long as these changes are substantially reversible, the material's capacity should not change with cycling. However, it has been observed that the capacity of the active material decreases to varying degrees with cycling. Therefore, after several cycles, the battery performance degrades below acceptable levels, and the battery is replaced. Furthermore, irreversible capacity loss typically occurs during the first cycle of the battery, which is significantly greater than the capacity loss in each subsequent cycle. Irreversible capacity loss (IRCL) is the difference between the initial charge capacity and the initial discharge capacity of a new battery. Lithium metal oxide-based cathodes can exhibit some IRCL effects, leading to some compensation for the amount of lithium available for cycling at the negative electrode. Due to the changes in battery materials during the initial cycling period, irreversible capacity loss results in a corresponding decrease in battery capacity, energy, and power.

[0029] Elemental silicon and other silicon-based active materials have attracted considerable attention as potential anode materials due to silicon's very high specific capacity in terms of lithium uptake and release. Elemental silicon can form alloys with lithium, which theoretically can have a lithium content corresponding to more than four lithium atoms per silicon atom (e.g., Li). 4.4 Therefore, the theoretical specific capacity of silicon is on the order of 4000 to 4400 mAh / g, significantly greater than the theoretical capacity of graphite, which is approximately 370 mAh / g. Graphite is believed to allow lithium intercalation to approximately one lithium atom corresponding to six carbon atoms (LiC6). Furthermore, similar to graphite, elemental silicon, silicon alloys, and silicon composites can exhibit low potentials relative to lithium metal. However, silicon undergoes a very large volume change when alloyed with lithium. Large volume expansions of approximately two to three times or more of the original volume have been observed, and these large volume changes are associated with a significant decrease in the cycle stability of batteries with silicon-based anodes. Low oxides of silicon, namely SiO2, have also been found... x (x < 2) is an ideal active material for lithium-based batteries, and in some implementations, it exhibits high specific capacity for lithium alloying. The mention of silicon low oxides provides the understanding that silicon dioxide is a fully oxidized form of silicon. For convenience, silicon low oxides are often referred to as silicon oxide, and unless otherwise specified, they are not limited to silicon monoxide (SiO). Silicon oxide is a widely used material in various fields, and the terminology may vary slightly between different fields; silicon oxide can also be used to refer to SiO2.

[0030] In a particularly noteworthy embodiment, the silicon-based active material may comprise elemental silicon, silicon oligooxides, and / or composites thereof (e.g., composites with carbon) as the primary active material. Silicon oligooxides have been found to be particularly effective for achieving longer cycle stability. To stabilize the silicon-based active material and increase conductivity, carbon may be incorporated into the composite active material. Long cycle stability remains challenging with carbon composites containing nanoscale elemental silicon and / or silicon oxide, although the applicant has achieved significant success in the cycle stability of batteries designed for consumer electronics and automotive applications. Longer cycle stability is illustrated here using copolymer negative electrode binders accompanying mixtures of electroactive graphite and silicon-based composites, along with other electrode design improvements, although for some applications, suitable cycling can be achieved using silicon-based composites as the sole negative electrode active material. As discussed in detail below, silicon-based electrodes may further incorporate additional conductive materials, such as nanoscale carbon.

[0031] The active materials used in lithium-ion secondary batteries typically include, for example, positive electrode (i.e., cathode) active materials with a moderately high average voltage relative to lithium and silicon-based active materials for the negative electrode (i.e., anode). Generally, a variety of cathode materials can be used. For example, commercially available cathode active materials can be used given current commercial production availability. Such cathode active materials include, for example, lithium cobalt oxide (LiCoO2), LiNi... 1 / 3 Mn 1 / 3 Co 1 / 3 O2 (L333 or NMC111), LiNiCoAlO2 (NCA), other lithium nickel manganese cobalt oxides (NMC), LiMn2O4 (lithium manganese oxide spinel), their modified forms, or mixtures thereof.

[0032] Nickel-rich lithium nickel cobalt manganese oxide (LiNi x Mn y Co z O2 (0.45≤x, 0.05≤y, z≤0.35) is of interest due to its lower cost and lower flammability risk compared to lithium cobalt oxides, and its ability to cycle within the desired voltage range. Specifically, the desired cycling results can be obtained from nickel-rich lithium nickel manganese cobalt oxide (N-NMC), which can be produced by the formula LiNi x Mn y Co z O2 represents a compound where x ≤ 0.45 and x + y + z ≈ 1. Commercially available formulations of these compounds include, for example, LiNi. 0.5 Mn 0.3 Co 0.2 O2 (BASF), LiNi 0.6 Mn 0.2 Co0.2 O2 (L&F from South Korea and Umicore from Belgium), LiNi 0.8 Mn 0.1 Co 0.1 O2 (L&F of South Korea, BASF of Germany, Umicore of Belgium, and LG Chemical of South Korea). In this industry, NCM and NMC are used interchangeably in the order listed for cobalt and manganese, and the expressions are equivalent, based only on personal preference. Furthermore, lithium cobalt oxides can be stabilized to cycle efficiently at higher voltages, as described in U.S. Patent 10,193,135 to Sharma et al., entitled "Positive Electrode Active Materials With Composite Coatings for High EnergyDensity Secondary Batteries and Corresponding Processes," which is incorporated herein by reference.

[0033] Similar to silicon, oxygen-deficient silicon oxides, such as silicon dioxide (SiO2), are formed. xWith a density of 0.1 ≤ x ≤ 1.9, silicon oxide can be intercalated with lithium or alloyed with lithium, making it suitable as an active material in lithium-ion batteries. Silicon oxide can bind a relatively large amount of lithium, resulting in a high specific capacity. However, the capacity of silicon oxide typically decays relatively quickly with battery cycling. Commercially available silicon-based materials containing SiO from various suppliers can form composites with carbon and silicon nanocrystals. These materials are available from Alfa Aesar (USA), Sigma-Aldrich (USA), Shin-Etsu (Japan), Osaka Titanium Corporation (Japan), and Nanostructured and Amorphous Materials Corp. (USA). Other specific suitable formulations of silicon-based compositions will be further described below. The applicant has achieved cycle stability of silicon oxide composite active materials using the electrode formulations described herein. In some implementations, it may be desirable to have a negative electrode comprising a combination of graphitic carbon active materials and silicon-based active materials to extend cycle life while keeping the reduction in specific capacity within acceptable limits, and the excellent cycling performance illustrated herein utilizes such active material blends. Preliminary results show that the modified copolymer binder described herein allows for sufficient cycling using silicon-based composite active materials without graphite, thus enabling its use in a wider range of applications.

[0034] Due to the significant volume changes of silicon-based materials during cycling, electrode design has become a crucial aspect of constructing batteries with silicon-based anodes to achieve desired cycling performance. Part of electrode design involves selecting a polymer binder that helps maintain electrode integrity during cycling. As further explained below, polyimide was initially identified as a polymer binder for silicon-based materials due to its mechanical strength. Therefore, polyimide provides some stability to the electrode because the mechanical forces in the polymer are related to the material changes that occur in the active material during lithium absorption or release. The applicant subsequently discovered that blends of various polymers containing polyimide and more flexible polymers further improved electrode performance. The results obtained herein from copolymer binders show additional improvements compared to polyimide-based binders.

[0035] Achieving stable cycling of silicon-based active materials in batteries with reasonable capacity and energy density requires extensive battery engineering. The applicant initially made significant progress in cycling of anodes with silicon-based active materials using polyimide binders and nanoscale carbon conductive materials. See U.S. Patent 10,290,871 to Masarapu et al., entitled “Battery Cell Engineering and Design to Reach High Energy,” which is incorporated herein by reference. High tensile strength and high elongation are believed to be important characteristics of polyimides that contribute to cycling performance. Polyimide binders can be processed with organic solvents, although recently developed polyimides are water-processable; see UBE Industries Polyimides.

[0036] The applicant utilizes a polymer blend containing polyimide and a more flexible binder, such as polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, or lithium-ionized polyacrylic acid, to achieve significantly improved cycle life. The negative electrode formed from the polymer blend incorporates nanoscale conductive carbon. The desired cycle life obtained from these polymer blends is described in U.S. Patent Application No. 2019 / 0207209 (hereinafter referred to as '209 Application') issued to Venkatachalam et al., entitled "Electrodes with Silicon Oxide Active Materials for Lithium-ion Cells Achieving High Capacity, High Energy Density, and Long Cycle Life Performance," which is incorporated herein by reference.

[0037] As the work presented herein demonstrates, further improvements to polymer binders now enable silicon-based active materials with high specific capacity to cycle stably for many more times. Other important battery engineering approaches are described in the '209 application, designed to achieve many cycles with a capacity reduction of no more than 80% relative to the active cell. Electrode and cell design features will be described in more detail below.

[0038] The polymeric adhesive described herein was chosen to achieve a balance between adhesive and cohesive forces. It is believed that the adhesive and cohesive force parameters described herein are somewhat related to the previously considered properties of tensile strength, elongation, and modulus of elasticity; however, adhesive and cohesive forces can be measured more directly using the methods described below. To achieve this balance between adhesive and cohesive forces, copolymers based on one monomer (polyacrylamide) providing good adhesive strength and another monomer (metal salt of polyacrylate) providing good cohesive strength were used. It was found that simultaneously achieving good adhesive and cohesive forces is important for achieving improved cycling performance. The polymeric adhesive is electrically water-processable. Reference Figure 1 The principles explained in this section are represented by Venn diagrams.

[0039] The monomer units of the copolymer adhesive are acrylamide and polyacrylic acid salts (SPAA). The salt cation can be a metal cation, such as lithium (LiPAA), sodium (NaPAA), or potassium (KPAA), although other metal or non-metal cations, such as ammonium NH4, can also be used. + If needed, mixtures of counterions can be used. S-PAA polymers have been found to impart strong cohesion to the corresponding electrodes. As further elaborated below, the cohesion of the electrode structure on the current collector is evaluated by bending around a mandrel of a specific diameter. The diameter of the mandrel around which the electrode structure can bend without losing the mechanical integrity of the electrode provides information about the cohesion of the electrode material. Adhesion is evaluated using commercial testing equipment, where forces are applied in a controlled manner to assess the force required to pull the electrode from the current collector. The ratio of monomer units can be selected to achieve the desired balance between adhesion and cohesive stability.

[0040] The copolymer can be synthesized according to the disclosed methods. Specifically, acrylate groups can be formed via nucleophilic substitution of amide groups by carboxylic acid ester groups, wherein the extent of the reaction controls the degree of acrylamide groups in the final polymer. Alternatively, the copolymer can be formed directly through a polymerization reaction. For direct synthesis, the relative amounts of carboxylic acid ester groups and acrylamide groups can be controlled. More information on the synthesis reaction is provided below. Furthermore, the molecular weight of the polymer can be appropriately controlled or selected.

[0041] While the applicant has made significant progress in cycling silicon-based active materials using polyimide and polyimide blends with lower modulus polymers, current binders can further improve cycling performance. As described herein, the battery can be cycled at a charge / discharge rate of 1C (charge / discharge over 1 hour) with a degradation of no more than 20% of the initial cycle after more than 800 cycles, which is followed by one or more formation cycles used to initialize the battery at the corresponding 1C rate.

[0042] Electrode structure

[0043] The electrodes of a battery comprise active materials, binders, and typically conductive additives. The electrodes are formed into sheets, dried, and pressed to achieve the desired density and porosity. Electrode sheets are typically formed directly onto a metal current collector, such as a metal foil or thin metal grid. For many battery structures, electrode layers are formed on both sides of the current collector to provide the desired performance in the assembled battery. Electrode layers on each side of the current collector can be considered elements of the same electrode structure because they are at the same potential within the battery; however, the current collector itself, while part of the electrode structure, is not typically considered part of the electrode due to its electrochemical inertness. Therefore, references to the physical aspects of the electrode usually refer to a single electrode composition within the electrode structure. Conductive current collectors facilitate electron flow between the electrode and the external circuitry.

[0044] In some implementations, when the positive or negative electrode is used at high load levels, the electrode density can be reduced to provide good cycle stability. Within reasonable limits, electrode density is a function of pressure. Generally, electrode density cannot be arbitrarily increased without sacrificing performance in terms of load levels while achieving the required cycle performance and capacity at higher discharge rates. Characteristic analyses of specific negative and positive electrode layers are described below.

[0045] In some embodiments, the current collector may be formed of nickel, aluminum, stainless steel, copper, etc. The electrode material may be cast as a thin film onto the current collector. Then, the electrode material and the current collector may be dried, for example, in an oven, to remove solvent from the electrode. In some embodiments, the dried electrode material in contact with the current collector foil or other structure can withstand approximately 2 to approximately 10 kg / cm². 2 The pressure. The current collector used in the positive electrode may have a thickness of about 5 micrometers to about 30 micrometers, in other embodiments about 10 micrometers to about 25 micrometers, and in further embodiments about 14 micrometers to about 20 micrometers. In one embodiment, aluminum foil current collector is used in the positive electrode. The current collector used in the negative electrode may have a thickness of about 2 micrometers to about 20 micrometers, in other embodiments about 4 micrometers to about 14 micrometers, and in further embodiments about 6 micrometers to about 10 micrometers. In one embodiment, copper foil is used as the current collector in the negative electrode. Those skilled in the art will recognize that other current collector thickness ranges within the above-defined range are contemplated and fall within the scope of this disclosure.

