HIGH CAPACITY ELECTRODES ENABLED BY 2D MATERIALS IN A VISCOUS AQUEOUS INK

Abstract

A composite for use the manufacture of an electrode, the composition comprising a spontaneously formed segregated network of nanosheets of conducting materials, or a combination thereof, and a particulate active material, in which no additional polymeric binder or conductive-additive are required.

Claims

1. A composite for use as an electrode, the composite comprising a spontaneously formed segregated network of nanosheets of conducting 2D inorganic materials, or a combination thereof, and a particulate active material, wherein an additional polymeric binder and conductive-additive are excluded, and wherein the nanosheets of conducting 2D inorganic materials form an interconnected scaffold to sandwich the particles of the particulate active material to form the segregated network.

2. The composite of claim 1, wherein the composite comprises from 5 wt % to 50 wt % of the spontaneously formed segregated network of nanosheets of conducting 2D inorganic materials, or a combination thereof.

3. The composite of claim 1, wherein the nanosheets of conducting 2D inorganic material are selected from transition metal dichalcogenides, transmission metal oxides or MXenes having a general formula of M.sub.n+1X.sub.nT.sub.x, where T is an (optional) functional group, or other inorganic layered materials, or a combination thereof.

4. (canceled)

5. (canceled)

6. (canceled)

7. (canceled)

8. The composite of claim 1, wherein the particulate active material is selected from micron-sized silicon powder, lithium, sulphur, graphene, graphite, and lithium nickel manganese cobalt oxide (NMC, LiNi.sub.xMn.sub.yCo.sub.zO.sub.2 where x+y+z=1), lithium cobalt oxide (LCO), lithium nickel cobalt aluminium oxide (NCA), lithium iron phosphate (LFP), lithium titanium oxide (LTO) alloying materials (Si, Ge, Sn, P etc.), chalcogenides (S, Se, Te), metal halides (F, Cl, Br, I), and any other suitable battery material.

9. The composite of claim 1, wherein the composite comprises from 50 wt % to 95 wt % of the particulate active material.

10. The composite of claim 1 for use as an electrode in an energy storage device such as a battery, a supercapacitor, an electrocatalyst, or a fuel cell.

11. A positive electrode or a negative electrode comprising a composite of a spontaneously formed segregated network of nanosheets of conducting 2D inorganic materials, or a combination thereof, and a particulate active material, wherein an additional polymeric binder and conductive-additive are excluded, and wherein the nanosheets of conducting 2D inorganic materials from an interconnected scaffold to sandwich the particles of the particulate active material to form the segregated network; wherein the nanosheets of conducting 2D inorganic materials optionally have a mass fraction (Mf) in the electrode of 5-50 wt %.

12. The positive electrode or the negative electrode of claim 11, wherein the nanosheets of conducting 2D inorganic materials have a mass fraction (Mf) in the electrode of 10-40 wt %.

13. The positive electrode or the negative electrode of claim 11, wherein the nanosheets of conducting 2D inorganic materials have a mass fraction (Mf) in the electrode of 20-30 wt %.

14. The positive electrode or the negative electrode of claim 11, wherein the positive and negative electrodes each have a thickness of between 50 μm and 2000 μm.

15. The positive electrode or the negative electrode of claim 11, wherein the positive electrode and the negative electrode each comprise a stack of two or more layers of the segregated network of nanosheets of the conducting 2D inorganic materials.

16. The positive electrode or the negative electrode of claim 11, wherein the electrodes have a thickness of between 200 μm to 500 μm.

17. A high areal capacity battery comprising a positive and negative electrode, wherein the positive and negative electrode comprise a composite of a spontaneously formed segregated network of nanosheets of conducting 2D inorganic materials, or a combination thereof, and a particulate active material, wherein an additional polymeric binder and conductive-additive are excluded, and wherein the nanosheets of conducting 2D inorganic materials form an interconnected scaffold to sandwich the particles of the particulate active material to form the segregated network; wherein the nanosheets of conducting 2D inorganic materials optionally have a mass fraction (Mf) in the electrode of 5-50 wt %.

18. A non-rechargeable battery or a rechargeable battery comprising an anode material, a cathode material, and an electrolyte, wherein the anode material and the cathode material comprise a composite of a spontaneously formed segregated network of nanosheets of conducting 2D inorganic materials, or a combination thereof, and a particulate active material, wherein an additional polymeric binder and conductive-additive are excluded, and wherein the nanosheets of conducting 2D inorganic materials form an interconnected scaffold to sandwich the particles of the particulate active material to form the segregated network.

19. A method for producing a positive or negative electrode, the method comprising mixing aqueous dispersions of nanosheets of conducting 2D inorganic materials, or a combination thereof, with a particulate active material powder to form a spontaneously formed segregated network, and depositing the spontaneously formed segregated network onto a substrate to yield an electrode.

20. The method of claim 19, wherein the mixture is slurry cast onto a substrate.

21. The method of claim 20, wherein when the mixture is slurry cast onto a substrate, the substrate is selected from glass, semi-conductors, metal, ceramic, aluminium foil, Copper foil or other stable conductive foils or layers.

22. The method of claim 19, wherein the dispersion of nanosheets of conducing 2D inorganic materials with the particulate active material has an apparent viscosity of between about 0.50 Pa/s to about 1.0 Pa/s.

23. (canceled)

24. (canceled)

25. The method of claim 19, wherein the spontaneously formed segregated network of nanosheets of conducting materials are dispersed in either an organic solvent alone or organic solvent water stabilised with 0.2 wt % to 10 wt % surfactant.

26. (canceled)

27. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] The invention will be more clearly understood from the following description of an embodiment thereof, given by way of example only, with reference to the accompanying drawings, in which:—

[0052] FIG. 1 illustrates a) Optical images of the MX-C ink, showing its viscous nature. TEM images of b) MX-C and c) MX-N nanosheets. Insets are the corresponding selected area electron diffraction (SAED) patterns of the nanosheets. d) Histograms of MX-C and MX-N flake lengths obtained via TEM statistics. e-f) Rheological properties of MX-C and MX-N inks with e) viscosity plotted as a function of shear rate and f) storage and loss moduli plotted as a function of strain. Also included is the control sample made of PAA (aqueous binder) and carbon black (CB) dispersed in water (PAA/CB-water).

[0053] FIG. 2 illustrates EDX of (a) MX-C and (b) MX-N samples. (c) AFM and height profiles showing the average thickness of the samples (MX-C: ˜1.5 nm and MX-N: ˜2 nm).

[0054] FIG. 3 illustrates a) Composite electrode preparation from Si/MXene ink-based slurry. b) The slurry drying process and c) scheme displaying the resulting Si/MXene composite. The MXene nanosheets form an interconnected scaffold and enable the formation of a thick electrode. d) Top-view and e) cross-sectional SEM images of nSi/MX-C electrode, showing the Si nanoparticles (NPs) are well wrapped by the MX-C nanosheets in a manner of sandwiching. f) Top-view SEM image of Gr-Si/MX-C electrode, indicating that the Gr-Si particles are well wrapped by the interconnected MX-C network.

