Nanoporous spinel li-mn-o cathode material

Abstract

A nanoporous spinel cathode material, composed of Li-Mn-O, for use in rechargeable batteries. A method for producing this material, which involves a multi-step process comprising providing a bulk spinel, which is then formed into a large supercell nanoparticle, amorphized into a nanosphere, and finally subjected to high pressure to create the desired nanoporous structure. The final material is intended for use in the manufacture of cathodes for rechargeable batteries.

Description

[0001] NANOPOROUS SPINEL Li-Mn-O CATHODE MATERIAL

[0002] FIELD OF THE INVENTION

[0003] THIS invention relates to a spinel cathode material for use in rechargeable batteries, more specifically in Lithium-ion Batteries.

[0004] BACKGROUND OF THE INVENTION

[0005] The advent of renewable energy, especially in the automotive industry, has promoted the need for rechargeable batteries for purposes of storage and release of electrical energy in accordance with the user requirements. Rechargeable lithium-ion batteries are one of the most significant and prospective candidates for reversible electrochemical energy storage devices. However, current challenges associated with lithium-ion batteries limit their application in electric vehicles as well as hybrid electric vehicles. Lithium-ion batteries, such those based on LiMn2O4, often present challenges such as capacity decay and poor cycling stability, which originates from the dissolution of the Mn3+via a disproportionation reaction in acid electrolytes.

[0006] Extensive research has been conducted to develop improved cathode materials for rechargeable batteries, in particular those that are suitable for use in large-scale batteries intended for electric vehicles (EVs). Spinel LiMn2O4stands out as the most promising cathode material, amongst various candidate materials, due to its high thermal stability, low cost, raw material abundance and environmental friendliness. Notwithstanding these qualities, spinel LiMn2O4suffer several drawbacks, some of which have been sought to be addressed in the prior art. For instance, Lee et. al, identified the challenge of surface dissolution of manganese in the electrolyte at temperatures of above 60°C, which in turn leads to a severe capacity fading. Lee et. al. proposed a heterostructure LiMn2O4with epitaxially grown layered (R3m) surface phase to address this problem and reported that the layered surface phase protects the host spinel from being directly exposed to the highly active electrolyte at temperatures of 60°C and above, thus reducing or preventing the manganese dissolution at the elevated temperatures. On the other hand, Potapenko et. al. identified the problem of the tendency of spinel Li-Mn to aggregate during annealing, which in turn affects its ability to achieve high discharge rates. Potapenko et. al. proposes nanosized Li[Lioo33Mni967]04 precursors, which are pyrolyzed in an inert environment (atmosphere. The particle size of the materials obtained in this manner is reported to be smaller, the degree of aggregation lower, and its high-rate properties are better than for analogues pyrolyzed in air. The material constructed from these precursors was found to be more durable and able to attain high discharge rates. This work was, however, conducted in the Lii-xMn2O4 range of 0 < x < 1 range. The above illustrates positive developments made in the art to improve the capacity, durability, and longevity of Li- Mn-O cathode materials. However, further improvements to the cathode materials are required to enable the ease of adoption of these cathode materials for purposes of rechargeable batteries, especially for use in larger-scale operations such as in Electric Vehicles.

[0007] S. Ledwaba, D.C. Sayle and P.E. Ngoepe, “Atomistic simulation and characterization of spinel Li1 +xMn2O4 (0 <x < 1) nanoparticles”, ACS Appl. Energy Mater., 3, 1429, 2020, (Ledwaba et.al.) have found that while Li-Mn-O heterostructured composite nanomaterials show promise as potential electrodes in energy storage devices, their complex structure and transformation at higher temperatures hinder the understanding of their expected operational performance and thus future adoption. Ledwaba et.al. 2020 developed a simulation of the amorphization and recrystallization of LiMn2O4 and found that Li-Mn-O nanoparticle models reveal that they comprise domains of defect-rich spinel, Mn3O4, layered Li2MnO3, and lithium-rich spinel Lii+xMn2.xO4 phases, which emanate from high temperature structural transformations. Ledwaba et. al. further found grain-boundaries and intrinsic defects within the model structures, as illustrated in Figure 1 . The discharge process was modelled by inserting surplus lithium atoms into the nanoparticles. This resulted in a decrease of both the Mn3O4phase and the layered Li2MnO3-type structure concentration and the retention of the spinel Lii+xMn2.xO4 phases. This is illustrated in Figure 1 .

