Synthesis of partially disordered phases in rock salt materials by electrochemical pulsing

Abstract

A method for treating a rock salt material for delta phase transformation includes obtaining a synthesized disordered rock salt (DRX) material; heating the DRX material to a temperature higher than a predetermined temperature; and electrochemically pulse the DRX material for a predetermined duration within one or more predetermined voltage windows and / or at one or more predetermined current density rates.

Description

Technical Field

[0001] The present invention relates to rock salt materials having a partially disordered spinel-like “δ phase” structure, and methods for accelerating the transformation of the δ phase structure in these materials to reduce the manufacturing time for electrode engineering of these materials. Background Technology

[0002] Demand from the automotive industry, including industry-wide goals to reduce greenhouse gas emissions, has driven the shift to electric vehicles, leading to rapid growth in the lithium-ion battery industry.

[0003] Modern lithium-ion batteries typically consist of a LiNi alloy. 1-x M x O2 cathode materials are typically made from cobalt (Co), manganese (Mn), aluminum (Al), or combinations thereof. Traditionally, cathode materials are made using layered structures, which provide excellent energy density and sustained power output, crucial for automotive applications. However, these conventional cathode materials present cost and affordability issues for vehicle manufacturing applications because they require rare metals (such as nickel or cobalt), which are expensive and have limited availability. The limited availability of these rare metals also raises concerns that these materials may not be a sustainable option for meeting long-term vehicle manufacturing needs.

[0004] Efforts to identify more abundant alternative cathode material compositions led to the identification of lithium iron phosphate (LiFePO4) as a viable and sustainable alternative. However, LiFePO4 suffers from a significant energy density drawback, which is undesirable for automotive applications. Therefore, there remains an urgent need for a cathode material that is both globally abundant and characterized by high energy density, and that is commercially viable for high-throughput manufacturing. Summary of the Invention

[0005] This invention includes a method for processing rock salt materials to transform a spinel-like nanodomain structure (referred to in technical terms as a delta phase structure). The method generally includes: obtaining a synthesized disordered rock salt (DRX) material; processing the DRX material into an electrode by mixing it with carbon and a binder; assembling a lithium-ion battery cell using the treated electrode; heating the lithium-ion battery cell to a temperature above a predetermined temperature; and subjecting the DRX material to an electrochemical pulse for a predetermined duration at one or more predetermined voltage windows and / or at one or more predetermined current density rates.

[0006] DRX material is a pre-synthesized DRX material, preferably having an excess of lithium (Li) and the general formula Li. 1+x TM 1- x O 2-y Fy Further preferably, the transition metal (TM) comprises manganese (Mn), optionally in combination with one or more additional metals, wherein the DRX material is rich in manganese. This method can use small-particle DRX materials having particles with a short axis less than about 500 nanometers (nm) or large-particle DRX materials having particles with a short axis greater than about 500 nanometers. Without being bound by theory, it is anticipated that the large-particle DRX materials used in the method of this invention will most commonly have particles with a short axis in the range of about 500 nanometers to about 5 micrometers (μm), although some DRX materials with a particle size greater than about 5 micrometers may also be suitable.

[0007] The DRX material is heated to a temperature above a predetermined temperature, which is approximately the temperature required for the DRX material to withstand the high currents used during formation cycling. When the DRX material is lithium-excessive, the predetermined temperature is a high temperature that increases the lithium diffusivity of the DRX material. The predetermined temperature can be in the range of about 25°C to about 50°C, and in some cases, it can be higher than 50°C.

[0008] The voltage window can range from about 1.5 V to about 4.8 V, preferably from about 2.5 V to about 4.5 V, and more preferably from about 3.0 V to about 4.5 V. The current density ratio can range from about 100 mA / g to about 1000 mA / g, in some cases from about 100 mA / g to about 500 mA / g, and in some cases from about 250 mA / g to about 500 mA / g (normalized to the mass of the electrochemically active material).

[0009] The predetermined duration can be a predetermined time period, and can range from about 1 day to about 5 days, in some cases from about 1 day to about 2 days, and in some cases may exceed 5 days. Alternatively, the predetermined duration can be a predetermined number of pulses, and can range from 10 to 100 pulses, in some cases from 20 to 40 pulses, and in some cases from 60 to 80 pulses.

[0010] The method according to the invention may further include: charging the DRX material to an initial standard charge after heating it to a temperature above a predetermined temperature and before subjecting the DRX material to an electrochemical pulse. The initial standard charge may exceed the maximum voltage of the voltage window for subsequent electrochemical pulses, and may be approximately 4.8 V.

[0011] The method according to the invention may further include performing at least one galvanostatic charge cycle on the DRX material at the end of a predetermined duration of the electrochemical pulse. This one or more galvanostatic charge cycles are test cycles, for example, to verify that the material has been transformed, or for any other test besides cell-level use. The test cycle may include charging the DRX material to a voltage exceeding the maximum value of the voltage window used for the electrochemical pulse, and discharging the DRX material to a charge below the minimum value of the voltage window used for the electrochemical pulse. The test cycle may include charging the DRX material to about 4.8 V and discharging the DRX material to about 2.0 V. This test cycle can also serve the dual purpose of forming a solid electrolyte interphase (SEI) film at the negative electrode, which may or may not be well-suited for SEI formation by an electrochemical pulse targeting the positive electrode.

[0012] The delta-phase structure is characterized by partially disordered spinel-like domains with short coherence lengths, measuring less than 10 nm in size, with an average size of approximately 4 nm. The disorder at the 16c / 16d sites, determined by synchrotron X-ray diffraction, can be approximately 5% from a single-phase, partially disordered spinel refinement model that periodically interrupts the spinel-like ordered (rather than the rock salt parent lattice). These interruptions in spinel-like order are caused by antiphase boundaries formed between different spinel-like domains, which nucleate during transformation and impinge on each other during their growth. These boundaries consist of disordered regions approximately 1 nm thick, and are maintained because the domains form different ordered spinel-like variants on a higher-symmetry rock salt lattice. The different domains that meet at the antiphase boundaries represent eight spinel translational and rotational variants, which arise from the decrease in symmetry from the cubic rock salt lattice (Fm3m) to the spinel lattice (Fd3m). No significant disordered regions are present, although some may exist. The fully transformed δ-phase structure is characterized by: a partially disordered nanodomain structure (approximately 5% 16c / 16d disorder and domains of approximately 4 nm), thin disordered antiphase boundaries between the different spinel-like variants, and a generally homogeneous structure with minimal disorder.

[0013] This invention includes DRX materials (and processing methods thereof) with large single-crystal grains, wherein the grain size is greater than 1 micrometer (e.g., an average of 2 to 3 micrometers), and the cycling efficiency is greater than 600 Wh / kg. The δ-phase structure in these DRX materials exhibits minimal residual disorder, high order within domains, and antiphase boundaries between adjacent domains. The δ-phase domains of these manganese-rich DRX materials contain at least four to at most eight spinel variants, generated as large, unpolished grains, and are transformed into a stable, fully transformed state via electrochemical pulse sequencing. These δ-phase DRX materials can be obtained by synthesizing disordered rock salt materials (e.g., via solid-state or molten salt methods) and subsequently transformed using electrochemical pulse sequencing.

[0014] This invention includes a positive electrode active material comprising a Li-TM-O compound, the Li-TM-O compound comprising a particle distribution with a particle size (P) in the range of 100 nm ≤ P ≤ 10 μm, wherein TM is one or more transition metals; wherein the particles in the particle distribution have a crystal structure comprising a disordered rock salt (DRX) lattice, in which multiple variant δ-phase domains of a spinel-like lattice are formed, each δ-phase domain being distinct from each other, and adjacent δ-phase domains being separated by antiphase boundaries. The crystal structure may contain at least four variant δ-phase domains, optionally eight variant δ-phase domains, wherein the antiphase boundaries between them are measured to be approximately 1 nm.

[0015] The measurements for each δ-phase domain are in the range of about 3 nm to about 10 nm, wherein the δ-phase domains are distinct from each other based on at least one difference selected from: lattice orientation; occupancy of 16c / 16d Wyckoff sites; and coherence length. Differences in lattice orientation may include translational differences in lattice orientation, rotational differences in lattice orientation, and combinations thereof. The percentage of disorder at 16c / 16d sites for each δ-phase domain is about 10.2% to about 3.6%; optionally, it is 10.2% to about 3.6%. The coherence length (L) for each δ-phase domain is L ≤ 10 nm; optionally, L ≤ 5 nm; optionally, L ≤ 4 nm; and optionally in the range of 2.4 nm ≤ L ≤ 3.9 nm.

[0016] The positive electrode active material is formed from transformed DRX material, which is pre-treated by an electrochemical pulse sequence to form δ-phase domains. The pre-treated synthetic DRX material has been obtained via a prior synthesis process, which includes one of the following: a solid-state synthesis process and a molten state synthesis process. The synthesized DRX material may optionally undergo particle size reduction treatment before the electrochemical pulse sequence treatment to transform the δ-phase domains; or it may undergo electrochemical pulse sequence treatment to transform the δ-phase domains without prior particle size reduction treatment.

[0017] The particle size distribution includes a particle size (P) of 100 nm ≤ P < 10 μm; optionally, 100 nm ≤ P ≤ 500 nm; optionally, 500 nm ≤ P < 1 μm; optionally, 1 μm ≤ P ≤ 10 μm; optionally, 1 μm ≤ P ≤ 5 μm; optionally, 2 μm ≤ P ≤ 3 μm. The transition metal (TM) may contain manganese alone or in combination with one or more other transition metals, wherein the amount of manganese is 0.6 ≤ Mn ≤ 0.7.

[0018] The general description above and the detailed description below are exemplary and explanatory only, and are intended to provide further explanation of the claimed invention. The accompanying drawings are included to provide a further understanding of the invention; are incorporated in and constitute a part of this specification; illustrate embodiments of the invention; and, together with the description, serve to explain the principles of the invention. Attached Figure Description

[0019] Other features and advantages of the invention can be realized from the following detailed description provided in conjunction with the accompanying drawings:

[0020] Figure 1 A schematic diagram of the method of the present invention is provided, which illustrates the synthesized DRX material, the pulse sequence processing of the DRX material, and the δ-phase DRX material (δ-DRX) generated from the pulse sequence processing.

[0021] Figure 2 The synthesized product with the formula Li is shown. 1.1 Mn 0.8 Ti 0.1 O 1.9 F 0.1 X-ray diffraction (XRD) scan of DRX materials.

[0022] Figures 3A to 3B Energy-dispersive X-ray spectral (EDS) images of manganese, titanium (Ti), oxygen (O), and fluorine (F) in DRX materials are shown, where: Figure 3A EDS images of the synthesized solid-state DRX material are shown; and Figure 3B EDS images of the DRX material after ball milling are shown.

[0023] Figures 4A to 4B The image shown is a scanning electron microscope (SEM) image of the DRX material, in which: Figure 4A SEM images of the synthesized solid-state DRX material are shown; and Figure 4B SEM images of the DRX material after ball milling are shown.

[0024] Figures 5A to 5B An embodiment of the electrochemical pulse cycling method of the present invention for rapidly transforming the δ-phase structure within a pre-synthesized DRX material is shown, wherein: Figure 5A A schematic diagram of a typical pulse loop method is provided; and Figure 5B Further detailed, non-limiting embodiments of the pulse cycle method are provided.

[0025] Figure 6 The results of temperature differences during pulse sequence processing on the transition of the δ phase are shown.

[0026] Figures 7A to 7D The results of constant current charging cycles on different DRX materials treated with pulsed cycles having varying voltage windows are shown, wherein: Figure 7A The first set of constant current charging cycles for DRX materials in different voltage windows is shown. Figure 7B A second set of constant current charging cycles for DRX materials within different voltage windows is shown; Figure 7C It shows Figure 7B The differential capacity (dQ / dV) plot of the constant current charging cycle; and Figure 7D The third set of data is shown, illustrating the galvanostatic charging cycles of the DRX material within different voltage windows.

