Optimisation of Mesoporous Battery and Supercapacitor Materials

Abstract

A process for processing an electroactive mesoporous material into a cathode, or an anode or a supercapacitor material using one or more of the steps of: (a) modifying the material to remove impurities or substitute materials in the powder by a hydrothermal process; (b) intercalating the material by injecting the material with the charge carrier ion using a hydrothermal process or supercritical CO.sub.2 fluid process where the solvent fluid contains a soluble material of the charge carrier ion; (c) sintering the intercalated material; (d) providing a layer of a conducting material within the material pores; (e) filling the pores and interparticle spaces with an electrolyte generally comprising the charge carrier ion and a solvent; and for solid state materials, (f) polymerizing the solvent to encapsulate the powders.

Claims

1. A process for processing an electroactive mesoporous material into a cathode, or an anode or a supercapacitor material using the steps of: (a) modifying the material to remove impurities or substitute materials in the material by a hydrothermal process; (b) intercalating the modified material by injecting the modified material with a charge carrier ion using a hydrothermal process or supercritical CO.sub.2 fluid process where a solvent fluid contains a soluble compound of the charge carrier ion; (c) sintering the intercalated material; (d) providing a layer of a conducting material within a plurality of pores in the sintered material (e) filling the pores and interparticle spaces with an electrolyte generally comprising the charge carrier ion and the solvent; and for solid state materials, (f) polymerizing the solvent to encapsulate the mesoporous material; where a common feature of the process steps involving fluid materials is that a capillary action of the pores in the mesoporous material pulls the fluid into the pores, and the fluid is chosen to substantially wet the pores of the material; and each process is carried out to ensure that the mesopore structure of the material in solid state is preserved; and wherein lithiation by hydrothermal processing of the mesoporous powder in a 1-5M solution of LiOH followed by sintering produces a spinel lithium manganese oxide Li.sub.1+x Mn.sub.2xO.sub.4(LMO); and wherein the lithium ratio is controlled to give the stoichiometric ratio of Li:Mn=1, to produce a tetragonal mesoporous material Li.sub.2Mn.sub.2O.sub.3 (OLO) for use as a source of excess lithium in a cathode battery formulation.

2. The process of claim 1 in which the electroactive material is produced by either flash calcination of a precursor material that creates porosity by volatilization of constituents or by synthesis of a material, where a particle distribution is typically that of powders in a range of 1-100 microns and the pore properties are: (a) a porosity in a range of 0.4-0.6; and (b) a pore distribution with pores in a range of 3-130 nm; and (c) a continuous pore structure which is hierarchical without a Lignification significant fraction of closed pores; and (d) a Young's modulus of less than 10% of that of the solid material.

3. The process of claim 1 in which the modification step (a) wherein the impurity extraction rate, or substitution rate, maintains a grain size of the material less than about 40 nm; and which enables the production of stable mesoporous forms of the material.

4. The process of claim 1 in which the intercalation step (b) and the sintering step (c) is be operated over the course of multiple steps to achieve a stoichiometric transformation of a lithiated material, and the thermal stage, is optimised to achieve a stable material, while minimising mesopore ripening and/or facilitating desirable forms of the material for use as an anode, a cathode or a supercapacitor.

5. The process of claim 1 in which the electron conducting step (d) uses organic compounds such as sucrose, polystyrene, acetic acid, oxalic acid and citric acid dissolved in water, which after hydrothermal synthesis and/or pyrolysis, a conducting film of carbon is adhered to the pore surfaces.

6. The process of claim 1 in which the electron conducting step (d) uses grains of polyaniline in a solvent to form electron conducting pathways through the mesopores when the solvent is removed.

7. The process of claim 1 in which the electrolyte used in step (e) is Li.sup.+PF.sub.6.sup. dissolved in a mixture of cyclic and linear organic carbonates such as ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate.

8. The process of claim 1 in which the polymerized electrolyte of step (f) has a high lithium conductivity, including materials such as polystyrene-polyethylene oxide block copolymers, nanoscale-phase separated materials, crosslinked materials with hairy nanoparticles, and lithium loaded nano-ceramic particles.