[0008] It has thus been determined that LiMn2O4undergoes a phase change from cubic to tetragonal during the process of charge cycling, as a result of the Jahn -Teller distortion of MnO6 within the LiMn2O4lattice at higher current densities. This leads to the cracking and pulverisation of the material, resulting in capacity fading overthe expected lifetime of the battery. The inventors of the present invention have determined that the cracking and pulverisation of LiMn2O4material during the charge cycling process results from the presence or occurrence of a transitional multi-grained structure during the phase change from the cubic LiiMn2O4phase to the tetragonal Li2Mn2C>4 phase. This multi-grained structure was found to occur at Lii 7sMn2O4 during charge cycling. This concentration where the structure undergoes a phase transition (Lii 75Mn2O4) had not been thoroughly highlighted in the literature previously. There is therefore a need to develop a cathode material for use in rechargeable batteries that has a higher recharge capacity and is able to last over a long period with reduced fading and / or damaging the battery material during the charge cycling process. The inventors of the present invention have found that by addressing the distortions that occur during this transitional phase it is possible to create a material that is able to withstand such cracking and / or pulverisation, thereby leading to a cathode material with an increased capacity.

[0009] The inventors of the present invention have discovered a Li-Mn-O heterostructured nano material which is robust and resilient to volume changes which cause fractures. The invention is expected to contribute significantly to the development of lithium ion batteries.

[0010] SUMMARY OF THE INVENTION

[0011] According to a first aspect of the invention there is provided a nanoporous spinel cathode material, comprising Li-Mn-O, wherein the nanoporosity of the material is characterized by an average pore size of approximately 69 A. Preferably, the material does not fracture during battery discharging and charging, at the transition from cubic to tetragonal structure.

[0012] According to a second aspect of the invention there is provided a method of producing the nanoporous spinel cathode material, comprising Li-Mn-O, of the present invention, comprising the steps, at a nanoparticle level, of: a) providing at least one bulk spinel LiMn2O4with approximately 56 atoms; b) forming the at least one bulk spinel LiMn2O4into a supercell nanoparticle comprising at least one thousand atoms; c) amorphising the supercell nanoparticle to form an amorphous nanosphere; d) subjecting the amorphous nanosphere to pressure to form nanoporous spinel cathode material having a nanoporosity designated at about 69 A.

[0013] Preferably, the bulk spinel LiMn2O4is characterized by a space group Fd-3m and a cubic lattice of a=b=c=8.239A.

[0014] Preferably, the at least one bulk spinel LiMn2O4is formed into a supercell nanoparticle comprising from about 26446 to about 30448 atoms.

[0015] Preferably, the supercell nanoparticle has a diameter of approximately 8nm. Preferably, the amorphisation of the supercell nanoparticle comprises heating the nanoparticle into an amorphous configuration at a constant temperature, under a constant number of atoms, constant volume and constant energy, thereby forming an amorphous nanosphere with a diameter of about 8 nm.

[0016] More preferably, the amorphous nanosphere is subjected to a pressure selected from a range of from about 5 to about 10 GPa, thereby forming an amorphous nanoporous structure, more particularly, a nanoporous spinel cathode material, having a nanoporosity designated at about 69 A.

[0017] According to a third aspect of the invention there is provided the use of the nanoporous spinel cathode material, comprising Li-Mn-O, of the present invention in the manufacture or preparation of a cathode for use in a rechargeable battery.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 - shows nanospherical LixMn2O4at various lithium concentrations. A multigrained nanosphere is noted at Lii 7sMn2O4, typically experienced during the cubic to tetragonal spinel transition.

