Lithium-rich nickel manganese oxide battery cathode materials and methods

Abstract

A method of forming an active material for a positive electrode of a lithium-ion battery includes quenching a powder of the active material in water. The water may include an additive solvated therein. The active material may include layered lithium rich nickel manganese oxide.

Description

[Technical Field]

[0001] The present invention relates to cathode materials for lithium-ion batteries, and more specifically, to lithium-rich nickel manganese oxide cathode materials and their preparation methods. [Previous Technology]

[0002] Cobalt-containing cathode materials in lithium-ion batteries account for a significant portion of the cost of modern battery cells, and cobalt is a key cost driver. The complexity of the cobalt supply chain makes it an unstable commodity. [Summary of the Invention]

[0003] According to various embodiments, a method for forming an active material for a positive electrode of a lithium-ion battery includes quenching powder of the active material in water. The water may include additives dissolved therein. The active material may include layered lithium-rich nickel-manganese oxide.

[0004] In another embodiment, the lithium-ion battery cell includes a negative electrode, an electrolyte, and a positive electrode. The positive electrode comprises a layered lithium-rich nickel-manganese oxide active material. The specific discharge capacity of the battery cell increases by at least 10% after 50 electrochemical cycles at a charge rate C / 20 and a discharge rate C / 2, and after 50 electrochemical cycles at a discharge rate C / 2, the specific capacity of the battery cell at a discharge rate C / 20 is at least 230 mAh / g. The particles of the active material powder may have at least one of a carbon coating or passivated oxygen bonds on their surface.

Implementation Method

[0021] As set forth herein, various aspects of the invention are described with reference to exemplary embodiments and / or accompanying drawings, in which exemplary embodiments of the invention are illustrated. However, the invention may be embodied in many different forms and should not be construed as limited to the exemplary embodiments shown in the drawings or described herein. It should be understood that the various disclosed embodiments may refer to specific features, elements, or steps described in connection with a particular embodiment. It should also be understood that, although described with respect to a particular embodiment, specific features, elements, or steps may be interchanged or combined with alternative embodiments in various undescribed combinations or arrangements.

[0022] Various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings to refer to the same or similar parts. Reference to specific examples and embodiments is for illustrative purposes and is not intended to limit the scope of the invention or the claims.

[0023] A range may be expressed herein as “about” a particular value and / or “about” another particular value. When such a range is expressed, examples include from a particular value and / or to another particular value. Similarly, when a value is expressed as an approximation by using the preceding terms “about” or “substantially”, it should be understood that the particular value forms another pattern. In some embodiments, a value of “about X” may include a value of + / - 1% X. It should further be understood that the endpoints of each range are significant and independent of the other endpoints.

[0024] Various embodiments of the present invention provide a method for rapidly and cost-effectively producing crystallographically stable and highly durable variants of layered lithium-rich nickel manganese oxide (“LLRNMO”). In one embodiment, the LLRNMO material has the formula Li[Ni xLi( 1 / 3 - 2x / 3)Mn( 2 / 3 - x / 3 )]O 2, wherein the nickel content x is between 0 < x < 0.5, such as 0.125 ≤ x ≤ 0.425, preferably 0.19 < x < 0.26. Another way to write the LLRNMO material formula is Li z(Mn yNi 1 - y) 2 - zO 2, wherein z is greater than 1.05 and less than 1.25, and y is in the range of 0.55 to 0.83 (i.e., where 1.05 < z < 1.25, and 0.55 ≤ y ≤ 0.83). In some embodiments, the LLRNMO material may have a Li:metal oxide (Mn and Ni metal oxide) ratio ranging from about 1.4 to about 1.6. Another way to represent this material is by the formula y(LiMO₂∙(1-y)LiMnO₃), where y is in the range of 0.8 to 1, and M is Ni or a combination of transition metals including at least one of Ni and Al, Ti, Fe, or Cr. In all cases, when producing such lithium-rich cathode materials, they typically exhibit a two-phase, two-phase composite, or solid solution structure, with evidence of the coexistence of a trigonal LiMO₂R₃-m (α-NaFeO₂ structure) phase and a monoclinic Li₂MO₃-C₂ / m phase, both of which have repeating layers consisting mainly of Li layers, oxygen layers, and transition metal (and some excess Li) layers. The distribution of transition metal sites of Ni, Mn, and Li in this structure has been found to depend on the synthesis method. Not wanting to be bound by a particular theory, the inventors believe that a more uniform distribution of Li, Mn, and Li atoms in the transition metal sites would result in a more electrochemically stable material exhibiting higher capacity, better transport kinetics, less capacity decay, and less loss of average voltage during discharge.

[0025] The original form of LLRNMO material (such as that prepared before its first charge) exhibits an X-ray diffraction pattern consistent with two different phases: one is, for example, a hexagonal phase and the second is a monoclinic phase. The hexagonal phase, also known as the rhombohedral phase, has the same space group as the hexagonal phase. The materials of embodiments of the present invention have exhibited high (>200 mAh / g) specific capacity and a high functional voltage window (2.0-4.8 V) without the need for cobalt (e.g., it can be a cobalt-free cathode material). In one embodiment, quenching the LLRNMO material in a liquid containing water to ultrafast cool the material produces a crystal structure for energy storage that is superior to those previously reported in prior art literature. These two phases can coexist within the material in different phase circular regions or can exist in a layered / superlattice arrangement.

[0026] LLRNMO materials have extensive literature and electrochemical properties specific to their structure. The main drawbacks of these materials include low rate-discharge capability and poor capacity retention due to structural instability, resulting from oxygen loss and the migration of transition metal ions during cycling. Several complex synthetic pathways using frameworks, dopants, or surface modifications and coatings on LLRNMO can help mitigate oxygen loss and thus improve functionality. Recent studies have shown that O₂-type oxygen structures can prevent the migration of unwanted irreversible transition metal ions, thereby significantly improving capacity retention.

[0027] Despite these detailed structural studies and related advanced synthesis techniques, there is almost no consistency in the synthetic routes used. Table 1 is a graph showing the LLRNMO cathode synthesis route, quenching technique, x-values ​​used to prepare these samples, and some performance metrics from these studies. In Table 1, "DC" refers to discharge capacity. Table 1 source# way Precursor Quenching X- 3rd DC (mAh / g) 4 Sol-gel, followed by combustion Acetates and nitrates Metal 0.50 170 0.33 225 0.25 230 0.17 235 5 The precipitate was then burned. Nitrates and hydroxides Slow cooling 0.33 128 0.42 138 0.50 155 Metal 0.33 135 0.42 150 0.50 145 0.17 225 0.25 255 0.33 250 0.42 235 0.50 200 7 hydrothermal Acetates, nitrates and hydroxides none 0.10 200 9 The precipitate was then burned. Nitrates and hydroxides LN2 0.33 190 0.33 110 10 The precipitate was then burned. Nitrates and hydroxides LN2 0.50 11 The precipitate was then burned. Nitrates and hydroxides Slow cooling 0.20 12 Sol-gel, followed by combustion Nitrates and glycine LN2 0.50 0.40 13 Sol-gel, followed by combustion Acetates and impurities Not mentioned 0.20 twenty one The precipitate was then burned. Chloride and hydroxide LN2 0.25 220 0.25 260 0.25 215 0.25 260 twenty two Sol-gel, followed by combustion Acetates and impurities Not mentioned 0.2 210 0.2 215 26 The precipitate was then burned. hydroxide LN2 0.33 28 The precipitate was then burned. sulfates and carbonates Not mentioned 0.20 29 The precipitate was then burned. Sulfates, carbonates and impurities Not mentioned 0.23 180 30 precipitation Sulfates and impurities Not mentioned 0.2 215 Sol-gel Acetate Not mentioned 215 hydrothermal Acetate and PVP Na 225

[0028] Table 1 shows the three main synthetic routes commonly used in LLRNMO cathodes: precipitation followed by combustion, hydrothermal synthesis, and sol-gel followed by combustion (which we used in this study). Table 1 also shows the commonly used precursors: nitrates, hydroxides, acetates, and impurities.