[0055] FIG. 4 illustrates Raman spectra for pure MX-C film and nSi/MX-C composite anode (MX-C M.sub.f=30 wt %). In the composite, the characteristic peaks from MX-C well match to those for pure MX-C film, indicating no phase change during the composite-electrode fabrication process. The characteristic Si peak at ˜520 cm.sup.−1 is evident in the composite spectrum.

[0056] FIG. 5 illustrates XRD patterns for pure MX-C film and nSi/MX-C composite anode (MX-C M.sub.f=30 wt %). We note that the X-ray source is Mo instead of Cu. XRD pattern of the composite corresponds well to the pure MX and Si, indicating that the crystal structures are not changed.

[0057] FIG. 6 illustrates a) Bar chart comparing the electrical conductivity comparison of various electrodes. The dashed lines are the electrical conductivity of MX-C and MX-N freestanding films. b) Electrical conductivity change of the nSi/MX-C and Gr-Si/MX-C electrodes upon bending, as shown in the insets. The almost constant conductivity values indicate the robust nature of the Si/MXene electrodes. c-d) Comparison of the mechanical properties comparison of various electrodes. c) Representative stress-strain curves for various electrodes. d) Top: tensile toughness (i.e. tensile energy density required to break film) plotted as a function of strain at break (%). Bottom: Tensile strength plotted as a function of Young's modulus. The mechanical properties indicate that the MXene nanosheets confer mechanical reinforcement component, resulting in much enhanced toughness and tensile strength.

[0058] FIG. 7 illustrates the electrical conductivity of nSi/MX-C as a function of MX M.sub.f (5-40 wt %). The line fits well to percolation-scaling law, where σ∝(ϕ−ϕ.sub.c,e).sup.n.sup.e, and ϕ.sub.c,e and n.sub.e are the electrical percolation threshold and exponent, respectively. The large exponent (n.sub.e=2.2) are expected for 2D conductive networks. The percolation threshold of MX-C is 0.5 wt %, much lower than the value observed from the typically used conductive agent, carbon black (ϕ.sub.c,e=3-25 wt %).

[0059] FIG. 8 illustrates SEM images of (a) filtrated MX-C and (b) slurry-casted MX-C films, showing a layered morphology with MX-C nanosheets stacked together. SEM images of (c) filtrated nSi/MX-C and (d) slurry-casted nSi/MX-C electrodes, showing a sandwiched structure with nSi particles covered by the MX-C interconnected network in both cases. The SEM images of these samples confirm that, the morphology difference impacted by the electrode fabrication method is trivial. Therefore, it is reasonable and fair to estimate the mechanical performance of all the slurry-casted electrodes (such as nSi/MX-C and Gr-Si/MX-C) by measuring the strain-stress curves of the corresponding vacuum-filtrated samples, as indicated in FIG. 6c-d.

[0060] FIG. 9 illustrates (a-e) galvanostatic charge-discharge (GCD) curves of nSi/MX-C anodes with different compositions (MX-C M.sub.f=5-40 wt %) at various current densities (0.15-3 A/g, corresponding to 1/20-1 C rate). (f) Bottom: 1.sup.st lithiation/de-lithiation capacities of nSi/MX-C anodes as a function of MX-C M.sub.f. Top: 1.sup.st Coulombic efficiency (CE) of nSi/MX-C anodes. All samples show a high 1.sup.st CE of 81-84% and typical GCD curves as expected for Si.

[0061] FIG. 10 illustrates Si specific capacity (C/M.sub.si) of nSi/MX-C anodes as a function of MX-C M.sub.f (5-40 wt %). C/M.sub.si is maximized to approach the theoretical value (dashed line, Si C.sub.SP=˜3500 mAh/g) at MX-C M.sub.f≥30 wt %, clearly suggesting the optimum MX-C M.sub.f of 30 wt %.

[0062] FIG. 11 illustrates a): Rate performance comparison for nSi/MX-C electrodes with various MX-C mass fractions. Note that the capacity values are normalized to the mass of silicon (C/M.sub.si). b) Asymmetric charge-discharge curves of the typical nSi/MX-C electrode. Inset is the as-obtained C/M.sub.Si at various delithiation rates. c) Left: 1.sup.st cycle charge-discharge curves at a 0.15 A/g (˜ 1/20 C-rate) of the nSi/MX-C electrodes (MX-C M.sub.f=30 wt %) with the M.sub.Si/A ranging from 0.9 to 3.8 mg/cm.sup.2. Insets are the optical images of these electrodes. Right: 1.sup.st Coulombic efficiency (top) and areal capacity (bottom) of nSi/MX-C (MX-C M.sub.f=30 wt %) with various M.sub.Si/A. The line slope indicates the average C/M.sub.Si (˜3200 mAh/g) achieved in various electrodes. d) Cycling performance comparison among the electrodes with various M.sub.Si/A. Also included is the control sample made with PAA and carbon black as the aqueous binder and conductive agent, respectively. e) Cross-sectional (left) and top-view (right) SEM images of nSi/MX-C (MX-C M.sub.f=30 wt %, M.sub.Si/A=2.4 mg/cm.sup.2) after cycling; also included is the EDX mapping, showing a uniform distribution of nSi and MX-C in the cycled electrode. f) Lifetime of nSi/MX-C and nSi/MX-N (MXene M.sub.f=30 wt %) electrodes at a low M.sub.Si/A (0.9˜1 mg/cm.sup.2) and a high rate (1.5 A/g). Also included is the Coulombic efficiency of nSi/MX-C (top).

[0063] FIG. 12 illustrates a) Typical galvanostatic charge-discharge (GCD) curves of Gr-Si/MX-C electrode (MX-C M.sub.f=30 wt %, M.sub.GrSi/A=3.3 mg/cm.sup.2) at various current densities. b) Left: GCD profiles of Gr-Si/MX-C electrodes with various M/A at 0.1 A/g (˜ 1/20 C-rate). Right: 1.sup.st CE (up) and C/A (down) of Gr-Si/MX-C plotted as a function of M.sub.Gr-Si/A. c) Cycling performance of Gr-Si/MX-C electrodes with various M.sub.GrSi/A at 0.2 A/g (˜1/10 C-rate). d-e) SEM images of the Gr-Si/MX-C electrode (M.sub.GrSi/A=3.3 mg/cm.sup.2) after cycling, showing that the MX-C binder tightly wrapped the Gr-Si particles and maintained the structural integrity. f) Areal capacity comparison of this work to other Si/conductive-binder (Si/C-binder) systems, showing that our Si/MX-C electrodes have exhibited both high M.sub.Active/A and C/A compared to the literature. g) Scheme of components inside the cell, highlighting the importance of utilizing high M.sub.Active/A electrodes in reducing the contribution from the inactive components. h) Cell-level specific capacity (C/M.sub.Total) on the anode side plotted as a function of M.sub.Active/A, and compared to the reported Si/C-binder systems. Dashed lines indicate the theoretical performances for the nSi (blue line) and Gr-Si (red line) particles.