[0046] negative electrode

[0047] The basic electrode design comprises a blend of an active composition, a polymer binder, and a conductive diluent. As described above, in some embodiments, the improved electrode design may involve a copolymer binder and an active composition comprising a silicon-based material and a nanoscale conductive carbon additive. The copolymer will be discussed in detail below. The active material may include, for example, a silicon-based composite material or an active material blend that is predominantly silicon-based, such as a silicon oxide composite, and in some embodiments, at least 10% by weight of different types of graphite. While graphite can provide conductivity to the electrode, it has also been found that, in some embodiments, a certain amount of different nanoscale conductive carbon remains important for the ability to produce a long-cycle negative electrode. Generally, nanoscale conductive carbon is believed to be electrochemically inactive, while graphite is electrochemically active. These negative electrode designs are then incorporated into the electrode, further improving upon previously discovered silicon-based electrodes.

[0048] There has been considerable interest in high-capacity silicon-based anode active materials. The applicant has achieved particular success in terms of cycle stability using materials primarily based on silica composites, despite extensive work on other silicon-based active materials. Additional cycle stability can be obtained using blends of silicon-based active materials with activated graphite carbon. For many applications, sufficient cycle stability can be achieved by cycling silicon-based active materials using the improved copolymer binder described herein, without the need for additional activated graphite carbon.

[0049] Typically, when cycling at a rate of C / 3 from 5 millivolts (mV) to 1.5 volts relative to lithium metal, the total capacity of the anode-doped active material can be at least about 500 mAh / g, at least 750 mAh / g in some embodiments, at least about 900 mAh / g in further embodiments, at least about 1000 mAh / g in other embodiments, at least about 1100 mAh / g in still embodiments, and at least about 1250 mAh / g in some embodiments. While the applicant has been able to achieve desired levels of cycling of silicon-based active materials in the anode, the degree of cycling stability and other design considerations have an impact on certain applications. Therefore, in some applications, higher cycling and lower energy density may be desirable, making a higher proportion of graphite active material suitable, and in applications where higher energy density is desired, improved binders provide reasonable cycling for active materials containing up to or entirely silicon-based composite active materials. For convenience, three ranges of active materials are discussed, forming a logical group, but this is not limiting to other, broader groups. Regarding the polymeric adhesives described herein, these adhesives are suitable for electrodes with any measurable amount of silicon-based active material, but they are particularly beneficial for electrodes with a slightly larger proportion of silicon-based active material.

[0050] In the first group of active materials, the doped active material may comprise at least about 25% by weight of silicon-based active material, in a further embodiment at least about 27.5% by weight of silicon-based active material, in other embodiments about 28% to about 45% by weight of silicon-based active material, and in yet another embodiment about 30% to about 42.5% by weight of silicon-based active material. Accordingly, the doped active material may comprise no more than about 75% by weight of graphite, in some embodiments about 50% to about 72.5% by weight of graphite, in further embodiments about 55% to about 72% by weight of graphite, and in yet another embodiment about 57.5% to about 70% by weight of graphite. Those skilled in the art will recognize that ranges of specific discharge capacity and concentration of other silicon-based active materials within the aforementioned specific range are contemplated and fall within the scope of this disclosure.

[0051] In the second group of active materials, the doped active material may comprise at least about 45 wt% silicon-based active material, in a further embodiment at least about 50 wt% silicon-based active material, in other embodiments about 55 wt% to about 95 wt% silicon-based active material, and in yet another embodiment about 60 wt% to about 90 wt% silicon-based active material. Accordingly, the doped active material may comprise about 5 wt% to about 60 wt% graphite, in a further embodiment about 7 wt% to about 50 wt% graphite, in yet another embodiment about 8 wt% to about 45 wt% graphite, and in yet another embodiment about 10 wt% to about 40 wt% graphite. Those skilled in the art will recognize that the specific discharge capacity and concentration range of other silicon-based active materials within the aforementioned specific range are contemplated and fall within the scope of this disclosure.

[0052] In the third group of active materials, the doped active material may comprise at least about 95% by weight of silicon-based active material, in a further embodiment at least about 97.5% by weight of silicon-based active material, and in other embodiments about 100% by weight of silicon-based active material. Accordingly, the doped active material may comprise no more than about 5% by weight of graphite, in a further embodiment no more than about 2.5% by weight of graphite, and in other embodiments about no graphite. Those skilled in the art will recognize that additional ranges of specific discharge capacity and concentration of other silicon-based active materials within the aforementioned explicit range are contemplated and fall within the scope of this disclosure.

[0053] As described above and in detail below, suitable silicon-based active materials may include composites containing a carbon component. Silicon-based active materials will be discussed in detail below. A composite refers to a particulate material whose components are tightly bound together into a single material, exhibiting effective homogeneity at an appropriate scale, unlike a dopant involving mixtures bound together with a polymer binder. Composite components may include, for example, silicon, oxygen, carbon, etc. While not wishing to be theoretically limited, the carbon component of a silicon-containing composite is generally not considered electrochemically active and is typically not graphite, although activity is an abstract concept because the tight bonding in the composite and crystal structure can be extremely complex and difficult to assess. In any case, those skilled in the art will readily understand that the carbon component of a composite material is different from that of different graphites not present in the active material dopant. The following examples are based on commercial composite compositions that are believed to primarily contain silicon low oxides and a certain amount of elemental silicon crystals and elemental carbon in the composite particulate material.

[0054] Commercially available graphite exists in both natural and synthetic forms, and suitable graphite includes both natural and synthetic graphite. Graphite is a crystalline form of carbon, in which carbon atoms are covalently bonded within sheets. As used herein, graphite refers to graphitic carbon that does not require perfect crystallinity, and some natural graphite materials may contain some crystalline impurities. However, graphite generally refers to materials dominated by a graphitic structure, which is generally accepted in the art. Graphite conducts electricity along the plane of covalent carbon sheets stacked in crystals. Crystalline carbon in graphite form can intercalate lithium, making it a proven electrochemically active material for lithium-ion batteries.

[0055] The average particle size of the graphite particles can be from about 1 micrometer to about 30 micrometers, in a further embodiment from about 1.5 micrometers to about 25 micrometers, and in other embodiments from about 2 micrometers to about 20 micrometers. Generally, it is desirable that the graphite does not include particles larger than the electrode thickness to avoid an uneven electrode surface, and graphite particles significantly smaller than one micrometer have lower crystallinity. In some embodiments, the D50 (mass-weighted median diameter) of the graphite carbon can be from about 5 micrometers to about 50 micrometers, in a further embodiment from about 7 micrometers to about 45 micrometers, and in another embodiment from about 10 micrometers to about 8 micrometers to about 40 micrometers. Furthermore, in some embodiments, the BET surface area (which can be evaluated according to ISO 4652) of the graphite carbon active material can be about 1 m². 2 / g to approximately 100m 2 / g, in a further implementation scheme, is approximately 5m 2 / g to approximately 85m 2 / g, and in another embodiment, approximately 7.5m 2 / g to approximately 60m 2 / g. Those skilled in the art will recognize that other ranges of particle size and surface area for graphitic carbon active materials are conceived and fall within the scope of this disclosure. In contrast, conductive carbon black and the like (referred to as subcrystalline) typically have a particle size of at least about 40 μm. 2 / g to 1000m 2 / g or a larger surface area.

[0056] Regarding polymer binders, the applicant has achieved reasonable cycling performance for silicon-based batteries using high tensile strength binders (e.g., polyimide binders). See U.S. Patent 9,601,228 (hereinafter referred to as the '228 patent) to Deng et al., entitled "Silicon Oxide-Based High Capacity Anode Materials for Lithium Ion Batteries," which is incorporated herein by reference. The applicant has further discovered that using binders having a blend of polyimide and a second polymer having a lower elastic modulus can improve cycling performance. See the '209 application cited above. This polymer binder blend, a blend of silicon-based active materials and graphite active materials, provides a significant improvement in the cycling performance of lithium-ion batteries.

[0057] As described herein, novel copolymer adhesives that provide further cycling stability have been identified. These copolymers have a first monomer unit and a second monomer unit, wherein the first monomer unit is believed to provide good adhesion between the electrode and the current collector, and the second monomer unit is believed to provide good cohesion to maintain electrode integrity when bent about a mandrel of selected radius. The copolymer composition, synthesis, and properties are discussed in detail below. The novel polymer blends are water-processable, which can be considered an advantage over organic solvent-processable adhesives.

[0058] To form the electrode, the powder can be mixed with a polymer in an aqueous liquid (e.g., pure water). The particulate components of the electrode, namely the active material and nanoscale conductive carbon, can be mixed with a polymer binder in a solvent to form a paste. The resulting paste can be pressed into the electrode structure. The electrode is then dried to remove water. Water removal is important because water is reactive in the assembled battery. For example, the electrode can be vacuum dried at a temperature of about 90°C to about 150°C. Excessive heat may degrade the polymer. Drying can typically be carried out for 15 minutes to 15 hours. Those skilled in the art will recognize that other drying temperatures and time ranges within the above-defined ranges are contemplated and fall within the scope of this disclosure.

[0059] The active material loading in the binder can be very high. In some embodiments, the negative electrode has about 75 to about 96% by weight of negative electrode active material, in other embodiments about 78 to about 94% by weight of negative electrode active material, and in further embodiments about 80 to about 90% by weight of negative electrode active material. In some embodiments, the negative electrode has about 4 to about 20% by weight of polymer binder, in other embodiments about 5 to 19% by weight of polymer binder, and in further embodiments about 6 to 18% by weight of polymer binder. Furthermore, in some embodiments, the negative electrode contains about 0.05 to about 7% by weight of nanoscale conductive carbon, in further embodiments about 0.075 to about 6.5% by weight, and in other embodiments about 0.1 to about 6% by weight of nanoscale conductive carbon. Those skilled in the art will recognize that other ranges of polymer loading within the explicit range described above are contemplated and fall within the scope of this disclosure.

[0060] For improved cycling performance, nanoscale carbon additives or combinations thereof have been found to be particularly desirable for anodes. Nanoscale conductive carbon typically refers to particles of high surface area elemental carbon, with at least two dimensions of the primary particles being submicron. Suitable nanoscale conductive carbons include, for example, carbon black, carbon nanotubes, and carbon nanofibers. In some embodiments, the nanoscale conductive carbon additive used in the anode may include carbon nanotubes, carbon nanofibers, carbon nanoparticles (e.g., carbon black), or combinations thereof. In some embodiments, to achieve improved performance, the conductive additive may have a conductivity of at least about 40 S / cm, at least about 50 S / cm in some embodiments, and at least about 60 S / cm in further embodiments. Those skilled in the art will recognize that other ranges of particle loading and conductivity within the defined scope are contemplated and fall within the scope of this disclosure.

[0061] Electrical conductivity is the reciprocal of resistivity and can be reported by the distributor, often measured using specific techniques developed by the distributor. For example, carbon black resistance is measured between two copper electrodes with Super PTM carbon black; see Timcal Graphite & Carbon, A Synopsis of Analytical Procedures, 2008, www.timcal.com. Suitable supplemental conductive additives may also be added to aid in long-term cycling stability. Alternatively, some suppliers describe the conductive carbon concentration used to achieve the conductive percolation threshold.

[0062] Carbon black refers to synthetic carbon materials and may also be called acetylene black, furnace black, thermal black, or other names indicating the synthesis method. Carbon black is often referred to as amorphous carbon, although it has been proposed that at least some forms of carbon black contain small, short-range or medium-range ordered crystalline domains corresponding to the crystal structures of graphite or diamond; however, for practical purposes, the material can be considered amorphous. According to ISO technical specification 80004-1 (2010), carbon black is a nanostructured material. The main particles of carbon black can be on the order of tens of nanometers or smaller, but the main particles are usually hard-melted into chains or other aggregates, and the smallest dispersible unit can be considered to be between about 80 nanometers and 800 nanometers, which is still submicron. Carbon black is commercially available; it has been synthesized to provide desired levels of conductivity, such as Super- (Timcal) (Ketjen (Akzo Nobel) (hawinigan Shawinigan Black (Chevron-Phillips) and Black Pearl (Black Pearls (Cabot)

[0063] Carbon nanofibers are fibers with high aspect ratios, typically comprising sheet-like, tapered, or other forms of graphene layers, with carbon nanotubes comprising graphene sheets folded into tubes. Carbon nanofibers can have diameters of 250 nanometers or smaller and are commercially available, for example, Carbon nanofibers (Pyrograf Products, Inc.) or from American Elements, Inc. Carbon nanotubes have been found to be desirable conductive additives that can improve the cycling performance of either the positive or negative electrode. Single-walled or multi-walled carbon nanotubes are also available from: American Elements (California, USA), Canano Technologies (China), Cabot (Massachusetts, USA), TUBALL™ (October, Luxembourg), Black Diamond (Texas, USA), Fuji Electric (Japan), Alfaisa (Massachusetts, USA), or NanoLabs (Massachusetts, USA).

