POLYSULFIDE-POLYOXIDE ELECTROLYTE MEMBRANE FOR ENERGY STORAGE DEVICE

An energy storage device is provided that includes a first electrode, a second electrode, and a polymer electrolyte membrane disposed between the first electrode and the second electrode. The polymer electrolyte membrane includes a copolymer network including a polyoxide and a polysulfide. The polymer electrolyte membrane is prelithiated by deep discharging of the battery of in a voltage range of −0.5 V to 5.0 V such that the polymer electrolyte membrane after deep discharging includes additional lithium ions stored therein as compared with prior to deep discharging.

BACKGROUND

Field of the Invention

The present invention generally relates to a polysulfide-polyoxide electrolyte membrane for an energy storage device, an energy storage device including the polysulfide-polyoxide electrolyte membrane, and a method of forming a battery having a prelithiated polysulfide-polyoxide electrolyte membrane. The energy storage device includes a first electrode, a second electrode, and a polymer electrolyte membrane disposed between the first electrode and the second electrode. The polymer electrolyte membrane includes a copolymer network including a polyoxide and a polysulfide. The polymer electrolyte membrane is prelithiated by deep discharging of the battery of in a voltage range of −0.5 V to 5.0 V such that the polymer electrolyte membrane after the deep discharging includes additional lithium ions stored therein as compared with prior to the deep discharging.

Background Information

Lithium-based batteries are desirable because they have a high energy density and, thus, can generate a large amount of power with a relatively thin electrode structure, thus permitting a reduction in the size of the battery as compared with other conventional batteries including anodes made of carbon or silicon. Lithium-based batteries use lithium metal anodes and/or cathodes formed of complex oxides such as lithium nickel manganese cobalt oxide (LiNiMnCoO2, also commonly referred to as “NMC”). However, there are several drawbacks with lithium metal anodes. For example, the performance of lithium metal anodes is limited by current density as such anodes are prone to excessive dendritic growth and accumulation of dead lithium resulting in severe volume expansion of the anode.

In order to improve the safety and energy storage capacity of lithium-based batteries using solid electrolytes, solid-state batteries have been developed that use a solid or polymer electrolyte to conduct lithium ions between the anode and cathode. Solid-state batteries allow for a much smaller battery size due to their improved energy density. Solid state lithium-based batteries also have an improved safety performance, an enhanced life cycle and higher charge/discharge rates as compared with conventional lithium-ion batteries using a liquid electrolyte, which can lead to undesirable dendrite formation and short-circuiting.

It has been believed that the specific battery capacity of a solid-state lithium-ion battery is limited primarily by the type of cathode material used in the battery. Conventional lithium cathode materials, such as NMC, LiCoO2, LiNiO2, other lithium transition metal oxides, and LiFePO4, have high cell potentials but a low specific battery capacity of only approximately 160-170 mAh/g. Other cathode materials, such as tin-containing materials, have a much higher specific battery capacity but a very low cell potential.

Therefore, it is desirable to provide a solid-state lithium-ion battery that simultaneously has a high cell potential and a high specific battery capacity to further improve the energy density of the battery. Conventional solid-state batteries have an energy density of approximately 150 Wh/kg. Therefore, further improvement is needed to increase the energy density of solid-state lithium-ion batteries.

SUMMARY

It has been discovered that the energy density of the solid-state lithium-ion battery can be significantly increased from the conventional value of 150 Wh/kg to approximately 400-500 Wh/kg by providing a polyoxide-polysulfide polymer electrolyte membrane that is prelithiated to store a large amount of excess lithium ions. The polymer electrolyte membrane before prelithiation has a high ionic conductivity, approaching that of superconductors, of greater than 10-3 S/cm (approximately 1.2-1.5 mS/cm) at room temperature and approximately 10'S/cm (approximately 8.8-10 mS/cm) at 90-100° C.