DETAILED DESCRIPTION OF THE DRAWINGS

[0064] Here, it is shown that the production of very thick electrodes which retain almost all of their intrinsic capabilities can be achieved via simultaneously boosting the electrical/mechanical properties of granular electrode materials by using, for example, 2D nanosheets of conductive (inorganic) material, specifically in the form of segregated networks, as both binder and conductive additive, without any additional polymer/polymeric binder or CB. By adding 2D nanosheets of conductive material to high-performance anode/cathode materials such as silicon and LiNi.sub.xMn.sub.yCo.sub.zO.sub.2 (NMC), a new type of hierarchical composite is shown where the 2D nanosheets arrange themselves into networked membranes that envelop the active material particles. These networks significantly improve the mechanical properties, allowing the fabrication of thick electrodes, and ensure their stability, even during repeated charge/discharge. At the same time the electrode conductivity is dramatically increased, facilitating fast charge distribution, even in thick electrodes. The production of extremely thick electrodes (up to 600 μm) with C.sub.SP approaching theoretical values for each electrode material, enables the production of full-cells with areal capacities and specific energies considerably higher than any previous reports. The thickness of the electrodes can also be further increased by stacking two or more layers of the segregated network of the nanosheets of 2D conductive materials, where the thickness of each layer is no more than 450-600 μm. The production involves simple and scalable production techniques, which can be applied to both anodes and cathodes and is compatible with any high-performance electrode material.

[0065] Materials and Methods

[0066] Multi-Layered MXene Preparation

[0067] Multi-layered MXene was prepared as follows: Typically, 0.5 g of lithium fluoride (LiF, Sigma Aldrich, USA) were added to 10 ml, 9 M of hydrochloric acid (HCl, 37 wt %, Sigma Aldrich, USA), followed by 10 min stirring at room temperature (RT) until the formation of a clear solution. After that, 0.5 g Ti.sub.3AlC.sub.2 MAX phase (Y-Carbon Corp., Ukraine) were slowly added over the course of 20 min at room temperature (RT) under magnetic stirring, then transferred to an oil bath and allowed to react for 24 h at 35° C. under continuous stirring. Once the reaction ended, the suspension was transferred to centrifuge tubes and centrifuged at 3500 rpm for 3 min. The supernatant was then decanted and 15 mL of fresh DI water was added to the suspension followed by vigorous shaking and then another round of centrifugation at 3500 rpm for 3 min. This washing process was repeated 4 times until the pH of the supernatant became ˜6. The supernatant was then decanted, leaving the m-Ti.sub.3C.sub.2T.sub.x on the bottom of the centrifuge tube for making the Ti.sub.3C.sub.2T.sub.x ink.

[0068] m-Ti.sub.3CNT.sub.x using a similar method were prepared as follows: 0.5 g Ti.sub.3AlCN was slowly added to a solution containing 0.66 g LiF and 10 ml HCl (6 M). The reaction time was set to 16 h. All the rest of the steps were similar to the Ti.sub.3C.sub.2T.sub.x counterpart.

[0069] MXene Ink Preparation:

[0070] MXene viscous ink was prepared as follows: 15 mL of deionized water (DI-water) was added to the as-etched, multi-layered MXene (Ti.sub.3C.sub.2T.sub.x or Ti.sub.3CNT.sub.x), followed by vigorous shaking by hand/vortex machine for 15 min. Then the mixture was centrifuged at 1500 rpm for 30 min. The top 80% supernatant was collected and centrifuged at 5000 rpm for 1 hr. After decanting the supernatant, 5 mL of DI-water was added to the sediment followed by vigorous shaking for 10 min, resulting in viscous MXene ink denoted as MX-C (Ti.sub.3C.sub.2T.sub.x) and MX-N (Ti.sub.3CNT.sub.x), respectively.

[0071] Electrode Fabrication:

[0072] Electrodes were prepared via a slurry-casting method using MXene viscous aqueous ink without the addition of any other conductive additives or polymeric binder. Typically, nanosized silicon powders, nSi, (or graphene-wrapped Si, Gr-Si, Angstron-Materials) were mixed with MX-C ink and ground into a uniform slurry before casting onto Cu foil using a doctor blade. After drying at ambient conditions for 2 h, electrodes were punched (12 mm in diameter) and vacuum-dried at 60° C. for 12 h to remove residual water. The MXene M.sub.f in the electrodes (ranging from 5 to 40 wt %) was controlled by changing the mass ratio of Si powders to MXene during the slurry preparation. In addition, electrodes with different mass loadings (M/A) were obtained by changing the height of doctor blade (150-2100 μm) when casting a slurry with 30 wt % of MXene. The resultant electrodes possessed various thicknesses and thus various mass loadings and were denoted as nSi/MX-C (or Gr-Si/MX-C). n-Si/MX-N electrodes were similarly fabricated by mixing nSi powder with the MX-N viscous aqueous ink. The mass fraction of MX-N M.sub.f in the electrodes was 30 wt %. Detailed compositions and thicknesses of the Si/MXene electrodes can be found in Table 2 and Table 3, respectively.

[0073] Other methods can be used to deposit the slurry preparation on a substrate. For example, the slurry preparation can be inkjet-printed (using a Dimatix DMP2800 Material printer, for example) on a variety of substrates, such as AlO.sub.x-coated PET (NB-TP-3GU100, Mitsubishi Paper Mills Ltd.), glass, Kapton, etc. The slurry preparation can also be extrusion-printed on substrates using a 3D printer. Other methods including ink jet printer methodology (a technique where the ink is deposited on a substrate in a controlled manner with accurate positioning), roll-to-roll coating or processing (a process of printing or patterning the slurry onto a roll of flexible plastic or metal substrate), spraying (electrospray, ultrasonic-spray, conventional aerosol spray), blade coating, filtration, screen printing, drop casting and 3D printing can all be used.

