SnO₂-Embedded Nanoporous Carbon Electrode with a Reaction-Buffer Space for Stable All-Solid-State Li Ion Batteries

Abstract

The conventional approach for fabricating all-solid-state batteries has required a highly dense layer of electrode and electrolyte. Their close contact interface is not suitable for alloy- or conversion-based active materials because their large volume change in lithiation/delithiation reactions causes a collapse of the contact interface or reaction limitations under mechanical constriction. In this study, we propose that a SnO2-embedded porous carbon electrode shows high cyclability and high capacity even at high constraint pressure owing to the nanopores, which work as a buffer space for the large volume change accompanied with SnO2–Sn conversion reaction and Sn–Li alloying–dealloying reaction. A detailed investigation between structural parameters of the electrode material and charge–discharge properties revealed Li ion conduction in carbon nanopores from a solid electrolyte located outside as well as the optimal conditions to yield high performance. SnO2-loading (75 wt %) in carbon nanopores, which provides the buffer space corresponding to the inevitable volume expansion by full lithiation, brought out an excellent performance at room temperature superior to that in an organic liquid electrolyte system: a high capacity of 1023 mAh/g-SnO2 at 50 mA/g, high capacity retention of 97% at 300th cycle at 300 mA/g, and high rate capability with over 75% capacity retention at 1000 against 50 mA/g, whose values are also superior to the system using the organic liquid electrolyte.

Direct Evidence of Reversible SnO2–Li Reactions in Carbon Nanospaces

“…The volume change is estimated to be approximately 3.7 times the volume of the cylindrical structure of SnO 2 . Since the estimated expansion value is only slightly smaller than the theoretical value of 4.05 times (detail calculation procedure in the Supporting Information), the reaction of SnO 2 with Li + would not be strictly limited by space confinement. Figure c–f shows the snapshots taken during the delithiation process.…”

Reduction of external pressure on all‐solid‐state battery using SnO2‐embedded porous carbon by CNT assistance

“…The large irreversible capacity at an initial cycle seems to stem from oxygen functional groups on porous carbons. [9] SnO 2 /PC-CNT//SE showed higher capacity compared with that of the SnO 2 /PC//SE cell at all the external pressures. The SnO 2 /PC-CNT//SE even under the external pressure of 3.1 MPa is comparable performance to the SnO 2 /PC//SE at 9.1 MPa.…”

“…In order to realize high capacity and stable charge-discharge reaction on ASSBs, it is important to design stable electrode structure even under the volume changing without the excessive cell construction. Recently, we have reported that SnO 2 nanoparticles embedded nanoporous carbon (SnO 2 /PC) shows high capacity and stable cycle stability in the ASSB system using a sulfide based solid electrolyte(SE), [8,9] The carbon pores played an important role as a buffer space for volume expansion of SnO 2 , and the performance of SnO 2 /PC was improved compared with a mixture of SnO 2 and conductive carbon. The SnO 2 /PC electrode is expected stably to work without high external pressure because the system does not require the direct contact between SnO 2 and SE.…”

“…The loading rate corresponds to 25 vol% against the total pore volume, whose value shows maximum electrochemical performance on the ASSB system. [9] The SnO 2 /PC-CNT was formed a self-supporting sheet by mixing with only 2.9 wt% of SWCNT (Figure S2 in the Supporting Information). The detail morphology of a SnO 2 /PC, a SnO 2 /PC and SWCNT mixture (SnO 2 /PC-CNT), and those mixtures with SE (SnO 2 /PC//SE, SnO 2 /PC-CNT//SE) was directly observed by scanning electron microscopy (SEM: JEOL JSM-7500FAM)(Figure S3).…”

Patterning Design of Electrode to Improve the Interfacial Stability and Rate Capability for Fast Rechargeable Solid-State Lithium-Ion Batteries

“…From a material point of view, the exploitation of the solid-state electrolyte comprising nonflammable materials including ceramics has a potential to improve the safety aspects of conventional LIB configurations − that release and store electrical energy by faradaic reactions through shuttling lithium-ions between negative and positive electrodes through the electrolyte. Also, the solid-phase electrolyte can substitute for plastic separators, helping to reduce overall weights and volumes in LIBs. , However, there is some challenge to overcome relatively poor ion conductivity of the solid-phase electrolyte at room temperature when compared with a conventional organic electrolyte solution. , Furthermore, given that electrochemical reactions take place at the electrode interface, a poor contact at the junction between the solid-phase electrolyte and electrodes accelerates reductions in LIB’s deliverable capacities at high C-rates and over continued charge/discharge cycles, , particularly in the case of utilizing high surface area nanomaterial electrodes that provide outstanding faradaic kinetics and an extended cycle life. − …”