Patent Publication Number: US-11380893-B1

Title: High energy cathodes, batteries, and methods of making the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part application under 35 U.S.C. § 120 of U.S. patent application Ser. No. 17/175,267, filed Feb. 12, 2021, which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to a cathode active material, methods of manufacturing the cathode active material, cathodes that include the cathode active material, and batteries that incorporate such cathodes. 
     BACKGROUND 
     Batteries are ubiquitous in modern technology, being used in a wide range of applications from small batteries for industrial and medical devices, to larger batteries for electric vehicles and grid energy storage systems. Perhaps the most well-known and widely-used battery technology at the present are lithium-ion batteries, which use an intercalated lithium compound as one electrode material and employ lithium ions shuttling between the cathode and anode in the pond of electrolyte. While lithium-ion batteries possess many advantages, they provide relatively low energy densities, and may require expensive materials for manufacture. 
     Lithium-air or lithium-oxygen batteries are considered to be ‘next generation’ lithium-ion battery technology, and is known to outperform today&#39;s lithium-ion batteries in many aspects, such as energy density and the cost of materials. These batteries consume oxygen and generate reactive oxygen species that function as the cathode active material. However, such batteries are prone to oxygen desorption at comparatively low temperatures during operation, and produce electrochemically irreversible byproducts that seriously hinder the rechargeability of the batteries. Such oxygen desorption or reactive oxygen species dissociation may also cause a thermal runaway reaction in the battery. 
     What is needed is an improved cathode, which incorporates improved cathode active materials, and which can provide greater energy density, more economical manufacturing costs, and lower materials costs, while at the same time exhibiting greater electrochemical reversibility and resistance to oxygen generation during use. 
     SUMMARY 
     The disclosure is directed to cathode active materials and their methods of manufacture, as well as cathodes incorporating the cathode active materials, and batteries that incorporate such cathodes. 
     In one example, the disclosure is directed to cathode active materials that include a metal compound having an empirical formula of MR x , where M is a metal; R is an atom, a molecule, or a radical having an oxidation state of −1; and x is a positive nonzero real number; and a metal oxide having an empirical formula of M′ y O z , where M′ is a metal, and y and z are independently positive nonzero real numbers; provided that the metal compound and the metal oxide are in contact. 
     In another example, the disclosure is directed to cathode materials that include a cathode active material having a metal compound and a metal oxide; where the metal compound has an empirical formula of MR x , where M is a metal; R is an atom, a molecule, or a radical having an oxidation state of −1; and x is a positive nonzero real number; and the metal oxide has an empirical formula of M′ y O z , where M′ is a metal, and y and z are independently positive nonzero real numbers; such that the metal compound and the metal oxide are in contact; and an electrically-conductive material; such that one or both of the metal compound and the metal oxide are in contact with the electrically-conductive material. 
     In another example, the disclosure is directed to batteries having a cathode and an electrolyte, where the cathode includes a cathode active material that includes a metal compound having an empirical formula of MR x , where M is a metal; R is an atom, a molecule, or a radical having an oxidation state of −1; and x is a positive nonzero real number; and a metal oxide having an empirical formula of M′ y O z , where M′ is a metal, and y and z are independently positive nonzero real numbers; where the metal compound and the metal oxide are in contact. 
     The disclosed features, functions, and advantages of the disclosed cathode active materials, cathodes, and batteries may be achieved independently in various embodiments of the present disclosure, or may be combined in yet other embodiments, further details of which can be seen with reference to the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart of an illustrative method of manufacturing a cathode active material according to the present disclosure. 
         FIG. 2  is a flowchart of an illustrative method of manufacturing a cathode according to the present disclosure. 
         FIG. 3  is a semi-schematic diagram of an illustrative battery that includes a cathode manufactured according to the present disclosure. 
         FIG. 4  is a plot demonstrating the high specific capacity and high voltage performance of an illustrative battery that incorporates cathode active material according to the present disclosure, as described in Example 2. 
         FIG. 5  is a plot demonstrating the advantageously high rechargeability of an illustrative battery that incorporates cathode active material according to the present disclosure, as described in Example 3. 
         FIG. 6  is a bar graph comparing the specific capacities of selected battery cathode materials in comparison with a cathode prepared according to the present disclosure, as described in Example 4. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure provides high energy density cathode active materials, which may be produced inexpensively, and can be used to prepare cathodes for use in batteries. Selected cathodes prepared according to the present disclosure evolve substantially no gaseous oxygen during operation of a battery that includes the cathode. In some aspects, cathodes prepared according to the present disclosure evolve gaseous oxygen at a rate of less than about 1 mg per 1 mAh during a full lifecycle of a battery that includes the cathode. As used herein, the term “full lifecycle of the battery” is intended to mean that the life of the battery is considered to have exceeded its normal useful life, which is assumed here to be the point at which the battery shows 80% of its original capacity for the first time. 
     Cathode active materials may dictate differences in composition when building positive electrodes for battery cells. While a battery is charging, the cathode active materials supply ions through an electrolyte and supply electrons through an external circuit. While the battery is discharging, the cathode active materials are accept ions through the electrolyte and accept electrons through the external circuit. On the other hand, anode active materials are responsible for supplying ions through the electrolyte and electrons through an external circuit while the battery is discharging and for accepting ions through the electrolyte and electrons through the external circuit while the battery is charging. 