9. The process of claim 2, wherein the mesoporous material is a manganese oxide produced using a manganese salt with volatile constituents, in which the manganese salt is one or more selected from the group of: manganese carbonate, manganese acetate, and manganese citrate; in which, when flash calcined in a controlled atmosphere, liberates CO.sub.2 and H.sub.2O, to give a calcined material, where the calcination conditions are selected to produce the mesoporous material, wherein the mesoporous material has a surface area exceeding 20 m.sup.2/g and a composition which is a mixture of Mn.sub.3O.sub.4, MnO, Mn.sub.2O.sub.3 and uncalcined materials, with the Mn.sub.3O.sub.4 form dominating.

10. The process of claim 4, wherein the adsorption of lithium was controlled for the spinel lithium manganese oxide Li.sub.1+xMn.sub.2xO.sub.4(LMO) where x=0-0.1, and the processing condition include capillary action to draw the liquid into the mesoporous powder, heating the slurry and shearing the slurry to promote uniform lithiation, and the hydrothermal processing includes the use of additives such as surfactants, selected to produce an LMO powder with the highest specific surface area and the crystalline form of the powder product is the mesoporous polyhedral material for use as a cathode material for batteries.

11. The process of claim 10, wherein a portion of about 5% of the tetragonal mesoporous material Li.sub.2Mn.sub.2O.sub.3 (OLO) is mixed with the LMO.

12. The process of claim 9, in which the hot calcined mesoporous material is postprocessed in a controlled atmosphere to achieve a material with a specific surface area of 60 m.sup.2/g which is a mixture of MnO.sub.2, Mn.sub.3O.sub.4, Mn.sub.2O.sub.3 and uncalcined precursors forms, with the MnO.sub.2 form dominating.

13. The process of claim 3, further comprising another processing step in which the fraction of MnO.sub.2 is increased in the mesoporous product material.

14. The process of claim 5, wherein the processed mesoporous material produces a conducting carbon film on the surface of the pores, so that the material, when loaded with an electrolyte composed of specified ions, the material is used in the production of a supercapacitor.

15. A process of extracting lithium carbonate from a spodumene, the process comprising: performing a flash calcination of a spodumene at a temperature of approximately 1000 C. to produce , spodumene; mixing the , spodumene in a pressurized heated mixture that includes supercritical carbon dioxide and water; and extracting lithium from the mixture, wherein the lithium is extracted within a time of two hours in the form of dissolved lithium carbonate.

16. The process of claim 15, further comprising: separating a mixture comprising the carbon dioxide, water and lithium carbonate from solid residual aluminosilicate; reducing a pressure of the pressurized mixture to atmospheric pressure; and precipitating crystalline lithium carbonate from the mixture.

17. The process of claim 16, wherein the lithium carbonate which is used in the production of lithium ion batteries, and the carbon dioxide gas and steam stream is compressed to form supercritical carbon dioxide and water streams which are recycled for use in the step of flash calcination of spodumene.

18. The process of claim 6, wherein the processed mesoporous material produces a conducting carbon film on the surface of the pores, so that the material, when loaded with an electrolyte composed of specified ions, the material is used in the production of a supercapacitor.

19. The process of claim 6, wherein the grains of polyaniline have a grain size in a range of 20 nm to 200 nm.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0055] FIG. 1A illustrates an image of a powder precursor material manganese carbonate MnCO.sub.3 which has been produced by flash calcination of the precursor material.

[0056] FIG. 1B illustrates an image of a powder precursor material the mesoporous manganese oxide Mn.sub.3O.sub.4 powder which has been produced by flash calcination of the precursor material.

[0057] FIG. 2 illustrates an embodiment of a process flow in which a mesoporous powdered material is processed into an intercalated solid state battery material.

[0058] FIG. 3A illustrates an image of LMO particle (Material X) from the process showing the polyhedral structure; FIG. 3B illustrates an image of Commerical LMO Material Z showing the octahedral structure of the small crystal grains. These figures illustrate an embodiment of a mesoporous cathode material showing an image of polyhedral lithium manganese oxide which has been produced from mesoporous manganese oxide by the processes of hydrothermal processing to remove impurities, intercalated by lithium by processing the powder in an aqueous solution of lithium hydroxide, then dried and thermally processed compared to a commercial material.

[0059] FIG. 4 illustrates an embodiment of a battery by showing the evolution of the charge capacity as of a cathode half-cell of polyhedral lithium manganese oxide through a number of charge/discharge cycles in at different charge/discharge rates, compared with the evolution of a cathode half-cell of standard octahedral lithium manganese oxide fabricated using the same processes.