[0027] Figures 8A to 8C The results of galvanostatic charging cycles for different DRX materials are shown, where: Figure 8A The results of the first full constant current charging of DRX material after pulse cycling with different numbers of pulses are shown; Figure 8B It shows Figure 8A The differential capacity (dQ / dV) plot of the constant current charging cycle; Figure 8C Showing from Figure 8A The initial cyclic stability of the DRX material.

[0028] Figures 9A to 9C The results of galvanostatic charging cycles for different DRX materials are shown, where: Figure 9A The results of the first full constant current charging of DRX material after pulse cycling with different current density ratios are shown. Figure 9B It shows Figure 9A The differential capacity (dQ / dV) plot of the constant current charging cycle; Figure 9C Showing from Figure 9A The initial cyclic stability of the DRX material.

[0029] Figures 10A to 10B The time efficiency of the pulse at different magnifications is shown, where Figure 10A The relationship between delivery capacity and pulse count is shown; and Figure 10BThe relationship between delivery capacity and elapsed time is shown during 80 pulse treatments of ball-milled solid material at 50°C at different rates from 3.0 V to 4.5 V.

[0030] Figure 11 XRD scans are shown, illustrating the evolution of spinel-like structural peaks in the DRX material after various pulse cycles.

[0031] Figures 12A to 12H Synchrotron radiation XRD images of DRX material subjected to different pulse numbers are shown, where Figure 12A XRD images of the powdered raw material are shown, and the remaining figures show ex-situ XRD images of the electrodes, where the DRX material is processed with different numbers of pulse cycles, wherein: Figure 12B The results after 5 pulses are shown; Figure 12C The results after 10 pulses are shown; Figure 12D The results after 20 pulses are shown; Figure 12E The results after 40 pulses are shown; Figure 12F The results after 60 pulses are shown; Figure 12G The results after 80 pulses are shown; and Figure 12H The results after 100 pulses are shown.

[0032] Figure 13 The scanning electron nanodiffraction (SEND) pattern performed on a solid-state synthetic material processed with a pulse sequence is shown.

[0033] Figures 14A to 14F The correlation between electrochemical changes, domain growth, and ordering during the δ phase transition is shown, where: Figure 14A The relationship between the peak differential capacity of the 3V plateau after the pulse and the estimated domain size is shown. Figure 14B The relationship between the peak differential capacity of the 3V plateau after the pulse and the estimated disorder at the 16c / 16d sites is shown. Figure 14C The relationship between the length of the 4V plateau after the pulse and the estimated domain size is shown; Figure 14D The relationship between the length of the 4V plateau after the pulse and the estimated disorder of the 16c / 16d sites is shown. Figure 14E The relationship between the length of the 4V plateau during the pulse and the estimated domain size is shown; Figure 14F The relationship between the length of the 4V plateau during the pulse and the estimated disorder of the 16c / 16d sites is shown.

[0034] Figure 15 The evolution of the 4V plateau characteristic in the voltage curve is shown during pulse sequence processing from 5 pulse cycles to 100 pulse cycles.

[0035] Figure 16 The differential capacity (dQ / dV) of the 3V platform is shown as a function of the total pulse sequence processing time, which is performed as 5 to 100 pulse cycles at 100 mA / g and cyclic processing at 20 mA / g.

[0036] Figure 17 A comparison of DRX materials subjected to various pulse cycles and charging cycles is shown, with the number of cycles equal for both methods.

[0037] Figure 18 The constant current charging cycle of different DRX materials processed via pulse cycling is shown with and without additional transition pulse cycles at an ineffective voltage window above and below the ideal range of about 3.0 V to 4.5 V.

[0038] Figure 19 The synthesis of Li by molten salt method is shown. 1.1 Mn 0.8 Ti 0.1 O 1.9 F 0.1 SEM image.

[0039] Figure 20 The constant current charging cycle of various DRX materials is shown by pulse cycling with different (constant) current density ratios.

[0040] Figure 21 The constant current charge cycle of various DRX materials treated with pulse cycling is shown, wherein a constant voltage is maintained at 3.0 V / 4.5 V until it drops to 10 mA / g, instead of as Figure 20 The constant current pulse in the figure shows the results achieved during the 1st and 10th operating cycles at various cyclic temperatures.

[0041] Figure 22 The comparative discharge capacity results of various DRX materials treated according to the method of the present invention and the comparative control DRX materials treated according to conventional methods are shown.

[0042] Figure 23 SEM micrographs of molten salt synthesized DRX material are shown, revealing single crystals with uniform grain sizes of 2 to 3 micrometers.

[0043] Figure 24 HAADF-STEM and EDS imaging of the molten salt synthesized DRX material is shown, revealing a uniform distribution of manganese, titanium, oxygen, and fluorine.

[0044] Figure 25XRD imaging of molten salt synthesized DRX material is shown, confirming that the product is phase-pure DRX.

[0045] Figure 26 The first complete cycle of molten salt synthesized DRX material and a sample of the original material is shown under constant current pulses at 50°C and low constant current rate.

[0046] Figures 27A to 27D The test results of galvanostatic pulsed, molten salt synthesized DRX material are shown, in which: Figure 27A The first charge of the DRX material electrode synthesized by molten salt is shown at 50 °C and 10 mA / g, where the voltage drop at about 3.5 V is attributed to the large overpotential in the low charge state of the large-particle DRX. Figure 27B Voltage and current curves are shown for constant voltage cycling from 10 A / g to 10 mA / g; Figure 27C The duration of each pulse cycle is shown during 80 pulse cycles in a pulse sequence; Figure 27D The specific capacity for each charge and discharge pulse cycle is shown.

[0047] Figures 28A to 28C Further test results for the molten salt synthesized DRX material are shown, in which: Figure 28A The cycling performance of molten salt synthesized DRX material at 25°C after 80 pulses of constant voltage holding is shown. Figure 28B The cycling performance of molten salt synthesized DRX material at 50°C after 80 pulses of constant voltage holding is shown; and Figure 28C The continuous cycling of pulsed, molten salt synthesized DRX material at 25°C and 50°C is shown, as well as the continuous cycling of control cells that were not pulsed prior to cycling.

[0048] Figure 29 This paper presents synchrotron radiation XRD images of molten salt synthesized DRX material after a delta phase transition following pulse sequence processing.

[0049] Figures 30A to 30F The multimodal structure characterization of the δ phase in the molten salt synthesized DRX material is shown, wherein: Figure 30A Low-magnification HAADF-STEM images of pulse-cycled, molten salt synthesized DRX materials are shown. Figure 30B Showing from Figure 30A The average SEND plot of the region marked by the solid line box in the middle; Figure 30C The spatial distribution of the δ phase is shown by virtual imaging of the unique diffraction points of the Fd3m space group (scale bar: 5 nm). Figure 30D Showing from Figure 30AAtomic resolution HAADF-STEM micrographs of the region marked by the solid line box along the

[110] zone axis; Figure 30E It shows the way Figure 30D The delta-phase lattice obtained by Fourier filtering at frequency F1; and Figure 30F It shows the way Figure 30D The δ-phase lattice is obtained by Fourier filtering of the frequency F2 in the lattice.

[0050] Figure 31 The diffraction patterns obtained from selected points based on the structural information obtained by synchrotron XRD refinement of DRX materials synthesized from molten salts in the δ phase transition are shown.

[0051] Figure 32 A virtual image of the labeled scattering range of the δ-phase structure is shown, in which the unique scattering angle peak of the spinel space group Fd3m is labeled with a peak vector of (0.175, 0.250). and (0.59, 0.67) A ring.

[0052] Figure 33 Raw atomic resolution HAADF-STEM images of the unfiltered delta phase are provided. Detailed Implementation

[0053] The invention is discussed below with reference to the embodiments shown in the accompanying drawings, but the invention is not limited to those embodiments.

[0054] Unless otherwise required, the use of any and all embodiments or exemplary language (e.g., “such as”) provided herein is intended only to better illustrate the invention and does not constitute a limitation on the scope of the invention. Unless otherwise expressly stated in the context, the language in the specification should not be construed as indicating that any unclaimed element is necessary or critical to the practice of the invention.

[0055] As used herein, unless otherwise expressly specified in the context, the singular forms “a / an” and “the” include a plural number of the referred objects. Unless otherwise indicated in the context, the term “or” shall be understood as inclusive “or”. Terms such as “first,” “second,” and “third,” when used to describe multiple devices or elements, are used only to convey the relative action, location, and / or function of individual devices and do not require a specific order of such devices or elements, or any specific number or arrangement of such devices or elements.

[0056] As used herein with respect to any property or condition, the term "substantially" means that the deviation is small enough that it does not significantly diminish the identified property or condition. As will be understood by those skilled in the art, the precise degree of deviation permissible in a given situation will depend on the specific context.

[0057] Those skilled in the art will understand in the appropriate context that the term "about / approximately" is used to describe values ​​that are higher than and / or lower than the stated value or range. In some cases, this may cover values ​​in the range of approximately + / - 10%; in others, it may cover values ​​in the range of approximately + / - 5%; in still others, it may cover values ​​in the range of approximately + / - 2%; and in yet another case, it may cover values ​​in the range of approximately + / - 1%.

[0058] It should be understood that the term "comprises / comprising" as used in this specification specifies the presence of the stated features, elements, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, elements, steps, operations, elements, components and / or groups thereof, unless otherwise indicated or clearly contradicted by the context.

[0059] As used herein, the term "δ(delta) phase" is intended to describe a specific partially disordered crystalline structure formed during the cycling process of manganese-rich rock salt materials. This structure is characterized by a coherent parent rock salt lattice upon which partial spinel-like ordering occurs. This ordering means that in the δ phase, lithium is primarily located at spinel-like 8a / 16c sites, while manganese and other transition metals primarily occupy 16d-like sites. However, in the presence of both lithium and transition metals, alternating sites are significantly occupied, constituting partial disorder in the material. This structure differs from the ordered spinel phase obtained at high temperatures, such as in the material LiMn₂O₄, where lithium and manganese are essentially entirely located at 8a and 16d sites, respectively.

[0060] As used herein, the terms “disordered rocksalt” and “DRX” are intended to describe the occupancy of multiple distinct crystalline sites on the parent rockalt lattice by lithium and transition metals. Unless otherwise stated or clearly contradicted by the context, these terms are also intended to cover rockalt materials with any degree of disorder, including “completely disordered rocksalt” and “partially disordered rocksalt.” In the case of a synthetically produced completely disordered rocksalt, a high degree of disorder means the complete absence of long-range order and the presence of only one unequal cation site at which all metals are distributed. In the case of the δ-phase formed during pulse cycling, the term “disorder” is used to indicate that while some long-range order and distinct 16c / 16d sites are present, it is still possible for lithium or transition metals to be present at any given site. For example, a given site can appear in a spinel-like environment where, if it is a 16c site, lithium is typically found in the discharged material, but instead, it is occupied by manganese ions. The term “disorder” can also indicate that the local definition of which sites are 16c sites and which are 16d sites differs at different locations in the material (in addition to local disorder).

[0061] 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 serve equivalent roles in lithium (transition) metal oxide cathode materials. These elements can be active during electrochemical processes through oxidation or reduction or remain in a fixed oxidation state. Some representative examples include manganese (Mn oxidized from a 3+ state to a 4+ state) and titanium (Ti only 4+). Other metals that are not conventionally considered "transition metals," such as, but not limited to, aluminum (Al), are frequently referred to as such in battery literature because they serve a similar purpose in materials as electrochemically inert metals (e.g., titanium). Therefore, metals outside the d-block can be included in DRX formulations and, in some cases, referred to as "transition metals."

