SLOW-RELEASE ADDITIVE FOR ABUSE TOLERANT LITHIUM-ION BATTERY CELL

A thermal runaway inhibiting composition for a battery includes a plurality of particles. Each particle includes an encapsulant configured to melt at a temperature greater than 70° C. and a flame retardant additive encapsulated by the encapsulant. Characteristically, the plurality of particles having a size distribution to inhibit thermal runaway when the thermal runaway-inhibiting composition is included in a battery cell.

TECHNICAL FIELD

In at least one aspect, a slow-release additive for lithium-ion batteries is provided.

BACKGROUND

Electrolyte additives, such as phosphates, are available in electrolytic solutions to offer improved thermal runaway resistance in a lithium-ion battery (LIB). The additives introduce barriers to obstruct electrochemical kinetics and mass transport. These additives may, however, have side effects, such as poor cell performance and low power. These low flammability electrolyte additives may also increase cell resistance. A non-invasive solution is needed to offer an electrolyte that is both non-flammability and high performance.

Accordingly, a non-invasive solution is needed to offer both non-flammability and high performance.

SUMMARY

In at least one aspect, a thermal runaway-inhibiting composition for a battery is provided. The thermal runaway-inhibiting composition includes a plurality of particles. Each particle includes an encapsulant configured to melt at a temperature greater than 70° C. and a flame retardant additive encapsulated by the encapsulant. Advantageously, the plurality of particles has a size distribution that allows inhibits of thermal runaway when the thermal runaway-inhibiting composition is included in a battery cell.

In another aspect, a non-invasive, slow-releasing component can be introduced into a LIB system via an electrolytic solution or electrode. For example, a wax encapsulated flame retardant additive can be introduced in the electrolytic solution and/or in the ceramic layer bed to activate upon high temperature (e.g., >100° C.). These encapsulated additive agents do not interfere with the original battery function. But at the very beginning stage of an exothermic situation, the encapsulant can melt or dissolve and release a quick passivating agent that can stifle further thermal reaction or oxygen release.

DETAILED DESCRIPTION

As used herein, the term “about” means that the amount or value in question may be the specific value designated or some other value in its neighborhood. Generally, the term “about” denoting a certain value is intended to denote a range within +/−5% of the value. As one example, the phrase “about 100” denotes a range of 100+/−5, i.e. the range from 95 to 105. Generally, when the term “about” is used, it can be expected that similar results or effects according to the invention can be obtained within a range of +/−5% of the indicated value.

As used herein, the term “and/or” means that either all or only one of the elements of said group may be present. For example, “A and/or B” shall mean “only A, or only B, or both A and B”. In the case of “only A”, the term also covers the possibility that B is absent, i.e. “only A, but not B”.

The phrase “composed of” means “including” or “consisting of” Typically, this phrase is used to denote that an object is formed from a material.

The term “one or more” means “at least one” and the term “at least one” means “one or more.” The terms “one or more” and “at least one” include “plurality” and “multiple” as a subset. In a refinement, “one or more” includes “two or more.”

The term “substantially,” “generally,” or “about” may be used herein to describe disclosed or claimed embodiments. The term “substantially” may modify a value or relative characteristic disclosed or claimed in the present disclosure. In such instances, “substantially” may signify that the value or relative characteristic it modifies is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of the value or relative characteristic.

When referring to a numeral quantity, in a refinement, the term “less than” includes a lower non-included limit that is 5 percent of the number indicated after “less than.” For example, “less than 20” includes a lower non-included limit of 1 in a refinement. Therefore, this refinement of “less than 20” includes a range between 1 and 20. In another refinement, the term “less than” includes a lower non-included limit that is, in increasing order of preference, 20 percent, 10 percent, 5 percent, or 1 percent of the number indicated after “less than.”

The term “microcrystalline wax” means a kind of wax that is a refined mixture of solid, saturated aliphatic hydrocarbons, and produced by de-oiling certain fractions from the petroleum refining process. Microcrystalline waxes differ from refined paraffin wax in that the molecular structure is more branched and the hydrocarbon chains are longer (higher molecular weight). The crystal structure of microcrystalline wax is much finer than paraffin wax. In particular, the crystal size of the microcrystalline wax is smaller and the molecular weight larger compared with paraffin wax. In a refinement, the microcrystalline wax has a weight-average molecular weight of 500 to 800 and a melting point of 60 to 90° C.

