Photo-rechargeable metal tellurium oxide alkali-ion battery

Abstract

A photo-rechargeable metal tellurium oxide alkali-ion battery containing a semiconductor photocatalyst that is capable of (i) carrying an electrical load while being photo-charged, and (ii) carrying an electrical load subsequent to the termination of light radiation, wherein the battery includes: electrodes having an anode and a cathode, wherein the cathode includes a photocatalyst and the anode an alkali metal; an external electrical circuit that allows electrons to pass externally between the electrodes for charging and to drive an electrical load during discharging; an electrolyte for facilitating the conduction of ions between the electrodes, for supporting chemical reactions occurring at the electrodes, and for maintaining charge neutrality within the battery; a semi-permeable barrier between the electrodes for allowing ions within the electrolyte to pass between the electrodes; and a photo-induced potential bias across the external electrical circuit for driving electrons, when light radiation is incident on the cathode, to flow between the electrodes in a certain direction via the external electrical circuit, and wherein the photocatalyst is a metal tellurium oxide having a layered structure, capable of having its electrons excited from its valence band to its conduction band upon incident light radiation; positive holes within the layered structure associated with such photo-induced excitation are stabilised by storing ions from the electrolyte and / or anode within the layered structure; and, subsequent to the termination of incident light radiation on the cathode, the stabilised alkali metal ions stored within the layered structure are oxidised allowing the alkali metal ions to return to the electrolyte and / or anode, and the electrons associated with the returned ions are released into the external electrical circuit to form an oxidative current that drives an electrical load.

Description

[0001] PHOTO-RECHARGEABLE METAL TELLURIUM OXIDE ALKALI-ION BATTERY

[0002] FIELD OF APPLICATION OF THE INVENTION

[0003] The present invention relates to a photo-rechargeable battery, that contains a semiconductor photocatalyst, in particular, a photo-rechargeable battery containing a photocatalyst that is capable of (i) carrying an electrical load while being photocharged, and (ii) carrying an electrical load subsequent to the termination of light radiation.

[0004] BACKGROUND TO THE INVENTION

[0005] With an ever increasing global population, together with an associated increase in business and industries, electrical energy security is of the utmost importance. From 1990 to 2021 , a period of only thirty years, global electricity demand has increased by 140% [1], Associated with this increase in global electricity demand, the use of fossil fuels (over this same period) has increased by 134%. In contrast, in the span of only twenty years, solar photovoltaic (PV) energy conversion and storage has increased from a base of zero in 1999 to 3.6% in 2021 (as a percentage of the total) [1],

[0006] The International Renewable Energy Agency (IRENA) predicts that the global PV installation capacity will reach 14000 GW by 2050 [2], In this regard it is expected that the growth in solar PV will continue. It is also forecasted that, form 2040 onwards, solar energy conversion technologies will dominate [3], The bulk of the global PV market, at the moment, constitutes 97% being supplied by silicon-based technologies [4], with the balance being made of thin film cadmium telluride (CdTe) technologies, amongst others [3],

[0007] The problem with current solar energy conversion technologies is that it is intermittent in that solar energy can only be converted into electrical energy during daytime hours when solar irradiation is incident on photovoltaic cells. The converted solar energy, that is electrical energy, is fed to a battery (typically a lithium-ion battery) that converts the electrical energy as chemical energy. The chemical energy in the battery can then, on demand, be converted back to electrical energy to drive a load. Current solar PV conversion and storage technologiesmake use of two successive conversion units, that is a PV cell / panel and a lithium-ion battery. From an operational and infrastructure point of view it would be advantageous to combine these two successive processes and units into a single device (a so called solar rechargeable battery). Such a unit should not only function as an energy store, converting solar energy into chemical energy, but should be able to drive an electrical load, converting solar energy into electrical energy, whilst also storing a portion of the converted energy. The ideal technology should be able to convert solar energy into electrical- and chemical energy at the same time.