[0062] As used herein, the terms “pulsing,” “pulse sequencing,” and “pulse-cycling” are intended to refer to the formation cycling or electrochemical pulse method of the present invention by applying a high-rate limiting voltage. This will be understood to be unrelated to and different from conventional galvanostatic cycling via a wider voltage range conventionally used in the research environment, which may also be referred to herein as “charge-cycling.”

[0063] Unless otherwise stated, the enumeration of value ranges in this document is used as a shorthand for each individual value falling within the respective range, including the endpoints of the range, each individual value within the range, and all intermediate ranges contained within the entire range, each of which is incorporated into the specification as if enumerated separately in this document.

[0064] Unless otherwise stated or clearly contradicted by the context, the methods described herein may be performed in any suitable order, including: the exact order disclosed, without any intermediate 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.

[0065] This invention relates to lithium-ion batteries comprising cathode materials with a disordered rock salt structure (DRX) having excess lithium. [1] These DRX materials are defined by a nearly random arrangement of cations, including lithium and one or more transition metals, in rock salt oxides or fluorine oxides.

[0066] When synthesized using excess lithium, DRX materials exhibit impressive energy densities, contrary to the typical 1:1 equilibrium ratio of lithium to one or more transition metals provided in ordered rock-salt LiMO2 formulations under other conditions. This is because excess lithium enhances the connectivity of lattice sites, allowing lithium to precolour through low-energy pathways between lattice sites. Unlike the rare metals in typical cathode materials, these DRX materials have the advantage of being synthesized using only earth-abundant metals such as manganese and titanium.

[0067] Unfortunately, DRX materials generally exhibit lower lithium diffusivity than materials with ordered structures, characterized by slower lithium transport, for example, in DRX materials. To offset this, these DRX materials are ball-milled to reduce the synthesized powder to a sufficiently small particle size, thereby enabling higher energy densities. However, these DRX materials still exhibit low electrode-level energy densities due to the need for high carbon content in the electrodes to provide increased surface electrical contact with the cathode particles produced by ball milling of DRX materials, and potentially further reducing cycle life, which is neither ideal nor practical for automotive applications.

[0068] Low levels of inactive dopants (e.g., Li) have been found. 1+x Mn 1-x-y M y O 2-z F zVariants of manganese-rich DRX materials with x ≤ 0.2, y ≤ 0.2, z ≤ 0.2) have achieved greater success. Partial structural transformations have been observed in manganese-rich DRX materials during electrochemical cycling, with regions of the DRX material transforming into the δ phase, characterized by features such as the presence of spinel-like ordered 3V and 4V plateaus. [2,3] It has been found that this partially disordered structure increases the energy density and rate performance of DRX materials due to improved lithium transport via low-energy 3D diffusion pathways in the transformed crystal structure. Furthermore, the improved performance of these partially transformed materials is maintained for a longer period, resulting in improved cycle life compared to DRX materials without such transformations.

[0069] Compared with the typical ordered spinel structure LiMn2O4 (Li 0.5 The stable cycling of these transformed δ-phase materials is significant compared to the rapid degradation of MnO2 in rock salt compositions where lithium is intercalated into Li2Mn2O4 (LiMnO2). This degradation is attributed to a two-phase reaction, which involves MnO2 intercalation into Li2Mn2O4 (LiMnO2). 3+ The collective Jahn-Teller distortion of ions, leading to anisotropic crystal volume increases, simultaneously produces inhomogeneous volume changes, resulting in the disintegration of the cathode particles. This makes LiMn₂O₄ usable only on the 4V platform, where lithium is extracted only from tetrahedral sites. Variant DRX materials that transform into the δ-phase have attracted considerable attention because they can cycle more lithium, resulting in higher energy densities without the poor cycle life issues associated with ordered spinel structures. In the following text, the spinel-like structure resulting from the partial transformation of variant DRX materials can be simply referred to as the δ-phase structure, as used in the scientific literature on these materials.

[0070] While DRX materials with a delta-phase structure offer excellent performance characteristics, a complete conversion of DRX materials to produce a delta-phase structure typically requires at least 20 to 30 charge / discharge cycles between 2.0 V and 4.8 V. Since DRX materials maintain relatively low currents immediately after synthesis and ball milling during the initial cycles (e.g., approximately 20 mA / g), such charge / discharge cycles (i.e., charge-discharge cycles) required for a complete conversion to a delta-phase structure take an average of 2 to 4 weeks. If the aim is to use DRX materials with larger particle sizes (e.g., without ball milling) to improve cycle life and electrode energy density, a complete conversion may not be achievable at all due to the poor diffusivity of the initial DRX material. Considering the demand for high production yields in commercial battery manufacturing, it is anticipated that partially converted DRX materials with a delta-phase structure will not be commercially viable if the conversion process continues to require 2 to 4 weeks of processing, as this is unlikely to be considered commercially feasible for the necessary manufacturing yields.

[0071] DRX materials with a delta-phase structure are a promising class of Earth-abundant materials with sufficient energy density for use as cathodes in lithium-ion batteries for automotive applications. A major drawback of these transformed DRX materials is the long processing time required to form the delta-phase structure using conventional methods.

[0072] This invention provides a method for accelerating the transformation of DRX materials to produce a delta-phase structure more rapidly, while achieving properties comparable to those produced by conventional processing methods. These methods of the present invention are expected to significantly improve the commercial viability of delta-phase materials as alternative chemistry for lithium-ion battery cathodes in automotive applications, thereby reducing reliance on materials that require more expensive and less readily available metals such as nickel and cobalt in other cases.

[0073] Generally, the method according to the present invention is carried out as follows: (1) Synthesizing or otherwise obtaining a previously synthesized DRX material; (2) Using DRX material as the active material in a cathode containing DRX, carbon and plastic binder to assemble a typical lithium-ion battery cell; (3) Raising the temperature of the battery cell containing DRX above a predetermined threshold; and (4) subject the DRX material to repeated electrochemical pulse cycles for a predetermined period of time (e.g., number of pulses or duration) within one or more predetermined voltage ranges and / or at one or more predetermined current density ratios.

[0074] The present invention also includes compounds, compositions and materials prepared by the foregoing methods, and products prepared therefrom, including but not limited to positive electrode active materials having Li-TM-O (e.g., Li-Mn-O) oxide or fluorine oxide compositions, and lithium-ion rechargeable batteries containing such positive electrode active materials.

[0075] Figure 1 A schematic diagram of the method of the present invention is provided, which shows the parent DRX material synthesized in the Fm3m space group; the charge / discharge state of the DRX material during the pulse cycle in the pulse sequence processing process; and the δ-phase DRX material (δ-DRX) obtained in the Fd3m space group by the pulse sequence processing process.

[0076] The synthesized DRX material can have any given composition, but preferably has the general formula: Li 1+x TM 1-x O 2- y F yWhere x < 0.2, y < 0.2. In a preferred embodiment, the transition metal TM will comprise manganese, and optionally one or more additional metals, such that the DRX material has the following general formula: Li 1+x Mn 1-x O 2-y F y Or Li 1+x Mn 1-x-y TM y O 2-z F z TM is selected from titanium (Ti) and / or one or more other metals, such as aluminum (Al), chromium (Cr), nickel (Ni), and other similar metals. Preferably, the DRX material is rich in manganese, where manganese is the most prevalent transition metal in the composition, preferably Mn > 0.6, more preferably Mn ≥ 0.7. The synthesized DRX material may be material that has previously undergone particle size reduction treatment (e.g., ball milling) prior to the pulse cycling of the present invention, or it may be material that has not previously undergone particle size reduction treatment. The particle size-reduced DRX material (i.e., small-particle DRX material) may contain particles with an average typical short axis of less than 500 nanometers (nm), and the unreduced DRX material (i.e., large-particle DRX material) may contain particles with a typical short axis of more than about 500 nanometers. In this context, particles will include single-crystal particles with corresponding diameters (such as materials synthesized by molten salt as described herein) and secondary particles with corresponding diameters consisting of smaller primary particles.

[0077] The DRX material will be heated to a predetermined high temperature, which is approximately the practical limit of industrial-scale cycling for the corresponding DRX material given the limitations of the pulse device, the thermal stability of the electrolyte, negative electrode or other cell components, and the constraints of the cell casing. As used herein, the term "elevated temperature" means a temperature above room temperature that improves the kinetics of high-rate pulse charging and discharging, thereby increasing lithium diffusivity during pulse cycling. For example, for manganese-rich DRX materials, the predetermined high temperature could be about 50°C, as set by the half-cell device used during the development of this invention, which was observed to be approximately the practical limit of the material's formation cycling. The range of high temperatures that can be used in the methods of this invention can be from about 25°C to about 50°C, including all individual temperatures and temperature ranges therein. However, high temperatures exceeding 50°C can be used according to embodiments of the invention, depending on the specific composition discussed. Increasing the temperature of the DRX material increases lithium diffusivity, thereby facilitating the extraction of lithium from tetrahedral positions in the crystal structure to create interstitial vacancies, which in turn promote easier migration of transition metal ions (e.g., manganese) to replace these vacancies. The high temperature also allows the DRX material to withstand increased current while maintaining a substantially uniform lithium content between the surface and bulk of the cathode material.

[0078] A cell containing DRX material is heated to above-temperature levels and subjected to a series of electrochemical pulses for a predetermined duration, during which the material is repeatedly charged and discharged within one or more predetermined voltage windows and / or at one or more predetermined current density rates. The aim is to promote the transition to the delta phase prior to use in standard cells. Rapid, repetitive pulse cycling promotes the complete transition of the DRX material while minimizing degradation, with the 3V and 4V plateau characteristics enhanced in early pulse cycles and slowed down in later pulse cycles.

[0079] The predetermined duration can be a predetermined time period or a predetermined number of pulses. When the predetermined duration is a time period, it can be less than about 1 to about 2 days if it is advantageous to process DRX material faster, or about 5 days or more if it is advantageous to increase the maximum capacity of DRX material. When the predetermined duration is a number of pulses, the number of pulses can be any number of pulses that has been predetermined to produce a target processing time, a target material property, or a combination of both. For example, 20 to 40 pulses can be used if it is advantageous to process faster, and 60 to 80 pulses (or more) can be used if it is advantageous to maximize the capacity of DRX material. Without being bound by theory, while pulse sequence processing exceeding 80 pulses can further increase the maximum capacity of DRX material, the expected return on capacity increase diminishes when the total number of pulses exceeds about 80, making it impossible to justify the trade-off of additional processing time for the gain in maximum capacity.

[0080] The voltage window can range from about 1.5 V to about 4.8 V, preferably from about 2.5 V to about 4.5 V, and more preferably from about 3.0 V to about 4.5 V. The current density ratio can range from about 100 mA / g to about 1000 mA / g, preferably from about 100 mA / g to about 500 mA / g, and more preferably from about 250 mA / g to about 500 mA / g. The current density ratio can fluctuate during pulse cycling, and in some embodiments, pulse cycling can be implemented using current density ratios within several of the aforementioned ranges.

[0081] The delta-phase structure is achieved through the migration of transition metal ions between interstitial sites within the crystal structure. In embodiments of manganese-rich DRX materials, the migration of manganese ions begins with movement to adjacent vacant interstitial tetrahedral sites, primarily those that do not share a face with any other ion. This requires a high vacancy concentration, and most lithium ions are extracted at higher voltages because manganese ions are unlikely to persist at tetrahedral sites in the presence of lithium. During lithium intercalation, during discharge, manganese ions may move to new octahedral sites due to the unfavorable interaction between tetrahedral manganese ions and lithium ions sharing a face; therefore, lithium needs to be cycled rather than held at a fixed voltage. 4 Manganese ions are mainly found in Mn. 2+ or Mn 3+ The migration of any one of them to a lower oxidation state is due to Mn 4+ It is fixed in the octahedral position, therefore requiring a low charge state and low to medium voltage. 5 .

