WO2018226156A1 - Liant à base de séricine pour électrodes - Google Patents

Liant à base de séricine pour électrodes Download PDF

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Publication number
WO2018226156A1
WO2018226156A1 PCT/SG2018/050278 SG2018050278W WO2018226156A1 WO 2018226156 A1 WO2018226156 A1 WO 2018226156A1 SG 2018050278 W SG2018050278 W SG 2018050278W WO 2018226156 A1 WO2018226156 A1 WO 2018226156A1
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WIPO (PCT)
Prior art keywords
electrode
sericin
pvdf
binder
lnmo
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PCT/SG2018/050278
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English (en)
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WO2018226156A8 (fr
Inventor
Xiaodong Chen
Jiyang DENG
Yuxin Tang
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Nanyang Technological University
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Publication of WO2018226156A1 publication Critical patent/WO2018226156A1/fr
Publication of WO2018226156A8 publication Critical patent/WO2018226156A8/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present disclosure refers generally to the field of electrode materials, in particular, to a sericin-based binder for an electrode.
  • LNMO spinel LiNio.5Mm.5O4
  • SEI solid-electrolyte interface
  • binder materials may be classified into 1) synthetic polymers, 2) natural polysaccharides, and 3) conductive polymers.
  • synthetic polymers are styrene-butadiene rubber (SBR) (Scheme 1) and poly( acrylic acid) (PAA) (Scheme 2).
  • Scheme 1 Scheme 1 :
  • FIG. 27A to FIG. 27C Another example of synthetic polymers are conjugated polymers, such as the catecholic binder shown in FIG. 26.
  • conjugated polymers such as the catecholic binder shown in FIG. 26.
  • a multidimensional network such as the network shown in FIG. 27A to FIG. 27C.
  • polysaccharides there are mentioned carboxymethylcellulose sodium (Na-CMC) (from cellulose), shown as FIG. 28, and alginate (brown), shown as FIG. 29.
  • FIG. 30 One example of a conductive polymer is shown as FIG. 30.
  • concentration profile (C(x)) across the diffusion direction x is a function of time (t) and diffusivity (D(x)) accounting difference of Li diffusivity in cathode and SEI/binder regions. This may be predicted from:
  • the degree of charge (DOC) calculated as an average of normalized concentration in the electrode region clearly indicates that the reduction of Li-ion migration barrier for the SEI/binder layer is essential to maximize DOC at a fixed time and SEI/binder thickness (FIG. 1C).
  • DOC degree of charge
  • the present disclosure refers to an electrode.
  • the electrode comprises an electroactive material and a binder dispersed in the electroactive material, wherein the binder comprises hydrolysed sericin.
  • the present disclosure refers to a method for producing an electrode.
  • the method comprises preparing a mixture comprising an electroactive material and a binder comprising hydrolysed sericin.
  • FIG. 1A is a schematic drawing of energy barriers for the Li-ion transport across a liquid electrolyte (E a i), solid-electrolyte interface (SEI)/binder ⁇ E a 2), and active materials ⁇ E a 3) under discharging, which need to be minimized for the high-rate applications.
  • E a i liquid electrolyte
  • SEI solid-electrolyte interface
  • E a 2 solid-electrolyte interface
  • active materials ⁇ E a 3 active materials
  • FIG. IB is a schematic drawing of the ideal SEI/binder system for the electrochemical stability of molecular orbital (MO) of battery electrolyte with the high voltage cathode electrode materials at a delithiated state.
  • MO molecular orbital
  • FIG. 1C is a graph showing the degree of charge ⁇ DOC) predicted from the numerical solution of one-dimensional Fick's second law as a function of time and Li diffusivity in SEI.
  • FIG. ID is a graph showing the degree of charge ⁇ DOC) predicted from the numerical solution of one-dimensional Fick's second law as a function of SEI thickness and time.
  • FIG. 2A is a schematic illustration of the composition of a single silk fiber originated from the cocoon.
  • the silk fiber is composed of fibroin protein (internal) and sericin protein (outer layer), possessing glue-like characteristics.
  • FIG. 2B is an illustration of the primary structure of silk sericin, which is linked together through peptide bond by a dehydration condensation process of amino acids.
  • the four major amino acids of sericin are shown in the bottom of FIG. 2B.
  • the secondary structure is formed via a hydrogen bond between amino acids.
  • FIG. 2C is a Fourier Transform Infrared (FTIR) spectra for the polyvinylidene fluoride (PVDF) powder, sericin powder, PVDF electrode, and sericin electrode.
  • FTIR Fourier Transform Infrared
  • FIG. 2D is a high-resolution X-ray photoelectron spectroscopy (XPS) spectra of Cls.
  • FIG. 2E is a high-resolution XPS spectra of Nls peaks for sericin.
  • FIG. 2F is a graph showing the viscosities of PVDF in N-methyl-2-pyrrolidone (NMP) solvent and sericin binder with a molecular weight of 2k Da (S2k), 25k Da (S25k), 100k Da (S lOOk) in aqueous solution (2 wt%).
  • the insets are their corresponding digital images of PVDF and sericin solution.
  • FIG. 2G is a graph showing the elastic modulus and hardness of PVDF and sericin films at dry state.
  • FIG. 3A is a Field-emission Scanning Electron Microscope (FESEM) image revealing that the LNMO particles are in micrometer size.
  • FIG. 3B is an X-ray diffraction pattern confirming the phase purity of LNMO.
  • FIG. 3C is a TEM image of the LNMO microparticles measured at a 1 ⁇ scale bar, showing that the surface of the microparticle is a clean surface without the SEI layer.
  • FIG. 3D is a TEM image of the LNMO microparticles measured at a 20 nm scale bar, showing that the surface of the microparticle is a clean surface without the SEI layer.
  • FIG. 3E is a FTIR spectra for the LNMO electrode materials.
  • FIG. 4A is a graph showing the 10 th cycle of cyclic voltammetry (CV) curves for stainless steel (SS), pure PVDF and pure sericin on SS in half cell configuration at a scanning rate of 0.2 mV/s.
  • CV cyclic voltammetry
  • FIG. 4B is a graph showing XRD patterns of the PVDF and sericin films. The sharp peaks indicate that the PVDF is highly crystalline while the broad peaks indicate the amorphous nature of sericin.
  • FIG. 4C shows the morphology for the pure PVDF.
  • FIG. 4D shows the morphology for the sericin thin films on SS.
  • FIG. 4E is a Nyquist spectra for the pure PVDF and sericin films (lower graph) measured by two stainless steel (SS, shown on top) as the blocking electrodes (inset scheme).
  • FIG. 4F shows a typical stress-strain curve for the sericin and PVDF electrodes.
  • FIG. 4G shows the average peel-off pressure for the sericin and PVDF electrodes.
  • FIG. 5A is a graph showing cyclic voltammetry (CV) curves of pure PVDF and sericin films on stainless steel (SS), PVDF and sericin electrodes in half-cell configurations with a voltage window from 0 to 5 V.
  • CV cyclic voltammetry
  • FIG. 5B is a graph showing cyclic voltammetry (CV) curves for the stainless steel (SS) with a voltage window from 0 to 5 V.
  • FIG. 5C is a graph showing CV curves for pure PVDF and sericin on SS with a voltage window from 2.7 to 5 V.
  • FIG. 5D is a graph showing CV curves for PVDF.
  • FIG. 5E is a graph showing CV curves for sericin electrodes. It is noticeable that some redox peaks from SEI layer are presented in the CV curves in FIG. 4A but the peak value is negligible when comparing to sericin and PVDF electrodes (FIG. 5D and FIG. 5E).
  • FIG. 6A shows a cyclic voltammetry (CV) curve of pure sericin film on aluminum foil in half-cell configurations for 5 cycles. The redox peak in (a) is corresponding to the reversible Li- ion reaction with SEI layer.
  • FIG. 6B shows a cyclic voltammetry (CV) curve of pure sericin film on aluminum foil with 5 ⁇ L ⁇ sericin loading in half-cell configurations for 5 cycles.
  • the concentration is 20 mg/mL for the sericin aqueous solutions.
  • FIG. 6A when the sericin loading amount increases, it is found that the new peak centred at 3.5 V is obvious, and it is reversible and stable after 2 cycles.
  • the new peaks should be corresponding to the reversible Li-ion reaction with the sericin. However, their reaction can be negligible due to the small weight fraction of surface group in sericin according to the elemental analysis (FIG. 7A), when comparing to sericin and PVDF electrodes (FIG. 5D and FIG. 5E).
  • FIG. 6C shows a cyclic voltammetry (CV) curve of pure sericin film on aluminum foil with 20 ⁇ L ⁇ sericin loading in half-cell configurations for 5 cycles.
