TW201944638A - Silicon anode of lithium-ions battery with specific structure - Google Patents

Abstract

A silicon-based anode of Li-ions batteries included nuclides. The nuclides equip with the same structure similar to Li4.1Si_Cmcm, Li13Si4_Pbam, Li2Si_C12m1 or LiSi_I41/AZ. Li4.1Si_Cmcm is originally existing only at high temperature. While, we clearly evidence the existence of Li4.1Si_Cmcm in the specifically-designed silicon anode. With the nuclides, the specifically-designed silicon anode can transform totally to Li4.1Si_Cmcm, Li13Si4_Pbam, Li2Si_C12m1 or LiSi_I41/AZ and display ultra-high capacity. With charging and discharging testing, the anode can keep capacity of 2500 mAh/g after 250 cycles. The capacity is six times more than that of graphite anode and is much higher than that of conventional silicon anode, because, the final phase of the specifically-designed silicon is different to that of the conventional one. Our design can also be applied to particles with specific morphology, like hollow particles. The design thus can improve the capacity of silicon in practice and meanwhile the stability. As known, the capacity of conventional silicon anode in practice is not quite high, huge volume expansion of conventional silicon anode will cause the cracking of anode and the failure of Li-ion batteries.

Description

   Special structure of lithium battery pure silicon anode   

The present invention relates to a lithium-silicon crystal with a special structure, and its use and manufacturing method for a lithium battery anode.

In recent years, the development of electric vehicles has been advancing with each passing day, and the performance of electric vehicles has also improved to a level comparable to that of supercars manufactured by internal combustion engine. The excellent performance of electric vehicles mainly depends on the characteristics of lithium-ion batteries: 1. High energy density for high endurance; 2. High power density for fast start; 3. Stability of charge and discharge and safety and durability. However, the current electric vehicle still has the problem of insufficient electric capacity, which brings anxiety to the driver's mileage, and thus the use of electric vehicles cannot be fully popularized. This has a considerable relationship with the lack of capacitance of the electrode materials of lithium batteries for vehicles.

Traditionally, lithium batteries use graphite as the anode material, but the theoretical capacity of graphite is only 372 mAh / g, which is no longer sufficient for automotive lithium batteries. The theoretical capacity of silicon is 4200mAh / g, which is about 11 times higher than graphite, so it is considered to replace traditional graphite electrodes as a new generation of battery anode materials.

In theory, Li ₂₂ Si ₅ _F23 lithium-silicon structure will be formed after charging and discharging of ordinary pure silicon anode, and it will provide a theoretical capacity of 4200mAh / g. However, in practical use, it is limited by thermodynamics and dynamics. Generally, after the pure silicon anode is charged and discharged, a structure of Li ₁₅ Si ₄ _I-43d will be formed, which can provide a theoretical capacitance of 3579mAh / g. However, the actual measurement results show that, under normal circumstances, the pure silicon anode can only obtain a capacitance of about 1600mAh / g after charging, which is far from the theoretical value. In addition, violent volume expansion (400%) will occur, resulting in electrode plate cracking and battery failure.

Therefore, an improved pure silicon anode is proposed, which can show higher capacitance and better stability in practical use, which has become a problem to be solved in the use of lithium batteries.

How to control the formation of lithium-silicon structure and generate corresponding capacitance is an important issue for the fabrication of pure silicon anodes. It is disclosed in the present invention that, in addition to Li ₂₂ Si ₅ _F23 and Li ₁₅ Si ₄ _I-43d structures, there are several lithium-silicon structures with different compositions. The Li _4.1 Si_Cmcm structure in Zeilinger et al. ( Chem. Mater. 2013 , 25, 4623-4632) pointed out that it is a high-temperature stable phase, which can exist only when the temperature is higher than 481 degrees. The present invention synthesizes and confirms for the first time that the Li _4.1 Si_Cmcm structure can exist in a normal temperature state and can be used as a material for a pure silicon anode.

Based on the above object, the present invention provides a lithium-silicon compound polymorph for a pure silicon anode of a lithium battery, which has substantially the same X-ray powder diffraction pattern (XRPD) as that shown in FIG. The X-ray absorption spectrum is the same as that shown in FIG. 6A.