[0074] Material Characterization:

[0075] The rheological properties of MXene inks, as well as the reference sample, were studied on the Anton Paar MCR 301 rheometer. Morphologies and microstructure of the Si/MXene electrodes were examined by scanning electron microscopy (SEM), Raman spectroscopy and XRD. The electrical conductivity of the electrodes was measured using a four-point probe technique. To exclude the conductivity contribution from the Cu foil, the composite slurry (made of Si materials with MXene aqueous ink) as well as the reference sample (nSi/PAA/CB) were casted onto glass plates and dried at ambient condition. Then, four lines made of Ag paint (Agar Scientific) were brushed in parallel on the films' surface. The sheet resistance of the films was measured using a Keithley 2400 source meter, and converted to the electrical conductivity based on the samples' geometric information (length, width and thickness). To evaluate the mechanical properties of the Si/MXene composites, strain-stress tests were performed. Since the slurry casted films cannot be peeled off from the substrates (either Cu foil or glass), therefore, the composite slurry was ground and then vacuum filtrated through nitrocellulose membrane (Whatman, USA). The total M/A in the MXenes as well as composite films (nSi/MX-C, nSi/MX-N and Gr-Si/MX-C) was controlled at 1˜2 mg/cm.sup.2 (thickness ˜20 ˜30 μm) while the MXene mass fraction, M.sub.f, was controlled to be 30 wt. %. After filtration and naturally drying, the films were peeled off from the membrane, cut into strips and stored under vacuum for further use. The strain-stress curves of the strips were measured on a Zwick Z0.5 Pro-Line Tensile Tester (100 N Load Cell) at a strain rate of 0.5 mm/min. Each data point was obtained by averaging the results from four measurements.

[0076] To study the robustness of the Si/MXene films, the two ends of the strips were fixed to the substrates. Two lines of Ag paint were brushed onto the two ends of the strip, which was connected to the multimeter through two pieces of Ag wire. The resistance of the samples upon bending/releasing at different degrees was recorded and converted to the electrical conductivity. The conductivity was further plotted as a function of (Lo-L)/Lo, indicative of different bending states, where Lo is the original length of the strip, (Lo-L) is the real-time horizontal length of the bended film.

[0077] Electrochemical Characterization:

[0078] The electrochemical performance of the Si/MXene electrodes was evaluated in the half-cell configuration (2032-type, MTI Corp.). Once the slurry-casted films were vacuum dried, electrodes with diameter=12 mm (geometric area: 1.13 cm.sup.2) were punched and weighed to determine the areal mass loading (M/A). The electrochemical properties of the Si/MXene composite electrodes were evaluated in a half-cell configuration (2032-type coin cells, MTI Corp.) which were assembled in an Ar-filled glovebox (UNIlab Pro, Mbraun). Inside the coin cell, the Si/MXene is the working electrode while the Li disc (diameter: 14 mm, MTI Corp.) is the counter and reference electrode. The separator was Celgard 2320 (Celgard, USA) and the electrolyte was 1 M lithium hexafluorophosphate (LiPF.sub.6) in ethylene carbonate/diethyl carbonate/fluoroethylene carbonate (EC/DEC/FEC, 3:6:1 in v/v/v, BASF).

[0079] Galvanostatic charge-discharge (GCD) tests were performed on a potentiostat (VMP3, Biologic) in a voltage range of 0.005-1.2 V. The areal capacities (C/A) of the electrodes were obtained by dividing the measured cell capacity by the geometric electrode area (1.13 cm.sup.2). The specific capacities of the electrodes were obtained by C/M. Here, M can be the mass of the electrode (M.sub.total) or the active Si material (M.sub.Si), resulting in the specific capacity per electrode (C/M.sub.total) or per active Si (C/M.sub.Si). To investigate the maximum accessible C/A of the electrodes, the cells were tested at a reasonably slow condition of ˜ 1/20 C-rate (0.15 A/g for nSi anodes and 0.1 A/g for Gr-Si anodes). The electrode was fully lithiated by discharging the cells at a very slow rate (˜ 1/20 C-rate, 0.15 A/g) then delithiated the electrode (charging the cell) at various rates, ranging from 1/20 to 1 C-rate. The cycling performance of the cells were measured at a rate of ˜1/10 C (0.3 A/g for nSi anodes and 0.2 A/g for Gr-Si anodes). After cycling, the cells were disassembled, rinsed with dimethyl carbonate (DMC) several times and dried inside the glove box at room temperature before the SEM analysis.

[0080] Results

[0081] MXene Inks Characterization

[0082] The synthesis of Ti.sub.3C.sub.2T.sub.x (MX-C) and Ti.sub.3CNT.sub.x (MX-N): After etching the MAX precursors in hydrochloric acid (HCl)-lithium fluoride (LiF) solution, multi-layered MXenes, with a certain degree of delamination were obtained. Upon vigorous manual shaking of the MXene/water suspension, the clay-like multi-layered MXenes further swelled and delaminated into MX-C and MX-N flakes, forming concentrated aqueous inks. The viscous feature of the MX-C ink is shown in FIG. 1a. Both MX-C/MX-N inks are made of clean flakes with a hexagonal atomic structure (FIG. 1b,c and FIG. 2a,b), agreeing with previous reports. The atomic force microscopy and height profiles (FIG. 2c) suggest these nanosheets are predominantly single-layered. These two types of inks possess a similar concentration (˜25 mg/mL), and the mean flake size is in the range of 2.1-2.8 μm in both cases (FIG. 1d).

[0083] As mentioned above, the critical cracking thickness (CCT) of Si-based anode is directly related to the viscosity of the slurry. Therefore, the rheological behaviours of MXene aqueous inks, together with a reference sample made of traditional dual-component additives (PAA/carbon black, CB) dispersed in water, were evaluated. All specimens (with the same solid concentration) demonstrate non-Newtonian characteristics and shear-thinning (pseudoplastic) behaviour; and the apparent viscosity (η, Pa.Math.s) decreases with shear rate (γ, s.sup.−1), as demonstrated in FIG. 1e. Such a behaviour can be well modelled using the Ostwald-de Wael power law:

η=kγ.sup.n-1,  (1)

[0084] where k and n are the consistency and shear thinning index, respectively. The empirical parameters of the studied suspensions are summarized in Table 1.

TABLE-US-00001 TABLE 1 Rheological parameters of MXene inks compared to PAA/CB-water Solid Consistency Shear thinning Additives system concentration index, k index, n MX-C ink 25 mg/ml 3.25 0.35 MX-N ink 25 mg/ml 0.17 0.64 PAA/CB-water 25 mg/ml 0.022 0.52

[0085] The apparent viscosity in the MX-C ink is one and two orders of magnitude higher than that of the MX-N ink and PAA/CB-water, respectively. In addition, the viscoelastic properties of the inks, in particular, storage and loss moduli, are important. These can be used to investigate regions of linear elastic deformation, yield points, and sample fluidisation, and give insight into the energetics of the sample network. The storage and loss moduli in these viscoelastic materials were plotted as a function of strain, showing much higher storage and loss modulus in MX-C, followed by MX-N and substantially higher than the PAA/CB-water system (FIG. 1f). Such a rheological behaviour in the MXene inks should facilitate the formation of thick Si/MXene electrodes, as will be discussed below.

[0086] Electrode Fabrication and Characterization

[0087] Commercial Si powders, namely, nanoscale Si (nSi, C.sub.SP=˜3,500 mAh/g, size ˜80 nm) and graphene-wrapped Si (Gr-Si, C.sub.SP=˜2,000 mAh/g, superstructure size ˜10 μm), were chosen as models for high-capacity materials.