[0020] Figure 2 - shows a specific porosity (Nanoporosity 2), microstructures at concentrations Lii ooMn204 (cubic spinel), Lii 7sMn2O4 (cubic to tetragonal transition) and Li2 ooMn204 (tetragonal spinel) are clear and smooth. For Nanoporosity (1) and Nanoporosity (3), microstructures at concentrations Lii ooMn204 and Li2 ooMn204 are smooth and fractured at Lii 75Mn2O4 (cubic to tetragonal transition).

[0021] Figure 3 - shows a schematic representation for the generation of Li-Mn-O nanoporous structures, where (a) is the spinel LiMn2O4parent bulk with 56 atoms, space group Fd-3m and a cubic lattice of a=b=c=8.239A, which is built into (b) a supercell of thousands of atoms (26642-30448), and amorphized to form (c) a nanosphere, and thereafter subjected to pressure to form (d-f) nanoporous (75, 69 and 67 A) structures.

[0022] Figure 4 - shows the volume variations of the nanoporous structures nanoporous 75, 69, and 67 A at various lithiation phases, depicting the effect of lithiation on the nanoarchitectures of the nanoporous materials as the Li content is increased and the cubic structure transition to the tetragonal structure. Most importantly, demonstrates that nanoporous 69 experiences the least volume expansion. Figure 5 - shows the stress Stress-strain curves for nanoporous 75, 69, and 67 A at (a) Lii ooMn204, (b) Lii75Mn2O4and (c) Li20oMn204showing the elastic deformation (A-B), plastic deformation (B-C) and the structural collapse point (C-D).

[0023] Figure 6 - shows a comparison of a simulated microstructure for nanosphere LiMn2O4and experimental schematic diagram of the phase transitions during deintercalation, The figure shows nanospherical LixMn2O4 with various lithium concentrations: (a) Lii0oMn204, (b) Lii2sMn2O4, (c) Lii 5oMn204, (d) Lii eoMn204, (e) Lii75Mn2O4, (f) Lii soMn204, (g) Li2ooMn204, and (h) Experimental schematic diagram of the phase transitions during deintercalation or intercalation from LixMn2O4(x = 1). Related to the reference of Okumura et al 2014. Manganese is coloured purple, lithium yellow, and oxygen red.

[0024] Figure 7 - shows a comparison of a simulated microstructure for nanoporous Lio ieMn02against experimental HRTEM. The figure shows the low temperature simulated nanoporous structure for the Lio ieMn02(Fig 7 a-c) which is compared with the micrograph of the High Resolution Electron Microscope experiment (Fig 7 d-e) from Jiao et al 2007.

[0025] Figure 8 - shows a comparison of simulated channels and tunnels in a nanoporous TiO2microstructure against HRTEM experimental measurements. The figure shows a model of nanoporous (mesoporous) TiO2In particular, Figure 8(a) shows an HRTEM image of the real material, from Ren et al 2010, which can be compared to the simulated atomistic model in Figure 8(b); the positions of possible entrance sites for Li intercalation are highlighted by the yellow arrows in each figure.

[0026] DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0027] The present invention is described herein below with reference to the accompanying drawings.

[0028] The present invention relates to a nanoporous spinel cathode material, comprising Li-Mn-O, preferably LiMn2O4, which finds application in reversible electrochemical energy storage devices, i.e. rechargeable batteries. The spinel cathode material of the present invention has a nanoporosity designated as 69 A. This nanoporous material has demonstrated more resilience to structural damage that occurs to spinel cathode material during the charging cycle. The nanoporous cathode material does not fracture due to expansion as the lithium (Li) concentration is increased during the charging cycle, i.e. Li(i+ S)Mn2O4(0 < 6 < 1). Therefore, the cathode material maintains its structural integrity during the charging cycle, especially at the critical concentration of Lii75Mn2O4, where the material undergoes a disruptive structural phase transition from cubic to tetragonal phase, as shown in Figure 1 . This allows the discharge to occur in the full concentration range from LiMn2O4to Li2Mn2O4. As such, the material has a significant potential to enhance its capacity and cycling ability. Also, the nanoporosity of the material allows for relatively easy lithium diffusion.