[0029] As can be seen in Table 1, the number of studies investigating the effect of nickel compositions on the performance of LLRNMO cathodes decreases over time; very few studies investigate multiple nickel compositions or nickel compositions with the formula Li[NixLi(1 / 3 - 2x / 3)Mn(2 / 3 - x / 3)]O2 with a nickel content below x=0.2. Table 1 also shows significant inconsistencies across the synthetic routes used in the studies. Furthermore, few studies provide detailed comparative assessments of the effects of synthetic methods on the performance of LLRNMO cathodes. In LLRNMO materials, the ordering and disorder of transition metals can be important, and both composition and synthetic techniques can provide mechanisms for influencing the degree of structural order and disorder. These compositional and synthetic variations can exert electrochemical properties, such as different defect concentrations, which can significantly affect the properties of LLRNMO cathodes.

[0030] Without being bound by a specific theory, it is believed that when a sample is quenched in liquid nitrogen, the particles are immediately encapsulated and shielded by the nitrogen gas, similar to the Leidenfrost effect, which significantly reduces the heat transfer rate. In the prior art, lithium-containing cathode materials used in lithium-ion batteries are not exposed to moisture because water leaches lithium from such cathode materials and forms a lithium hydroxide coating on the material. Furthermore, water is known to cause malfunctions in lithium-ion battery packs, such as those containing lithium iron phosphate cathode materials.

[0031] In contrast, the inventors unexpectedly determined that water quenching does not negatively affect the LLRNMO cathode and does not cause lithium leaching from such LLRNMO cathodes. Water quenching induces bubble nucleation and dissipative vaporization, which effectively increases the heat transfer rate. Therefore, water quenching should have a heat transfer rate approximately two orders of magnitude greater than that of liquid nitrogen quenching. Furthermore, the water and additives, when combined (i.e., other materials are soluble in water), can react with the high-temperature LLRNMO, resulting in advantageous surface end-capping and / or coatings due to the quenching process, which enhance electrochemical stability and durability when used in lithium-ion battery packs.

[0032] Furthermore, in many prior art quenching methods described above, quenching is performed on pellets of material that have been pressed, sintered, or partially sintered, and these pellets are large, intact objects (e.g., having a width of approximately several centimeters). In contrast, in the embodiments of the present invention shown in Figures 15A and 15B, loose and / or ground powder having aggregates with an average diameter of 20 micrometers or smaller (e.g., 0.1 to 20 micrometers, for example, 0.1 to 1 micrometer or 1 to 20 micrometers) is quenched such that when the particles come into contact with a quenching liquid (e.g., water), all the material cools rapidly and at substantially the same rate. Each aggregate is composed of microcrystals with an average size of about 25 nm to about 500 nm, such as in the range of 50 nm to 200 nm, as shown in Figures 15C-15D. Each microcrystal may contain a single crystal of LLRNMO material. The microcrystals may be partially fused together in the aggregate or completely fused together in the aggregate. If the crystallites are completely fused within the agglomerate (i.e., within the powder particles), each crystallite comprises a single crystal grain of the powder particle, which is separated from other single crystal grains within the same powder particle by grain boundaries. The average grain size of the powder particles can range from about 25 nm to about 500 nm, such as in the range of 50 nm to 200 nm. As shown in Figure 15C, the agglomerate can be relatively porous, allowing water to reach the crystallites within the agglomerate.

[0033] The cathode material powder particles can be quenched at an average rate of at least 50°C / s, such as 50°C / s to 10,000°C / s. For example, the cathode material can be quenched at a rate of 87.5°C / s to 8750°C / s, such as at least 1750°C / s, for example, 1750°C / s to 8750°C / s, including 4375°C / s to 8750°C / s. Therefore, the cathode material can be quenched from its combustion temperature (e.g., sintering temperature) of at least 900°C to the temperature of water containing the quenching medium (e.g., a room temperature water bath at 25°C) in 10 seconds or less, such as 0.1 seconds to 10 seconds, such as 0.5 seconds or less, including 0.2 seconds or less, such as 0.1 to 0.2 seconds. Alternatively, the cathode material can be quenched from 900°C to room temperature (e.g., 25°C) in 1 to 10 seconds. The quenching process may include a slow cooling rate of several seconds that occurs when powder is removed from the boiler environment and rapidly conveyed to the quenching bath environment.

[0034] In some embodiments, the water in the quenching bath may include additives. In one embodiment, quenching may be carried out in a quenching aqueous solution comprising about 0.01 to about 1.0 mol / L of an acid, such as about 0.1 to 1.0 mol / L, or about 0.5 to 1.0 mol / L, such as sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, citric acid, acetic acid, phosphoric acid, orthophosphoric acid, combinations thereof, or the like. The acid may be configured to stabilize the surface of the LLRNMO particles by reacting with and / or passivating the dangling bonds and / or OH end groups of the LLRNMO powder particles quenched in water containing acid additives.

[0035] In some embodiments, acid quenching can lead to the formation of a spinel structure (e.g., a surface layer) on the surface of the LLRNMO powder particles. The spinel structure can form a framework that stabilizes the particles and provides a three-dimensional pathway for lithium diffusion. Specifically, the acid can induce an exchange of Li ions in the particles with H ions in the acid, and subsequent structural transformation of the particle surface, thereby resulting in the formation of the spinel surface layer.

[0036] In another embodiment, in addition to or instead of acid additives, the quenching solution may include carbohydrate additives. For example, carbohydrates may include sugars such as fructose, galactose, glucose, lactose, maltose, sucrose, combinations thereof, or the like. In some embodiments, the quenching solution may include about 0.01 to about 1.0 mol / L, such as about 0.1 to 1.0 mol / L or about 0.5 to 1.0 mol / L of carbohydrate additive. During the quenching process in water containing carbohydrate particles, the carbohydrates can form a dense amorphous carbon coating on the surface of the LLRNMO powder particles. The carbon coating may be permeable to Li ions but impermeable to the electrolyte of a Li-ion battery. The carbon coating may also allow for volume changes in LLRNMO crystallites during battery charging and discharging.

[0037] Compared to conventional quenching methods, the water quenching process can cool LLRNMO materials more uniformly and rapidly. The quenching process can produce LLRNMO material powder with the desired crystal structure and particle size. For example, the LLRNMO material being quenched can be a loose powder with an average particle size of about 1 µm or less, such as an average particle size range of about 0.02 µm to about 1 µm, or about 0.05 µm to about 0.5 µm. In some embodiments, the LLRNMO material may include crystalline phases and / or microcrystals with an average crystal size in the range of about 25 nm to about 500 nm, such as about 50 nm to about 300 nm. Each powder particle may contain one or more microcrystals. The loose, sintered, and quenched powder particles can be incorporated into a binder (e.g., a carbon binder) to form a cathode electrode for a Li-ion battery.

