Lmo cathode compositions

Abstract

A cathode composition for a lithium-ion battery or battery having the chemical formula is disclosed, wherein the composition is in the form of a single phase having a rock salt crystal structure, and the value of x is greater than 0 and less than or equal to 0.3. The composition is also formulated as a positive or negative electrode for use in an electrochemical cell.

Description

Technology Field

[0001] The present invention relates to a set of electroactive lithium-rich manganese cathode compositions having a rock salt structure. More specifically, the present invention relates to a set of high-capacity lithium-rich manganese oxide cathode compositions that can be used as bulk or composite cathode materials in electrochemical cells. Background Technology

[0002] The performance and cost of lithium-ion batteries depend primarily on the composition of the cathode. Currently available lithium-based cathode compositions are graded mainly based on energy density, electrochemical performance, and the cost of the raw materials required to manufacture them. Since manganese in the Earth's crust is much more abundant than cobalt and nickel, manganese would be the ideal single transition metal center for lithium-based cathode compositions. While compositions containing nickel, cobalt, and aluminum can currently achieve much higher capacity and energy density, the cost of these metals is significantly higher. Furthermore, these nickel, cobalt, and aluminum-based compositions remain costly due to issues with voltage profile evolution during cycling (due to the inclusion of cobalt and nickel) and exhibit significant stability problems, such as gas loss during cycling. There is a need for simple, robust, and cost-effective lithium-rich materials that provide equivalent or superior energy density and performance. means of solving the problem

[0003] In a first aspect, the present invention, A cathode composition for a lithium-ion battery having the chemical formula is provided, wherein the composition is in the form of a single phase having a rock salt crystal structure, and the value of x is greater than 0 and less than or equal to 0.3.

[0004] Conventional aligned or layered lithium and manganese-rich compositions (Li 1+x Tm 1-xIn O2 (where Tm is mainly Mn), lithium ions are located in both alkali and transition metal sites. This is compared to the ideal LiCoO2R3 / m type structure in which lithium and cobalt ions completely occupy alternating layers within the structure.

[0005] It has been revealed that a cathode composition having improved stability and capacity performance can be achieved by a lithium-rich manganese oxide composition as defined above. The cathode composition of the present invention also exhibits improved electrochemical cycling compared to the conventional layered lithium manganese oxide structure of the prior art.

[0006] In particular, the composition is provided as a single-phase rock salt crystal structure (i.e., a face-centered cubic lattice having an Fm3(bar)m space group). The specifically identified compound can be reproducibly prepared at high speeds using conventional ball milling techniques by mixing LiMnO2 and Li2MnO3 precursors in different ratios. Additionally, thin films of the cathode composition can be prepared using other conventional techniques, such as PVD techniques including but not limited to sputtering and sublimation / evaporation of the target material.

[0007] In certain examples, the value of x may be 0.1 or greater. The value of x may be 0.17 or greater. The value of x may be 0.2 or greater. The value of x may be 0.2 or greater and 0.3 or less. The value of x may be 0.1 or greater and 0.2 or less. The value of x may be equal to 0.2.

[0008] In a specific example, x is 0.2. Therefore, this specific composition is Li 1.2 Mn 0.8 It is O2. This specific composition has demonstrated improved charge capacity and stability over several cycles.

[0009] The composition can be expressed by the general formula (a) LiMnO2·(1-a)Li2MnO3, where two precursors are provided in a ratio defined by a, where a has a value in the range of greater than 0 and less than 1, and the precursors are mixed by a ball milling process to provide a bulk composition having a rock salt structure. In one example, a has a value in the range of greater than 0.05 and less than 0.95.

