Solid state microwave route for cationic disordered rock salt oxide and oxyfluoride cathodes

Abstract

Ionic solids (e.g., disordered rock salt oxide / oxyfluoride (DRX) compositions) useful as lithium ion cathodes are synthesized by microwave processes that are two orders of magnitude faster than conventional solid and mechanochemical synthesis processes. The microwave synthesis can be carried out in ambient air, so that the synthesis time, the energy consumption and the cost are greatly reduced. In one illustrative embodiment of the method, the precursor powders are mixed and pressed into pellets. Then putting the pellets into a ceramic crucible surrounded by activated carbon; and then the crucible is placed in 1200W microwaves to be continuously heated for 5-20 minutes. And after the microwave radiation is stopped, immediately and quickly taking out the pellets from the crucible, and quenching in water. The pellets are then dried and milled into a powder, which is the final DRX product.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of US 63 / 420,230 filed on October 28, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to compositions of matter useful as electrodes and methods of making the same. Background Art

[0004] The growing demand for energy-dense, portable power sources has driven the development of lithium-ion batteries and, potentially, sodium (Na)-ion batteries. The cathode component is typically the most expensive and is limited in terms of charge storage capacity. The major portion of transition metals currently used in lithium (Li)-ion cathodes consists of Co and / or Ni, whose toxicity (Co), complex supply chain, and price fluctuations are driving the development of more sustainable (e.g., manganese (Mn)-based) cathode chemistries.

[0005] Cationic disordered rock salt oxides / oxyfluorides (DRX) are promising candidates for high energy density Mn-based and Co / Ni-free Li-ion (and possibly Na-ion) cathodes due to their high energy density and compositional flexibility. DRX materials are currently synthesized via two routes 1-5 : (I) solid-state synthesis, in which the precursors are heated at high temperatures (>800°C) under a flow of argon (Ar) for an extended period of time (typically 12 hours); and (II) mechanochemical synthesis, in which the precursors are ball milled in a sealed inert environment for a minimum duration (>40 hours).

[0006] These methods require an inert atmosphere to reduce the formation of impurities and are energy intensive. Furthermore, scaling up mechanochemical synthesis methods for industrial-scale manufacturing is not straightforward. What is needed is an improved method for synthesizing rock salt structures. Summary of the invention

[0007] The present disclosure provides a method for rapidly synthesizing ionic compounds that can be used as lithium-ion (or sodium-ion) battery electrodes. The method includes: mixing precursors together to form a mixture; exposing the mixture to microwave radiation with a power of 100 to 1500 watts for a duration of less than 1 hour (e.g., 5 to 20 minutes), thereby producing an ionic compound having a rock salt-type crystal structure and a disordered arrangement of cations; stopping the microwave radiation and quenching the microwaved powder (within 15 seconds after the microwave heating stops) to maintain the structure and disordered cation arrangement at room temperature. The disordered rock salt-type structure can be determined by powder X-ray diffraction (XRD), where the peak can be indexed as a cubic rock salt space group Fm-3m (space group #225). Short-range order of cations can occur within this long-range disordered structure and is observed as a broad peak in the XRD spectrum. The powder can then be further processed into a form that can be used as a lithium-ion (or sodium-ion) battery electrode.

[0008] The key parts of the method include: 1) rapidly heating the precursor using microwave radiation, thereby initiating the reaction to form the product at high temperature, and 2) rapidly quenching the heated powder (e.g., in water) to ensure a pure final product. Conventional methods for synthesizing DRX involve sintering / calcining the precursor at ≥1000°C for ≥10 hours, or ball milling the precursor at about 500 rpm for 40 hours. These conventional techniques are time and energy intensive, while the rapid microwave technique of the present invention is two orders of magnitude faster and provides significant time and energy savings. In addition, microwave synthesis does not require an inert atmosphere to produce pure DRX (unlike solid-state and mechanochemical milling methods), which increases the scalability and cost-effectiveness of the present method for commercial / industrial manufacturing of electrodes.

[0009] Exemplary DRX lithium metal oxides / oxyfluorides that can be made by the inventive methods described herein include those having a cation-disordered rocksalt structure and the following general formula: Li x M' y M″ 2-x-y O 2-z F z , wherein 1.05≤x≤1.35, 0.1≤y≤0.9 and 0≤z≤0.7, M′ is a low-valent (e.g., ≤3+) transition metal, and M″ is a high-valent (e.g., ≥4+) transition metal. M′ is selected from at least one of V, Cr, Mn, Fe, Co, Ni, Mg, Cu, Al, and M″ is selected from Ti 4+ 、Zr 4+ , Nb 5+ 、V 5+ 、Mo 6+ At least one of .

[0010] The DRX products obtained from the microwave synthesis of the present invention can exhibit favorable structural and electrochemical properties similar to those DRX products formed by conventional solid-state synthesis, although they are obtained at a fraction of the typical synthesis time, energy, and cost. In addition, the microwave synthesis of the present invention produces particles with improved particle morphology, including smaller and more uniform particle size, compared to solid-state and mechanochemical synthesis methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other features and advantages of the present invention can be ascertained from the following detailed description provided in conjunction with the accompanying drawings described below, wherein like reference numerals represent corresponding parts throughout:

[0012] Figure 1 A flow chart illustrating a method according to the present invention for preparing disordered rock salt oxide / oxyfluoride (DRX) ionic compounds is provided.

[0013] Figure 2 Examples of rock-salt-type oxide crystal structures are shown, including: (a) a disordered rock-salt structure in which all cation sites are equivalent (e.g., α-LiFeO 2 ); (b) layered structures (e.g., α-NaFeO 2 ); (c) spinel-like low-temperature structure (e.g., LT-LiCoO 2 ); and (d) γ-LiFeO 2 Structure. Large open circles represent anionic (e.g., oxygen) sites, and small gray and black solid circles represent cationic sites (e.g., alkali metal / lithium sites and transition metal sites, respectively). Half gray / half black circles represent equivalent cationic sites and can be occupied by either alkali metal atoms or transition metal atoms. 6-7

[0014] Figure 3 The properties of Li-Mn-Ti-O(LMTO)DRX obtained by solid-state (ss) synthesis via microwave heating (mw) for 5, 10 and 20 min and a calcination step at >1000°C for 12 h are shown, including: (a) synchrotron X-ray diffraction (SXRD) of the synthesized DRX powders, (b) Scanning electron microscopy (SEM) image of synthesized DRX particles; and (c) SEM image of DRX ball-milled with Super C65 conductive additive.

[0015] Figure 4 shows the properties of LMTO, including: (a) 7 Li pj-MATPASS; (b) collected on the mw-LMTO with a short inter-scan delay (50 ms) and a T2 filter (15 rotor cycle delay) 19F spin echo solid-state NMR spectroscopy to suppress 19 F probe background signal; and (c) collected on the mw-LMTO with a long inter-scan delay (20 s). 19 F spin echo solid-state NMR spectroscopy to better quantify the LiF impurity signal.

[0016] Figure 5 shows the properties of LMTO, including: (a) mw-LMTO and ss-LMTO and Mn 2 O 3 and MnO 2 Mn K-edge X-ray absorption near-edge spectrum (XANES) of the reference sample; (b) X-ray PDF boxcar fit of the mw-LMTO DRX; and (c) X-ray PDF boxcar fit of the ss-LMTO DRX. Fits for two space groups are shown: a cubic 225 structure corresponding to a completely random arrangement of cations in the DRX structure, and a tetragonal 141 structure representing a preferential cation ordering within the DRX structure. Fits were performed over a variety of r ranges and show that the cubic DRX structure model best fits the experimental data over long correlation lengths r, but the tetragonal structure best fits the data over short correlation lengths r. The mw-LMTO sample was obtained using a 5 min microwave heating step.

[0017] Figure 6 shows the constant current cycle diagrams of the synthesized LMTO, including: (a) LMTO synthesized by the solid-state method; (b) LMTO synthesized by the microwave method; (c) the differential capacity diagram obtained during the first five cycles; (d) the evolution of the discharge capacity and coulombic efficiency of the ss-LMTO and mw-LMTO DRX cathodes within 50 cycles; and (e) the rate performance of the ss-LMTO and mw-LMTO DRX cathodes, the rate values ​​shown in the figure are in mA / g. The mw-LMTO sample was obtained with a 5-minute microwave heating step.

[0018] FIG7 shows: (a) synchrotron radiation XRD patterns of Li-Mn-Nb-OF(LMNO / F)DRX synthesized by microwave heating (mw) for 5, 10 and 20 min and solid-state (ss) synthesis with a calcination step at >1000°C for 12 h. and SEM images of (b) synthesized DRX particles and (c) DRX ball-milled with Super C65.

[0019] Figure 8 shows: (a) LMNO / F 7 Li pj-MATPASS NMR spectra; (b) mw-LMNO / F and mw-LMTO collected with a short interscan delay (50 ms) and a T2 filter (15 rotor cycle delay). 19F NMR spin echo spectroscopy to suppress 19 F probe background signal; and (c) mw-LMNO / F and mw-LMTO collected with a long inter-scan delay (20 s). 19 F NMR spin echo spectroscopy to better quantify the LiF impurity signal.

