Sodium ion battery cathode material

Abstract

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

Description

Background Art

[0001] Li-ion batteries (LIBs) have become widely used in recent decades, especially for electric vehicles (EVs) and plug-in electric vehicles (PHEVs) that have been equipped with LIBs or powered directly by LIBs. LIBs have been widely used in portable electronic devices, electric vehicles, and grid storage as the main power source. The cost of mining and refining raw materials for lithium and other metals (such as Ni, Mn, and Co) used for charging materials has driven the demand for more easily available battery cathode materials. Summary of the invention

[0002] A method for producing sodium-ion batteries (NIBs) that employ a doped P2-type phase using a novel Na-Mn-Li-O oxide composition with different ions to mitigate structural degradation and improve electrochemical performance at high voltages. The configuration herein demonstrates low-cost NIBs due to abundant and environmentally friendly elements, unlike Co and Ni, which are required in most conventional cathode materials.

[0003] Batteries for electric vehicles and hybrid vehicles are typically formed of cathode materials (including cathode material metals, including lithium) and anode materials (such as carbon or graphite). The configuration of this article is based in part on the following observations: nickel, manganese and cobalt (NMC) are usually combined with lithium to form cathode materials for Li-ion batteries. Unfortunately, there are disadvantages in the conventional methods of EV (electric vehicle) batteries, that is, typical cathode material metals are nickel, manganese, cobalt and aluminum, and procurement may involve expensive mining, refining and transportation costs. Therefore, the configuration of this article substantially overcomes the shortcomings of LIB by providing sodium ion (Na ion) batteries (NIB). Although lithium ion batteries (LIB) are dominant, sodium ion batteries (NIB) have become more attractive in recent years due to their low cost, abundant sodium ions in the earth's crust, environmental compatibility and mechanisms similar to LIB.

[0004] The configuration herein demonstrates a method of forming a sodium ion battery (NIB) by determining a stoichiometric ratio of sodium, manganese, and lithium for a battery cathode, combining and stirring the sodium, manganese, and lithium to form a particle mixture of the determined stoichiometric ratio, adding a doping element to the particle mixture, and sintering the particle mixture for a predetermined time and temperature to form a cathode material.

[0005] In the disclosed method, a method for producing a secondary (rechargeable) battery includes determining a stoichiometric ratio for a cathode material and adding Na 2 CO 3 , Mn 2 O 3 and LiOH·H 2O powder combination to provide effective cost and performance. Lithium hydroxide monohydrate is an inorganic compound (LiOH·H 2 O), which is typically in the form of a white crystalline powder and is strongly alkaline. Battery-grade lithium hydroxide is primarily used to produce cathode materials for high-energy lithium-ion batteries for applications such as electric vehicles, electric bicycles, power tools, and energy storage systems.

[0006] The combined powders are mixed, for example, using an agate mortar and pestle, to form a precursor mixture. The precursor mixture is sintered at about 800° C. for 14 hours in an air atmosphere while heating at 2° C. min -1 The solid state reaction is initiated by heating and cooling at a rate of 100°. Additional features include doping the mixture with materials based on materials similar to Mn, thereby providing improved performance while using more readily available raw cathode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The above and other objects, features and advantages of the present invention will be apparent from the following description of specific embodiments of the present invention as shown in the accompanying drawings, in which like reference numerals refer to like parts throughout the different views. The drawings are not necessarily to scale, but emphasis is placed on illustrating the principles of the present invention.