[0060] FIG. 5 illustrates an embodiment of battery performance by showing the evolution of the cathode charge capacity of a battery of polyhedral lithium manganese oxide as the cathode and LTO as the anode, with excess anode, compared with the evolution of a cathode charge capacity in which a standard octahedral lithium manganese oxide is used as the cathode, where the cells were fabricated using the same processes. Full cell cycle life tests comparing the specific capacity of a battery of polyhedral lithium manganese oxide (Polyhedral versus Octahedral LMO) as the cathode and lithium titanium oxide as the anode, with excess anode.

[0061] FIG. 6 illustrates an embodiment for extraction of lithium from the mineral spodumene which shows a process flow in which lithium carbonate is extracted from flash calcined mesoporous , spodumene produced by flash calcination of a spodumene using supercritical CO.sub.2.

DESCRIPTION

[0062] Preferred embodiments of the invention will now be described with reference to the accompanying drawings and to non-limiting examples.

[0063] The present disclosure is directed towards a process flow in which a mesoporous powder material is used to manufacture battery materials. The embodiments described herein generally uses an example of a mesoporous manganese oxide prepared from flash calcining manganese carbonate using the process described by Sceats et. al. FIG. 1 illustrates the desired properties of a mesoporous material using Mn.sub.3O.sub.4 as an example. Manganese carbonate, MnCO.sub.3, a precursor material shows typical, impervious, crystals derived from a crystallisation step in a hydrothermal processing step from extraction of manganese from minerals, principally for use in steel production.

TABLE-US-00001 TABLE 1 Manganese Carbonate precursor composition Relative Molar Fraction* Mn 92.9 Si 4 Fe 1 Al 2 Pb 0.1 100 *Excludes volatiles and oxygen

[0064] Such a precursor material, and its calcined product, has a typical manganese composition shown in Table 1. This is relevant because the levels of such impurities would not normally qualify these materials for use in current battery manufacturing processes. The disclosures of this invention demonstrate that high performance batteries may be made from such a material using process steps disclosed herein. It is noted that many battery materials are optimised by adding other materials into formulations to optimise performance, eg to suppress manganese ion disproportionation in the cathode material, so that bulk impurities may not have a dominant impact per se.

[0065] The preferable particle sizes cover the range of 1-150 m, and it is preferable that the distribution is broad so that packing of the particles in a battery of supercapacitor, with electrolytes and other additives, gives a preferably dense material.

[0066] FIG. 1B shows the image of the material which is produced by flash calcination in air, which is identified from its X-ray diffraction profile as Mn.sub.2O.sub.3.Math.MnO, described as Mn.sub.3O.sub.4, as a spinel material which is desirable for intercalation by lithium for battery applications. The particles of the Mn.sub.3O.sub.4 product are about the same size as the MnCO.sub.3 particles, so that the loss of the CO.sub.2 and the partial oxidation of Mn(II) to Mn(III) is such that particle size is not significantly diminished. Thus the porosity of the material is very high, and is readily estimated from material densities as about 0.5. For later reference, the net porosity of the mesoporous LMO can be estimated from its material density as about 0.4. These two porosities are sufficiently low that that the post processing steps described in the following embodiments by liquid capillary action can be carried out. The pore distribution properties of the materials has been measured to show that there is a wide distribution of pores in the range of 10 nm to about 130 nm, which are mesopores, and that they are hierarchically disposed to form a permeable network. This originates from the method of manufacture by flash calcination by which the pores evolve to allow the volatile gases to escape the particle, and these pores may facilitate the diffusion of liquids to enable the processes disclosed in this invention to proceed. The movement of liquids through this porous network is assisted by the capillary suction of mesopores, and in the case of aqueous solutions and related liquids, this is promoted by the wettable nature of oxide surfaces. Another feature of these mesoporous materials is that their Youngs modulus is much lower than the bulk crystals because the high porosity and the small grain size is such that the grains are bonded by thin necks, which enables flexibility during the process steps and the charge/discharge steps. The Youngs modulus of the mesoporous Mn.sub.3O.sub.4 of 7% of the bulk and LMO is about 15% of the bulk. In the case of manganese materials, this benefit may be diminished because of the disproportionation reactions of the Mn(II) ions in the structure at the grain surfaces driven by the breakdown rection products of electrolytes, and suppression of this is desirable.