The prelithiated polymer electrolyte membrane exhibits pseudo-capacitive and/or electric double layer capacitor (“EDLC”) behavior that further affords extra storage capacity of lithium ions through coordination bonding of dissociated lithium cations with ether oxygen or nucleophilic amines within the polymer electrolyte network as well as at the interface of the polymer electrolyte membrane and the cathode. Upon lithiation, there are excess lithium ions available to facilitate ion transport through the coordinated bonded lithium ions with ether oxygen or amine complexes, hence both ion conduction and storage capacity can be enhanced reaching a comparable level to an EDLC. In contrast, if the same prelithiation process were performed by deep discharging a lithium-ion battery having a liquid electrolyte, the liquid electrolyte would boil and leak causing the battery explosion and ultimately catching fire.

The prelithiated polymer electrolyte membrane is an electrochemically stable interface layer having a unique ability for extra storage of lithium ions above and beyond that of the cathode due to the co-network chain architecture of the polymer electrolyte membrane.

Therefore, it is desirable to provide a lithium-ion battery, such as a solid-state lithium-ion battery, that includes such a prelithiated polymer electrolyte membrane in which a copolymer of a polyoxide and a polysulfide is used to store excess lithium ions and thereby improve the energy density of the battery.

In view of the state of the known technology, one aspect of the present disclosure is to provide a method of forming a battery having a prelithiated polymer electrolyte membrane. The method includes forming a polymer electrolyte membrane, forming a battery including an anode, a cathode and the polymer electrolyte membrane disposed between the anode and the cathode, and performing deep discharging of the battery in a voltage range of −0.5 V to 5.0 V to prelithiate the polymer electrolyte membrane. The polymer electrolyte membrane includes a copolymer network including a polyoxide and a polysulfide, and at least one of the anode and the cathode comprises a material that includes lithium.

Another aspect of the present disclosure is to provide an energy storage device. The energy storage device includes a first electrode, a second electrode, and a polymer electrolyte membrane disposed between the first electrode and the second electrode. The polymer electrolyte membrane includes a copolymer network including a polyoxide, which may be referred to as a polyoxide-containing compound, and a polysulfide, which may be referred to as a polysulfide-containing compound. The polymer electrolyte membrane is prelithiated by deep discharging of the battery of in a voltage range of −0.5 V to 5.0 V such that the polymer electrolyte membrane after the deep discharging includes additional lithium ions stored therein as compared with prior to the deep discharging.

Because the polymer electrolyte membrane includes a co-network of a polyoxide and a polysulfide, the polymer electrolyte membrane has a unique ability for extra storage of lithium ions. Therefore, by prelithiating the polymer electrolyte membrane through deep discharge, excess lithium ions may be stripped from the anode and stored in the polymer matrix of the polymer electrolyte membrane as well as the interface with the electrode. Thus, the energy density of the energy storage device may be significantly improved such that the energy storage device functions as a supercapacitive battery or a supercapacitor.

A further aspect of the present disclosure is to provide a polymer electrolyte membrane comprising a copolymer network, a plasticizer, and a lithium salt. The copolymer network includes a crosslinked network of a polyoxide and a polysulfide. The polyoxide has the following formula:

where R′ is selected from the group consisting of: CH3—; CH3—CH2—; CH3—CH2—CH2—; CH3—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—; an isopropyl group; an isobutyl group; an isopentyl group; a sec-butyl group; a tert-butyl group; a tert-pentyl group; a tert-hexyl group; a phenyl group; a benzyl group; and an acrylic acid 2-(2-acryloyloxy-ethoxymethyl)-2-acryloyloxymethyl-butyl ester group, and x, y and z are integer numbers, the sum of which (x+y+z) ranges from 15 to 20, covering various combinations of ethoxylated trimethylolpropane tri-acrylate (“EO-TMPTA”) (x+y+z=15) and polyethylene glycol triacrylate (“PEG3A”) (x+y+z=20). The polysulfide has the following formula:

where a, b and c are integer numbers, the sum of which (a+b+c) ranges from 3 to 28, preferably 5 to 26, covering various combinations of Thioplast® G1 (a+b+c=26 to 28) and Thioplast® G4 (a+b+c<5) since both grades work well together and also individually.