[0029] The inventors of the present invention have found that this nanoporous material showed promising results compared to its counterparts. The material shows desirable characteristics even at the abrupt concentration of Lii 75Mn2O4, at which most structures are prone to damage, or have their integrity compromised.

[0030] Ledwaba et. al. reported that the spinel-Mn2C>4 framework was, in principle, capable of delivering a capacity of approximately 297 mAhg-1 when a Li ion (Li+) is inserted into or extracted from each of the 8a tetrahedral and 16c octahedral sites. However, it was noted that the strong Jahn-Teller distortion of MnO6octahedra, which occurs due to the formation of manganese ions (Mn3+), leads to a partly reversible phase transition associated with the 2.7 V plateau. This distortion induces an increase in the axial ratio (c / a) of the unit cell from 1 .0 in the cubic phase to 1.6 in the distorted tetragonal phase due to the lithiation of Li(i+S)Mn2O4 (0 < 6 < 1). The anisotropic strain caused by this leads to the fracture of large particles and results in internal contact loss upon cycling.

[0031] METHOD OF GENERATION OF NANOPOROUS SPINEL CATHODE MATERIAL

[0032] The study by Ledwaba et.al. described the use of the simulated amorphization and recrystallization method to generate atom-level models of LixMn2O4(1 < x < 2) nanoparticles, often referred to as primary particles. This was followed by the simulation of the charge / discharge process, which involved subsequently inserting lithium ions into the nanoparticles while closely monitoring the effect of lithiation on the structural integrity of the host electrode material. The conditions for simulation were guided by high-temperature molecular dynamics simulation data reported in previous work. Proper harvesting and analysis of the microstructures for nanoparticles with different lithium concentrations were expected to help elevate understanding of the cubic to tetragonal spinel transition, which is crucial for the performance of this cathode.

[0033] Ledwaba et. al. sets out the potential models used to describe the interactions between Li- Mn-O ions, the codes used to perform the dynamical simulations, the construction of atomistic models, their amorphization and recrystallization as well as the discharge process.

[0034] The method used in Ledwaba, et. al. was used in the generation of the models of the nanoporous spinel cathode material of the present invention and is described herein below. Simulations in respect of the present invention are based on interatomic potentials that were previously generated and reported for the Born model of the ionic solids, in which the Mn4+, Mn3+, Li+and O2-ions interact via long-range Coulombic interactions coupled with short-range parameterized interactions.

[0035] Simulation code

[0036] The DL_POLY code, as described in Ledwaba et.al, was used to perform all the molecular dynamics (MD) simulations. This code utilizes three-dimensional periodic boundary conditions to represent the model infinitely in space. All simulations were performed within the NVE and NVT ensembles, for amorphization and recrystallization, respectively.

[0037] Generating atomistic models

[0038] The nanoparticle was generated by cleaving a sphere with desired radius from the parent bulk. Stoichiometry was assured by removing either Mn / O / Li atoms from the outer surface to facilitate charge neutrality resulting in a supercell nanoparticle with at least one thousand (1000) atoms, and more particularly 26 642 atoms.

[0039] Amorphization and recrystallization

[0040] Amorphisation is the process whereby a material transitions from a structured crystalline state to a disordered state, known as an amorphous or glass-like state. This process is achieved by rapid heating of the structure to reach its melting point to enhance its reactivity. The atoms in the structure are therefore scattered in random positions. The step-wise procedure in the LMO spinel amorphisation entails initially heating up a crystalline structure into an amorphous configuration under constant number of atoms, constant volume and constant energy, the NVE ensemble, known as the microcanonical ensemble, which is then allowed to nucleate and recrystallise spontaneously under constant number of atoms, constant volume and constant temperature, the NVT ensemble.