In some particular aspects of embodiments of the present invention, of the lithium - silicon compound selected from the polymorph in which one or more of _{Li 4.1 Si_Cmcm, Li1 3 Si 4} _Pbam, Li 2 Si_C12 / m1 ordered lattice and LiSi_I41AZ Structured group, where: The Li _4.1 Si_Cmcm ordered lattice structure is characterized by X-ray powder diffraction (XRPD) under Cu target Kα X-ray radiation, including 2θ peaks at 15.75 ± 0.1 degrees, 20.72 ± 0.1 degrees, 24.11 ± 0.1 degrees, 26.05 ± 0.1 degrees, 27.15 ± 0.1 degrees, 39.52 ± 0.1 degrees, 41.36 ± 0.1 degrees, and 43.16 ± 0.1 degrees; the Li1 ₃ Si ₄ _Pbam ordered lattice structure is characterized by the use of Cu The target Kα X-ray has X-ray powder diffraction (XRPD) including 2θ peaks at 12.33 ± 0.1 degrees, 20.72 ± 0.1 degrees, and 22.6 ± 0.1 degrees; the characteristics of the Li ₂ Si_C12 / m1_ ordered lattice structure are X-ray powder diffraction (XRPD) under Cu target Kα X-ray radiation contains 2θ peaks at 14.05 ° and 23.61 °; the LiSi_I41AZ ordered lattice structure is characterized by having X under Cu target Kα X-ray radiation X-ray powder diffraction (XRPD) contains 2θ peaks at 18.77 ± 0.1 degrees and 19.28 ± 0.1 degrees.

In some particular aspects of embodiments of the present invention, of the lithium - silicon compound selected from the polymorph in which one or more of _{Li 4.1 Si_Cmcm, Li1 3 Si 4} _Pbam, Li 2 Si_C12 / m1 ordered lattice and LiSi_I41AZ A group of structures, which has an obvious absorption peak at an X-ray absorption spectrum at an incident light energy of 1847 eV.

According to another aspect of the present invention, a pure silicon anode for a lithium battery is provided. The anode includes one or more core species, wherein the core species includes a lithium-silicon compound polymorph as claimed in claim 1 or 2.

In some embodiments of the present invention, the pure silicon anode for a lithium battery includes one or more nuclear species, and the size of the nuclear species ranges from 1 nm to 5,000,000 nm.

In another aspect, the present invention provides a method for preparing the above-mentioned pure silicon anode for a lithium battery, comprising: plating a surface of a pure silicon anode material powder with a protective layer and leaving small portions to produce a bare surface; The groove is compacted and placed on a copper substrate, and covered with a sieve to prevent the powder from scattering; then the lithium charging and delithiating reactions are performed, and the electrolyte is EC / DEC + FEC; the voltage is controlled so that the The exposed surface generates a lithium flux with a lithium ion concentration per unit area higher than 4 atomic percent; the charge / discharge rate is controlled between 0.5C and 30C.

In some embodiments of the present invention, the pure silicon anode for a lithium battery may consist of a hollow, multilayer, porous, nanowire, nanocolumn, or nanoparticle appearance. The appearance of the shell layer The thickness, film thickness, mold wall thickness, and line width range from 1 to 100 nanometers.

The present invention further discloses a method for allowing a pure silicon anode to obtain a final structure of Li _4.1 Si_Cmcm after charging and discharging, and exhibiting an abnormally high capacitance. The method is to implant a nano-grade nuclear seed with one or more of Li _4.1 Si_Cmcm, Li ₁₃ Si ₄ _Pbam, Li ₂ Si_C12m1, and LiSi_I41 / AZ on a pure silicon anode. During the charge and discharge process, the nucleation growth theory is used. That is, the final structure of Li4.1Si_Cmcm can be formed.

100‧‧‧ Pure silicon anode powder with nuclear species

102‧‧‧ Nuclear

104‧‧‧ Silicon Powder

200‧‧‧lithium battery

202‧‧‧Anode

204‧‧‧ cathode

206‧‧‧Isolation

Figure 1A based on a pure silicon implanted with an anode _{Li 4.1 Si_Cmcm, Li 13 Si 4} _Pbam, Li 2 Si_C12m1, a schematic view of a manufacturing method LiSi_I41 / AZ wherein one or more of the nuclear species.

FIG. 1B is a schematic diagram of a pure silicon anode powder containing nuclei.

Figure 2 shows the X-ray absorption spectrum of a silicon-based powder after implantation into a nuclear seed.

Figure 3 is a schematic diagram showing the structure change of a pure silicon anode when a lithium battery is charged and discharged.

4A and 4B are structural diagrams of Li4.1Si_Cmcm, and the differences between the structure and the general lithium-silicon structure Li ₁₅ Si ₄ —I-43d.