[0020] Fig. 9 Shown: mw-LMNO / F and ss-LMNO / F vs. Mn 2 O 3 and MnO 2 Mn K-edge XANES of the reference sample. The mw-LMNO / F sample was obtained using a 5 min microwave heating step.

[0021] Figure 10 shows: (a) galvanostatic cycling diagram of LMNO / F synthesized by solid-state method; (b) galvanostatic cycling diagram of LMNO / F synthesized by microwave method; (c) differential capacity diagram obtained during the first five cycles; (d) evolution of discharge capacity and coulombic efficiency of ss-LMNO / F and mw-LMNO / F DRX cathodes over 50 cycles; and (e) rate performance of ss-LMNO / F and mw-LMNO / F DRX cathodes, with rate values ​​shown in mA / g. The mw-LMNO / F sample was obtained with a 5-min microwave heating step.

[0022] Figure 11 shows: (a)-(c) The mw-LMTO and LMTO / F synthesized with different microwave heating times in the presence and absence of excess Li, respectively. 19 F solid-state NMR spectra, where the NMR spectra shown in (a) and (c) were obtained with a short recycle delay (50 ms) and the NMR spectrum shown in (b) was obtained with a long recycle delay (20 s); and (d) the mw-LMTO / F composition of 5 min compared to the LMNO / F samples obtained after different microwave heating times. 19 F spectrum shows that niobium (Nb)-based DRX has still a higher degree of fluorination.

[0023] Figure 12 shows (a) Li 1.2 Mn 0.5 Ti 0.3 O 1.8 F 0.2 and (b) various LMTO / F and LMNO / F DRX combinations with short (50 ms) recycle delays. 19 F NMR.

[0024] 13 a shows a SEM image of a LMTO sample synthesized by conventional solid-state synthesis as described in the second example, wherein the precursor powder mixture was heated at high temperature (>1000° C.) for 12 hours under argon flow.

[0025] FIG. 13 b shows a SEM image of a LMTO sample synthesized by the microwave synthesis method of the present invention after microwave treatment for 5 minutes according to the description in the first example.

[0026] Figure 14a shows a particle size map of the LMTO particles in the SEM image of Figure 13a (conventional solid state synthesis), where the maximum diameter of each of the 814 particles in the image was measured using the ruler tool provided by the software package. No weighting factor was applied.

[0027] Figure 14b shows a particle size map of the LMTO particles in the SEM image of Figure 13b (microwave synthesis), where the maximum diameter of each of the 1500 particles in the image was measured using the ruler tool provided in the software package. No weighting factor was applied.

[0028] Fig.15 The particle size distribution data of powdered LMTO samples synthesized by solid-state and microwave methods obtained with a PSD analyzer are shown, wherein the SEM images in FIGS. 13a to 13b are representative. DETAILED DESCRIPTION

[0029] In the following description, reference is made to the accompanying drawings which form a part of the present invention, in which is shown one or more ways of implementing the present invention. It should be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

[0030] The use of examples or exemplary language (e.g., "such as") provided herein is intended only to better illustrate the invention and shall not be construed as limiting the scope of the invention unless otherwise required. Language in the specification should not be construed as indicating any non-claimed element as essential or critical to the practice of the invention unless the context clearly indicates otherwise.

[0031] As used herein, the singular forms "a / an" and "the" include plural meanings unless the context clearly dictates otherwise. The term "or" should be understood as an inclusive "or" unless the context indicates otherwise. When used to describe multiple devices or elements, terms such as "first", "second", "third", etc. are only used to convey the relative action, positioning and / or function of the individual devices, and do not require a specific order of such devices or elements, or any specific number or ranking of such devices or elements.

[0032] As used herein with respect to any property or circumstance, the word "substantially" means that the degree of deviation is small enough so as not to significantly detract from the identified property or circumstance. As will be understood by those skilled in the art, the precise degree of deviation permitted in each case will depend on the specific context.

[0033] The use of the term "about" or "approximately" is intended to describe values ​​above and / or below the stated value or range, as would be understood by one of ordinary skill in the art in the respective context. In some cases, this may encompass values ​​within a range of approximately + / -10%; in other cases, values ​​within a range of approximately + / -5%; in still other cases, values ​​within a range of approximately + / -2%; and in still further cases, this may encompass values ​​within a range of approximately + / -1%.

[0034] It should be understood that when used in this specification, the terms “comprises and / or comprising” specify the presence of stated features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof, unless otherwise stated herein or clearly contradicted by the context.

[0035] As used herein, the term "transition metal" is intended to describe metals in the d block (Groups 3 to 12) of the periodic table and other metals that play an equivalent role in lithium (transition) metal oxide cathode materials. These elements can play an active role in electrochemical processes by oxidation or reduction, or remain in a fixed oxidation state. Some representative examples include manganese and titanium. Other metals that are not "transition metals" in the traditional context may also be included in the term because they play a similar role as electrochemically inert metals (such as Ti) in the material, so it should be understood that metals outside the d block may be included in DRX formulations and are referred to as "transition metals" in some cases.

[0036] Recitation of ranges of values ​​herein, unless otherwise indicated, is used as a shorthand for referring individually to each separate value falling within the respective range, including the end points of the range, each separate value within the range, and all intermediate ranges encompassed by the entire range, each of which is incorporated into the specification as if individually recited herein.

[0037] Unless otherwise indicated or clearly contradicted by context, the methods described herein may be implemented by performing the steps in any suitable order, including: the exact order disclosed without any intervening steps or with one or more additional steps between the disclosed steps; performing the disclosed steps in an order different from the exact order disclosed; performing one or more steps simultaneously; and omitting one or more disclosed steps.

[0038] The present disclosure reports a method for rapid synthesis of cationic disordered ionic compounds, such as rock salt oxides / fluorides (DRX), which can be used as high energy density, sustainable and low-cost electrode (e.g., cathode) materials, such as in lithium ion rechargeable batteries. As described herein, the method includes microwave heating of a precursor (e.g., for 5 to 20 minutes in ambient atmosphere) followed by rapid quenching. The method can be extended to commercial / industrial scale manufacturing of electrodes. Exemplary materials that can be manufactured by microwave synthesis include, but are not limited to: having the general formula Li x M' y M″ 2-x-y O 2-z F z DRX oxides and oxyfluorides, wherein 1.05≤x≤1.35, 0.1≤y≤0.9 and 0≤z≤0.7, wherein M′ is a low-valent (e.g., ≤3+) transition metal selected from at least one of V, Cr, Mn, Fe, Co, Ni, Mg, Cu, Al, and M″ is selected from Ti 4+ 、Zr 4+ , Nb 5+ 、V 5+ 、Mo 6+ at least one high-valent (eg, ≥4+) transition metal.

[0039] The following are examples illustrating various embodiments of the present invention, including Li synthesized by microwave (mw) and conventional solid-state (ss) methods. 1.2 Mn 0.4 Ti 0.4 O 2 (LMTO) and Li 1.3 Mn 0.4 Nb 0.3 O 2-x F x Comparative study of (LMNO / F). For fluorinated MnTi-based DRX (LMTO / F), compositions with different transition metal stoichiometries and fluorine contents have been synthesized and characterized.

[0040] First Example: Microwave Synthesis of DRX Oxides / Oxyfluorides

[0041] Figure 1A flow chart illustrating one example of a method for synthesizing a rock salt composition for use in the comparative studies and characterizations presented herein is shown. Block 100 represents the selection of the desired amounts of precursor compounds and mixtures thereof in the desired stoichiometry. The selection of Li 2 CO 3 and LiF as Li and F sources for the synthesis of LMTO and LMNO / F compounds. However, other Li- and F-containing compounds may also be used, such as but not limited to Li 2 O、LiNO 3 , polytetrafluoroethylene (PTFE), etc. Select Mn 2 O 3 As a redox-active transition metal precursor, one can generally choose an oxide of the transition metal of interest. TiO 2 and Nb 2 O 5 As d for LMTO and LMNO / F 0 Metals. Again, one can often choose an oxide of the metal of interest.

[0042] For the microwave synthesis of LMTO, Li 2 CO 3 、LiF、Mn 2 O 3 and TiO 2 The precursor powder is prepared so that the stoichiometry of Mn, Ti and F is consistent with the formula Li 1.2 Mn 0.4 Ti 0.4 O 1.9 F 0.1 The chemical composition of Li 2 CO 3 A 10% molar excess was measured to compensate for possible Li losses during heating. LiF was added in sufficient amount to provide approximately 5% fluorination, acting as a sintering agent to allow faster diffusion of the elements during synthesis.