[0064] The positive and negative electrodes used in the batteries described herein can have high active material loading and relatively high electrode density. For a given active material loading, density is inversely proportional to thickness; therefore, electrodes with higher density are thinner than those with lower density. Load equals density multiplied by thickness. In some embodiments, the negative electrode of the battery has a density of at least about 1.5 mg / cm³. 2 The loading level of the negative electrode active material is approximately 2 mg / cm³ in other embodiments. 2 Approximately 8 mg / cm 2 In other implementations, it is approximately 2.5 mg / cm³. 2 Approximately 6 mg / cm 2 In other implementations, it is approximately 3 mg / cm³. 2 Approximately 4.5 mg / cm 2 In some embodiments, the density of the active material at the negative electrode of the battery is approximately 0.5 g / cc (cc = cubic centimeters (cm³)). 3 The concentration is approximately 2 g / cc, in other embodiments approximately 0.6 g / cc to approximately 1.5 g / cc, and in yet another embodiment approximately 0.7 g / cc to approximately 1.3 g / cc. Similarly, the silicon oxide electrode may have an average dry thickness of at least about 15 micrometers, in further embodiments at least about 20 micrometers, and in yet another embodiment about 25 micrometers to approximately 75 micrometers. The resulting silicon oxide electrode may exhibit at least about 3.5 mAh / cm³. 2 The capacity per unit area, in a further implementation scheme, is at least approximately 4.5 mAh / cm². 2 And in another implementation, at least about 6 mAh / cm³. 2 Those skilled in the art will recognize that other ranges of active material loading and electrode density within the aforementioned specific scope are conceived and fall within the scope of this disclosure.

[0065] Negative electrode copolymer adhesive

[0066] As shown in this paper, copolymers of acrylamide monomer units with metal-polyacrylic acid / acrylate (M-PAA) have been found to offer improved cycling performance compared to previously successful adhesive systems based on polyimide for silicon-based active materials. The relative amounts of the acrylamide and M-PAA moieties can be adjusted to correspondingly modulate the adhesive properties. Further testing of the polymer showed that the good cycling adhesive exhibits both good adhesion and good cohesion. While not wishing to be limited by theory, it is reasonable to assume that good cohesion and good adhesion contribute to the mechanical stability of the electrode during battery cycling, and that the active material undergoes significant reversible morphological changes during cycling. Although not illustrated herein, the copolymer can also be blended with other polymers used to form electrode adhesives.

[0067] This paper focuses on random copolymers, although block copolymers should exhibit similar ideal adhesive properties. As described below, in "random" copolymers, the monomer moieties can still possess some degree of order within the copolymer because the synthesis kinetics are influenced by adjacent moieties. For copolymers, two potential parameters affecting adhesive properties can be considered: the ratio of acrylamide moieties to M-PAA moieties and the average molecular weight. Polymer molecular weight is typically measured indirectly and can be assessed using recognized evaluation techniques specific to particular polymer types, which in many cases involve rheological measurements. For polyacrylamide, the molecular weight can be calculated based on the measured intrinsic viscosity using established equations. Copolymer parameters are controlled through the synthesis procedure.

[0068] The molar ratio of the acrylamide portion to the M-PAA portion can range from about 5:95 to about 95:5, in further embodiments from about 10:90 to about 90:10, in other embodiments from about 20:80 to about 80:20, in still other embodiments from about 25:75 to about 75:25, and in some embodiments from about 30:70 to about 70:30. Regarding the average molecular weight, in some embodiments, the average molecular weight of the copolymer can be from about 50,000 Daltons to about 5,000,000 Daltons, in further embodiments from about 75,000 Daltons to about 2,000,000 Daltons, and in still other embodiments from about 100,000 Daltons to about 1,000,000 Daltons. Those skilled in the art will recognize that other portion ratios and average molecular weight ranges within the above-defined ranges are contemplated and fall within the scope of this disclosure.

[0069] The copolymer can be characterized by adhesion and cohesion, and the corresponding results are given in the examples. Adhesion is measured by forming electrodes on the current collector surface using a selected electrode formation scheme. Dimensions, such as thickness, can be selected to have values ​​corresponding to the electrode design of the battery. Adhesion is then measured using a 180-degree peel adhesion test, as detailed in the examples. Adhesion is evaluated by a force value from the test, which can be normalized according to the width of the bonded element. In some embodiments, the normalized force can be at least 6 lbf / m, in further embodiments at least about 8 lbf / m, and in other embodiments at least about 10 lbf / m. Cohesion is also evaluated using electrodes on one surface of the current collector. The electrode structure is bent on a cylindrical mandrel with the current collector side facing down, such that the opposite sides of the structure are parallel in a “U” shape. If the electrode retains its integrity after bending, it indicates that the electrode retains its cohesion. The mandrel diameter is reduced to 2 mm, which is the smallest mandrel diameter tested. Typically, in some embodiments, the copolymer exhibits cohesive stability around a mandrel with a diameter of 6 mm, in further embodiments around a mandrel with a diameter of 4 mm, in other embodiments around a mandrel with a diameter of 2 mm, and in other embodiments less than 2 mm. Results of adhesive and cohesive forces are given in the examples. Those skilled in the art will recognize that other ranges of adhesive and cohesive forces within the aforementioned specific range are contemplated and fall within the scope of this disclosure.

[0070] In one method of synthesizing copolymers, the starting material may be polyacrylamide, which is then hydrolyzed to replace the amide groups with carboxylic acid ester groups. For example, the synthesis by hydrolysis and the properties of the resulting polymers are described in the following literature: a review article by Kurenkov et al., “Alkaline Hydrolysis of Polyacrylamide,” Russian Journal of Applied Chemistry, Vol. 74(4), 2001, pp. 543-554; Higuchi, “Kinetic Aspects of Alkaline Hydrolysis of Poly(acrylamide),” Polymer Journal, Vol. 3(3), 1972, pp. 370-377; and Kulicke et al., “Preparation and characterization of a series of poly(acrylamide-co-acrylates) with a copolymer composition between 0 to 96.3 mol% acrylate units.” "0 and 96.3 mol-% acrylate units with the same degree and distribution of polymerization", Colloid & Polymer Science, Vol. 263, 1985, pp. 530-540, all of which are incorporated herein by reference. As explained in these references, the copolymers obtained by hydrolysis may not be entirely random copolymers, due to the influence of adjacent groups on reaction kinetics. A comparison between copolymers formed by the hydrolysis and direct polymerization of polyacrylamide is described in Klein et al., "Preparation and Characterization of Poly(acrylamide-co-acrylic acid)", Makromo. Chem., Vol. 179, 1978, pp. 1895-1904, which is incorporated herein by reference. Klein et al. concluded that polymers synthesized by direct copolymerization and polymers synthesized by hydrolysis have the same monomer sequence.Various poly(acrylamide-co-acrylate) polymers are also commercially available.

[0071] Although hydrolysis of the amide groups can break polymer chains, conditions can be controlled to keep any chain breakage at a low level. Using this control in copolymer synthesis, the molecular weight of the resulting copolymer can be obtained from the molecular weight of the starting polyacrylamide, which is adjusted for changes in the molecular weight of the repeating moiety. Starting polyacrylamide is commercially available, and suitable suppliers include, for example, PolySciences Inc. (USA), Sigma-Aldrich (USA), and TCI (Japan). While the copolymers of the examples are synthesized as described below, these copolymers are also commercially available and used as flocculants for liquid purification. In the field of flocculants, the copolymers described herein may be referred to as anionic polyacrylamide.

[0072] While the examples and discussion herein generally focus on the use of copolymers alone as electrode binders, the applicant has successfully used polymer blends to improve binder performance. The copolymers described herein can also be used in polymer blends. Suitable polymer blends typically comprise at least 25% by weight of poly(acrylamide-co-M-PAA), at least about 35% by weight in further embodiments, and about 40% to about 90% by weight in other embodiments. Those skilled in the art will recognize that other ranges within the aforementioned defined polymer blend ratios are contemplated and fall within the scope of this disclosure.

[0073] High-capacity silicon-based anode materials

[0074] Typically, the battery designs described herein are based on high-capacity anode active materials. Specifically, when cycled relative to lithium metal at a rate of C / 10 from 0.005 volts to 1.5 volts, the anode active material typically exhibits a specific capacity of at least about 800 mAh / g, at least about 900 mAh / g in further embodiments, at least about 1000 mAh / g in other embodiments, at least about 1150 mAh / g in some embodiments, and at least about 1400 mAh / g in others. This means that the specific capacity of the negative electrode active material can be evaluated in batteries with a lithium metal relative electrode. However, in the batteries described herein, the negative electrode exhibits a reasonably comparable specific capacity when cycled relative to a high-capacity lithium metal oxide positive electrode active material. In batteries with non-lithium metal electrodes, the specific capacity of each electrode can be evaluated by dividing the battery capacity by the respective weight of the active material. As described herein, the desired cycling results and good capacity are observed when using a combination of silicon-based active materials and graphite carbon active materials.

[0075] Similar to graphite, elemental silicon, silicon alloys, and silicon composites may exhibit low potentials relative to lithium metal. However, elemental silicon typically undergoes very large volume changes when alloyed with lithium. Large volume expansions of approximately two to four times or more of the original volume have been observed, and these large volume changes are associated with a significant decrease in the cycle stability of batteries with silicon-based negative electrodes.

[0076] Commercially available silicon low-oxide, elemental silicon, and carbon composites can be used in the batteries described herein. Furthermore, other formulations of silicon-based anode active materials with high capacity and reasonable cycle performance have been developed. Several silicon-based compositions are described below as potential and promising alternatives to commercially available SiO-based compositions.

[0077] Furthermore, in some formulations, the high-capacity silicon-based material in the negative electrode of a lithium-ion battery exhibits a large irreversible capacity loss (IRCL) during the first charge / discharge cycle. The high IRCL of the silicon anode can consume a significant portion of the battery's usable energy output. Because the cathode (i.e., the positive electrode) provides all the lithium in a conventional lithium-ion battery, a high IRCL in the anode (i.e., the negative electrode) leads to a low-energy battery. To compensate for the large anode IRCL, supplemental lithium can be added directly or indirectly to the negative electrode material to offset the IRCL. The use of supplemental lithium to improve the performance of silicon-based electrodes is also described in '294 application and '228 patent, both of which are cited above and incorporated herein by reference. The use of supplemental lithium in improved battery designs will be further described below.

[0078] The anode of the battery described herein can utilize a nanostructured active silicon-based material to better accommodate volume expansion, thereby maintaining the mechanical electrode stability and cycle life of the battery. Nanostructured silicon-based anode compositions are disclosed in '294 application, '228 patent, and U.S. Patent 9,139,441 ('441 patent) to Angushamy et al., entitled "Porous Silicon Based Anode Material Formed Using Metal Reduction," which is incorporated herein by reference. Suitable nanostructured silicon may include, for example, nanoporous silicon and nanoparticle silicon. Furthermore, nanostructured silicon can form complexes with carbon and / or alloys with other metal elements. The aim of designing improved silicon-based materials is to further stabilize the anode material during cycling while maintaining high specific capacity and, in some embodiments, reducing irreversible capacity loss during the first charge and discharge cycles. Furthermore, a pyrolytic carbon coating has been observed to stabilize the silicon-based material for battery performance.

[0079] Desired high-capacity negative electrode active materials may include porous silicon (pSi)-based materials and / or composites of porous silicon-based materials. Generally, pSi-based materials comprise highly porous crystalline silicon, which provides a high surface area and / or high porosity relative to bulk silicon. While nanostructured porous silicon can be formed by various methods, such as electrochemical etching of silicon wafers, particularly good battery performance is obtained from nanostructured porous silicon obtained by metal reduction of silicon oxide powder. In particular, this material exhibits exceptionally good cycle performance while maintaining a high specific capacity. The formation of composites of pSi-based materials with carbon-based materials or metals can also mechanically stabilize the negative electrode to improve cycle performance. Further description of pSi-based materials produced by silicon oxide reduction can be found in the '441 patent cited above.

[0080] Regarding composite materials, the nanostructured silicon component can be bonded to, for example, carbon nanoparticles and / or carbon nanofibers in a compact composite material. For example, these components can be milled to form a composite in which the materials are tightly bonded. Generally, this bonding is believed to possess mechanical properties, such as a softer silicon coated onto or mechanically adhered to a harder carbon material. In another or alternative embodiment, silicon can be milled together with metal powders to form alloys, which may have corresponding nanostructures. The carbon component can be combined with silicon-metal alloys to form multi-component composites.

[0081] Furthermore, carbon coatings can be applied to silicon-based materials to improve conductivity, and carbon coatings also appear to stabilize silicon-based materials by improving cycling performance and reducing irreversible capacity loss. The desired carbon coating can be formed by pyrolyzing an organic composition. The organic composition can be pyrolyzed at relatively high temperatures, such as about 800°C to about 900°C, to form a hard, amorphous coating. In some embodiments, the desired organic composition can be dissolved in a suitable solvent, such as water and / or a volatile organic solvent, for binding with the silicon-based component. The dispersion can be well mixed with the silicon-based composition. After drying the mixture to remove the solvent, the dried mixture and the silicon-based material coated with the carbon precursor can be heated in an oxygen-free atmosphere to pyrolyze the organic composition, such as an organic polymer, certain low-molecular-weight solid organic compositions, etc., and form a carbon coating.