[0008] Figure 1A 1F shows a topographic image of a sodium ion battery (NIB) including Si and Ti doping;

[0009] Figure 2 An X-ray powder diffraction (XRD) pattern is shown;

[0010] Figure 3 The layered structure of the P2 cathode is shown;

[0011] FIG. 4A to FIG. 4C Rietveld refinement curves of PR, 1Ti and 1Si are shown;

[0012] Figure 5 shows the percentage of half-cell capacity retention during 150 cycles for each sample of PR, 1Ti, and 1Si; and

[0013] Figure 6 The voltage holding ratios of PR (original material), 1Ti, and 1Si are shown. DETAILED DESCRIPTION

[0014] In the configuration depicted below, example configurations of NIBs are shown, including doping with elements such as Si and Ti. P2-type sodium-manganese based layered cathodes are potential candidates for Na-ion batteries (NIBs) to replace Li-ion technology in certain applications due to their high capacity from both cation and anion redox. However, structural instability stemming from irreversible oxygen redox at high voltages remains a challenge. Here, a highly sustainable cobalt-free P2-Na 0.72 Mn 0.75 Li 0.24 X 0.01 O 2 (X = Ti / Si) cathode. The half-cell achieved excellent capacity retention and voltage retention after 150 cycles. This finding shows that Ti is localized on the surface, while Si diffuses into the bulk of the particle. Therefore, Ti can act as a protective layer that mitigates side reactions in carbonate-based electrolytes. At the same time, Si can modulate the local electronic structure and suppress oxygen redox activity. Notably, the hard carbon (≈300–335 W h kg based on cathode mass) -1 ) after 500 cycles for P2-Na 0.72 Mn 0.75 Li 0.24 Si 0.01 O 2 provides 83% capacity retention and for P2-Na 0.72 Mn 0.75 Li 0.24 Ti 0.01 O 2 A capacity retention of 66% is provided; this electrochemical stability is the best compared to other oxygen redox-based cathodes reported so far. The excellent cycling performance also stems from the ability to suppress intra-particle microcracks and planar slip. In summary, this improvement provides a new composition for the development of high-performance, low-cost cathodes for NIBs and highlights the unique role of Ti / Si ions.

[0015] Inspired by the successful commercialization of Li-ion batteries (LIBs), many have recently turned their interest to NIBs as an alternative for next-generation energy storage devices. Due to the concerns over the high prices and availability limitations of Li and Co in recent years, the use of NIBs has become more attractive given their advantages, including low cost, environmental friendliness, similarities with LIB mechanisms and fabrication, and the abundance of Na in the earth's crust. A variety of Na-ion cathodes have been extensively studied to meet the growing market demand and practical applications, such as Prussian blue, polyanionic compounds, and layered transition metal oxides.

[0016] 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 Na ion diffusion pathways, wide operating voltage and high energy density. The difference between the two is the stoichiometric ratio of Na and the stacking arrangement of Na atoms relative to the transition metal (TM) layers (for P2, 2 Na ions in prismatic sites and for O3, 3 Na ions in octahedral sites), which have a great influence on the redox capacity. The evolution of the sodium ion cathode is as follows. The P2-type Na cathode was first developed with Na 0.70 MnO 2.25 Later, the well-known Na-deficient P2 type was developed between the potential range of 1.5-4.3 V, with a composition of Na 0.67 Mn 0.67 Ni 0.33 O 2 (The reversible capacity is about 135 mA hg -1 and Na 0.67 Mn 0.5 Fe 0.5 O 2 (The reversible capacity is about 190 mA hg -1 ). At the same time, inert elements such as Li are introduced into the P2 structure. + / Mg 2+ / Zn 2+ and vacancies (increasing the O / TM ratio) can favor the formation of non-bonding O 2p orbitals, where these ions replace TM ions. Therefore, high capacity is feasible with the assistance of anionic redox (O2– / O–) over 4.3 V.