  • the concentration is 20 mg/mL for the sericin aqueous solutions.
  • FIG. 6A when the sericin loading amount increases, it is found that the new peak centred at 3.5 V is obvious, and it is reversible and stable after 2 cycles.
  • the new peaks should be corresponding to the reversible Li-ion reaction with the sericin. However, their reaction can be negligible due to the small weight fraction of surface group in sericin according to the elemental analysis (FIG. 7A), when comparing to sericin and PVDF electrodes (FIG. 5D and FIG. 5E).
  • FIG. 6D shows a cyclic voltammetry (CV) curve of pure sericin film on aluminum foil with 20 ⁇ L ⁇ sericin loading in half-cell configurations for 5 cycles.
  • the concentration is 20 mg/mL for the sericin aqueous solutions.
  • FIG. 6A when the sericin loading amount increases, it is found that the new peak centred at 3.5 V is obvious, and it is reversible and stable after 2 cycles.
  • the new peaks should be corresponding to the reversible Li-ion reaction with the sericin. However, their reaction can be negligible due to the small weight fraction of surface group in sericin according to the elemental analysis (FIG. 7A), when comparing to sericin and PVDF electrodes (FIG. 5D and FIG. 5E).
  • FIG. 7A shows the element analysis for sericin powder. Elemental analysis revealed that sericin protein contains 39% C, 14% N, 6% H. Considering that dominated element H exists in peptide backbone (-CO-NH-), the fraction of surface functional groups (-NH 2 , -OH, -COOH) in sericin can be deemed very small. In addition, sericin only takes 10% weight of the whole cathode electrode. Therefore, the effect of Li-ion reaction with surface functional groups can be negligible, which is consistent with the CV observation.
  • FIG. 7B shows the thermal stability of sericin studied by thermal gravimetric analysis (TGA) in nitrogen gas. From the TGA, it is known that 4 wt% weight loss at 100 °C for sericin is corresponding to the loss of water, and the weight loss from 100 °C to 150 °C is negligible. Therefore, sericin binder (after electrode preparation with drying step) is thermally stable during LIBs working since its operation temperature is usually below 100 °C.
  • TGA thermal gravimetric analysis
  • FIG. 8A shows a scanning electron microscope (SEM) micrograph of sericin films at a molecular weight of 2K Da.
  • SEM scanning electron microscope
  • FIG. 8B shows a SEM micrograph of sericin films at a molecular weight of 25K Da. The image indicates that the protein could form homogeneous and continuous film. No micropores were found for the film.
  • FIG. 9A is a FESEM image of the PVDF- electrode at a 10 ⁇ magnification. From the observation, for the as-prepared PVDF electrode, the surface of the PVDF electrode is rough with more exposed surface LNMO microparticles on the outside of the film.
  • FIG. 9B is a FESEM image of the PVDF- electrode at a 1 ⁇ magnification. From the observation, for the as-prepared PVDF electrodes, the surface of the PVDF electrode is rough with more exposed surface LNMO microparticles on the outside of the film.
  • FIG. 9C is a FESEM image of the PVDF- electrode at a 200 nm magnification. From the observation, for the as-prepared PVDF electrodes, the surface of the PVDF electrode is rough with more exposed surface LNMO microparticles on the outside of the film. However, it is hard to distinguish the binder on LNMO surface from the PVDF- electrode.
  • FIG. 9D is a FESEM image of the sericin electrodes at a 10 ⁇ magnification. From the observation, for the as-prepared sericin electrode, the surface of the sericin electrode is smooth and flat.
  • FIG. 9E is a FESEM image of the sericin electrodes at a 1 ⁇ magnification. From the observation, for the as-prepared sericin electrode, the surface of the sericin electrode is smooth and flat.
  • FIG. 9F is a FESEM image of the sericin electrodes at a 200 nm magnification. From the observation, for the as-prepared sericin electrode, the surface of the sericin electrode is smooth and flat. However, it is hard to distinguish the binder on LNMO surface from the sericin electrode.
  • FIG. 10A shows a TEM image of the sericin electrode at 0.2 ⁇ magnification. Consistent with the FESEM observation in FIG. 9 A to FIG. 9F, the more bonding site for water- soluble nature of sericin protein with LNMO materials (FIG. 10A and FIG. IOC), which is due to strong interaction between a rich hydroxy group of LNMO with the water-soluble binder.
  • FIG. 10B shows a TEM image of the PVDF electrode at 0.2 ⁇ magnification. Consistent with the FESEM observation in FIG. 9A to FIG. 9F, the more bonding site for water- soluble nature of sericin protein with LNMO materials (FIG. 10A and FIG. IOC), which is due to strong interaction between a rich oxhydryl group of LNMO with the water-soluble binder.
  • FIG. IOC shows a TEM image of the sericin electrode at 100 nm magnification. Consistent with the FESEM observation in FIG. 9A to FIG. 9F, the more bonding site for water- soluble nature of sericin protein with LNMO materials (FIG. 10A and FIG. IOC), which is due to strong interaction between a rich oxhydryl group of LNMO with the water-soluble binder.
  • FIG. 10D shows a TEM image of the PVDF electrode at 100 nm magnification. Consistent with the FESEM observation in FIG. 9A to FIG. 9F, the more bonding site for water- soluble nature of sericin protein with LNMO materials (FIG. 10A and FIG. IOC), which is due to strong interaction between a rich oxhydryl group of LNMO with the water-soluble binder.
  • FIG. 11A is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) image for the sericin-LNMO electrode at 0.5 ⁇ magnification. STEM-EDX mapping is conducted for proving the better coverage of sericin on LNMO than that of PVDF on LNMO.
  • STEM-EDX mapping is conducted for proving the better coverage of sericin on LNMO than that of PVDF on LNMO.
  • FIG. 11B is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the sericin-LNMO electrode.
  • STEM scanning transmission electron microscopy
  • EDX energy dispersive X- ray
  • FIG. llC is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the sericin-LNMO electrode, mapping the carbon coverage. STEM-EDX mapping reveals that the signals of C from sericin are uniformly distributed on the LNMO surface.
  • STEM-EDX mapping reveals that the signals of C from sericin are uniformly distributed on the LNMO surface.
  • FIG. 11D is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the sericin-LNMO electrode, mapping the nitrogen coverage. STEM- EDX mapping reveals that the signals of N element from sericin are uniformly distributed on the LNMO surface.
  • STEM- EDX mapping reveals that the signals of N element from sericin are uniformly distributed on the LNMO surface.
  • FIG. HE is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the sericin-LNMO electrode, mapping the manganese coverage.
  • STEM scanning transmission electron microscopy
  • EDX energy dispersive X- ray
  • FIG. 11F is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the sericin-LNMO electrode, mapping the nickel coverage.
  • STEM scanning transmission electron microscopy
  • EDX energy dispersive X- ray
  • FIG. 11G is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) image for the PVDF-LNMO electrode.
  • STEM scanning transmission electron microscopy
  • EDX energy dispersive X- ray
  • FIG. 11H is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the PVDF-LNMO electrode.
  • STEM scanning transmission electron microscopy
  • EDX energy dispersive X- ray
  • FIG. HI is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the PVDF -LNMO electrode, mapping the carbon coverage.
  • STEM scanning transmission electron microscopy
  • EDX energy dispersive X- ray
  • FIG. 11J is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the PVDF -LNMO electrode, mapping the fluorine coverage.
  • STEM scanning transmission electron microscopy
  • EDX energy dispersive X- ray
  • FIG. 11K is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the PVDF -LNMO electrode, mapping the manganese coverage.
  • STEM scanning transmission electron microscopy
  • EDX energy dispersive X- ray
  • FIG. 11L is a scanning transmission electron microscopy (STEM)-energy dispersive X- ray (EDX) analysis for the PVDF -LNMO electrode, mapping the nickel coverage. The signal for the Nickel (Ni) mapping from the PVDF coating is very strong.
  • FIG. 12A shows a measurement of tensile adhesion strength for the PVDF and sericin electrode, wherein this Figure describes the tensile adhesion strength testing setup of a tensile machine (MTS C42).
  • FIG. 12B shows a measurement of tensile adhesion strength for the PVDF and sericin electrode, wherein this Figure describes the peel-off experiment of the sericin and PVDF electrode by transparent tape.
  • the PVDF electrode can be peeled off from the Al current collector, while the sericin electrode stuck well on Al current collector, indicating the good adhesion of sericin electrode with the current collector.
  • FIG. 13A shows the electrochemical performances of the PVDF and sericin electrodes as a long-time cycling performance at 1 C.
  • the top plateaus and bottom plateaus are charging/discharging capacities for the sericin- and PVDF- electrode, respectively.
  • FIG. 13C shows the corresponding charging/discharging profiles of the sericin electrode at different current rates.