[0008] Different pathways have been followed to try and develop a single device that converts solar energy into both electrical and chemical energy at the same time. Initial strategies entailed the development of a hybrid design that involved combining a unit for solar to electrical conversion and another unit for electrical to chemical conversion, into a single unit. These designs consist of three electrodes, with one of the electrodes that is shared between two sub-units. The first design (involving a CdSe photoelectrode) was investigated as far back as 1976 [5, 6], In this three electrode design, two electrodes allow for solar to electrical energy conversion, for example a dye- sensitized solar cell (DSSC), while two electrodes allow for the conversion of electrical energy into chemical energy, for example a lithium-ion battery (with one electrode in this design being common between the two pairs) [7-10], This concept was expanded to link a DSSC with a redox flow battery

[0011] , A subsequent design involved the introduction of a built-in dye-sensitized TiO2 photo-electrode into a Li-I redox flow battery

[0012] , The drawback, however, of these designs that make use of embedded DSSCs or photovoltaic cells, is that they make for an overly complex unit that result in increased capital expenditure and having associated reliability issues. To simplify the afore-mentioned three-electrode strategies, various two-electrode units were design and investigated [13-23], One such design involved incorporating a CdS@Pt photocatalyst onto the backside of an aqueous cathode of a Li-S battery (having a Li anode)

[0014] , There is, however, a downside to this design in that hydrogen gas is released at the cathode during charging, which requires the battery to be topped up with water from time to time. Not only does this design have an operational drawback, associated with additional operational cost, but it also comes with increased capital expenditure in that the use of platinum (as part of the photocatalyst / cathode) ads additional cost to the unit. A subsequent design of a photo-rechargeable lithium-ion battery involved a photocathode that consists of V2O5 nanofibers mixed with reduced graphene oxide (rGO) and poly(3-hexylthiophene-2,5-diyl) (P3HT) supported on a carbon felt current collector (and a Li anode)

[0019] , Another photo-rechargeable lithium- ion battery involved a LiV2Os photocathode and a Li anode

[0020] , In a further development, a linear membraneless photorechargeable battery was designed and investigated in that illumination of 2D carbon nitride potassium poly(heptazine imide) (K-PHI) results in the storage of photoexcited electrons and the photo-intercalation of potassium ions, with internal charge transport and storage being attained by employing poly(9,9-dioctyl-fluorene-alt-benzothiadiazole) as hole transport material and poly(3,4-ethylendioxythiophene) polystyrene sulfonate as hole storage material [16, 21 ], Lastly, an aqueous zinc-tellurium battery was equipped with a Janus-jointed perovskite / Te photocathode by incorporating the photo-absorber and the energy storage material (CHsNHsPbh / TiC ) into the cathode, which renders the battery photo- rechargeable

[0023] ,

[0009] Given the above, there is a clear need that exists in the art to harness photocatalysts in a manner that will allow for superior, unique and novel application(s) in solar technology, particularly in the absence of solar radiation, i.e. in the dark.

[0010] OBJECT OF THE INVENTION

[0011] It is thus an object of the present invention to provide a photo-rechargeable battery capable of (i) being photo-charged, (ii) carrying an electrical load during photocharging, and (iii) carrying an electrical load subsequent to the termination of light radiation, thereby eliminating the need for a separate charging mechanism, such as a photovoltaic cell, to charge the battery and, thereby consolidates photo to electrical energy conversion and electrical to chemical energy storage into a single device / technology. SUMMARY OF THE INVENTION