[0017] Recent studies on Li substitution in Na-Mn-O oxides have revealed that the redox reaction of unhybridized O 2p anions can be achieved at 1.5–4.5 V (vs. Na / Na + ) have attractive specific capacities. P2 / O2-type Na 5 / 6 [Li 1 / 4 Mn 3 / 4 ]O 2 , the reversible capacity is 200mAh at the cut-off voltage upper limit of 4.4V g-1 In addition, P2-type Na 0.6 Li 0.2 Mn 0.8 O 2 After the activation process, it can provide about 190mAh g after 100 cycles at a voltage between 2.0-4.6V. -1 . P2 type Na 0.72 [Li 0.24 Mn 0.76]O 2 It has been shown to have a value of about 210 mA hg -1 On the other hand, other types of layered cathode structures have been explored, such as P3-type Na 0.6 (Li 0.2 Mn 0.8 ) 2 and O3 NaLi 1 / 3 Mn 2 / 3 O 2 (about 190mA hg -1 ). Compared with the latter configuration, the former was found to have significant voltage decay and irreversible O 2p redox after 50 cycles. Inevitably, the high lattice strain of Na, irreversible oxygen loss, and the presence of Mn 3+ The structural rearrangement caused by the Jan-Taylor deformation deteriorates the structural stability and electrochemical performance. Therefore, in order to solve these problems, it is necessary to find suitable elements to add 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 ways. Among various elements, tetravalent Si and Ti have several advantages in maintaining structural stability due to the strong covalent bonding of Si-O and Ti-O. In fact, partial substitution of inert Ti in Na layered oxides has shown positive results in reducing structural evolution, reducing lattice strain, increasing voltage / capacity retention, and improving the reversibility of TM / O migration during sodium insertion / stripping. Studies on Li-rich layered oxides have shown that Si in TM sites can reduce the O 2p band at the Fermi level, promote the formation of oxygen vacancies, and reduce the degree of covalency between TM-O, thereby allowing greater reversibility of anion redox. However, conventional methods have not shown reports on the role of Si or Ti as dopants in Na layered oxides.

[0018] The configuration herein discloses P2-Na synthesized via a facile solid-state reaction 0.72 Mn 0.75 Li 0.24 X 0.01 O 2 (X = Ti / Si) layered oxides. With the addition of Ti / Si, the structural stability is significantly improved after 150 cycles at 1C in Na half-cells, with improved capacity (about 86%–87%) and voltage retention (about 97%). The configurations in this paper show that Ti prefers to be at the surface, while Si diffuses into the bulk. Specifically, Ti improves the rate performance and Si extends the cycle life. Additional analysis also confirms that for P2-Na 0.72 Mn 0.75 Li 0.24 Si0.01 O 2 The (1Si) sample has excellent structural integrity after cycling, with more Mn on the surface 4+ (less structural deformation from the Chiang-Taylor effect), reduced microcracks, no plane slip, and low stacking faults. The main reason for the capacity drop is believed to originate from microcracks and plane slip within the particles. Based on theoretical calculations, Si can regulate the state density of the surrounding O atoms; thereby inhibiting the irreversible O redox activity. In addition, the performance of the full button cell has 66% (P2-Na 0.72 Mn 0.75 Li 0.24 Ti 0.01 O 2 (1Ti)) and 83% (1Si), among which the original material (P2-Na 0.72 Mn 0.76 Li 0.24 O 2 (PR)) retains only 25% of the initial capacity. Remarkable energy densities of 300–335 W h kg-1 based on cathode mass can be achieved at 0.5C with the 1Ti / 1Si sample. In short, this work reveals a novel and low-cost P2-type composition as a high-energy-density cathode material for NIBs.