  • FIG. 13D shows the potential polarization of the PVDF and sericin electrodes between charge and discharge plateaus at different rates (defined by the charging/discharging voltage separation at half-capacity).
  • FIG. 13E shows the cycling-evolution of SEI resistance (RSEI) and charge transfer resistance (RCT) at the discharge state (-3.5 V) based on electrochemical impedance spectroscopy measurement of the PVDF and sericin electrodes. Inset is the corresponding Nyquist plot.
  • FIG. 13F shows the Li-ion diffusion coefficient (Du + ) of the cycled sericin and PVDF electrodes at a charging state. Inset is magnified plot from FIG. 13F at the delithiated plateau.
  • FIG. 14 is a statistical study of the sericin- and PVDF- electrodes at various current densities between 0.5 C to 20 C based on five samples, which further proves the outstanding performance from the disclosed sericin (FIG. 13A and FIG. 13B).
  • FIG. 15D shows long-term cycling performance of the full cell LIBs with PVDF and sericin binders.
  • the weight ratio for the T1O2 anodes and LNMO cathodes are 1 : 9 with the excess of the cathode materials without the optimization. All the capacity performance and rate performance were calculated based on the T1O2 anode mass only.
  • FIG. 16A shows the cycle-evolution of impedance spectra of sericin-based LNMO electrode measured in half-cell configuration.
  • FIG. 16B shows the cycle-evolution of impedance spectra of PVDF-based LNMO electrode measured in half-cell configuration.
  • FIG. 16C shows an enlarged section of the cycle-evolution of impedance spectra of sericin-based LNMO electrode as shown in FIG. 16A.
  • FIG. 16D shows an enlarged section of the cycle-evolution of impedance spectra of PVDF-based LNMO electrode as shown in FIG. 16B.
  • FIG. 17A shows a galvanostatic intermittent titration technique (GITT) profile of sericin (upper line) and PVDF (lower line) electrode during charge as a function of time.
  • GITT test is another reliable testing to study the lithium diffusivity. The battery was first charged/discharged with a small current for a short time followed by rest for a long time. An assumption is made that the lithium inside the electrode tries to diffuse to achieve a homogeneous solid solution phase during rest for a thermodynamic equilibrium state. This diffusion process is indicated by voltage decrease/increase during the rest after charge/discharge.
  • FIG. 17A shows the overall GITT profile of sericin and PVDF electrode during charge. The lithium diffusivity (Dn + ) is obtained from
  • nt M g A ⁇ where t is the charge/discharge time, WIB is the mass of electrode, VM and MB are the molar volume and molar mass of the electrode, respectively, A is the electrode surface area, ⁇ and Et represent the potential change which is shown in FIG. 17B.
  • FIG. 17B is a demonstration of a single titration.
  • FIG. 18A shows the surface composition evolution of the PVDF and sericin electrodes probing by high-resolution XPS measurements upon cycling. All the peaks were calibrated versus the Cls peak of hydrocarbon species at 284.8 eV. The Cls spectra of PVDF-electrode at different stages: pristine electrode, after 10 and 50 charging/discharging cycles. The sample was ion sputtered for 30 s to remove surface contamination.
  • FIG. 18B shows the surface composition evolution of the PVDF and sericin electrodes probing by high-resolution XPS measurements upon cycling. All the peaks were calibrated versus the Cls peak of hydrocarbon species at 284.8 eV. The Cls spectra of sericin-electrode at different stages: pristine electrode, after 10 and 50 charging/discharging cycles. The sample was ion sputtered for 30 s to remove surface contamination.
  • FIG. 18C shows the Ols spectra of PVDF-electrode at different stages: pristine electrode, after 10 and 50 charging/discharging cycles. The sample was ion sputtered for 30 s to remove surface contamination.
  • FIG. 18D shows the Ols spectra of sericin electrode at different stages: pristine electrode, after 10 and 50 charging/discharging cycles. The sample was ion sputtered for 30 s to remove surface contamination.
  • FIG. 19 shows the Fls spectra of the PVDF and sericin electrodes at pristine state, 10th cycle, and 50th cycle. Peak assignment guidelines are indicated as dashed lines in the graph.
  • the two Fls peaks for the PVDF electrode at pristine state comes from CF 2 of PVDF polymer chain and the bonding between PVDF with LNMO.
  • the left peak of PVDF electrode may contain species of CF 2 from PVDF binder, residual LiPF 6 and its decomposition intermediate Li x PF y O z .
  • the peak at 684.5 eV of PVDF electrode at lowest energy could refer to the bonding between PVDF and LNMO.
  • the peak at 685 eV of both PVDF and sericin electrode is possibly related to LiF, a common composition of SEI.
  • the peak at 687 eV of sericin electrode can include LiPF 6 and Li x PF y O z .
  • the shape difference between the PVDF and sericin electrode is probably due to the dominance of CF 2 signal in PVDF electrode.
  • FIG. 20 shows the P2p spectra of the PVDF and sericin electrodes at pristine state, 10th cycle, and 50th cycle. Peak assignment guidelines are indicated as dashed lines in the graph. The line symmetry was adjusted to include the existence of the spin-orbit splitting effect of P2p peaks. After the cells had been cycled, two peaks at 134.1 eV (Li x PF y Oz) and 137.3 eV (LiPF 6 ) appeared in both electrodes, indicating the similar SEI composition of the PVDF and sericin electrodes.
  • FIG. 21 A shows the self-discharge process and Li-ion diffusion activation energies for the sericin and PVDF electrodes. Real-time monitoring of voltage change of the delithiated sericin and PVDF electrodes under a rest condition.
  • the inset schemes are the proposed self- discharge process of the high voltage cathode electrodes, due to the oxidation of ethylene carbonate at a delithiated state.
  • FIG. 21B shows the voltage stability time for sericin and PVDF electrodes with the different weight ratio of binders.
  • the stability time is defined as the time before the voltage of the cell drops to 4.6 V. No significant voltage drop for 30% weight percentage of sericin binder (*) even after 600 h.
  • the insets are the proposed binder functions for the PVDF (top) and sericin (bottom) electrode.
  • FIG. 21C is a FESEM image of the PVDF-electrode after 100 cycles at a magnification scale of 20 ⁇ .
  • FIG. 21D is a FESEM image of the PVDF-electrode after 100 cycles at a magnification scale of 1 ⁇ .
  • FIG. 21E is a FESEM image of the sericin-electrode after 100 cycles at a magnification scale of 20 ⁇ .
  • FIG. 21F is a FESEM image of the sericin-electrode after 100 cycles at a magnification scale of 1 ⁇ .
  • FIG. 21 G shows the activation energy barriers for the sericin and PVDF electrodes measured at 3.5 V after 100 cycles.
  • FIG. 22A is a FESEM image for the PVDF electrode after 100 rechargeable cycles at a magnification scale of 10 ⁇ .
  • FIG. 22B is a FESEM image for the PVDF electrode after 100 rechargeable cycles at a magnification scale of 10 ⁇ .
  • FIG. 22C is a FESEM image for the PVDF electrode after 100 rechargeable cycles at a magnification scale of 1 ⁇ .
  • FIG. 9A to FIG. 9F big cracks are formed on the PVDF electrode after cycling, while the sericin electrode maintains the structure integrity due to the strong adhesion between sericin and the substrate.
  • FIG. 22D is a FESEM image for the sericin electrode after 100 rechargeable cycles at a magnification scale of 10 ⁇ .
  • FIG. 22E is a FESEM image for the sericin electrode after 100 rechargeable cycles at a magnification scale of 10 ⁇ .
  • FIG. 22F is a FESEM image for the sericin electrode after 100 rechargeable cycles at a magnification scale of 1 ⁇ . Compared to the continued film formation without crack for both sericin and PVDF electrodes (FIG. 9A to FIG. 9F), big cracks are formed on the PVDF electrode after cycling, while the sericin electrode maintains the structure integrity due to the strong adhesion between sericin and the substrate.
  • FIG. 23A is a TEM image for the PVDF electrode after 100 rechargeable cycles at a magnification scale of 500 nm.
  • FIG. 23B is a TEM image for the PVDF electrode after 100 rechargeable cycles at a magnification scale of 500 nm.
  • FIG. 23C is a TEM image for the PVDF electrode after 100 rechargeable cycles at a magnification scale of 50 nm. It is clear that the SEI layer for the PVDF electrode is thicker than that for the sericin electrode, which is due to the oxidation of the electrolyte by the delithiated cathode at high voltage.
  • FIG. 23D is a TEM image for the sericin electrode after 100 rechargeable cycles at a magnification scale of 500 nm.
  • FIG. 23E is a TEM image for the sericin electrode after 100 rechargeable cycles at a magnification scale of 500 nm.