[0041] In the simulation of the present invention, spinel structured crystalline seed in the form of a cube morphology was fixed at the centre of the supercell nanoparticle during amorphization. The supercell is heated up into an amorphous configuration at constant temperature selected from the range of 1500 to 1700 K under constant number of atoms, constant volume and constant energy. The NVE ensemble for the spinel LMO (specified in the CONTROL file of the simulation), known as the microcanonical ensemble, and the temperature of range of 1500- 1700 K is sufficient to amorphise the structure, with a box of 100 A in volume, time-steps of 0.0001 - 0.001 ps with steps of 100 000 to 1000 000 and the elwald precision of 1 d-5, allowing the material to move in low-energy configurations within the available timescale in the simulation.

[0042] More specifically, the CONTROL file, which captures the conditions of the simulation: temperature of 1700K, time-steps of 0.0001- 0.001 ps with steps of 100 000 to 3000 000 and the elwald precision of 1d-5, are employed to allow the material to move in low-energy configurations within the available timescale in the simulation,

[0043] In the present invention, molecular dynamics simulations using the DL_POLY code, as described in Ledwaba et.al, were performed to generate and simulate three nanoporous structures of different lattice sizes (75, 69 and 67 A) under the NST ensemble, in a quest of finding a material that would respond better to volume changes during the lithiation process. In addition to the generation of the nanoparticle as described in Ledwaba et. al., the nanoporous spinel cathode material, composed of Li-Mn-O and comprising the porosity described above, was produced using the following method:

[0044] Initially, as illustrated in Figure 3, a conventional unit cell of spinel LiMn2O4structure containing 56 atoms is provided. This material is characterized by a space group Fd-3m and a cubic lattice parameter of a=b=c=8.239 A. The bulk spinel LiMn2O4is then constructed into a supercell comprising at least one thousand atoms. Specifically, the supercell contains between 26642 and 30 448 atoms when discharged (approximately 8 nm) to ensure adequate structural complexity. The resulting supercell is amorphized to form a nanosphere. The LMO spinel crystalline supercell is heated up into an amorphous configuration under the NVE ensemble. The simulation conditions are a temperature of 1700 K, a supercell with a box size of 100 A , time-steps of 0.0001- 0.001 ps with steps of 100 000 to 1000 000 and the elwald precision of 1d-5. The NVE ensemble, therefore, allows the formation of the nanosphere during the simulation process.

[0045] The nanosphere is then subjected to pressure selected from a range of from 5 to10 GPa under the NPT ensemble, constant number of atoms, constant pressure and constant temperature. This then allows the atoms to move comfortably, filling the cell and creating pore cavities in the materials. Thus, resulting in nanoporous spinel cathode materials with different cell dimensions. This step is crucial for introducing the desired nanoporosity within the material. The nanoporous 75 A will be harvested first, then 69 A, and finally 67 A, as the simulation is in progress. The prolonged simulation or completion of the calculation will result in the formation of the nanobulk material with the cell entirely filled with atoms, without any pores. This step is crucial for introducing the desired nanoporosity within the material. The nanosphere is subjected to pressure to create a nanoporous spinel cathode material, with three nanoporous structures of different lattice sizes, namely, 75, 69 and 67 A. The nanoporosity of the present invention is characterize by an average pore size of approximately 69 A.

[0046] Lithium intercalation

[0047] Lithium atoms were introduced into the spinel nanoparticles, specifically, four models were generated: Lii25Mn2O4, Lii5Mn2O4, Lii 75Mn2O4and Li2oMn204. More specifically, three nanospheres with different lattice sizes, namely, 75, 69 and 67 A, were obtained with concentrations containing 4758, 5709, 6661 and 7360 lithium atoms, respectively. The program uploaded the insertion sites from the structure file, randomly selected a tunnel site and inserted a lithium ion at its vacant co-ordinates. Charge neutrality was maintained by reducing an Mn4+ion, closest to the - inserted - lithium cation, to Mn3+. This process was repeated for all the lithium ions inserted in the structure.