[0043] For the microwave synthesis of LMNO / F, Li 2 CO 3 、LiF、Mn 2 O 3 and Nb 2 O 5 The precursor powder is prepared so that the stoichiometry of Li, Mn, Nb and F is consistent with the formula Li 1.3 Mn 0.4 Nb 0.3 O 1.9 F 0.1 Similarly, about 5% fluorine content was added as a sintering agent. For LMNO / F, no excess Li was added.

[0044] For the microwave synthesis of fluorinated MnTi DRX, the Li 2 CO 3 、LiF、Mn 2 O 3 and TiO 2 The precursor powders were prepared such that the stoichiometry of Li, Mn, Ti and F matched the target composition. No excess Li was added.

[0045] The precursors may also be prepared in other forms, such as pellets. For the results presented herein, once the precursor powder was measured, it was hand ground until thoroughly homogeneous and pressed into 200 mg pellets.

[0046] Box 102 represents microwave heating of precursor pellets. For the results presented herein, a double crucible configuration was arranged whereby a smaller (e.g., alumina) crucible was placed in the center (or interior) of a larger crucible, and a heat transfer medium (e.g., activated carbon) was added to the larger crucible to surround the smaller inner crucible. A layer of protective precursor powder was added to the small crucible, and the precursor (e.g., pellets) was carefully placed on top of the protective powder in the smaller crucible. The configuration was placed in a 1200 watt conventional microwave in an ambient atmosphere and irradiated with microwaves at a set power level (6) and time (5 to 20 minutes). The activated carbon is heated by resonance with the microwaves, so that the pellets can be initially heated by a conductive process (e.g., interdiffusion), where heat is transferred from the activated carbon to the pellets by thermal conduction. The activated carbon can be in physical contact with the pellets to enhance the process. However, above the critical temperature, the pellet material becomes susceptible to microwave radiation, so that heating occurs by direct interaction of the pellet with the microwaves, resulting in very high reaction temperatures (>1500° C., preferably >1600° C.) within a short time (e.g., 5 to 20 minutes). During this time, the DRX phase forms.

[0047] Block 104 represents quenching. For the results presented herein, the pellets were rapidly quenched in distilled water immediately after microwave heating. The quenching process stabilizes the high temperature DRX phase at room temperature while preventing the formation of any layered / ordered oxide impurities during the cooling process. In some examples, the quenching can be performed with a medium other than distilled water, such as ethanol or liquid nitrogen.

[0048] Block 106 represents further processing. For the results presented herein, the pellets were dried on a hot plate and ground to obtain a fine powder of the final DRX product. Figure 2 a to Figure 2 d shows that you can use Figure 1 An example of an ionic lattice of a composition of matter produced by the method, showing a disordered arrangement of cations on the lattice sites.

[0049] Second example: Conventional solid-state synthesis of LMTO and LMNO / F

[0050] The Li for ss-LMTO was synthesized 1.2 Mn 0.4 Ti 0.4 O 2 Composition, and synthesis of Li for ss-LMNO 1.3 Mn 0.4 Nb 0.3 O 2 Composition. 2 CO 3 , Mn 2 O 3 and TiO 2 (LMTO) or Nb 2 O 5 (LMNO / F) was used as a precursor for solid-state synthesis. For LMTO, stoichiometric amounts of Mn and Ti were used with 10% molar excess of Li. For LMNO / F, stoichiometric amounts of Mn, Nb, and Li were used, but no excess Li was added.

[0051] As for the solid-state synthesis, the precursor was ground and pressed into pellets of about 200 mg. The pellets were annealed at 1100 °C under an argon flow for 12 h and allowed to slowly cool to room temperature and gently ground to produce the final ss-DRX powder. This procedure is similar to those reported in the literature for the solid-state synthesis of similar disordered oxide compositions.

[0052] Third Example: Characterization of LMTO obtained using the synthesis method described in the first and second examples

[0053] (a) Structural characterization

[0054] Figure 3 a shows synchrotron X-ray diffraction (SXRD) data indicating the formation of phase-pure LMTO DRX obtained by microwave (5, 10, 20 minutes) and conventional solid-state (12 hours) synthesis methods. The broad low-angle (about 3° in 2θ) peak indicates the presence of cation short-range order. Although mw-LMTO DRX was obtained after rapid quenching, these SXRD results indicate that a similar degree of cation short-range order exists in this material compared to LMTO DRX compounds obtained by conventional solid-state synthesis (sintering at 1000°C followed by slow cooling).

[0055] Figure 3 b to Figure 3The SEM micrograph in c shows the presence of large crystalline DRX particles in all synthesized LMTO samples. The average particle size depends on the microwave heating time. After 5 minutes of heating, the particles are on the order of about 1 μm. After 10 to 20 minutes of heating, the particles are on the order of about 3 to 5 μm. Compared with the ss-DRX compound, the mw-DRX compound has a smaller and more uniform particle size.

[0056] (b) Composition analysis of the compositions obtained using the synthesis methods described in the first and second examples

[0057]

[0058] From ICP, F-ISE and 7 Li solid-state NMR stoichiometry, normalized to Mn. DRX Li

[0059] Refers to Li only in a DRX-like environment. %Li impurity corresponds to the mole fraction of Li contained in the diamagnetic impurity phase.

[0060] The ratios of Li, Mn, Ti and F in the samples were determined by inductively coupled plasma (ICP). 2 CO 3 ) hinders the determination of DRX stoichiometry using SXRD and ICP alone. 7 Li solid-state nuclear magnetic resonance (NMR) can detect the amorphous phase and provide quantitative information on the molar ratio of Li in the LMTO DRX phase to Li present in the amorphous and crystalline diamagnetic impurities (see Figure 4a). The narrow peak at 0 ppm is related to the diamagnetic Li impurities (LiF, Li 2 CO 3 ), while the broad and asymmetric signal is associated with Li in a range of local environments within the disordered and paramagnetic LMTO DRX phase.

[0061] Four paramagnetic Gaussian components are used to simulate the disordered environment and a single diamagnetic 50% Lorentzian component is used for the fully relaxed spin echo. 7 The integration of the model gives an upper limit for the amount of Li impurity present; this value slightly underestimates the amount of Li in DRX because Li is close to the paramagnetic Mn 3+ , resulting in a rapid decay of the NMR signal. However, this effect is relatively small.

[0062] Li impurity quantification shows that the fraction of Li in the diamagnetic impurity phase decreases with increasing microwave heating time. After 20 minutes of heating time, the mole fraction of Li in the diamagnetic impurity in the mw-LMTO sample is comparable to the mole fraction of Li present in the LMTO sample obtained by conventional solid-state synthesis (12 hours sintering step). Longer reaction times would volatilize excess Li, resulting in less impurities.

[0063] By combining ICP and 7 Li NMR allows the Li stoichiometry of the LMTO DRX phase to be obtained. As shown in Table 1, all DRX samples (regardless of synthesis method and time) have very similar Li stoichiometry of 1.14 to 1.15. It should be noted again that because 7 Li NMR underestimates the amount of Li, so this is a lower limit for Li in DRX.

[0064] The mw-LMTO obtained after heating for 5, 10 and 20 min is associated with 7 The Li solid-state NMR signal is very similar but is associated with the LMTO phase prepared by solid-state synthesis. 7 The Li signal is slightly different, indicating a slightly different distribution of the local Li environment in the latter sample.

[0065] In one or more examples, LiF acts as a sintering agent during the microwave synthesis process.

[0066]

[0067] pass 19 LiF impurity phase in LMTO DRX sample obtained by fitting F solid-state NMR spectrum

[0068] / The mole fraction of F present in the region.

[0069] The fluoride ion selective electrode (F-ISE) results show that even for a fast 5 minute reaction time, approximately half of the fluorine initially present in the precursor is lost. This suggests that for mw-LMTO, minimal fluorination occurs. Furthermore, as with ICP, the F-ISE cannot distinguish between fluorine present in DRX and fluorine as an impurity in LiF, making the DRX fluorination level likely to be even lower. Both X-ray and neutron diffraction techniques are unable to distinguish between F and O due to the similar scattering cross sections of the two elements. On the other hand, 19 F NMR is an effective probe of F species present in DRX and potential LiF phases / regions. The sharp F NMR centered at -204 ppm 19 The F ss-NMR signal corresponds to the LiF impurity phase / region, while the F in the DRX structure results in the broad and asymmetric signals in Figures 4b to 4c.

[0070] Figures 4b to 4c show the time delays obtained using fast (50 ms) and slow (20 s) repetitive delays, respectively. 19 F NMR spectra. While a short recycle delay enables acquisition of a large number of scans (48k) for signal averaging and obtaining spectra with high signal-to-noise ratios in a reasonable amount of time, it also results in truncation of the slowly relaxing LiF signal at -204 ppm. Therefore, spectra acquired with a longer recycle delay of 20 seconds provide more quantitative information about the amount of LiF phase / region in the sample.

[0071] Collected here 19 The F spectrum is only semi-quantitative, since a portion of the F incorporated into the DRX cathode (F directly bonded to paramagnetic Mn) cannot be observed experimentally. However, even after a 48 K scan, the F spectra obtained with a fast cycling delay 19 The small signal-to-noise ratio observed in the F spectrum (Figure 4b) further indicates that very little F was incorporated into the DRX phase.