[0082] Similar to silicon, oxygen-deficient silicon oxides, such as silicon dioxide (SiO2), are formed. x With a density of 0.1 ≤ x ≤ 1.9, intercalable lithium / alloyed lithium allows oxygen-deficient silicon oxide to be used as an active material in lithium-ion batteries. These oxygen-deficient silicon oxide materials are commonly referred to as silicon oxide-based materials and in some embodiments may contain varying amounts of silicon, silicon oxide, and silicon dioxide. Oxygen-deficient silicon oxide can incorporate relatively large amounts of lithium, allowing the material to exhibit a large specific capacity. However, it has been observed that the capacity of silicon oxide typically decays rapidly with battery cycling, as observed in elemental silicon.

[0083] Silica-based compositions have been developed into composites with high capacity and excellent cycling performance, as described in the aforementioned '228 patent. In particular, oxygen-deficient silica can form composites with conductive materials such as conductive carbon or metal powders, which surprisingly significantly improve cycling performance while providing high specific capacity values. Furthermore, grinding silica into smaller particles, such as submicron structures, can further enhance material properties.

[0084] Generally, a wide range of composites can be used, including silicon oxide, carbon components such as graphite particles (Gr), inert metal powders (M), elemental silicon (Si), especially nanoparticles, pyrolytic carbon coatings (HC), carbon nanofibers (CNF), or combinations thereof. The component structure may or may not be consistent with the component structure within the composite material. Therefore, the general composition of the composite material can be expressed as αSiO-βGr-χHC-δM-εCNF-φSi, where α, β, χ, δ, ε, and φ are optional relative weights such that α+β+χ+δ+ε+φ=1. Typically, these weights are 0.35<α<1, 0≤β<0.6, 0≤χ<0.65, 0≤δ<0.65, 0≤ε<0.65, and 0≤φ<0.65. Certain subsets of these composite ranges are particularly meaningful. In some embodiments, a composite having SiO and one or more carbon-based components is desirable, which can be represented by the formula αSiO-βGr-χHC-εCNF, where 0.35 < α < 0.9, 0 ≤ β < 0.6, 0 ≤ χ < 0.65, and 0 ≤ ε < 0.65 (δ = 0 and φ = 0), in further embodiments 0.35 < α < 0.8, 0.1 ≤ β < 0.6, 0.0 ≤ χ < 0.55, and 0 ≤ ε < 0.55, in some embodiments 0.35 < α < 0.8, 0 ≤ β < 0.45, 0.0 ≤ χ < 0.55, and 0.1 ≤ ε < 0.65, and in other embodiments 0.35 < α < 0.8, 0 ≤ β < 0.55, 0.1 ≤ χ < 0.65, and 0 ≤ ε < 0.55. In another or alternative embodiment, a composite having SiO, inert metal powder and optionally one or more conductive carbon components can be formed, which can be represented by the formula αSiO-βGr-χHC-δM-εCNF, wherein 0.35<α<1, 0≤β<0.55, 0≤x<0.55, 0.1≤δ<0.65, and 0≤ε<0.55. In yet another or alternative embodiment, a composite of SiO with elemental silicon and optionally one or more conductive carbon components may be formed, which may be represented by the formula αSiO-βGr-χHC-εCNF-φSi, where 0.35 < α < 1, 0 ≤ β < 0.55, 0 ≤ χ < 0.55, 0 ≤ ε < 0.55, and 0.1 ≤ φ < 0.65, and in a further embodiment 0.35 < α < 1, 0 ≤ β < 0.45, 0.1 ≤ χ < 0.55, 0 ≤ ε < 0.45, and 0.1 ≤ φ < 0.55. Those skilled in the art will recognize that other ranges within the clearly defined foregoing scope are contemplated and fall within the scope of this disclosure. As used herein, reference to composite material means the application of significant bonding forces, such as those from HEMM milling, to tightly bind the materials, which differs from simple blending not considered to form a composite.

[0085] Used for synthesizing various Si-SiO xSolution-based methods for -CM (M = metal) composites are described in U.S. Patent Application No. 2014 / 0308585, published by Han et al., entitled “Silicon-Based Active Materials for Lithium Ion Batteries and Synthesis With Solution Processing,” which is incorporated herein by reference. Silicon-carbon composites having graphene sheets are described in U.S. Patent Application No. 2014 / 0370387, published by Angushamy et al., entitled “Silicon-Silicon Oxide-Carbon Composites For Lithium Battery Electrodes and Methods for Forming the Composites,” which is incorporated herein by reference. It is believed to contain SiO₂. x -Si-C or SiO x Commercial materials of the -Si composite were used in the batteries of the embodiments.

[0086] The capacity of the anode significantly affects the energy density of a battery. For the same output, a higher specific capacity of the anode material results in a lower weight of the anode in the battery. When the negative electrode is made of a silicon-based material, the electrode can have a discharge specific capacity of about 800 mAh / g to 2500 mAh / g at a C / 3 rate relative to lithium metal at a C / 3 discharge rate of 1.5 volts to 5 millivolts, in further embodiments about 900 mAh / g to about 2300 mAh / g, and in other embodiments about 950 mAh / g to about 2200 mAh / g. Those skilled in the art will recognize that other ranges of discharge specific capacities within the above-defined range are contemplated and fall within the scope of this disclosure.

[0087] positive electrode

[0088] By utilizing the improved negative electrode described above, various positive electrode chemical properties can be effectively introduced. The selected composition can be incorporated into the positive electrode along with suitable binders and conductive materials. This section focuses on particularly ideal positive electrode active materials for high-voltage cycling and moderately high capacity. Furthermore, this section describes the composition and characteristics of the entire electrode.

[0089] To some extent, the desired application of the final battery can influence the choice of cathode composition. From this perspective, several compositions are described below. For automotive and similar applications, specific cathode chemistry has been found to be desirable for achieving high energy density and retaining at least 80% of capacity after more than 600 cycles, although some materials offer promising results with slightly lower cycle stability. Specifically, nickel-rich lithium nickel manganese cobalt oxide has been found to provide very long cycle performance based on the improved electrolyte described herein. Examples of nickel-rich lithium nickel manganese cobalt oxide are given below. Lithium cobalt oxide can also be used to provide high energy density, although cobalt leads to higher costs. Other suitable cathode active materials include, for example, lithium nickel cobalt manganese oxide rich in lithium and manganese, lithium manganese oxide spinel (e.g., LiMn2O4), lithium iron phosphate (LiFePO4), lithium nickel oxide (LiNiO2), lithium nickel cobalt oxide (LiNiCoO2), lithium nickel cobalt manganese oxide (LiNiMnCoO2), lithium nickel cobalt aluminum oxide (LiNiCoAlO2), etc.

[0090] In another embodiment, a nickel-rich lithium nickel manganese cobalt oxide blend is mixed with a (lithium + manganese)-rich lithium nickel manganese cobalt oxide blend to provide reasonable cathode performance. Furthermore, the nickel-rich lithium nickel manganese cobalt oxide, used alone as an active material, can provide the desired high energy density, attributed to its average discharge voltage and good cycling performance when paired with the silicon-based anode described herein. Generally, such a blend may contain selected amounts of various active materials, and in some embodiments, the blend has at least 5 wt% of nickel-rich lithium nickel manganese cobalt oxide and at least 5 wt% of (lithium + manganese)-rich lithium nickel manganese cobalt oxide. Those skilled in the art will recognize that other ranges within the defined proportions of the aforementioned active composite metal oxides are contemplated and fall within the scope of this disclosure. In some embodiments, a blend of about 50 wt%:50 wt% nickel-rich lithium nickel manganese cobalt oxide and (lithium + manganese)-rich lithium nickel manganese cobalt oxide may be used.

[0091] Nickel-rich lithium nickel manganese cobalt oxide (N-NMC) can provide the desired cycle and capacity characteristics for the lithium-ion batteries described herein. Specifically, the nickel-rich composition can be approximately composed of LiNi x Mn y Co zO2 represents x+y+z≈1, 0.45≤x, 0.025≤y, z≤0.35, and in a further embodiment, 0.50≤x, 0.03≤y, z≤0.325, and 0.55≤x, 0.04≤y, z≤0.3. The amount of nickel can affect the charging voltage selected to balance cycle stability and discharge energy density. For x values ​​in the range of 0.525≤x≤0.7, the selected charging voltage can be from 4.25V to 4.375V. For x values ​​in the range of 0.7≤x≤0.9, the selected charging voltage can be from 4.05V to 4.325V. Those skilled in the art will recognize that other compositions and ranges of selected charging voltages within the above-defined ranges are contemplated and fall within the scope of this disclosure. These compositions have been found to provide relatively stable higher voltage cycling, good capacity, and desired impedance. N-NMC powders can be synthesized using various techniques, such as coprecipitation as further described below, and these powders are commercially available, for example, from BASF (Germany), TODA (Japan), L&F Materials Corp. (South Korea), YMCO (Belgium), and Jinhe Materials Corp. (China). Of particular interest are commercially available N-NMC compounds, including NMC622 (LiNi). 0.6 Mn 0.2 Co 0.2 O2) and NMC811 (LiNi 0.8 Mn 0.1 Co 0.1 O2).

[0092] For N-NMC compositions, the average voltage tends to be slightly higher with increasing nickel content, but the charging voltage required for stable cycling tends to be slightly lower with increasing nickel content. Therefore, although NNMC active materials can provide good cycling performance and relatively high capacity and energy density, there may be trade-offs in the selection of active materials.

[0093] As described above, the desired blend may contain N-NMC and (lithium-rich + manganese-rich) lithium nickel manganese cobalt oxide (LM-NMC or These compositions can be made from approximately the formula Li. 1+b Ni α Mn β Co γ A δ O 2-z F zThis indicates that b + α + β + γ + δ ≈ 1, where b ranges from about 0.04 to about 0.3, α ranges from 0 to about 0.4, β ranges from about 0.2 to about 0.65, γ ranges from 0 to about 0.46, δ ranges from about 0 to about 0.15, and z ranges from 0 to 0.2, provided that α and γ are not 0, and where A is a metal other than lithium, manganese, nickel, and cobalt. In some embodiments, α may be Mg, Sr, Ba, Cd, Zn, Al, Ga, B, Zr, Ti, Ca, Ce, Y, Nb, Cr, Fe, V, or combinations thereof. Furthermore, in additional or alternative embodiments, it is of the formula Li 1+b Ni α Mn β Co γ A δ O2, wherein 0.05 ≤ b ≤ 0.125, 0.225 ≤ α ≤ 0.35, 0.35 ≤ β ≤ 0.45, 0.15 ≤ γ ≤ 0.3, 0 ≤ δ ≤ 0.05, and at most five molar percent of oxygen may be replaced by fluorine dopant. Those skilled in the art will recognize that other compositional ranges within the aforementioned specific ranges are also contemplated and fall within the scope of this disclosure. (Lithium + Manganese)-rich NMC active materials achieve long cycle stability at relatively high cycle voltages, as described in U.S. Patent 8,928,286 to Amiruddin et al., entitled “Very Long Cycling of Lithium Batteries With Lithium Rich Cathode Materials,” which is incorporated herein by reference.

[0094] LM-NMC cathode materials can be advantageously synthesized via co-precipitation and sol-gel methods detailed in the '160 and '873 patents. In some embodiments, the cathode material is synthesized by precipitating a mixed metal hydroxide or carbonate composition from a solution containing +2 cations, wherein the hydroxide or carbonate composition has a selected composition. The metal hydroxide or carbonate precipitate is then subjected to one or more heat treatments to form a crystalline layered lithium metal oxide composition. The carbonate co-precipitation method described in the '873 patent yields a desired lithium-rich metal oxide material containing cobalt in its composition, exhibiting high specific capacity and excellent tap density. These patents also describe the effective use of metal fluoride coatings to improve performance and cycle life.

[0095] It has been found that coating LM-NMC cathode active materials can improve the performance of the corresponding batteries. Suitable coating materials that are generally believed to be electrochemically inert during battery cycling include metal fluorides, metal oxides, or metal non-fluorinated halides. The results related to LM-NMC in the following examples were obtained using LM-NMC materials coated with metal fluorides. An improved metal fluoride coating with an appropriately designed thickness is described in U.S. Patent 9,843,041 to Lopez et al., entitled “Coated Positive Electrode Materials for Lithium Ion Batteries,” which is incorporated herein by reference. Suitable metal oxide coatings are further described in, for example, U.S. Patent 8,535,832B2 to Karthikeyan et al., entitled “MetalOxide Coated Positive Electrode Materials for Lithium-Based Batteries,” which is incorporated herein by reference. The discovery of a desired coating of non-fluoride metal halides as cathode active materials is described in U.S. Patent 8,663,849B2 to Venkatachalam et al., entitled “Metal Halide Coatings on Lithium-Ion Battery Positive Electrode Materials and Corresponding Batteries,” which is incorporated herein by reference.