     Preparing Cathode Active Material 
     An illustrative method of manufacturing a high energy cathode active material according to the present disclosure is depicted in flowchart  10  of  FIG. 1 . The method includes preparing a solution of a hygroscopic species and a reactive oxygen species, at step  12  of flowchart  10 ; heating the solution at a temperature that is less than about 400° C. for a time sufficient for a precipitate of the cathode active material to form, at step  14  of flowchart  10 ; collecting the cathode active material, at step  16  of flowchart  10 ; and drying the collected cathode active material at a temperature that is less than about 400° C., at step  18  of flowchart  10 . The precipitate can be a reactive oxygen species derivative, a reactive oxygen species derivative combined with the hygroscopic species, or a reactive oxygen species combined with the hygroscopic species. 
     The hygroscopic species used to prepare the cathode active material can be any hygroscopic species that forms a precipitate when heated with an appropriate reactive oxygen species in a solution. Typically, the hygroscopic species is a compound or substance that attracts water from its environment, either by chemical reaction, by incorporating water of hydration, or by physical adsorption. In particular, the hygroscopic species may be substantially free of transition metals. Particularly useful hygroscopic materials can include one or more ionic compounds and/or one or more organic compounds. 
     Where the hygroscopic species includes one or more ionic compounds, the ionic compounds are typically salts, and more typically chloride, bromide, pentoxide, sulfide, sulfate salts. The ionic compound can also be an acid capable of donating a proton. 
     Where the hygroscopic species includes one or more organic compounds, the organic compounds can be selected from those organic compounds that incorporate one or more nitrogen or oxygen atoms. For example, the one or more organic compounds can be selected from among truxenone, truxenone derivatives, phenoxazine, phenoxazine derivatives, phenothiazine, phenothiazine derivatives, quinone, quinone derivatives, diamine derivatives, phenazine, phenazine derivatives, quinoxaline, quinoxaline derivatives, pyrazine, pyrazine derivatives, triazine, triazine derivatives, dimethoxybenzene, dimethoxybenzene derivatives, cyclopropenium derivatives, and amide derivatives. 
     The reactive oxygen species can be any species that includes one or more reactive oxygen moieties. For example, the reactive oxygen species can include one or more reactive oxygen moieties such as peroxides, superoxides, superoxide radicals, hydroxyl radicals, peroxyl radicals, perhydroxyl radical, hydroperoxyl radicals, alkoxyl radicals, singlet oxygen, hypochlorous acid, and alpha-oxygen. In one embodiment of the present disclosure, the reactive oxygen species includes at least one peroxide moiety. In an alternative embodiment, the reactive oxygen species can include one or more of Li 2 O 2 , H 2 O 2 , HOCl, and  1 O 2 . 
     Upon reaction, the reactive oxygen species is typically converted to a reactive oxygen species derivative. The reactive oxygen species derivative can be any species that is derived from the reactive oxygen species, and can be distinguished from the reactive oxygen species in that the reactive oxygen species derivative no longer includes a reactive oxygen moiety such as a peroxide, superoxide, superoxide radical, hydroxyl radical, peroxyl radical, perhydroxyl radical, hydroperoxyl radical, alkoxyl radical, singlet oxygen, hypochlorous acid, and alpha-oxygen. 
     Any method of preparing the solution of the hygroscopic species and reactive oxygen species is a suitable method for the purposes of the method of flowchart  10 . For example, preparing a solution of the one or more hygroscopic species and the one or more reactive oxygen species can include the addition of each of the desired hygroscopic species and reactive oxygen species to a single solution to form the desired combined solution. Alternatively, one or both of the hygroscopic species and reactive oxygen species can be initially dissolved in a solvent, and the hygroscopic species solution and the reactive oxygen species solution can then be combined to form the combined solution, or both can be added to an existing solution to form the combined solution. 
     The resulting solution is then heated at a temperature that is less than about 400° C., but high enough to result in formation of a precipitate of the desired cathode active material. Preferably, the solution is heated at temperature that is less than about 300° C., and more preferably the solution is heated at a temperature that is less than about 200° C. It should be appreciated that it is normally not possible to heat a solution to temperatures higher than the boiling point of the solution under standard conditions, and so the combined solution should be transferred to a sealed vessel, or autoclave, for heating under elevated pressure. The atmosphere of the sealed vessel, or autoclave can be replaced with high purity oxygen gas during the heat treatment. 
     When the combined solution has been heated for a time sufficient for a precipitate of the cathode active material to formed, the cathode active material can be collected. Any appropriate separation method can be used to collect the cathode active material precipitate, but typically the precipitate mixture is filtered, and washed. Included in the step of collecting the cathode active material, the filtered and washed cathode active material can be dried under vacuum or under an inert gas atmosphere, typically at a temperature less than about 400° C. Preferably, the cathode active material is dried at a temperature that is less than about 300° C., and more preferably less than about 200° C. 
     Testing or further handling of the collected and dried cathode active material should be done under dry conditions, for example in a relative humidity of less than about 25%. Preferably, such handling would be performed in a dry room. 
     Cathode Active Material 
     During preparation of the cathode active material, the hygroscopic species and the reactive oxygen species typically undergo a reaction to produce a cathode active material that includes one or more new materials. In one aspect of the present disclosure, the combination of the hygroscopic species and the reactive oxygen species produces a cathode active material that includes a metal compound and a metal oxide. In one embodiment, the cathode active material includes a metal compound that includes one or more of the hygroscopic species used in the reaction. Typically, the cathode active material includes the metal compound and the metal oxide in such a way that the metal compound and the metal oxide are in contact. 