TABLE-US-00002 TABLE 2 Si/MX-C electrodes with various formulas Sample Vol. of MX-C ink MX-C nSi (or Gr—Si) conditions (Conc. = 25 mg/ml) content powder  5 wt % MX-C 0.2 ml  5 mg 95 mg 10 wt % MX-C 0.4 ml 10 mg 90 mg 20 wt % MX-C 0.8 ml 20 mg 80 mg 30 wt % MX-C 1.2 ml 30 mg 70 mg 40 wt % MX-C 1.6 ml 40 mg 60 mg

[0088] Si powders were ground with MXene aqueous inks to give a concentrated, homogenous and viscous slurry, which can be coated onto Cu foil using an industry-compatible slurry-casting technique without adding any polymeric binders or CB (FIG. 3a). Importantly, the high viscosity of MXene inks (and other inks comprising 2D conductive nanosheets of TMDs, graphene or transition metal oxides, or combinations thereof) enables an extremely thick coating of the slurry (up to 650 μm and 2100 μm for the nSi and Gr-Si, respectively for the slurry thickness, as shown in FIG. 3b and Table 3). In the wet slurry, the ultrathin MXene nanosheets distribute randomly and further knit into an interconnected network while wrapping the Si particles. Upon evaporation, mechanically robust electrodes are thus formed, as shown in FIG. 3c. The surface of the dried electrodes remains smooth with thickness up to ˜350 μm before cracking first occurs (Table 3), yielding a CCT much larger than the achievable thickness with traditional binders (<100 μm).

TABLE-US-00003 TABLE 3 Blade thickness and M/A of the as-fabricated Si/MXene electrodes. Sample Sample Sample Blade thickness Electrode thickness M.sub.Total/A M.sub.Active/A Electrode density nSi/MX-C  150 μm  23 μm  1.2 mg/cm.sup.2  0.9 mg/cm.sup.2 0.52 g/cc (MX-C  200 μm  35 μm  1.9 mg/cm.sup.2  1.3 mg/cm.sup.2 0.54 g/cc M.sub.f = 30 wt %)  300 μm  46 μm  2.6 mg/cm.sup.2  1.8 mg/cm.sup.2 0.57 g/cc  400 μm  53 μm  3.4 mg/cm.sup.2  2.4 mg/cm.sup.2 0.64 g/cc  600 μm  79 μm  5 mg/cm.sup.2  3.5 mg/cm.sup.2 0.63 g/cc  650 μm  83 μm  5.4 mg/cm.sup.2  3.8 mg/cm.sup.2 0.65 g/cc Gr—Si/MX-C  600 μm 102 μm  4.6 mg/cm.sup.2  3.2 mg/cm.sup.2 0.45 g/cc (MX-C  900 μm 150 μm  7.4 mg/cm.sup.2  5.2 mg/cm.sup.2 0.49 g/cc M.sub.f = 30 wt %) 1500 μm 250 μm 12.6 mg/cm.sup.2  8.6 mg/cm.sup.2 0.50 g/cc 1800 μm 290 μm 14.8 mg/cm.sup.2 10.4 mg/cm.sup.2 0.51 g/cc 2100 μm 351 μm 18.6 mg/cm.sup.2   13 mg/cm.sup.2 0.53 g/cc

[0089] Top-down and cross-sectional scanning electron microscopy (SEM) images with energy-dispersive X-ray (EDX) mapping confirm that the nSi particulates are uniformly wrapped by the interconnected MX-C skeleton (FIG. 2d,e). No phase changes of the active materials are observed during the slurry processing, as indicated by Raman spectra (FIG. 4) and X-ray diffraction (XRD, FIG. 5). The nSi/MX-N exhibits a similar porous morphology as that of nSi/MX-C. On the other hand, the Gr-Si/MX-C showcases a hierarchical nano-/macro-structure, in which the Gr-Si pseudo-spherical superstructures (˜10 μm) are uniformly coated with robust, interconnected MX-C nanosheets (FIG. 3f). Such a morphology provides extensive free volume that allows the expansion of the nanoscale Si during the electrochemical processes, which will be discussed below.

[0090] Electrical and Mechanical Characterization

[0091] To achieve high thickness and so high C/A, the Si-based anodes should possess high conductivity and mechanical toughness to ensure efficient charge transport and structural stability, respectively. Previous studies revealed that the electrical conductivity issue becomes more severe in high M/A electrodes, which limit the rate capability of the electrode. Here MXenes were employed to solve this issue. Other similar nanosheets of 2D conductive materials are also envisaged to solve this issue, such as, for example, Graphene, Silicene, Germanene, BiTe, HfTe.sub.2, MoTe.sub.2 (1T), NbS.sub.2, NbSe.sub.2, PdSe.sub.2, PdTe.sub.2, PtSe.sub.2, PtTe.sub.2, TaSe.sub.2, TaS.sub.2, TiS.sub.2 (1T), TiSe.sub.2, TiTe.sub.2, WTe.sub.2, ZrSiS. ZrTer.sub.2, ZrTe.sub.3, ZrTes, BSCCO, Cr.sub.2Si.sub.2Te.sub.6, BiTITe, CuFeTe, FeSe, FeTe, FeTeSe, HfTe.sub.2, VSe.sub.2, and WTe.sub.2. Electrical measurements were performed on a range of Si/MXene electrodes as well as reference samples. FIG. 6a reveals that by adding 30 wt % MXene to the Si, the conductivity has been improved roughly by ×1200 times for the nSi/MX-C (3448 S/m), ×120 times for the nSi/MX-N (336 S/m), and ×50 times for the Gr-Si/MX-C (1010 S/m) compared to their respective traditional systems (nSi/PAA/CB and Gr-Si/PAA/CB). Moreover, the nSi/MX-C electrode conductivity scales with MX-C mass fraction (M.sub.f) and can be explained in the frame of percolation theory (FIG. 7). Importantly, the high electrical conductivity in the nSi/MX-C and Gr-Si/MX-C electrodes can be well-maintained upon repeatedly bending even in a twisted configuration (FIG. 6b), indicating the robust nature inherited from the pure MX-C film. It should be noted that this is significant as the composite electrodes (nSi/MX-C and Gr-Si/MX-C) combines high M/A, an advanced electron transport network and mechanical flexibility, holding great promise for future wearable power sources.