[0010] In certain examples, the value of a may be 0.15 or higher and 0.7 or lower. The value of a may be 0.15 or higher and 0.4 or lower. As shown in the following embodiments of the present invention, the cathode composition may be selected from one of 0.7LiMnO2·0.3Li2MnO3; 0.6LiMnO2·0.4Li2MnO3; 0.5LiMnO2·0.5Li2MnO3; 0.4LiMnO2·0.6Li2MnO3; 0.3LiMnO2·0.7Li2MnO3; 0.2LiMnO2·0.8Li2MnO3; 0.15LiMnO2·0.85Li2MnO3; and 0.4LiMnO2·0.6Li2MnO3:

[0011] In a second aspect, the present invention provides a cathode (or more generally an electrode). The cathode may be prepared as a thin film of a cathode composition as part of a PVD technology, or alternatively, the cathode may be prepared using the cathode composition as a cathode active in a composite electrode.

[0012] In the example, a cathode comprising the cathode material of the present invention comprises three fractions. The first fraction is a compound of the present invention as described above (variable mass percentages of 60-98%, but generally 70, 75, 80, 90, and 95%). The second fraction of the cathode comprises an electroactive additive such as carbon, e.g., Super P and carbon black, which constitutes 60-90% of the remaining mass percentage excluding the first fraction. The third fraction is generally a polymer binder such as PVDF, PTFE, NaCMC, and NaAlginate. In some cases, additional fractions may be included and the total percentages may be changed. The overall electrochemical performance of the cathode can be improved by the introduction of the electroactive additive, and the structural properties of the resulting cathode can also be improved by adding a material that enhances the cohesiveness of the cathode composition and the adhesion of the material to a specific substrate.

[0013] In a third embodiment, the present invention provides an electrochemical cell comprising a cathode, an electrolyte, and an anode according to the above description. The electrolyte may take the form of a liquid or a solid, such as a gel or ceramic, for example. Brief explanation of the drawing

[0014] To make the present invention easier to understand, embodiments of the present invention will now be described by way of example with reference to the accompanying drawings. Figure 1 shows the powder X-ray diffraction patterns of various Li-Mn-O compounds with space groups and lattice parameters. Figure 2 shows the material Li synthesized in Example 1. 1.2 Mn 0.8 This shows the powder X-ray diffraction pattern of the O2 (or 0.4LiMnO2·0.6Li2MnO3) compound. Figures 3a and 3b show Li at C / 10 and 45°C, respectively. 1.2 Mn 0.8 O2 and Li1.1 Mn 0.9 The first cycle galvanostatic load curve for the first cycle of O2 is plotted, and Figures 3c and d show Li 1.2 Mn 0.8 O2 and Li 1.1 Mn 0.9 The change in charge and discharge capacity as a function of cycles for each O2 is illustrated. Figure 4 shows Li produced by a conventional planetary ball mill at 400 rpm with ZrO2 balls (top line) compared to WC balls (bottom line) with a high-energy ball mill at 700 rpm. 1.2 Mn 0.8 The X-ray diffraction pattern of O2 is illustrated. Figure 5 shows Li using starting materials Li2MnO3, Li2O2, and Mn2O3 (top line) compared to starting materials Li2MnO3 and LiMnO2 (bottom line). 1.2 Mn 0.8 The X-ray diffraction pattern of O2 is illustrated. Figure 6 shows Li2MnO3, Li2O2, and Mn2O3 prepared from Li2MnO3 with C / 10 charging and C / 5 discharging. 1.2 Mn 0.8 The electrochemical data of O2 is plotted. FIG. 7 shows the precursor (bottom line), Li ball milled for 40 minutes (second from the bottom line), ball milled for 5 hours (second from the top line), and ball milled for 10 hours (top line). 1.2 Mn 0.8 The X-ray diffraction pattern of O2 is illustrated. The present invention will now be described with reference to the following examples. Specific details for implementing the invention

[0015] Example 1 - Synthesis of Lithium-Rich Manganese Oxide Material

[0016] Materials containing LiMnO2 and Li2MnO3 precursors were mixed in different molar ratios according to Table 1 using tungsten carbide (WC) milling vessels and balls. All materials were always processed in an inert atmosphere (an argon-filled glove box) and were not exposed to the ambient atmosphere; that is, they were always protected from moisture and oxygen. A planetary ball mill (the Fritsch Planetary Micro Mill PULVERISETTE 7 Premium line, capable of delivering approximately 150% higher energy than that achievable through conventional milling) was used. Milling was performed at a speed of 700 rpm for 10 minutes, followed by a 30-minute rest period. Phase purity was evaluated after repeating these milling and rest cycles more than 30 times, for a total milling time of more than 5 hours. However, phase purity can be achieved with less milling time. Phase transformation was evaluated by X-ray diffraction. If phase transformation was not complete, the same program was repeated.