[0082] Without being bound by theory, it is anticipated that during the cycling of DRX materials, transition metals (e.g., manganese) may migrate during charging at medium to high voltages, while during discharging, they may migrate completely to new octahedral sites. Heating the DRX material to a predetermined high temperature can facilitate faster charging / discharging cycles via the pulsed cycling of the present invention, which differs from conventional charge / discharge cycles.

[0083] The following section provides a discussion of a series of tests performed on a coin cell with a lithium metal anode, in which Li... 1.1 Mn 0.8 Ti 0.1 O 1.9 F 0.1 The material was selected as a manganese-rich DRX for partial transformation of the δ-phase structure. Although the discussion below relates to working examples using this particular material, it should be understood that the method is not limited to this single example and can be applied to any selected composition, preferably a manganese-rich material. While the examples below discuss DRX materials prepared using specific synthetic methods, it should be understood that the invention is not limited to these synthetic methods, and the invention can be used with DRX (or other manganese-rich) materials synthesized via any number of various methods.

[0084] Figure 2 The synthesized product with the formula Li is shown. 1.1 Mn 0.8 Ti 0.1 O 1.9 F 0.1X-ray diffraction analysis data of the DRX material. This DRX material was synthesized via a solid-state method at 1100 °C, and carbon was used for ball milling to reduce the particle size. The synthesized solid-state material ( Figure 3A ) and ball-milled materials ( Figure 3B Energy-dispersive X-ray spectroscopy (EDS) of manganese, titanium, oxygen, and fluorine particles in the material confirmed that it was single-phase and had a uniformly distributed composition. SEM imaging revealed that the initially synthesized solid material had a relatively wide particle size distribution, including particles with measured values ​​from less than 0.5 micrometers to greater than 10 micrometers. Figure 4A The subsequently ball-milled material exhibits a more uniform particle size distribution ranging from approximately 100 nanometers to approximately 500 nanometers, including secondary particle agglomerates. Figure 4B Particle size distribution (PSD) was measured using laser diffraction particle size analysis with a Malvern Mastersizer 3000 equipped with an Aero S unit.

[0085] Figure 5A A schematic diagram of the pulse cycling method of the present invention for the delta-phase structural transition within synthesized DRX material is shown. As illustrated in the diagram, a typical pulse cycle includes a resting period of the synthesized DRX material. Preferably, during or before this resting period, the DRX material is heated to a high temperature to improve the lithium diffusivity in the DRX material. The DRX material is maintained at the high temperature throughout the pulse cycle. The pulse cycle begins with an initial charge to a standard voltage at a predetermined current density multiple, followed by discharge. Figure 5A The schematic diagram illustrates one embodiment where the standard voltage is 4.8 V, but any voltage can be used, including those corresponding to the upper limit voltage of the pulse sequence processing. The DRX material is then subjected to pulse sequence processing, during which it undergoes repeated pulse cycles for a predetermined duration within a predetermined voltage window, where the duration is a predetermined time period or a predetermined number of pulses. At the end of the predetermined duration (e.g., pulse time or pulse number), the pulse sequence processing transitions to a conventional galvanocurrent cycle, which involves charging at a predetermined current density multiplier (e.g., 20 mA / g) to a maximum charge value (e.g., 4.8 V) and then discharging to a minimum charge value (e.g., 2.0 V). Although the schematic diagram illustrates pulse sequence processing performed within a voltage window of 3.0 to 4.5 V, it should be understood that the process can be performed within different voltage windows, at different temperatures, at different multipliers, and for different durations than those shown in the schematic diagram.

[0086] Figure 5BA further detailed, non-limiting embodiment of the pulse cycling process according to the invention is shown. In this embodiment, the process is performed by heating the DRX material to a high temperature of approximately 50°C, followed by an initial resting period of approximately 6 hours (hours 0 to 6), during which the DRX material is charged to approximately 4.8 V and discharged to approximately 3.0 V over approximately 2 hours (hours 6 to 8). Then, while the DRX material is held at the high temperature, a pulse sequence processing is performed over approximately 54 hours (hours 8 to 62). During the pulse sequence processing, the DRX material is subjected to multiple pulse cycles, each pulse cycle having a charging phase followed by a discharging phase, in which the charge increases from approximately 3.0 V to approximately 4.5 V over 20 minutes, and in the discharging phase, the charge decreases from approximately 4.5 V to approximately 3.0 V over 20 minutes, such that each individual pulse cycle has a period of approximately 40 minutes, thereby generating 81 pulse cycles within the pulse sequence processing window. After pulse sequence processing, the DRX material was left to rest at a stable voltage of approximately 3.25 V for approximately 5 hours (hours 62 to 67), followed by conventional galvanocurrent cycling. During galvanocurrent cycling, the DRX material was charged from approximately 3.25 V to approximately 4.8 V over approximately 6 hours (hours 67 to 73), discharged from approximately 4.8 V to approximately 2.0 V over approximately 11 hours (hours 73 to 84), and charged again from approximately 2.0 V to approximately 3.0 V over approximately 4 hours (hours 84 to 88).

[0087] Using high temperatures (e.g., 50°C) is beneficial for promoting higher δ-phase transition rates. This was observed in tests on two DRX materials prepared according to the method of the present invention, although one material was subjected to a pulse sequence treatment at 25°C and the other at 50°C. Figure 6 As shown, when the two materials were subsequently cycled at 100 mA / g for 24 hours, the material treated at high temperature was found to exhibit a higher specific capacity.

[0088] Figure 7A It shows a formulation with Li 1.1 Mn 0.8 Ti 0.1 O 1.9 F 0.1Results of the first full galvanostatic charge-cycle of various DRX materials, wherein the materials were charged and cycled at a rate of 20 mA / g (per gram of active material) at 25 °C within a voltage range of 2.0 V to 4.8 V. Each material was treated by pulse cycling, although each material was treated with pulse sequences in different voltage windows. Each sample was subjected to pulse sequences at a moderate rate of 100 mA / g (per gram of active material) for 5 days at a high temperature of 50 °C. Each sample was treated with pulse sequences in different 1 V voltage windows, ranging from 1.5 V to 4.8 V in 0.5 V increments; although one sample was tested in a cutoff voltage window of 4.0 to 4.8 V due to electrolyte oxidation. These tests show that the transition of the delta phase structure occurs at moderate voltages, as only pulse cycling performed in the voltage window between 2.5 and 4.5 V produced significant 3 V and 4 V plateau characteristics of the delta phase structure.

[0089] Figure 7B Additional results from the first full galvanostatic charge cycle of various DRX materials are shown, each DRX material being treated again by pulse cycling along with the original (control) sample, wherein each sample was cycled at a rate of 20 mA / g at a temperature of 25°C within a voltage range of 2.0 V to 4.8 V. Similarly, each sample of the present invention was previously formed by a pulse sequence treatment for 5 days at a moderate rate of 100 mA / g (per gram of active material) and a high temperature of 50°C, although the pulse sequence treatment was performed within different voltage windows. Figure 7B As shown, while pulse sequence processing was found to promote the transition of the delta phase structure across all voltage ranges, voltages above 3V promoted a relatively greater degree of transition, as evidenced by the formation of characteristic 3V and 4V plateau features of the delta phase structure. Further observation revealed that the voltage windows of 3.0V to 4.5V and 3.0V to 4.8V exhibited almost equal behavior, indicating minimal manganese migration in the 4.5V to 4.8V range. Figure 7C The corresponding differential capacity (dQ / dV) plots for these other samples are shown, illustrating the different degrees of development of the 3V and 4V platform characteristics.

[0090] Figure 7D Additional results are shown from the first full galvanocurrent charge cycle of various DRX materials, each of which again achieves results through a combination of charging and charging with different currents. Figure 4AThe samples were processed under the same pulse cycles as in the tests, although in these tests, the three samples were processed in different 1V voltage windows within a preferred voltage window of 2.5V to 4.5V with increments of 0.5V, and the three samples were processed using pulse sequences within extended voltage windows of 2.5V to 4.0V, 3.0V to 4.5V, and 3.0V to 4.8V, respectively. Through this further testing, it was observed that the sample processed using pulse sequences within a voltage window of 3.0V to 4.5V produced results closest to those expected for a complete transition of the delta phase structure, also based on the development of significant 3V and 4V plateau characteristics.

[0091] Figure 8A The test results from the first full galvanostatic charge cycle of various DRX materials are shown. Each DRX material was treated by pulse cycling, where each sample was subjected to a pulse sequence treatment at a rate of 100 mA / g and a high temperature of 50 °C within a voltage window of 3.0 to 4.5 V. Original material (control) samples are also included. The materials were charged from 2.0 V to 4.8 V at 25 °C. However, each sample was subjected to pulse sequence treatment for different durations, in this case based on a predetermined number of pulses, where individual samples were treated for 5, 10, 20, 40, 60, 80, and 100 pulses. It can be seen that the capacity of the materials rapidly increases, achieving 195 mAh / g in only about 5 pulses, thus requiring less than one day of pulses. At this point, the typical 3 V and 4 V plateau characteristics of spinel-like ordering are already visible, indicating that the formation of the spinel-like environment begins with only a few pulses. As the number of pulses increases, these characteristics become more pronounced, with the plateau characteristics becoming flatter and longer, which can be observed in… Figure 8B The increased peak height and area are more clearly observed in the differential capacity curve. With 60 to 100 pulses, the change in the voltage curve slows significantly, with the 80 and 100 pulses showing almost identical capacity growth and plateau formation. It can be seen that the specific capacity results obtained from the 80-pulse and 100-pulse samples are so characteristically similar that the data curves of these results are... Figure 8A The pulse durations largely overlap. This supports the theory that pulses longer than 80 pulses may produce little difference. Compared to the transition requiring more than 20 days via a typical charge cycle at 20 mA / g, 80 pulses at 100 mA / g can achieve the delta phase transition in approximately 7 days.

[0092] These pulsed battery cells and the control group under long-term cycling, such as Figure 8CAs shown. Surprisingly, pulsed sequential treatment of these materials resulted in increased capacity without a corresponding negative impact on subsequent cycle life. For example, cells pulsed 80 times exhibited higher capacity than the control over the entire duration of 100 cycles. Materials were found to require 60 to 80 pulses to produce a complete transition. Although incomplete transitions were observed in samples subjected to only 20 to 40 pulses, these samples achieved maximum capacities comparable to or exceeding those of the control material treated with conventional galvanic cycling, while also displaying peaks indicating δ-phase structure in in-situ XRD scans (see [link to XRD pattern]). Figure 11 Therefore, while a pulse sequence of 60 to 80 pulses may be required to achieve a larger maximum capacity, a pulse sequence of 20 to 40 pulses may be expected if a smaller maximum capacity is considered an acceptable trade-off for reducing processing time.

[0093] Figure 9A Test results from the first full galvanostatic charge cycle of various DRX materials are shown. Each DRX material was treated by pulse cycling, where each sample was subjected to a pulse sequence of 80 pulses within a voltage window of 3.0 to 4.5 V at an elevated temperature of 50 °C. However, each sample was subjected to pulse sequences at different rates, with individual samples treated at 100 mA / g, 250 mA / g, 500 mA / g, and 1 A / g. Control samples are also provided. The materials were cycled at a rate of 20 mA / g and a temperature of 25 °C within a range of 2.0 to 4.8 V. As the rate during pulses increased from 100 mA / g to 200 mA / g, 500 mA / g, and 1 A / g, the degree of transformation and the capacity delivered in the first full cycle decreased. With higher rates, the degree of 4V feature formation and the flattening of the 3V plateau feature region both decreased, as can be seen more clearly in the dQ / dV curves shown in Figure 9B. Figure 9C The initial cyclic stability of the same sample is shown. These results indicate that pulse sequence treatment at higher currents leads to an incomplete transition similar to pulse sequence treatment with fewer pulses. For example, samples treated with a pulse sequence of 10 pulses at 100 mA / g were observed to exhibit this incomplete transition. Figure 8A ) produced from samples processed using a pulse sequence with 80 pulses at 500 mA / g ( Figure 9A The observed similar maximum capacity and platform characteristics.