[0012] According to the invention, there is provided a photo-rechargeable metal tellurium oxide (MTO) alkali-ion battery that includes: a) electrodes having an anode and a cathode, wherein the cathode includes a photocatalyst and the anode consists of a compound that includes an alkali metal; b) an electrical connection between the electrodes defining an external electrical circuit that allows electrons to pass externally between the electrodes for charging and to drive an electrical load during discharging; c) an electrolyte for facilitating the conduction of ions between the electrodes, for supporting chemical reactions occurring at the electrodes, and for maintaining charge neutrality within the battery; d) a semi-permeable barrier between the electrodes for allowing ions within the electrolyte to pass between the electrodes; e) a photo-induced potential bias across the external electrical circuit for driving electrons, when light radiation is incident on the cathode, to flow between the electrodes in a certain direction via the external electrical circuit; wherein the photocatalyst is a metal tellurium oxide having a layered structure, which is capable of having its electrons excited from its valence band to its conduction band upon incident light radiation; wherein positive holes within the layered structure associated with such photo induced excitation are stabilised by storing ions from the electrolyte and / or anode within the layered structure; and wherein, subsequent to the termination of incident light radiation on the cathode, the stabilised alkali metals stored within the layered structure are oxidised allowing the alkali ions to return to the electrolyte and / or anode, and the electrons associated with the returned ions are released into the external electrical circuit to form an oxidative current that drives an electrical load.

[0013] In terms of the present specification, the following terms will be understood to denote the following.

[0014] Intercalation refers to the reversible inclusion or insertion of a molecule or ion into materials / compounds having layered structures.

[0015] Light radiation denotes either solar radiation, ultraviolet (UV) radiation, visible (light) and infrared radiation, and a combination thereof.

[0016] It is to be appreciated that a photocatalyst differs from a photocatalyst in that the former relies solely on incident photons to generate electron-hole pairs and drive redox reactions, whereas the latter requires illumination and an externally applied electrical bias to promote catalytic charge transfer at an electrode; and that the photocatalyst allows for (upon illumination) intrinsic photo-induced charge separation to occur, wherein electrons are conducted through an external circuit, and the resulting positive holes are stabilised by reversible ion intercalation within the lattice structure of the cathode. It is further to be appreciated that the alkali ions are reversably stabilised in the form an ‘alkali metal’ metal tellurium oxide (AMTO; A = alkali metal, MTO = metal tellurium oxide) at the cathode. Once stabilised, subsequent to the termination of incident light radiation, the akali ions may return to the electrolyte to allow the electrons that were bound to the ions (that formed the ‘alkali metal’ metal tellurium oxides, i.e. AMTO) to flow through the external electrical circuit to drive the electrical load.

[0017] In an embodiment of the invention, the cathode may be selected from the group consisting of graphite, lithium metal, silicon, tin, lithium alloys, conductive polymers, a photocatalyst, and a combination thereof.

[0018] In an embodiment of the invention, the metal in the metal tellurium oxide may be at least one of the transition metals, the lanthanides, the actinides, and the non-metals of the periodic table.

[0019] In an embodiment of the invention, the metal tellurium oxide is selected from the group consisting of bismuth tellurium oxide, indium tellurium oxide, antimony tellurium oxide, cadmium tellurium oxide, cobalt tellurium oxide, copper tellurium oxide, europium tellurium oxide, iron tellurium oxide, lead tellurium oxide, manganese tellurium oxide, nickel tellurium oxide, zinc tellurium oxide, tin tellurium oxide, that is any transition metal tellurium oxide, and a combination thereof.

[0020] In a preferred embodiment, the metal tellurium oxide may be selected from the group comprising cobalt (II) tellurium oxide, nickel tellurium oxide, and a combination thereof. In an embodiment of the invention, the anode may include a material selected from lithium (Li), sodium (Na) or potassium (K), the alkali metals.

[0021] In a further embodiment of the invention, the anode may comprise a material selected from the group consisting of lithium metal oxide such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and a combination thereof.

[0022] In a preferred embodiment of the invention, the anode comprises an alkali-metal oxide, such as lithium cobalt oxide (LiCoC ), lithium vanadium oxide (UV2O5), sodium cobalt oxide, or potassium cobalt oxide.

[0023] In an embodiment of the invention, the electrolyte may be selected from at least one of sodium chloride, lithium hexafluorophosphate (LiPFe), sodium hexafluorophosphate (NaPFe), potassium hexafluorophosphate (KPFe), lithium perchlorate (LiCIC ), sodium sulphate (Na2SO4), lithium hydroxide (LiOH), sodium hydroxide (NaOH), and potassium hydroxide (KOH).

