Scalable synthesis of silicon-nanolayer-embedded graphite for high-energy lithium-ion batteries

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1 ARTICLE NUMBER: DOI: /NENERGY Scalable synthesis of silicon-nanolayer-embedded graphite for high-energy lithium-ion batteries Minseong Ko, Sujong Chae, Jiyoung Ma, Namhyung Kim, Hyun-Wook Lee, Yi Cui and Jaephil Cho NATURE ENERGY 1

2 DOI: /NENERGY Supplementary Figures Supplementary Figure 1 Morphology comparison with PG and SGC hybrids. a-d, FESEM images of PG and SGC hybrids at low (a, c) and high (b, d) magnification, respectively. The high magnification image of SGC hybrid (d) confirmed that the surface roughness change toward more smooth and even surface. Supplementary Figure 2 Morphology comparison with PG and SGC hybrids. a-c, Surface texture changes of PG (a), SG (b) and SGC hybrid (c) at low and high magnification (insets) SEM images, respectively. 2 NATURE ENERGY

3 DOI: /NENERGY SUPPLEMENTARY INFORMATION Supplementary Figure 3 Extended cycling performance of SGC with Coulombic efficiencies Supplementary Figure 4 Electrochemical property of new Si-Graphite hybrids a, Reversible discharge capacity versus cycle plot of new Si-Graphite Hybrids and 9 wt%-sgc at 0.5 C for 100 cycles. b, Magnified form of the stabilized efficiency. Supplementary Figure 5 STEM image and EDS analysis for new Si-Graphite hybrids. a, Cross sectional STEM image of new Si-Graphite Hybrids. b, EDS mapping for cross sectional view. NATURE ENERGY 3

4 DOI: /NENERGY Supplementary Figure 6 TEM image of new Si-Graphite hybrids Supplementary Figure 7 Electrochemical characterization of graphite and carbon(c)- coated graphite. a, Galvanostatic charge/discharge voltage profiles of graphite and C-coated graphite. b, Reversible discharge capacity versus cycle plot of graphite and C-coated graphite with Coulombic efficiencies 4 NATURE ENERGY

5 DOI: /NENERGY SUPPLEMENTARY INFORMATION Supplementary Figure 8 Schematic view of the cylindrical cell. a, Specification and schematic of typical cell. b, Schematic top view of internal structure of cell. In an cell (Fig. S8), there is an unused space between the can and jelly roll where the volume change can be accommodated. This unused space can be controlled by the battery manufacturer for specific purposes such as an easier process or for specific battery applications. In particular, the cylinder has the ability to withstand high internal pressure without deforming 1. Therefore, the battery designs allow the electrode to increase internally. In addition, the volume change of an anode depends on the electrode density and full-cell design. It should be noted that the volume expansion of SGC (38%) after 50 cycles was measured in a half-cell with 1.6 g cc -1 of high electrode density, which was obtained from severe calendaring in the electrode preparation process. Meanwhile, in a full-cell, N/P ratio is considered for optimizing the utilization of active materials and the battery performances. Typically, the value of N/P ratio is about in commercial cells 2. The N/P ratio (>1) leads marginal areal capacity of anode in a full-cell, resulting in the decrease of utilization ratio for the anode. Hence, compared to the half-cell, the volume change can be mitigated in the fullcell, because the anode materials do not exhibit their whole capacity in the full-cell. Supplementary Figure 9 EDS mapping of the cross sectional SGC hybrids for in situ TEM analysis. a-c, A STEM image (a) and its element mapping (b,c) by energy dispersive spectroscopy (EDS). NATURE ENERGY 5

6 DOI: /NENERGY Supplementary Tables Supplementary Table 1 Particle size distribution (PSD) and BET analysis of graphite and carbon coated graphite Sample PSD ( m) Dmin D10 D50 D90 Dmax BET (m 2 g -1 ) Graphite C-coated graphite Supplementary Table 2 Energy density information for LCO/Graphite and LCO/SGC full-cells Electrode information Electrode area (cm 2 ) 1.54 LCO Graphite SGC Loading level (mg cm -2 ) Thickness ( m) Full-cell information LCO/Graphite LCO/SGC Cell capacity (mah) Average voltage (V) Energy density estimation LCO/Graphite LCO/SGC Volumetric energy density (Wh l -1 ) Specific energy density (Wh kg -1 ) NATURE ENERGY

7 DOI: /NENERGY SUPPLEMENTARY INFORMATION Supplementary Notes Supplementary Note 1 SiH4 use per unit kilogram of the raw materials. Process conditions in laboratory scale are used for estimation, where the total amount of SiH4 gas is 56 L at 1 atmosphere for 1 kg of a batch. The uniform Si coating layer was deposited in the furnace which combined with gas flow system using simple thermal-decomposition at 650 C and atmospheric pressure with a flow rate of 1.5L/min for 37min. With the density of monosilane (ρ SiH4 ), g/dm 3, Total weight of used monosilane = 56L ρ SiH4 = 56(0.1mm) g (0.1 mm) 3 = g In terms of the synthesis process, both Si and carbon coating processes can be conducted in one furnace sequentially. Supplementary Note 2 Estimation for gravimetric and volumetric energy densities Gravimetric energy density (Wh kg -1 ) = (Cell capacity) (Average voltage) (Electrode area) (Loading level of cathode and anode) (Cell capacity) (Average voltage) Volumetric energy density (Wh l -1 ) = (Electrode area) (Total thickness of cathode, anode and separator) NATURE ENERGY 7

8 DOI: /NENERGY Supplementary References 1. Fan, J., GP L210: A New Milestone in the Commercial Cell, Aerosp. Electron. Syst. Mag. of the IEEE 17, 7-10 (2002). 2. Obrovac, M. N., Chevrier, V. L., Alloy Negative Electrodes for Li-Ion Batteries. Chem. Rev. 114, (2014). 8 NATURE ENERGY