[0072] From the data obtained with a slow cycle delay (20 seconds) and shown in FIG4c 19 It can be clearly seen in the F spectrum that the diamagnetic LiF impurity peak at -204 ppm is quite prominent. 19 The fitting of the F spectrum shows that the very small amount of fluorine present in this sample is mainly incorporated into the LiF impurity phase (39 mol % fluorine). It should be noted that this value is an overestimation (upper limit) of the LiF fraction in the sample because the LiF from the DRX cathode 19 A portion of the F NMR signal is not experimentally visible. Increasing the microwave heating time to 10 and 20 min reduced the amount of LiF impurity but also reduced the total amount of F in the DRX sample, as shown by a decrease in the intensity of the broad paramagnetic signal.

[0073] Overall, the F incorporation into the DRX phase is very small, and the F from the LiF precursor is better described as a sintering agent rather than a precursor in the LMTO synthesis.

[0074] (c) Local structure and electronic structure analysis of LMTO

[0075] (i) K-edge XAS of Mn

[0076] K-edge X-ray absorption spectroscopy (XAS) data of Mn were acquired to explore the differences in the local coordination and oxidation states of the Mn species in the mw-LMTO and ss-LMTO DRX compounds of interest. The XANES edge energy shifts indicate that the average Mn oxidation state of mw-LMTO is slightly higher than that of ss-LMTO. The slightly higher Mn oxidation state observed for the microwave samples is most likely due to the more oxidizing ambient air environment used for microwave synthesis compared to the inert argon atmosphere used for solid-state synthesis.

[0077] (ii) X-ray PDF analysis

[0078] X-ray pair distribution function (PDF) analysis provides information about the short-range order that critically affects the lithium-ion transport and, therefore, the electrochemical performance of the DRX cathode. PDF analysis of the SXRD data collected on the mw-LMTO and ss-LMTO compounds was performed using two different structural models: a cubic rock-salt model corresponding to a random distribution of cations (space group Fm-3m, #225) and a tetragonal model representing an ordered cation arrangement (space group I4 1 / amd, #141). The results are shown in Table 5.

[0079] For both models, fits were performed at different correlation lengths r to understand how the DRX structure evolves from short to long range. At long correlation lengths, the cubic 225 space group provided the best fit to the data, consistent with the SXRD results and the description of those compounds as being cationically disordered on average.

[0080] However, at shorter correlation lengths (1.6 to 3.2 Å), Figure 5 clearly shows that the cubic structure results in a poor fit. In contrast, the tetragonal 141 space group provides a better fit, indicating the presence of short-range order of the cations.

[0081] In both the mw-LMTO and ss-LMTO DRX structures, the transition from short-range cation order to long-range disordered cation arrangement occurs at similar correlation lengths r, indicating that the extent of short-range cation order is not much different when DRX is synthesized using these two methods.

[0082] (d) Electrochemistry of ss-LMTO and mw-LMTO

[0083] DRX samples synthesized by microwave (with a 5-min heating step) and solid-state methods were post-treated in the same way: DRX powder was mixed with Super C65 at a mass ratio of 70:20 in a planetary ball mill at 400 rpm for 6 h to reduce the particle size and carbon-coate the active material to improve its ionic and electronic conductivity.

[0084] SEM images ( Figure 3 c) shows that the solid-state and microwave-post-treated particles have the same size, so that the differences in electrochemical performance can be attributed to the composition of the active material and the bulk structure or the presence of impurity phases.

[0085] The DRX+Super C65 powder was further mixed with PTFE to produce a material:carbon:binder weight ratio of 70:20:10. 2 Up to 5mg / cm 2 The cathode film was rolled with a loading of 1.5 wt % LiPF in 1:1 EC:DMC solvent using a cathode film, a lithium metal anode, a Celgard 2325 trilayer membrane, and a commercially available 1 M LiPF 6 Salt was used as the electrolyte to assemble CR2023 type button cells.

[0086] The galvanostatic curves of ss-LMTO and mw-LMTO shown in Figures 6a to 6b are very similar. Both exhibit initial discharge capacities of 200 mAh / g and 130 mAh / g and 50 cycle discharge capacities, respectively, corresponding to a capacity decay of 35% (see Figure 6d).

[0087] The mw-DRX has a higher open circuit voltage (OCV) than the ss-cathode (3.0 V vs. 2.7 V), consistent with the higher Mn oxidation state observed in the XANES data.

[0088] The Coulombic efficiency is also the same (Figure 6d) and remains close to about 99% throughout the first 50 cycles. The differential capacity analysis shown in Figure 6c shows that the redox processes of ss-DRX and mw-DRX are very similar, with the lower voltage oxidation and reduction peaks corresponding to Mn redox and the higher voltage peak corresponding to O redox. For mw-LMTO, the O oxidation peak appears at a slightly higher voltage than the solid-state sample.

[0089] The operating voltage, energy density, voltage holding, and voltage hysteresis of the ss-LMTO and mw-LMTO cathodes are also the same. Figure 6e shows the rate performance of the LMTO cathode and shows that the ss-DRX performs better at higher rates. This may be due to the presence of LiF and Li in the mw-DRX sample. 2 CO 3 Impurities are slightly more numerous and may be addressed by further fine-tuning of microwave synthesis conditions.

[0090] Fourth Example: Characterization of LMNO / F obtained using the synthesis method described in the first and second examples

[0091] The microwave synthesis method can be applied to other DRX compositions, such as niobium (Nb)-based Li 1.3 Mn 0.4 Nb 0.3 O2-x F x (LMNO / F). Here, no excess Li was used during the microwave synthesis, in contrast to the 10% molar excess of Li used in the synthesis of the LMTO system discussed in the third example.

[0092] LMNO compositions were also prepared by conventional solid-state synthesis for comparison. Likewise, phase-pure DRX (based on synchrotron XRD) was obtained by microwave heating (and by conventional solid-state synthesis), and the particle size could be adjusted by adjusting the microwave heating time between 5 and 20 minutes.

[0093]

[0094] The mole fraction of Li contained in the diamagnetic impurity phase / region of LMNO / F is given by 7 Fitting of Li solid-state NMR spectra

[0095] get.

[0096] (a) Solid State 7 Li / 19 F NMR

[0097] ICP analysis is not usually performed on DRX compounds (eg, LMNO / F) because acid digestion of niobium-containing compounds is notoriously difficult. 7 Li and 19 F NMR still provides valuable information on the amount and degree of fluorination of the Li-containing impurity phase / region of DRX.

[0098] The higher average Mn oxidation state in the LMNO / F compound (see XANES analysis below) and the different d 0 The presence of transition metals (Nb vs Ti) and the type and / or degree of cation short-range ordering in the LMNO / F 7 The Li NMR spectrum shows slightly different line shapes from those of LMTO. 2

[0099] The results in Table 3 show that longer microwave heating time leads to less diamagnetic Li impurities and overall, LMNO / F has more Li impurities than LMTO.

[0100] The 19 The F NMR spectrum shows that there is no LiF impurity in mw-LMNO / F, and there is significantly more fluorine in the DRX-like local environment in this sample compared to mw-LMTO. Therefore, mw-LMNO / F is actually an oxyfluoride with a low F content (the upper limit of fluorination is 5% based on the amount of fluorine precursor).

[0101] (b) K-edge XAS and PDF analysis of Mn

[0102] The K-edge XANES spectrum of Mn shows that the average Mn oxidation state of mw-LMNO / F is slightly higher than that of ss-LMNO / F, despite the presence of F in the microwave sample but not in the solid sample (the incorporation of F lowers the average Mn oxidation state). This indicates the presence of Li vacancies in the microwave sample.

[0103] PDF analysis also shows that there is no significant difference in the nature and extent of the cation short-range order between the LMNO / F DRX phases synthesized by microwave heating and by conventional solid-state synthesis.

[0104] (c) Electrochemistry of ss-LMNO / F and mw-LMNO / F

[0105] As with the LMTO system, the electrochemical properties of solid-state and microwave (with a 5-minute heating step) LMNO / F are very similar (Figure 10a to Figure 10b). The capacity of both mw-DRX and ss-DRX samples develops from 270 mAh / g during the first discharge to 130 mAh / g after 50 charge-discharge cycles. This corresponds to a capacity decay of 50% and is more severe than that of the LMTO system. The energy density and voltage decay of mw-LMNO / F and ss-LMNO / F are also comparable.

[0106] The Coulombic efficiency is stable at about 99%. As with LMTO, the lower voltage oxidation and reduction peaks in the differential capacity diagram (Figure 10c) correspond to Mn redox, while the higher voltage peak corresponds to O redox, with mw-LMNO / F showing a slightly higher voltage O redox peak than ss-LMNO / F.