[0024] In terms of the invention, when light radiation is incident on the metal tellurium oxide photocatalyst, the semiconductor characteristic and the layered structure of the metal tellurium oxide photocatalyst allows for the simultaneous excitation of electrons (from the valence band to the conduction band) and photo induced intercalations wherein the electrons within the layered structure, associated with such photo-induced electron excitation are to be stabilised by positive ions from the electrolyte and / or anode moving into the layered structure; constituting an intercalation process. The above and other characteristics, features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying figures which illustrate, by way of example, the principles of the invention. This description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached figures.

[0025] BRIEF DESCRIPTION OF THE DRAWINGS

[0026] A preferred embodiment of the invention is described below with reference to the accompanying figures, wherein:

[0027] Figure 1 is a schematic diagram showing the working principle of the photo- rechargeable metal tellurium oxide alkali-ion battery in accordance with the present invention;

[0028] Figure 2 is the XRD diffractogram of synthesised cobalt (II) tellurium oxide nanomaterials calcined at 900°C;

[0029] Figure 3 is the XRD diffractogram of synthesised nickel tellurium oxide calcined at 700°C;

[0030] Figure 4 illustrates the construction of the photo-rechargeable metal tellurium oxide (MTO) alkali-ion battery; Figure 5 illustrates photo charge and electrical discharge cycles (monitoring potential, E) at different electrical discharge loads, i.e. -1 pA, -2 pA, and -5 pA, with electrical discharging in the dark, for a nickel tellurium oxide (NTO) lithium-ion photo-rechargeable battery;

[0031] Figure 6 illustrates photo charge and electrical discharge cycles (monitoring potential, E) at different electrical discharge loads, i.e. -1 pA, -2 pA, and -5 pA, with electrical discharging in the dark, for a cobalt tellurium oxide (CTO) lithium-ion photo-rechargeable battery;

[0032] Figure 7 illustrates photo charge and electrical discharge cycles (monitoring potential, E) at different electrical discharge loads, i.e. -1 pA, -2 pA, and -5 pA, with electrical discharging in the dark, for a nickel tellurium oxide (NTO) potassium-ion photo-rechargeable battery;

[0033] Figure 8 illustrates photo charge and electrical discharge cycles (monitoring potential, E) at different electrical discharge loads, i.e. -1 pA, -2 pA, and -5 pA, with electrical discharging in the dark, for a cobalt tellurium oxide (CTO) potassium-ion photo-rechargeable battery;

[0034] Figure 9 illustrates photo charge and electrical discharge cycles (monitoring potential, E) at different electrical discharge loads, i.e. -1 pA, -2 pA, and -5 pA, with electrical discharging in the dark, for a nickel tellurium oxide (NTO) sodium-ion photo-rechargeable battery; Figure 10 illustrates photo charge and electrical discharge cycles (monitoring potential, E) at different electrical discharge loads, i.e. -1 pA, -2 pA, and -5 pA, with electrical discharging in the dark, for a cobalt tellurium oxide (CTO) sodium-ion photo-rechargeable battery;

[0035] Figure 11 illustrates photo charge and electrical discharge cycles (monitoring current in milli-amperes, mA) at different electrical discharge loads, i.e. - 1 pA, -2 pA, and -5 pA, with electrical discharging in the dark, for a cobalt tellurium oxide (CTO) lithium-ion photo-rechargeable battery; and

[0036] FIGURE 12 illustrates photo charge and electrical discharge cycles (monitoring potential, E) at different electrical discharge loads, i.e. -1 pA, -2 pA, and -5 pA, with electrical discharging in the light, for a cobalt tellurium oxide (CTO) lithium-ion photo-rechargeable battery.

[0037] The presently disclosed subject matter will now be described more fully hereinafter with reference to the accompanying examples, whereafter, representative embodiments are shown. The presently disclosed subject matter can, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of such an embodiment to those skilled in the art. EXPERIMENTS AND PREFERRED EMBODIMENTS OF THE INVENTION

[0038] Photocatalyst

[0039] It is known in the art that photocatalysts are mostly active until illumination is terminated due to the recombination of the negative charge in the conduction band and the positive holes in the valence band. In some instances, sustained photocatalytic / photo-electrocatalytic activity has been reported, subsequent to light interruption, but with limited success.