[0096] As described above, the positive electrode typically comprises an active material, wherein a conductive material is present in the binder. The active material loading in the electrode can be substantial. In some embodiments, the positive electrode comprises about 85% to about 99% of the positive electrode active material, in other embodiments about 90% to about 98% of the positive electrode active material, and in further embodiments about 95% to about 97.5% of the positive electrode active material. In some embodiments, the positive electrode has about 0.75% to about 10% of the polymer binder, in other embodiments about 0.8% to about 7.5% of the polymer binder, and in further embodiments about 0.9% to about 5% of the polymer binder. The positive electrode composition may also typically contain conductive additives different from the electroactive composition. In some embodiments, the positive electrode may have 0.4% to about 12% by weight of conductive additives, in further embodiments about 0.45% to about 7% by weight, and in other embodiments about 0.5% to about 5% by weight of conductive additives. Those skilled in the art will recognize that other ranges of particle loading within these defined ranges are contemplated and fall within the scope of this disclosure. The positive electrode active material is as described above. Suitable polymeric binders for the positive electrode include, for example, polyvinylidene fluoride (PVDF), polyethylene oxide (PE), polyimide, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyacrylates, rubbers (e.g., ethylene-propylene-diene monomer (EPDM) rubber or styrene-butadiene rubber (SBR)), copolymers thereof, or mixtures thereof. For the positive electrode, polyvinylidene fluoride (PVDF) can be used with good results, and the positive electrode in the examples uses a PVDF binder. Conductive additives for the negative electrode are described in detail, and nanoscale conductive carbon can be effectively used for the positive electrode.

[0097] For a given load level, the electrode density (of the active material) is inversely proportional to its thickness; therefore, a denser electrode is thinner than a less dense one. Load equals density multiplied by thickness. In some embodiments, the positive electrode of the battery has a density of approximately 10 to approximately 50 mg / cm³. 2 The loading level of the positive electrode active material is approximately 12 to approximately 45 mg / cm³ in other embodiments. 2 In other embodiments, the concentration is approximately 13 to approximately 40 mg / cm³. 2 In some implementations, the concentration is approximately 15 to approximately 37.5 mg / cm³. 2 In other embodiments, the concentration is approximately 20 to approximately 35 mg / cm³. 2In some embodiments, the positive electrode of the battery has an active material density of about 2.5 g / cc to about 4.6 g / cc, in other embodiments from about 3.0 g / cc to 4.4 g / cc, and in yet another embodiment from about 3.25 g / cc to about 4.3 g / cc. In further embodiments, after compression and drying of the positive electrode material, the thickness of the positive electrode on each side of the current collector can be about 45 micrometers to about 300 micrometers, in some embodiments from about 80 micrometers to about 275 micrometers, and in yet another embodiment from about 90 micrometers to about 250 micrometers. Those skilled in the art will recognize that other ranges of active material loading, electrode thickness, and electrode density within the above-defined ranges are contemplated and fall within the scope of this disclosure.

[0098] Lithium supplement

[0099] The improved high-energy battery designs described herein generally include supplemental lithium, and this section relates to methods for incorporating supplemental lithium for suitable implementations. Generally, the inclusion of supplemental lithium is desirable for batteries with silicon-based negative electrode active materials, due to the relatively high irreversible capacity loss exhibited by these materials during the initial charging of the battery. Various methods can be used to introduce supplemental lithium into the battery, although after the corresponding initial reaction and / or charging, the negative electrode becomes associated with excess lithium from the supplemental lithium for cycling. Regarding the negative electrode in a battery with supplemental lithium, the structure and / or composition of the negative electrode may change relative to its initial structure and composition after the first cycle and after additional cycles.

[0100] Depending on the method of introducing supplemental lithium, the positive electrode may initially contain a supplemental lithium source and / or a sacrificial electrode incorporating supplemental lithium. Alternatively or additionally, supplemental lithium may be associated with the negative electrode. In some embodiments, supplemental lithium may be introduced into the negative electrode using electrochemical methods rather than purely chemical or mechanical methods. If the supplemental lithium is initially located in the positive electrode or a separate electrode, the negative electrode may be in an unaltered form without lithium until the battery is charged or, in the presence of an electrolyte and separator, at least until the circuit between the negative electrode and the electrode containing supplemental lithium is closed. For example, in addition to other electrode components, the positive electrode or supplemental electrode may also contain elemental lithium, lithium alloys, and / or other sacrificial lithium sources.

[0101] If sacrificial lithium is included in the positive electrode, lithium from the sacrificial lithium source is loaded into the negative electrode during the charging reaction. The voltage during charging based on the sacrificial lithium source can differ significantly from the voltage when charging based on the positive electrode active material. For example, elemental lithium in the positive electrode can charge the negative electrode active material without an external voltage applied, because the oxidation of elemental lithium drives the reaction as long as the circuit is closed. For some sacrificial lithium source materials, an external voltage is applied to oxidize the sacrificial lithium source in the positive electrode and drive lithium into the negative electrode active material. Charging can typically be performed using constant current, stepwise constant voltage charging, or other convenient charging schemes. However, at the end of the charging process, the battery should be charged to the desired voltage, which subsequently involves the extraction of lithium from the positive electrode active material (e.g., deintercalation or dealloying).

[0102] In a further embodiment, at least a portion of the supplemental lithium is initially associated with the negative electrode. For example, the supplemental lithium may be in the form of elemental lithium, lithium alloys, or other lithium sources that are more negatively charged than the negative electrode active material. Elemental lithium may be in the form of a thin film (e.g., a film formed by evaporation, sputtering, or ablation), lithium or lithium alloy foil, and / or powder. Elemental lithium, especially elemental lithium in powder form, may be coated for processing purposes to stabilize the lithium, and commercial lithium powders, such as those from Livent Corporation, are sold with a proprietary coating for stabilization. The coating typically does not alter the properties of the lithium powder used for electrochemical applications. After the negative electrode comes into contact with the electrolyte, a reaction can occur, and the supplemental lithium is transferred to the negative electrode active material. Because the electrode is internally conductive, a closed circuit is not required to provide the electron flow generated by the reaction. A solid electrolyte interface (SEI) layer may also be formed during this process. Thus, the supplemental lithium is loaded into the negative electrode active material, at least a portion of which is typically consumed during the formation of the SEI layer. The supplementary lithium placed in the negative electrode should be more negatively charged than the active material in the negative electrode, because there is no way to make the supplementary lithium source react with the active material in the same electrode by applying voltage.

[0103] In some embodiments, supplementary lithium associated with the negative electrode may be incorporated as a powder into the negative electrode. Specifically, the negative electrode may contain an active negative electrode composition and a supplementary lithium source, as well as any conductive powder (if present), within a polymer binder matrix. In another or alternative embodiment, the supplementary lithium is placed along the electrode surface. For example, the negative electrode may comprise an active layer having the active negative electrode composition and a supplementary lithium source layer on the surface of the active layer. The supplementary lithium source layer may comprise lithium or lithium alloy foil, supplementary lithium powder in the polymer binder, and / or supplementary lithium source material particles disposed on the surface of the active layer. In an alternative configuration, the supplementary lithium source layer is located between the active layer and the current collector. Furthermore, in some embodiments, the negative electrode may contain supplementary lithium source layers on both surfaces of the active layer.

[0104] An arrangement for performing the electrochemical preloading of lithium may include electrodes having silicon-based active material formed on a current collector, placed in a container containing an electrolyte, and a sheet of lithium source material contacting the electrodes. The lithium source material sheet may include lithium foil, lithium alloy foil, or lithium source material in a polymer binder, and optionally also includes conductive powder in direct contact with the preloaded lithium anode, allowing electrons to flow between the materials to maintain electroneutrality during the corresponding reaction. In the subsequent reaction, lithium is loaded into the silicon-based active material via intercalation, alloying, or other methods. In alternative or additional embodiments, the anode active material may be mixed in the electrolyte and the lithium source material for replenishing lithium before forming the electrode with the polymer binder, allowing the respective materials to react spontaneously in the electrolyte.

[0105] In some implementations, a lithium source within the electrodes can be assembled into the battery, where the electrodes are pre-loaded with lithium. A separator can be placed between the individual electrodes. Current can be allowed to flow between the electrodes to provide controlled electrochemical pre-lithiation. Depending on the composition of the lithium source, applying a voltage to drive lithium deposition within the silicon-based active material may or may not be necessary. The apparatus for performing this lithiation process may include a container holding an electrolyte and a battery comprising an electrode serving as the negative electrode in the final rechargeable battery, a current collector, a separator, and a sacrificial electrode containing the lithium source, such as lithium metal foil, wherein the separator is located between the sacrificial electrode and the electrode having the silicon-based active material. A convenient sacrificial electrode may comprise lithium powder in lithium foil, intercalated polymers, or lithium alloys, although any electrode with extractable lithium can be used. The container for the lithiated battery may include a conventional battery case, a beaker, or any other convenient structure. This configuration offers the advantage of being able to measure the current to quantify the degree of negative electrode lithiation. Furthermore, the negative electrode can be cycled once or multiple times, where the negative electrode active material is almost completely loaded with lithium. In this way, the SEI layer can be formed to a desired degree during the preloading of lithium into the negative electrode active material. Then, during the preparation of the negative electrode with the selected preloaded lithium, the negative electrode is fully formed.

[0106] Generally, for embodiments using supplemental lithium, the amount of supplemental lithium pre-loaded or available for loading into the active composition may be at least about 2.5% of the capacity, in further embodiments about 3% to about 55% of the capacity, in other embodiments about 5% to about 52.5% of the capacity, and in some embodiments about 5% to about 50% of the capacity of the negative electrode active material. Supplemental lithium may be used to substantially balance the IRCL of the negative electrode, although other amounts of supplemental lithium may be used as needed. In some embodiments, the amount of supplemental lithium added has an oxidation capacity corresponding to 60% to 180% of the first cycle IRCL of the negative electrode, in further embodiments it is 80% to 165%, and in other embodiments it is 90% to 155%. Those skilled in the art will recognize that other percentage ranges within the clearly defined ranges above are contemplated and fall within the scope of this disclosure. Therefore, due to the addition of supplemental lithium, the effect of the IRCL of the negative electrode can be effectively reduced or eliminated, such that the measured IRCL of the battery represents part or most of the effect of the IRCL from the positive electrode, which is not reduced by the presence of supplemental lithium. Those skilled in the art will recognize that other IRCL scopes within the aforementioned explicit scope are contemplated and fall within the scope of this disclosure.

[0107] Equilibrium of cathode and anode

[0108] It has been found that the overall performance of a battery depends on the capacity and relative balance of the negative and positive electrodes. Electrode balance has been found to be crucial for achieving particularly high energy density and good cycle performance. In some implementations, there may be trade-offs between achieving longer cycle stability and energy density. To obtain longer cycle stability, it may be desirable to balance the battery to achieve a relatively lower energy density, but with the ability to operate stably over a wider range of operating parameters for extended periods. High energy density can still be achieved by using appropriately selected active materials, desired electrode design, and improved electrolyte formulation, while maintaining a capacity degradation of no more than 80% after more than 800 cycles. Electrode balancing can be evaluated using several alternative methods, which can be effectively implemented when specific evaluation methods are appropriately considered.

[0109] Active material testing can be performed in lithium-ion batteries with a single lithium metal electrode, often referred to as half-cells, which differ from lithium-ion batteries (called full-cells) where both electrodes contain lithium alloyed or intercalated materials. In half-cells with silicon electrodes, the lithium electrode acts as the negative electrode, and the silicon electrode acts as the positive electrode, the opposite of its usual role as the negative electrode in lithium-ion batteries.

[0110] The capacity of the positive electrode active material can be estimated from the material's capacity, which can be measured by cycling the material relative to lithium metal foil. For example, for a given positive electrode, the capacity can be evaluated by determining the insertion and extraction capacity during the first charge / discharge cycle, where lithium is deintercalated or extracted from the positive electrode at a C / 20 rate up to a selected charging voltage (typically from 4.2V to 4.5V) based on the material chemistry and battery design, and then intercalated or inserted back into the positive electrode up to 2V, with slight adjustments (e.g., typically 0.1V) based on the voltage of the final anode relative to lithium metal to a higher charging voltage relative to lithium metal. Similarly, for a given silicon-based electrode, the insertion and extraction capacity can be evaluated using a battery having a positive electrode containing silicon-based active material and a lithium foil negative electrode. The capacity is evaluated by determining the battery's insertion and extraction capacity during the first charge / discharge cycle, where lithium is intercalated / alloyed to the silicon electrode at a C / 20 rate up to 5mV, and then deintercalated / dealloyed up to 1.5V. In practical applications, the observed capacity may differ from the measured capacity due to various factors such as high-speed operation and changes in voltage range. This could be due to battery design or the fact that the composition of the relative electrodes is not lithium metal. For some evaluation methods, subsequent capacity after the first cycle can be used to assess electrode balance, and if necessary, a higher discharge rate, such as C / 3 or C / 10, can be used. Using balance after one or several formation cycles may be desirable, as balance is more based on the conditions during battery use.