Fig. 5 is an X-ray diffraction pattern of Li _4.1 Si_Cmcm, Li ₁₃ Si ₄ _Pbam, Li ₂ Si_C12m1, and LiSi_I41 / AZ.

6A and 6B based _{Li 4.1 Si_Cmcm, Li 13 Si 4} _Pbam, Li 2 Si_C12m1, LiSi_I41 / AZ X-ray absorption spectrum, and the structure is calculated after the theory, simulated X-ray absorption spectra.

The X-ray absorption spectra of Li _4.1 Si_Cmcm, Li ₁₃ Si ₄ _Pbam, Li ₂ Si_C12m1, LiSi_I41 / AZ, and Li17Si4_F-43m, Li15Si4_I-43d, Li12Si7_Pnma, and Li5Si2_R-3m in Fig. 7A and Fig. 7B are calculated after theoretical calculation. X-ray absorption spectrum.

FIG. 8 is a capacitance test chart of a pure silicon anode of a lithium battery made by crystallization of the present invention.

FIG. 9 is a schematic diagram of a lithium battery to which the anode for a lithium battery of the present invention belongs.

FIG. 10A is a schematic diagram of a pure silicon anode in which the nuclear species is used in a hollow spherical shell structure.

FIG. 10B is a result of observation of a pure silicon anode powder with a hollow spherical shell structure using a transmission electron microscope.

Pre-lithiation is an electrochemical reaction. Lithium charging and delithiation reactions are performed on a silicon anode. After the lithium-filling and delithiating reactions, the overall silicon anode will transform into an amorphous structure and leave nanometer-sized nuclei. In the present invention, before carrying out the lithium-charging reaction, a special protective layer is manufactured on the surface of the powder and a specific position is left for the lithium-charging reaction (uneven powder coating). Therefore, the lithium flux (Li ⁺ ion flux) at the specific position is relatively Higher, one or more crystal structures of Li _4.1 Si_Cmcm, Li ₁₃ Si ₄ _Pbam, Li ₂ Si_C12m1, LiSi_I41 / AZ are formed there, which is different from the Li ₁₅ Si ₄ _I-43d crystal structure of the conventional electrode.

Please refer to FIG. 1A and FIG. 1B. In the invention, the powder surface of the pure silicon anode material is plated with a protective layer and leaves a small part to expose the powder surface. Then, the powder is compacted and placed in a groove on a copper substrate, and the screen is covered with a screen to prevent the powder. shed. Next, an electrochemical method is used to perform the lithium charging and delithiating reactions. The electrolyte is EC / DEC + FEC, and the electrolyte is LiPF ₆ . Because the lithium charging reaction will only occur at the location where the protective layer is not partially covered, and the voltage and charging rate are appropriately controlled (between 0.5C ~ 30C), a relatively high lithium flux (unit area) can be generated at this location. Lithium ion concentration is above 4 atomic percent). By controlling the lithium-charged reaction time under high lithium flux, the lithiation reaction only occurs on the surface, and does not allow lithium to diffuse into the powder, that is, it can be controlled that the lithium-charge is controlled by the surface reaction, not by the diffusion reaction. After the lithium-charged reaction, a reverse bias voltage is applied to carry out the delithiation reaction. After that, a powder containing special nuclear species can be obtained. The X-ray absorption spectrum of silicon that has not undergone a lithium-filled delithiation reaction and silicon that has been seeded with nuclear species after the reaction is shown in Figure 2.

See Figure 3. When the pure silicon anode material powder has the nucleus according to the present invention, during the charging process (lithiation process), the entire powder can be formed into Li _4.1 Si_Cmcm, Li ₁₃ Si ₄ _Pbam, Li ₂ through the theory of nucleation and growth. One or more of Si_C12m1, LiSi_I41 / AZ.

The present invention uses X-ray diffraction spectrum and X-ray absorption spectrum to identify a specially designed pure silicon anode. After charging (lithiation) reaction, Li _4.1 Si_Cmcm, Li ₁₃ Si ₄ _Pbam, Li ₂ Si_C12m1, LiSi_I41 / One or more of AZ's lithium-silicon structures. For the difference between the final phase Li _4.1 Si_Cmcm and the commonly formed lithium-silicon structure Li ₁₅ Si4_I-43d, please refer to FIGS. 4A and 4B.