[0040] Materials and Synthesis of the Photocatalyst

[0041] Cobalt (II) nitrate hexahydrate (Co(NO3)26H2O, 98%) and telluric acid (H6TeO6, 98%) were procured from Associated Chemical Enterprises and Sigma-Aldrich respectively, along with other reagents such as Nation (5 wt% in aliphatic alcohols and water) and ammonia solution (32%) from Merck Chemical (Pty.) Ltd. Vulcan Carbon XC-72 and ultrapure Milli-Q water (18 MQ cm-1) were utilised for solution preparations. Employing the sol-gel method, cobalt tellurium oxides were synthesised. The procedure involved combining H6TeO6(0.1 mol. dm-3) in a 50 cm3ethanol-water mixture, adding CO(NO3)26H2O (0.2 mol. dm-3), citric acid (0.6 mol. dm-3), and ethylene glycol (2.5 cm3). The pH was adjusted to 11 , the mixture heated to 70°C to form a gel, oven-dried at 120°C, and the resultant powder calcined at temperatures ranging from 400°C to 1100°C for 5 hours, producing samples labelled CTO-400 to CTO-1100 and kept in a desiccator for further analysis and use. Preparation of the Cathode Photocatalyst Ink

[0042] The cathode active material is an alkali ion cobalt oxide and is either LiCoCh (lithium cobalt oxide), NaCoC (sodium cobalt oxide) or KCoO2 (potassium cobalt oxide). The ink is made up of 85 wt% LiCoCh (source of lithium ions), 7.5 wt% carbon black (to improve conductivity, and 7.5 wt% PVDF (polyvinylidene fluoride, acting as a binder for the ink). NMP (N-methyl-2-pyrrolidone) is used as a ‘solvent’ for the solid materials (the alkali ion cobalt oxide, the carbon black and the PVDF) in a 2:1 ratio of solvent to solids. The exact ratio of solids and solvent is put into a vial with a small magnetic stirrer and mixed for 12 hours to ensure a slurry of good homogeneity.

[0043] Preparation of the Anode ‘Alkali-ion’ Metal Oxide Ink

[0044] The anode active material is the metal tellurium oxide photocatalyst, e.g. cobalt tellurium oxide or nickel tellurium oxide. The ink is made up of 85 wt% metal tellurium oxide (the photocatalyst), 7.5 wt% carbon black (to improve conductivity, and 7.5 wt% PVDF (polyvinylidene fluoride, acting as a binder for the ink). NMP (N-methyl-2- pyrrolidone) is used as a ‘solvent’ for the solid materials (the metal tellurium oxide photocatalyst, the carbon black and the PVDF) in a 2:1 ratio of solvent to solids. The exact ratio of solids and solvent is put into a vial with a small magnetic stirrer and mixed for 12 hours to ensure a slurry of good homogeneity. Photocatalyst Compositional Characterisation

[0045] The identity and purity of the synthesised compounds was identified employing a X- ray diffraction (XRD) apparatus (PANalytical X’Pert Pro).