[0111] In most commercially available carbon-based batteries, the anode is approximately 7 to 10% excess over the cathode to prevent lithium plating. A significant problem with this excess anode is the increased battery weight, which reduces the battery's energy density. High-capacity silicon-based anodes can have an IRCL of approximately 10% to approximately 40%, compared to graphite anodes with a first-cycle IRCL of ~7%. After the first charge-discharge cycle, a large portion of the battery's capacity may become ineffective, significantly increasing the battery's burden.

[0112] For high-capacity anode materials, the irreversible capacity loss of the negative electrode is typically greater than that of the positive electrode, which generates additional usable lithium for the battery. If the negative electrode has a significantly higher irreversible capacity loss than the positive electrode, the initial charging of the negative electrode irreversibly consumes lithium, making it impossible for the negative electrode to supply enough lithium to the positive electrode to meet its full lithium acceptance capacity during subsequent discharge. This results in wasted positive electrode capacity and correspondingly increases weight that does not contribute to cycling. Most or all of the lithium loss in the net IRCL (negative electrode IRCL minus positive electrode IRCL) can be compensated by replenishing lithium as described above. Electrode balance assessment during the first formation cycle may or may not consider replenished lithium. In subsequent cycles after this formation cycle or several cycles later, any excess replenished lithium not consumed by IRCL is typically alloyed into the anode material. Electrode balance can be assessed at a selected rate in post-formation cycling phases (e.g., the fourth cycle), and these capacities can be estimated based on electrode performance.

[0113] From the perspective of providing stable long-term cycling performance, it may be desirable to balance the electrodes to provide efficient use of both electrode capacities and to avoid lithium metal plating during cycling. Generally, electrode balancing is considered when assembling the electrodes with a reference electrode relative to the initial capacity of the lithium metal.

[0114] Generally, at a constant discharge rate, the battery life can be terminated when the energy output decreases by approximately 20% from the initial capacity, although other values ​​can be chosen as needed. For the materials described herein, the negative electrode typically experiences a greater capacity decay with cycling than the positive electrode, making it necessary to avoid lithium metal deposition with cycling, which would result in a larger excess capacity in the negative electrode and thus further stabilize the cycle. Roughly speaking, if the negative electrode capacity decays approximately twice as fast as the positive electrode capacity, at least 10% additional negative electrode capacity needs to be included in the cycle count. In robust battery designs, at least approximately 10% additional negative electrode capacity may be required under various discharge conditions. Generally, a balance can be selected such that the sum of the initial positive electrode charge capacity obtained at a C / 20 rate from the open circuit voltage to the battery design charging voltage (typically from 4.2V to 4.6V) plus any supplemental lithium oxidation capacity, relative to the initial negative electrode charge capacity evaluated relative to lithium at a C / 20 rate from the open circuit voltage to 1.5V, is about 110% to about 195%, in a further embodiment about 120% to about 185%, and in another embodiment about 130% to about 190%. Alternatively, the electrode balance can be evaluated in the fourth cycle at a discharge rate of C / 10 or C / 3, wherein the negative electrode capacity is about 110% to about 195% of the positive electrode capacity, in a further embodiment about 120% to about 185%, and in another embodiment about 130% to about 190%. Those skilled in the art will recognize that other balance ranges within the aforementioned explicit ranges are contemplated and fall within the scope of this disclosure. Such a balance is illustrated in the battery design described below.

[0115] Typical characteristics of storage batteries

[0116] The aforementioned negative and positive electrode structures can be assembled into a suitable battery. As described above, electrodes are typically formed in conjunction with current collectors to create the electrode structure. A separator is located between the positive and negative electrodes to form the battery. The separator is electrically insulating while providing at least selected ion conduction between the two electrodes. A variety of materials can be used as the separator. Some commercial separator materials are formed from polymers, such as polyethylene and / or polypropylene, which are porous sheets providing ion conduction. Commercial polymer separators include, for example, those from Asahi Kasei Corporation of Japan. A series of separator materials. In addition, ceramic-polymer composites have been developed for separator applications. These ceramic composite separators are stable at higher temperatures, and the composite reduces the risk of fire. Polymer-ceramic composites for lithium-ion battery separators are trademarked by Evonik Industries, Germany. Sold by Tiejin Lielsort Korea Co., Ltd. under the trademark For sale. Furthermore, the separator can be formed using porous polymer sheets coated with a gel-forming polymer. This separator design is further described in U.S. Patent 7,794,511 B2 to Wensley et al., entitled “Battery Separator for Lithium Polymer Battery,” which is incorporated herein by reference. Suitable gel-forming polymers include, for example, polyvinylidene fluoride (PVDF), polyurethane, polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile, gelatin, polyacrylamide, polymethyl acrylate, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polytetraethylene glycol diacrylate, copolymers thereof, and mixtures thereof.

[0117] During charging and discharging, the electrolyte provides ion transport between the anode and cathode of the battery. A solution containing solvated ions is called an electrolyte, and an ionic composition that dissolves in a suitable liquid to form solvated ions is called an electrolyte salt. The electrolyte of a lithium-ion battery may contain one or more selected lithium salts. Suitable lithium salts typically have inert anions. Suitable lithium salts include, for example, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonylimide), lithium trifluoromethanesulfonate, lithium tri(trifluoromethanesulfonyl)methyl, lithium tetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate, lithium chloride, lithium difluorooxalatoborate, and combinations thereof. In some embodiments, the electrolyte comprises a lithium salt with a concentration of 1M to 2M, although larger or smaller concentrations may be used.

[0118] For lithium-ion batteries of interest, non-aqueous liquids are typically used to dissolve the lithium salts. Solvents generally do not dissolve the electroactive materials. In some embodiments, suitable solvents may include, for example, propylene carbonate, dimethyl carbonate, diethyl carbonate, 2-methyltetrahydrofuran, dioxolane, tetrahydrofuran, methyl ethyl carbonate, γ-butyrolactone, dimethyl sulfoxide, acetonitrile, formamide, dimethylformamide, triethylene glycol dimethyl ether (triethylene glycol dimethyl ether), diethylene glycol dimethyl ether (diethylene glycol dimethyl ether), DME (dimethyl glycol ether, or 1,2-dimethoxyethane, or ethylene glycol dimethyl ether), nitromethane, and mixtures thereof. Particularly useful solvents for high-voltage lithium-ion batteries are further described in U.S. Patent 8,993,177 to Amiruddin et al., entitled “Lithium-ion battery with high voltage electrolytes and additives,” which is incorporated herein by reference.

[0119] For some embodiments of batteries with silicon-based negative electrode active materials, electrolytes with fluorinated additives have shown further improvements in battery performance. Fluorinated additives may include, for example, ethylene fluorocarbonate, ethylene fluorocarbonate, ethylene monochlorocarbonate, ethylene monobromocarbonate, 4-(2,2,3,3-tetrafluoropropoxymethyl)-[1,3]dioxolane-2-one, 4-(2,3,3,3-tetrafluoro-2-trifluoromethyl-propyl)-[1,3]dioxolane-2-one, 4-trifluoromethyl-1,3-dioxolane-2-one, bis(2,2,3,3-tetrafluoropropyl) carbonate, bis(2,2,3,3,3-pentafluoropropyl) carbonate, or mixtures thereof. In some embodiments, the electrolyte may contain about 1% to about 55% by weight of halogenated carbonates, in further embodiments about 3% to about 50% by weight, and in other embodiments about 5% to about 45% by weight of halogenated carbonates. Those skilled in the art will recognize that ranges of other halogenated carbonate concentrations within the aforementioned specific range are contemplated and fall within the scope of this disclosure. Furthermore, electrolytes containing fluoroethylene carbonate have been found to have excellent low-temperature performance, as described in published U.S. Patent Application 2013 / 0157147 ('147 application) to Li et al., entitled "Low Temperature Electrolyte for High Capacity Lithium Based Batteries," which is incorporated herein by reference. Other fluorinated additives include, for example, fluorinated ethers, such as U.S. Patent Application No. 2018 / 0062206, entitled "Fluorinated Ether as Electrolyte Co-Solvent for Lithium Metal Based Anode," granted to Li et al., and WO 2018 / 051675, entitled "Lithium Secondary Battery," granted to Takuya et al., both of which are incorporated herein by reference. Fluorinated electrolytes are available from Daikin America, Inc.

[0120] The applicant has recently developed improved electrolytes for silicon-based rechargeable batteries. These improved electrolytes are described in co-pending U.S. Patent Application 16 / 556,670 (hereinafter referred to as '670 Application') entitled "Lithium Ion Cells With High Performance Electrolyte and Silicon Oxide Active Materials Achieving Very Long Cycling Performance," which is incorporated herein by reference. The new electrolyte formulation uses a large amount of fluoroethylene carbonate solvent and does not contain other unstable components, and appropriately selects other solvent components to provide the obtained stability.

[0121] The electrodes described herein can be assembled into various commercial battery / rechargeable battery designs, such as prismatic batteries, wound cylindrical batteries, button batteries, or other reasonable battery / rechargeable battery designs, although the embodiments relate to button batteries. Batteries may comprise single or multiple pairs of electrodes assembled with parallel and / or series electrical connections. Electrode stacks may have additional electrodes ending the stack with the same polarity as the other end of the stack for ease of placement in a container. While the electrode structures described herein can be used in batteries for single-charge or single-use applications, the resulting batteries typically possess the cycle characteristics required for use as secondary batteries over multiple battery cycles.

[0122] In some implementations, the positive and negative electrodes can be stacked, with an insulator positioned between them, and the resulting stacked structure can be rolled into a cylindrical or prismatic configuration to form a battery structure. Suitable conductive tabs can be soldered or similarly connected to the current collector, and the resulting jelly roll structure can be placed in a metal can or polymer package, wherein the negative and positive electrode tabs are soldered to suitable external contacts. Electrolyte is added to the can, and the can is sealed to complete the battery. Some currently used commercial rechargeable batteries include, for example, cylindrical 18650 batteries (18 mm in diameter, 65 mm in length) and 26700 batteries (26 mm in diameter, 70 mm in length), but other battery / rechargeable battery sizes, as well as prismatic batteries and foil pouch batteries / rechargeable batteries of selected sizes, can also be used.

[0123] Due to their ease of stacking and relatively low container weight, pouch batteries may be particularly ideal for a variety of applications, including some vehicle applications. The design of pouch batteries for vehicle batteries incorporating high-capacity cathode active material is further described in U.S. Patent 8,187,752 entitled "High Energy Lithium Ion Secondary Batteries" to Buckley et al. and U.S. Patent 9,083,062B2 entitled "Battery Packs for Vehicles and High Capacity Pouch Secondary Batteries for Incorporation into Compact Battery Packs" to Kumar et al., both of which are incorporated herein by reference. While pouch battery designs are particularly convenient for use in certain battery pack designs, pouch batteries can be effectively used in other environments and offer high capacity in a convenient form. The desired results are presented in embodiments of prismatic pouch batteries with electrode stacking.

[0124] Figures 2 to 5 A representative embodiment of a pouch battery is shown. In this embodiment, the pouch battery 100 includes a pouch casing 102, an electrode core 104, and a pouch cover 106. The electrode core will be discussed further below. The pouch casing 102 includes a cavity 110 and an edge 112 surrounding the cavity. The cavity 110 is sized such that the electrode core 104 can be fitted within the cavity 110. The pouch cover 106 can be sealed around the edge 112 to seal the electrode core 104 within a sealed battery, such as... Figure 3 and Figure 4 As shown. Terminal contacts 114 and 116 extend outward from their self-sealing soft packaging for electrical contact with electrode core 104. Figure 4 for Figure 3 A schematic cross-sectional view of the battery as seen along line 4-4. Many other implementations of pouch batteries may have different edge and sealing structures.

[0125] Figure 5An embodiment of an electrode core 104, typically comprising an electrode stack, is shown. In this embodiment, the electrode stack 130 includes negative electrode structures 132, 134, 136, positive electrode structures 138, 140, and insulators 150, 152, 154, 156 disposed between adjacent positive and negative electrodes. The insulators may be provided as a single folded sheet, with the electrode structures placed within the folds of the insulators. The negative electrode structures 132, 134, 136 include negative electrodes 160, 162, 164, 166, and 168, 170, respectively disposed on either side of current collectors 172, 174, 176. The positive electrode structures 138, 140 include positive electrodes 180, 182 and 184, 186, respectively disposed on opposite sides of current collectors 188, 190. Connectors 192, 194, 196, 198, and 200 are connected to current collectors 172, 188, 174, 190, and 176, respectively, to facilitate series or parallel connection of the electrodes. For vehicle applications, the connectors are typically connected in parallel, such that connectors 192, 196, and 200 are electrically connected to accessible external contacts of the container, and connectors 194 and 198 are electrically connected to opposite external contacts of the container.

[0126] As described above, wound electrodes can be used accordingly for cylindrical or generally prismatic batteries. Wound batteries for cylindrical lithium-ion batteries are further described in U.S. Patent 8,277,969 to Kobayashi et al., entitled "Lithium Ion Secondary Battery," which is incorporated herein by reference. Prismatic batteries with wound electrodes are described in U.S. Patent 7,700,221 ('221 patent) to Yeo, entitled "Electrode Assembly and Lithium Ion Secondary Battery Using the Same," which is incorporated herein by reference. Neither Kobayashi's '969 patent nor Yeo's '221 patent describes how to achieve reasonable cycling or high energy density using silicon-based active materials. The design of prismatic batteries with wound electrodes is further described, for example, in the '221 patent cited above. The specific design of stacked electrode assemblies or wound batteries is influenced by the target size and target capacity of the battery.

