Sodium-ion battery cathode material

Abstract

Sodium-ion batteries (NIBs) employ a doped P2-type phase using a novel Na-Mn-Li-O oxide composition with different ions to mitigate structural degradation at high voltages and enhance electrochemical performance. The sodium-ion batteries (NIBs) exhibit the stoichiometric ratios of sodium, manganese, and lithium for the battery cathode, and these are combined and stirred to form a granular mixture at a determined stoichiometric ratio. A doping element is added to the granular mixture, and the granular mixture is sintered at a predetermined time and temperature to form the NIB battery cathode material.

Description

Background Art

[0001] Background In recent years, lithium-ion batteries (LIBs) have been widely put into practical use, particularly for electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) equipped with or directly powered by LIBs. LIBs are widely used as the main power source in portable electronic devices, electric vehicles, and grid storage. Due to the raw material costs in the mining and refining of lithium and other metals used in charge materials such as Ni, Mn, and Co, the demand for more accessible battery cathode materials is increasing.

Summary of the Invention

Means for Solving the Problems

[0002] Summary A method for manufacturing a sodium-ion battery (NIB) employs a doped P2-type phase using a novel Na-Mn-Li-O oxide composition having different ions in order to reduce structural degradation at high voltages and enhance electrochemical performance. With the configuration herein, NIBs are achieved at low cost with abundant and environmentally friendly elements without using Co and Ni required by many conventional cathode materials.

[0003] Batteries for electric vehicles and hybrid vehicles are typically formed from a positive electrode material containing a lithium-containing positive electrode material metal and a negative electrode material such as carbon or graphite. The configuration herein is based in part on the finding that nickel, manganese, and cobalt (NMC) are often combined with lithium to form a positive electrode material for Li-ion batteries. Unfortunately, conventional methods for batteries for EVs (electric vehicles) have the drawback that typical positive electrode material metals are nickel, manganese, cobalt, and aluminum, which can involve high-cost mining, purification, and transportation costs for procurement. Accordingly, the configuration herein substantially overcomes the drawbacks of LIBs by providing a sodium ion (Na-ion) battery (NIB). While lithium-ion batteries (LIBs) are mainstream, sodium ion batteries (NIBs) have received increasing attention in recent years due to their low cost, the abundance of sodium ions in the earth's crust, environmental compatibility, and a mechanism similar to that of LIBs.

[0004] The configuration herein demonstrates a method of forming a sodium ion battery (NIB) by determining the stoichiometric ratio of sodium, manganese, and lithium for the battery positive electrode, combining sodium, manganese, and lithium, and stirring to form a granular mixture at the determined stoichiometric ratio. A doping element is added to the granular mixture, and the granular mixture is sintered at a predetermined time and temperature to form the positive electrode material.

[0005] In the method of the present disclosure for generating a secondary (rechargeable) battery, the method includes determining the stoichiometric ratio for the positive electrode material and combining Na2CO3, Mn2O3, and LiOH·H2O powders based on this stoichiometric ratio, thereby providing efficient cost and performance. Lithium hydroxide monohydrate is typically an inorganic compound (LiOH·H2O) in the form of a white crystalline powder and is strongly alkaline. Battery-grade lithium hydroxide is mainly used for the manufacture of positive electrode materials for high-energy lithium-ion batteries for applications such as electric vehicles, electric bicycles, electric tools, and energy storage systems.

[0006] The combined powders are mixed with a mortar and pestle, etc. to form a precursor mixture. The precursor mixture is sintered at about 800 °C for 14 hours at a heating and cooling rate of 2 °C / min in an air atmosphere to induce a solid-state reaction. An additional feature includes doping the mixture with a material based on its similarity to Mn, thereby improving performance while using a more readily available raw material for the cathode material.