[0046] Construction of the Photo-rechargeable Battery

[0047] Construction of the battery is done within a glovebox that is filled with nitrogen gas to ensure that no oxygen or moisture enters the battery. The photo-rechargeable battery consists of two electrodes, the cathode and the anode, that are separated by an ion exchange membrane, typically Celgard. Each of the electrodes consists of a low-iron sodalime glass substrate that is 2.2mm in thickness and coated on one side with 7Q / sq fluorine doped tin oxide (SnO2:F), acquired from Solaronix, Switzerland. The fluorine doped tin oxide coating ensures electrical conductivity. Onto this coating, a gasket is fixed through heat treatment. The gasket is a Meltonix 1170-60 sealing film, with a thickness of 60 microns, having an inner open area dimension of 8mm x 8mm, acquired from Solaronix, Switzerland. Within the 8mm x 8mm ‘opening’ of the gasket, a slurry / suspension of the active material (the MTO photocatalyst ink, on the cathode, and the lithium cobalt oxide or sodium cobalt oxide or potassium cobalt oxide, on the anode) is coated using the doctor blade technique. The coated glass substrate is put onto a hotplate and heated at 100°C for 10 minutes to dry the slurry / suspension and to remove excess NMP solvent. The electrodes are placed into a vacuum oven at 120°C for 12 hours. Onto the active material, the cathode photocatalyst and the anode ‘alkali-ion’ metal oxide, a few drops of an ‘alkali-ion’ electrolyte, either lithium hexafluorophosphate (LiPFe), sodium hexafluorophosphate (NaPFe), or potassium hexafluorophosphate (KPFe), is dropped. An ion permeable membrane is put onto the cathode to cover the whole of the active material and gasket. The anode is placed onto the cathode with the active areas of the cathode and anode facing one another exactly. The two electrodes are held together using paper clamps. For the MTO lithium ion battery Celgard 2325 is used as the ion permeable membrane while a Whatman GF / F glass microfiber filter is used as ion permeable membrane for the MTO sodium ion and MTO potassium ion battery. In the case of the MTO lithium ion battery two drops of the electrolyte is used while three drops of the electrolyte is used for the MTO sodium and MTO potassium ion batteries.

[0048] If lithium cobalt oxide (LiCoO2) is used as anode material, then lithium hexafluorophosphate (LiPFe) is used as electrolyte; if sodium cobalt oxide (NaCoO2) is used as anode material, then sodium hexafluorophosphate (NaPFe) is used as electrolyte; if potassium cobalt oxide (KCOO2) is used as anode material, then potassium hexafluorophosphate (KPFe) is used as electrolyte. LiPFe was acquired in solution form and used as is. NaPFe and KPFe salts were dissolved in equal quantities of ethylene carbonate and dimethyl carbonate.

[0049] Photo-electrical Characterisation of the Photo-rechargeable Battery

[0050] The photo-rechargeable MTO alkali-ion battery is connected to a potentiostat for photo-electrical via a two-electrode connection, i.e. a connection made to the cathode and a connection made to the anode. A SunLite 50 x 50mm ABA Solar Simulator, with a lamp power of 100W (employing a Xe arc lamp) exhibiting a Class AAM1 ,5G spectral match, is used as solar simulator (acquired fromABET Technologies, USA) to illuminate the photo-rechargeable MTO alkali-ion battery perpendicularly on the electrode coated with the MTO photocatalyst. With the aid of the potentiostat the potential of the battery is monitored against time as well as the current produced against time. The potential and current are monitored during charge discharge cycles of the battery whereby the solar simulator is switched on and off during specific time periods.

[0051] Results and Discussion

[0052] The working principle of the photo-rechargeable metal tellurium oxide alkali-ion battery (PR_MTO_AIB) is as follows (with reference to Figure 1 ); as an example, a photo- rechargeable metal tellurium oxide lithium-ion battery (PR_MTO_LIB) is discussed. Solar radiation is incident on the cathode that contains the metal tellurium oxide (MTO), a semiconductor. The MTO absorbs the incident radiation resulting in an electron being excited from the valence band (VB) of the MTO to the conduction band (CB) of the MTO leaving a positive hole in the VB, and is referred to as photo-induced charge separation. The excited electron is stabilised within the MTO layered structure by combining with a lithium-ion from the electrolyte, the lithium hexafluorophosphate (LiPFe), and is referred to as photo-induced intercalation. The reduction in the concentration of lithium ions in the electrolyte on the cathode side is replenished by lithium ions moving through the membrane / separatorfrom the electrolyte on the anode side of the battery. The reduction in the concentration of lithium ions in the electrolyte on the anode side is replenished by lithium ions moving from the lithium metal oxide (LMO; for example lithium cobalt oxide) at the counter electrode, the anode. The resulting positive hole within the MTO (at the cathode) ‘pulls’ an electron from the counter electrode, i.e. the LMO (the anode), through the external electrical circuit, which results in a lithium ion being released that moves into the electrolyte at the anode. This process entails the photo-induced charging of the MTO_AIB. The reverse of this process will drive an electrical load and relates to the discharging of the MTO_AIB; the working principle of discharging is as follows. The photo-excited electron, stabilised through intercalation within the MTO structure, moves through the external circuit, driving the electrical load. The associated lithium ion moves out of the MTO structure back into the electrolyte of the electrode (now the anode), through the membrane / separator, into the electrolyte of the counter electrode (now the cathode) and finally back into the LMO where it is stabilised by the electron that has moved through the external electrical circuit.