[0127] The improved negative electrode can be used in a variety of applications and battery / rechargeable battery designs. For electrode stacking, the electrode area can be rationally selected based on the volume and design constraints of a specific application. Larger batteries are typically designed for vehicle applications, such as drones, cars, trucks, or other vehicles. However, the improved negative electrode described in this article can be effectively used in consumer electronics applications, based on smaller battery forms. Furthermore, it should be noted that vehicles can use smaller consumer electronics batteries, and Tesla vehicles are currently known for using thousands of small consumer electronics batteries in their battery packs.

[0128] Performance characteristics

[0129] The combination of design features described herein provides longer cycle stability while maintaining desired battery performance. Achieving long-term cycling involves balancing the improved electrode binder described above with battery design parameters. In the embodiments of particular interest, the positive electrode typically comprises nickel-rich lithium nickel manganese cobalt oxide or lithium cobalt oxide, although other commercially available cathode materials are also suitable.

[0130] The negative electrode can be tested in a half-cell configuration using a lithium foil electrode to evaluate its performance, which is independent of the positive electrode characteristics. Specifically, the negative electrode can be cycled relative to lithium metal at a selected rate over a voltage range of 0.005V to 1.5V. The improved negative electrode described in this paper cycles better in a half-cell configuration compared to a reference electrode, but cycle stability is improved if quantified more explicitly in the full-cell configuration described below.

[0131] The selected charging voltage can be influenced by the positive electrode active material. Typically, the selected charging voltage for these batteries is from about 4.05V to 4.4V, with examples including 4.3V. The battery can exhibit very good cycle performance. In some embodiments, the discharge capacity exhibited by the battery in the 700th cycle can be at least about 75% of the discharge capacity in the 6th cycle at room temperature when cycled from the selected charging voltage to 2.5V at a 1C rate from the selected charging voltage, relative to the discharge capacity in the 6th cycle at room temperature; in other embodiments, the discharge capacity in the 700th cycle is at least about 80% of the discharge capacity in the 6th cycle; and in still other embodiments, at least about 82%. Similarly, relative to the discharge capacity of the sixth cycle at room temperature when cycled from the selected charging voltage to 2.5V at a 1C rate, the discharge capacity exhibited by the battery in the 825th cycle may be at least about 75% of the discharge capacity of the sixth cycle at room temperature when cycled from the selected charging voltage to 2.5V at a 1C rate, in other embodiments at least about 80% of the discharge capacity of the sixth cycle, and in yet another embodiment at least about 82.5%. Those skilled in the art will recognize that other ranges within the foregoing explicit scope are contemplated and fall within the scope of this disclosure. Example

[0132] Example 1 - Different Adhesive Systems

[0133] This embodiment demonstrates the mechanical properties of an electrode structure achieved by using a suitable polymer binder.

[0134] To evaluate the mechanical properties of electrodes with selected polymer binders, copper foil samples were laminated with electrodes having different polymer binder systems. The polymer binder system was a mixture of polymer binder, conductive carbon nanoparticles, and an active composition. To form the binder system test samples, each polymer binder was mixed with water or N-methylpyrrolidone (“NMP”) (Sigma-Aldrich), as shown in Table 1, and stirred overnight to form a set of polymer binder solutions. Additionally, commercially available silica / silicon / carbon composite powder (hereinafter referred to as SiO₂) was used. x The silicon-based carbon (Si / C) and selected amounts of graphite and nanoscale carbon conductive additives are thoroughly mixed to form a homogeneous powder mixture. This homogeneous powder mixture is then added to each polymer binder solution and mixed for approximately 2 hours to form a homogeneous slurry. Each slurry is applied to a copper foil to form a thin wet film, and the laminated copper foil is dried in a vacuum oven to remove the solvent, i.e., water or NMP, and to cure the polymer. The laminated copper foil sample is then pressed between the rolls of a sheet metal rolling mill to obtain the desired lamination thickness. Except for the binder, the anode compositions are identical, and these compositions contain 80% to 90% by weight of active material, with the remainder being nanoscale conductive carbon and polymer binder. The active composition contains 55% to 85% by weight of a silicon oxide-based composite, with the remainder being graphite. Once formed, the anode is vacuum-dried at 100 to 150°C for several hours. The same electrode compositions are used in all embodiments.

[0135] Fifteen samples with different binder polymers were formed. Table 1 summarizes the composition of the tested polymer binders and the solvents used to prepare the laminated copper test samples. Binders 1 to 15 were used to prepare samples 1 to 15. Polyacrylamide copolymers (samples 8 and 12 to 15) were prepared by mixing polyacrylamide (400,000 to 800,000 MW, PolySciences Inc., USA) with concentrated NaOH (Sigma-Aldrich, USA) for 2 hours to 1 week. This protocol generally followed the procedure outlined in the reference cited above: Klein et al., “Preparation and Characterization of Poly(acrylamide-co-acrylic acid)”, *Makromo. Chem.*, Vol. 179, 1978, pp. 1895-1904. The reaction time was controlled to obtain copolymers with the desired monomer unit ratio. The reaction was terminated by quenching with methanol (ACS grade, VWR, USA). The polymer product was redissolved in water, and the pH was adjusted to 7 with HCl (1M ACS grade, VWR, USA) to neutralize excess sodium hydroxide. Sodium chloride was removed by quenching with additional methanol (ACS grade, VWR, USA), and the copolymer was redissolved in water. The final ratio of PAM to NaPAA in the copolymer is defined by letters, where A > B > C > D > E > F > G, where A is a 100:0 ratio and G is a 0:100 ratio. Figure 6 Overview of the synthesis of polyacrylamide copolymers.

[0136] Table 1

[0137]

[0138]

[0139] Adhesion force (adhesion strength)

[0140] The electrode structure was tested to assess the adhesion strength of the electrode to the copper foil of the test sample. The adhesion strength was measured using a 180-degree peel adhesion test. The adhesion force was measured and plotted as a function of peel distance (in millimeters). The test setup is schematically shown below. Figure 7The Ametek Chatillon TCD225 series force gauge was used. A 70×25 mm double-sided tape 204 (McMaster-Carr 7139a16) was attached to a glass plate 202. The glass plate 202 was fixed to the lower clamp 200 of the force gauge. The electrode structure consisted of an electrode 206 and a copper foil 208. The electrode 206 (150×30 mm) was compressed and placed face down on the double-sided tape 204. The copper foil 208 (~220×30 mm) was connected to the other side of the force gauge 210. The copper foil was stretched 20 mm at a speed of 2 mm per minute. The peel force was measured in pounds-forces (lbf). The peel force can be normalized according to the tape width to obtain pounds-forces per meter (lbf / m).

[0141] It should be noted that the test sample was tested until the electrode structure detached from the copper foil current collector. Upon delamination, visual analysis showed almost no electrode material residue on the copper foil, indicating that the cohesive strength was generally greater than the adhesive strength. During delamination, the peel force became approximately constant, and this normalized value was used as the adhesive force.

[0142] Figure 8 The results for test samples 1 through 8 are shown (unnormalized). Normalized values ​​can be obtained by dividing the plotted numbers by 0.025 m (25 mm). Sample 7 (polyacrylamide) showed the highest adhesion strength, followed by sample 8 (poly(acrylamide-co-sodium acrylate)). Samples 7 and 8 showed greater adhesion strength to copper foil than sample 1 (polyimide). Sodium polyacrylate (sample 5) showed better adhesion strength than lithium polyacrylate (sample 3). The blend of sodium polyacrylate and polyimide (sample 6) showed lower adhesion strength than both the polyimide adhesive (sample 1) and the sodium polyacrylate adhesive (sample 5).

[0143] Figure 9 The results (unnormalized) for testing other sodium polyacrylate / polyimide blends and lithium polyacrylate / polyimide blend adhesive compositions (samples 4, 6, and 9-11) with different polyacrylate molecular weights are shown. Sample 9 exhibited the highest adhesion, followed by samples 6 and 4. Samples 10 and 11, with lower molecular weights, showed negligible adhesion. Comparison Figure 9 and Figure 8Surprisingly, the results showed that certain blends of sodium polyacrylate or lithium polyacrylate with polyimide exhibited lower adhesion to copper compared to lithium polyacrylate (Sample 3) or sodium polyacrylate (Sample 5). In particular, the poor adhesion of Samples 10 and 11 was a surprising result, given the relatively good adhesion of the polyimide (Sample 1), lithium polyacrylate (Sample 3), and sodium polyacrylate (Sample 5) (unblended) adhesives. Typically, sodium polyacrylate / polyimide blends exhibit similar adhesion strength to sodium polyacrylate. Figure 8 It also exhibits higher adhesion than lithium polyacrylate / polyimide blends.

[0144] Figure 10 Results (unnormalized) of testing other poly(acrylamide-co-sodium acrylate) compositions (samples 12 to 15) with different weight percentages of each monomer unit are shown, and comparisons are provided with the poly(acrylamide-co-sodium acrylate) compositions of sample 5 (sodium polyacrylate), sample 7 (polyacrylamide), and sample 8. Figure 10 This also indicates that the adhesion strength of the poly(acrylamide-co-sodium polyacrylate) samples depends on the composition of the copolymer. Overall, the results of the fifteen samples tested show that polyacrylamide and certain polyacrylamide-based copolymer adhesives have the highest adhesion performance. The results indicate that both polyacrylamide adhesives and polyacrylamide-based copolymer adhesives can provide high adhesion to copper foil current collectors.

[0145] Cohesive strength

[0146] The flexibility of the electrode structure test sample was also tested. The test protocol was basically as described in ASTM D522 / D522M-17, "Standard Test Method for Mandrel Bend Test of Attached Organic Coatings," but with slight modifications. In this test, as... Figure 11 The illustration shows that each electrode structure sample 232 was subjected to 180-degree bending on a mandrel 230 with a gradually decreasing diameter until the coating failed due to crack formation, with the smallest mandrel diameter being 2 mm. Table 2 shows the mandrel diameter at failure for each sample. The smaller mandrel diameter at failure is associated with higher flexibility of the polymer binder coated on copper or increased electrode flexibility. Increased electrode flexibility is associated with increased cohesion within the polymer binder system.

[0147] Table 2

[0148] sample mandrel diameter at failure 1 6mm 2 <2mm 3 <2mm 4 >20mm 5 <2mm 6 10mm 7 10mm 8 3mm 9 3mm 10 <2mm 11 <2mm 12 6mm 13 3mm 14 2mm 15 <2mm

[0149] Four poly(acrylamide-sodium co-acrylate) adhesive systems exhibited good flexibility, failing at 3 mm (samples 8 and 13), 2 mm (sample 14), and less than 2 mm (sample 15). This flexibility indicates good particle adhesion within the adhesive system. Another poly(acrylamide-sodium co-acrylate) adhesive system (sample 12) showed lower flexibility, failing at 6 mm. Samples 8 and 13 to 15 were more flexible than the polyimide adhesive system (sample 1) and the polyacrylamide adhesive system (sample 7). Samples 8 and 13 showed similar flexibility to the sodium carboxymethyl cellulose / styrene-butyl rubber (sample 2), lithium polyacrylate (sample 3), and sodium polyacrylate (sample 5) adhesive systems.

[0150] Three polyacrylate metal salt / polyimide blend adhesive systems exhibited good flexibility, failing at 3 mm (sample 9, sodium-based) and less than 2 mm (samples 10 and 11, lithium-based and sodium-based, respectively). Sample 9 (polyacrylate molecular weight range 900K to 1400K) and samples 10 to 11 (polyacrylate molecular weight range 100K to 300K) showed similar flexibility to the lithium-polyacrylate adhesive system (sample 3), the sodium-polyacrylate adhesive system (sample 5), and the sodium carboxymethyl cellulose / styrene-butyl rubber adhesive system (sample 2). Samples 9 to 11 showed higher flexibility than the polyimide adhesive system (sample 1). The other two polyacrylate metal salt / polyimide blend adhesive systems showed relatively poor flexibility. Sample 6 (sodium-based) failed at 10 mm. Sample 4 (lithium-based) failed at more than 20 mm, which was the lowest flexibility of the tested samples. Samples 6 and 4 both had polyacrylate molecular weight ranges of 300K to 500K. Results for metal-polyacrylate / polyimide blends showed a correlation between the molecular weight of the metal-polyacrylate component and flexibility.

[0151] Sample 8 exhibits a combination of high adhesion strength to copper foil, good flexibility, and good particle cohesion. In the metal-polyacrylate / polyimide blend adhesive system, Sample 9 shows a good combination of adhesion strength, flexibility, and particle cohesion.

[0152] Example 2 - Performance of the adhesive system in a semi-button cell

[0153] This example demonstrates the effect of binder molecular weight and binder copolymer composition on the cycle performance of silicon-based electrodes using binder formulations containing lithium polyacrylate / polyimide blends and sodium polyacrylate / polyimide blends.