Referring toFIG.1, a schematic of a representative particle of a thermal runaway-inhibiting composition for a battery. The thermal runaway-inhibiting composition includes a plurality of particles10. Each particle10includes an encapsulant12(e.g., solid organic shell) configured to melt at a temperature greater than 70° C. Flame retardant additive14is encapsulated by the encapsulant12, the flame retardant additive being present in a sufficient amount to inhibit thermal runaway in a battery when the composition is included therein. Examples of flame retardant additives include but are not limited to trimethyl phosphate (TMP), triphenyl phosphate (TPP), triallyl phosphates, and combinations thereof.

In a variation, the encapsulant12has a melting point from about 70° C. to about 120° C. In some variations, the encapsulant12has a melting point greater than or equal to in increasing order of preference, 70° C., 75° C., 80° C., 85° C., or 90° C. and less than or equal to in increasing order of preference 130° C., 125° C., 120° C., 115° C., or 110° C.

Typically the encapsulant12is composed of wax, and in particular, a microcrystalline wax. In a refinement, the plurality of particles have an average particle size from about 1 to 50 microns.

With references toFIGS.2A and2B, an electrode for a lithium-ion battery having flame-resistant properties using the composition ofFIG.1is provided. Electrode20includes a current collector22and an electrochemically active layer24disposed over the current collector.FIG.2Adepicts a variation in which a single side of the current collector is coated whileFIG.2Bdepicts a variation in which both sides are coated. A thermal runaway-inhibiting composition is dispersed in and/or coating the electrochemically active layer24. The thermal runaway-inhibiting composition includes a plurality of particles10. Each particle10includes an encapsulant configured to melt at a temperature greater than 70° C. and a flame retardant additive encapsulated by the encapsulant as set forth above. Advantageously, the plurality of particles has a size distribution to inhibit thermal runaway when the thermal runaway-inhibiting composition is included in a battery cell.

In a variation, electrode20includes the thermal runaway-inhibiting composition in an amount of 5 to 25 percent of the combined weight of the electrically active layer24and the thermal runaway-inhibiting composition. In some variations, electrode20includes the thermal runaway-inhibiting composition in an amount of at least in increasing order of preference 3 wt %, 5 wt %, 7 wt %, 10 wt %, 12 wt %, or 15 wt % of the combined weight of the electrically active layer24and the thermal runaway-inhibiting composition. In a refinement, electrode20includes the thermal runaway-inhibiting composition in an amount of at most in increasing order of preference 50 wt %, 40 wt %, 35 wt %, 30 wt %, 25 wt %, or 20 wt % of the combined weight of the electrically active layer24and the thermal runaway-inhibiting composition.

With reference toFIG.3, a schematic of a rechargeable lithium-ion battery cell incorporating the positive electrode ofFIG.1is provided. Battery cell30includes positive electrode32, negative electrode34, and separator36interposed between the positive electrode and the negative electrode. Positive electrode32includes a positive electrode current collector42and positive electrode active material44disposed over the positive electrode current collector. Typically, positive electrode current collector42is a metal plate or metal foil composed of a metal such as aluminum, copper, platinum, zinc, titanium, and the like. Currently, aluminum is most commonly used for the negative electrode current collector. Similarly, negative electrode34includes a negative electrode current collector46and a negative active material layer48disposed over and typically contacting the negative current collector. Typically, negative electrode current collector46is a metal plate or metal foil composed of a metal such as aluminum, copper, platinum, zinc, titanium, and the like. Currently, copper is most commonly used for the negative electrode current collector. The battery cell is immersed in electrolyte50which is enclosed by battery cell case52. Electrolyte50imbibes into separator36. In other words, the separator36includes the electrolyte thereby allowing lithium ions to move between the negative and positive electrodes. The electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium for transmitting ions taking part in the electrochemical reaction of a battery.