[0038] LLRNMO materials (e.g., sintered and quenched loose powder particles) may have a hexagonal principal phase and a monoclinic secondary phase. Therefore, the ratio of hexagonal phase content to monoclinic phase content is greater than 1, such as at least 2, for example, 2 to 20. For example, sintered and quenched LLRNMO materials may have a superlattice structure comprising hexagonal principal phase layers separated by monoclinic secondary phase interlayers. Alternatively, sintered and quenched LLRNMO materials may comprise a hexagonal phase matrix containing monoclinic phase nanoregions (i.e., regions less than one micrometer wide). Mn and Ni may be homogeneously distributed within the crystal structure of the LLRNMO material (e.g., excess Mn, Ni, and Li are homogeneously and uniformly distributed on transition metal lattice sites).

[0039] The crystal structure of the formed LLRNMO material can be altered by electrochemical cycling. For example, when the LLRNMO material is used as an active material in an electrochemical battery, the monoclinic phase may no longer be present at a detectable level after the first charge / discharge cycle. It is believed that the monoclinic phase can be consumed during lithium-ion insertion and / or extraction.

[0040] Material synthesis

[0041] Several methods for producing LLRNMO active materials and the unexpected performance results therein are described below according to various embodiments. In some embodiments, a static, batch firing process is used to form the active material. In other embodiments, continuous processing or mixing methods may be used to form the active material.

[0042] According to various embodiments, a cathode active material represented by the formula Li z(Mn yNi 1-y) 2- zO 2 is formed, where z=1.16 and y=0.7. Specifically, a gel / solid synthesis method can be used to produce active material precursors. The synthesis of the active material includes mixing stoichiometric amounts of Li(CH 3COO)*2H 2O, Mn(CH 3COO) 2*4H 2O and Ni(NO 3) 2*6H 2O in water to form a solution, while heating the solution at 100°C until a gel is formed. The gel is poured into a dedicated alumina crucible and calcined at 400°C for 90 minutes to produce ash free of organic matter. The resulting ash is ground and calcined again in the crucible at 500°C for 3 hours, then allowed to cool naturally, and then ground again to form a powder. Under ambient fume hood conditions, the powder is calcined (e.g., sintered) at 900°C for 24 hours in a box furnace. After calcination, the powder is quenched. Specifically, quenching includes water quenching (Hq), which is performed by inverting the process crucible over a stirring vessel filled with room temperature water. In some embodiments, the water includes a solvent additive. Two other slower quenching methods are used as more common comparative variations: sheet metal quenching (Mq) and liquid nitrogen quenching (Lq). Mq relates to applying material to a metal foil. Lq is a slower quenching method than Hq because it is believed that the N2 gas generated during quenching forms an insulating envelope around the hot material and reduces heat transfer. After quenching, the active material is filtered and dried in a vacuum oven at a temperature not exceeding 50°C.

[0043] Table II shows the various active material samples and the names used to refer to each sample. Table II Li Zhongzhi x Quenching type metal foil liquid nitrogen water 0.25 25Mq 25Lq 25Hq 0.17 17Mq 17Lq 17Hq 0.10 10Mq 10Lq 10Hq 0.05 0.5Mq 05Lq N / a 0.00 N / a 00Lq N / a

[0044] Material Characterization

[0045] Figure 1A is an illustration of the exponentially normalized and shifted XRD pattern of the original LLRNMO active material powder with the following formula: Li[Ni xLi( 1 / 3 - 2x / 3)Mn ( 2 / 3 - x / 3 )]O 2, where the nickel content x=0.25. This formula can also be written as Li z(Mn yNi 1 - y) 2 - zO 2, where z=1.16 and y=0.7, and formed using Hq, Lq and Mq (i.e., water, liquid nitrogen and metal quenching, respectively). Figure 1B includes a top plot showing the trend between lattice parameter "a" and the nickel content of the sample, and a bottom plot showing the trend between lattice parameter "c" and the nickel content of the sample, which were obtained by single-phase Ritter-Wade fitting.

[0046] As shown in Figure 1A, the X-ray diffraction evaluation of the materials reveals that they possess a hexagonal (e.g., rhombohedral) phase associated with the LiNiO2 space group (R-3m) and a monoclinic phase associated with the Li2NiO3 space group (C2 / c). This indicates that all samples have the expected layered structure. Notably, the monoclinic phase diffraction peaks are most distinct in the samples produced by the Hq method, indicating that this method produces a more defined crystal structure.

[0047] A superlattice peak indicating this compound family is also present near 22°. The XRD patterns of the 10Lq and 10Mq samples also show significant peaks to the left of their (101), (104), (015), (107), and (108) peaks, indicating the presence of phase impurities with similar structures and larger lattice parameters than the bulk phase. The lack of other peaks suggests that, in this case, all impurities are isomorphic to the bulk phase of the material. The XRD pattern of the 10Hq sample shows only small additional (107), (108), and (110) peaks. Although less obvious in the XRD patterns, the 17Mq and 25Mq samples also show signs of phase impurities; small secondary peaks are present to the left of the (104) peak and the (107) peak, respectively. In addition, the (108) peak of the 25Mq sample has a shoulder to its left. Careful examination of the maximum value (104) indicates the differences between the secondary peaks in this group. The secondary peaks of the 25Hq and 10Mq samples suggest that the isomorphic impurities may be nickel-rich layered structures, while the peaks of the 10Lq and 25Mq samples suggest that the isomorphic impurities may be ordered rock salt. This data suggests that these peak groups should have two sources: one is an additional layered phase and the other is contaminated rock salt. In this paper, "secondary layered phase" will refer to local regions with compositional differences and corresponding structural deformations, especially regions with higher nickel content and the resulting larger lattice parameters, while "contaminant" will refer to the rock salt phase.

[0048] The lattice parameters of the powders in Figure 1A were obtained using Ritterweird refinement based on a single phase. The weighted R values ​​of all samples were less than 6, and the lattice parameters of the known compositions fell within the range seen in the literature (see S1 available online at stacks.iop.org / JES / 167 / 160518 / mmedia, which is incorporated herein by reference in its entirety). Refinement was limited to single phases. Figure 1B shows that, regardless of the quenching technique, the lattice parameter "a" decreases with the nickel content in the sample. The lattice parameter "c" generally exhibits the same trend, but deviates from this trend for samples quenched by liquid nitrogen at x=0.10, 0.17, and 0.25. Quenching methods at x≥0.10 indicate that slower quenching methods produce larger lattice parameters "a," and the lattice parameter "c" exhibits the same overall trend, except for the 10Lq and 17Lq samples.

[0049] Electrochemical Testing

[0050] The synthesized LLRNMO active material (i.e., sintered and quenched loose powder) was mixed with Super-P carbon black and polyvinylidene fluoride (PVDF) at a ratio of 8:1.2:0.8, so that the active LLRNMO accounted for 80% of the total mass. The resulting blend was then mixed into approximately 15 ml of N-methyl-2-pyrrolidone for at least one hour. Two 10-minute sonication treatments were then performed, followed by further mixing of the resulting slurry on a hot plate at 100°C for at least 30 minutes. The mixture was then sprayed onto a 10 × 10 cm, 10 μm thick aluminum foil heated to above 100°C. The foil was then air-dried overnight in a 70°C oven, and samples were then taken onto a circular electrode plate. The resulting perforations were then used to fabricate a 2032-type button cell, which included a lithium foil anode, a 1.0 M LiPF6 50 / 50 ethyl carbonate / dimethyl carbonate solution as the electrolyte, a Celgard battery separator, a 0.5 mm stainless steel gasket, and a wave spring on the cathode side to ensure mechanical contact within the battery. Each button cell was assembled and sealed using a button cell press in a dry, low-oxygen argon atmosphere.