[0092] To further demonstrate the mechanical reinforcement provided by MXene nanosheets, the mechanical properties of all Si/MXene composite electrodes (such as nSi/MX-C and Gr-Si/MX-C, etc.) were estimated and compared by measuring the stress-strain curves of the corresponding vacuum-filtrated films. This is justified by the roughly similar morphologies of the samples fabricated by the two methods (FIG. 8). The tensile toughness (area under the stress-strain curve) is of particular interest and has been improved by ×40 and ×15 in the nSi/MX-C and Gr-Si/MX-C, respectively from the traditional electrode (nSi/PAA/CB) at the equivalent composition (Si M.sub.f=70 wt %), as shown in FIG. 6c,d. Even though the toughness and Young's modulus in the Si/MXene composites are lower than the pure MXene films, as expected they are higher than the traditional binder system. This allows a substantial improvement of the CCT, whose magnitude depends on the mechanical properties of the deposited materials. Consequently, mechanically robust electrodes with thickness up to 350 μm for the Gr-Si/MX-C are produced. This is much higher than the achievable thickness in the traditional binder systems. In addition, it's worth noting that the dried composite films cannot be peeled off from the Cu substrate, indicative of a strong adhesion force in the Cu/composite interface.

[0093] The superiority of MXene viscous ink over traditional dual-component electrode additives can be attributed to the excellent electrical and mechanical properties of MXene nanosheets. The metallic conductivity of both MX-C and MX-N enables fast electron transport across the composites, and thus allows reversible electrochemical reactions and high-rate performance. Furthermore, the interconnected MXene network results in effective mechanical reinforcement, allowing the production of thick electrodes and potentially preserving the structural integrity of the entire electrode upon cycling. This means that the dual-functionalized MXene network should render the Si/MXene composites with good Li.sup.+ storage performance, as discussed below. The same can be said for other viscous inks comprising conductive or semi-conductive 2D nanosheets of TMDs, graphene or transition metal oxides, or combinations thereof.

[0094] Electrochemical characterization of nSi/MXene anodes

[0095] Investigating the electrochemical responses of nSi/MX-C electrodes. The dQ/dV and galvanostatic charge-discharge (GCD) profiles of nSi/MX-C electrodes (with various compositions) indicate typical curves that are typical for Si (FIG. 9a and FIG. 10a-e). All electrodes show a high 1.sup.st Coulombic efficiency (CE) of 81˜84% (FIG. 9b). This is significantly higher than other Si-based systems. The specific capacity per nSi mass (C/M.sub.Si) at different current densities suggests that by adding 30 wt % MX-C conductive binder, both the rate capability (FIG. 11a) and Si electrochemical utilization are maximized, approaching the theoretical capacity. Therefore, 30 wt % MXene was chosen in all Si/MXene composites. To probe the potentially achievable capacities of nSi, asymmetric charging-discharging was performed on the nSi/MX-C (M.sub.f=30 wt %, M.sub.Si/A=0.9 mg/cm.sup.2); the composite was lithiated slowly then delithiated at different rates. FIG. 11b shows representative asymmetric GCD curves with specific capacities presented in the inset. Almost theoretical values are achieved and maintained up to 5 A/g, suggesting that the high-rate response is enabled by the MX-C conductive network. Such an efficient interconnected network also facilitates the production of high M.sub.Si/A electrodes (FIG. 11c, left panel), resulting in a C/A as high as 12.2 mAh/cm.sup.2 (FIG. 11c, right panel). The C/A of nSi/MX-C electrodes scales linearly with M.sub.Si/A over the entire thickness regime, leading to high C/M.sub.Si (˜3200 mAh/g, dashed line) agreeing quite well with FIG. 11b. This indicates that even in the high M.sub.Si/A electrodes, almost theoretical capacities have been achieved due to the presence of MX-C conductive binder.

[0096] The cycling stabilities of nSi/MX-C electrodes with various M.sub.Si/A were measured at 0.3 A/g (FIG. 11d). While the high M.sub.Si/A electrode shows a relatively rapid capacity decay, reasonably stable capacities are achieved in the electrodes with low-medium range M.sub.Si/A (FIG. 11d). For example, the capacity retention in the M.sub.Si/A=0.9 mg/cm.sup.2 is 84% after 50 cycles, in sharp contrast to 50% in the conventional electrode (M.sub.Si/A=0.8 mg/cm.sup.2, FIG. 11d). Post-cycling SEM images suggest that the interconnected MX-C scaffold has been preserved in the medium M.sub.Si/A electrode (FIG. 11e) but is disrupted in the high M.sub.Si/A electrode due to the large volume change. The degradation of Li-metal inside the cell is also part of the reason for the relatively poor cyclability of the M.sub.Si/A=3.8 mg/cm.sup.2 electrode. To further study the long-term stability of the M.sub.Si/A=0.9 mg/cm.sup.2 electrode, a rapid charge/discharge-rate was applied. The reasonable stability, coupled with high CE over 280 cycles (FIG. 11f), can be credited to the synergistic effect between the high-capacity Si particles and the interconnected MX-C network; the latter well accommodates the large volume change and efficiently wraps the Si nanoparticles. Such a synergistic effect is not confined to MX-C; indeed, any other viscous ink composed of concentrated, conductive MXene nanosheets should work as an efficient conductive binder. As a quick example, the nSi/MX-N anode delivers an initial capacity of 1602 mAh/g at 1.5 A/g and maintains 1106 mAh/g after 70 cycles (FIG. 11f).

[0097] Performance of Gr-Si/MX-C Anode

[0098] To further improve the electrode M/A, and thus C/A, microsized Gr-Si particles were used as active materials. GCD profiles (FIG. 12a) of Gr-Si/MX-C electrodes with various compositions reveal typical curves for Si. The 1.sup.st CE in these electrodes is reasonably high (81˜83%), suggesting the lithiation/delithiation processes are reversible. The rate performance suggests that 30 wt % MX-C is capable of maximizing the specific capacity at various current densities. In addition, increasing the MX-C M.sub.f gradually not only boosts the utilization of Gr-Si to the theoretical value (C.sub.sp=˜2,000 mAh/g), but will also dramatically improve the mechanical properties of the electrode. Thus, Gr-Si/MX-C electrodes, with M.sub.GrSi/A ranging from 1.3 to 13 mg/cm.sup.2, were fabricated at a constant composition (MX-C M.sub.f=30 wt %). The 1.sup.st GCD profiles of these Gr-Si/MX-C electrodes are shown in FIG. 12b, suggesting a high 1.sup.st CE (81-83%). The C/A values scale linearly with M.sub.GrSi/A and give a specific capacity per Gr-Si (C/M.sub.GrSi) as high as 1850 mAh/g. The cycling performance of these electrodes is also M.sub.GrSi/A-dependent, being fairly stable in the M.sub.GrSi/A=3.3 mg/cm.sup.2 electrode (C/A=˜5 mAh/cm.sup.2, FIG. 12c) while less stable in the M.sub.GrSi/A=13 mg/cm.sup.2 electrode. This sharp discrepancy can be majorly attributed to the non-infinite supply of Li as well as the possible disruption of the MX-C continuous network in the thick electrode. On the other hand, intact MX-C nanosheets are well preserved and uniformly cover the Gr-Si superstructures in the M.sub.GrSi/A=3.3 mg/cm.sup.2 electrode, as demonstrated in FIG. 12d,e.