By forming the polymer electrolyte membrane using the polyoxide and the polysulfide, the polymer electrolyte membrane has a unique storage capacity for excess lithium ions. Therefore, it has been discovered that this particular polymer electrolyte membrane can be prelithiated by deep discharge to strip a large amount of lithium ions from the anode and store those lithium ions in the polymer electrolyte membrane. This prelithiation results in a battery having an improved energy density as compared with conventional solid-state batteries.

DETAILED DESCRIPTION OF EMBODIMENTS

Referring initially toFIG.1, a process1is illustrated for forming a battery having a prelithiated polymer electrolyte membrane in accordance with a first embodiment. The battery is a solid-state lithium-ion battery that includes a polymer electrolyte membrane. The solid-state lithium-ion battery may be incorporated in a vehicle, a mobile device, a laptop computer or other suitable personal electronic devices.

In Step2, a polymer electrolyte membrane is formed. The polymer electrolyte membrane includes a copolymer network of a polyoxide and a polysulfide. The polyoxide can be any suitable polyoxide having the following formula:

where R′ is selected from the group consisting of: CH3—; CH3—CH2—; CH3—CH2—CH2—; CH3—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—; an isopropyl group; an isobutyl group; an isopentyl group; a sec-butyl group; a tert-butyl group; a tert-pentyl group; a tert-hexyl group; a phenyl group; a benzyl group; and an acrylic acid 2-(2-acryloyloxy-ethoxymethyl)-2-acryloyloxymethyl-butyl ester group, and x, y and z are integer numbers, the sum of which (x+y+z) ranges from 15 to 20, covering various combinations of EO-TMPTA (x+y+z=15) and PEG3A (x+y+z=20). The polyoxide is preferably formed from an EO-TMPTA prepolymer in which (x+y+z=15).

The polysulfide can be any suitable thiol-terminated polysulfide. For example, the polysulfide may be a star-branched polysulfide having the following formula:

where a, b and c are integer numbers, the sum of which (a+b+c) ranges from 3 to 28, preferably 5 to 26. The flexibility of the polymer electrolyte membrane can be adjusted by changing the length of the polymer chain. For example, the longer the chain, the more the flexibility of the polymer electrolyte membrane will be increased. For example, the polysulfide can be a Thioplast® G prepolymer, preferably Thioplast® G1 or Thioplast® G4.

The polymer electrolyte membrane is formed by mixing the first monomer for the polyoxide with a monomer for forming the polysulfide, along with a polymerization initiator. The first monomer may be mixed with the monomer for forming the polysulfide in any suitable ratio. For example, the first monomer may be mixed with the monomer for forming the polysulfide in a ratio of 3:7 to 7:3.

Furthermore, the polymerization initiator may be mixed with the monomer mixture in an amount of 3% by weight relative to a total amount of the monomer mixture and the polymerization initiator. The monomer mixture and the polymerization initiator may then be stirred at a temperature of approximately 40-60° C., preferably 55° C., for approximately 1-3 hours, preferably 2 hours.

The monomer mixture and the polymerization initiator may then be mixed with a plasticizer and a lithium salt to form a polymer film solution. The plasticizer may be any suitable plasticizer. For example, the plasticizer can be succinonitrile (“SCN”), vinylene carbonate (“VC”), vinyl imidazolium (“VIM”), tetramethyl succinonitrile, or a mixture thereof. The plasticizer is preferably SCN. Alternatively, the plasticizer can be dimethyl phthalate, diethyl phthalate, diisobutyl phthalate, di-n-butyl phthalate, butyl benzyl phthalate, bis(2-ethylhexyl) phthalate, diisononyl phthalate, bis(2-propylheptyl) phthalate, diisodecyl phthalate, diisoundecyl phthalate, ditridecyl phthalate, bis(2-ethylhexyl)terephthalate, a trimellitate such as tri-(2-ethylhexyl)trimellitate, tri-(isononyl)trimellitate, tri-(isodecyl)trimellitate, or tri-(isotridecyl)trimellitate, tricresyl phosphate, 2-ethylhexyldiphenyl phosphate, tri-2-ethylhexyl phosphate, triethylene glycol di-2ethylhexanoate, or a mixture thereof.