[0007] Brief Description of the Drawings The foregoing and other objects, features, and advantages of the present invention will become apparent from the following description of specific embodiments of the present invention, which is illustrated in the accompanying drawings, wherein like reference numerals refer to the same parts throughout different figures. The drawings are not necessarily to scale, and emphasis is placed on illustrating the principles of the present invention.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying out the Invention

[0009] Detailed Description In the configuration shown below, an exemplary configuration of a NIB doped with elements such as Si and Ti is shown. The P2-type sodium-manganese-based layered cathode is a promising candidate for sodium-ion batteries (NIBs) to replace Li-ion technology in certain applications due to its high capacity from both cationic and anionic redox. However, the structural instability due to irreversible oxygen redox under high voltage still remains an issue. Here, a cobalt-free P2-Na 0.72 Mn 0.75 Li 0.24 X 0.01 O2 (X = Ti / Si) cathode has been developed. Excellent capacity retention and voltage retention rates have been achieved in half-cells after 150 cycles. This finding indicates that Ti localizes on the surface while Si diffuses into the bulk of the particles. Therefore, Ti can function as a protective layer to reduce side reactions in carbonate-based electrolytes. On the other hand, Si can control the local electronic structure and suppress oxygen redox activity. In particular, a full cell using hard carbon (about 300 - 335 W h kg based on the cathode mass -1 ) shows, after 500 cycles, 83% for P2-Na 0.72 Mn 0.75 Li 0.24 Si 0.01 O2 and 83% for P2-Na 0.72 Mn 0.75 Li 0.24 Ti 0.01It shows a capacity retention rate of 66% for O2, and this electrochemical stability is the best compared to other cathodes based on oxygen redox reported at present. This excellent cycle performance also results from the ability to suppress microcracking and planar slip in the particles. Overall, this improvement provides a novel composition for developing high-performance and low-cost cathodes for NIBs, and clearly shows the unique role of Ti / Si ions.

[0010] Driven by the success of the commercialization of lithium-ion batteries (LIBs), in recent years, NIBs have received much attention as an alternative to next-generation energy storage devices. Due to concerns about the high prices and limited availability of Li and Co in recent years, considering the advantages including low cost, environmental compatibility, similarity to the mechanism and manufacturing of LIBs, and the abundance of Na as an element in the earth's crust, the use of NIBs has become more attractive. To meet the demand in the growing market and practical applications such as Prussian blue, polyanion compounds, and layered transition metal oxides, multiple sodium-ion cathodes have been extensively studied.

[0011] Among various types of NIB cathode materials, Mn-based layered oxides, especially the so-called P2 and O3 types, are promising candidates due to their low cost, variable composition, suitable sodium-ion diffusion pathways, wide operating voltage, and high energy density. The difference in both is the stoichiometric ratio of Na and the stacking arrangement of Na atoms with respect to the transition metal (TM) layer (two Na ions in the trigonal prism site in P2 and three Na ions in the octahedral site in O3), which greatly affects the redox ability. The progress of sodium-ion cathodes is as follows. The P2-type Na cathode was first introduced with the composition of Na 0.70 MnO 2.25 . Subsequently, the well-known Na-deficient P2-type had a reversible capacity of Na 0.67 Mn 0.67 Ni 0.33 O2 (about 135 mA h g -1 ) and Na 0.67 Mn 0.5 Fe 0.5O2 (with a reversible capacity of about 190 mA h g -1 ). On the other hand, the introduction of inert elements such as Li + / Mg 2+ / Zn 2+ and vacancies (increase in the O / TM ratio) enables these ions to replace TM ions, promoting the formation of non-bonding O 2p orbitals. Therefore, high capacity can be achieved through the assistance of anion redox (O2− / O−) beyond 4.3 V.