[0051] The LAND battery tester is used to perform potential-limited constant current testing on the button cells produced by the method described above using a constant current. At least three cells of each variant are cycled between 2.0 V and 4.8 V at ambient temperature. The cells are charged and discharged twice at approximately C / 20 rate to adjust the cathode material. Then, the cells are charged and discharged 25 times at a C / 20 charge rate and a C / 2 discharge rate. These 27 cycles can be referred to as one cycle, and all cells undergo two cycles.

[0052] Figure 2A shows the specific discharge capacity of the sample with x=0.25 (i.e., Li[Ni xLi( 1 / 3 - 2x / 3)Mn ( 2 / 3 - x / 3 )]O 2 sample, where x=0.25) during cycling, and Figures 2B-2D show the full charge and discharge curves of button batteries including samples of 25Hq, 25Lq and 25Mq respectively. Figure 3A shows the specific discharge capacity of the sample with x=0.17 during cycling, and Figures 3B-3C show the full charge and discharge curves of button batteries including samples of 17Hq, 17Lq and 17Mq respectively. Figure 4A shows the specific discharge capacity of the sample with x=0.10 during cycling, and Figures 4B-4C show the full charge and discharge curves of button batteries including samples of 10Hq, 10Lq and 10Mq respectively.

[0053] Table III below shows the discharge capacity (DC) of the samples during cycling and the C / 20:C / 2 ratio of DC28 / DC27. Rate capability is obtained by obtaining the ratio of C / 20 discharge capacity to C / 2 discharge capacity, such as the discharge capacity in cycles 27 and 28. Note that discharge cycles 1, 2, and 28 are at the C / 20 rate, while discharge cycles 3, 27, and 54 are at the C / 2 rate. Table III Discharge capacity (mAh g) -1 ) (C / 20):(C / 2) DC28 / DC27 DC1 DC2 DC3 DC27 DC28 DC54 25Hq 186 200 190 217 258 245 1.19 25Lq 180 175 152 160 200 160 1.25 25Mq 127 120 80 90 125 75 1.39 17Hq 195 205 175 197 255 205 1.29 17Lq 110 120 107 150 190 160 1.27 17Mq 110 120 90 150 210 170 1.40 10Hq 35 40 37 110 140 165 1.27 10Lq 75 77 60 75 120 87 1.60 10Mq 75 80 55 75 125 90 1.67

[0054] Referring to Figures 2A-2C, the x=25 samples synthesized by different quenching methods exhibit different relative specific charging capacities in the first charging 4.5 V steady-state segment. Specifically, the steady-state segment of 25Hq accounts for 60.7% of the initial charging capacity, the steady-state segment of 25Lq accounts for 44.4%, and the steady-state segment of 25Mq accounts for only 34.5% of the capacity.

[0055] The initial capacity of 25Hq was the highest at 186 mAh g⁻¹ for the x=0.25 sample, and the lowest at 127 mAh g⁻¹ for 25Mq. As seen in Table III, all x=0.25 samples, except for the 25Mq sample, showed improved capacity during cycling. Of all three samples, 25Hq showed the greatest capacity increase. During cycling, the 25Mq sample also exhibited severe voltage decay, with the voltage dropping below 3 V. Although the 25Hq and 25Lq samples also had an inflection point at 2.8 V on their discharge curves, they did not show this severe voltage decay. No voltage decay was observed in the C / 20 discharge of the 25Hq and 25Lq samples; however, the 25Mq sample experienced voltage decay during C / 20 discharge. The average discharge voltage of the 0.25 samples reflects this voltage decay, with 25Mq having the lowest average voltage during cycling and 25Lq having a slightly higher average discharge voltage than 25Hq.

[0056] Regarding rate capacity, as shown in Table III, the C / 20:C / 2 ratios of the 25Hq, 25Lq and 25Mq samples are 1.19, 1.25 and 1.39, respectively.

[0057] Referring to Figures 3A-3D, the charging curve of the x=0.17 sample has a more typical single flat 4.5 V steady segment on the first charge, accounting for about 56.8% of the initial charge capacity, while the 17Lq and 17Mq samples show a less certain 4.5 V steady segment accounting for about 20% of the initial charge capacity in both cases.

[0058] The capacitance of all x=0.17 samples increased by approximately 10 mAh g⁻¹ between the first two C / 20 discharges. As seen in Table III, the second round of C / 20 discharge increased the capacitance of 17Hq, 17Lq, and 17Mq by 31%, 73%, and 91%, respectively. The voltage decay characteristics of the x=0.17 samples are shown in Figure 3. There is a nearly uniform voltage decay characteristic for all three samples, and the average plateau voltage decreases by approximately 0.4 V during cycling. However, no voltage decay was observed in the C / 20 discharge curves of these samples. The x=0.17 samples also exhibited a similar average discharge voltage over time. The main difference is how the average voltage of 17Mq increases in the first cycle, but by the second cycle, it follows the same voltage decay trend as 17Hq and 17Lq.

[0059] Referring to Figures 4A-4D, regarding the charging curves of the x=0.10 sample, the 10Hq charging curve differs from that of the 10Lq and 10Mq samples, which have similar curves. Only the 10Hq sample has a defined 4.5 V plateau, but all three samples have a persistent inflection point at 4.5 V. The inflection point of 10Hq disappears, while the inflection points of 10Lq and 10Mq persist until the 54th cycle. The inflection point of the 10Mq sample is the most pronounced.

[0060] As shown in Table III, all x=0.10 samples experienced an initial capacity increase during the first C / 20 cycle at a rate of 5 mAh g⁻¹. Subsequently, for the 10Hq, 10Lq, and 10Mq samples, the capacity increased by 300%, 60%, and 67%, respectively, during the second C / 20 discharge. By the end of the first C / 2 discharge, the capacity of all x=0.10 samples exceeded or caught up with the initial C / 20 capacity. During the two C / 2 discharge cycles, the capacity of 10Hq increased by 197% and 50% respectively in the first and second cycles, the capacity of 10Lq increased by 25% and 16%, and the capacity of 10Mq increased by 36% and 20%. The discharge plateau for 10Lq and 10Mq samples began at approximately 3.0 V, while the plateau for 10Hq samples began at 3.2 V; the voltage characteristics of 10Hq during cycling differed from those of 10Lq and 10Mq. The voltage characteristics of all x=0.10 samples were rate-dependent, and the average discharge voltage of the C / 20 discharge of all three samples increased during cycling. However, the C / 2 discharge of the 10Lq and 10Mq samples showed signs of voltage decay, while the discharge of the 10Hq sample did not.

[0061] In addition, the 10Lq and 10Mq samples have an inflection point at 2.2 V that exists only on the C / 20 discharge curve. These voltage characteristics of the x=0.10 sample show that the average discharge voltage of the 10Lq and 10Mq samples is higher than that of the 10Hq sample, and also show a greater degree of voltage decay.

[0062] Regarding rate capacity, as shown in Table III, the C / 20:C / 2 ratios of the 10Hq, 10Lq, and 10Mq samples are 1.27, 1.60, and 1.67, respectively. It should be noted that the effective charge and discharge of each cycle also develops significantly with each cycle, which makes the DC28 / DC27 ratio of the 10Hq sample actually a C / 10:C / 1 ratio.

[0063] The voltage curves observed during the cycling process reveal the phase transitions that change during the test. The expected voltage plateau seen in the x=0.25 sample indicates the occurrence of the expected classical phase transition.

[0064] Figures 5A-5I are normalized and shifted XRD patterns of LLRNMO powders before and after cycling for samples of 25Hq, 25Lq, 25Mq, 17Hq, 17Lq, 17Mq, 10Hq, 10Lq and 10Mq respectively.