     The resulting metal compound may be described by the empirical formula MR x , where M is a metal, and R is a moiety that is an atom, a molecule, or a radical. R may have a formal oxidation state of −1, −2, or −3. Typically, R has an oxidation state of −1. The value of x is a positive and nonzero real number. Each R moiety may be an organic moiety, or a halogen. Typically, when R is an organic moiety, R is an organic moiety that includes one or more heteroatoms independently selected from nitrogen, chlorine, bromine, fluorine, sulfur, phosphorous, and boron. 
     The resulting metal oxide may be described by the empirical formula M′ y O z , where M′ is a metal that is the same or different than M of the metal compound, and y and z are each positive nonzero real numbers, which may be the same or different. The metal oxide may include a metal superoxide and/or a metal peroxide. 
     M and M′, which may be the same or different, may be selected from lithium, sodium, potassium, beryllium, magnesium, calcium, vanadium, iron, nickel, copper, zinc, and aluminum. 
     The resulting cathode active material may include at least a portion of the metal compound and at least portion of the metal oxide that, considered in combination, form a cluster. In one aspect of the disclosure, the resulting cluster may be described by the empirical formula M a M′ b R c O d , where each of a, b, c, and d are positive nonzero real numbers, which may be the same or different. 
     The resulting cathode active material composition may include a ratio of metal compound:metal oxide that may vary from 5:95 to 75:25 by weight. The composition ratio of MR x :M′ y O z  may be about 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, or 75:25. Typically, the cathode active material is at least 25 wt % metal oxide. Preferably, the cathode active material is at least 50% metal oxide. Even more preferably, the cathode active material is at least 75 wt % metal oxide. 
     The average particle size of the cathode active material may vary from about 5 nm to about 50 μm, exhibiting an average pore size of about 0.1 nm to about 1 μm. Typically, the average particle size of the cathode active material is less than about 50 μm. Preferably, the average particle size of the cathode active material is greater than about 500 nm and less than about 50 μm. More preferably, the average particle size of the cathode active material is greater than about 5 μm and less than about 50 μm. Typically, the average pore size of the cathode active material is less than about 1 μm. Preferably, the average pore size of the cathode active material is greater than about 1 nm and less than about 500 nm. More preferably, the average pore size of the cathode active material is greater than about 5 nm and less than about 200 nm. 
     In some embodiments, the cathode active material is at least partially enclosed by a coating layer at an outer surface. The coating layer may vary from about 1 nm to about 1 μm in thickness. Preferably, the thickness of the coating layer is about 2 nm to about 500 nm. More preferably, the thickness of the coating layer is about 5 nm to about 200 nm. When present, the coating layer may include carbon and oxygen. 
     High Energy Cathodes 
     The cathode active materials disclosed herein can be used to prepare high energy cathodes, as set out in flowchart  20  of  FIG. 2 . As shown, the method of manufacturing a cathode for use in a battery includes preparing a solution of a hygroscopic species and a reactive oxygen species, at step  21  of flowchart  20 ; heating the solution  5  at a temperature that is less than about 400° C. for a time sufficient for a precipitate of the cathode active material to form, at step  22  of flowchart  20 ; collecting the cathode active material, at step  24  of flowchart  20 ; drying the collected cathode active material at a temperature that is less than about 400° C., at step  26  of flowchart  20 ; combining the collected cathode active material with one or more of an electrically-conductive material, a polymeric binder, a plasticizer, and a carboxylic acid,  10  at step  28  of flowchart  20 ; and depositing the combined cathode material on a current collector to create the cathode, at step  30  of flowchart  20 . 
     Steps  21 ,  22 ,  24 , and  26  of flowchart  20  are directly analogous to corresponding steps  12 ,  14 ,  16 , and  18  of flowchart  10 , as described above. 
     As set out in step  28  of flowchart  20 , the cathode active material can be combined with one or more of an electrically-conductive material, a polymeric binder, a plasticizer, and a carboxylic acid. Typically, the cathode active material is combined with an electrically-conductive material. Additionally, the cathode active material may be further combined with one or more of a polymeric binder, a plasticizer, and a carboxylic acid. 
     Where the cathode includes an electrically-conductive material, it can be added to one of the hygroscopic species or reactive oxygen species prior to preparation of the cathode active material, or the cathode active material can be combined with an electrically-conductive material after it is formed. In general, the cathode active material is in contact with the electrically-conductive material. 
     Where the cathode active material includes a metal compound and a metal oxide, each of the metal compound and the metal oxide are in contact with the other, and one or both the metal compound and the metal oxide are in contact with the electrically-conductive material. 
     Where the cathode includes the cathode active material and the electrically-conductive material, the cathode composition may include a ratio of the cathode active material:electrically-conductive material that may vary from 20:80 to 99:1 by weight. The composition ratio of cathode active material:electrically-conductive material may be about 20:80, about 25:75, about 30:70, about 35:65, about 40:60, about 45:55, about 50:50, about 55:45, about 60:40, about 65:35, about 70:30, about 75:25, about 80:20, about 85:15, about 90:10, about 95:5, about 96:4, about 97:3, about 98:2, or about 99:1. 
     Typically, the cathode composition is at least 20 wt % cathode active material. Preferably, the cathode composition may be at least 40 wt % cathode active material. More preferably, the cathode composition may be at least 60 wt % cathode active material. 