[0048] Discharge Process

[0049] In order to determine the effect of lithiation on the structural integrity of the host Li-Mn-O material, the nanospheres were characterised using graphical techniques, particularly for the composition Lii 75Mn2O4and Li2ooMn204. This illustrated the dominance of the spinel component on the microstructures. This may imply that after transformation from Lii 75Mn2O4, the predominance of the spinel phase occurs, unlike composites observed at lower Li concentrations.

[0050] Another important aspect of the study by Ledwaba et.al. is the generation of simulated composite or heterostructured cathode primary nanoparticles. Careful inspection of Li-Mn-O microstructural features, captured in structural snapshots and simulated XRDs, reveals that the nanoparticles crystallize into interconnected patterns with the presence of layered Li2MnO3-type and spinel domains, including Li4Mn5Oi2and Mn3O4.

[0051] Further, effort was expended on the development of various nano-architecture cathodes to improve their electrochemical performance in lithium ion batteries (LIBs). It was also noted from literature, that porous LiMn2O4shows better rate capability and cycling ability compared to its counterparts that lack porousity because the interconnected nanoporous framework could offer high accessibility for the electrolyte and preferably accommodate structural conversion during reduplicative Li+ ion intercalation / deintercalation processes. The inventors of the present invention found that the nanoporous material of the present invention, having a nanoporousity of 69 A, can withstand the structural changes that occur as a result of the distortions to LiMn2C>4 spinel cathode material due to expansion as the lithium concentration is increased during the charging cycle, i.e. Li(i+ a)Mn2C>4 (0 < 6 < 1), especially at a critical concentration of LiusM^C , without fracturing or pulverising. This is illustrated in Figure 2, wherein the microstructures at Lii 75Mn2O4, i.e. during the microstructural transition from cubic to tetragonal phase transition, and Li2 ooMn2C>4 (tetragonal spinel) exhibit a homogeneous and defect-free morphology. The transition is characterized by reduced presence of discontinuities, thus resulting in an uninterrupted grain structure.

[0052] Notably, the same structural integrity was not observed for nanoporous spinel cathode material, with nanoporous structures of sizes 75 and 67 A. With reference to Figure 2, it can be seen that for nanoporosities at 75 A and 67 A, while microstructures at concentrations Lii ooMn204 and Li2 ooMn204 are smooth, they exhibit fractures, illustrated by the grain boundaries, at Lii 75Mn2O4 (cubic to tetragonal transition).

[0053] The material of the present invention, of nanoporosity of 69 A has further illustrated its superiority over the other two nanoporosities, in that it shows a relatively high yield strength compared to counterparts with the othertwo nanoporosities, i.e. 75 and 67 A. This implies that it is not easily prone to fracture and can withstand the harsh conditions of cracking during the process of charging and discharging (cycling).

[0054] Further, referring to Figure 4, it can be seen that the plot for the nanoporous material of the present invention, at 69 A (green plot) displays the least expansion at the abrupt concentration of Lii 75Mn2O4, where cracking and / or pulverisation is expected to occur. Also, as can be seen from Figure 5, the stress-strain plots illustrate the high yield strength of porous 69 A versus the other nanoporous Li-Mn-O structures at 67 A and 75 A.

[0055] Specifically, nanoporous 69 A shows outstanding and promising results which illustrate the potential of creating a suitable material for reversible electrochemical energy storage devices that will mitigate problems typically experienced with such devices, including lithium ion battery.

[0056] The material has the potential to address current energy storage challenges such as battery degradation and can be applied in electronic devices, backups, and electric vehicles.