[0017] LiMnO2 Li2MnO3 Resulting composition stoichiometry 0.7 0.3 0.7LiMnO2·0.3Li2MnO3 Li 1.1 Mn 0.9 O2 0.6 0.4 0.6LiMnO2·0.4Li2MnO3 Li 1.13 Mn 0.87 O2 0.5 0.5 0.5LiMnO2·0.5Li2MnO3 Li 1.17 Mn 0.83 O2 0.4 0.6 0.4LiMnO2·0.6Li2MnO3 Li 1.2 Mn 0.8 O2 0.3 0.7 0.3LiMnO2·0.7Li2MnO3 Li 1.23 Mn 0.77 O2 0.2 0.8 0.2LiMnO2·0.8Li2MnO3 Li 1.27 Mn 0.73 O2 0.15 0.85 0.15LiMnO2·0.85Li2MnO3 Li 1.28 Mn 0.72 O2

[0018] Alternative starting materials including, but not limited to, Mn2O3, MnO2, Li2O, Li2O2, Mn2O4, and LiMn2O4 may be used here. 1.2 Mn 0.8 Additional routes for the production of O2 were attempted with Li2O, Mn2O3, and MnO2, in which phases such as those shown in Fig. 2 were formed. Alternatively, a conventional planetary ball mill, the Retsch PM 100 mill, was used. Here, both mills used ZrO2 balls to mill Li at a milling speed of 400 rpm. 1.2 Mn 0.8 O2 was used to prepare. From this, it can be clearly understood that as the density and rotational speed of the milling medium decrease, energy collisions are significantly reduced. The conditions used in both mills were Li 1.2 Mn 0.8We succeeded in obtaining a disordered rock salt phase with an O2 composition (Fig. 4), which indicates that manufacturing at high energy is not the only route for the production of the material.

[0019] Alternatively, such cathode compositions can be prepared by considering mechanical fusion or conventional physical vapor deposition techniques.

[0020] Example 2 - Structural Analysis and Characterization of Lithium-Rich Manganese Oxide Material

[0021] The material according to Example 1 was irradiated by powder X-ray diffraction (PXRD) performed using a Panalytical Aeris benchtop XRD with Cu Kα radiation. The measurement range is 10–90° 2θ.

[0022] Figure 2 illustrates the representative powder X-ray diffraction patterns of the synthesized compositions. This is characteristic of a disordered cationic rock salt structure. All patterns show broad principal peaks consistent with a face-centered cubic lattice having the Fm3(bar)m space group, as shown in Figure 2. It should be noted that broad peaks are displayed due to the ball-milling process, which produces materials with small crystallite sizes without being bound by theory. There is no evidence for the existence of layered precursors having layered LiMnO2 or Li2MnO3 structures with space groups R3(bar)m or C2 / m, which would indicate that the ball-milling synthesis converted the precursor material into the composition of the present invention. Li 1.2 Mn 0.8 The XRD examples in Fig. 2 shown for O2 illustrate all samples in which the peak positions shift slightly with changes in bulk lattice parameters as a result of changes in composition. Also, other common Li p Mn f O qIt should be noted that the crystalline phase of the material (database pattern shown in Fig. 1 for comparison) is not visible in the final product. Fig. 7 also illustrates how the reaction proceeds as the initial precursor is slowly removed during continuous milling, with the disordered rock salt phase becoming the dominant feature.

[0023] Example 3 - Electrochemical Analysis of Lithium-Rich Manganese Oxide Material

[0024] The material according to Example 1 was electrochemically characterized through constant current cycling performed with BioLogic BCS series potentiostats. All samples were assembled in Swagelok-type cells with metallic lithium counter / reference electrodes as powder cathodes, and Li was used at a current rate of C / 10 defined by a capacity of 300 mAh / g. + It was cycled between 2 and 4.8 V for / Li. The electrolyte used was LP40 (a 1M solution of LiPF6 in EC;DEC at a 1:1 w / w ratio).