     Any electrically-conductive material that facilitates the performance of the resulting cathode is a suitable electrically-conductive material for the purposes of the present disclosure. In some embodiments, the electrically-conductive material includes a porous carbon material that is, or includes, one or more of carbon black, carbon nanotubes, carbon nanofibers, carbon dots, activated carbon, amorphous carbon, microporous carbon, mesoporous carbon, porous carbon, graphite, graphene, graphene oxide, graphene nanoribbons, nitrogen-doped carbon, nitrogen-doped graphene, and nitrogen-doped graphene oxide. The electrically-conductive material can have any suitable and compatible physical form, such as particles, powders, paper, foam, fibers, sheets, discs, rods, foils, or any combination thereof. In one embodiment, the electrically-conductive material includes a porous carbon material having particles with an average particle size (diameter) of about 5 nm to about 50 μm, and exhibiting an average pore size of about 0.1 nm to about 1 μm. 
     Typically, the average particle size or diameter of the electrically-conductive material is less than about 50 μm. Preferably, the average particle size of the electrically-conductive material is greater than about 50 nm and less than about 50 μm. More preferably, the average particle size of the electrically-conductive material is greater than about 500 nm and less than about 50 μm. Typically, the average pore size of the electrically-conductive material is less than about 1 μm. Preferably, the average pore size of the electrically-conductive material is greater than about 1 nm and less than about 500 nm. More preferably, the average pore size of the electrically-conductive material is greater than about 5 nm and less than about 200 nm. 
     In some embodiments, the average particle size of the cathode active materials and the electrically-conductive materials are inversely correlated. In such embodiments, where the average particle size of the cathode active material is in the range of about 10 μm to about 50 μm, the average particle size of the electrically conductive material may be about 10 nm to about 50 nm. Alternatively, where the average particle size of the cathode active material is in the range of about 10 nm to about 50 nm, the average particle size of the electrically conductive material may be about 10 μm to about 50 μm. Typically, one or more of the cathode active material and the electrically-conductive material includes particles with an average particle size or diameter of greater than about 50 nm and less than about 50 μm, preferably greater than about 500 nm and less than about 50 μm, and more preferably greater than about 5 μm and less than about 50 μm. 
     In one embodiment, the step of combining the cathode active material with an electrically-conductive material includes combining the cathode active material with a porous carbon material. The porous carbon material is optionally doped with one or more heteroatoms selected from boron, nitrogen, sulfur, phosphorous, fluorine, chlorine, and bromine. When present, the porous carbon material may include one or more of carbon black, carbon nanotubes, carbon nanofibers, carbon dots, activated carbon, graphite, graphene, graphene oxide, and graphene nanoribbons. 
     Where the cathode includes a polymeric binder, it can be added to one of the hygroscopic species or reactive oxygen species prior to preparation of the cathode active material, or the cathode active material can be combined with a polymeric binder after it is formed. 
     The polymeric binder can be added in order to help form a solid cathode from the cathode active material. An appropriate polymeric binder for the purposes of this disclosure can include one or more of polycaprolactone, poly(acrylic acid), poly(methyl methacrylate), polytetrafluoroethylene, poly(vinylidene fluoride), polyacrylonitrile, poly(ethylene terephthalate), polyvinylpyrrolidone, poly(4-vinylpyridine), polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate, polyethylene, polypropylene, polylactic acid, polyvinyl butyral, polystyrene, polyurethane, polycarbonate, among others. In a particular embodiment, the polymeric binder includes one or poly(ethylene oxide) (PEO) or poly(vinylidene fluoride). 
     Alternatively, or in addition, the cathode can incorporate a plasticizer, which can be used to make the resulting cathode softer and more flexible. The plasticizer can include one or more of succinonitrile, glutaronitrile, adiponitrile, ethylene carbonate, sulfolane, 3-methyl-2-oxazolidinone, butylene carbonate, phthalate derivatives, trimellitates, adipates, sebacates, and maleates, among others. In a particular embodiment, the plasticizer can include succinonitrile. 
     Alternatively, or in addition, the cathode can incorporate one or more carboxylic acids. When present, the carboxylic acid can be a monocarboxylic acid or a polycarboxylic acid. When the carboxylic acid is a polycarboxylic acid, it is optionally oxalic acid. 
     As set out at step  30  of flowchart  20 , the combined cathode material, including cathode active material and optionally including one or more of a conductive material, a polymeric binder, a plasticizer, and a carboxylic acid is deposited on a current collector in order to form the desired cathode. 
     The current collector can include any suitable and compatible conductive material. In some embodiments, the cathode current collector includes one or more metals such as alkaline earth metals, transition metals, rare earth metals, post-transition metals, and alkali metals. In some embodiments, the cathode current collector includes at least one of aluminum, aluminum alloy, nickel, nickel alloy, duplex steel, stainless steel. In one embodiment, the cathode current collector is a metallic current collector that includes a metal or metal alloy that in turn includes one or more of molybdenum, titanium, and zirconium. In an alternative embodiment, the cathode current collector is an electrically-conductive material that includes porous carbon in electrical contact with the cathode active material. 
     The cathode current collector can be solid or perforated. When perforated, the pore size of the cathode current collector can vary from about 500 nm to about 1 mm, with a separation distance between pores of about 10 μm to about 100 mm. 
     The cathode material, with additional conductive materials, polymeric binder, and plasticizers, if present, can be applied to the current collector using any suitable application technique. For example, the combined cathode material can be cast into a film and deposited onto the desired current collector. 