X-ray diffraction spectrum, please refer to Figure 5. It is performed using synchrotron X-ray. The X-ray wavelength is 0.6888 (unit = Ångström), and the X-ray energy resolution is 10 ^-4 (△ E / E, E is X-ray. Energy) and use a two-dimensional detector to collect the diffraction signal. After that, the result was converted into a diffraction pattern corresponding to the X-ray wavelength (1.5406, unit = Angström) of the copper target for easy comparison.

The X-ray absorption spectrum is performed by using synchrotron X-rays. When the X-ray energy is scanned from 1770eV to 2130eV, the X-ray signal after collecting the sample is collected using a Lytel detector. Record the incident X-ray energy and the transmitted X-ray intensity to obtain the X-ray absorption spectrum of Si K-edge. Please refer to FIG. 6A and FIG. 6B. Because the X-ray absorption spectrum consists of the mutual interference between X-rays being absorbed by the atoms, X-rays being scattered by the atoms, and scattered X-rays, it can reflect the valence of the atoms, the environment around the atoms, and the symmetry of the atomic structure. At the same time, in order to confirm the significance of the identification of X-ray absorption spectrum, theoretical calculations and spectral simulations were also performed using FDMNES. This theoretical calculation takes into account atomic absorption and multiple scattering, and then simulates an X-ray absorption spectrum.

Please refer to FIG. 6A and FIG. 6B. The experimentally obtained absorption spectrum has a significant absorption peak at the energy position of 1847eV. Comparing the experimental X-ray absorption spectrum with the simulated spectra of various lithium-silicon structures, it can be found that the absorption peaks of 1847eV are similar to the absorption peaks of four structures: Li _4.1 Si_Cmcm, Li ₁₃ Si ₄ _Pbam, Li ₂ Si_C12m1, and LiSi_I41 / AZ. Equivalent energy positions indicate the existence of one or more of these four structures. They also indicate that the four structures have the same atomic surroundings, atomic symmetry, or electronic structure. The results of this analysis, x-ray diffraction pattern with echoes, proved pure silicon anode of the present invention, the presence of _{Li 4.1 Si_Cmcm, 13 Si 4 _Pbam} , 2 Si_C12m1, one LiSi_I41 / AZ structure wherein one or more of Li Li. In contrast, the simulated spectra of the four structures Li ₁₇ Si ₄ _F-43m, Li ₁₅ Si ₄ _I-43d, Li ₁₂ Si ₇ _Pnma, and Li ₅ Si ₂ _R-3m (as shown in Figures 7A and 7B), especially the general pure The simulated spectrum of Li ₁₅ Si ₄ _I-43d formed after the silicon anode is lithiated, it can be found that the strongest absorption peak of these four structures will fall around 1838eV, which is significantly different from the absorption peak of the experimental spectrum. The pure silicon anode according to the present invention does not have four structures of Li ₁₇ Si ₄ _F-43m, Li ₁₅ Si ₄ _I-43d, Li ₁₂ Si ₇ _Pnma, and Li ₅ Si ₂ _R-3m. He said configuration of the four, Li pure silicon anode of the present invention is formed after lithiation _{4.1 Si_Cmcm, Li 13 Si 4 _Pbam} , Li 2 Si_C12m1, atoms ambient LiSi_I41 / AZ four structures atom or symmetrical relationship The electronic structure is significantly different.

See Figure 2. Identification using X-ray absorption spectroscopy can clearly find the existence of nuclear species. Nuclide structure _{Li 4.1 Si_Cmcm, Li 13 Si 4} _Pbam, Li 2 Si_C12m1, LiSi_I41 / AZ wherein one or more of. The nuclear species has the same atomic environment, atomic structure symmetry, or electronic structure as the above four structures.

See Figure 6. When the pure silicon anode material powder has the nucleus according to the present invention, during the charging process (lithiation process), the entire powder can be formed into Li _4.1 Si_Cmcm, Li ₁₃ Si ₄ _Pbam, Li ₂ through the theory of nucleation and growth. One or more of Si_C12m1, LiSi_I41 / AZ. The nuclear species has the same atomic surroundings, atomic structure symmetry, or electronic structure as the above four structures.