[0094] Although the capacity delivered during a 100 mA / g pulse decreases slowly throughout the pulse, the capacity delivered within the pulse decreases with increasing pulse rate, such as... Figure 10A and Figure 10BAs shown. This indicates that when using high pulse magnification, the utilization rate of material near the surface of these particles is greater than that of the bulk, as is often seen in electrode materials at high magnification. This is also supported by the fact that materials with fewer pulses at low magnification ( Figure 8B Compared to materials pulsed at higher magnification, Figure 9B The DRX-like tilting feature centered at approximately 3.2 V was retained more during discharge. These findings suggest a trade-off between increasing the pulse rate to save time while ensuring all materials are accessed sufficiently to facilitate conversion. Long-term cycling data for these high-rate pulsed materials are available in... Figure 9C As shown in the figure, similar to materials pulsed at 100 mA / g for different numbers of times, materials pulsed at high rates maintained capacities comparable to or higher than the control throughout the cycle. Even materials pulsed at 500 mA / g and 1 A / g provided capacities of approximately 215 mAh / g and approximately 195 mAh / g in subsequent cycles. This constitutes pulses of less than 24 hours and 12 hours, representing a significant improvement compared to the greater than 20 days required for conventional charge cycling at 20 mA / g.

[0095] Although not bound by theory, it is expected that samples treated with pulse sequences at higher magnifications using more pulses will have a greater degree of δ-phase structure transition at the surface, although this transition will be smaller throughout the bulk material. Samples treated with pulse sequences at lower magnifications using fewer pulses will have a more uniform but not sufficiently complete δ-phase structure transition throughout the bulk material.

[0096] Advantageously, such as Figure 8C As shown in Figure 8, it has been observed that DRX materials treated with the pulse cycling method of this invention exhibit capacity curves that reach relative stability much faster in subsequent cycles than DRX materials treated with conventional constant current cycling (i.e., the "control"). In contrast, the control is observed to have an initial low capacity, followed by a significant increase in capacity before stabilization. This is particularly relevant for pulse sequence processing with fewer pulses (…). Figure 8C ) and pulse sequence processing with higher magnification ( Figure 9C The pulse cycling process was real. Although control samples were observed to require approximately three weeks (at 20 mA / g) to fully transform the δ-phase structure, characterized by a stable capacity level greater than approximately 220 mAh / g, DRX materials treated via pulse cycling were observed to produce δ-phase structures with similar capacities in as little as 1 to 2 days. It is also noteworthy that no stability trade-off was observed in the DRX materials treated via pulse cycling, as those materials maintained capacities similar to or even greater than those of conventionally treated control samples during subsequent cycles.

[0097] Figure 11 The original, ball-milled DRX material and its in-situ XRD spectra after 5, 20, and 80 pulses are shown. After only 5 pulses, in addition to the peaks common to the DRX and spinel structures (such as...),... Figure 11 Apart from the "D" marking in the spectrum, you can see the following in the spectrum: Figure 11 The text describes prominent and broad spinel-like features marked with "S". The S-marked peaks, absent in rock salt structures, are caused by cell doubling, as spinel cells are simply 2 × 2 × 2 rock salt superstructures with specific cation orders. This also explains why only the spinel peaks are broad, as spinel-like ordering can maintain short-range coherence without disrupting long-range rock salt lattices. After 20 or 80 pulses, these features become narrower and stronger. Taken together, these changes indicate a continued decrease in disorder within the spinel-like environment, coupled with an increase in coherence length. This can be interpreted as the growth and continued ordering of spinel-like "domains" within the material, which respectively reduce the width of these new features and increase their overall intensity.

[0098] Figures 12A to 12H Rietveld refinement details of XRD patterns on samples collected after 0, 5, 10, 20, 40, 60, 80, and 100 pulse cycles are shown. It is noteworthy that... Figure 12A Compared to the original material without any pulses, in Figure 12B The study observed significant spinel-like ordered diffraction features after only 5 pulses, and how the changes slowed down thereafter. Figure 12G The XRD pattern of the electrode after 80 pulses at 100 mA / g is shown. Figure 12A Compared to the original material, this material exhibits strong and broad features indicating significant spinel-like order. Table 1 below shows... Figures 12A to 12H Fine-tuned structural parameters of DRX material.

[0099] Previously, two-phase models containing spinels with short coherence lengths failed to achieve acceptable refinement. Only single-phase models containing only partially disordered spinels with short coherence lengths yielded good fits. For spinel-like domains with coherence lengths of approximately 4 nm, the best fit yielded 16c / 16d disorder values ​​as low as 2-3%. Higher 16c / 16d disorder is incompatible with the intensity of spinel-like diffraction features. The significant spinel antisite caused by manganese occupation of 8a is unlikely to occur, as this would significantly enhance the intensity of the (220) peak at approximately 12º, which has already been well captured by models with only 16c / 16d disorder. Since 16c / 16d disorder itself only leads to a decrease in the intensity of spinel-like peaks, rather than a broadening of them, disorder alone cannot explain the low coherence lengths of ordered spinel-like domains in the δ phase. Since there is no obvious residual DRX phase in the diffraction, the width of the spinel-like feature can only be explained by the ordered periodic interruption of the spinel-like feature, which comes either from the disordered “walls” between domains or from the antiphase boundary between spinel domains with different rotational or translational symmetries.

[0100] exist Figures 12A to 12H In the samples involved, as the number of pulses increased from 5 to 100, the 16c / 16d disorder decreased rapidly, while the ordered coherence length continued to increase. Between 60 and 100 pulses, the change in domain size slowed down and then stopped, consistent with the lack of change in the voltage curve at this point. The apparent rapid formation of spinel-like features, combined with the slow increase in coherence length, indicates that spinel domains form throughout the material in earlier pulse cycles and coalesce in the range of 60 to 80 pulses in later pulse cycles to form larger domains before the process stops. Figure 13 The SEND mapping performed on the pulse sequence solid-state synthesized DRX material after 80 pulse cycles is shown, which reveals the spatial distribution of the δ phase obtained by virtual imaging using the unique diffraction spots of the Fd3m space group. This spatial distribution exhibits a high degree of order throughout the material and has no residual disordered regions, consistent with XRD refinement.

[0101] Figures 14A to 14F The correlation between electrochemical changes, domain growth, and ordering during the δ phase transition is shown. Figure 14A The relationship between the peak differential capacity of the 3V plateau after the pulse and the estimated domain size is shown. Figure 14B The relationship between the peak differential capacity of the 3V plateau after the pulse and the estimated disorder at the 16c / 16d sites is shown. Figure 14C The relationship between the length of the 4V plateau after the pulse and the estimated domain size is shown; Figure 14D The relationship between the length of the 4V plateau after the pulse and the estimated disorder of the 16c / 16d sites is shown. Figure 14E The relationship between the length of the 4V plateau during the pulse and the estimated domain size is shown; and Figure 14F The relationship between the length of the 4V plateau during the pulse and the estimated disorder of the 16c / 16d sites is shown.

[0102] Figures 14A to 14F The findings shown indicate that the clearest structural relationship to the evolution of the δ phase transition is the correlation between the peak differential capacity (dQ / dV) of the 3V plateau characteristic during charging and the coherence length (which is considered an estimate of the domain size), as... Figure 14A As shown in the diagram, the 3V plateau-like feature observed in the cycle becomes flatter as the estimated domain size increases in these materials, resulting in larger peaks. Figure 14C The relationship between coherence length and delivery capacity above 3.5 V can be seen, thus providing a simpler proxy for the degree of transition.

[0103] An equivalent measure can be obtained from the capacity of the 4V region within the pulse itself (although the capacity is slightly less than that in a cycle), indicating that the point at which the transition stops can be determined during the pulse sequence without requiring a normal charging cycle. The evolution of the voltage curve during the pulse, including the initial increase and cessation of that increase in the 4V characteristic, is shown in the figure. Figure 15 As shown, in contrast to the coherence length, the refined 16c / 16d disorder rapidly decreases to below 5% and appears to be independent of electrochemical changes after approximately 40 pulses. These refinement details and estimated coherence lengths and 16c / 16d disorder levels are given in Table 1 above.

[0104] By using the differential capacity peak of the 3V platform as a proxy for the degree of transformation, we can compare the evolution of control and pulse sequence-treated materials. Figure 16 The peak differential capacity of the control and pulse-sequence-treated materials, along with the cumulative time consumed in either a charge cycle treatment at 20 mA / g or a pulse-sequence treatment at 100 mA / g, were plotted. As shown in the figure, 2 to 3 days of the present invention's pulse-sequence treatment (40 pulses) achieves a transition comparable to that of conventional charge cycles (control) requiring 20 days under other conditions, and 7 days of the present invention's pulse-sequence treatment (80 pulses) achieves a transition comparable to that of conventional charge cycles (control) requiring 50 days under other conditions. Due to Figure 16 The pulse sequence processing shown is only at 100 mA / g, so it is expected that the δ phase transition can be further accelerated by optimizing the pulse sequence processing procedure.

[0105] Figure 17The electrochemistry of the DRX material after different numbers of pulse-sequence treatments at 100 mA / g is shown as a comparison with that of a control cell after the same number of conventional charge cycles at 20 mA / g. It is evident that the formation of the 4V plateau feature occurs to a similar degree after the same number of pulse / charge cycles, although the 4V plateau feature in the control stops growing after approximately 40 charge cycles, while the plateau feature in the pulse-sequence-treated material continues to grow until approximately 60 pulse cycles.

[0106] This indicates that the effectiveness of a single pulse cycle is roughly equivalent to that of a full charge cycle, thus supporting the view that not all parts of the voltage window contribute equally to the delta phase transition. However, the evolution of the 3V plateau differs significantly between pulse-sequence processing and charge cycling. In pulse-sequence-processed materials, the 3V plateau becomes flatter and longer, but does not change significantly after additional pulse cycles. Conversely, the 3V characteristic of charge-cycled materials becomes shorter with additional charge cycles. During charge cycling, the 3V plateau characteristic shortens, while the capacity of the 4V plateau characteristic continues to increase, resulting in the material's capacity peaking after 20 to 30 charge cycles, although the delta phase transition is not completed at this point. While not bound by theory, this is expected to be explained by material degradation or impedance growth that occurs at low voltages but within the voltage range (3.0 to 4.5 V) used in pulse-sequence processing.

[0107] Figure 18 The results of further tests conducted to determine whether additional cycling might have a further effect on the partially transformed DRX materials are presented. The results show the first full-current-constant charge cycles of three individual DRX materials, each processed via pulse-cycle treatment, where each sample was initially subjected to a pulse sequence treatment at a rate of 500 mA / g within a voltage window of 3.0 to 4.5 V at a high temperature of 50 °C. This initial pulse cycling resulted in a partial transformation of the delta-phase structure in each sample. One of these samples was then tested without any further treatment, while the other two were subjected to further treatment. The first of the further-treated samples underwent an additional pulse sequence treatment for an additional 24 hours within a voltage window of 2.0 to 3.25 V, and the second of the further-treated samples underwent an additional pulse sequence treatment for an additional 24 hours within a voltage window of 3.75 to 4.8 V. Subsequent tests on the three samples produced highly similar outputs, indicating that 3.0 to 4.5 V is the optimal voltage window for pulse cycling of DRX materials, with little effect on the delta-phase structure transformation from additional pulse sequence treatment in other voltage ranges.