  • FIG. 23F is a TEM image for the sericin electrode after 100 rechargeable cycles at a magnification scale of 50 nm. It is clear that the SEI layer for the PVDF electrode is thicker than that for the sericin electrode, which is due to the oxidation of the electrolyte by the delithiated cathode at high voltage.
  • FIG. 24A shows the morphology of the Li4Ti 5 0i2 nanoparticles with the size less than 100 nm.
  • FIG. 24B shows the cycling performances of the Li4Ti 5 0i2 electrode with PVDF and sericin binders at 1 C.
  • FIG. 24C shows the cycling performances of the Li4Ti 5 0i2 electrode with PVDF and sericin binders at different curate rates.
  • FIG. 25A demonstrates the effect of sericin molecular weight on the electrochemical performance.
  • FIG. 25B demonstrates the effect of sericin molecular weight on voltage stability (self- discharge behavior).
  • FIG. 26 shows conjugated polymers as an example for synthetic polymers which are used as binders.
  • FIG. 27A shows a multidimensional network based on alginate as an example for synthetic polymers which are used as binders.
  • FIG. 27B shows a multidimensional network based on ⁇ -CD polymer as an example for synthetic polymers which are used as binders.
  • FIG 27C shows the lithiation and delithiation process of the binders presented in FIG. 27A and FIG. 27B.
  • FIG. 28 shows the structure of carboxymethylcellulose sodium as an example of a natural polysaccharide which is used as binder.
  • FIG. 29 shows the structure of alginate (brown) as an example of a natural polysaccharide which is used as binder.
  • FIG. 30 is a photographic representation (top) and shows the structure of a conductive polymer which is used as binder.
  • FIG. 31 illustrates the synthetic pathway for obtaining a conductive polymer, such as the conductive polymer shown in FIG. 30.
  • FIG. 32 is a graphical illustration of a protein binder. The advantages of a protein binder is that they are natural and water soluble, have a multi-level structure, provide for functional groups for interaction, are widely available and cost effective.
  • FIG. 33 is a photographic illustration of sericin, wherein on the left there is shown the silk pulp and in the top middle the extracted powder.
  • Sericin is a natural adhesive, comprises 18 amino acids with a total content of hydroxyl groups on the side chains of the amino acids being 45.8%, is flexible and strong, water soluble and can be obtained from waste recovery, as it is produced on the 50,000 tons scale.
  • Sericin has a content of about 32% of serine, which is an amino acid shown on the top right.
  • FIG. 34A are digital images of PVDF (i) and sericin with a molecular weight of 2k (ii), 25k (iii) and 100k (iv) in aqueous solution (2 wt%).
  • the image shows that the sericin with different weight has the hydrophilic properties, allowing the sericin to be soluble in water.
  • FIG. 34B shows the viscosities of PVDF in NMP solvent and sericin binder with a molecular weight of 2k (S2k), 25k (S25k), 100k Da (SlOOk) in aqueous solution (1 and 2 wt%).
  • S2k 2k
  • S25k 25k
  • SlOOk 100k Da
  • FIG. 34C shows elastic modulus and hardness of PVDF and sericin films at dry state.
  • the Young's modulus and hardness of PVDF and sericin films were probed via nanoidentication technique (FIG. 34C). The results showed that in a dry state, all of three films made of the sericin exhibited better stiffness compared with PVDF film.
  • Elastic modulus and hardness for sericin films were 8.66 and 0.45 GPa for S2k, 9.27 and 0.50 GPa for S25k, 13.57 and 0.64 GPa for SlOOk respectively, far exceeding the values for PVDF film, which were only 2.14 and 0.19 GPa.
  • Rigidity of binder is very important for retaining the capacity of high volumetric expansion electrode during cycling.
  • FIG. 35 shows the electrode morphology for graphite electrode at a scale bar of 1 ⁇ .
  • the battery has a composition of graphite: carbon black:binder being 8: 1: 1 by weight. Big particles are graphite, and small particles are carbon black (for conductive), binder cannot be seen.
  • FIG. 36A shows CV curves for PVDF and sericin as the binder, respectively in a Lithium- ion battery assembled using graphite as the anode.
  • FIG. 36B shows discharging-charging performance for Lithium-ion batteries assembled using graphite as the anode using PVDF and sericin binders.
  • FIG. 36C shows cycle performance and the corresponding Coulombic efficiency for Lithium-ion batteries assembled using graphite as the anode using PVDF and sericin binders.
  • FIG. 36C shows the charge-discharge capacities of samples at a current density of 70 mA/g over 100 cycles. For all samples, a slow increase of capacity is observed in the first 5 cycles probably due to the gradual activation of graphite materials. As such, the Coulombic efficiency in the first cycle is also limited to around 65%.
  • the efficiency with the sericin binder provided a first discharge capacity of 286.lmAh.g ⁇ 1 and the first cycle Coulombic efficiency of the cell was 94.5%, then as high as 99.0% at the 10 th cycle.
  • a stable discharge capacity of 298.6 mAh.g 1 had been achieved after about 50 cycles.
  • capacity fade of the cell was not observed at the range of 50 to 80 cycles.
  • the first discharge capacity of 324.5 mAh.g 1 could be achieved if SlOOk binder was used. Its first charge capacity was 339.6 mAh.g 1 .
  • the first cycle Coulombic efficiency of the cell was 95.6% and up to 99.1% at the 10 th cycle.
  • SlOOk always had a higher capacity over 100 cycles.
  • S2k and S25k had a stable discharged capacity though their capacities were lower than SlOOk and PVDF, which were about 240.0 and 270.0 mAh.g 1 respectively.
  • FIG. 36D shows the capacities delivered by Lithium-ion batteries assembled using graphite as the anode using PVDF and sericin binders at the current of 70 mA/g, respectively.
  • FIG. 37A shows the first six cycles of CV curves using PVDF as binder.
  • FIG. 37B shows the first six cycles of CV curves using sericin 2 kDa (S2k) as binder. The results show the sericin does not react with the electrolyte, and it is stable when cycling, similar to the PVDF.
  • FIG. 37C shows the first six cycles of CV curves using sericin 25 kDa (S25k) as binder, similar to the PVDF. The results show that sericin does not react with the electrolyte, and it is stable when cycling, similar to the PVDF.
  • FIG. 37D shows the first six cycles of CV curves using sericin 100 kDa (S lOOk) as binder. The results show the sericin does not react with the electrolyte, and it is stable when cycling, similar to the PVDF.
  • FIG. 38A shows the evolution of electrochemical impedance spectroscopy (EIS) measured at different cycle number for PVDF.
  • FIG. 38B shows the evolution of EIS measured at different cycle number for S2k; c) S25k; and d) SI 00k.
  • FIG. 38C shows the evolution of EIS measured at different cycle number for S25k.
  • FIG. 38D shows the evolution of EIS measured at different cycle number for SlOOk.
  • FIG. 39 shows evolution of R C T and RSEI along the cycling for PVDF and SI 00k binders, respectively.
  • FIG. 40A is an XPS spectrum of Cls peaks for sericin measured for the Sericin- Graphite Interaction. Peaks are identified at 285.0 eV for C-H species, 286.2 eV for C-0 species and at 288.0 eV for peptide bond. The data indicate that sericin is chemically binding to graphite surface.
  • FIG. 40B is an XPS spectrum of Ols peaks for sericin measured for the Sericin- Graphite Interaction. Peaks are identified at 533.2 eV for C-0 species and at 532 eV for C-O-C and C-OH. The data indicate that sericin is chemically binding to graphite surface.
  • FIG. 41 is a graphical illustration demonstrating how PVDF and sericin work as the binder to connect the active material (graphite flake) with the conductive agent (acetylene black).
  • FIG. 42 shows the XRD patterns of PVDF and sericin.
  • FIG. 43A is a SEM image of Li 4 Ti 5 0i 2 (LTO) nanoparticle.
  • FIG. 43B shows the cycling performance at 0.5 C of the batteries using PVDF, S2k, and SI 00k as binder, respectively.
  • the electrode performance indicates the electrode performance is comparable when using PVDF or sericin as the binder.
  • FIG. 43C shows the rate capability of batteries using PVDF, S2k, and S lOOk as binder, respectively.
  • the electrode performance indicates the electrode performance is comparable when using PVDF or sericin as the binder. Excellent rate performances have been demonstrated using the high rate LTO material with the sericin as the binder.
  • FIG. 43D shows the cycling performance at 20 C of the batteries using PVDF, S2k, and SlOOk as binder, respectively.
  • the electrode performance indicates the electrode performance is comparable when using PVDF or sericin as the binder.
  • FIG. 44A shows the cycling performance at 0.2 A/g of a lithium- ion battery assembled using Sn0 2 as anode, and using PVDF, S2k, and SlOOk as binder, respectively.