See Figure 8. When _{Li 4.1 Si_Cmcm, Li 13 Si 4} _Pbam, 2 Si_C12m1, LiSi_I41 / AZ or a method in which the structure for a variety of Li, and Li _4.1 Si_Cmcm final phase-pure silicon anode formed. The capacitance of pure silicon anodes can be greatly increased. When the special pure silicon anode of the present invention is used to assemble the pole piece and make a half-cell (the electrolyte is EC + DEC + 10% FEC), a charge-discharge test is performed (charge-discharge rate 0.1C). It can be found that after 250 cycles of charge and discharge cycles, the pure silicon anode of the present invention can still retain a capacity of about 2500 mAh / g. Compared with traditional stone-ground electrodes, the capacitance is increased by more than 6 times. Compared with the Li ₁₅ Si ₄ _I-43d structure formed after charging of ordinary pure silicon anodes, the capacitance has improved significantly.

See Figure 9. It is a schematic diagram of the present invention for making a lithium battery. The lithium battery 100 includes an anode 102, a cathode 104, and a separator 106 between the anode 102 and the cathode 104.

Please refer to FIG. 10A and FIG. 10B. According to the present invention, the method for manufacturing special nuclear species can also be used on silicon anodes with various appearances (such as hollow powder).

However, the above are only the preferred embodiments of the present invention, and are not intended to limit the scope of implementation of the present invention. For example, all changes and modifications of the structure, shape, characteristics, and spirit according to the scope of the patent application for the present invention are equally changed and modified. Shall be included in the scope of patent application of the present invention.

Claims (7)

    A lithium-silicon compound polymorph for a pure silicon anode of a lithium battery, which has an X-ray powder diffraction pattern (XRPD) substantially the same as that shown in FIG. 5 and has substantially the same as that shown in FIG. 6A X-ray absorption spectrum.     A lithium anodes for lithium pure silica - silicon compound polymorphs, in which one or more selected from a _{Li 4.1 Si_Cmcm, Li1 3 Si 4} _Pbam, Li 2 Si_C12 m1 and LiSi_I41AZ ordered lattice structure / composition of Group, wherein: the Li _4.1 Si_Cmcm ordered lattice structure is characterized by having X-ray powder diffraction (XRPD) under Cu target Kα X-ray radiation, including 2θ peaks at 15.75 ± 0.1 degrees, 20.72 ± 0.1 degrees, 24.11 ± 0.1 degrees, 26.05 ± 0.1 degrees, 27.15 ± 0.1 degrees, 39.52 ± 0.1 degrees, 41.36 ± 0.1 degrees, and 43.16 ± 0.1 degrees; the Li1 ₃ Si ₄ _Pbam ordered lattice structure is characterized by the use of Cu target Kα X X-ray powder diffraction (XRPD) under light radiation contains 2θ peaks at 12.33 ± 0.1 degrees, 20.72 ± 0.1 degrees, and 22.6 ± 0.1 degrees; the Li ₂ Si_C12 / m1_ ordered lattice structure is characterized by the use of Cu The target Kα X-ray radiation has X-ray powder diffraction (XRPD) including 2θ peaks at 14.05 ± 0.1 degrees and 23.61 ± 0.1 degrees; the LiSi_I41AZ ordered lattice structure is characterized by having Cu target Kα X-ray radiation X-ray powder diffraction (XRPD) contains 2θ peaks at 18.77 ± 0.1 degrees and 19.28 ± 0.1 degrees.     For example, the lithium-silicon compound polymorph of claim 2 has an apparent absorption peak at an X-ray absorption spectrum at an incident light energy at a position of 1847 ± 2eV.         A pure silicon anode for a lithium battery, comprising one or more core species, wherein the core species comprises a lithium-silicon compound polymorph as claimed in claim 2 or 3.         For example, the pure silicon anode for lithium battery of claim 4, the size of the core is between 1nm ~ 5,000,000nm.     A method for preparing a pure silicon anode for a lithium battery as claimed in claim 4, comprising: plating a surface of a pure silicon powder with a protective layer and leaving minute portions to create one or more bare surfaces, the surface area being less than 50 nm ² The powder is compacted and placed in a groove on a copper substrate, and covered with a sieve to prevent the powder from scattering; the lithium charging and delithiating reactions are performed, and the electrolyte is EC / DEC + FEC; the voltage is controlled to Make the lithium ion concentration per unit area on the exposed surface higher than 4 atomic percent lithium flux; control the charging rate between 0.5C ~ 30C (0.5C is equivalent to completing the charge in 2 hours, 1C is equivalent to 1 Recharge within hours, and so on).     For example, pure silicon anodes for lithium batteries in claim 4 may consist of hollow, multilayer, porous, nanowires, nanopillars, or nanoparticle features. The shell thickness, film thickness, mold Wall thickness and line width, ranging from 1 to 100 nanometers.