[0065] Referring to Figures 5A-5I, the XRD patterns of all x=0.25 samples after cycling show the disappearance of the 2θ=22° superlattice peak, indicating that the transition metal must migrate to balance the structure. However, all other R-3m index peaks are retained, indicating that the overall structure is preserved. Similar results are seen in the x=0.17 and 10Hq samples. This loss of transition metal ordering is related to the loss of oxygen and lithium and thus reduces the capacitance, while the increase in capacitance seen in Figures 2A-4C shows that this is not the case for these samples. This data therefore indicates that the migration of transition metals does not always cause capacitance loss.

[0066] The 10 Mq samples exhibit substantially different crystal structures after cycling tests, but both the 10 Mq and 10 Lq samples still show some visible peaks at 22°, further indicating that the electrochemical phase transitions observed in Figures 4A-4C are not the same as those observed in the cycling data in Figures 2A-3C. The substitutional phase transitions observed in 10 Lq and 10 Mq suggest a limitation on the synthesis of LLRNMO, which exists somewhere within a nickel content of 0.17 > x > 0.10.

[0067] Figure 6 includes 50 k× SEM micrographs of cathodes coated with 25 Hq, 25 Lq, and 25 Mq samples before and after cycling. Figure 7 includes 50 k× SEM micrographs of cathodes coated with 17 Hq, 17 Lq, and 17 Mq samples before and after cycling. Figure 8 includes 5 k× SEM micrographs of cathodes coated with 10 Hq, 10 Lq, and 10 Mq samples before and after cycling.

[0068] Referring to Figures 6-8, the morphology of the cathodes after preparation and cycling is shown in Figures 6 and 7, and is uniform in all samples with x=0.25 and x=0.17. The morphology of the sample with x=0.10 is shown in Figure 8, and is not uniform. 10Hq is consistent with the samples with higher nickel content, while 10Lq and 10Mq are consistent with each other. All samples have a consistent morphology before and after cycling; there is no evidence of changes in surface structure or particle morphology due to electrochemical cycling.

[0069] Both nickel content and quenching method affect the structure and electrochemical properties of LLRNMO cathodes. Generally speaking, when the material has a higher Ni content and / or a faster quenching rate during synthesis, it has a higher capacitance and more typical voltage characteristics, but the results are sometimes slightly different.

[0070] The XRD patterns of LLRNMO powders demonstrate the structure dependence on both nickel content and quenching method. Subtle crystallographic variations are expected for samples with various nickel contents, and are observed between x=0.25 and x=0.17 and the 10Hq sample. The XRD patterns of 10Lq and 10Mq show numerous secondary peaks, while the XRD pattern of 10Hq does not. The secondary peaks seen in the 10Lq and 10Mq patterns are consistent with those seen in the XRD patterns of 25Mq and 17Mq. These examples demonstrate the critical importance of quenching rate in determining structure, phase content, and phase purity.

[0071] The secondary layered phases found in many samples may be the result of localized relative nickel-rich heterogeneity with corresponding larger lattice parameters. The (110) peak splitting is present in the XRD patterns of all samples (except 25Hq and 25Lq), indicating that slower quenching produces nickel heterogeneity. The XRD patterns of the 25Mq and 17Mq samples have additional secondary peaks at (101), (104), and (107) visible in the 10Lq and 10Mq samples. Although it must be noted that the (104) secondary peak in 25Mq and 10Lq may be due to contamination. These additional peaks, although different, appear in all quenched metal samples, indicating how the structure depends on the nickel content and quenching. This data supports the concept that slower quenching methods produce separated nickel-rich phase regions and form contaminants in the material, thus determining the local ordering of nickel in the sample regardless of the Ni content. Figure 14 shows a schematic diagram of the proposed secondary layered phase structure.

[0072] Since Ni²⁺ ions have a larger ionic radius than Mn ions, it is believed that there is less local lattice expansion in the presence of less Ni. Samples with higher nickel content should have a higher degree of long-range ordered distribution of nickel ions, and a more favorable ordering results in smaller lattice parameters. Rapid quenching of such samples maintains long-range order and smaller lattice parameters, while slower quenching will allow for contamination nucleation and the evolution of nickel heterogeneity, both of which will distort the average lattice parameter. The intersection of lattice parameter "a" seen in Figure 1B is at x=0.11, which further indicates the presence of a synthesis constraint 0.17 > x > 0.10.

[0073] The electrochemical properties of the sample are affected by both the nickel content and the quenching method. The first charging characteristic of the material indicates purity and capacity, which is due to the fact that known high-performance materials exhibit a single, stronger stable phase consistent with the phase transition of oxygen and lithium loss catalyzed by nickel.

[0074] Figures 9A-9C are graphs showing the smooth spline fit of dQ / dV to V data for the first charging cycle of samples x=0.25, x=0.17 and x=0.10.

[0075] Referring to Figures 9A-9C, the 4.5 V peak seen on the dQ / dV plot indicates that all samples have an initial 4.5 V plateau to some extent. However, Figures 2A-4C show that only some samples have an inflection point at 4.5 V on subsequent charges. This indicates that all samples initially undergo similar phase transitions, but the persistence of the inflection point in some samples suggests that the reaction may not always be completed during the initial charge. The samples with secondary peaks in the plots are the same as those with inflection points in the latter half of the cycle, and are therefore correlated. This is further supported by how higher nickel content would drive the secondary layered phase peaks to the left of the main peak. Although some samples, such as 25 Mq and 10 Lq, show signs of rock salt contamination, this contamination does not rule out the possibility of some other phase transitions. In any case, these transitions occur with a larger number of cycles and gradually decay, indicating that the final samples still undergo complete and irreversible transformations.

[0076] The presence of inflection points on non-water-quenched samples (except for some samples on 10Hq) provides further evidence that these inflection points are related to phase heterogeneity. The 10Hq samples begin at these inflection points, but by the 54th cycle, their charging curves are more closely similar to the x=0.17 sample than the initially similar x=0.10 sample. Therefore, this data is consistent with the evolution of nickel heterogeneity over the extended 4.5 V phase transition.

[0077] Figures 10A-10C show the smoothed spline fitting of dQ / dV relative to V data for the second charging cycle of samples x=0.25, x=0.17, and x=0.10. Figures 11A-11C show the first and last C / 2 discharges of samples 25 Hq, 25 Lq, and 25 Mq, and Figure 11D shows the average discharge voltage per cycle for samples 25 Hq, 25 Lq, and 25 Mq during the cycling process. Figures 12A-12C show the first and last C / 2 discharges of samples 17 Hq, 17 Lq, and 17 Mq, and Figure 12D shows the average discharge voltage per cycle for samples 17 Hq, 17 Lq, and 17 Mq during the cycling process. Figures 13A-13C show the first and last C / 2 discharges of the 10Hq, 10Lq and 10Mq samples, and Figure 13D shows the average discharge voltage of the 10Hq, 10Lq and 10Mq samples in each cycle during the cycling process.

[0078] The discharge curves of the samples also show the cycling characteristics over time, which are affected by the nickel composition and quenching method. Referring to Figures 10A-10C, the peak of the water-quenched sample is initially lower in voltage than that of the liquid nitrogen and metal-quenched samples, indicating that the heterogeneity of nickel affects the voltage. Except for 25 Mq, the average discharge voltage of the water-quenched sample also tends to be lower than that of other samples of the same composition. The dQ / dV plots of 17 Lq and 17 Mq, and Figures 11A-13D show how the discharge curves evolve with different characteristics as cycling. The voltage of the x=0.17 sample, although the most uniform in voltage characteristics, also shows a greater degree of voltage decay. The exception to this case is the 25 Mq sample, which shows voltage decay during cycling; and the x=0.10 sample, which shows voltage increase at its C / 20 discharge and voltage decay at its C / 2 discharge. It is also worth noting that the average voltage decay experienced by most samples is attributed to the evolution of the larger capacitance at those voltages compared to sample decomposition. The significant differences in discharge characteristics found in the samples indicate differences in quenching rates, which are also reflected in different electrochemical reactions.