  • the sericin provides advantages over PVDF binder because the better mechanical property enables to sustain the volume expansion.
  • the sericin binder may be a potential candidate for replacing PVDF due to its lower cost, being environmentally friendly, and to improve the comprehensive properties of Li-ion batteries.
  • FIG. 44B is a SEM image of Sn0 2 .
  • FIG. 45A shows the rate capability of batteries with the loading mass of 1.63 mg.
  • the lithium-ion batteries (S lOOk sericin as binder) are assembled using Ti0 2 -B as anode with increased loading mass.
  • FIG. 45B shows the rate capability of batteries with the loading mass of 0.7 mg, with the addition of carbon nanotubes (CNT).
  • the lithium-ion batteries (SlOOk sericin as binder) were assembled using Ti0 2 -B as anode with increased loading mass.
  • FIG. 46A shows CV with the scan rate of 0.1 mV/s in lithium-ion batteries assembled using Ti0 2 and LNMO as electrodes using PVDF as binder.
  • FIG. 46B shows CV with the scan rates ranging from 0.1 to 2.0 mV/s in lithium-ion batteries assembled using Ti0 2 and LNMO as electrodes using PVDF as binder.
  • FIG. 46C shows CV with the scan rate of 0.1 mV/s in lithium-ion batteries assembled using Ti0 2 and LNMO as electrodes using sericin as binder.
  • FIG. 46D shows CV with the scan rates ranging from 0.1 to 2.0 mV/s in lithium-ion batteries assembled using Ti0 2 and LNMO as electrodes using sericin as binder.
  • FIG. 47 shows the power density and energy density for both PVDF and SlOOk. Lithium- ion batteries assembled using Ti0 2 and LNMO as electrodes and sericin as binder. The battery performance based on sericin is better than the PVDF.
  • FIG. 48 shows the basic components of Lithium-ion batteries, which are battery electrodes, separator and electrolyte.
  • the battery electrodes may comprise active materials, binder and a carbon additive.
  • the separator may be a porous polymer film.
  • the electrolyte may be a lithium salt in an organic solvent.
  • FIG. 49 shows the improved Energy Density of Lithium-ion Batteries by enhancing voltage and capacity.
  • FIG. 50 shows the energy profile between reductant, electrolyte and oxidant.
  • FIG. 51A shows the current solutions for a 5 V cathode, involving an electrolyte oxidation above 4.5 V in terms of surface coating.
  • FIG. 51B shows the normalized capacity in relation to the cycle number of the current solutions for a 5 V cathode, involving an electrolyte oxidation above 4.5 V in terms of solid electrolyte.
  • FIG. 51 C shows the Coulombic efficiency in relation to the cycle number of the current solutions for a 5 V cathode, involving an electrolyte oxidation above 4.5 V in terms of solid electrolyte.
  • FIG. 52 graphically illustrates the PVDF binder as linear polymer chains, which shows poor surface coverage and exposure to electrolyte.
  • FIG. 53 graphically illustrates the ideal binder, which would be ionically conductive through an artificial SEI layer, has a conformal wetting (wetting nature) to enable better surface passivation and a stable SEI layer and shows good mechanical adhesion.
  • CB refers to carbon black in this Figure.
  • FIG. 54 shows the structure and a photograph of alginate (brown) as an example for recent progresses in binders for LIB electrodes.
  • FIG. 55 is a graph illustrating the reversible deintercalation capacity of alginate brown, CMC binder and PVDF binder in relation to its cycle number.
  • FIG. 56 graphically illustrates the principle of a self-healing polymer, wherein the 'self- healing' properties arise from hydrogen-bonding sites.
  • FIG. 57 graphically illustrates one of the advantages from solid-state electrolytes, which has been identified to be a lone pair electron on the oxygen of ether group (as encountered in polyethylene oxide (PEO)).
  • the Li-ion moves between complexation sites assisted by the segmental motion of the polymer matrix.
  • the limitation of this system is insufficient ionic conductivity at high crystallinity, as illustrated in the graph on the right of this Figure.
  • FIG. 58 is a graph illustrating the voltage in relation with the specific capacity of a high- rate anode (LTO) with a sericin binder.
  • LTO high- rate anode
  • the LTO electrode shows less SEI formation at a high rate anode.
  • FIG. 59 is a graph illustrating the voltage in relation with the specific capacity of a high- rate anode (LTO) with a sericin binder.
  • the LTO anode has a mass ratio of LTO to the carbon and to the binder as follows: 8: 1 : 1.
  • FIG. 60 is a graph illustrating the specific capacity in relation with the cycle number using the sericin binder in a full cell demonstration. It is shown that the sericin binder is suitable for both cathode and anode electrode application.
  • FIG. 61 is a graph illustrating the voltage in relation with the specific capacity using the sericin binder in a full cell demonstration. It is shown that the sericin binder is suitable for both cathode and anode electrode application.
  • Various embodiments refer to an electrode comprising an electroactive material and a binder dispersed in the electroactive material, wherein the binder comprises hydrolysed sericin.
  • hydrolysed sericin refers to sericin, which is a silk protein extracted from silk, which has undergone hydrolysis. Accordingly, sericin which is directly extracted from silk protein, is not a hydrolysed sericin disclosed herein. In some parts of this disclosure, for example in the experiments, the term “sericin” is used, however, it is understood that the term refers to "hydrolysed sericin” as defined herein, unless stated otherwise.
  • the binder comprising hydrolysed sericin has attributes of being both highly hydrophilic due to an abundance of polar functional groups, as well as being in the amorphous state.
  • Sericin itself is a water-soluble peptide with a high hydrophilicity, as more than 30% of the amino acids in the peptide are selected from serine, which contributes to the high hydrophilicity due to the presence of hydroxyl groups in the serine amino acid.
  • hydrolysis which may be carried out by exposing sericin to acidic or basic conditions, or to enzymes, the hydrolysed sericin may contain more polar functional groups than unhydrolysed sericin.
  • breakage of the peptide bonds also means that average molecular weight of the hydrolysed sericin is decreased compared to that of sericin originally extracted from silk.
  • the hydrolysed sericin may furthermore undergo separation and/or purification to result in a highly purified hydrolysed sericin with relatively sharp molecular weight ranges.
  • Hydrolysed sericin is comprised in a binder disclosed herein.
  • binder or “binding agent” as used herein refers to any material or substance that holds or draws other materials together to form a cohesive whole mechanically, or chemically, by adhesion or cohesion. In order to form a cohesive whole, the binder would possess properties of binding or attraction between with the electroactive material. This binding or attraction refers to any kind of chemical bonding such as covalent bond, hydrogen or ionic bond, and any kind of physical bonding such as dipole dipole, hydrophobic interaction or Van der Waals forces.
  • the binder according to various embodiments is able to exhibit efficient ion transport (for example lithium ions in a LIB), which may be due to the high abundancy of lone -pair electrons from, for example, the hydroxyl groups of the serine amino acids and/or the amino groups of the peptide N-terminus, enabling ions to move between complexation sites.
  • the improved mobility of ions through complexation sites may thus result in a higher conductivity of the binder material, by facilitating ionic transport through the formation of ions coordinated bonds.
  • a higher ionic conductivity may also be due to the amorphous nature of the hydrolysed sericin.
  • the strong hydrogen bonds interaction which arises from the high hydrophilicity enables an excellent film formation property.
  • Hydrolysed sericin is able to adhere well to the electroactive material, and provides good cohesion of the electroactive material and ability to mechanically hold the electroactive material in the electrode. This also means that it is able to act as a surface coating for minimizing direct electrode-electrolyte interaction. These translate into an improved electrode with good initial capacities and cycling behavior.
  • the binder comprising hydrolysed sericin according to embodiments disclosed herein does not exhibit peeling off or cracking, and has a good solubility, translating into good homogeneity of slurries at room temperature.
  • electroactive material refers to a material, which is usually utilized for the configuration of the positive and/or negative electrodes (cathode or anode) and which is subject to electrochemical reactions (redox reactions) during the operation of the battery cell.
  • electroactive material depends on whether it is located in the cathode or the anode.
  • the hydrolysed sericin may, on average, have a lower molecular weight than sericin directly extracted from silk.
  • a lower molecular weight may result in a higher density of functional groups, which, in turn, increases the hydrophilicity, resulting in the advantageous effects as detailed further above. This is because a lower molecular weight would mean that more individual peptide bonds from the extracted sericin are broken into a carboxylic acid and an amine functionality.
