A Silicon Monoxide Lithium-Ion Battery Anode with Ultrahigh Areal Capacity

Highlights The large-sheet holey graphene framework/SiO (LHGF/SiO) composite displays notably high recoverable strain, suggesting considerably improved mechanical flexibility and robustness The LHGF/SiO anode with a mass loading of 44 mg cm−2 delivers a high areal capacity of 35.4 mAh cm−2 at current density of 8.8 mA cm−2 and retains a capacity of 10.6 mAh cm−2 at 17.6 mA cm−2 The LHGF/SiO anode with an ultra-high mass loading of 94 mg cm−2 delivers an extraordinary areal capacity up to 140.8 mAh cm−2, about 1–2 order of magnitude higher than those in typical commercial devices Supplementary Information The online version contains supplementary material available at 10.1007/s40820-022-00790-z.


S1.1 Estimation of the Porosity of Compressed Electrodes
The density of the silicon oxide is 2.13 g cm -3 , and we assumed the density of the graphene was 2.0 g cm -3 (since the density of a graphene is approximately 1.5-2.0 g cm -3 ). The theoretical density of the composite is calculated as [S1]: The estimation of the porosity of the composite electrodes (ϕ) is: cal. exp. cal.

S1.2 Impedance Theory for Pores According to the Transmission Line Model (TLM)
For non-faradaic and faradaic processes at porous electrodes, the overall impedance is expressed as Eqs. S3 and S4, respectively. ion,L nonfaradaic ion,L dl,A dl,A The limiting values of the real (Z'ω) as ω→0 in non-faradaic, and faradaic processes are shown by Eqs. S3 and S4, respectively.
where Rion is the mobility of Li ions inside the porous electrodes. From these mathematical equations, Rion can be expressed as shown in Eq. S7 and S8: S8] where Rion,L is ionic resistance per unit pore length. In addition, Rct is expressed as Eq. S9: where Rct,A is the charge-transfer resistance per unit electroactive surface area. Using this combination approach, we have succeeded in separating the individual electrochemical parameters and corresponding kinetic interpretation from temperature dependence [S1, S2].

S1.3 Relaxation Time Constant According to the Complex Impedance Theory
The impedance Z(ω) can be written the complex form: An approach by using the impedance data to consider the cell as a whole: Eq. S10 and S11 lead to Eq. S12: It is to define: leading to: where C ' (ω) is the real part of the capacitance C(ω), C '' (ω) is the imaginary part of the capacitance C(ω). The low-frequency value of C ' (ω) corresponds to the cell that is measured during constant-current discharge. It corresponds to an energy dissipation by an irreversible process that can lead to a hysteresis. The C '' (ω) is utilized to characterize the distribution of double electrode layer capacitance responsiveness. This time constant has earlier been described as a dielectric relaxation time characteristic of the whole system [S3-S5].

S1.4 Capacitive Contribution in LHGF/SiO
The capacitive contribution from the electrodes were obtained by separating the diffusion controlled capacity from the capacitance-controlled capacity according to the following equation: where i is the total current response at a fixed potential (V) during the CV test, k1v is the contribution from the surface controlled process, and k2v 1/2 is the contribution from the diffusion controlled process. Hence, the percentage of surface contribution is calculated by: The LHGF/SiO-75 electrode shows a surface contribution of 3% at 0.1 mV s -1 . Upon gradually increasing the scan rate to 0.2 and 0.5 mV s −1 , the surface contribution raises to 5% and 9%, respectively. The areal capacity of the diffusion-controlled process (height of the red columns in Fig. 4d) decreases with the increases of the scan rate due to diffusion limitations. The CV characteristics suggest that the diffusion contribution determined from the voltammetric-sweep-rate-dependence method is primarily faradaic process in our materials [S12].   The relationship between peak current and scanning rate at low or high scanning rates. c Diffusion (red) and surface (blue) controlled contribution to Li + storage of LHGF/SiO-75% at 0.1 mV s -1 . d The proportion of diffusion controlled and surface controlled behavior under various scanning rates Fig. S10 a and b, Galvanostatic charge/discharge curves of two type electrode. a at 50 mA g -1 rate b at 500 mA g -1 rate. The mass loading is 11 mg cm -2 . c Rateperformances of LHGF/SiO-50% and LGF/SiO-50% electrode under same mass loading (11 mg cm -2 )  BET (m 2 g -1 )
[2] Pore volume (Vpore.), porosity (ϕ) and the compacted density (ρexp.) of composite electrodes after compression were calculated based on 20 samples. Notes: [1] The gravimetric capacities are normalized by the total mass of electrodes including binders and carbon black; capacities in brackets are normalized by the active material only.
[2] Assuming passive components (metal current collector and the separator) are about 10 mg cm -2 .
[3] Calculated based on the industry standard (active materials account for 33% of total weight of the package when assuming the mass loading of the active material is about 10 mg cm -2 ) [S5, S11].