[0019] Figure 1A Figure 1F shows the topography images of Si and Ti doped sodium ion batteries (NIB). Figure 1A To Figure 1F, Figure 1A to Figure 1B An enlarged SEM image of PR is shown; Figure 1C to Figure 1D shows 1Ti, and Figure 1D 1E shows 1Si. The morphology of P2-NMO particles shows a plate-like structure with an average particle size of 2-4 um. Figure 2 The X-ray powder diffraction (XRD) pattern is shown, and Figure 3 The layered structure of the P2 cathode is shown. Figure 2 and Figure 3 ,from Figure 2 All X-ray powder diffraction (XRD) patterns are consistent with the structure of the P2 cathode ( Figure 3 ) matches well, and this structure corresponds to an ABBA oxygen stacking order with two Na atoms in the prismatic sites (space group: P6 3 / mmc). Therefore, the resulting cathode material has two sodium ions in the prismatic sites to form Figure 3 In contrast, the 19–22 oThe small signal near indicates the superstructural ordering of Li / Mn within the TM layer. This is caused by the difference in ionic radius equal to or greater than 15%. Figure 1B As shown in the inset of , 1Ti and 1Si samples have different intensities of these peaks compared to PR, confirming that these ions have an effect on the ordering of the TM layers even at an amount of only 1 mol.%. FIG. 4A to FIG. 4C Rietveld refinements in were performed to further confirm the structural parameters associated with PR. In general, the oxygen sites at the c-axis, unit cell volume, and Z position increased after the addition of 1 mol.% Ti / Si. The effect of Ti / Si ions on the occupancy of Na at the 2d site is greater than that at the 2b site as the refined values ​​show a significant decrease at the 2d site compared to the reference pattern. These may be related to the changes in the local ordering between the Li / Mn layers, which are partially replaced by Ti / Si, causing differences in electrostatic forces and binding energies at the atomic scale.

[0020] In an example arrangement, a method of forming a sodium ion (NIB) battery includes determining a stoichiometric ratio of sodium, manganese, and lithium for a battery cathode as disclosed above, and combining and stirring the sodium, manganese, and lithium to form a particle mixture of the determined stoichiometric ratio. The added sodium, manganese, and lithium are further each prepared in a Na+ phase having a purity of at least 98%. 2 CO 3 , Mn 2 O 3 and LiOH·H 2 O form. A doping element or compound (such as Ti or Si) is added to the particle mixture; and the particle mixture is sintered for a predetermined time and temperature to form a cathode material for NIB. The stoichiometric ratio is typically about twice the molar ratio of lithium for both sodium and manganese, and in some cases, the molar ratios of sodium and manganese are equal, wherein the molar ratio of sodium and manganese is at least three times the molar ratio of lithium.

[0021] The temperature and duration of sintering can be adjusted according to relevant factors; in a specific example, sintering includes heating between 700°C and 900°C for between 12-16 hours. The molar amounts of the charging material metals and doping elements can vary slightly. Doping typically includes adding an amount of doping element in a molar ratio of less than 10% of any one of sodium, manganese and lithium, and optionally less than 2%, typically in a significantly lesser amount. Example arrangements include a molar amount of a doping element of Ti or Si less than 5% of the molar amount of Li, or optionally less than 2%.

[0022] The rate performance of the 1Ti sample shows better ionic conductivity at high rates compared to PR. Although the specific capacity of PR at low rates is about 1.25 times that of 1Ti and 1Si (250 vs. 200 mA h g at 0.1C), the specific capacity of PR at low rates is about 1.25 times that of 1Ti and 1Si. -1 ), but the capacity decay at each rate is more significant. At 5C, the performance of both 1Ti and 1Si is better than that of PR, which is due to the refinement results showing a slight increase in Na laths. Note that 0.5mol.% and 2mol.% Ti / Si were also systematically examined to determine the optimal dopant ratio, and the composition was confirmed by ICP-MS, where there was an acceptable difference of = <10% between the nominal ratio caused by instrumental analysis and the experimental data, and the doping amount was relatively small (Table I). Compared with 1mol.%, 0.5mol.% is too small to obtain good structural stability, while 2mol.% of these redox inert ions will reduce the specific capacity. In order to avoid a lower specific capacity than PR, only 1mol.% Ti / Si was selected because these ions are electrochemically inert and do not contribute to the redox reaction. In addition, by adding these dopants, the participation of O anion redox in the Na insertion process is much smaller than that of PR, because these ions provide stronger bonding strength with O, resulting in a lower overall specific capacity. Reference Figure 5 , Figure 5 It is shown that the cycling stability at 1C for 1Ti 501 and 1Si 502 is also maintained at 86.82% and 87.44%, respectively, after 150 cycles between 1.5 and 4.5, while that for PR 500 is 74.51%. It is noteworthy that the involvement of oxygen redox at high voltage also plays a role in providing additional capacity, as shown in previous reports. At high voltage, unfavorable side reactions with the electrolyte as well as structural transformations due to oxygen redox and Mn / Li migration are inevitable, which leads to the performance degradation of the P2-NMO cathode during extended cycling. Ref. Figure 6 , it can be seen that the 1Ti 601 and 1Si 602 samples give a remarkable voltage retention of about 97% after 150 cycles (similar to 93% for PR 600). In fact, the 1Ti and 1Si samples do not show any planar slip or microcracks with the particles after cycling, factors that are considered to be the main cause of capacity degradation.