     The resulting cathode can be incorporated into a battery  32 , as shown in  FIG. 3 . Battery  32  typically includes a cathode  34  according to the present disclosure. Cathode  34  can include the combined cathode material  36  as described above, including the cathode active material, applied to a cathode current collector  38 . The anode  40  of battery  32  includes an anode material  42  applied to an anode current collector  44 . The cathode  34  and anode  40  are typically separated by an electrolytic separator  46 . The battery components are typically held within a battery case  48 , which encloses the battery components, and can keep the battery components under a desired gas composition or atmosphere  50 . It should be appreciated that regardless of how battery  32  is depicted herein, the batteries of the present disclosure may assume any conventional or suitable battery configuration, including cylindrical, prismatic, pouch, or flow batteries, among others. 
     Anode  40  can include an anode active material. In some embodiments, the anode includes one or more of lithium, sodium, potassium, magnesium, calcium, vanadium, aluminum, zinc, silicon, graphite, graphene, porous carbon, activated carbon, silicon compound, a metal oxide, and combinations thereof. The anode active material can be present as a coating, a foil, a mesh or screen, or other discrete anode component. Alternatively, or in addition, the anode active material can be incorporated into the anode as a component element, or component compound. In some embodiments, anode  40  includes a non-metal oxide as an anode active material. In some embodiments, the anode may include silicon, graphite, graphene, activated carbon, or a metal, or combinations thereof. Where the anode includes a metal, that metal may be an alkali metal or an alkaline earth metal. In some embodiments, the anode includes a metal oxide. In some embodiments, the anode includes a metal oxide such as Li 4 Ti 5 O 12 , TiO 2 , TiNb 2 O 7 , Nb 2 O 5 , Li 3 VO 4 , H 2 Ti 6 O 13 , LiMnBO 3 , LiV 0.5 Ti 0.5 S 2 , Li 3 V 2 O 5 , Li 3+   x V 2 O 5 , Li 3 MoO 4 , Li 5 W 2 O 7 , or any combination thereof. 
     Anode  40  may include an anode material  42  that is an anode active material, where the anode active material is at least partially enclosed by a coating layer at an outer surface. The coating layer may vary from about 1 nm to about 1 μm in thickness. Preferably, the thickness of the coating layer is about 2 nm to about 500 nm. More preferably, the thickness of the coating layer is about 5 nm to about 200 nm. When present, the coating layer may include carbon and oxygen. 
     Anode current collector  44  can include a metal or metal alloy, such as copper, a copper alloy, nickel, a nickel alloy, duplex steel, stainless steel, silver, a silver alloy, or any combination thereof. In some embodiments. The anode current collector  44  can be in contact with (e.g., coated with) an electrically-conductive material, such as a porous carbon material that is or includes carbon black, carbon nanotubes, carbon nanofibers, carbon dots, activated carbon, amorphous carbon, microporous carbon, mesoporous carbon, porous carbon, graphite, graphene, graphene oxide, graphene nanoribbons, nitrogen-doped carbon, nitrogen-doped graphene, nitrogen-doped graphene oxide, and combinations thereof. In some embodiments, the electrically-conductive material is in the form of particles, powders, paper, foam, fibers, sheets, discs, rods, foils, or any combination thereof. 
     In some embodiments, battery  32  can be a so-called “anode-free” battery, where anode  40  includes anode current collector  44 , but no anode material  42 . In such embodiments, anode current collector  44  may be disposed on or in the electrolyte such that the electrolyte is between cathode  34  and anode current collector  44 . Alternatively, or in addition, anode current collector  44  can be or include an exterior housing of the battery (i.e., battery case  48 ). 
     Electrolytic separator  46  can be disposed between cathode  34  and anode  40 , and typically includes an electrolyte to provide for ion transport within battery  32 , and act as a conduit for ion transport through its interaction with the anode material  42  and the cathode material  36 . Electrolytic separator  46  can be in contact with the electrolyte, and can include a polymer material, such as for example a polymer film such as polyethylene, polypropylene, poly(tetrafluoroethylene), or poly(vinyl chloride), among others. Typically, the polymer film, when present, includes polypropylene and/or polyethylene. Alternatively, or in addition, electrolytic separator  46  can include, nonwoven fibers (such as nylon, polyesters, and glass, among others), a glass, a ceramic, or any combination thereof. In some embodiments, the separator includes glass fibers. In some embodiments, the separator includes a surfactant coating or treatment to enhance the wettability of a liquid-based electrolyte. 
     The electrolyte present in battery  32  can include a solid electrolyte, liquid electrolyte, a liquefied gaseous electrolyte, or any combination thereof. In some embodiments, the electrolyte is an aqueous electrolyte. Alternatively, the electrolyte can include a nitrogen-containing compound, such as an organic amide compound. Such organic amide compounds can include, for example, one or more of dimethylformamide (DMF), diethylformamide (DEF), dimethylacetamide (DMAC), dipropylacetamide (DPAC), diethylacetamide (DEAC), dimethylpropionamide (DMP), diethylpropionamide (DEP), 2,2,2-trifluorodimethylacetamide (FDMA), 3-methoxypropionitrile (MPN), methoxyacetonitrile (MAN), acetonitrile (ACN), valeronitrile (VN), succinonitrile (SN), glutaronitrile, adiponitrile, acrylonitrile, propionitrile, tolunitrile, methoxybenzonitrile, malononitrile, or any combination thereof. In one embodiment, the electrolyte includes dimethylacetamide or trifluorodimethylacetamide. 
     Alternatively, or in addition, the electrolyte can include one, two, three, or more carbonate compounds, or compounds including an amide functional group. Suitable carbonate compounds include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), dipropyl carbonate (DPC), fluoroethylene carbonate (FEC), or any combination thereof. 
     The electrolyte can optionally include a plasticizer, such as succinonitrile, glutaronitrile, adiponitrile, ethylene carbonate, sulfolane, 3-methyl-2-oxazolidinone, butylene carbonate, phthalate derivatives, trimellitates, adipates, sebacates, maleates, or any combination thereof. 
     In some embodiments, the battery  32  can be a so-called “single-material” battery, where the cathode active materials disclosed herein can also be used as the electrolyte and/or the separator. In such embodiments, the cathode active materials that are not in contact with the electrically-conductive materials or the current collector may function as the electrolyte and/or the separator of the battery. 