[0012] In recent years, studies on Li substitution in Na-Mn-O oxides have revealed attractive specific capacities in the range of 1.5 - 4.5 V (vs. Na / Na + ) by utilizing the unhybridized O 2p anion redox. A P2 / O2-type Na g-1 with a reversible capacity of 200 mA h 5 / 6 [Li 1 / 4 Mn 3 / 4 O2 has been introduced at a cut-off voltage of 4.4 V. P2-type Na 0.6 Li 0.2 Mn 0.8 O2 has also been reported to be able to provide about 190 mA h g -1 after 100 cycles at a voltage of 2.0 - 4.6 V after the activation process. P2-type Na 0.72 [Li 0.24 Mn 0.76 O2 shows a high initial capacity of about 210 mA h g -1 (2.0 - 4.5 V), but it has been shown that the capacity rapidly decreases. On the other hand, other types of layered cathode structures such as P3-type Na 0.6 (Li 0.2 Mn 0.8 )O2 and O3-type NaLi 1 / 3 Mn 2 / 3 O2 (with a reversible capacity of about 190 mA h g -1 ) have also been investigated. In contrast to the latter configuration, significant voltage decay and irreversible O 2p redox have been observed in the former after 50 cycles. Inevitably, the high lattice strain of Na, irreversible oxygen loss, and Mn 3+The structural rearrangement induced by the Jahn-Teller distortion reduces the structural stability and electrochemical performance. Therefore, to address these problems, it is necessary to explore suitable elements added to the Na-Mn-Li-O composition (P2-NMO), and adjusting the local substitution of Mn ions is considered to be one of the most effective means. Among various elements, tetravalent Si and Ti have some advantages in maintaining structural stability due to the strong covalent bonds of Si-O and Ti-O. In fact, it has been shown that partial substitution of inert Ti in Na layered oxides gives positive results in terms of reducing structural changes, alleviating lattice strain, increasing the voltage / capacity retention rate, and improving the reversibility of TM / O migration during the sodiation / desodiation process. In studies on Li-rich layered oxides, it has been shown that Si at the TM site can reduce the O 2p band at the Fermi level, promote the formation of oxygen vacancies, and reduce the covalent nature between TM-O, enabling higher reversibility of anion redox. However, in the conventional approach, no reports have been shown regarding the role of Si or Ti as dopants in Na layered oxides.

[0013] In the configuration herein, P2-Na synthesized by an easy solid-state reaction 0.72 Mn 0.75 Li 0.24 X 0.01 O2 (X = Ti / Si) layered oxides are disclosed. By adding Ti / Si, the structural stability is significantly improved with both capacity (about 86 - 87%) and voltage retention rate (about 97%) after 150 cycles at 1C in the Na half-cell. The configuration herein shows that Si tends to diffuse into the bulk while Ti tends to exist on the surface. In particular, Ti improves the rated capacity and Si extends the cycle life. Further analysis shows that for the P2-Na 0.72 Mn 0.75 Li 0.24 Si 0.01 O2(1Si) sample, excellent structural integrity, Mn on the surface 4+Increases (reduction of structural strain due to the Jahn-Teller effect), decreases in microcracking, absence of planar slip, and low stacking faults are also confirmed. The main cause of capacity degradation is thought to be due to microcracking and planar slip in the particles. Based on theoretical calculations, Si can control the density of states of surrounding O atoms and thus suppress irreversible O redox activity. Furthermore, the performance of the full coin cell has a capacity retention rate of 66% (P2-Na 0.72 Mn 0.75 Li 0.24 Ti 0.01 O2(1Ti)) and 83% (1Si) after 500 cycles at 0.5C, while the pristine material (P2-Na 0.72 Mn 0.76 Li 0.24 O2(PR)) maintains only 25% of its initial capacity. A remarkable energy density of 300 - 335 Wh kg-1 based on the cathode mass at 0.5C can be achieved with the 1Ti / 1Si sample. In short, this study presents a novel and low-cost P2-type composition as a high-energy density cathode material for NIBs.

[0014] Figures 1A - F show morphological images of a sodium - ion battery (NIB) containing Si and Ti doping. Referring to Figures 1A - 1F, Figures 1A and B show enlarged SEM images of PR, Figures 1C and D show enlarged SEM images of 1Ti, and Figures 1D and E show enlarged SEM images of 1Si. The morphology of P2 - NMO particles shows a plate - like structure with an average particle size of 2 - 4 μm. Figure 2 shows a powder X - ray diffraction (XRD) pattern, and Figure 3 shows the layer structure of the P2 cathode. Referring to Figures 2 and 3, from Figure 2, all the powder X - ray diffraction (XRD) patterns are in good agreement with the structure of the P2 - type cathode (Figure 3) corresponding to an ABBA oxygen stacking arrangement with two Na atoms in the trigonal prism sites (space group: P63 / mmc). Thus, the resulting cathode material exhibits two sodium ions in the trigonal prism sites to form the P2 - layered oxide structure of Figure 3. In contrast, small signals around approximately 19 - 22°, which are different from the pure P2 phase, represent the superstructure arrangement of Li / Mn in the TM layer. This is induced by a difference in ionic radius of more than 15%. As shown in the inset of Figure 1b, the 1Ti and 1Si samples have distinct intensities of these peaks compared to PR, ensuring the influence of these ions on the arrangement of the TM layer even at a small amount of 1 mol.%. The Rietveld refinements in Figures 4A - 4C for PR, 1Ti, and 1Si respectively are also calculated to further confirm the structural parameters related to PR. Usually, after the addition of 1 mol.% of Ti / Si, the oxygen sites in the c - axis, unit cell volume, and Z position increase. Comparing with the reference pattern, since the refined values show an obvious decrease at the 2d site, Ti / Si ions affect the Na occupancy at the 2d site rather than the 2b site. These may be related to the local arrangement changes in the Li / Mn interlayer partially substituted by Ti / Si, causing differences in electrostatic force and binding energy at the atomic level.