[0079] Compared to the voltage decay of the x=0.17 sample, the voltage decay of 25Hq and 25Lq is smaller, and their associated voltage plateaus are also at different voltages. The smaller voltage decay of 25Hq and 25Lq is mainly consistent with the phase transition to the spinel phase during cycling, which is associated with a 3 V plateau. The more severe voltage decay of the x=0.17 sample is also mainly consistent with the phase transition to the spinel phase. In both cases, but especially in the x=0.17 sample, the voltage plateaus are close to the average voltage of Ni²⁺ / ³⁺ / ⁴⁺ redox in manganese-rich environments, indicating that these plateaus are driven by nickel redox and therefore by nickel redistribution. This voltage loss and nickel redistribution are mainly consistent with the evolution of the spinel phase, with the main inconsistency being the increase in capacitance. The evolution of the spinel phase is associated with both the initial capacity increase and loss, and appears to be generally related to significant structural decomposition. Therefore, the voltage decay of the structurally stable 25Hq, 25Lq and x=0.17 samples may not be attributable at all to the evolution of the spinel-like phase.

[0080] The evolution of the spinel phase does not cause characteristic differences in discharge rates, specifically for the x=0.10 sample. The C / 20 discharge of the x=0.10 sample begins at a voltage similar to that of the decaying sample and increases during cycling; the C / 2 discharge of the x=0.10 sample experiences a certain degree of voltage decay. Although the lower initial potential of the samples may affect their higher manganese concentration and subsequent lower potential of nickel redox, the inconsistent voltage behavior cannot be fully explained by the formation of the spinel phase, especially considering their rapid capacity increase. In contrast, the lower manganese concentration, capacity loss, and faster voltage decay of 25 Mq indicate the formation of the spinel phase. These factors, in fact, how its discharge voltage plateau begins at 3 V, are consistent with the voltage decay mechanism of spinel phase evolution. Phase impurities evolving during slow quenching may make the 25 Mq more susceptible to spinel phase evolution. The voltage plateau at 25 Mq falls within the range of the Mn³⁺ / ⁴⁺ redox couple, and manganese and nickel may form mixed redox couples that could also lead to voltage decay. The discharge plateaus at 10 Lq and 10 Mq are similar to those at 25 Mq starting at 3 V, indicating that these samples can also undergo a certain degree of transformation to the spinel phase. Except for 10 Mq, the XRD patterns of all samples show peaks indicating R-3m layered structures, further suggesting that the evolution of the spinel phase is not entirely responsible for voltage decay or capacitance changes.

[0081] Figure 14 is a schematic diagram showing how phase impurity inclusions in a 25Mq sample with an R-3m structure and lattice parameter a' > a lead to the secondary peaks seen to the left of the 25Mqs (104) peak. As shown in Figure 14, the redox reaction of nickel that drives the evolution of these stable segments indicates that the nickel content becomes homogenized over time.

[0082] Except for the 25 Mq sample, the electrochemical cycling data of the LLRNMO cathode showed a constant increase in capacitance. Although the x=0.25 sample showed a smaller increase in capacitance, the x=0.17 sample showed a more significant increase, and the x=0.10 sample showed even greater increases. Therefore, the percentage increase in specific capacity during cycling showed an inverse relationship with nickel content, independent of the quenching method. The largest increase in capacitance was observed in the 10 Hq sample, followed by the 10 Mq and 10 Lq samples. Since impurities are related to nickel heterogeneity, this relationship indicates that the increase in capacitance is at least partially driven by the homogenization of nickel content during cycling through the "electrochemical annealing" process.

[0083] Comparative XRD analysis of the post-cycle cathode material relative to the original cathode material showed very similar characteristics in all samples except 10 Lq and 10 Mq, where the transition metal superlattice peaks disappeared after cycling. 10 Lq exhibited some retained superlattice peaks after cycling, and the 10 Mq sample showed the appearance of several new peaks, marking a significant difference between the two samples. This difference further demonstrates the importance of quenching rate, as slower quenching conditions resulted in the lower limit of LLRNMO synthesis, where 0.17 > x > 0.10. However, the characteristics of the 10 Hq sample were different, showing that faster quenching produced stability and long-term performance associated with samples with higher Ni content.

[0084] Electrochemical testing of these materials demonstrates that rapidly quenched materials exhibit excellent capacity and capacity retention, and are the only variant to show an increase in capacity during cycling. After 50 full charge / discharge cycles, this material produces a specific capacity of nearly 230 mAh / g at a C / 2 rate, which is far superior to materials cooled by other methods.

[0085] The discovery of extremely rapid cooling of such materials during synthesis using immersion in water resulted in materials with excellent and differentiated crystal structures, as well as previously reported electrochemical properties. Specifically, this water-quenched material was found to: (a) exhibit a significant increase in capacity over 50 cycles; (b) not exhibit the voltage decay typically reported (where the average discharge voltage of the battery decreases significantly with use); (c) have a specific capacity exceeding 250 mAh / g after 25 cycles at a C / 2 rate and after 4 cycles at a C / 2 rate; and (d) have a specific capacity exceeding 230 mAh / g (e.g., 231 to 240 mAg / g) after 50 cycles at a C / 2 rate, with an average voltage drop of less than 10% during discharge (e.g., as illustrated in Figure 11D, for example).

[0086] A method for forming an active material for a positive electrode of a lithium-ion battery includes quenching powder of the active material in water, wherein the active material comprises layered lithium-rich nickel-manganese oxide.

[0087] In one embodiment, the method also includes sintering the active material powder prior to quenching. The sintering (i.e., sintering) can be carried out at a temperature of, for example, at least 800°C, such as 800 to 1000°C, such as 900°C. In one embodiment, the water is at room temperature prior to quenching. The sintered active material powder is provided directly to the quenching bath after sintering (i.e., sintering), while the active material powder is at 20% or less of the sintering (i.e., sintering) temperature. The active material powder can be quenched at a rate of at least 1750°C / second (such as 1750°C / second to 8750°C / second).

[0088] In one embodiment, the powder particles of the active material are in the form of aggregates with an average size (e.g., average diameter) ranging from about 0.1 µm to about 10 µm, and the aggregates of the active material powder are composed of microcrystals with an average crystal size ranging from about 25 nm to about 500 nm. After quenching, the powder of the active material contains a hexagonal phase and a monoclinic phase.

[0089] In one embodiment, excess Li, Ni, and Mn atoms are uniformly and evenly distributed throughout the transition metal lattice sites, such that there is no crystal volume greater than 1 × 1 × 1 nm in the material, wherein the ratio of Ni, Mn, and Li atoms differs from the ratio of Ni, Mn, and Li atoms in the host material by more than 3%. In other words, if the Ni:Mn:Li ratio in the host material (e.g., in crystals or aggregates) is X:Y:Z, then there is no crystal volume greater than 1 × 1 × 1 nm in the material where the ratio of Ni, Mn, and Li atoms differs from X:Y:Z by more than 3%. Therefore, in this embodiment, there is no crystal volume greater than 1 × 1 × 1 nm in the material, wherein the Ni, Mn, and Li atoms are either excessive or insufficient in volume atomic ratio (+ / -3%, exceeding or falling below).