The plasticizer and lithium salt may be mixed with the monomer mixture and the polymerization initiator in any suitable amount to form the polymer film solution. For example, the monomer mixture may be mixed in an amount of 15-30%, preferably 30%, by weight relative to a total weight of the monomer mixture, the plasticizer and the lithium salt. The plasticizer and lithium salt may each be mixed in an amount of 35-55%, preferably 35%, by weight relative to a total weight of the monomer mixture, the plasticizer and the lithium salt.

The polymer film solution may be subsequently stirred at a temperature of approximately 40-60° C., preferably 55° C., for approximately 1-3 hours, preferably 1 hour. The polymer film solution may then be UV cured at a wavelength of approximately 320 nm for approximately 10-30 minutes, preferably 20 minutes, to form the polymer electrolyte membrane.

In Step4, the battery is formed by disposing the polymer electrolyte membrane between an anode and a cathode. The cathode includes a cathode active material. The cathode active material is any suitable cathode active material that is compatible with the polymer electrolyte membrane. For example, the cathode active material may be a lithium transition metal oxide such as NMC or lithium cobalt oxide, lithium phosphate, lithium iron phosphate or a mixture thereof. The cathode active material may be formed of particles having a diameter of approximately 15 nm to 5 μm.

The cathode may also include a binder and/or an electrically conductive additive. The binder may be any suitable electrode binder material. For example, the binder may include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, a cellulose material or any combination thereof. The electrically conductive additive may be any suitable sacrificial electrode additive, such as a material that acts as an additional source of lithium ions. For example, the electrically conductive additive can be a carbon material. The cathode has a thickness of approximately 50 μm to 150 μm, preferably 100 μm.

The cathode includes at least 80 percent by weight of the cathode active material, preferably at least 90 percent by weight of the cathode active material. The cathode also includes up to five percent by weight of the additive plus the binder. For example, the cathode may include approximately two percent by weight of the additive and approximately three percent by weight of the binder. The weight percentage values described above are relative to a total weight of the cathode.

The anode is formed of an anode active material. The anode may also optionally include a binder and an additive. The binder and additive may be the same binder and additive used for the cathode. The anode active material is lithium or a lithium alloy. The anode is preferably formed entirely of lithium metal. The anode includes approximately 90-95 percent by weight of the anode active material and five to ten percent by weight of any additive plus any binder. The anode has a thickness of approximately 10 nm to 3 μm.

In Step6, deep discharging is performed to prelithiate the polymer electrolyte membrane. The deep discharging is performed by discharging the battery in a voltage range of −0.5 V to 5.0 V to strip lithium ions from the anode and store them in the polymer electrolyte membrane. For example, the battery may be discharged from a starting voltage of approximately 2.5 V to 5.0 V down to a final voltage of approximately 0.01 V to −0.5 V. This process may be performed several times, preferably four to five times, until the polymer electrolyte membrane is saturated with lithium ions. By increasing the amount of lithium ions stored in the polymer electrolyte membrane, the energy density of the battery can be improved to about 400-500 Wh/kg.

FIG.2shows a supercapacitive battery10in accordance with a second embodiment. The supercapacitive battery10is a solid-state battery. The supercapacitive battery10can be incorporated in a vehicle, a mobile device, a laptop computer or other suitable personal electronic device. The supercapacitive battery10includes a cathode12, a polymer electrolyte membrane14and an anode24.

The cathode12includes a cathode active material. The cathode active material is any suitable cathode active material that is compatible with the polymer electrolyte membrane. For example, the cathode active material may be a lithium transition metal oxide such as NMC or lithium cobalt oxide, lithium phosphate, lithium iron phosphate or a mixture thereof. The cathode active material is formed of particles having a diameter of approximately 15 nm to 5 μm.