[0015] In an exemplary configuration, a method of forming a sodium-ion (NIB) battery includes determining the stoichiometric ratios of sodium, manganese, and lithium for a battery cathode, as disclosed above, and combining and stirring sodium, manganese, and lithium to form a granular mixture in the determined stoichiometric ratios. The added sodium, manganese, and lithium further take the form of Na2CO3, Mn2O3, and LiOH·H2O, respectively, each having a purity of at least 98%. A doping element or compound such as Ti or Si is added to the granular mixture, and the granular mixture is sintered at a predetermined time and temperature to form a cathode material for the NIB. The stoichiometric ratios are typically molar amounts of both sodium and manganese that are about twice the molar ratio of lithium, and in some cases have equal molar amounts of both sodium and manganese, and the molar amounts of sodium and manganese are at least three times the molar amount of lithium.

[0016] The sintering temperature and time can be adjusted according to relevant factors. In a specific example, sintering includes heating at 700 °C to 900 °C for 12 to 16 hours. The molar amounts of the charge material metals and doping elements can be varied to some extent. Doping generally includes adding an amount of a doping element in an amount less than 10% and optionally less than 2% of the molar ratio of any of sodium, manganese, and lithium, and in many cases substantially less than that. The exemplary configuration includes a doping element of Ti or Si in an amount less than 5% or optionally less than 2% of the molar amount of Li.

[0017] The rate performance of the 1Ti sample shows good ionic conductivity at high rates compared to PR. PR is about 1.25 times higher than those of 1Ti and 1Si at low rates (250 vs 200 mA h g at 0.1C) -1)It has a large specific capacity, but the capacity degradation between each rate is more significant. At 5C, as is clear from the refinement results, both 1Ti and 1Si show performance exceeding PR due to a slight increase in the Na slab. The Ti / Si of 0.5 mol.% and 2 mol.% has also been systematically investigated to determine the optimal dopant ratio, and the composition has been confirmed by ICP-MS, with an acceptable difference of 10% or less between the nominal ratio by instrumental analysis and the experimental data. It should be noted that the dopant amount is relatively small (Table I). In contrast to 1 mol.%, 0.5 mol.% is too little to obtain good structural stability, while these 2 mol.% of these redox-inactive ions reduce the specific capacity. To avoid a specific capacity lower than PR, only 1 mol.% of Ti / Si is selected because these ions are electrochemically inert and do not contribute to the redox reaction. In addition, by adding these dopants, the involvement of O anion redox during the Na intercalation process is significantly smaller than PR, which is because these ions bring a stronger binding strength to O, resulting in a lower overall specific capacity. Referring to Figure 5, Figure 5 shows that the cycle stability of 1Ti 501 and 1Si 502 is also maintained at 86.82% and 87.44% at 1C after 150 cycles in the range of 1.5 - 4.5, while PR 500 is 74.51%. As shown in previous reports, it is worth noting that the involvement of oxygen redox at high voltages also plays a role in providing additional capacity. At high voltages, unfavorable side reactions with the electrolyte and structural changes due to oxygen redox and Mn / Li migration cannot be avoided, which leads to performance degradation of the P2-NMO cathode in long-term cycles. Referring to Figure 6, it can be seen that the 1Ti 601 and 1Si 602 samples show a remarkable voltage retention rate of about 97% after 150 cycles (close to 93% of PR600). In fact, the 1Ti and 1Si samples show neither planar slip or microcracking along the particles after cycling, and these factors are considered to be the main causes of capacity degradation.