[0154] As shown in Table 1, twelve button-type batteries were formed to test the composition of the adhesive systems corresponding to adhesives 4 to 15. The button-type batteries were formed from the anode prepared as described above.

[0155] Button-type batteries are formed using lithium foil as the relative electrode, and are called half-cells. A negative electrode, a separator, a lithium foil, and a current collector corresponding to the lithium foil are cut to a certain size. The separator for button-type batteries described herein includes a commercially available three-layer polyolefin separator. An electrolyte containing dimethyl carbonate and fluoroethylene carbonate is placed in the battery, and the battery is sealed. The button-type battery is then cycled in a rechargeable battery from 0.005V to 1.5V, with the first cycle charge / discharge rate at C / 10, the second cycle charge / discharge rate at C / 5, and the remaining cycles charge / discharge rate at C / 3.

[0156] Figure 12 The capacity versus cycle life of batteries with poly(acrylamide-sodium co-acrylate) binders (binders 8 and 12 to 15) was compared with that of batteries with sodium polyacrylate binders (binder 5) and polyacrylate binders (binder 7). Binders 8 and 12 to 15 have the same molecular weight range, but the relative amounts of each monomer unit in the copolymer differ. Copolymer binders 8, 14, and 13 showed the best cycling performance. Copolymer binder 15 showed poorer cycling performance, but its performance was better than that of sodium polyacrylate (binder 5) and more stable than that of polyacrylate (binder 7). The data show that good cycling performance can be obtained with copolymer binders, but also that cycle life depends on the relative amounts of monomer units in the copolymer. The optimal cycle life corresponds to intermediate amide-acrylate ratios E (binder 8), D (binder 14), and C (binder 13).

[0157] The standardized capacity of both charge and discharge is plotted as a function of the number of cycles. Figure 13 The results show the effect of binder molecular weight on half-cell cycling. Binder 6 (300K to 500K) exhibited the best cycling performance, demonstrating good cycling stability after 40 cycles. Binder 4 (300K to 500K) retained 80% of its capacity after 40 cycles. Binder 9 (900K to 1400K) retained only about 50% of its capacity after 40 cycles. Binders 10 and 11 (100K to 300K) showed poor cycling performance. The results indicate that binders with excessively low or high molecular weights negatively impact cycling performance. The results also show that, within the same molecular weight range, the sodium polyacrylate / polyimide blend (binder 6) cycles slightly better than the lithium polyacrylate / polyimide blend (binder 4).

[0158] Example 3 - Performance of the adhesive system in a button cell battery

[0159] This embodiment demonstrates the improved cycling performance of a silicon-based electrode formulated with a polyacrylamide copolymer binder.

[0160] As shown in Table 1, nine button cell sets were formed to test the binder system compositions corresponding to binders 1 to 8 and 12. The button cells were formed from the anode prepared as described in Example 2 above. Once prepared, the negative electrode was electrochemically pre-lithiated with sufficient lithium to compensate for the 100% to 160% lithium loss due to irreversible capacity loss at the anode. These full cells were referenced based on their anode binder compositions.

[0161] The cathode system is formed from nickel-rich lithium nickel manganese cobalt oxide (N-NMC622). The positive electrode has an active material loading of approximately 93% to 97.5% by weight, which is mixed with 1% to 4% by weight of PVDF binder and 1% to 3% by weight of nanoscale carbon. The cathode material is mixed with NMP solvent, dispersed on an aluminum foil current collector, pressed, and dried. To form a coin cell, a section of negative electrode and separator are cut to a specified size, and a section of positive electrode is also cut to a specified size. The electrodes and the separator between them are placed in a coin cell casing. The separator used for the coin cell described herein includes a commercially available three-layer polyolefin separator. An electrolyte comprising dimethyl carbonate and fluoroethylene carbonate is placed in the battery, and the battery is sealed. The electrolyte is selected according to the teachings of the aforementioned '670 application.

[0162] The assembled battery was cycled between 4.3V and 2.5V at a 1C charge and 1C discharge rate. Prior to the 1C cycle, the battery was previously cycled according to a rate protocol that included two sets of charge / discharge rates: C / 10, C / 5, C / 3, and 1C cycles. The cycle results for normalized capacity are plotted in... Figure 14 In the middle section, polyimide (binder 1) showed approximately 80% capacity retention at a cycling rate of 1C after 800 cycles. Batteries with common binders such as carboxymethyl cellulose / SBR (binder 2), lithium polyacrylate (binder 3), and sodium polyacrylate (binder 5) cycled less than 200 times. Polyacrylamide (binder 7) cycled approximately 750 times. Poly(acrylamide-co-sodium acrylate) (binder 8) exhibited the best cycling performance. Binder 8 was cycled for 925 cycles, with approximately 600 cycles exceeding 95% capacity.

[0163] Figure 15 This study shows the relationship between battery capacity and cycle life for binders with different ratios of polyacrylamide to sodium acrylate moiety. Specifically, Figure 15Batteries containing binder 5 (ratio G), binder 7 (ratio A), copolymer binder 8 (ratio E), and copolymer binder 12 (ratio B) were compared with a battery containing polyimide (binder 1). Copolymer binder 8 maintained over 85% capacity after approximately 850 cycles. Polyimide (binder 1) maintained over 85% capacity after approximately 700 cycles. Binder 7 and copolymer binder 12 maintained over 85% capacity after approximately 650 cycles. Sodium polyacrylate (binder 5) exhibited significantly worse cycle performance than aqueous poly(acrylamide-co-acrylate metal salt) binders (binders 8 and 12). A lower polyacrylamide-to-sodium acrylate ratio resulted in a higher cycle life for the copolymer binder.

[0164] In summary, aqueous poly(acrylamide-co-acrylate) polymer anolyte adhesives offer superior adhesion and cohesive properties compared to polyimide and polyacrylamide, while providing improved cycle life and cycle stability compared to polyacrylamide. Initial data indicate that copolymer adhesives offer a better combination of performance characteristics compared to metal-polyacrylate / polyimide blend adhesives.

[0165] The above embodiments are intended to illustrate and not limit. Other embodiments are within the scope of the claims. Furthermore, although the invention has been described with reference to specific embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the spirit and scope of the invention. Any references to the foregoing documents are limited and therefore do not introduce a subject matter contrary to the express disclosure herein. With regard to the specific structures, compositions, and / or processes described herein using elements, components, or other divisions, it should be understood that the disclosure herein covers specific embodiments; embodiments comprising specific elements, components, components, other divisions, or combinations thereof; and embodiments substantially composed of such specific elements, components, or other divisions, or combinations thereof, which may include additional features that do not alter the essential nature of the subject matter, as suggested in the discussion, unless otherwise specifically indicated.

Claims

1. A negative electrode for a lithium-ion battery, the negative electrode comprising: Active materials containing silicon-based active materials; Nanoscale conductive carbon; and Polymer adhesives consisting of the following: At least 35% by weight of poly(acrylamide-co-acrylate), said poly(acrylamide-co-acrylate) having at least 15 mol% acrylate portion and at least 25 mol% acrylamide portion; and Optional polyimide, metal salt of polyacrylate, polyacrylamide, styrene-butadiene rubber, or mixtures thereof, The negative electrode on the metal foil current collector has a 180-degree peel adhesion force at a force of at least 6 psi, and a cohesive force corresponding to maintaining electrode integrity when bent around a mandrel with a diameter of 6 mm.

2. The negative electrode of claim 1, wherein the silicon-based active material comprises a silicon oxide-based active material, and the active material comprises 20% to 100% by weight of the silicon oxide-based active material and 0% to 80% by weight of graphite.

3. The negative electrode as described in claim 1, wherein the silicon-based active material is a silicon-based composite material comprising carbon, silicon low oxides, and / or nanoscale silicon.

4. The negative electrode as claimed in claim 1, wherein the silicon-based active material comprises silicon low oxide.

5. The negative electrode according to any one of claims 1 to 4, wherein the nanoscale conductive carbon comprises carbon nanotubes, carbon black, carbon nanofibers, or mixtures thereof.

6. The negative electrode according to any one of claims 1 to 4, wherein the poly(acrylamide-co-acrylate) has sodium, lithium, potassium, ammonium or a combination thereof as counterions.

7. The negative electrode according to any one of claims 1 to 4, wherein the poly(acrylamide-co-acrylate) has sodium counterions and an average molecular weight of 300,000 g / mol to 2,000,000 g / mol.

8. The negative electrode according to any one of claims 1 to 4, wherein the negative electrode comprises 78% to 96% by weight of the active material, 0.1% to 7% by weight of the nanoscale conductive carbon, and 4% to 20% by weight of the polymer binder, wherein the poly(acrylamide-co-acrylate) comprises poly(acrylamide-co-acrylate sodium).

9. A negative electrode structure comprising a metal foil current collector and a negative electrode as claimed in any one of claims 1 to 4, wherein the 180-degree peel adhesion is at least 10 lbf / m, and the cohesive force corresponds to maintaining electrode integrity when bent around a mandrel with a diameter of less than 3 mm.

10. The negative electrode structure of claim 9, wherein the negative electrode comprises 78% to 96% by weight of the active material, 0.1% to 7% by weight of the nanoscale conductive carbon, and 4% to 20% by weight of the polymer binder, wherein the poly(acrylamide-co-acrylate) comprises poly(acrylamide-co-acrylate sodium).

11. A lithium-ion battery, the lithium-ion battery comprising: A negative electrode structure comprising a metal foil current collector and a negative electrode as described in claim 10 located on the metal foil current collector; A positive electrode structure comprising a current collector and an electrode located on the current collector, the electrode comprising lithium metal oxide, conductive carbon, and a polymer binder; An isolator is located between the negative electrode structure and the positive electrode structure; Electrolytes, comprising lithium salts and non-aqueous solvents; and A container that encloses the negative electrode structure and the positive electrode structure, the separator, and the electrolyte.

12. The lithium-ion battery of claim 11, When the lithium-ion battery is cycled at a rate of 1C between 2.5 volts and a selected charging voltage from the 10th to the 700th cycle, the capacity of the lithium-ion battery in the 700th cycle is at least 80% of the capacity in the 5th cycle.

13. The lithium-ion battery of claim 12, wherein the active material comprises a blend of silicon-based active material and 5% to 60% by weight graphite.

14. The lithium-ion battery of claim 12 or claim 13, wherein the poly(acrylamide-co-acrylate) has sodium, lithium, potassium, ammonium or a combination thereof as counterions.

15. The lithium-ion battery of claim 12 or claim 13, wherein the poly(acrylamide-co-acrylate) has sodium counterions and an average molecular weight of 300,000 g / mol to 2,000,000 g / mol.

16. The lithium-ion battery of claim 12 or claim 13, wherein the silicon-based active material comprises a composite material of carbon, silicon low oxide, and / or nanoscale silicon.

17. The lithium-ion battery of claim 12 or claim 13, wherein the lithium metal oxide comprises lithium cobalt oxide or is composed of the formula LiNi x Mn y Co z O2 represents a nickel-rich lithium nickel manganese cobalt oxide, where 0.45 ≤ x, 0.05 ≤ y, z ≤ 0.

35.

18. The lithium-ion battery of claim 17, wherein the lithium metal oxide further comprises 20% to 80% by weight of Li 1+b Ni α Mn β Co γ A δ O 2-z F z The expression represents a lithium metal oxide rich in (lithium + manganese), where b + α + β + γ + δ ≈ 1, b ranges from 0.04 to 0.3, α ranges from 0 to 0.4, β ranges from 0.2 to 0.65, γ ranges from 0 to 0.46, δ ranges from 0 to 0.15, and z ranges from 0 to 0.2, provided that neither α nor γ is 0, and A is a metal different from lithium, manganese, nickel, and cobalt.

19. The lithium-ion battery of claim 12 or claim 13, wherein the lithium metal oxide comprises lithium of the formula Li 1+b Ni α Mn β Co γ A δ O 2-z F z The expression represents a lithium metal oxide rich in (lithium + manganese), where b + α + β + γ + δ ≈ 1, b ranges from 0.04 to 0.3, α ranges from 0 to 0.4, β ranges from 0.2 to 0.65, γ ranges from 0 to 0.46, δ ranges from 0 to 0.15, and z ranges from 0 to 0.2, provided that neither α nor γ is 0, and A is a metal different from lithium, manganese, nickel, and cobalt.

20. The lithium-ion battery of claim 12 or claim 13, wherein the 180-degree peel adhesion is at least 10 lbf / m, and the cohesive force corresponds to maintaining electrode integrity when bent around a mandrel with a diameter of less than 3 mm.

21. The lithium-ion battery of claim 12 or claim 13, wherein the silicon-based active material comprises a silicon oxide-based active material, and the negative electrode comprises an active material comprising 40% to 95% by weight of the silicon oxide-based active material and 5% to 60% by weight of graphite.

22. The lithium-ion battery of claim 12 or claim 13, wherein when the lithium-ion battery is cycled at a rate of 1C between 2.5 volts and a selected charging voltage from the 10th cycle to the 825th cycle, the capacity of the lithium-ion battery in the 825th cycle is at least 80% of the capacity in the 5th cycle.

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