  • the hydrolysed sericin may have an average molecular weight of about 150 kDa or less. In other embodiments, the hydrolysed sericin may have an average molecular weight in the range of about 1 kDa to about 150 kDa, or in the range of about 1 kDa to about 120 kDa, or in the range of about 1 kDa to about 100 kDa, or in the range of about 1 kDa to about 80 kDa, or in the range of about 1 kDa to about 60 kDa, or in the range of about 1 kDa to about 40 kDa, or in the range of about 1 kDa to about 20 kDa, or in the range of about 1 kDa to about 10 kDa. In one example, the hydrolysed sericin has an average molecular weight in the range of about 2 kDa, or of about 25 kDa, or of about 100 kDa.
  • the electrode may be a positive electrode or a negative electrode.
  • the positive electrode may also be termed as the cathode, while the negative electrode may also be termed as an anode.
  • the term "positive electrode” refers to an electrode (often called a cathode) where electrochemical reduction and lithiation occurs during a discharging process and the term “negative electrode” refers to an electrode (often called an anode) where electrochemical oxidation and delithiation occurs during a discharging process.
  • charge and “charging” refer to a process for providing electrochemical energy to a cell.
  • discharge and “discharging” refer to a process for removing electrochemical energy from a cell, e.g., when using the cell to do perform desired work.
  • lithiumate and “lithiation” refer to a process for adding lithium to an electrode by reduction of lithium ions
  • delivery and “delithiation” refer to a process for removing lithium from an electrode by oxidation of lithium ions.
  • the hydrolysed sericin may be a binder which may have a particularly good interaction in combination with certain cathodes.
  • a binder which comprises hydrolysed sericin, being able to form a stable SEI layer may have particularly beneficial effects if it is dispersed in a high voltage cathode material.
  • the electrode may be a negative electrode.
  • the electroactive material may be selected from the group consisting of a metal, a metal alloy, a metal oxide, a carbon based material, a silicon based material, and a combination thereof.
  • metal refers to both metals and to metalloids such as silicon and tin, whether in an elemental or ionic state.
  • alloy refers to a mixture of two or more metals.
  • the electroactive material of the negative electrode may comprise a carbon based material, which may be selected from any allotrope of carbon, including single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotube (MWCNTs), carbon nanofibers (CNFs), fullerene, graphite, graphene, and combinations thereof.
  • the carbon based material is graphite.
  • the electroactive material of the negative electrode may comprise a metal oxide.
  • the electroactive material comprises a metal oxide, which is a relatively hydrophilic material
  • the interaction between the abundant hydroxyl groups on the surface of the hydrolysed sericin with the metal oxide may be stronger, resulting in an improved coverage of the metal oxide before cycling and the particles may be more coherent to form a smooth film with smaller particles exposed. This may lead to a higher structural integrity of the electrode after cycling compared to using other binder materials, which, in turn, results in less cracking.
  • the metal oxide may comprise a layered lithium transition metal oxide and/or spinel lithium manganese oxide.
  • the electroactive material of the negative electrode may comprise a silicon based material.
  • the silicon based material may be selected from the group consisting of Si, Si0 2 , SiO x and a combination thereof.
  • the metal oxide may be selected from the group consisting of T1O2, Sn0 2 , and a combination thereof.
  • the electroactive material for the positive electrode is selected from a high voltage cathode material.
  • a 'high voltage cathode material' refers to an electrochemical material which is capable of delivering a high voltage of more than 2.5 V in a LIB.
  • any of these materials may be provided as a doped nanocomposite, wherein the electrochemical material is doped with a carbon based material (as defined further above).
  • a carbon based material as defined further above.
  • such a material may also be a relatively hydrophilic material.
  • the interaction between the abundant hydroxyl groups on the surface of the hydrolysed sericin with the high voltage cathode material may be stronger, resulting in an improved coverage of the high voltage cathode material before cycling and the particles may be more coherent to form a smooth film with smaller particles exposed. This may lead to a higher structural integrity of the electrode after cycling compared to using other binder materials, which, in turn, results in less cracking.
  • the high voltage cathode material provides a voltage of more than 3.0 V, or more than 3.5 V, or more than 4.0 V.
  • the high voltage cathode material may comprise a layered oxide, a spinel oxide, an olivine polyanion or a combination thereof.
  • the layered oxide may comprise LiCo0 2 , LiMn0 2 , LiNio.5Mno.5Ch, LiNii/ 3 Coi/ 3 Mm/ 3 0 2 or a combination thereof.
  • the spinel oxide may comprise lithium and at least one of nickel, cobalt, manganese or a combination thereof.
  • the spinel oxide is of the general structure (I):
  • LiNi x Mn2-x04 wherein 0 ⁇ x ⁇ 1.
  • the spinel oxide comprises LiMn 2 04, LiNio.5Mm.5O4 or a combination thereof.
  • the spinel oxide is LiNio.5Mm.5O4 (LNMO).
  • LNMO LiNio.5Mm.5O4
  • the benefit of the hydrolysed sericin being able to form a stable SEI/binder system is more pronounced. This is because LNMO belongs to the electrode materials operating at a high voltage, which often results in the formation of the unstable SEI layer, in the absence of the disclosed binder. By being able to turn this unstable SEI layer into a stable SEI/binder system, the negative effects often observed for high voltage electrode materials such as LNMO (as mentioned above) can be reduced or eliminated.
  • electroactive material may be provided in the form of microparticles or nanoparticles, or a combination thereof.
  • the dispersion between binder and electroactive material may result in a more homogenous mixture, which provides for a higher stability of the ensuing electrode material.
  • the electroactive material may be present in an amount ranging from about 60 wt% to about 95 wt% of the electrode, or in an amount ranging from about 70 wt% to about 95 wt% of the electrode, or in an amount ranging from about 80 wt% to about 95 wt% of the electrode, or in an amount ranging from about 60 wt% to about 90 wt% of the electrode, or in an amount ranging from about 60 wt% to about 85 wt% of the electrode, or in an amount of about 80 wt% of the electrode.
  • the binder may be present in an amount ranging from about 1 wt% to about 30 wt% of the electrode, or in an amount ranging from about 1 wt% to about 20 wt% of the electrode, or in an amount ranging from about 1 wt% to about 10 wt% of the electrode, or in an amount ranging from about 5 wt% to about 30 wt% of the electrode, or in an amount ranging from about 10 wt% to about 30 wt% of the electrode, or in an amount ranging from about 5 wt% to about 15 wt% of the electrode, or in an amount of about 10 wt%.
  • the electrode may further comprise a conductive agent.
  • the conductive agent may be used to maximize flow rate, increase extraction efficiency, and decrease electrode regeneration time of the electrochemical cell by facilitating the formation of thinner electrodes.
  • Either one of or both the negative electrode and the positive electrode may contain the conductive agent.
  • the conductive agent that is comprised in the negative electrode and the positive electrode may be the same or different.
  • the conductive agent may be selected from the group consisting of a carbon black, nickel powder and a combination thereof.
  • the conductive agent is a carbon black selected from the group consisting of acetylene black, furnace black, Ketjen black, channel black, lamp black, thermal black and a combination thereof.
  • the conductive agent is acetylene black.
  • the conductive agent may be present in an amount ranging from about 1 wt% to about 30 wt% of the electrode, or in an amount ranging from about 1 wt% to about 20 wt% of the electrode, or in an amount ranging from about 1 wt% to about 10 wt% of the electrode, or in an amount ranging from about 5 wt% to about 30 wt% of the electrode, or in an amount ranging from about 10 wt% to about 30 wt% of the electrode, or in an amount ranging from about 5 wt% to about 15 wt% of the electrode, or in an amount of about 10 wt%.
  • a method for producing an electrode comprises preparing a mixture comprising an electroactive material and a binder comprising hydrolysed sericin. While the mixing may be carried out at any temperature, in preferred embodiments, the mixing of the reagents may be carried out at a temperature between about 5 to about 50 °C, or at between about 10 to about 50 °C, or at between about 15 °C to about 50 °C, or at between about 5 to about 40 °C, or at between about 5 °C to about 30 °C, or at between about 10 °C to about 20 °C, or at between about 20 °C to about 30 °C.
  • the binder may be provided as an aqueous solution comprising the hydrolysed sericin.
  • the aqueous solution may be prepared by dissolving the binder in water at a temperature of about 20 °C to about 100 °C for a time period of about 10 min to about 10 h.
  • the temperature at which the aqueous solution is prepared may be in the range of about 20 °C to about 100 °C, or in the range of about 20 °C to about 80 °C, or in the range of about 20 °C to about 60 °C, or in the range of about 40 °C to about 100 °C, or in the range of about 60 °C to about 100 °C, or in the range of about 50 °C to about 70 °C, or at a temperature of about 60 °C.