[0107] The OCV of mw-LMNO / F (3.0 V) is higher than that of ss-LMNO (2.7 V), which is consistent with the higher average Mn oxidation state observed by XAS.

[0108] Likewise, the most significant difference between the two LMNO / F cathode samples is their rate performance, where ss-DRX performs better, as shown in Figure 10e. This may also be due to the presence of a small amount of impurity phase in the microwave sample.

[0109] Fifth example: Fluorination of MnTi DRX system by microwave synthesis

[0110] ICP on LMTO and 7The Li NMR results indicate that excess Li is not required to obtain phase-pure DRX via microwave synthesis. This is probably because evaporation of Li does not occur to a large extent in such a short (5 min) reaction time. Therefore, it was investigated whether F-containing MnTi compositions can be obtained without using excess Li in the precursor mixture, as it is expected that excess Li may result in more volatile F and affect its incorporation into the DRX structure. Targeted Li 1.2 Mn 0.4 Ti 0.4 O 1.9 F 0.1 (LMTO / F) compositions were prepared without excess Li, as shown in FIG. 19 The F NMR results indicate that F is significantly incorporated into the bulk DRX structure. Again, it should be noted that 19 F NMR cannot be used to quantify the absolute amount of F present in the DRX phase.

[0111] Longer reaction times lead to less LiF impurities (Figure 11c), but at the expense of less fluorination of DRX (consistent with LiF evaporation). Thus, fast reaction times are preferred for fluorination of DRX compounds.

[0112] 19 Comparison of the F NMR signal intensities shows that the mw-LMTO / F phase is still stronger than the mw-LMNO / F composite (Li 1.3 Mn 0.4 Nb 0.3 O 1.9 F 0.1 ) contains less fluorine (Figure 11d).

[0113] By adjusting the target DRX composition, more fluorine can be incorporated into the DRX structure (Figure 12a). 1.2 Mn 0.5 Ti 0.3 O 1.8 F 0.2 The composition contains LMNO / F(Li 1.3 Mn 0.4 Nb 0.3 O 1.9 F 0.1 ) sample (Figure 12b). The DRX phase (Li 1.2 Mn 0.6 Ti 0.2 O 1.8 F 0.2 and Li 1.2 Mn 0.7 Ti 0.1 O 1.7 F 0.3) synthesis.

[0114] Example 6: Particle size measurement

[0115] 13a-13b are SEM images of LMTO samples synthesized by solid-state and microwave methods, respectively, showing the resulting powder 1300, which includes a lithium metal oxide / oxyfluoride compound for a rechargeable battery having the following general formula: Li x Mn' y Ti″ 2-x-y O 2-z F z , where 1.05≤x≤1.35, 0.1≤y≤0.9, and 0≤z≤0.7 (measured by inductively coupled plasma optical emission spectroscopy (ICP-OES), see Table 1). The specific recipe for synthesizing these samples is Li 1.2 Mn 0.4 Ti 0.4 O 2 (ss-LMT44 and mw-LMT44) Figures 14a-14b show the particle size distribution of the particles in the powder measured in the SEM images.

[0116] The particle size distribution data in Figure 14b shows that the powders produced using microwave synthesis as described herein have a median particle size of at least 1.00 μm to 3 μm, with a standard deviation of no more than 1.5 μm. The median particle size of the particles 1302 was obtained by measuring the size of the particles 1302 along their longest dimension 1304 in the SEM image using the protocol described in the next section. In addition, the median particle size of the particles obtained without further processing after synthesis to reduce the particle size was measured.

[0117] Example 7: Particle size measurement

[0118] Fig.15 Additional particle size distribution data for particles in other powdered LMTO samples synthesized by solid-state and microwave methods are provided, and the SEM images in Figures 13a to 13b are also representative. The various LMTO samples are listed below.

[0119] The particle size distribution data are given in Table 4B below, which is discussed below.

[0120]

[0121]

[0122] The samples in Table 4a above were prepared using microwave and solid state synthesis methods as given above in Examples 1 and 2. All microwave synthesized samples were prepared by a microwave heating step with a duration of 5 minutes. Solid state synthesized samples ss-LMT53 and ss-LMT62 were prepared by a calcination step with a duration of 12 hours.

[0123]

[0124] The particle size distribution data demonstrate that microwave synthesis of a given composition generally produces a smaller average particle size (e.g., Dx(50)) and a more uniform particle size distribution (e.g., a smaller span) than achieved by solid-state synthesis of the same given composition. According to these data, the median particle size of powders produced using microwave synthesis is in the range of about 5.0 to about 6.0 μm (e.g., 5.3 to 5.68 μm), wherein 90% of the powder particles (e.g., Dx(90)) have a maximum diameter in the range of about 10 μm to about 13 μm (e.g., 10.4 μm to 12.5 μm), and the particle size span ((Dx(90)-Dx(10)) / Dx(50)) is about 1.4 to about 1.8 (e.g., 1.394 μm to 1.804 μm). These particle distributions are significantly smaller than those produced by solid-state synthesis, where median particle sizes were found to be in the range of about 9.0 to about 28.0 μm (e.g., 8.95 to 28.4 μm), with 90% (e.g., Dx(90)) of the powder particles having a maximum diameter in the range of about 18 μm to about 62 μm (e.g., 18 μm to 61.5 μm), and a particle size span ((Dx(90)-Dx(10)) / Dx(50)) of about 1.7 to about 1.9 (e.g., 1.733 to 1.93). It was further observed that the particle distributions of microwave synthesized powders generally had a greater percentage of particles having a maximum diameter below 3 μm (e.g., "% < 3 μm").

[0125] Experimental methods and protocols used to obtain the data in the examples

[0126] X-ray diffraction (XRD) of ≈40 mg of sample was performed at beamline 17-BM at the Advanced Photon Source at Argonne National Laboratory. Figure 3 a) and the distribution function measurement (Figure 5). All samples were measured at room temperature (≈303K). The scattering intensity was measured by a Perkin Elmer amorphous-Si flat panel detector. The measured wavelength is The TOPAS software suite was used for Pawley refinement of these data sets. The pair distribution function g(r) data set was obtained by reducing the image files obtained from the regional detector at 17-BM to .chi files using GSAS II. The Qmax was used as The .chi files were further converted to g(r) data files using the xPDFsuite package 47. The least squares refinement of the PDF data was performed using PDFGUI.

[0127] Scanning electron microscopy (SEM) images were obtained using a Thermo Fisher Apreo C LoVac SEM instrument at an accelerating voltage of 5 keV and a current of 0.4 nA ( Figure 3 b. Figure 3 c, Figure 7, Figure 13a, Figure 13b).

[0128] Bulk chemistry was determined using an Agilent 5800 ICP-OES and F-ISE measurements were performed using a Cole-Parmer system. DRX samples were digested in a mixture of nitric acid and hydrochloric acid. For ICP-OES, the digestion solution was diluted with distilled water. For F-ISE measurements, the solution was diluted with 23 sodium acetate buffer and fluoride ionic strength regulator solution (TISAB, Cole-Parmer).

[0129] The amount of Li, Mn, Ti, and Nb in the positive electrode active material powder was measured by the ICP method using an Agilent 5800ICP-OES instrument (as listed in Table 1). 10 mg of powder sample was dissolved in a mixture of 4 mL of concentrated nitric acid and 1 mL of concentrated hydrochloric acid. Then, 1 mL of aliquots of the dissolved sample solution were transferred to a falcon tube, and 13 mL of distilled water were added to obtain a 14x volume dilution. The diluted solution was used for ICP-OES measurement. The measured Li, Mn, and Ti are expressed as the mol% of the sum of these contents.

[0130] The amount of F in the positive electrode active material powder (as listed in Table 1) was measured using the F-ISE measurement method. About 0.5 g of the dissolved sample solution prepared above was measured and added to a plastic HDPE bottle. About 2 g of distilled water was added to the bottle. Finally, about 25 mL of a mixture of 15% sodium acetate aqueous solution: Tisab buffer (obtained from Cole-Parmer) in a weight ratio of 10: 1 was added to adjust the final solution pH to between 5 and 8 and provide an ionic strength regulator for fluoride. The final solution was used for F-ISE measurement. Since the mass of each component of the final solution was measured, the amount of F in the original dissolved sample solution can be inverted and the mol% of F relative to Li, Mn and Ti can be obtained from the ICP results. The measured Li, Mn, Ti, and F are expressed as the mol% of the sum of these contents.

[0131] According to the following steps, the particle size distribution of the positive electrode active material powder provided in the sixth example was measured by SEM using ImageJ software. SEM measurements were performed using a Thermo Fisher Apreo C LoVac SEM instrument at 25°C under a high vacuum environment of <1e-5 Torr. The files (Figures 13a to 13b) were then loaded into the ImageJ software at magnifications of 800x to 1500x. The SEM should have appropriate contrast and brightness so that the edges of the particles can be clearly observed. Set the scale according to the SEM magnification. Manually adjust the size of the particles on the longest axis. For ss-LMTO, 814 particles in the image of Figure 13a were measured. For 5 minutes of mw-LMTO, 1500 particles in the image of Figure 13b were measured. For each sample, the mean, median, and standard deviation of the measured set particle size were calculated. The results of the statistical analysis of the mean, median, and standard deviation are shown in Figures 14a to 14b.