[0067] FIG. 2 shows an example embodiment of the process steps enabled by the mesoporous nature of the material produced by flash calcination. in the first step 201 a mesoporous oxide powder 202, such as Mn.sub.3O.sub.4 shown in FIG. 1B, is first optimised by a hydrothermal process which is designed to remove impurities such as those shown in Table 1 and/or to introduce new ions into the mesoporous materials, in one of more steps, to ultimately improve the battery performance. In the case of manganese materials, the approach if to modify the surface to minimise the surface degradation processes from electrolyte decomposition, where the electrolyte is introduced in a subsequent step. An example is the hydrolysis of the electrolyte Li.sup.+PF.sub.6.sup. which reacts with the solvent at battery operating temperatures to release oxidising species that degrade the surface of the LMO grains. This can be reduced by cleaning the Mn.sub.3O.sub.4 and substitution of ions on the surface that resist the oxidation step. The known art of hydrometallurgy and ion exchange chemistry enables the additives and activators for this process, and application of techniques to permeate a liquid particles for this process. The material 203 is described as a modified mesoporous metal oxide. The first stage of the second step 204 is hydrothermal intercalation of the conducting ion, in which an aqueous solution of a salt containing the conducting ion, such as LiOH is infused into the modified mesoporous oxide particles where the conduction ion is incorporated into the particle as a chemical process to absorb lithium ions, and the second stage 205 is to dry and thermally sinter the intercalated material to form a stable crystalline grained structure. The product is a mesoporous intercalated metal oxide powder 206. The driving force for the conducting ion to intercalate is the lower free energy of the intercalated material. The third step is to form a conducting carbon film on the pore surfaces of the mesoporous powder through a process in which the first stage 207 is the infusion of a solution of an organic material, such as sugar, and the second stage 208 is the pyroprocessing step of gasification of volatiles and the formation of a carbon film adhered to the intercalated grain surface to make a thin carbon film for electron transport, through which the conduction ion can migrate to reach the electrolyte in the pores when incorporated into a battery. The product 209 is a mesoporous intercalated oxide powder with enhanced electronic conduction within the coating and a fast ion conduction through the coating. The fourth step is to form a solid state material in which the pores of the mesoporous material 209 are filled in a first step 210 in which a polymerizable liquid is infused into the particle pores, and between the powder particles which is then set in the second step 211 by inducing the polymerization by the application of light or heat where the polymer material has the desirable attributes of fast ionic conduction. In this embodiment the desirable polymerizable material may contain nanoparticles of materials with a high ionic conductivity. The material produced 212 is a of a solid state electrode of the powder and polymer which has the desirable attributes of fast reversible electron and ion mobilities and energy storage.

[0068] FIG. 3A of mesoporous LMO material, denoted as Material X, showing an image of polyhedral lithium manganese oxide which has been produced from mesoporous manganese oxide by the processes of hydrothermal processing to remove impurities, intercalated by lithium by processing the powder in an aqueous solution of lithium hydroxide, then dried and sintered, which shows the same structure as reported by Li et. al; and FIG. 3B from a dense commercial polycrystalline material, denoted as Material Z which shows the octagonal structure.

[0069] An embodiment of the LMO in a half cell battery produced by the processes disclosed herein as the curve 401 which shows the evolution of the charge capacity of a cathode half-cell X through a number of charge/discharge cycles, compared with the evolution 402 and 403 of several commercial LMO materials Y, Z fabricated using the same processes and subject to the same charging/discharging conditions. The commercial sample Y is a typical LMO from the manufacturers specifications, whereas the sample Z is a best-of-class LMO based on its specifications. The higher charge density of the X compared Y and Z shows better performance of the LMO with the produced by the inventions described herein, and established the superior properties which may be associated with the suppression of manganese dissolution by polyhedral LMO.

[0070] FIG. 4 illustrates an embodiment of a battery by showing the evolution of the charge capacity as of the cathode half-cell X of polyhedral LMO as a function of the charge/discharge rate C, compared with the evolution of a cathode half-cell of commercial lithium manganese oxide Y and Z fabricated using the same processes. The charge rate C is the reciprocal of the time in hours used to charge or discharge the cell. The ability of X to operate at higher rates than Y and Z may be associated with the mesoporous open structure of the polyhedral LMO.