     Where a battery of the present disclosure is a single-material battery, the battery may includes a cathode and electrolyte having a composition that may include a ratio of cathode:electrolyte that varies from 15:85 to 95:5 by weight. The composition ratio of the cathode:electrolyte may be about 15:85, 20:80, 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5. Typically, the cathode:electrolyte ratio is at least 15 wt % cathode. Preferably, the cathode:electrolyte ratio is at least 30 wt % cathode. More preferably the cathode:electrolyte ratio is at least 45 wt % cathode. 
     In addition, the electrolyte of electrolytic separator  46  and/or atmosphere  50  can include a greenhouse gas. When present in the electrolyte, the greenhouse gas can be dissolved or liquified greenhouse gas. The term “greenhouse gas” typically refers to a gas that absorbs and emits radiant energy within the thermal infrared range. Non-exclusive examples of greenhouse gases include carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), ozone (O 3 ), sulfur hexafluoride (SF 6 ), nitrogen trifluoride (NF 3 ), hydrofluorocarbons, chlorofluorocarbons, and perfluorocarbons, among others. Where a greenhouse gas is a halocarbon compound, it may include, for example, carbon tetrachloride (CCl 4 ), tetrafluoromethane (CF 4 ), or hexafluoroethane (C 2 F 6 ), among others. 
     Where a greenhouse gas is dissolved in a liquid electrolyte, the greenhouse gas can be introduced via an apparatus that includes a pressure gauge, a gas inlet, a gas outlet, and a chemically resistant frit or foam submerged in the liquid electrolyte. The liquid electrolyte can be kept under a greenhouse gas atmosphere at a pressure above standard atmospheric pressure for at least 10 seconds to at least 100 seconds, or longer. 
     It should be appreciated that while the descriptions of the various embodiments herein are written in the context of a battery having a single cell, the same or similar principles may be applied to a battery assembly that includes more than one battery cell (i.e., battery packs, etc.). Such multiple-battery assemblies should be understood to fall within the scope of the present disclosure. 
     Example 1. Manufacture of a High Energy Cathode 
     Cathodes according to the present disclosure are manufactured and tested using the following procedures. 
     Lithium hydroxide (LiOH) monohydrate and lithium chloride (LiCl) hydrate are dissolved in a 1:4 oxalic acid (OA)-methanol (MeOH) mixture with vigorous stirring to prepare a 0.1 M LiOH/0.1 M LiCl solution. 100 mg of carbon nanotube (CNT) is added to the solution with stirring, and the resulting mixture was ultrasonicated for 10 minutes to cause the carbon nanotube to interweave. A solution of hydrogen peroxide (H 2 O 2 ) and carbamide peroxide (CH 6 N 2 O 3 ) was added dropwise to the reaction mixture at a temperature of 65° C., with vigorous stirring. The molar ratio of the components of the reaction mixture was H 2 O 2 :CH 6 N 2 O 3 :LiOH:LiCl=1:1:1:1. 
     The reaction mixture is then transferred to a TEFLON-lined stainless-steel autoclave and heated to 130° C. for 12 hours. The resulting precipitate is separated from the mother liquor by filtration, washed with acetone and dried under vacuum at 110° C. for 24 hours. The collected material is then quickly transferred to an argon-filled glovebox with minimal exposure to air, and mixed with porous carbon, succinonitrile as a plasticizer, and polytetrafluoroethylene as a polymeric binder. The resulting mixture is cast onto a 316L stainless-steel mesh current collector, with a wire diameter of 0.05 mm and apertures of 0.08 mm to yield the high energy cathode. 
     The prepared cathode is placed in a coin cell (CR2032) with lithium metal foil as an anode and a polypropylene separator wetted with an electrolyte solution of 0.5 M bistrifluoro-methanesulfonimidate (LiTFSI)/0.5 M lithium nitrate (LiNO 3 ) in FEC-DMAC (1:1 volume ratio). The electrolyte solution was stored for 7 days under CO 2  atmosphere at above 5 bar of pressure before use. 
     Example 2. Determining the Charge-Discharge Profile of the High Energy Battery 
     The high energy battery prepared in Example 1 is subjected to cyclic charge-discharge by applying constant current to the battery. The high capacity performance of the battery is demonstrated in the plot of  FIG. 4 , which is a plot of charge discharge profile with voltage (V versus Li/Li+) versus specific capacity (mAh/g). 
     As shown, the battery of Example 1 achieves a specific capacity of over 500 mAh/g based on the weight of the cathode active material at a current density of 1 mA/cm 2 . The plot also demonstrates a high operating average discharge voltage of 3.41 V with a clear discharge plateau at around 3.48 V. Furthermore, the absence of any indication of an oxygen reduction reaction at around 2.5V shows that the cathode active material does not evolve gaseous oxygen during charging. 
     Example 3. Determining the Rechargeability of the High Energy Battery 
     The high energy battery prepared in Example 1 is subjected to repeated discharge and recharge. As shown in  FIG. 5 , the battery maintained a high capacity over 15 cycles at a current density of 1 mA/cm 2 . 
     Example 4. Specific Capacity Comparison 
     The specific capacity of the cathode materials prepared in Example 1 is compared to the specific capacities of conventional lithium-ion batteries with metal oxide cathodes. As shown in  FIG. 6 , as cathode prepared as in Example 1 exhibits a higher practical specific capacity than conventional lithium-ion batteries with metal oxide cathodes selected from LiFePO 4  (A), LiNi x Mn y Al z O 2  (B), LiNi x Co y Al z O 2  (C), LiCoO 2  (D), LiNiO 2  (E), LiMnO 2  (F), LiMnPO 4  (G), LiTiS 2  (H), and Li 2 MnO 3 (I) (values for conventional battery compositions shown in the graph taken from publicly-available literature (see https://doi.org/10.1016/j.mattod.2014.10.040). 
     Example 5. Additional Selected Embodiments 
     This section describes additional aspects and features of the disclosed cathode active materials, cathodes, and batteries presented without limitation as a series of paragraphs, some or all of which may be alphanumerically designated for clarity and efficiency. Each of these paragraphs can be combined with one or more other paragraphs, and/or with disclosure from elsewhere in this application, in any suitable manner. Some of the paragraphs below expressly refer to and further limit other paragraphs, providing without limitation examples of some of the suitable combinations. 
     A1. A cathode active material, comprising: a metal compound having an empirical formula of MR x , wherein M is a metal; R is an atom, a molecule, or a radical having an oxidation state of −1; and x is a positive nonzero real number; and a metal oxide having an empirical formula of M′ y O z , wherein M′ is a metal, and y and z are independently positive nonzero real numbers; wherein the metal compound and the metal oxide are in contact.
 