In a variation, electrode20includes the thermal runaway-inhibiting composition in an amount of 5 to 25 percent of the combined weight of the electrolyte50and the thermal runaway-inhibiting composition. In some variations, electrode20includes the thermal runaway-inhibiting composition in an amount of at least in increasing order of preference 3 wt %, 5 wt %, 7 wt %, 10 wt %, 12 wt %, or 15 wt % of the combined weight of the electrolyte50and the thermal runaway-inhibiting composition. In a refinement, electrode20includes the thermal runaway-inhibiting composition in an amount of at most in increasing order of preference 50 wt %, 40 wt %, 35 wt %, 30 wt %, 25 wt %, or 20 wt % of the combined weight of the electrolyte50and the thermal runaway-inhibiting composition.

With reference toFIG.4, a schematic of a rechargeable lithium-ion battery incorporating the positive electrode ofFIG.1and the battery cells ofFIG.2is provided. Rechargeable lithium-ion battery40includes at least one battery cell of the design inFIG.2. Typically, rechargeable lithium-ion battery40includes a plurality of battery cells30iof the design ofFIG.2where i is an integer label for each battery cell. The label i runs from 1 to nmax, where nmax is the total number of battery cells in rechargeable lithium-ion battery40. Each lithium-ion battery cell30iincludes a positive electrode32which includes a positive electrode active material, a negative electrode34which includes a negative active material, and an electrolyte50, The electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent serves as a medium for transmitting ions taking part in the electrochemical reaction of a battery. The plurality of battery cells can be wired in series, in parallel, or a combination thereof. The voltage output from battery40is provided across terminals42and44.

Referring toFIGS.3and4, separator36physically separates the negative electrode34from the positive electrode32thereby preventing shorting while allowing the transport of lithium ions for charging and discharging. Therefore, separator36can be composed of any material suitable for this purpose. Examples of suitable materials from which separator36can be composed include but are not limited to, polytetrafluoroethylene (e.g., TEFLON®), glass fiber, polyester, polyethylene, polypropylene, and combinations thereof. Separator36can be in the form of either a woven or non-woven fabric. Separator36can be in the form of a non-woven fabric or a woven fabric. For example, a polyolefin-based polymer separator such as polyethylene and/or polypropylene is typically used for a lithium-ion battery. In order to ensure heat resistance or mechanical strength, a coated separator includes a coating of ceramic or a polymer material may be used.

Referring toFIGS.3and4, electrolyte50includes a lithium salt dissolved in the non-aqueous organic solvent. Therefore, electrolyte50includes lithium ions that can intercalate into the positive electrode active material during charging and into the anode active material during discharging. Examples of lithium salts include but are not limited to LiPF6, LiBF4, LiSbF6, LiAsF6, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiCl, LiI, LiB(C2O4)2, and combinations thereof. In a refinement, the electrolyte includes the lithium salt in an amount from about 0.1 M to about 2.0 M.

Still referring toFIGS.3and4, the electrolyte includes a non-aqueous organic solvent and a lithium salt. Advantageously, the non-aqueous organic solvent serves as a medium for transmitting ions, and in particular, lithium ions participate in the electrochemical reaction of a battery. Suitable non-aqueous organic solvents include carbonate-based solvents, ester-based solvents, ether-based solvents, ketone-based solvents, alcohol-based solvents, aprotic solvents, and combinations thereof. Examples of carbonate-based solvents include but are not limited to dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, and combinations thereof. Examples of ester-based solvents include but are not limited to methyl acetate, ethyl acetate, n-propyl acetate, methylpropionate, ethylpropionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, and combinations thereof. Examples of ether-based solvents include but are not limited to dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and the like, and the ketone-based solvent may include cyclohexanone, and the like. Examples of alcohol-based solvent include but are not limited to methanol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and the like. Examples of the aprotic solvent include but are not limited to nitriles such as R—CN (where R is a C2-20linear, branched, or cyclic hydrocarbon that may include a double bond, an aromatic ring, or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, and the like. Advantageously, the non-aqueous organic solvent can be used singularly. In other variations, mixtures of the non-aqueous organic solvent can be used. Such mixtures are typically formulated to optimize battery performance. In a refinement, a carbonate-based solvent is prepared by mixing a cyclic carbonate and a linear carbonate. In a variation, electrolyte30can further include vinylene carbonate or an ethylene carbonate-based compound to improve battery cycle life.