[0108] Additional tests were conducted to investigate the partial transformation of the δ-phase structure in large-particle DRX materials. Li 1.1Mn 0.8 Ti 0.1 O 1.9 F 0.1 Also selected as a manganese-rich DRX material, although for these tests, this DRX material was synthesized in potassium chloride (KCl) via a molten salt (MS) method. 6 Using the same precursors as in earlier tests, a more uniform morphology could be obtained than that that could be achieved through solid-state synthesis. This DRX material underwent no particle size reduction treatment (e.g., no ball milling), resulting in particles with typical short axes of 2 to 5 micrometers, such as... Figure 19 The SEM image of the particles obtained is shown.

[0109] Figure 20 The results of the first full galvanostatic charge cycle of large-particle DRX material after pulse cycling are shown, where both samples underwent a pulse sequence treatment of 80 pulses within a voltage window of 3.0 to 4.5 V at a high temperature of 50 °C. However, to compensate for the larger particle size, the pulse sequence treatment of these materials was performed at a lower current density rate. The first of the test samples was pulsed at a rate of 50 mA / g, and the second of the test samples was pulsed at a rate of 20 mA / g. The results show that no transformation was observed in the sample pulsed at 50 mA / g, while a transformation was found in the sample pulsed at 20 mA / g, although the treatment of this transformed sample took approximately 4 weeks.

[0110] Figure 21 Additional test results are shown, which were conducted to evaluate whether the increased rate capacity of the DRX material during the delta-phase structural transition would enable the material to effectively balance at 3.0 V or 4.5 V if pulse cycling with a constant voltage rise or fall to a certain current multiplier (as opposed to constant current pulses). These large particle samples were pulse-cycled using constant voltage pulses at 3.0 V / 4.5 V and maintained to + / - 10 mA / g. These tests showed that after less than 2 weeks of treatment, the material underwent a complete (or almost complete) transition, with a specific capacity of approximately 225 mAh / g when cycled at 50 °C and approximately 175 mAh / g when cycled at 25 °C.

[0111] Figure 22Comparative results are provided for three samples treated by pulse cycling and a control (large particle) sample treated by conventional charging cycling. The first of the pulse-cycled samples was prepared as small particle material (by ball milling) and treated with a pulse sequence of 80 pulses at a rate of 100 mA / g and a temperature of 50 °C within a voltage window of 3.0 to 4.5 V; the other two of the pulse-cycled samples were prepared as large particle samples (without ball milling) and treated with a pulse sequence using a constant voltage pulse of 3.0 / 4.5 V held up to + / -10 mA / g at 50 °C.

[0112] The samples subsequently cycled at 25°C were then tested, with the exception of one large-particle sample which was cycled at 50°C. The control sample was observed to have relatively low capacity, never fully converting to achieve usable capacity. Meanwhile, the samples prepared according to the pulse cycling process exhibited relatively high capacity and considerable stability. Surprisingly, the large-particle sample cycled at 50°C showed essentially similar properties to the small-particle sample cycled at 25°C, which is atypical for battery cycling at high temperatures. This indicates that large-particle DRX / δ-phase materials can be stabilized at high temperatures when treated with pulse cycling, which will be quite important as the availability of large-particle materials will significantly simplify electrode engineering.

[0113] Li was also synthesized via the molten salt method. 1.1 Mn 0.8 Ti 0.1 O 1.9 F 0.1 As a manganese-rich material, further tests were performed to investigate the δ-phase transition in large-particle DRX materials. The synthesis temperature was increased to 1100 °C in the molten salt method, the holding time was reduced to 20 minutes, a relatively high KCl to precursor ratio of 3:1 was used, along with the same solid-state precursors (Li₂CO₃ and transition metal oxides) commonly used in the synthesis of DRX. This yielded spherical single-crystal Li₂. 1.1 Mn 0.8 Ti 0.1 O 1.9 F 0.1 DRX particles have a diameter of 2 to 3 micrometers, such as Figure 23 The SEM images are shown in the image. Almost no particles smaller than 1 micrometer in diameter were observed. Figure 24 TEM-EDS imaging of these particles confirms the uniform distribution of manganese, titanium, and fluorine in the material. Figure 25 XRD imaging was shown, thus confirming that the product is phase-pure DRX.

[0114] With longer diffusion lengths of these molten salt synthesized materials, at a distance approximately 10 times greater than the radius, it was found that the capacity of the material per pulse was significantly lower than that of the solid-state material when using a current of 100 mA / g. This indicates that not all materials can be obtained in 2- to 3-micron particles. Figure 26 As shown, when a lower current of 20 mA / g is applied, more capacity is delivered in each pulse, at the cost of the pulse taking several weeks to complete, and the material reaches a capacity of 184 mAh / g after the pulse.

[0115] To reduce the processing time for these larger particles, the pulse sequence processing was modified to use pulse cycles with a constant voltage hold until the lower limit of the current is reached. The improved pulse sequence processing begins with an initial charge at 10 mA / g to 4.8 V, followed by 80 pulse cycles with constant voltage holds at 3.0 V and 4.5 V to 10 mA / g. This improved pulse sequence processing allows for a slower initial pulse, providing additional time for Li+ cycling in the initial DRX material. However, as the transformation proceeds and the material diffusivity increases, higher rates can be expected to be maintained in more constant voltage pulses, resulting in a higher average current density and an increased average current density in subsequent cycles. Figure 27A The first charge of the molten salt material electrode at 50 °C and 10 mA / g is shown, where the voltage drop at about 3.5 V is attributed to the large overpotential in the large-particle DRX under low charge. Figure 27B Voltage and current curves are shown for a constant voltage cycle from 10 A / g to 10 mA / g. Figure 27C The duration of each pulse cycle is shown during the 80 pulse cycles. Figure 27D The specific capacity for each charge and discharge cycle is shown. The higher charge capacity is attributed to electrolyte oxidation events, which temporarily approach or exceed 10 mA / g during voltage hold at 4.5 V and 50 °C. The improved pulse sequence processing takes approximately 9 days, while a typical pulse cycle for charge and discharge voltage hold lasts approximately 3 hours.

[0116] The DRX material, produced by the improved pulse sequence, underwent subsequent cycle performance testing using 80 pulse cycles with a constant voltage hold. Figure 28AThe 1st, 50th, and 100th full charge and discharge cycles of these tests are shown. The clearly formed 3V and 4V plateau features demonstrate that the improved pulse sequence processing successfully transformed the DRX material into the delta phase, thus providing an initial discharge capacity of 174 mAh / g. The voltage profile of this material is very similar to that of smaller-particle, ball-milled solid-state materials, but with two important differences. First, in the molten composite material, the 3V and 4V plateau features appear sharper than the smooth features present in the solid-state material. Second, the lower capacity of the larger-particle material is primarily due to the lower capacity at the end of the 3V plateau feature, while the 4V plateau feature exhibits a similar capacity to that seen in the ball-milled material.

[0117] The stability of large-particle DRX materials was further tested by cycling them through an improved pulse sequence processing procedure using 80 pulse cycles held at a constant voltage, while simultaneously maintaining the material at 50°C after each pulse. Figure 28B As shown, the material delivers 225 mAh / g and 700 Wh / kg in the first cycle at 50°C, with slight decreases at the 50th and 100th cycles. This demonstrates that high capacity can still be achieved in large-particle materials, even if some capacity is unavailable at room temperature due to kinetic limitations.

[0118] Figure 28C The continuous cycling of the large-particle material at 25 °C is shown, resulting in some initial capacity gain, after which the capacity remains significantly stable. During cycling, the capacity of the material increases from 174 mAh / g to over 190 mAh / g before stabilization, resulting in a capacity exceeding 600 Wh / kg. From 50 to 100 cycles, the capacity remains almost constant, with no significant voltage decay or other changes in the voltage profile. The capacity retention at 50 °C is also quite good, retaining 94.7% and 90.3% of the initial capacity at the 50th and 100th cycles, respectively. To confirm that the δ phase formed here is indeed equivalent to the δ phase formed in the ball-milled solid material, additional synchrotron XRD imaging was performed on the molten salt material recovered after the constant-voltage pulse sequence processing. Figure 29 As shown, refinement of these XRD patterns confirms that this molten salt synthesized material, similar to the solid-state synthesized material, has a structure with an estimated average spinel-like domain size of approximately 5 nm and a high degree of order (e.g., 16c / 16d disorder of less than 5%). The additional peak at approximately 10° in these XRD patterns is attributed to diffusion diffraction of carbon in the electrode.

[0119] Figure 30A A low-magnification HAADF-STEM image of a typical large molten salt particle, approximately 2 micrometers in size, is shown after the pulse. Figure 30B The text shows that in Figure 30A The average value of the SEND diffraction patterns collected within the solid-line box marked in the middle, where sharp diffraction spots indicate high crystallinity of the particles after pulse cycling and suggest that the particles remain single-crystal. Structural information was refined from synchrotron XRD of the same sample. Figure 29 ), and index the diffraction pattern from the selected point and Figure 31 Provided by China. Figure 30C By integrating the unique diffraction peaks of the δ phase from each SEND pattern and over the entire scattering range acquired (from 0.175 Å) −1 Up to 1.2 Å −1 The virtual image obtained within is normalized to account for thickness in depicting the δ-phase formation range. The radial integral range is within... Figure 32 As shown in the figure, a uniform transition from the DRX to the δ phase exists, with no large retained disordered regions. (Collected from...) Figure 30A Atomic resolution HAADF-STEM micrographs of the region marked by the solid line box along the

[110] zone axis were taken to study the cation ordering in the δ phase. Figure 30D This shows a HAADF-STEM micrograph with a low-pass Butterworth filter, the original image of which is shown in [the original image]. Figure 33 Provided in [the image / source]. The Fast Fourier Transform of this HAADF-STEM micrograph is [data / format]. Figure 30D The inset in the lower right corner shows the marked frequency components (F1) and (F2) belonging to a lower symmetry spinel-like (Fd3m) lattice. Filtering the marked frequency components (F1) and (F2) yields... Figure 30E and Figure 30F The lattice fringes shown are derived from the parent DRX phase (Fm3m) through filtering. Figure 30D The frequency components not marked with circles in the illustration were obtained. The parent lattice is in Figure 30E and 30F The pattern shown is an underlaid diagonal. Figure 30E The spinel lattice fringes in the image show multiple half-lattice vector translations representing antiphase boundaries. One such boundary is formed by... Figures 30D to 30F The dashed boxes in the figure indicate these boundaries. These boundaries are formed when one ordered spinel variant comes into contact with another, distinguished by one of the rotational or translational symmetry operations lost in the spinel symmetry of the parent rock salt. Domain size estimates obtained by counting the average number of lattice fringes between antiphase boundaries range from 3 to 10 nanometers.

[0120] The microstructure of the DRX δ phase originates from the way it is formed from the parent DRX material. The common oxygen sublattice and higher symmetry of rock salt allow for a variety of possible spinel variants, consistent with the norm of the quotient group of the space group of rock salt and spinel. These variants differ in that they occupy 16c / 16d Wyckoff sites on the Fd3m lattice. The δ phase has been observed to consist of nanoscale domains of these variants separated by antiphase boundaries, where these domains achieve high order with no significant residual disorder regions, such as... Figure 1 As shown. Without being bound by theory, it is thought that the formation of the δ phase may begin in multiple different locations in the rock salt material, independent of adjacent atomic nuclei, and these nuclei grow to contact each other.