[0090] In one embodiment, the active material powder, after quenching, comprises a composite of a hexagonal and a monoclinic phase, specifically a combination of LiMO₂R-3m and Li₂MnO₃C₂ / m phases, wherein M is at least one of Ni or Mn. In one embodiment, the active material powder comprises a solid solution having a crystal structure that predominantly or completely possesses C₂ / m symmetry. In another embodiment, the active material powder comprises a solid solution having a crystal structure that predominantly or completely possesses R-3m symmetry.

[0091] In one embodiment, the active material is substantially cobalt-free. In other words, the active material does not contain cobalt, contains cobalt as an unavoidable impurity, or contains 0 to 0.5 atomic percent cobalt. In one embodiment, the active material is represented by the formula Li z(Mn yNi 1 - y) 2 - zO 2, where z is greater than 1.05 and less than 1.25, and y is in the range of 0.55 to 0.83. Alternatively, the active material is represented by the formula Li[Ni xLi( 1 / 3 - 2x / 3)Mn ( 2 / 3 - x / 3 )]O 2, where 0 < x < 0.5. In one embodiment, the active material is substantially cobalt-free, and the active material is represented by the formula Li[Ni xLi( 1 / 3 - 2x / 3)Mn ( 2 / 3 - x / 3 )]O 2, where 0.19 < x < 0.26. In another embodiment, the active material is substantially cobalt-free; and the active material is represented by the formula Li[MxLi(1 / 3 - 2x / 3)Mn(2 / 3 - x / 3)]O2, where 0.19 < x < 0.26, and where M includes at least one of Ni and Ti, Fe, Al or Cr.

[0092] In one embodiment, the water in the quenching bath contains an additive dissolved therein. For example, the water contains an additive at a concentration of 0.01 moles per liter to 1.0 moles per liter.

[0093] In one embodiment, the additive comprises an acid selected from sulfuric acid, citric acid, acetic acid, phosphoric acid, hydrochloric acid, ammonium phosphate, or combinations thereof. In another embodiment, the additive comprises a carbohydrate selected from fructose, galactose, glucose, lactose, maltose, sucrose, or combinations thereof. The additive may comprise both an acid and a carbohydrate.

[0094] In one embodiment, the active material is mixed with a binder and then incorporated into the positive electrode of a lithium-ion battery cell. The cell further comprises a negative electrode and an electrolyte. At room temperature, within a voltage range of 2 V to 4.8 V, at a charge rate C / 20 and a discharge rate C / 2, the specific discharge capacity of the battery cell increases by at least 10% after 50 electrochemical cycles. Prior to the electrochemical cycles of the battery, the active material comprises a hexagonal phase and a monoclinic phase; and after the electrochemical cycles (e.g., after the first cycle), the active material powder does not contain the monoclinic phase.

[0095] In another embodiment, the lithium-ion battery cell includes a negative electrode, an electrolyte, and a positive electrode, the positive electrode comprising a layered lithium-rich nickel manganese oxide active material, wherein the specific discharge capacity of the battery cell increases by at least 10% after 50 electrochemical cycles at a charge rate C / 20 and a discharge rate C / 2, and the battery cell has a specific capacity of at least 230 mAh / g after 50 electrochemical cycles at a discharge rate C / 2.

[0096] In one embodiment, the average discharge voltage of the battery cell decreases by no more than 10% after 50 electrochemical cycles at a discharge rate C / 2. For example, the average discharge voltage of the battery cell may decrease by only 5% to 10% after 50 electrochemical cycles at a discharge rate C / 2, as shown, for example, in Figure 11D.

[0097] In one embodiment, at room temperature, within a voltage range of 2 V to 4.8 V, after undergoing two electrochemical cycles at a charge rate of C / 20 and a discharge rate of C / 20, followed by twenty-five electrochemical cycles at a charge rate of C / 20 and a discharge rate of C / 2, followed by two additional electrochemical cycles at a charge rate of C / 20 and a discharge rate of C / 20, and then twenty-five additional electrochemical cycles at a charge rate of C / 20 and a discharge rate of C / 2, the specific discharge capacity of the battery cell increases by at least 10%.

[0098] In one embodiment, after 50 electrochemical cycles at a discharge rate C / 2, the battery cell has a specific capacity of at least 180 mAh / g, such as at least 230 mAh / g. For example, after 50 electrochemical cycles at a discharge rate C / 2, the battery cell has a specific capacity of 180 to 240 mAh / g, such as 230 to 240 mAh / g.

[0099] In one embodiment, the active material comprises powder embedded in a binder, and the average particle / agglomerate size of the powder is in the range of about 0.1 µm to about 10 µm, and the average crystal size is in the range of about 25 nm to about 500 nm. The particles of the active material powder have at least one of a spinel surface layer, a carbon coating (e.g., generated by a carbohydrate additive in a quenching bath), and / or passivated oxygen bonds on the surface (e.g., generated by an acid additive in a quenching bath).

[0100] The foregoing description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will readily be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments without departing from the scope of the invention. Therefore, the invention is not intended to be limited to the embodiments shown herein, but should be accorded the broadest scope consistent with the principles and novel features disclosed herein. [Simplified Explanation of the Diagram]

[0005] The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with the foregoing summary description and the hereinafter detailed description, serve to explain the features of the invention.

[0006] Figure 1A is a graph showing the intensity (arbitrary unit) versus angle 2θ (degrees), illustrating the exponentially normalized and shifted XRD pattern of the original layered lithium-rich nickel manganese oxide (LLRNMO) powder. Figure 1B includes a top plot showing the trend between lattice parameter "a" and the nickel content of the sample, and a bottom plot showing the trend between lattice parameter "c" and the nickel content of the sample, which were obtained by single-phase Rietveld fitting.

[0007] Figure 2A shows the specific discharge capacity of lithium-rich nickel-manganese oxide material samples. These samples have the formula Li[Ni xLi( 1 / 3 - 2x / 3)Mn ( 2 / 3 - x / 3 )]O 2, where the nickel content x=0.25. During cycling, Figures 2B-2D show the full charge and discharge curves of button batteries including 25Hq, 25Lq and 25Mq samples, respectively.

[0008] Figure 3A shows the specific discharge capacity of the sample with x=0.17 during the cycling process, and Figures 3B-3D show the full charge and discharge curves of button batteries including samples with 17Hq, 17Lq and 17Mq respectively.

[0009] Figure 4A is a graph showing the specific discharge capacity of the sample with x=0.10 during the cycling process, and Figures 4B-4D show the full charge and discharge curves of button batteries including samples with 10Hq, 10Lq and 10Mq respectively.

[0010] Figures 5A-5I are normalized and shifted XRD patterns of LLRNMO powders before and after cycling for samples of 25Hq, 25Lq, 25Mq, 17Hq, 17Lq, 17Mq, 10Hq, 10Lq and 10Mq respectively.

[0011] Figure 6 includes 50 k× SEM micrographs of cathodes coated with 25 Hq, 25 Lq and 25 Mq samples before and after cycling.

[0012] Figure 7 includes 50 k× SEM micrographs of cathodes sprayed with 17Hq, 17Lq and 17Mq samples before and after cycling.

[0013] Figure 8 includes 5 k× SEM micrographs of cathodes sprayed with 10 Hq, 10 Lq and 10 Mq samples before and after cycling.

[0014] Figures 9A-9C are graphs showing the smooth spline fit of dQ / dV to V data for the first charging cycle of samples x=0.25, x=0.17 and x=0.10.

[0015] Figures 10A-10C are graphs showing the smooth spline fit of dQ / dV to V data for the second charging cycle of samples x=0.25, x=0.17 and x=0.10.