Referring toFIGS.2,3, and4, the negative electrode and the positive electrode can be fabricated by methods known to those skilled in the art of lithium-ion batteries. Typically, an active material (e.g., the positive or negative active material) is mixed with a conductive material, and a binder in a solvent (e.g., N-methylpyrrolidone) into an active material composition and coating the composition on a current collector. The electrode manufacturing method is well known and thus is not described in detail in the present specification. The solvent includes N-methylpyrrolidone and the like but is not limited thereto.

Referring toFIGS.2,3, and4, the positive electrode active material layer44includes positive electrode active material, a binder, and a conductive material. The positive electrode active materials used herein can be those positive electrode materials known to one skilled in the art of lithium-ion batteries. In particular, the positive electrode32may be formed from a lithium-based active material that can sufficiently undergo lithium intercalation and deintercalation. The positive electrode32active materials may include one or more transition metals, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof. Common classes of positive electrode active materials include lithium transition metal oxides with layered structure and lithium transition metal oxides with spinel phase. Examples of lithium transition metal oxides with layered structure include, but are not limited to lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), a lithium nickel manganese cobalt oxide (e.g., Li(NixMnyCoz)O2), where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1), a lithium nickel cobalt metal oxide (e.g., LiNi(1-x-y)CoxMyO2), where 0<x<1, 0<y<1 and M is Al, Mn). Other known lithium-transition metal compounds such as lithium iron phosphate (LiFePO4) or lithium iron fluorophosphate (Li2FePO4F) can also be used. In certain aspects, the positive electrode32may include an electroactive material that includes manganese, such lithium manganese oxide (Li(1+x)Mn(2-x)O4), a mixed lithium manganese nickel oxide (LiMn(2-x)NixO4), where 0≤x≤1, and/or a lithium manganese nickel cobalt oxide.

The binder for the positive electrode active material can improve the binding properties of positive electrode active material particles with one another and with the positive electrode current collector42. Examples of suitable binders include but are not limited to polyvinyl alcohol, carboxylmethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, a styrene-butadiene rubber, an acrylate styrene-butadiene rubber, an epoxy resin, nylon, and the like, and combinations thereof. The conductive material provides positive electrode10with electrical conductivity. Examples of suitable electrically conductive materials include but are not limited to natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, copper, metal powders, metal fibers, and combinations thereof. Examples of metal powders and metal fibers are composed of including nickel, aluminum, silver, and the like.

Referring toFIGS.1,2, and3, the negative active material layer26includes a negative active material, includes a binder, and optionally a conductive material. The negative active materials used herein can be those negative materials known to one skilled in the art of lithium-ion batteries. Negative active materials include but are not limited to, carbon-based negative active materials, silicon-based negative active materials, and combinations thereof. A suitable carbon-based negative active material may include graphite and graphene. A suitable silicon-based negative active material may include at least one selected from silicon, silicon oxide, silicon oxide coated with conductive carbon on the surface, and silicon (Si) coated with conductive carbon on the surface. For example, silicon oxide can be described by the formula SiOzwhere z is from 0.09 to 1.1. Mixtures of carbon-based negative active materials, silicon-based negative active materials can also be used for the negative active material.

The negative electrode binder improves the binding properties of negative active material particles with one another and with a current collector. The binder can be a non-aqueous binder, an aqueous binder, or a combination thereof. Examples of non-aqueous binder may be polyvinylchloride, carboxylated polyvinylchloride, polyvinylfluoride, an ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof. Aqueous binders can be rubber-based binders or polymer resin binders. Examples of rubber-based binders include but are not limited to styrene-butadiene rubbers, acrylated styrene-butadiene rubbers, acrylonitrile-butadiene rubbers, acrylic rubbers, butyl rubbers, fluorine rubbers, and combinations thereof. Examples of polymer resin binders include but are not limited to polyethylene, polypropylene, ethylenepropylene copolymer, polyethyleneoxide, polyvinylpyrrolidone, epichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylenepropylenediene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, a polyester resin, an acrylic resin, a phenolic resin, an epoxy resin, polyvinyl alcohol and combinations thereof.