[0121] In the tests described in this paper, complete transformation of the DRX samples was observed after pulse sequence processing, with the resulting δ-phase microstructure and electrochemical voltage distribution remaining remarkably stable. The near-complete formation of the δ-phase after pulse processing is evident in the following SEND images: Figure 13 (Data shown in Supplementary Figure S7) illustrates the results of solid-state synthesis of DRX materials; Figure 30C The results of molten salt synthesis of DRX materials are shown. This material does not exhibit significant large-length-scale (>1 nm) disordered regions, as seen in... Figure 30E and Figure 30F The HAADF-STEM micrographs show lattice fringes corresponding to the spinel phase (Fd3m space group) predominantly in almost all areas.

[0122] Some residual disorder is visible at the boundaries of these well-ordered spinel domains, consistent with the small amount of 16c / 16d site disorder required for a good fit of the XRD pattern, but the individual domains appear highly ordered. Although the average diffraction pattern from the SEND image shows sharp peaks, indicating that high crystallinity was maintained after the formation of the δ phase... Figure 30B However, the unique XRD peaks of the Fd3m phase (with odd-numbered exponents) exhibit selective broadening, indicating that the ordering introducing these reflections has a small domain size. Estimating the crystallite size from the width of these odd-numbered exponent peaks using the Scherrer equation yields a domain size of approximately 4 nanometers, which is consistent with... Figure 30D and Figure 30E The spinel domains shown in the Fourier-filtered atomic resolution STEM-HAADF imaging are consistent.

[0123] The presence of domain boundaries and the overlap of different rotated or translated domains may prove difficult to discern the degree of (or)disorder in the delta phase structure by visually examining STEM micrographs. However, if distinct phases such as DRX, spinel, and layered structures are present, these regions can be clearly identified in local diffraction patterns in SEND imaging. These phases can be distinguished from overlapping spinel domains by the tandem use of SEND and HAADF-STEM measurements. While not bound by theory, the delta phase is expected to comprise highly ordered spinel domains separated by thin antiphase boundaries measured to be approximately 1 nm, with no evidence of a significant proportion of other phases.

[0124] The efficiency of pulsed sequence processing in forming the delta phase over a finite voltage range is consistent with the manganese migration kinetics and spinel transformation thermodynamics in Li-TM-O (Li-Mn-O) oxide and fluorine oxide systems. Manganese migration is most favorable when manganese is in a low valence and adjacent to tetrahedral sites that do not share any faces with the octahedron occupied by another transition metal. This configuration is referred to as the 1-TM (tetrahedral) site. In manganese-rich DRX having the compositions described herein, assuming a random cation configuration, a given tetrahedral site has a 26.6% chance of being adjacent to both 1Mn and 3Li (“1-Mn” sites). Considering this high probability that the tetrahedron is the 1-Mn site, and the presence of 8 tetrahedra around each manganese, there should be a very large potential for manganese to jump during the first charge of the DRX structure.

[0125] This explains why a significant spinel-like order was observed as early as the fifth pulse cycle in the pulse sequence processing of DRX materials. As the transformation proceeds, the amount of manganese experiencing migration-favorable conditions is expected to decrease, as the formation of spinel-like order locks manganese ions into a configuration without such 1-TM tetrahedra (ordered spinel LiMn₂O₄ has only 0, 2, and 4-TM sites). Given the reduced number of potential transitions, the growth of the δ phase is expected to slow dramatically, with the δ phase essentially completely transformed after approximately 60 to 80 pulse cycles.

[0126] The preferred voltage window for efficient formation of δ-DRX can be based on the combined requirement for low-valence manganese and lithium vacancies. In order to allow low-energy jumps of manganese adjacent to the 1-Mn site, the other three octahedral sites shared with this tetrahedron should be free of Li+ during charging, and the manganese valence should remain below 4+, as Mn4+ exhibits very low mobility. During discharge, the octahedral sites are refilled with lithium to destabilize the tetrahedral octahedron of manganese and push it into other adjacent octahedral sites (or possibly back to its original position), resulting in a spinel-like configuration of octahedral manganese. These conditions require the material to access a range of lithium contents, [1] leaving most octahedra vacant; and [2] prompting lithium to reoccupy these octahedra (<3.5 V).

[0127] These conditions can explain the observations of the pulse sequence processing described in this paper. For example, the similarity of the DRX material pulsed at 3.0 to 4.5 V and 3.0 to 4.8 V is reasonable because the average valence of manganese is already close to 4+ at 4.5 V, thus allowing for transitions to vacant Mn during the final charging phase. 3+ Very few. This also explains why discharge cutoff at low voltages does not lead to a transition when relatively fewer octahedral vacancies are present. It can also be noted that the stoichiometry of this material over the effective voltage range is similar to that of spinel Li. 1.1–x Mn 0.8 Ti 0.1 O 1.9 F 0.1 The stoichiometry is such that (where 0.5 ≤ x ≤ 0.8). Therefore, this region may be effective without being bound by theory, as it combines a strong driving force toward spinel with favorable kinetic conditions for manganese migration.

[0128] Material synthesisThe solid-state materials used in the tests described in this paper were synthesized using conventional solid-state methods. Li₂CO₃ (Sigma Aldrich, 99.9%), Mn₂O₃ (Alfa Aesar, 99%), TiO₂ (Sigma Aldrich, 99.9%), and LiF (Alfa Aesar, 99.9%) were used as precursors. All precursors were mixed stoichiometrically with ethanol in a Retsch PM 200 planetary ball mill at 250 rpm for 12 hours. A 10% excess of Li₂CO₃ was added to compensate for possible losses during the synthesis at 1100 °C. The precursors were dried overnight in an oven at 70 °C and then granulated. In the case of molten salt synthesis, the same precursors were manually mixed with KCl (Sigma Aldrich, 99%) at a precursor:KCl weight ratio of 1:3 for 10 minutes prior to granulation. In both molten salt and solid-state synthesis, pressed particles were heated to 1100°C at a rate of 10°C / min in a tube furnace under an argon atmosphere and held at that temperature for 20 minutes, then allowed to cool naturally to room temperature. For molten salt materials, the heated particles were washed twice with deionized water and once with ethanol, then dried overnight under vacuum at 70°C. For solid-state materials, the prepared particles were hand-milled before ball milling with carbon. All powders were transferred to and stored in an argon-filled glove box. SEM images of the synthesized and ball-milled powders were collected using a Zeiss Gemini Ultra-55 analytical field emission SEM. The SEM images were analyzed to measure particle size. The "major axis" was defined as the longest dimension of the particle in the image, while the "minor axis" was the longest dimension perpendicular to the major axis. The particle size P measured on the SEM image is the area equivalent diameter (DA), also known as the circular-equivalent diameter, which is the diameter of a sphere that has the same projected area as the particle projection seen on the SEM image.

[0129] ElectrochemistryThe cathode membranes used in the tests described in this paper consisted of active material, Super C65 (Timcal), and polytetrafluoroethylene (PTFE, DuPont, Teflon 8A) in a weight ratio of 70:20:10. Prior to cathode fabrication, the solid material was ball-milled with Super C65 under an argon atmosphere for 1 hour using a SPEX 800M mixer / mill. The molten salt material was then manually mixed with Super C65 in a mortar using a pestle for 20 minutes. The manually mixed molten salt and the ball-milled carbon-containing solid mixture were then manually mixed with PTFE in a mortar using a pestle. The mixture was then rolled into a film in a glove box. The active material loading density of all membranes was approximately 3 to 4 mg / cm³. 2 A commercially available 1M LiPF6 solution in ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio 1:1) was used as the electrolyte. A glass microfiber filter (Whatman) was used as the separator. FMC lithium metal foil was used as the negative electrode. The coin cells were assembled in a glove box and tested on an Arbin battery test instrument. Specific capacity was calculated based on the weight (70%) of the active material in the positive electrode film. Pulsing was performed in a multi-zone temperature chamber connected to the same Arbin test instrument, where the temperature chamber was set to either 25°C or 50°C, and cycling was performed using a combination of typical constant current or constant voltage procedure steps. Samples synthesized from molten salt were pulsed at + / -10 A / g using an initial constant current step until a cutoff of 4.5 V or 3.0 V was reached, followed by constant voltage holding until the current dropped to + / -10 mA / g. After pulses, the cells were directly switched to cycling at 25°C. For galvanostatic intermittent titration (GITT) measurements, each step in the voltage curve corresponds to a galvanostatic charge / discharge of 10 mAh / g at a rate of 20 mA / g, followed by a 6-hour relaxation step.

[0130] Non-in-situ synchrotron radiation X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS)Synchrotron radiation XRD and XAS spectra were measured at beamline 7-BM of the National Synchrotron Light Source II (NSLS-II). To avoid the diffuse diffraction characteristics of PTFE coinciding with the spinel-like ordered (111) peak, an in-situ positive electrode film for XRD was prepared by mixing the active material Super C65 and polyvinylidene fluoride (PVDF) in NMP at a weight ratio of 7:2:1 and casting it onto aluminum. The resulting electrode film was dried overnight and then assembled into a cell for pulse / cycle testing. After pulse / cycle testing, the cell used for preparing the in-situ sample was held at the desired voltage for 6 hours. The cell was then disassembled and the positive electrode film was washed with diethyl carbonate (DEC). The cyclic PVDF film for XRD was peeled off the aluminum to allow encapsulation into a Kapton capillary. The PTFE film for XAS was sealed in Kapton tape for transport and measurement. All synchrotron radiation XRD finishing was performed using the TOPAS software package. A single-phase spinel structure model was used to refine the XRD patterns of the cyclic and pulsed electrodes. As previously reported on δ- and γ-LiFeO2-type ordering, the reflection peaks generated by spinel-type ordered structures with odd-numbered l-values ​​were selectively broadened. The broadening factor applied to the spinel-like peaks was used in the Scherrer equation to estimate the domain coherence length. Ex-situ XAS measurements at the K-edges of manganese and titanium were performed on the same film in transmission mode as those used in the electrochemical measurements. Energy calibration was performed by simultaneously measuring the spectra of manganese and titanium foils. Data processing was performed using the Athena software package.

[0131] Transmission electron microscopy sample preparationTo prepare ex-situ samples for SEND and HAADF-STEM characterization, the same intact electrodes used for electrochemical testing were collected after pulse and washed with diethyl carbonate (DEC) and transferred under argon. Thin layers suitable for transmission electron microscopy (TEM) imaging were prepared using a dual-beam focused ion beam (FIB) method on a Helios G4 UX instrument at the National Center for Electron Microscopy (NCEM) in Berkeley. To protect the sample, a 100 nm thick layer of platinum (Pt) was deposited on the surface using a 5 kV electron beam and a beam current of 1.6 nA before lifting. Subsequently, a 1.5 μm layer of platinum was deposited on top of the electron beam-deposited Pt using a gallium (Ga) ion beam at 30 kV and 0.26 nA. After lifting the thin layer from the positive electrode film, it was welded to the FIB grid using platinum. The thickness of the thin layer was reduced to approximately 1 μm using a gallium ion beam accelerating at 30 kV and a current of 0.75 nA. To prevent beam damage, the thickness was subsequently reduced to approximately 100 nanometers using an accelerating voltage of 5 kV and a current of 0.15 nA. A final thinning step was performed using a 2 kV ion beam. To remove the amorphous layer and further thin to obtain a region approximately 50 nanometers thick, a low-energy argon ion beam of 900 eV was used for 8 minutes in a nanomilling machine.

[0132] Scanning electron nanodiffraction (SEND) SEND spectra were collected using a ThemIS 60-300 microscope equipped with a Gatan K2 detector at NCEM Berkeley. The indicated convergence half-angle was 0.62 mrad. SEND spectra were analyzed using the py4DSTEM package, version 0.14.8. To reconstruct a virtual image of the spinel phase spatial extent, integration was performed only on the unique peaks of the spinel phase. These radial extents are... Figure 32 The peaks are marked in the middle. The scattering angles of these peaks are (0.175, 0.250) Å. -1 and (0.59, 0.67) Å -1 By starting from 0.175 Å -1 Up to 1.2 Å -1 The region between the scattering angles is integrated, and the thickness of the integrated virtual image is normalized.