[0018]

Table 1

[0019] In an exemplary configuration, a sodium ion cathode material doped with Ti and Si is shown. In one configuration, the cathode material compound for a secondary Na ion battery comprises a sintered granular mixture consisting of: 0.72 moles of Na, 0.75 moles of Mn, 0.24 moles of Li, and 0.01 moles of Ti or Si.

[0020] P2-Na 0.72 Mn 0.76 Li 0.24 O2(PR) was synthesized by an easy solid-state reaction, and stoichiometric ratios of Na2CO3 (VWR, 99.5%), Mn2O3 (SIGMA-ALDRICH®, 99.9%) and LiOH·H2O (Sigma-Aldrich, ≧98.0%) powders were thoroughly mixed in an agate mortar and pestle. The mixed powders were then sintered at 800 °C for 14 hours in an air atmosphere with a heating and cooling rate of 2 °C / min. Similarly, Ti / Si samples were prepared by adding 1 mol% TiO2 (Sigma-Aldrich, 99.7%) or SiO2 (ALFA AESAR®) as Ti and Si sources respectively, followed by the same sintering conditions as PR. The final products were denoted as 1Ti and 1Si for P2-Na 0.72 Mn 0.75 Li 0.24 Ti 0.01 O2 and P2-Na 0.72 Mn 0.75 Li 0.24 Si 0.01 O2 respectively. Note that 0.5 mol% Si (0.5Si), 0.5 mol% Ti (0.5Ti), 2 mol% Si (2Si) and 2 mol% Ti (2Ti) were also prepared by similar means to investigate the optimal composition.

[0021] Structural, morphological, and atomic distribution analyses were tested by X-ray diffraction (XRD; PANalytical Empyrean, Cu Kα target) and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy. The FullProf Suite program was used for the crystal information obtained with Na 0.67 Li 0.17 Mn 0.83 O2 (ICSD No. 04-020-1867). Inductively coupled plasma mass spectrometry (ICP-MS) was performed on the as-prepared samples to confirm the molar ratios. For postmortem analysis, the electrodes were disassembled in a glove box under an argon atmosphere, rinsed with dimethyl carbonate (DMC), and dried in the glove box prior to characterization by XPS (X-ray photoelectron spectroscopy) and TEM (transmission electron microscopy). The surface information of pristine powders and electrodes after cycling was examined by X-ray photoelectron spectroscopy (XPS; PHI 5000 VersaProbe II) under the following test conditions: 100 μm beam (25 W) + Al Kα radiation (hυ = 1486.6 eV), Ar + ion and electron beam sample neutralization, fixed analyzer transmission mode, and pass energy 23.5 eV. The XPS spectra were processed using XPSpeak41 software. Depth analysis of the electrodes after cycling was prepared by Ar + sputtering from the electrode surface for 1 minute. Note that all spectra were calibrated according to the peak position of C 1s (284.8 eV). High-resolution transmission electron microscopy (HRTEM) of pristine and cycled electrodes was analyzed using an Argonne Chromatic Aberration-corrected TEM (ACAT, FEI Titan 80-300 transmission electron microscope equipped with an image corrector that corrects both spherical and chromatic aberrations). Electron energy loss spectroscopy (EELS) was acquired using the ACAT operating at 200 KV in image-coupled S / TEM mode. The TEM samples were prepared by Ar +It was prepared using ion milling, followed by an ion milling polishing process at an acceleration voltage of 0.3 kV. Note that the electrodes after the cycle were thoroughly washed with dimethyl carbonate (DMC) before post-mortem analysis and dried in a glove box.