[0099] Comparison with Published Data

[0100] To demonstrate the advantage of high areal capacity Si/MXene composites for high-energy Li-ion batteries, the C/A described herein was compared to other reported Si/conductive-binder systems. The C/A of Si/MXene composites exceeds the literature results, which are generally lower than 4 mAh/cm.sup.2 (FIG. 12f and Table 4).

TABLE-US-00004 TABLE 4 Literature comparison of the Si/conductive-binder systems. Other details such as electrode composition, mass loading and specific capacity are also included. For the M/A, we sorted out the values based on the total electrode mass (Si + conductive agent/binder, M.sub.Total/A,) as well as on only the active material mass (Msi/A). Specific capacity values are presented in the same manner (both C/MTotal and C/Msi). Mass loading Max. areal Conductive- Electrode (M.sub.Total/A and Specific capacity capacity binder composition M.sub.Si/A) (C/M.sub.Total and C/M.sub.Si) (C/A) Ref. Conductive-binder based Si anodes (nano Si) Total: 5.43 mg cm.sup.−2 Si:MXene = (Si: 3.8 mg 2240 mAh g.sup.−1 @ 0.05 12.2 mAh MXene ink 70:30 cm.sup.2) C (Si: 3200 mAh g.sup.−1) cm.sup.−2 Reference RGO Si:RGO:Carbon NA ~650 mAh g.sup.−1 @ 100 NA 8 paper = mA g.sup.−1 23:1:76 (Si: ~2800 mAh g.sup.−1) Self- Si:RGO = Si/RGO: ~1680 mAh g.sup.−1 @ 50 ~0.9 mAh cm.sup.−2 9 assembled 50:50 0.3~0.5 mg mA g.sup.−1 RGO cm.sup.−2 (Si: ~3360 mAh g.sup.−1) RGO Si:RGO = ~1 mg cm.sup.−2 ~1750 mAh g.sup.−1 @ 100 ~1.8 mAh 10 40:60 (Si: 0.4 mg cm.sup.−2) mA g.sup.−1 cm.sup.−2 (Si: ~4300 mAh g.sup.−1) PFFOMB Si:PFFOMB = 0.45 mg cm.sup.−2 1665 mAh/g @ 0.1 C 0.8 mAh cm.sup.−2 11 66.6:33.3 (~0.3 mg cm.sup.−2) (Si: 2500 mAh g.sup.1) PEEM Si:PEEM = 0.33 mg cm.sup.−2 2475 mAh g.sup.−1 0.8 mAh cm.sup.−2 12 66.6:33.3 (Si: 0.22 mg (Si: 3750 mAh g.sup.−1) cm.sup.−2) PANi Si:PANi = 0.4~0.53 mg 1875 mAh/g @ 0.3 A g.sup.−1 1 mAh cm .sup.2 13 75:25 cm.sup.−2 (Si: 2500 mAh g.sup.−1) (Si 0.3~0.4 mg cm.sup.−2) PFP-PEG Si:Co-polymer = ~0.7 mg cm.sup.−2 -1750 mAh g.sup.−1 @ 1/25 C ~1 mAh cm.sup.−2 14 co-polymer 90 : 10 (Si: 0.6 mg cm.sup.−2) (Si: 1575 mAh g.sup.−1) Liquid-PAN Si Graphene: ~1 mg cm.sup.−2 ~1250 mAh g.sup.−1 @ 500 ~1.2 mAh 15 (LPAN) LPAN = (Si: 0.62 mg mA g.sup.−1 cm.sup.−2 61:5:33 cm.sup.−2) PEFM Si:PEFM = 0.5 mg cm.sup.−2 2475 mAh g.sup.−1 @ 1/25 C 1.2 mAh cm.sup.−2 16 66:33 (Si: 0.3 mg cm.sup.−2) (Si: 3750 mAh g.sup.−1) PPQ Si:PPQ = ~0.8 mg cm.sup.−2 2290 mAh/g @ 0.028 C 1.8 mAh cm1.sup.2 17 70:30 (Si: 0.55 mg (Si: 3271 mAh g.sup.−1) cm.sup.−2) Biopolymer Si:Lignin = ~2.8 mg cm.sup.−2 ~800 mAh g.sup.−1 @ 180 ~2.2 mAh 18 lignin 50:50 (Si: 1.4 mg cm.sup.−2) mA/g cm.sup.−2 (Si: ~1600 mAh g.sup.−1) CNT and Si:CNT/PEDOT = 2 mg cm.sup.−2 1100 mAh g.sup.−1 @ 0.2 A 2.2 mAh cm.sup.−2 19 PEDOTPSS 57:43 (Si: 1 mg cm.sup.−2) g.sup.−1 (Si: 2180 mAh g.sup.1) PPyE Si:PPyE = 2 mg cm.sup.−2 1243 mAh g.sup.−1 @ 0.2 2.5 mAh cm.sup.−2 30 66.6:33.3 (Si: 1.34 mg mA cm.sup.−2 cm.sup.−2) (Si: 1866 mAh g.sup.−1) PANI Si: PANI = 0.8~1.2 mg ~2440 mAh g.sup.−1 @ 200 3 mAh cm.sup.−2 21 75:25 cm.sup.−2 mA g.sup.−1 (Si: 0.6~0.9 (Si: ~3250 mAh g.sup.−1) mg cm.sup.−2) PEDOT:PSS Si:PEDOT/PSS = 1.5 mg cm.sup.−2 2200 mAh g.sup.−1 @ 0.5 A 3.3 mAh cm.sup.−2 22 80:20 (Si: 1.2 mg cm.sup.−2) g.sup.−1 (Si: 2750 mAh g.sup.−1) PAA/PANI Si:PAA/PANI 1.6 mg cm.sup.−2 2250 mAh g.sup.−1 @ 0.1 C 3.8 mAh cm.sup.−2 23 IPN IPN = (Si: 1 mg cm.sup.−2) (Si: 3750 mAh g.sup.−1) 60:40 PPy Si:PPy = ~2 mg cm.sup.−2 ~2000 mAh g.sup.−1 @ 0.1 C ~4 mAh cm.sup.−2 24 66:33 (Si: 1.3 mg cm.sup.−2) (Si: ~3000 mAh g.sup.−1) Conductive binder-Si/carbon composite active material Total: 18.6 mg Gr—Si:MXene = cm.sup.−2 1250 mAh g.sup.−1 @ 0.05 C 23.3 mAh MXene ink 70:30 (Si: 13 mg cm.sup.−2) (Gr—Si: 1791 mAh g.sup.−1) cm.sup.−2 Reference PEM Si-alloy:CB: ~4 mg cm.sup.−2 ~700 mAh g.sup.−1 @ 1 C 3 mAh cm.sup.−2 25 PEM = 80:15:5 PPy Si:Graphite:PPy = ~3.9 mg cm.sup.−2 ~800 mAh g.sup.−1 @ 0.1 C ~3 mAh cm.sup.−2 25 20:70:10 PPyMAA Si:Graphite: ~4 mg cm.sup.−2 580 mAh g.sup.−1 @ 0.1 C ~2.4 mAh 27 PPyMAA = cm.sup.−2 10:80:10