[0053] The synthesised cobalt tellurium oxide (CTO), calcined at 900°C, consists of 54.8% CosTeOe, 43.5% CoO, and 1.6% CO3O4. This has been determined by means of x-ray diffraction (XRD) with the x-ray diffractrogram shown in Figure 2. The synthesised nickel tellurium oxide (NTO) consist of a pure phase of NisTeOe, ascertained by means of XRD (Figure 3).

[0054] Employing the synthesised CTO and NTO, a PR_MTO_AIB is constructed as described earlier (Figure 4). This battery is subjected to photo-induced charging and electrical discharging cycles, measuring the potential (in volt) of the battery against time (in seconds), as described earlier. A typical result is shown in Figure 5 for the NTO_LIB (nickel tellurium oxide lithium-ion battery). Initial irradiation of the battery for 30 minutes resulted in the potential of the battery to increase from just below 0.5V to 0.75V (section A, Figure 5). Termination of irradiation (for 7 minutes) result in the battery to go into a rest mode, in the dark, with the potential dropping to 0.5V (section B, Figure 5). Applying an electrical load of 1 micro-amp (1 pA), for 7 minutes in the dark, the potential of the battery drops to about -0.22V (section C, Figure 5). Termination of this electrical load, allows the battery to go into rest (for 7 minutes) with the potential increasing to about 0.15V (section D, Figure 5). In the following section (section E, Figure 5) the battery is again subjected to photo-irradiation with the potential of the battery increasing back to 0.75V. This is followed by a number of cycles at a discharge rate of 1 pA, followed by a discharge rate of 2 pA, and finally a discharge rate of 5 pA. This clearly shows that the battery is charged as a result of photoirradiation and can be recharged consecutively after it has been subjected to an electrical load. The same photo-charge electrical-discharge cycles can be observed for a cobalt tellurium oxide lithium-ion battery (Figure 6), a nickel tellurium oxide potassium-ion battery (Figure 7), a cobalt tellurium oxide potassium-ion battery (Figure 8), a nickel tellurium oxide sodium-ion battery (Figure 9), and a cobalt tellurium oxide sodium-ion battery (Figure 10). As evidenced by the former results, this design / technology is applicable to all alkali ions and metal tellurium oxides.

[0055] An alternative means of following the photo-charge electrical-discharge cycles is to measure the current (in milli-amperes) against time (in seconds). This was done for a cobalt tellurium oxide lithium-ion battery (Figure 11 ). The same initial photo-charge, dark rest, photo-charge, dark rest, dark electrical discharge, dark rest cycles can be observed. Apart from dark electrical discharge, electrical discharge can also be conducted while the battery is subjected to photo-irradiation. This shows that the battery can be simultaneously photo-charged and electrically discharged. In doing this the depth of electrical discharge is substantially less as the battery is photo-charged at the same time (Figure 12; for the cobalt tellurium oxide lithium-ion battery).

[0056] Thus, the Applicant believes that the photo-rechargeable metal tellurium oxide alkali- ion battery, surprisingly, enables the coupling of photo-induced charge separation and photo-induced alkali-ion intercalation to allow for the battery to carry a load in the absence of solar radiation and enables the conversion and storage of solar energy as chemical energy. This novel feature provides significant and surprising advances in the field of rechargeable batteries, whilst reducing capital costs by eliminating the need for both a PV cell and a rechargeable battery.