[0057] USE OF THE MOLECULAR DYNAMICS SIMULATED AMORPHISATION RECRYSTALLISATION METHOD The inventors of the present invention have relied on the simulated molecular dynamics amorphisation recrystallization method to model and illustrate processes that would occur at the atomic and nano level, including the formation of the spinel LiMn2C>4 parent bulk into a supercell, the amorphization thereof to form a nanosphere, and thereafter forming the nanoporous (75, 69 and 67 A) structures, and well as the lithiation and discharge cycles.

[0058] Three examples, from publications, are provided on the validity and the ability of the simulated molecular dynamics amorphisation recrystallization methods in predicting experimental outcomes. These are demonstrated on the nano-architectures of spinel LiMn2O4, Li-MnO2and TiO2. Such validity provides confidence and certainty of the simulated predictions used in the present invention, involving the porosity size that will suppress the structural disruptive transition from the spinel cubic to tetragonal transition in LiMn2O4at the concentration of Lii 75Mn2O4.

[0059] LiMn2O4

[0060] In figure 6, the red spheres show simulated spinels LixMn2O4at different lithium concentrations (x ranges from 1 to 2), calculated by Ledwaba et al 2020. An extensively multigrained sphere is noted at Lii 75Mn2O4where a structural change from cubic to tetragonal spinel occurs. This corresponds to the experimental structural change shown in the grey square obtained by T. Okumura, Y. Yamaguchi, M. Shikano and H. Kobayashi, “Further Findings of X-Ray Absorption Near-Edge Structure in Lithium Manganese Spinel Oxide Using First-Principles Calculations”. J. Mater. Chem. A , 2, 8017, 2014 (Okumura et al 2014). Therefore, the validity of the simulated amorphisation recrystallisation method is confirmed by experiment.

[0061] MnO2

[0062] A simulated pore for the nanoporous Li0i6MnO2model, shown in Figure 7c, from T.X.T. Sayle, P.E. Ngoepe and D.C. Sayle, “Simulating mechanical deformation in nanomaterials with application for energy storage in nanoporous architectures”, ACS Nano (2009), 3, 3308 (Sayle et al 2009), generated by molecular dynamics amorphisation recrystallization method, compares very well in shape to the experimental pore, depicted in Figure 7e, from F. Jiao, and P.G. Bruce, “Mesoporous crystalline B-MnO2- A reversible positive electrode for rechargeable lithium batteries”, Adv. Mater., 19, 657, 2007 (Jiao et al 2007), obtained by High Resolution Transmission Electron Microscope. Figure 7a reveals Li ions located within the framework walls of the nanoporous MnO2and also decorating its internal surfaces. An enlargement of a particular region of the MnO2surface, Figure 7f, reveals 1x1 tunnels, which terminate at the internal surfaces and remain “open” enabling Li (charge carriers) to insert into the host; Figure 7g reveals several Li species that reside within the 1x1 tunnels of the host. Hence the validity of the simulated amorphisation recrystallization method is confirmed by experiment.