[0133] Atomic resolution HAADF-STEM Atomic resolution HAADF-STEM imaging was performed using a TEAM I microscope (a Thermo Fisher Scientific Titan 80-300 kV with dual aberration correction) at NCEM Berkeley. The microscope was operated at 300 kV with an indicated convergence angle of 30 mrad. The particles were tilted to the

[110] zone axis prior to atomic resolution imaging. The original HAADF images were obtained in […]. Figure 33As shown. Adaptive local thresholding of 51 pixels was performed in MATLAB to remove any non-uniform illumination from the image. To remove high-frequency noise, a third-order low-pass Butterworth filter with a cutoff frequency of 160 pixels was applied in the frequency domain. The filtered HAADF-STEM image is shown in... Figure 30D As shown in the image. Bragg filtering was performed to identify the spinel lattice by filtering the two spinel peaks in the FFT of the HAADF-STEM micrograph, as... Figure 30D As illustrated in the illustration, the HAADF-STEM image is first windowed using a Tuckey (or cone cosine) window. This windowing reduces spectral leakage and edge artifacts, thus improving the accuracy of subsequent frequency-based analysis. Subsequently, a filter mask is applied to the spinel frequency components in Fourier space, and an inverse Fourier transform is performed to obtain the spinel lattice in real space. Only half of the spinel peaks are considered for filtering because conjugate points contain the same information in the Fourier transform of the real-valued image through Hermitian symmetry. Figure 30D The spinel peak marked in the middle Figure 30E and Figure 30F The image shows a spinel lattice, where the spinel peak labeled F1 is filtered in... Figure 30E The image shows the filtering of the spinel peak labeled F2. Figure 30F As shown in the diagram. Following a similar method, the parent DRX lattice is stacked on the obtained spinel lattice. Figure 30D In the diagram, the frequency components corresponding to the corresponding DRX grid in Fourier space are marked as unmarked circles. These mathematical filtering operations are implemented using internal MATLAB scripts.

[0134] Energy dispersive X-ray spectroscopy Energy-dispersive X-ray (EDX) elemental maps were obtained using a FEI TitanX 60-300 transmission electron microscope located at the NCEM facility in Berkeley. Spectra were collected at a Bruker-FEI Super-X four-quadrant detector at an accelerating voltage of 300 kV. Different elemental maps were plotted using the Mn-Kα, Ti-Kα, OKα, and FKα peaks. The EDS data were analyzed using Bruker Esprit software.

[0135] This invention provides an electrochemical pulse cycling method for in-situ formation of a δ-phase structure in manganese-rich DRX. Although conventional processes for forming a δ-phase in DRX materials are impractically too long for commercial purposes, the method according to the invention sufficiently accelerates the δ-phase transformation to make these materials commercially usable.

[0136] Advantageously, the method of the present invention is also applicable to activating micron-sized single crystals, thereby eliminating the need for ball milling of DRX materials using carbon. This large-particle, low-surface-area material exhibits near-perfect cycling. No significant capacity or voltage decay occurs during pulses, meaning that the transition can be facilitated without compromising subsequent cycling. Once the δ-phase transition is complete, minimal structural changes occur, contrary to the voltage decay observed in lithium and manganese-rich layered cathodes. The lack of activation and degradation of large single crystals makes δ-DRX materials commercially viable as abundant and inexpensive cathode materials on Earth.

[0137] Using synthesized micron-sized materials, and correspondingly reducing the amount of carbon (which is typically introduced during the ball milling of the material), can lower the production cost of composite cathodes for DRX materials. The improved cycle stability of these larger particles can also significantly reduce the amount of dedicated particles and electrolyte engineering required to achieve long cycle life. This also allows for the use of voltage windows that forgo lower cutoff voltages below 2V, thus eliminating the low-voltage tail. These materials further enable the production of thermally safe and stable manganese-based DRX cathodes with a reasonable rate capability of approximately 200 mAh / g and greater than 600 Wh / kg, exceeding 100 charge / discharge cycles.

[0138] Although the 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; the scope of the invention is not limited to the disclosed embodiments; and the scope of the 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 embodiments disclosed herein, without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0139] All publications, patents, and patent applications mentioned herein are expressly incorporated herein by reference to the extent necessary for understanding or completing the disclosure of this invention, to the same extent that they are individually incorporated. No express or implied license is granted to any of the patents included herein.

[0140] 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 this disclosure.

[0141] References

Claims

1. A positive electrode active material, comprising: Li-TM-O compounds comprising a particle distribution with a particle size (P) in the range of 100 nm ≤ P ≤ 10 μm, wherein TM is one or more transition metals; The particles in the particle distribution have a crystal structure comprising a disordered rock salt (DRX) lattice, in which multiple variant δ-phase domains of a spinel-like lattice are formed, each δ-phase domain being distinct from one another, and adjacent δ-phase domains being separated by antiphase boundaries.

2. The positive electrode active material according to claim 1, wherein... The measured value of the antiphase boundary is approximately 1 nanometer.

3. The positive electrode active material according to any one of claims 1 to 2, wherein... The measured values ​​for each δ-phase domain range from approximately 3 nanometers to approximately 10 nanometers.

4. The positive electrode active material according to any one of claims 1 to 3, wherein... The δ-phase domains are distinct from each other based on at least one difference selected from: lattice orientation; occupancy of 16c / 16d Wyckoff sites; and coherence length.

5. The positive electrode active material according to any one of claims 1 to 4, wherein... The δ-phase domains are distinct from each other based on at least one lattice orientation difference, which is selected from: translational differences in lattice orientation, rotational differences in lattice orientation, and combinations thereof.

6. The positive electrode active material according to any one of claims 1 to 5, wherein... The percentage of disorder at 16c / 16d sites in each δ phase domain is approximately 10.2% to approximately 3.6%; optionally, it is 10.2% to approximately 3.6%.

7. The positive electrode active material according to any one of claims 1 to 6, wherein... The coherence length (L) of each δ-phase domain is L≤10 nm; optionally, L≤5 nm; optionally, L≤4 nm; and optionally in the range of 2.4 nm≤L≤3.9 nm.

8. The positive electrode active material according to any one of claims 1 to 7, wherein... The crystal structure contains at least four variant δ-phase domains, and optionally eight variant δ-phase domains.

9. The positive electrode active material according to any one of claims 1 to 8, wherein... The particle distribution includes a particle size (P) of 100 nanometers ≤ P < 1 micrometer; optionally, 100 nanometers ≤ P ≤ 500 nanometers.

10. The positive electrode active material according to any one of claims 1 to 8, wherein... The particle distribution includes a particle size (P) of 1 micrometer ≤ P < 10 micrometers; optionally, 1 micrometer ≤ P ≤ 5 micrometers; optionally, 2 micrometers ≤ P ≤ 3 micrometers.

11. The positive electrode active material according to any one of claims 1 to 10, wherein... The transition metal (TM) comprises manganese alone or a combination of manganese with one or more other transition metals.

12. The positive electrode active material according to any one of claims 1 to 11, wherein... The transition metal (TM) contains a manganese content of 0.6 ≤ Mn ≤ 0.

7.

13. The positive electrode active material according to any one of claims 1 to 12, wherein... The positive electrode active material is formed from DRX material, which has been previously treated by an electrochemical pulse sequence to form δ-phase domains.

14. The positive electrode active material according to claim 13, wherein... The DRX material is obtained by prior synthesis including one of the following: solid-state synthesis method; molten state synthesis method.

15. The positive electrode active material according to claim 13, wherein... The synthesized DRX material may optionally undergo a particle size reduction process prior to electrochemical pulse sequence processing; or be transformed via electrochemical pulse sequence processing without prior particle size reduction processing.

16. A method for treating DRX material in a positive electrode active material according to any one of claims 1 to 15, comprising: Obtain the previously synthesized DRX material; Heat the DRX material to a predetermined temperature; and The DRX material is subjected to an electrochemical pulse for a predetermined duration at a predetermined current density ratio within a predetermined voltage window.

17. The method of claim 16, wherein The DRX material is a DRX material synthesized prior to this process.

18. The method according to claim 16 or 17, wherein The DRX material is a lithium-excess material.

19. The method according to any one of claims 16 to 18, wherein The DRX material has the general formula Li 1+x TM 1-x O 2-y F y , where TM contains manganese.

20. The method according to any one of claims 16 to 19, wherein The DRX material is rich in manganese.

21. The method according to any one of claims 16 to 20, wherein The DRX material comprises particles with a short axis of less than 500 nanometers.

22. The method according to any one of claims 16 to 20, wherein The DRX material comprises particles with short axes ranging from about 500 nanometers to about 5 micrometers.

23. The method according to any one of claims 16 to 22, wherein The predetermined temperature is approximately the temperature required for the formation cycle of the DRX material.

24. The method according to any one of claims 16 to 23, wherein The DRX material is a lithium-excess material, and the predetermined temperature is a high temperature that increases the lithium diffusion rate of the DRX material.

25. The method according to any one of claims 16 to 24, wherein The predetermined temperature is in the range of about 25°C to about 50°C.

26. The method according to any one of claims 16 to 25, wherein The predetermined temperature is approximately 50°C.

27. The method according to any one of claims 16 to 26, wherein The voltage window ranges from about 1.5 V to about 4.8 V.

28. The method according to any one of claims 16 to 27, wherein The voltage window ranges from about 2.5 V to about 4.5 V.

29. The method according to any one of claims 16 to 28, wherein The voltage window ranges from about 3.0 V to about 4.5 V.

30. The method according to any one of claims 16 to 29, wherein The current density ratio is in the range of about 100 mA / g to about 1000 mA / g.

31. The method according to any one of claims 16 to 30, wherein The current density ratio is in the range of about 100 mA / g to about 500 mA / g.

32. The method according to any one of claims 16 to 31, wherein The current density ratio is in the range of about 250 mA / g to about 500 mA / g.

33. The method according to any one of claims 16 to 32, wherein The predetermined duration is a predetermined time period.

34. The method of claim 33, wherein The time period is approximately 1 day to approximately 5 days.

35. The method of claim 34, wherein The time period is approximately 1 to approximately 2 days.

36. The method of claim 34, wherein The time period is approximately 5 days.

37. The method according to any one of claims 16 to 32, wherein The predetermined duration is the predetermined number of pulses.

38. The method of claim 37, wherein The number of pulses is between 10 and 100.

39. The method of claim 38, wherein The number of pulses is 20 to 40.

40. The method of claim 38, wherein The number of pulses is 60 to 80.

41. The method according to any one of claims 16 to 40, further comprising: After heating the DRX material to the predetermined temperature, and before applying an electrochemical pulse to the DRX material, the DRX material is charged to an initial standard charge.

42. The method of claim 41, wherein The initial standard charge exceeds the maximum charge of the voltage window.

43. The method of claim 41, wherein The initial standard charge is approximately 4.8 V.

44. The method according to any one of claims 16 to 43, further comprising: At the end of the predetermined duration of the electrochemical pulse, the DRX material is subjected to at least one constant current charging cycle.

45. The method of claim 44, wherein The constant current charging cycle includes: The DRX material is charged to a charge exceeding the maximum value of the voltage window, and the DRX material is discharged to a charge below the minimum value of the voltage window.

46. ​​The method of claim 44, wherein The constant current charging cycle includes charging the DRX material to about 4.8 V and discharging the DRX material to about 2.0 V.

47. The DRX material processed by the method according to claim 16.

48. The DRX material of claim 47, wherein the DRX material comprises particles with a short axis of less than about 500 nanometers.

49. The DRX material of claim 47, wherein the DRX material comprises particles with short axes ranging from about 500 nanometers to about 5 micrometers.

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