The cathode12may also include a binder and/or an electrically conductive additive. The binder may be any suitable electrode binder material. For example, the binder may include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, a cellulose material or any combination thereof. The electrically conductive additive may be any suitable sacrificial electrode additive, such as a material that acts as an additional source of lithium ions. For example, the electrically conductive additive can be a carbon material. The cathode12has a thickness of approximately 50 μm to 150 μm, preferably 100 μm.

The cathode12includes at least 80 percent by weight of the cathode active material, preferably at least 90 percent by weight of the cathode active material. The cathode also includes up to five percent by weight of the additive plus the binder. For example, the cathode12may include approximately two percent by weight of the additive and approximately three percent by weight of the binder. The weight percentage values described above are relative to a total weight of the cathode12.

The polymer electrolyte membrane14includes a copolymer network16of a polyoxide and a polysulfide. The polyoxide can be any suitable polyoxide having the following formula:

where R′ is selected from the group consisting of: CH3—; CH3—CH2—; CH3—CH2—CH2—; CH3—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—; an isopropyl group; an isobutyl group; an isopentyl group; a sec-butyl group; a tert-butyl group; a tert-pentyl group; a tert-hexyl group; a phenyl group; a benzyl group; and an acrylic acid 2-(2-acryloyloxy-ethoxymethyl)-2-acryloyloxymethyl-butyl ester group, and x, y and z are integer numbers, the sum of which (x+y+z) ranges from 15 to 20, covering various combinations of EO-TMPTA (x+y+z=15) and PEG3A (x+y+z=20). The polyoxide is preferably formed from an EO-TMPTA prepolymer in which (x+y+z=15).

The polysulfide can be any suitable thiol-terminated polysulfide. For example, the polysulfide may be a star-branched polysulfide having the following formula:

where a, b and c are integer numbers, the sum of which (a+b+c) ranges from 3 to 28, preferably 5 to 26. The flexibility of the polymer electrolyte membrane can be adjusted by changing the length of the polymer chain. For example, the longer the chain, the more the flexibility of the polymer electrolyte membrane will be increased. For example, the polysulfide can be a Thioplast® G prepolymer, preferably Thioplast® G1 or Thioplast® G4.

The polymer electrolyte membrane14includes approximately 15-30%, preferably 30%, by weight of the copolymer network16relative to a total weight of the polymer electrolyte membrane14. In particular, the polymer electrolyte membrane14includes approximately 10-15% by weight of the polyoxide and approximately 5-10% by weight of the polysulfide. The polymer electrolyte membrane14also includes approximately 35-55%, preferably 35%, by weight of the plasticizer18and approximately 35-55%, preferably 35%, by weight of the lithium salt20, relative to a total weight of the polymer electrolyte membrane14.

The polymer electrolyte membrane14is prelithiated and therefore also contains excess lithium ions22. The polymer electrolyte membrane14is prelithiated by deep discharging the battery10in a voltage range of −0.5 V to 5.0 V to strip lithium ions22from the anode24and store them in the polymer electrolyte membrane14. For example, the battery10may be discharged from a starting voltage of approximately 2.5 V to 5.0 V down to a final voltage of approximately 0.01 V to −0.5 V. This process may be performed several times, preferably four to five times, until the polymer electrolyte membrane14is saturated with lithium ions. By increasing the amount of lithium ions22stored in the polymer electrolyte membrane14, the energy density of the battery10can be significantly improved to about 400-500 Wh/kg.

The anode24is formed of an anode active material. The anode24may also optionally include a binder and an additive. The anode active material is lithium or a lithium alloy. The anode active material is preferably formed entirely of lithium metal.

The binder and additive may be any suitable binder and additive for a lithium-based anode. For example, the binder and additive may be the same binder and additive used for the cathode12. The anode24includes approximately 90-95 percent by weight of the anode active material and five to ten percent by weight of any additive plus any binder. The24anode has a thickness of approximately 10 nm to 3 μm.

FIG.3shows a supercapacitor30in accordance with a third embodiment. The supercapacitor30can be incorporated in a vehicle, a mobile device, a laptop computer or other suitable personal electronic device. The supercapacitor30includes a first electrode32, a polymer electrolyte membrane34and a second electrode44.