  • the time period for preparing the aqueous solution may be in the range of about 10 min to about 8 h, or of about 10 min to about 6 h, or of about 10 min to about 4 h, or of about 10 min to about 2 h, or of about 30 min to about 10 h, or of about 1 h to about 10 h, or of about 1 h to about 8 h, or of about 1 h.
  • the method further comprises adding a conductive agent to the mixture.
  • the method may further comprise casting the mixture on a surface and drying the mixture.
  • the surface may be an even or a curved surface.
  • the surface may be an even surface.
  • the surface material may be a metal surface, preferably aluminum foil or copper foil.
  • the drying may comprise an initial drying step at a temperature of about 20 °C to about 120 °C at ambient pressure for about 10 min to about 5 h.
  • the temperature at which the initial drying step is carried out may be in the range of about 20 °C to about 100 °C, or in the range of about 20 °C to about 80 °C, or in the range of about 20 °C to about 60 °C, or in the range of about 40 °C to about 120 °C, or in the range of about 60 °C to about 120 °C, or in the range of about 50 °C to about 70 °C, or at a temperature of about 60 °C.
  • the time period for the initial drying step may be in the range of about 10 min to about 8 h, or of about 10 min to about 6 h, or of about 10 min to about 4 h, or of about 10 min to about 2 h, or of about 30 min to about 10 h, or of about 1 h to about 10 h, or of about 1 h to about 8 h, or of about 2 h.
  • the drying may further comprise exposing the mixture to a temperature of between 50 °C to about 100 °C under reduced pressure for about 2 h to about 100 h.
  • the temperature at which the drying step is carried out may be in the range of about 60 °C to about 100 °C, or in the range of about 70 °C to about 100 °C, or in the range of about 90 °C to about 100 °C, or at a temperature of about 100 °C.
  • the time period for the drying step may be in the range of about 10 h to about 100 h, or of about 10 h to about 80 h, or of about 10 h to about 60 h, or of about 10 h to about 40 h, or of about 10 h to about 20 h, or of about 16 h.
  • the present disclosure refers to hydrolysed sericin to be used with LiNio.5Mm.5O4.
  • Spinel LiNio.5Mm.5O4 (LNMO) is one of the most promising cathode materials for achieving high energy density lithium-ion batteries attributed to its high operating voltage (about 4.75 V).
  • the commonly used battery electrolyte suffers from severe oxidation, forming unstable solid-electrolyte interphase (SEI) layers. This would induce capacity fading, self-discharge, as well as inferior rate capabilities for the electrode during cycling, hindering the commercialization for practical applications.
  • SEI solid-electrolyte interphase
  • the electrolyte oxidation is effectively negated by introducing an electrochemically stable silk hydrolysed sericin protein, which is capable to stabilize the SEI layer and suppress the self-discharge behavior for LNMO.
  • robust mechanical support of hydrolysed sericin coating maintains the structural integrity during the fast charging/discharging process.
  • the sericin -based LNMO electrode according to embodiments disclosed herein possesses a much lower Li-ion diffusion energy barrier (26.1 kJ/mol) than that of polyvinylidene fluoride (PVDF)-based LNMO electrode (37.5 kJ/mol) at lithiated state, delivering a remarkable battery performance at high rates.
  • This disclosure introduces a new paradigm for manipulating the interfacial chemistry of electrode to solve the key obstacle for LNMO commercialization, opening a powerful avenue for unlocking the current challenges for a wide family of high operating voltage cathode materials (for example cathode materials operating at more than 4.5 V) towards practical applications.
  • Example 1 Materials and electrodes fabrication
  • LiNio.5Mm.5O4 microparticles (XNN5, XING Neng Group) , Li4TisOi2 nanoparticles and acetylene black (Sigma- Aldrich Inc.) were used as the active material and conductive agent for the composite electrode without further treatment.
  • Different kinds of binders were investigated in the experiment: (1) Three kinds of silk sericin were purchased from Aotesi Biochemicals Co. Ltd (Huzhou, China), which were hydrolyzed sericin peptides with the molecular weight of 2 kDa, 25 kDa, and -100 kDa, respectively.
  • Sericin aqueous solution was obtained by dispersing homogeneously a certain amount of sericin in distilled water with stirring at 60 °C for 1 h.
  • PVDF Poly(vinylidene fluoride)
  • NMP N-methyl-2-pyrrolidone
  • the black slurry thus obtained was cast onto a sheet of aluminum foil for LiNio.5Mn1.5O4 electrode and copper foil for Li4TisOi2 respectively, and dried in air at 60 °C for 2 h, and then dried in vacuum at 100 °C for overnight to remove residual solvent.
  • X-ray diffraction data were obtained by Bruker 6000 X-ray diffractometer using a Cu Ka source.
  • the curve fitting was conducted using mixtures of Gaussian and Lorentzian line shapes. The peaks were calibrated versus the Cls peak of hydrocarbon species at 284.8 eV.
  • TGA, Q500 thermogravimetric analysis
  • Elemental analyses of sericin powder were carried out for three times using an EA 1108 CHNS analyzer.
  • the degree of charge ⁇ DOC is approximately calculated using finite difference solution of Fick's second law for the symmetrical one-dimensional model, where the diffusivities for region 1 and region 2 are taken to be Di and Z1 ⁇ 2, respectively.
  • the diffusivities of electrode and binder/SEI are approximated to be independent on the concentration.
  • the tensile adhesion strength was conducted on a mechanical tester (MTS C42).
  • the thin film of active material attached to the Al foil was cut into rectangular shape.
  • the active material side was then adhered to a wood bar by epoxy resin.
  • the setup and the experiment of the tensile test are shown in FIG. 12A.
  • Example 5 Ionic conductivity measurements of the pure sericin and PVDF films
  • Electrochemical properties were investigated using 2032 coin cells. The half and full cells were assembled inside an Ar-filled glove box with oxygen and water contents below 0.6 ppm. Lithium metal foil was used as the counter and reference electrodes. A solution of 1.0 M LiPF 6 in ethylene carbonate: diethyl carbonate (EC: DEC, 1 : 1 by weight, Ferro Corp) was used as the battery electrolyte. Similarly, the electrochemical stability of sericin and PVDF thin films on stainless steel (or Al foil) for a wide voltage window (0-4.9 V or 3-4.9 V) was studied by cyclic voltammograms (CHI660, CH Instruments) in the above battery electrolyte at a scanning rate of 0.2 mV/s.
  • CHI660 cyclic voltammograms
  • Electrochemical impedance study was carried out on a Zahner Xpot electrochemical workstation by applying a sine wave with an amplitude of 10.0 mV over the frequency range 100 kHz-0.1 Hz for LiNio.5Mn1.5O4 electrode.
  • the loading density of electrode materials was 1.0-1.5 mg cm 2 .
  • adhesive protein macromolecules with hierarchical structures and electrochemical stability serve as an excellent candidate.
  • Sericin is a natural adhesive protein with high viscosity to envelop fibroin fibers, forming robust silkworm silk (FIG. 2).
  • sericin is electrochemically inert in resistance switching devices, rendering it as an electrochemically stable binder candidate with a wide voltage window.
  • sericin is water-soluble attributed to its rich polar side groups, which would make the electrode processing environmentally-friendly by avoiding toxic organic solvent as well as promote the strong interaction with the hydrophilic LNMO materials. Beyond those, sericin is abundant and widely available with an annual production more than 50,000 tons, but most of which are discarded in waste water during raw silk manufacturing process.
  • hydrolyzed sericin protein is an effective binder for fast- charging high voltage LNMO electrode, which may be used to meet current challenges of high voltage LNMO cathode.
  • the uniform sericin coating formed from hydrolyzed sericin can strongly suppress the electrolyte oxidation, which negates interface impedance and diffusion energy barrier, leading to the fast charging capability.
  • the current understanding may be extended to other high voltage cathode materials by forming a stable SEI/binder system to match the requirement of next-generation LIBs with high power and energy densities.
  • the polypeptide backbone of sericin is naturally synthesized via dehydration condensation of 18 types of amino acids, among which serine, aspartic acid, glycine, and threonine are four main amino groups.
  • Such a unique polypeptide backbone forms the primary structure (FIG. 2B) with rich polar side group (amino, carboxyl, and hydroxyl), endowing sericin with a highly hydrophilic nature.
  • the primary structures of sericin either coil or fold into different shapes, giving an alternative structure of amorphous random coil and organized ⁇ -sheet.
  • the major molecular conformation is a random coil with the water-soluble property, while the ⁇ -sheet structure is difficult to dissolve.
  • FIG. 2C shows the FTIR spectra of sericin powder and sericin-binder LNMO electrode (denoted as sericin electrode in the following).
  • FTIR spectra of PVDF powder and PVDF-binder LNMO electrode were also presented.