[0023]

[0024] Table I

[0025] In example configurations, Ti and Si doped sodium ion cathode materials are presented. In one configuration, a cathode material compound for a secondary Na-ion battery comprises a sintered particle mixture consisting of:

[0026] 0.72 mol Na;

[0027] 0.75 mol Mn;

[0028] 0.24 mol Li; and

[0029] 0.01 mol Ti or Si.

[0030] P2-Na 0.72 Mn 0.76 Li 0.24 O 2 (PR) was synthesized via a facile solid-state reaction in which a stoichiometric ratio of Na 2 CO 3 (VWR, 99.5%), Mn 2 O 3 ( 99.9%) and LiOH·H 2 O (Sigma-Aldrich, ≥98.0%) powders were thoroughly mixed in an agate mortar and pestle. The mixed powders were then heated at 800 °C in air atmosphere at 2 °C min -1 The Ti / Si samples were sintered for 14 h at heating and cooling rates of 1 mol% TiO 2 (Sigma-Aldrich, 99.7%) or SiO 2 (ALFA ) as Ti and Si sources and followed the same sintering conditions as PR. 0.72 Mn 0.75 Li 0.24 Ti 0.01 O 2 and P2-Na 0.72 Mn 0.75 Li 0.24 Si 0.01 O 2 , the final products are denoted as 1Ti and 1Si, respectively. Note that 0.5mol% Si (0.5Si), 0.5mol% Ti (0.5Ti), 2mol% Si (2Si), and 2mol% Ti (2Ti) were also prepared by the same means to explore the optimized composition.

[0031] The structure, morphology and elemental distribution were examined by X-ray diffraction (XRD; PANalytical Empyrean, Cu Kα target) and scanning electron microscopy combined with energy dispersive X-ray spectroscopy. The FullProfSuite program was used to analyze the Na 0.67 Li 0.17 Mn0.83 O 2 as a reference pattern to obtain crystallinity information (ICSD No. 04-020-1867). In order to confirm the molar ratio, the samples prepared in this way were subjected to inductively coupled plasma mass spectrometry (ICP-MS). For subsequent analysis, the electrodes were disassembled in an argon-filled glove box, rinsed with dimethyl carbonate (DMC) and dried in the glove box before XPS (X-ray photoelectron spectroscopy) and TEM (transmission electron microscopy) characterization. The surface information of the original powder and the cycled electrode was studied by X-ray photoelectron spectroscopy (XPS; PHI5000VersaProbe II) under the following test conditions; a 100-μm beam (25 W) with Al Kα radiation (hυ = 1486.6 eV), Ar + Ion and electron beam sample neutralization, fixed analyzer transmission mode and 23.5eV pass energy. XPS spectra were processed using XPSpeak41 software. Depth analysis of cycled electrodes was performed by 1 minute Ar + The electrodes were prepared by sputtering. Note that all spectra were calibrated according to the peak position of C1s (284.8 eV). HRTEM of pristine and cycled electrodes was analyzed on 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 in image-coupled S / TEM mode using an ACAT operated at 200 KV. TEM samples were acquired using an Ar with an accelerating voltage of 4 kV. + The electrodes were prepared by ion milling followed by ion milling polishing process with an accelerating voltage of 0.3 kV. Note that the cycled electrodes were washed thoroughly with dimethyl carbonate (DMC) and dried in a glove box before post analysis.