[0071] FIG. 5 illustrates an embodiment of battery performance by showing the evolution of the cathode charge capacity of a battery of polyhedral lithium manganese oxide X as the cathode and graphite as the anode, with excess cathode, compared with compared with the evolution of a cathode charge capacity of a cell fabricated with commercial LMO Y, where the cells were fabricated using the same processes. The superior performance of X compared to Y is expected from the results of FIG. 4.

[0072] FIG. 6 shows an example embodiment of the process steps whereby Lithium is extracted from the mineral -spodumene, LiAl(SiO.sub.3).sub.2 to produce lithium carbonate. The first step is the calcination of -spodumene 701 to produce ,-spodumene 702, preferably using the process is described by Sceats, Vincent et. al. in which flash calcination is used to minimise the residence time in the reactor 703, so that any silica does not have time to soften and coat the product, which would otherwise reduce the extraction of lithium from the silica and aluminium oxide. The usual extraction processes of lithium use dissolved acid or calcium oxide roasting processes to produce LiOH in a number of process steps using hydrometallurgical processes and pyroprocesses. LiOH, as LiOH.Math.H.sub.2O is difficult to transport because of hydration binds the powder, and many established lithium battery processes use Li.sub.2CO.sub.3 as the feedstock. This embodiment uses supercritical CO.sub.2, and moisture, to extract the Li as Li.sub.2CO.sub.3 from ,-spodumene. It is noted that a pure CO.sub.2 stream is produced in the calcination of MnCO.sub.3 using the flash calcination method of Sceats et. al., and this stream may be used as a source of CO.sub.2, and that the CO.sub.2 is recycled. Thus a supercritical CO.sub.2 stream, 704 is injected into a high pressure vessel 705 containing the ,-spodumene 702 and water 706 in a batch process and the temperature is raised to the point in which the lithium from the ,-spodumene is quickly released and dissolved in the fluid, and extracted from the particle, leaving an amorphous aluminosilicate material. The fluid is removed from the reactor and is decompressed in a vessel 707. The CO.sub.2 gas and moisture are removed leaving behind a fine powder 708 of Li.sub.2CO.sub.3 as the product. This material is easy to transport as a fine powder, or may be processed by a recrystallisation process (not shown). The CO.sub.2 and moisture 709 are recompressed in the compressor 710 and the outputs are supercritical CO.sub.2 704 and the water 706. The aluminosilicate is recovered as a product from the reactor vessel 711. The innovation used herein is to use the high reactivity of the ,-spodumene to speed up the extraction process which inhibits the application of the prior art.

[0073] In another embodiment, the use of high pressure CO.sub.2, as the solvent for lithiation may be used, when saturated with the Li.sub.2CO.sub.3. This approach takes account of the lower free energy of the intercalated material and the process may be controlled by the pressure and temperature of the saturated CO.sub.2 solvent. This is a specific embodiment of the lithiation process described in FIG. 2. This material may be lithiated with the process of FIG. 6 and preferably with the CO.sub.2 and some moisture from the process in FIG. 6, may be used directly to lithiate mesoporous battery materials, such as Mn.sub.3O.sub.4 to produce LMO. The mining process of FIG. 8 may be decoupled physically from the manufacturing process described in this embodiment.

[0074] It is known that lithium batteries may run with excess cathode or anode materials to overcome the loss of lithium from SEI layers and the like. In another embodiment, the material Li.sub.2MnO.sub.3, known as a member of a class of Over-Lithiated Oxide (OLO) materials. Li.sub.2MnO.sub.3 may be formed as a mesoporous material using excess lithium in the intercalation of Mn.sub.3O.sub.4. The loss of lithium during charge and discharge cycles may be overcome by using either a mix of these materials or over lithiating the Mn.sub.3O.sub.4 material to form and mix of LMO and OLO, which has the advantage that the loss of lithium from OLO generates LMO which then contributes to performance. Most generally, the production of mesoporous materials and lithiation processes may be used to manufacture a wide range of OLO materials.

[0075] In this specification, the word comprising is to be understood in its open sense, that is, in the sense of including, and thus not limited to its closed sense, that is the sense of consisting only of. A corresponding meaning is to be attributed to the corresponding words comprise, comprised and comprises where they appear.

[0076] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms, in keeping with the broad principles and the spirit of the invention described herein.

[0077] The present invention and the described preferred embodiments specifically include at least one feature that is industrial applicable.