  • the peaks at 1404, and 1187 cm 1 were related to C-H 2 wagging vibration and C-F 2 symmetric stretching vibration of PVDF chain respectively.
  • a broad peak located at 3600-3200 cm “1 corresponded to the O-H stretching vibration, which was also observed in LNMO materials (FIG. 3E).
  • the PVDF and sericin electrodes inherit the peak signature of PVDF and sericin powder correspondingly, in addition to some low-wavenumber peaks due to vibration of Ni-0 and Mn-0 bonds.
  • the chemical bonding environment of sericin was further confirmed by XPS (FIG. 2D and 2E).
  • the sericin powder can be dissolved in water with yellowish color, while the PVDF is only dissolvable in N-methyl-2-pyrrolidone (NMP) solvent with colorless (inset in FIG. 2F).
  • NMP N-methyl-2-pyrrolidone
  • sericin should possess a suitable viscosity in water comparable to PVDF in NMP solution with same weight ratio.
  • K the values of the Mark-Houwink parameters.
  • the viscosity of sericin solution increases with the molecular weight from 2, 25 to 100 kDa at the same weight ratio of sericin (2 wt%).
  • the viscosity was close to that of water, while for high molecular weight (100 kDa) of sericin, the solution viscosity was comparable to that of PVDF with a high molecular weight of 534 kDa.
  • a L F / R F A (3) where L F is the film thickness, and A is the area of the film.
  • the calculated ionic conductivities for sericin and PVDF film at 25 °C were l.lxlO "7 and 4.6xl0 "8 S cm 1 , respectively.
  • the higher ionic conductivity for the sericin film may be due to its amorphous nature (FIG. 4B) as well as the lone-pair electrons of nitrogen from amino groups, facilitating ionic transport by the formation of Li -ion coordinated bonds.
  • the sericin electrode exhibited smoother and flatter surface than the PVDF electrode does, indicating a more uniform coverage on LNMO microparticles by sericin binder, which is consistent with the observation of pure sericin and PVDF films (FIG. 4C and FIG. 4D).
  • more binding sites of sericin protein on LNMO surface was also confirmed by TEM images (FIG. 10A to FIG. 10D) and energy dispersive X-ray mapping (FIG. 11A to FIG. 11L), which was due to strong interaction between rich hydroxyl groups of LNMO (FIG. 3E) and the water-soluble binder.
  • FIG. 13C The charging/discharging profiles of the sericin electrode at different current rates are shown in FIG. 13C, and the corresponding polarization values (defined by the charging/discharging voltage separation at half-capacity) are summarized in FIG. 13D.
  • FIG. 13D A linear relationship between voltage polarizations of the sericin or PVDF electrodes and the current rates was observed, indicating an ohmic behavior of both electrodes.
  • the sericin electrode exhibited lower charging/discharging voltage polarization.
  • the voltage polarization for the sericin electrode is 0.17 V, much smaller than 0.52 V of the PVDF electrode.
  • the full battery delivers capacities of 205.6, 180.6, 146.8, 76.3, and 37.2 mAh g 1 at current rate of 1, 2, 4, 10, and 20 C, respectively, whereas for sericin binder, higher capacities of 240.9, 215.4, 183.2, 127.7, and 85.8 mAh g 1 were delivered (FIG. 15C).
  • the stability of the electrodes was evaluated by long term cycling of the full cells for 1000 cycles, and the full cell with sericin electrode delivered both higher capacity and better capacity retention (FIG. 15D). After 1,000 cycles, the capacity of the full cell using sericin binder sustained 100.6 mAh g _1 with more than 80% capacity retention, while the full cell with PVDF binder only delivered a capacity of 24.3 mAh g 1 .
  • the resistance of the SEI layer originated from the electrolyte oxidation was larger and grows faster (FIG. 13E).
  • the R SEI for the sericin electrode was more stable after 30 cycles, indicating the formation of a stable surface protection layer.
  • the charge- transfer resistance of sericin binder was only 271 ⁇ after 100 cycles, much smaller than that of PVDF binder (1367 ⁇ ), indicating a higher energy barrier for both electrons and Li-ion transport in the PVDF electrode.
  • the ionic conductivity measured by galvanostatic intermittent titration technique (see 'Brief description of Figures', FIG. 17A and FIG. 17B), exhibited that the sericin electrode had higher Li-ion diffusivity compared to the PVDF electrode during charging state (FIG. 13F). Li-ion diffusion usually follows the Arrhenius relationship:
  • E A is the effective energy barrier
  • ke is the Boltzmann constant
  • Do is the pre-factor estimated empirically.
  • the peak at 284.8 eV is the signature of aliphatic carbon C-C and all other peaks are calibrated according to 284.8 eV C-C peak.
  • the peak at 285.7 - 285.9 eV can be attributable to overlapped C-0 from SEI or sericin binder, C-N from sericin binder, or C * H 2 -CF 2 from PVDF binder (The asterisk is used to indicate the specific atom being observed, and it is used only when two or more atoms of the same element are presented in different bonding situations.).
  • the peak at 287.0 - 287.1 eV comes from carbonyl group of SEI or sericin binder.
  • the peak at even higher chemical shift includes carbonate and semicarbonate compound from SEI, or CH 2 -C * F 2 from PVDF polymer chain.
  • Ols spectra of the PVDF electrode showed a peak for LNMO lattice oxygen at 529.6-529.9 eV and a peak for lattice surface defects associated with electron-deficient oxygen at 531.7-532.2 eV.
  • Cls and Ols spectra of both PVDF and sericin electrodes exhibited similar peak evolution, indicating the formation of SEI layers.
  • the increase of peak intensity at 290.4-290.9 eV of both electrodes is regarded as the formation of semicarbonate (ROC0 2 Li) and carbonate (Li 2 C0 3 ) species, while the increases at 288.7-288.8, 287.0-287.1, and 285.7-285.9 eV correspond to ester compound, carbonyl compound and alkyl group with carbonate oxygen from decomposition of diethyl carbonate and ethylene carbonate respectively.
  • the peak intensities for Cls spectra peaks pertaining to SEI composition continued to increase, while for sericin electrode they kept relatively constant compared with the 10th cycle, indicating that the SEI layer continued to change on the PVDF electrode while kept relatively intact on the sericin electrode. From the above discussion, it was found that the SEI composition for the PVDF and sericin electrodes was similar, and the compactness of the SEI layer should play an important effect on the electrode performance.
  • the uniform sericin binder would prevent the direct contact between the LNMO and electrolyte, which can effectively negate the oxidation process, elongating the voltage stability time.
  • the voltage stability time of LNMO electrode (defined as the time before the voltage of the cell drops to 4.6 V) with a different weight ratio of the binder was evaluated (FIG. 21B).
  • the voltage stability time was boosted dramatically with the increase of the sericin ratio, while the increase of PVDF ratio had no significant enhancement on the stability time.
  • PVDF binder had linear long-chain structure (inset of FIG. 21B), the interaction with other electrode components were mainly via van der Waals forces.
  • the average tensile strength for sericin electrode was 1.6 MPa, which is higher than that of PVDF electrode (0.9 MPa). Therefore, robust mechanical support of sericin coating maintained the structural integrity of the LNMO electrode during the fast charging/discharging processes.
  • the sericin electrode had a lower energy barrier for Li-ion diffusion as well as smaller voltage polarization than that of the PVDF electrode, delivering a remarkable electrochemical performance at high rates.
  • the sericin electrode can deliver a high capacity of 91.8 mAh/g at 5 C, while the PVDF electrode only exhibited a low capacity of 28.5 mAh/g.
  • the fundamental understanding was helpful to inspire the development of other natural or synthetic polymers (polypeptide, polyethylene oxide, poly(vinylpyridine), polystyrene sulfonate, etc.) as a potential binder system to match the next-generation LIBs with high-voltage cathode electrodes.

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Abstract

La présente invention concerne une électrode comprenant un matériau électroactif et un liant dispersé dans le matériau électroactif, le liant comprenant de la séricine hydrolysée. En particulier, ladite électrode est un matériau de cathode à haute tension comprenant un oxyde en couches, un oxyde de spinelle ou un polyanion d'olivine, l'oxyde en couches comprenant du LiCo02, du LiMnO2, du LiNi0.5Mn0.5O2 et du LiNi1 /3Co1/3Mn1/3O2. L'invention concerne également un procédé de production de l'électrode.
PCT/SG2018/050278 2017-06-05 2018-06-05 Liant à base de séricine pour électrodes WO2018226156A1 (fr)

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CN116477619A (zh) * 2023-04-22 2023-07-25 青岛华腾石墨科技有限公司 一种天然石墨的相改性方法

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CN116477619A (zh) * 2023-04-22 2023-07-25 青岛华腾石墨科技有限公司 一种天然石墨的相改性方法

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