[0063] TiO2

[0064] Simulated tunnels forthe nanoporous TiO2model, shown in Figure 8(b), from M.G. Matshaba, D.C. Sayle and P.E. Ngoepe, “Structure of surface entrance sites for Li intercalation into TiO2nanoparticles, nanosheets, and mesoporous architectures with application for Li-ion batteries”, J. Phys. Chem. C, 2016, 120, 14001 (Matshaba et al 2016), generated by molecular dynamics amorphisation recrystallization method, compares well with the experimental tunnels, depicted in Figure 8a Ren et al (2010), obtained by High Resolution Transmission Electron Microscope. Polyhedral rendering of the structure (TiOepolyhedra) is shown in Figure 8(c), which reveals more clearly the 1 x 1 tunnels in which the Li ions intercalate and reside. TiO6octahedra in the plane of the page are blue, and TiO6octahedra below the plane of the page are white. Accordingly, in the plane of the page, there are vacant 1 x 1 tunnels above the white TiO6polyhedra into which the Li ions intercalate and reside. It is difficult to appreciate the entrance sites with these two dimensional images of the structure, and therefore Connolly surfaces were calculated to reveal the accessible surface. The image in Figure 8(d) shows the Connolly surface and enables a perspective view of the surface of the internal pore. An enlarged segment of the pore is shown in Figure 8(e), which reveals the entrance sites for Li intercalation into the 1 x 1 tunnels; a ball and stick model of the atom positions is shown inset in Figure 8(e) to illustrate how the individual atoms facilitate the structure of the entrance sites. Li+ions are shown entering the 1 x 1 tunnels for illustration. The simulated and experimental images of the entrances are depicted in Figures 8(f) and 8(g) respectively and are comparable. In addition, the simulated and experimental images of the nanoporous TiO2tunnel entrances that are depicted in Figures 8(f) and 8(g) respectively and are highly comparable (Matshaba et al 2016, 7 and K. Yoshida, T. Kawail , T. Nambaral , S. Tanemura, K. Saitoh and N. Tanaka, “Direct observation of oxygen atoms in rutile titanium dioxide by spherical aberration corrected high-resolution transmission electron microscope”, Nanotech, 17, 3944, 2006 (Yoshida et al 2006). Hence the validity of the simulated amorphisation recrystallisaiton method, is confirmed by experiment.

[0065] In view of the above the inventors are confident of reliance on the simulated molecular dynamics amorphisation recrystallization method for modelling and illustrating the processes of the present invention. The invention has been described above with reference to specific embodiments. The invention is not limited by any particular implementation, configuration, or application. The invention is intended to cover various modifications and equivalent arrangements, which will be apparent to those skilled in the art, included within the spirit and scope of the summary of the invention.

[0066] Dated on this 28 day of August 2025.

[0067] OMN ATTORNEYS INCORPORATED

Claims

CLAIMS1 . A nanoporous spinel cathode material, comprising Li-Mn-O (LixMn2O4), wherein the nanoporosity of the material is characterized by an average pore size of approximately 69 A.

2. The nanoporous spinel cathode material of claim 1 , wherein the material does not fracture during battery discharging and charging, at the transition from cubic to tetragonal structure.

3. A method of producing the nanoporous spinel cathode material, comprising Li-Mn-O, of claim 1 , comprising the steps, at a nanoparticle level, of: a) providing at least one bulk spinel LiMn2O4with approximately 56 atoms; b) forming the at least one bulk spinel LiMn2O4into a supercell nanoparticle comprising at least one thousand atoms; c) amorphising the supercell nanoparticle to form an amorphous nanosphere; and d) subjecting the amorphous nanosphere to pressure to form nanoporous spinel cathode material having a nanoporosity designated at about 69 A.

4. The method of claim 3, wherein the at least one bulk spinel LiMn2O4is characterized by a space group Fd-3m and a cubic lattice of a=b=c=8.239A.

5. The method of any one of claim 3 or 4, wherein the at least one bulk spinel LiMn2O4is formed into a supercell nanoparticle comprising from about 26446 to about 30448 atoms..

6. The method of any one of claim 3 to 5, wherein the supercell nanoparticle has a diameter of approximately 8nm.

7. The method of any one of claim 3 to 6, wherein the amorphising of the supercell nanoparticle comprises heating the nanoparticle into an amorphous configuration at a constant temperature, under a constant number of atoms, constant volume and constant energy.

8. The method of claim 7, wherein the amorphization of the nanoparticle forms an amorphous nanosphere with a diameter of about 8 nm.

9. The method of any one of claim 3 to 8, wherein the amorphous nanosphere is subjected to a pressure selected from a range of from about 5 to about 10 GPa, thereby forming an amorphous nanoporous structure.

10. The method of claim 9, wherein the nanoporous structure is a nanoporous spinel cathode material, having a nanoporosity designated at about 69 A.

11. The use of the nanoporous spinel cathode material of claim 1 , in the manufacture or preparation of a cathode for use in a rechargeable battery.

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