A2. The cathode active material of paragraph A1, wherein M and M′ may be the same or different, and are selected from lithium, sodium, potassium, beryllium, magnesium, calcium, vanadium, iron, nickel, copper, zinc, and aluminum.
 
A3. The cathode active material of paragraph A1, wherein at least a portion of the metal compound and a portion of the metal oxide in combination form a cluster having an empirical formula of M a M′ b R c O d , where each of a, b, c, and d are positive nonzero real numbers which may be the same or different.
 
A4. The cathode active material of paragraph A1, wherein each R is independently an organic moiety or a halogen.
 
A5. The cathode active material of paragraph A4, wherein when R is an organic moiety, R is an organic moiety that includes one or more heteroatoms independently selected from nitrogen, chlorine, bromine, fluorine, sulfur, phosphorous, and boron.
 
A6. The cathode active material of paragraph A1, wherein the metal oxide includes a metal superoxide and/or a metal peroxide.
 
B1. A cathode material, comprising: a cathode active material including a metal compound and a metal oxide; wherein the metal compound has an empirical formula of MR x , wherein M is a metal; R is an atom, a molecule, or a radical having an oxidation state of −1; and x is a positive nonzero real number; and the metal oxide has an empirical formula of M′ y O z , wherein M′ is a metal, and y and z are independently positive nonzero real numbers; such that the metal compound and the metal oxide are in contact; and an electrically-conductive material; such that one or both of the metal compound and the metal oxide are in contact with the electrically-conductive material.
 
B2. The cathode material of paragraph B1, wherein M and M′ may be the same or different, and are selected from lithium, sodium, potassium, beryllium, magnesium, calcium, vanadium, iron, nickel, copper, zinc, and aluminum.
 
B3. The cathode material of paragraph B1, wherein the electrically-conductive material includes a porous carbon material.
 
B4. The cathode material of paragraph B3, wherein the porous carbon material is doped with one or more heteroatoms selected from boron, nitrogen, sulfur, phosphorous, fluorine, chlorine, and bromine.
 
B5. The cathode material of paragraph B1, wherein the electrically-conductive material includes one or more of carbon black, carbon nanotubes, carbon nanofibers, carbon dots, activated carbon, graphite, graphene, graphene oxide, and graphene nanoribbons.
 
B6. The cathode material of paragraph B1, further comprising one or more of a polymeric binder, a plasticizer, and a carboxylic acid.
 
C1. A battery having a cathode and an electrolyte, wherein the cathode includes a cathode active material that includes a metal compound having an empirical formula of MR x , wherein M is a metal; R is an atom, a molecule, or a radical having an oxidation state of −1; and x is a positive nonzero real number; and a metal oxide having an empirical formula of M′ y O z , wherein M′ is a metal, and y and z are independently positive nonzero real numbers; wherein the metal compound and the metal oxide are in contact.
 