[0016] Figures 11A-11C are diagrams showing the first and last C / 2 discharges of 25 Hq, 25 Lq and 25 Mq samples, and Figure 11D is a diagram showing the average discharge voltage of 25 Hq, 25 Lq and 25 Mq samples in each cycle during the cycling process.

[0017] Figures 12A-12C are diagrams showing the first and last C / 2 discharges of samples 17Hq, 17Lq and 17Mq, and Figure 12D is a diagram showing the average discharge voltage of samples 17Hq, 17Lq and 17Mq in each cycle during the cycling process.

[0018] Figures 13A-13C are diagrams showing the first and last C / 2 discharges of 10Hq, 10Lq and 10Mq samples, and Figure 13D is a diagram showing the average discharge voltage of 10Hq, 10Lq and 10Mq samples in each cycle during the cycling process.

[0019] Figure 14 shows how phase impurity inclusions in a 25Mq sample with an R-3m structure and lattice parameter a'>a lead to the secondary peak seen to the left of the 25Mqs (104) peak.

[0020] Figures 15A-15B are SEM micrographs of the aggregates, and Figures 15C-15D are high-magnification SEM micrographs of microcrystals (e.g., grains) in the aggregates.

Claims

1. A method for forming an active material for a positive electrode of a lithium-ion battery, the method comprising quenching the powder of the active material in water, wherein the water contains an additive dissolved therein.

2. The method of claim 1, further comprising sintering the active material powder prior to the quenching.

3. The method of claim 2, wherein the active material is fired at a temperature of at least 800°C.

4. The method of claim 1, wherein the water is at room temperature prior to the quenching, and the powder of the active material is quenched at a rate of at least 1750°C / second.

5. The method of claim 1, wherein the active material comprises a layered lithium-rich nickel-manganese oxide.

6. The method of claim 5, wherein excess Li, Ni and Mn atoms are uniformly and evenly distributed throughout the transition metal lattice sites such that there is no crystal volume greater than 1×1×1 nm in the material, wherein the ratio of Ni, Mn and Li atoms differs from the ratio of Ni, Mn and Li atoms in the host material by more than 3%.

7. The method of claim 5, wherein the particles of the powder of the active material are in the shape of aggregates with an average size in the range of about 0.1 µm to about 20 µm, and the aggregates of the powder of the active material are composed of microcrystals with an average size in the range of about 25 nm to about 500 nm.

8. The method of claim 5, wherein the powder of the active material after quenching comprises a complex of a hexagonal phase and a monoclinic phase, and is a combination of LiMO 2R-3m and Li 2MnO 3C2 / m phases, wherein M is at least one of Ni or Mn.

9. The method of claim 5, wherein the powder of the active material comprises a solid solution having a crystal structure having predominantly or completely C2 / m symmetry.

10. The method of claim 5, wherein the powder of the active material comprises a solid solution having a crystal structure having predominantly or completely R-3m symmetry.

11. The method of claim 5, wherein the active material is represented by the following formula: Li[Ni xLi( 1 / 3-2x / 3)Mn (2 / 3-x / 3)]O 2, where 0 < x < 0.

5.

12. As in request item 11, wherein: The active material is substantially free of cobalt; and the active material is represented by the following formula: Li[Ni xLi( 1 / 3-2x / 3)Mn (2 / 3-x / 3)]O 2, where 0.19 < x < 0.

26.

13. As in request item 7, wherein: The active material is substantially free of cobalt; and the active material is represented by the following formula: Li[M xLi( 1 / 3-2x / 3)Mn (2 / 3-x / 3)]O 2, where 0.19 < x < 0.26, and where M includes at least one of Ni and Ti, Fe, Al or Cr.

14. The method of claim 1, wherein the additive comprises at least one of an acid or a carbohydrate.

15. The method of claim 14, wherein the water contains the additive at a concentration of 0.01 moles per liter to 1.0 moles per liter.

16. The method of claim 14, wherein the additive comprises the acid.

17. The method of claim 16, wherein the acid is selected from sulfuric acid, citric acid, acetic acid, phosphoric acid, hydrochloric acid, ammonium phosphate, or combinations thereof.

18. The method of claim 14, wherein the additive comprises the carbohydrate.

19. The method of claim 18, wherein the carbohydrate is selected from fructose, galactose, glucose, lactose, maltose, sucrose, or combinations thereof.

20. The method of claim 5, further comprising placing the active material into the positive electrode of the lithium-ion battery cell, the lithium-ion battery cell further comprising a negative electrode and an electrolyte, wherein: Prior to the electrochemical cycle of the battery, the active material contains a hexagonal phase and a monoclinic phase; and after the electrochemical cycle, the active material powder does not contain the monoclinic phase.

21. As in request item 20, wherein: At room temperature, within a voltage range of 2 V to 4.8 V, the specific discharge capacity of the battery cell increases by at least 10% after 50 electrochemical cycles at charge rate C / 20 and discharge rate C / 2; and after such 50 electrochemical cycles at discharge rate C / 2, the battery cell has a specific capacity of at least 230 mAh / g.

22. A lithium-ion battery cell comprising: a negative electrode; an electrolyte; and a positive electrode comprising a layered lithium-rich nickel manganese oxide active material, wherein the specific discharge capacity of the battery cell increases by at least 10% after 50 electrochemical cycles at a charge rate C / 20 and a discharge rate C / 2, and after such 50 electrochemical cycles at a discharge rate C / 2, the battery cell has a specific capacity of at least 230 mAh / g, wherein the particles of the active material powder have at least one of a carbon coating or passivated oxygen bonds on their surface.

23. The lithium-ion battery cell of claim 22, wherein at room temperature, within a voltage range of 2 V to 4.8 V, after undergoing two electrochemical cycles at a charge rate C / 20 and a discharge rate C / 20, followed by twenty-five electrochemical cycles at a charge rate C / 20 and a discharge rate C / 2, followed by two additional electrochemical cycles at a charge rate C / 20 and a discharge rate C / 20, and then twenty-five additional electrochemical cycles at a charge rate C / 20 and a discharge rate C / 2, the specific discharge capacity of the battery cell increases by at least 10%.

24. The lithium-ion battery cell of claim 23, wherein the average discharge voltage of the battery cell decreases by no more than 10% after 50 electrochemical cycles at a discharge rate C / 2.

25. The lithium-ion battery cell of claim 22, wherein the active material is represented by the following formula: Li[MxLi(1 / 3-2x / 3)Mn(2 / 3-x / 3)]O2, wherein 0 < x < 0.5, and M comprises Ni or a combination of Ni with at least one of Ni, Al, Fe or Cr.

26. The lithium-ion battery cell as claimed in claim 25, wherein: The active material is substantially free of cobalt; and the active material is represented by the following formula: Li[M xLi( 1 / 3-2x / 3)Mn (2 / 3-x / 3)]O 2, where 0.19 < x < 0.26 and M contains Ni.

27. The lithium-ion battery cell of claim 22, wherein the active material is represented by the formula y(LiMO 2)∙(1- y)LiMnO 3, wherein y is between 0.8 and 1, and M contains at least Ni and Mn.

28. The lithium-ion battery cell as described in claim 22, wherein: The active material powder has particles in the form of aggregates with an average size in the range of about 0.1 µm to about 10 µm, and the aggregates of the active material powder are composed of microcrystals with an average crystal size in the range of about 25 nm to about 500 nm.

29. The lithium-ion battery cell of claim 22, wherein excess Li, Ni and Mn atoms are uniformly and evenly distributed throughout the transition metal lattice sites, such that the material has no crystal volume greater than 1×1×1 nm, wherein the ratio of Ni, Mn and Li atoms differs from the ratio of Ni, Mn and Li atoms in the bulk material by more than 3%.

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