[0132] The data on the particle size distribution (PSD) provided in the seventh example, such as the particle size (Dx (10), Dx (50), Dx (99)) and span at set percentiles, were obtained by laser PSD measurement method. Laser PSD was measured using a Malvern Mastersizer 3000 equipped with a Hydro3000MV wet dispersion accessory. First, 5 drops of surfactant (Dolapix) were added to a beaker. Then, 0.5 grams of cathode were added using a spatula. The beaker was then filled with 40 mL of deionized (DI) water. The solution was then sonicated using continuous pulses for 30 seconds to improve dispersibility. The solution was then dispersed in a Mastersizer Hydro Can using a 5 mL pipette until an obscuration of 7% was reached. Two measurements were made to measure the scattering of the red light source and the blue light source, and the average of the two measurements was reported. It should be noted that the narrow span (in addition to particle size uniformity) is an indicator of the apparent sphericity of the particles, and the span value is used in the example to measure the sphericity.

[0133] Advantages and improvements

[0134] Cationic disordered rock salt oxides / oxyfluorides (DRX) are a class of industrially relevant lithium-ion cathode materials because they are made from earth-abundant transition metals and enable the deployment of more sustainable, lower cost and higher energy density secondary batteries. The cathode material of a battery is the component that limits the overall energy density of the battery and is typically the most expensive component. Currently, most lithium-ion batteries use cobalt (Co)-based and nickel (Ni)-based cathode materials, which are plagued by complex supply chains, high price fluctuations and high raw material costs. Therefore, there is a need to develop cathode materials that rely on more sustainable elements such as Mn and Fe. DRX materials can accommodate a variety of different transition metals, and manganese-based DRX cathodes show good electrochemical performance and are expected to enable the commercialization of low-cost and high-energy density Co / Ni-free batteries.

[0135] However, current methods for synthesizing DRX cathodes involve time-consuming and energy-intensive steps, either sintering the precursor powders at ≥800°C for ≥10 hours, or mechanochemically ball milling the precursor powders at about 500 rpm for a long time (40 hours), which is usually performed in a sealed inert argon (Ar) environment. On the other hand, the microwave synthesis method disclosed herein is a fast and energy-efficient method for synthesizing DRX compounds, which can be performed in 5 to 20 minutes (more than two orders of magnitude faster than conventional methods). In addition, the microwave synthesis method does not require an inert argon atmosphere as required by conventional solid-state and mechanochemical techniques. Therefore, the microwave synthesis method should be very attractive to battery cathode manufacturers as a significantly more scalable and cost-effective method for producing DRX compounds.

[0136] The microwave synthesis method of the present invention is also beneficial because it can produce DRX compositions and atomic structures similar to those obtained in conventional solid-state synthesis, but with shorter processing times and corresponding energy savings. For example, the results show that when the microwave heating time is increased from 5 minutes to 10 minutes to 20 minutes, and when the solid-state synthesis is performed after a 12-hour calcination step, LMTO (Li 1.2 Mn 0.4 Ti 0.4 O 2 ) is the same. 1.3 Mn 0.4 Nb 0.3 O 2-x F x X-ray PDF analysis of (LMNO / F) compounds demonstrated that there was no significant difference in the cation short-range order between mw-DRX and ss-DRX. For both LMNO and LMNO / F, long-term galvanostatic cycling showed that the electrochemical performance between mw-DRX and ss-DRX was very similar.

[0137] The presence of a larger amount of Li impurities at shorter microwave heating times indicates that excess Li is not required to synthesize phase-pure DRX via this new microwave synthesis method, which provides the possibility of producing suitable DRX materials with reduced emphasis on Li content. The experiments also show that the F incorporated into the bulk DRX structure depends on the amount of excess Li used during the microwave synthesis and the d 0 The nature of the transition metal. For example, very little F was incorporated in LMTO prepared with 10% excess Li. More significant fluorination was achieved in the MnTi-DRX system without excess Li, especially when the reaction time was short. Compared to LMTO, a larger amount of F could be incorporated into the Li-Mn-Nb-O DRX structure prepared without excess Li, and LiF was not present in the synthesized microwave cathode sample. Therefore, the microwave synthesis method of the present invention provides further possibilities for LMTO compositions to produce greater benefits through the incorporation of F in the presence of relatively small Li contents.

[0138] Slightly different Mn oxidation states can be obtained in DRX compounds obtained by microwave synthesis and conventional solid-state synthesis. From XANES, the oxidation state of Mn in mw-LMTO and mw-LMNO / F DRX is slightly higher than that in ss-LMTO and ss-LMNO / FDRX, which is due to the use of a more oxidizing environment (ambient air vs. argon) in the former method. Slightly different average redox potentials were also observed for DRX compounds obtained by microwave synthesis and conventional solid-state synthesis. Differential capacity analysis showed that the redox of oxygen occurred at a slightly higher voltage for mw-DRX compounds.

[0139] Surprisingly and unexpectedly, the microwave synthesis of the present invention can obtain powders of lithium metal oxides or oxyfluoride compounds having a particle size distribution that is advantageously useful for rechargeable batteries while reducing the number of post-synthesis processing steps (e.g., no further grinding, milling or other process steps to reduce particle size are required, or the number of such steps is reduced).

[0140] Methods, compositions and electrode embodiments

[0141] Exemplary compositions, methods, and electrodes according to the invention include, but are not limited to, the following.

[0142] 1. A method for preparing a cathode active material that can be used as an electrode, comprising:

[0143] mixing the ionic compound precursors together to form a precursor mixture,

[0144] subjecting the precursor mixture to microwave treatment, comprising exposing the precursor mixture to microwave radiation having a power and duration to form a microwaved powder comprising an ionic compound comprising a rock salt type crystal structure comprising a disordered arrangement of cations, wherein the rock salt type crystal structure can be labeled as a cubic Fm-3m space group (#225); and

[0145] The microwave irradiation was stopped and the microwaved powder was quenched (within 15 seconds after the stop) to form a cathode active material that maintained a rock salt type crystal structure at room temperature.

[0146] 2. The method according to Example 1 further comprises: grinding the cathode active material into a milled powder, and further processing the milled powder into a form that can be used as an electrode, wherein the electrode comprises a lithium-ion battery electrode.

[0147] 3. A method according to any one of Examples 1 or 2, wherein the ionic compound comprises cations and anions, the cations comprising at least one of mobile alkali metal ions and transition metal ions or major element ions, and the anions comprising at least one of oxygen ions or fluoride ions.

[0148] 4. The method according to Example 3, wherein the mobile alkali metal ions include lithium or sodium.

[0149] 5. A method according to any one of Examples 3 or 4, wherein the ionic compound precursor does not include excess mobile alkali metal ions to compensate for the loss of the corresponding element during exposure to microwave radiation.

[0150] 6. A method according to any one of Examples 3 or 4, wherein the ionic compound precursor includes an excess of mobile alkali metal ions to compensate for the loss of the corresponding element during exposure to microwave radiation.

[0151] 7. A method according to any one of Examples 1 to 6, wherein the rock salt type crystal structure comprises a disordered rock salt (DRX) oxide structure.

[0152] 8. The method of any one of Examples 1 to 7, wherein the ionic compound is described by:

[0153] At longer correlation lengths, this corresponds to a cubic rock-salt-type crystal structure containing a random distribution of disordered arrangements of cations, and

[0154] At shorter correlation lengths, the cations are arranged in a more ordered manner.

[0155] 9. The method of any one of Examples 1 to 7, further comprising: selecting a specific quenching rate (°C / min) to a temperature in the range of 77 to 323 K to prevent the formation of any layered / ordered oxide impurities during quenching.

[0156] 10. The method of any one of Examples 1 to 9, wherein the cathode active material comprises an oxyfluoride.

[0157] 11. The method according to any one of Examples 1 to 10, wherein the ionic compound precursor is selected to form a compound of formula A x M' y M″ 2-x-y O 2-z F z A cathode active material, wherein 1.05≤x≤1.35, 0.1≤y≤0.9 and 0≤z≤0.7, A is a mobile alkali metal ion, M′ is a transition metal ion or a main element ion, and M″ is a transition metal ion having a higher valence than M′.

[0158] 12. The method according to Example 11, wherein A is Li + Or Na + At least one of V, Cr, Mn, Fe, Co, Ni, Mg, Cu, Al, and M" is Ti 4+ 、Zr 4+ , Nb 5+ 、V 5+ 、Mo 6+ At least one of .

[0159] 13. A method according to any one of Examples 1 to 12, wherein the microwave is carried out in an inert atmosphere.

[0160] 14. A method according to any one of Examples 1 to 12, wherein the microwaves are carried out in an atmosphere consisting essentially of air at ambient (atmospheric) pressure.