[0101] The C/A of reported Si/conductive-binder systems is typically limited by the M.sub.Active/A (<2 mg/cm.sup.2). Even with a high M.sub.Active/A (˜4 mg/cm.sup.2), graphite-Si/conductive-binder electrodes display a much lower C/A than the results presented here due to the excessive graphite content in the electrodes. The ultrahigh C/A of the Si/MXene electrodes can be attributed to the advanced electrode architecture; 1) the viscous nature of the MXene aqueous ink enables the formation of thick composite electrodes (thus high M.sub.Acitve/A) using a simple/scalable manufacturing process; 2) The high aspect ratio and metallic conductivity of MXene nanosheets endow the composite electrodes with mechanical robustness, high strength and excellent conductivity, facilitating fast electron transport; 3) the interconnected MXene scaffold efficiently accommodates the volume change and stress induced by the Si lithiation/delithiation, and boosts the utilization of active materials.

[0102] It should be noted that producing high M.sub.Active/A electrodes is of technological significance; it not only delivers a higher C/A to the electrode, but also decreases the mass portion of inactive components, such as current collector (Cu foil for anode side) and separator. Consequently, the cell-level performance of the anode, which includes the mass of Cu foil (M.sub.Cu-foil/A=9 mg/cm.sup.2), electrode and half of the separator (M.sub.Separator/A=2 mg/cm.sup.2), can be improved significantly (FIG. 12g). Taking this into consideration, the true performance of the electrodes of the invention were calculated along with other reported Si/conductive-binder systems according to:

[00001]$\begin{array}{cc}C/M_{\mathrm{Total}}=\frac{C/A}{\frac{M_{\mathrm{Active}}}{A}+\frac{M_{C-\mathrm{binder}}}{A}+\frac{M_{\mathrm{Cu}-\mathrm{foil}}}{A}+\frac{0.5M_{\mathrm{separator}}}{A}},& \left(3\right)\end{array}$

[0103] The C/M.sub.Total was plotted versus the corresponding M.sub.Active/A, as shown in FIG. 12h. This comparison clearly suggests that the electrodes of the invention exhibit much higher specific capacities on the cell level, highlighting the advantages of MXene viscous inks over other conductive binders. For example, the nSi/MX-C electrode showcases a C/M.sub.Total=790 mAh/g at M.sub.Si/A=3.8 mg/cm.sup.2, while the Gr-Si electrode demonstrates 815 mAh/g at M.sub.GrSi/A=13 mg/cm.sup.2. Importantly, results presented herein are quite close to the theoretical limit (dashed lines in FIG. 12h) for all samples, indicating that almost full utilization of Si active materials has been reached at the highest M.sub.Active/A electrode of the invention. Moreover, the shape of the Gr-Si/MX-C electrode is instructive; the theoretical curve (blue dashed line) nearly saturates at high M.sub.Grsi/A >14 mg/cm.sup.2. In other words, even if increase the electrode thickness was further, the C/M.sub.Total of the Gr-Si/MX-C anode will only increase marginally. This means that the electrode architecture has allowed one to reach the absolute maximum C/M.sub.Total possible for the Gr-Si material used.

[0104] In summary, the efficient utilization of 2D nanosheets of MXenes, TMDs, or transition metal oxides, or combinations thereof, (and optionally graphene) as a new class of conductive binder for high volume-change Si electrodes is of fundamental importance to the electrochemical energy storage field. The interconnected network of these nanosheets not only provides sufficient electrical conductivity and free space for accommodating the volume change issue, but also resolves the mechanical instability of Si. Therefore, the combination of a viscous ink of 2D nanosheets (of either MXene, TMDs, transition metal oxides or combinations thereof) and high-capacity Si demonstrated here offers a powerful technique to construct advanced nanostructures with exceptional performance. Of equal importance is that the formation of these high-mass-loading Si/(MXene, TMDs, or transition metal oxides, or combinations thereof) electrodes can be achieved by means of a commercially-compatible, slurry-casting technique, which is highly scalable and low cost, allowing for large-area production of high-performance, Si-based electrodes for advanced batteries. Graphene can also be used as a 2D nanosheet material in the viscous ink. Also, considering that more than 30 MXenes are already reported, with more predicted to exist, there is certainly much room for further improving the electrochemical performance of such electrodes by tuning the electrical, mechanical and physicochemical properties of this exciting 2D MXene family.

[0105] In addition to unprecedented conductivity enhancement, these spontaneously formed segregated networks dramatically increase mechanical robustness, promoting stability and allowing the production of extremely thick electrodes. In addition, wrapping the active materials particles in a flexible, porous 2-dimensional membrane facilitates stable, repeatable, expansion/contraction of the lithium-storing material without impeding lithium diffusion. In addition, these membranes should keep silicon fragments localized even after pulverization, further promoting stability. The composite and electrode formed by the invention are free-standing, that is, can be readily handled without any cracking, delamination or breakage.

[0106] Compared to electrodes prepared from traditional mixtures of active material and polymer-binder and conductive-additive, the spontaneously formed segregated networks of the composite of the claimed invention make an electrode comprising said composite having very high mechanical toughness. This toughness allows very thick electrodes to be made because it prevents crack formation during charging/discharging (mud-cracking effect) and improves stability. These thick electrodes store more Li ions and yield higher energy density.

[0107] Compared to electrodes prepared from traditional mixtures of active material and polymer-binder and conductive-additive, these networks make the electrode have very high conductivity. This conductivity allows the electrode to reach its theoretical Li storage capacity (Li ions per unit mass). The very high conductivity facilitates this maximisation of capacity, even for very thick electrodes.

[0108] The segregated network of the composite of the claimed invention spontaneously forms a 2D membrane which acts as a scaffold to hold the active material particles in place.

[0109] All the above can be achieved using nanosheets of conducting materials at a concentration of 20-30 wt %. The dispersion of the nanosheets in the composite provides the architecture for an electrode. The nanosheets of conducting material spontaneously self-organise or self-arrange themselves around the particulate active materials to form the membranes which are locally 2-dimensional but extend throughout the electrode wrapping all particles. The 2D membranes wrap around the particles and fill space within the electrode architecture. The membranes can be considered to be a fractal object with fractal dimensions of between 2 and 3. Without any polymeric binders or carbon black in the composite, more active material can be added to the composite to reach the theoretical maximum capacity when used in thick electrodes.

[0110] In the specification the terms “comprise, comprises, comprised and comprising” or any variation thereof and the terms include, includes, included and including” or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation and vice versa.

[0111] The invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail.

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