[0032] The cathode was anode, Na metal, glass microfiber separator (Whatman GF / D), and 1.0 M NaPF in ethylene carbonate (EC) and diethyl carbonate (DEC) (2:3 by volume) containing 5 vol% fluoroethylene carbonate (FEC). 6 As electrolyte, the argon-filled glove box (<0.1 ppm O 2 and H 2 O). The 12-mm electrode was composed of active cathode material, super C65 carbon black, and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1. The active material loading was 3.0 ± 0.5 mg cm -2 . Using the Land battery test system (LAND CT2001A) relative to Na / Na +Between 1.5-4.5V (1C = 200mAh g -1 ) test cells. For full cell tests, the voltage window was set between 1.4–4.2 V with an activation cycle of 0.1 C and 0.5 C in subsequent cycles. The capacity ratio of anode to cathode (N / P ratio) was controlled at 1.4–1.5:1.0. Hard carbon (MSE Supplies LLC) was used as the anode with a weight ratio of 8:1:1 (active material: Super C65:PVDF). The hard carbon (HC) was dried at 120 °C before use. In order to minimize the low Coulombic efficiency in the first cycle of HC (due to the irreversibility of Na), a half-cell was formed with Na metal and charged at 0.01–2.0 V (vs. Na / Na + ) for 3 cycles at 0.1C to activate the HC electrode. Then, when fully charged to 2.0 V, the half-cell was disassembled. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) data were collected using a constant current analyzer (Bio-Logic SAS VMP3). For EIS analysis, the frequency range and amplitude were 10 mHz–100 kHz and 10 mV, respectively. For CV analysis, the 1.5–4.5 V (vs. Na / Na + ) between 0.1mV s -1 The battery tests were performed at room temperature.

[0033] While the systems and methods defined herein have been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention as encompassed by the appended claims.

Claims

1. A method for forming a sodium ion (NIB) battery, the method include: Determine the stoichiometric ratios of sodium, manganese and lithium for the battery cathode; combining and stirring the sodium, manganese and lithium to form a particulate mixture of a determined stoichiometric ratio; adding a doping element to the particle mixture; as well as The particle mixture is sintered for a predetermined time and temperature to form a cathode material.

2. The method according to claim 1, in, The doping element includes Ti or Si.

3. The method according to claim 1, in, Sintering involves heating between 700°C and 900°C for between 12-16 hours.

4. The method according to claim 1, in, The cathode material has two sodium ions in prismatic sites to form a P2 layered oxide structure.

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

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

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

8. The method according to claim 1, in, The sodium, manganese and lithium further include Na 2 CO 3 , Mn 2 O 3 and LiOH·H 2 O.

9. The method according to claim 1, in, 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, in, The stoichiometric ratio includes equal molar amounts of both sodium and manganese, with the molar amounts of sodium and manganese being at least three times the molar amount of lithium.

11. The method according to claim 1, in, The sodium, manganese and lithium have a purity of at least 98%.

12. The method according to claim 5, in, The doping element includes Ti or Si, and the molar amount thereof is less than 5% of the molar amount of Li.

13. The method according to claim 5, in, The doping element includes Ti or Si in a molar amount less than 2% of the molar amount of Ni and Mn.

14. A cathode material compound for a secondary Na-ion battery, the cathode material compound comprising: A sintered particle mixture consisting of: 0.72 mol Na; 0.75 mol Mn; 0.24 mol Li; and 0.01 mol Ti or Si.

15. A method for forming a P2 Na-ion battery cathode material, the method include: The cathode material elements are mixed and stirred in stoichiometric proportions, and the cathode material elements include: 0.72 mol Na; 0.75 mol Mn; 0.24 mol Li; and 0.01 mol Ti or Si; and These mixed and stirred cathode material elements were sintered at 800° C. for 14 hours to obtain an active cathode material for a battery.

16. The method of claim 15, further comprising: include: The stirred cathode material elements were heated and cooled at 2°C per minute.

Images