[0025] FIGS. 3a to 3d illustrate the potential curves during the first cycle of charging and subsequent discharging for compositions 0.7LiMnO2·0.3Li2MnO3 and 0.4LiMnO2·0.6Li2MnO3 according to Example 1. Both samples exhibit a high discharge capacity of 200 mAh / g or more at C / 10. The first discharge capacity values ​​for all prepared materials are described in detail in the table below.

[0026] The 0.4LiMnO2·0.6Li2MnO3 compound exhibits a gradient region at the start of charging, centered at approximately 4.2V Li+ / Li and a high potential plateau that appears irreversible in the first discharge. These general characteristics are consistent for all manufactured materials with Li > 1.1 per formula unit, with a plateau length correlated with the amount of lithium in the material, meaning that the more lithium present, the longer the plateau becomes.

[0027] The 0.7LiMnO2·0.3Li2MnO3 compound exhibits different first charges. A long gradient region is observed up to a high cutoff voltage of 4.8 V versus Li+ / Li. No potential flat region is observed, and the irreversibility during discharge is reduced, resulting in a higher first-cycle Coulomb efficiency.

[0028] Phase purity First charge capacity (mAh / g) First discharge capacity (mAh / g) Coulomb efficiency in the first cycle 0.7LiMnO2·0.3Li2MnO3 No crystalline phases were detected except for the rock salt structure (Fm3(bar)m). 230 209 90.8% 0.6LiMnO2·0.4Li2MnO3 No crystalline phases were detected except for the rock salt structure (Fm3(bar)m). 279.5 249.6 89.3% 0.5LiMnO2·0.5Li2MnO3 No crystalline phases were detected except for the rock salt structure (Fm3(bar)m). 281 250 88.9% 0.4LiMnO2·0.6Li2MnO3 No crystalline phases were detected except for the rock salt structure (Fm3(bar)m). 315.9 245.3 77.7% 0.3LiMnO2·0.7Li2MnO3 No crystalline phases were detected except for the rock salt structure (Fm3(bar)m). 317.8 264 83.1% 0.2LiMnO2·0.8Li2MnO3 No crystalline phases were detected except for the rock salt structure (Fm3(bar)m). 346.2 239.6 69.2% 0.15LiMnO2·0.85Li2MnO3 No crystalline phases were detected except for the rock salt structure (Fm3(bar)m). 376.9 242.9 64.4%

Claims

Claim 1 A cathode composition for a lithium-ion battery having the chemical formula, wherein the composition is in the form of a single phase having a rock salt crystal structure, the value of x is greater than 0 and less than or equal to 0.13, and the single phase crystal structure represents the Fm3(bar)m space group. Claim 2 A cathode composition according to claim 1, wherein the value of x is 0.1 or greater. Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 A cathode composition according to claim 1, wherein the composition is represented by the chemical formula (a)LiMnO2·(1-a)Li2MnO3, the two precursors are provided in a ratio defined by a, where a has a value in the range of greater than 0 and less than 1, and the precursors are mixed by a ball milling process. Claim 9 A cathode composition according to claim 8, wherein the value of a is 0.15 or more and 0.7 or less. Claim 10 A cathode composition according to claim 8, wherein the value of a is 0.15 or more and 0.4 or less. Claim 11 In claim 8, the cathode composition is 0.4LiMnO2·0.6Li2MnO3. Claim 12 An electrode comprising a cathode composition according to any one of claims 1 to 2. Claim 13 In claim 12, the electrode comprises electroactive additives and / or a binder. Claim 14 In claim 13, the electrode, wherein the electroactive additive is selected from at least one of carbon or carbon black. Claim 15 In claim 13, the polymer binder is selected from at least one of PVDF, PTFE, NaCMC, or NaAlginate, for the electrode. Claim 16 An electrochemical cell comprising an electrolyte, an anode, and a cathode according to claim 12.

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