C2. The battery of paragraph C1, wherein the cathode evolves substantially no gaseous oxygen during operation of the battery.
 
C3. The battery of paragraph C1, wherein the battery exhibits at least 500 mAh/g of discharge capacity at a current density of greater than or equal to 0.1 mA/cm 2 .
 
C4. The battery of paragraph C1, wherein the battery can produce at least 3.0 V of average operating discharge potential at a current density of greater than or equal to 0.1 mA/cm 2 .
 
C5. The battery of paragraph C1, wherein the battery is substantially rechargeable.
 
C6. The battery of paragraph C1, wherein the battery is operable at a room temperature.
 
C7. The battery of paragraph C1, further comprising an anode, wherein the anode includes an anode active material at least partially enclosed by a coating layer on an outer surface of the anode material, wherein the coating layer includes carbon and oxygen.
 
C8. The battery of paragraph C1, further comprising an electrolyte, wherein the electrolyte includes an organic amide compound.
 
C9. The battery of paragraph C8, further comprising a greenhouse gas that is liquified, in contact with the electrolyte, or dissolved in the electrolyte.
 
C10. The battery of paragraph C9, wherein the greenhouse gas includes one or more of carbon dioxide (CO 2 ), methane (CH 4 ), sulfur hexafluoride (SF 6 ), a perfluorocarbon compound, a chlorofluorocarbon compound, and a hydrofluorocarbon compound.
 
C11. The battery of paragraph C1, further comprising a separator, wherein the separator includes a polymeric material.
 
C12. The battery of paragraph C1, further comprising a current collector including an alloy of one or more of molybdenum, titanium, and zirconium.
 
     ADVANTAGES, FEATURES, BENEFITS 
     The cathode active materials of the present disclosure permit the fabrication of high energy cathodes for batteries that are economical, provide high discharge capacities, high discharge potentials, and are not subject to oxygen evolution during operation. 
     Selected batteries of the present disclosure exhibit discharge capacities of at least 100 mAh/g at a current density of greater than or equal to 0.1 mA/cm 2 . In some embodiments, the batteries of the present disclosure can exhibit discharge capacities of greater than 200 mAh/g, greater than 300 mAh/g, and greater than 500 mAh/g at current densities of greater than or equal to 0.1 mA/cm 2 . 
     Selected batteries of the present disclosure can exhibit average operating discharge potentials greater than 1.0 V. In some embodiments, the batteries of the present disclosure can exhibit average operating discharge potentials greater than 2.0 V, greater than 3.0 V, or even greater than 4.0 V. Typically, such batteries may produce an average operating discharge potential of at least 3.0 V at a current density of greater than or equal to 0.1 mA/cm 2 . 
     Selected batteries of the present disclosure may be substantially rechargeable. In one aspect of the disclosure, a battery may be considered substantially rechargeable if it exhibits a cycle number greater than 100. Alternatively, or in addition, selected batteries of the present disclosure may operate efficiently at room temperature, which in one embodiment may be defined as 15° C.-30° C. 
     Cathodes prepared according to the methods of the present disclosure can operate with an evolution of less than 1 mg per 1 mAh of gaseous oxygen during a full lifecycle of the battery including the cathode. In some cases, the cathodes of the present disclosure exhibit substantially zero evolution of gaseous oxygen during operation. 
     The cathode active material of the present disclosure exhibits a standard redox potential above 3.0 V versus Li/Li + . 
     The term “substantially” as used herein means to be more-or-less conforming to the particular dimension, range, shape, concept, or other aspect modified by the term, such that a feature or component need not conform exactly. For example, a “substantially cylindrical” object means that the object resembles a cylinder, but may have one or more deviations from a true cylinder. Similarly, the term “about” refers to a deviation of up to 10% of the stated value, if it is physically possible, both downwards and upwards, and otherwise only in the meaningful direction. 
     Unless related to specific examples, all specifications regarding quantities and portions, particularly those for delimiting the disclosed subject matter, are supposed to indicate a ±10% tolerance, for example: 11% means from 9.9% to 12.1%. For terms such as “a solvent”, the word “a” is not to be regarded as a numerical word but as an indefinite article or as a pronoun, unless the context indicates otherwise. 
     The term “combination” or “combinations” means, unless otherwise stated, all types of combinations, starting from two of the relevant constituents, to a plurality or all of such constituents. 
     The illustration of the steps of a method, whether shown in the drawings or described in the description, should not be considered to illustrate the specific order of the method steps, unless the order is specifically provided. The order of such steps may differ from what is depicted and described, and/or two or more steps may be performed concurrently or with partial concurrence, unless specified differently. 
     The features and variants specified in the individual embodiments and examples can be freely combined with those of the other examples and embodiments and in particular be used to characterize the invention in the claims without necessarily implying the other details of the respective embodiment or the respective example. 
     CONCLUSION 
     The disclosure set forth above may encompass multiple distinct examples with independent utility. Although each of these has been disclosed in one or more illustrative form(s), the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense, because numerous variations are possible. To the extent that section headings are used within this disclosure, such headings are for organizational purposes only. The subject matter of the disclosure includes all novel and nonobvious combinations and subcombinations of the various elements, features, functions, and/or properties disclosed herein. The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. Other combinations and subcombinations of features, functions, elements, and/or properties may be claimed in applications claiming priority from this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.