The first electrode32includes a carbon material. The carbon material is preferably an activated carbon material or a graphene material. For example, the carbon material is carbon black having a surface area of approximately 60 m2/g to 200 m2/g, porous activated carbon having a surface area of approximately 600 m2/g to 1500 m2/g, graphene having a surface area of approximately 1700 m2/g to 2000 m2/g, carbon nanotube(s) having a surface area of approximately 300 m2/g to 1000 m2/g, or a mixture thereof. The first electrode32has a thickness of approximately 35 μm to 150 μm.

The polymer electrolyte membrane34includes a copolymer network36of a polyoxide and a polysulfide. The polyoxide can be any suitable polyoxide having the following formula:

where R′ is selected from the group consisting of: CH3—; CH3—CH2—; CH3—CH2—CH2—; CH3—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—CH2—; CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—; an isopropyl group; an isobutyl group; an isopentyl group; a sec-butyl group; a tert-butyl group; a tert-pentyl group; a tert-hexyl group; a phenyl group; a benzyl group; and an acrylic acid 2-(2-acryloyloxy-ethoxymethyl)-2-acryloyloxymethyl-butyl ester group, and x, y and z are integer numbers, the sum of which (x+y+z) ranges from 15 to 20, covering various combinations of EO-TMPTA (x+y+z=15) and PEG3A (x+y+z=20). The polyoxide is preferably formed from an EO-TMPTA prepolymer in which (x+y+z=15).

The polysulfide can be any suitable thiol-terminated polysulfide. For example, the polysulfide may be a star-branched polysulfide having the following formula:

where a, b and c are integer numbers, the sum of which (a+b+c) ranges from 3 to 28, preferably 5 to 26. The flexibility of the polymer electrolyte membrane can be adjusted by changing the length of the polymer chain. For example, the longer the chain, the more the flexibility of the polymer electrolyte membrane will be increased. For example, the polysulfide can be a Thioplast® G prepolymer, preferably Thioplast® G1 or Thioplast® G4.

The polymer electrolyte membrane34includes approximately 15-30%, preferably 30%, by weight of the copolymer network36relative to a total weight of the polymer electrolyte membrane34. In particular, the polymer electrolyte membrane34includes approximately 10-15% by weight of the polyoxide and approximately 5-10% by weight of the polysulfide. The polymer electrolyte membrane34also includes approximately 35-55%, preferably 35%, by weight of the plasticizer38and approximately 35-55%, preferably 35%, by weight of the lithium salt40, relative to a total weight of the polymer electrolyte membrane34.

The polymer electrolyte membrane34is prelithiated and therefore also contains excess lithium ions42. The polymer electrolyte membrane34is prelithiated by deep discharging the supercapacitor30in a voltage range of −0.5 V to 5.0 V to strip lithium ions42from the anode44and store them in the polymer electrolyte membrane34. For example, the supercapacitor30may be discharged from a starting voltage of approximately 2.5 V to 5.0 V down to a final voltage of approximately 0.01 V to −0.5 V. This process may be performed several times, preferably four to five times, until the polymer electrolyte membrane34is saturated with lithium ions. By increasing the amount of lithium ions42stored in the polymer electrolyte membrane34, the energy density of the supercapacitor30can be significantly improved to about 400-500 Wh/kg.

The second electrode44is formed of a carbon material. The carbon material is preferably an activated carbon material or a graphene material. For example, the carbon material is carbon black having a surface area of approximately 60 m2/g to 200 m2/g, porous activated carbon having a surface area of approximately 600 m2/g to 1500 m2/g, graphene having a surface area of approximately 1700 m2/g to 2000 m2/g, carbon nanotube(s) having a surface area of approximately 300 m2/g to 1000 m2/g, or a mixture thereof. The second electrode44has a thickness of approximately 35 μm to 150 μm.

GENERAL INTERPRETATION OF TERMS

The terms of degree, such as “approximately” or “substantially” as used herein, mean a reasonable amount of deviation of the modified term such that the end result is not significantly changed.