[0022] The half-cell was assembled in a glove box under an argon atmosphere (<0.1 ppm of O2 and H2O) with Na metal as the positive and negative electrodes, a glass microfiber separator (Whatman GF / D), and 1.0 M NaPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC) (2:3 by volume) containing 5 vol% fluoroethylene carbonate (FEC) as the electrolyte. The 12 mm electrode contained the positive active material, super C65 carbon black, and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1. The amount of active material used was 3.0 ± 0.5 mg cm -2 It was. The cell was tested with a Land Battery Testing System (LAND CT2001A) at 1.5 - 4.5 V vs. Na / Na + (1C = 200 mAh g -1 )). For the full-cell test, the voltage window was set to 1.4 - 4.2 V, with the activation cycle at 0.1C and subsequent cycles at 0.5C. The capacity ratio of the negative electrode to the positive electrode (N / P ratio) was controlled to be 1.4 - 1.5:1.0. Hard carbon (MSE Supplies LLC) was used as the negative electrode, with a weight ratio of 8:1:1 (active material:super C65:PVDF). The hard carbon (HC) was dried at 120 °C before use. To minimize the low Coulombic efficiency (due to the irreversibility of Na) in the first cycle of HC, the HC electrode was formed with a half-cell using Na metal at 0.1C, 0.01 - 2.0 V (vs. Na / Na +) It was activated by performing 3 cycles. Then, the half-cell was disassembled when it was fully charged to 2.0 V. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) data were collected using a constant current analyzer (Bio-Logic SAS VMP3). For the EIS analysis, the frequency range and amplitude were 10 mHz to 100 kHz and 10 mV, respectively. For the CV analysis, the scan rate of 0.1 mV s -1 was applied from 1.5 to 4.5 V (vs. Na / Na + ). The cell tests were conducted at room temperature.

[0023] Although the systems and methods defined herein have been particularly shown and described with reference to their embodiments, those skilled in the art will understand that various modifications in form and detail may be made without departing from the scope of the invention as included in the appended claims.

Claims

1. A method of forming a sodium ion (NIB) battery, comprising: determining the stoichiometric ratio of sodium, manganese, and lithium for a battery cathode; combining and stirring the sodium, manganese, and lithium to form a granular mixture in the determined stoichiometric ratio; adding a doping element to the granular mixture; sintering the granular mixture at a predetermined time and temperature to form a cathode material. A method as described above.

2. The method according to claim 1, wherein the doping element comprises Ti or Si.

3. The method according to claim 1, wherein the sintering comprises heating at 700 °C to 900 °C for 12 to 16 hours.

4. The method according to claim 1, wherein the cathode material exhibits two sodium ions at trigonal prism sites to form a P2 layered oxide structure.

5. The method according to claim 1, further comprising adding an amount of the doping element in an amount less than 10% of the molar ratio of any of the sodium, manganese, and lithium.

6. The method according to claim 5, further comprising adding an amount of the doping element in an amount less than 10% of the molar ratio of any of the sodium, manganese, and lithium.

7. The method according to claim 6, wherein the amount of the doping element is 2% or less of the molar ratio of any of the sodium, manganese, and lithium.

8. The sodium, manganese and lithium are Na ２ CO ３ , Mn ２ O ３ and LiOH.H ２ The method of claim 1 , further comprising O.

9. The method according to claim 1, wherein the stoichiometric ratio includes molar amounts of both sodium and manganese that are at least twice the molar ratio of lithium.

10. The method according to claim 9, wherein the stoichiometric ratio includes equal molar amounts of both sodium and manganese, and the molar amounts of sodium and manganese are at least three times the molar amount of lithium.

11. The method according to claim 1, wherein the sodium, manganese, and lithium are at least 98% pure.

12. The method according to claim 5, wherein the doping element comprises Ti or Si in an amount less than 5% of the molar amount of Li.

13. The method according to claim 5, wherein the doping element comprises Ti or Si in an amount less than 2% of the molar amounts of nickel and manganese.

14. A cathode material compound for a secondary Na ion battery, comprising: 0.72 moles of Na, 0.75 moles of Mn, 0.24 moles of Li, and 0.01 mol of Ti or Si A cathode material compound comprising a sintered granular mixture consisting thereof. **Claim 15** A method for forming a P2 Na-ion battery cathode material, comprising: 0.72 mol of Na, 0.75 mol of Mn, 0.24 mol of Li, and 0.01 mol of Ti or Si Mixing and stirring the stoichiometric ratio of cathode material elements; Sintering the mixed and stirred cathode material elements at 800 °C for 14 hours to obtain a cathode active material for the battery; A method comprising the above steps. **Claim 16** The method according to claim 15, further comprising heating and cooling the stirred cathode material elements at 2 °C / min.

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