[0057] Although only certain embodiments of the invention have been described herein, it will be understood by any person skilled in the art that other modifications, variations, and possibilities of the invention are possible. Such modifications, variations and possibilities are therefore to be considered as falling within the spirit and scope of the invention and hence form part of the invention as herein described and / or exemplified.

[0058] It is further to be understood that the example is provided for illustrating the invention further and to assist a person skilled in the art with understanding the invention and is not meant to be construed as unduly limiting the reasonable scope of the invention. CLAIMS

[0059] 1 . A photo-rechargeable metal tellurium oxide alkali-ion battery that includes: i. electrodes having an anode and a cathode, wherein the cathode includes a photocatalyst and the anode consists of a compound that includes an alkali metal; ii. an electrical connection between the electrodes defining an external electrical circuit that allows electrons to pass externally between the electrodes for charging and to drive an electrical load during discharging; iii. an electrolyte for facilitating the conduction of ions between the electrodes, for supporting chemical reactions occurring at the electrodes, and for maintaining charge neutrality within the battery; iv. a semi-permeable barrier between the electrodes for allowing ions within the electrolyte to pass between the electrodes; v. a photo-induced potential bias across the external electrical circuit for driving electrons, when light radiation is incident on the cathode, to flow between the electrodes in a certain direction via the external electrical circuit; wherein the photocatalyst is a metal tellurium oxide having a layered structure, which is capable of having its electrons excited from its valence band to its conduction band upon incident light radiation; wherein positive holes within the layered structure associated with such photo induced excitation are stabilised by storing ions from the electrolyte and / or anode within the layered structure; and wherein, subsequent to the termination of incident light radiation on the cathode, the stabilised alkali metal ions stored within the layered structure are oxidised allowing the alkali metal ions to return to the electrolyte and / or anode, and the electrons associated with the returned ions are released into the external electrical circuit to form an oxidative current that drives an electrical load.

[0060] 2. The photo-rechargeable metal tellurium oxide alkali-ion battery according to claim 1 , wherein the cathode is selected from the group consisting of graphite, lithium metal, silicon, tin, lithium alloys, conductive polymers, a photocatalyst, and a combination thereof.

[0061] 3. The photo-rechargeable metal tellurium oxide alkali-ion battery according to claim 1 or claim 2, wherein the cathode comprises a photocatalyst, wherein the photocatalyst comprises a metal tellurium oxide, and wherein the metal in the metal tellurium oxide is at least one of the transition metals, the lanthanides, the actinides, and the non-metals of the periodic table.

[0062] 4. The photo-rechargeable metal tellurium oxide alkali-ion battery according to any one of the preceding claims, wherein metal tellurium oxide comprises cobalt tellurium oxide.

[0063] 5. The photo-rechargeable metal tellurium oxide alkali-ion battery according to any one of the preceding claims, wherein the metal tellurium oxide comprises nickel tellurium oxide. 6. The photo-rechargeable metal tellurium oxide alkali-ion battery according to claim 1 , wherein the anode includes at least one of lithium (Li), sodium (Na) and potassium (K).

[0064] 7. The photo-rechargeable metal tellurium oxide alkali-ion battery according to claim 1 or claim 6, wherein the anode comprises an alkali-metal oxide comprising at least one of lithium metal oxide, sodium metal oxide, potassium metal oxide, wherein the metal in the alkali-metal oxide comprises at least one of a transition metal.

[0065] 8. The photo-rechargeable metal tellurium oxide alkali-ion battery according to claim 7, wherein the transition metal is at least one of cobalt, manganese, iron, and vanadium.

[0066] 9. The photo-rechargeable metal tellurium oxide alkali-ion battery according to any one of the preceding claims, wherein the electrolyte may be selected from at least one of sodium chloride, lithium hexafluorophosphate (LiPFe), sodium hexafluorophosphate (NaPFe), potassium hexafluorophosphate (KPFe), lithium perchlorate (LiCICU), sodium sulphate (Na2SO4), lithium hydroxide (LiOH), sodium hydroxide (NaOH), and potassium hydroxide (KOH).

Claims

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