[0161] 15. The method according to any one of Examples 1 to 14, further comprising:

[0162] contacting the precursor mixture with a heat transfer medium having an absorption spectrum resonantly tuned to the frequency of the microwave radiation; and

[0163] wherein said microwaves comprise exposing said precursor mixture in thermal contact with said heat transfer medium to said microwave radiation, and:

[0164] In a first stage, the heat transfer medium is heated by resonant absorption of the microwave radiation, and the heat transfer medium transfers at least some of the thermal energy to the precursor mixture via conduction through thermal contact so as to heat the precursor mixture above a critical temperature at which the precursor material becomes more susceptible to absorbing the microwave radiation; and

[0165] In the second stage, when the precursor mixture is above the critical temperature, microwave radiation heats the precursor mixture to a higher reaction temperature (above 1500° C., preferably above 1600° C.), thereby initiating the formation of an ionic compound comprising a disordered arrangement of cations.

[0166] 16. The method of Example 15, wherein the heat transfer medium comprises activated carbon.

[0167] 17. The method of any one of Examples 15 or 16, wherein:

[0168] The microwave treatment includes subjecting the precursor mixture placed in the crucible to microwave treatment using a heat transfer medium; and

[0169] Quenching includes:

[0170] After removing the microwaved powder from the crucible, placing the microwaved powder in a quenching medium; and

[0171] After quenching, the positive electrode active material is dried.

[0172] 18. A method according to any one of Examples 15 to 17, wherein quenching comprises immersing the microwaved powder in a non-reactive liquid, wherein the non-reactive liquid comprises water (e.g., distilled water), ethanol, or liquid nitrogen.

[0173] 19. The method of Example 2, wherein further processing does not require ball milling or mechanochemical milling of the ionic compound precursor or precursor mixture.

[0174] 20. The method of any one of Examples 1 to 19, wherein a fluorinated compound is added to the mixture of ionic compound precursors and used as a sintering agent to allow cations and anions to diffuse faster during microwaves to form a rock salt type crystal structure.

[0175] 21. A composition of matter useful as a cathode active material in an electrode, comprising a plurality of particles (e.g., Figure 3 b or as shown in Figure 13b).

[0176] 22. The composition of matter according to Example 21, wherein each particle comprises a compound of the formula: A x M' y M″ 2-x- y O 2-z F z , wherein 1.05≤x≤1.35, 0.1≤y≤0.9 and 0≤z≤0.7, A is a mobile alkali metal ion (eg, Li or Na), M′ is a transition metal ion, and M″ is a transition metal ion having a higher valence than M′.

[0177] 23. A composition of matter according to any one of Examples 21 or 22, comprising a powder comprising particles comprising a lithium metal oxide or a fluoride oxide compound for a rechargeable battery.

[0178] 24. The composition of matter according to any one of Examples 21 to 23, wherein the lithium metal oxide or oxyfluoride has the following general formula: Li x Mn' y Ti″ 2-x-y O 2-z F z , wherein 1.05≤x≤1.35, 0.1≤y≤0.9 and 0≤z≤0.7 are measured by ICP-OES, and the powder comprises particles having a median particle size of about 5 μm to about 6 μm and a span ranging from about 1.4 to about 1.8.

[0179] 25. The composition of matter of any one of Examples 21 to 24, formed by a method comprising the steps of:

[0180] mixing the ionic compound precursors together to form a precursor mixture,

[0181] subjecting the precursor mixture to microwave treatment, comprising exposing the precursor mixture to microwave radiation having a power and duration to form a microwaved powder comprising an ionic compound comprising a rock salt type crystal structure comprising a disordered arrangement of cations, wherein the rock salt type crystal structure can be labeled as a cubic Fm-3m space group (#225); and

[0182] The microwave irradiation was stopped and the microwaved powder was quenched (within 15 seconds after the stop) to form a cathode active material that maintained a rock salt type crystal structure at room temperature.

[0183] 26. The composition of matter according to any one of Examples 22 to 25, wherein A is Li + Or Na + , M' is Mn, M" is Ti, and 80% by number of the particles have a maximum diameter in the range of 0.5 to 5 microns, the particles being synthesized by quenching of a microwave precursor without further processing to reduce the particle size (e.g., milling or grinding).

[0184] 27. A composition of matter according to Example 26, wherein the maximum diameter of the particles is a diameter measured using a software tool applied to a scanning electron microscope image of the particles.

[0185] 28. A composition of matter according to any of Examples 26 or 27, wherein the maximum diameter has a standard deviation of no more than 1.13 microns.

[0186] 29. The composition of matter of any one of Examples 26 to 28, wherein 50% of the particles have a maximum diameter of less than 2.5 microns.

[0187] 30. The composition of matter of any one of Examples 22 to 29, wherein:

[0188] The transition metal ion has an oxidation state associated with the elemental composition of the compound formed by microwave heating of the precursor in air, and

[0189] The lithium content in the precursor before microwave treatment does not contain excess lithium to account for lithium volatility during microwave treatment, thereby reducing fluorine loss during microwave treatment.

[0190] 31. The composition of matter according to any one of Examples 22 to 30, wherein A is at least one of Li or Na, M' is at least one of V, Cr, Mn, Fe, Co, Ni, Mg, Al, and M" is Ti 4+ 、Zr 4+ , Nb 5+ 、Mo 6+ At least one of .

[0191] 32. The composition of matter of any one of Examples 22 to 31, further comprising fluorine replacing oxygen.

[0192] 33. A composition of matter according to any one of Examples 22 to 32, wherein the fluorine content is greater than 0.1 or 0.2.

[0193] 34. A method or composition of matter according to any of the preceding examples, wherein the duration of the microwaves is in the range of 2 minutes to 60 minutes.

[0194] 35. A composition of matter useful as a cathode active material in an electrode, comprising:

[0195] A plurality of particles comprising a compound of the formula: A x M' y M″ 2-x-y O 2-z F z , measured by ICP, where: 1.05≤x≤1.35, 0.1≤y≤0.9 and 0≤z≤0.7, A is Li + Or Na + , M' is Mn, and M" is Ti; and

[0196] wherein the particles have a median particle size of about 5 μm to about 6 μm and a span in the range of about 1.4 to about 1.8; and / or

[0197] 90% of the particles by number have a maximum diameter in the range of about 10.4 μm to about 12.5 μm, and 50% of the particles by number have a maximum diameter less than about 5.3 μm to about 5.7 μm, and the particles are synthesized without grinding, polishing, milling or any other further processing to reduce the particle size.

[0198] 36. A powder of lithium metal oxide or oxyfluoride compound for use in a rechargeable battery having the general formula: Li x Mn' y Ti″ 2-x-y O 2-z F z, wherein 1.05≤x≤1.35, 0.1≤y≤0.9 and 0≤z≤0.7 as measured by ICP-OES, and wherein the powder has a median particle size of about 5 to about 6 μm, and a span in the range of about 1.4 to about 1.8.

[0199] 37. A powder according to Example 36, wherein the lithium metal oxide or oxyfluoride has a cationic disordered rock salt (DRX) structure.

[0200] 38. A powder according to any of Examples 36 or 37, wherein the median particle size of the intermediate product is obtained without further processing to reduce the particle size.

[0201] 39. A powder according to any one of Examples 36 to 38, which is manufactured using the method described in any one of Examples 1 to 20 or 34.

[0202] 40. A powder according to any one of Examples 36 to 39, wherein the median particle size is the particle size measured by sizing the particles along their longest dimension in a scanning electron microscope image.

[0203] 41. A powder according to any one of Examples 36 to 40, wherein the median particle size is the particle size measured for particles obtained without further processing to reduce the particle size.

[0204] 42. An electrochemical cell (e.g., a lithium-ion or sodium-ion cell) comprising:

[0205] anode;

[0206] Electrolytes; and

[0207] A cathode coupled to an anode via the electrolyte, wherein the cathode comprises the composition of matter of any one of Examples 21 to 35, and wherein during battery operation, mobile alkali ions (Li or Na) are intercalated or deintercalated from the cathode.

[0208] Although the present invention has been described with reference to specific embodiments, those skilled in the art will understand that the foregoing disclosure relates only to exemplary embodiments; that the scope of the present invention is not limited to the disclosed embodiments; and that the scope of the present invention may cover, in whole or in part, any combination of the disclosed embodiments, as well as additional embodiments that include various changes and modifications relative to the examples disclosed herein, without departing from the scope of the present invention as defined by the appended claims and their equivalents.

[0209] To the extent necessary to understand or complete the present disclosure, all publications, patents, and patent applications mentioned herein are expressly incorporated by reference to the same extent as if each were individually incorporated.

[0210] The present invention is not limited to the exemplary embodiments shown herein, but is characterized by the appended claims, which in no way limit the scope of the disclosure.

[0211] References

[0212] The following references are incorporated herein in their entirety:

[0213] (1) Lee, J.; Kitchaev, DA; Kwon, DH; Lee, CW; Papp, JK; Liu, YS; Lun, Z.; Clément, RJ; Shi, T.; McCloskey, BD; Guo, J.; Balasubramanian, M.; Materials.Nature2018,556(7700),185-190.

[0214] (2) Ji, H.; Urban, A.; Kitchaev, DA; Kwon, D.-H.; Artrith, N.; Ophus, C.; Huang, W.; Cai, Z.; Shi, T.; Kim, JC; Kim, H.; Ceder, G. Hidden Structural and Chemical OrderControls Lithium Transport in Cation-Disordered Oxides for RechargeableBatteries.Nat.Commun.2019,10(1),592.

[0215] (3)Hyeseung Chung;Zachary Lebens-Higgins;Baharak Sayahpour;CarlosMejia;Antonin Grenier;E.Kamm,G.;Yixuan Li;Ricky Huang;J.Piper,L.F.;W.Chapman,K.;Jean-Marie Doux;Shirley Meng,Y.Experimental Considerations to Study Li-Excess Disordered Rock Salt Cathode Materials.J.Mater.Chem.A 2021,9(3),1720-1732.

[0216] (4)Baur,C.; I.;Chable,J.;Chang,J.H.;Johnsen,R.E.;Ruiz-Zepeda,F.;Ateba Mba,J.M.;Naylor,A.J.;Garcia-Lastra,J.M.;Vegge,T.;Klein,F.;Schür,A.R.;Norby,P.; K.;Hahlin,M.;Fichtner,M.Improved Cycling Stability inHigh-Capacity Li-Rich Vanadium Containing Disordered Rock Salt OxyfluorideCathodes.J.Mater.Chem.A 2019,7(37),21244-21253.

[0217] (5)Crafton,M.J.;Yue,Y.;Huang,T.-Y.;Tong,W.;McCloskey,B.D.;Crafton,M.J.;Huang,T.;McCloskey,B.D.;Yue,Y.;Tong,W.Anion Reactivity in Cation-Disordered Rocksalt Cathode Materials:The Influence of FluorineSubstitution.Adv.Energy Mater.2020,10(35),2001500.

[0218] (6)Ji,H.;Urban,A.;Kitchaev,D.A.;Kwon,D.-H.;Artrith,N.;Ophus,C.;Huang,W.;Cai,Z.;Shi,T.;Kim,J.C.;Kim,H.;Ceder,G.Hidden structural and chemical ordercontrols lithium transport in cation-disordered oxides for rechargeablebatteries.Nature Communications 2019,10,592.

[0219] (7)Clément,R.J.;Lun,Z.;Ceder,G.Cation-disordered rocksalt transitionmetal oxides and oxyfluorides for high energy lithium-ion cathodes.EnergyEnviron.Sci.2020,13,345.

[0220] (8)Wu,V.C.,Evans,H.A.,Giovine,R.,Preefer,M.B.,Ong,J.,Yoshida,E.,Cabelguen,P.-E.,Clément,R.J.,Rapid and Energy-Efficient Synthesis ofDisordered Rocksalt Cathodes.Adv.Energy Mater.2023,13,2203860.

Claims

1. A method for preparing an active material that can be used as an electrode, the method comprising: include: mixing the ionic compound precursors together to form a precursor mixture, exposing the precursor mixture to microwave radiation having a power and duration sufficient to form a microwaved powder comprising an ionic compound having a rock salt type crystal structure having a disordered arrangement of cations, the rock salt type crystal structure being in a cubic Fm-3m space group; and The microwaved powder is quenched to form an active material that retains the rock-salt type crystal structure at room temperature.

2. The method according to claim 1, further comprising: include: The active material is ground into a milled powder, and the milled powder is processed into a form that can be used as an electrode, including a lithium ion battery electrode.

3. The method according to any one of claims 1 or 2, wherein the ionic compound comprises a cation and an anion, the cation comprising at least one of a mobile alkali metal ion and a transition metal ion or a major element ion, and the anion comprising at least one of an oxygen ion or a fluorine ion.

4. The method of claim 3, wherein the mobile alkali metal ions comprise lithium or sodium.

5. The method according to any one of claims 3 or 4, wherein the ionic compound precursor does not include excess mobile alkali metal ions to compensate for the loss of the corresponding element during exposure to microwave radiation.

6. A method according to any one of claims 3 or 4, wherein the ionic compound precursor comprises an excess of mobile alkali metal ions to compensate for the loss of the corresponding element during exposure to microwave radiation.

7. The method according to any one of claims 1 to 6, wherein the rock-salt type crystal structure comprises a disordered rock-salt (DRX) oxide structure.

8. The method according to any one of claims 1 to 7, wherein the ionic compound: At longer correlation lengths, it is described by a cubic rock-salt-type crystal structure corresponding to a disordered arrangement of randomly distributed containing cations, and At shorter correlation lengths, it is described by a more ordered arrangement of the cations.

9. The method according to any one of claims 1 to 7, further comprising: include: The specific quenching rate (°C / min) to a temperature in the range of 77 to 323 K is selected to prevent the formation of any layered / ordered oxide impurities during the quenching.

10. The method of any one of claims 1 to 9, wherein the cathode active material comprises an oxyfluoride.

11. The method according to any one of claims 1 to 10, wherein the ionic compound precursor is selected to form a compound of formula A x M' y M″ 2-x-y O 2-z F z A cathode active material, wherein 1.05≤x≤1.35, 0.1≤y≤0.9 and 0≤z≤0.7, A is a mobile alkali metal ion, M′ is a transition metal ion or a main element ion, and M″ is a transition metal ion having a higher valence than M′.

12. The method according to claim 11, wherein A is Li + Or Na + At least one of, M' is at least one of V, Cr, Mn, Fe, Co, Ni, Mg, Al, and M" is Ti 4+ 、Zr 4+ , Nb 5+ 、Mo 6+ At least one of .

13. The method according to any one of claims 1 to 12, wherein the microwaves are carried out in an inert atmosphere.

14. A method according to any one of claims 1 to 12, wherein the microwaving is carried out in an atmosphere consisting essentially of air at ambient (atmospheric) pressure.

15. The method according to any one of claims 1 to 14, further comprising: include: contacting the precursor mixture with a heat transfer medium having an absorption spectrum resonantly tuned to the frequency of the microwave radiation; and wherein said microwaves comprise exposing said precursor mixture in thermal contact with said heat transfer medium to said microwave radiation, and: In a first stage, the heat transfer medium is heated by resonantly absorbing the microwave radiation, and the heat transfer medium transfers at least some thermal energy to the precursor mixture via conduction through thermal contact so as to heat the precursor mixture above a critical temperature at which the precursor material becomes more susceptible to absorbing microwave radiation; and In the second stage, when the precursor mixture is above the critical temperature, the microwave radiation heats the precursor to a higher reaction temperature, initiating the formation of a disordered array of ionic compounds comprising cations.

16. The method of claim 15, wherein the heat transfer medium comprises activated carbon.

17. The method according to any one of claims 15 or 16, in: Microwave Includes: Microwave-treating the precursor mixture placed in the crucible with a heat transfer medium; as well as The quenching includes placing the microwaved powder in a quenching medium after the microwaved powder is removed from the crucible.

18. The method according to any one of claims 15 to 17, wherein the quenching include: The microwaved powder is immersed in a non-reactive liquid including water, ethanol or liquid nitrogen.

19. The method of claim 2, wherein further processing does not require ball milling or mechanochemical grinding.

20. A method according to any one of claims 1 to 19, wherein a fluorinated compound is added to the mixture of ionic compound precursors and used as a sintering agent to allow faster diffusion of cations and anions during microwaving to form a rock salt type crystal structure.

21. A powder of lithium metal oxide or oxyfluoride compound for use in a rechargeable battery, the powder comprising a general formula Li x Mn' y Ti″ 2-x-y O 2-z F z , in: 1.05≤x≤1.35, 0.1≤y≤0.9, and 0≤z≤0.7 as measured by inductively coupled plasma optical emission spectroscopy (ICP-OES), and The powder comprises particles having a median particle size of about 5 μm to about 6 μm and a span ranging from about 1.4 to about 1.

8.

22. The powder according to claim 21, wherein the lithium metal oxide or oxyfluoride has a cationic disordered rocksalt (DRX) structure.

23. A powder according to any one of claims 21 or 22, wherein the median particle size is the particle size measured by sizing the particles along their longest dimension in a scanning electron microscope image.

24. A powder according to any one of claims 21 to 23, wherein the median particle size is the particle size measured for particles obtained without further processing to reduce the particle size.

25. The powder according to any one of claims 21 to 24, synthesized by the method according to any one of claims 1 to 20.

26. An electrochemical cell, the electrochemical cell include: anode; Electrolytes; and A cathode coupled to an anode via the electrolyte, wherein the cathode comprises the powder according to any one of claims 21 to 25, and wherein Li is intercalated or deintercalated from the cathode during battery operation.

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