Kyle C. Klavetter

SnO2 and TiO2-supported-SnO2 lithium battery anodes with improved electrochemical performance

Li-ion battery anodes made of SnO2 nanoparticles and a TiO2-supported SnO2 nanocomposite formed of equimolar amounts of the Sn and Ti oxides were investigated, respectively. By limiting the voltage window of the charge/discharge cycles to the range 50 mV–1.0 V, both the SnO2-based anode and the SnO2/TiO2-based anode show improved cycling stability. Compared to the SnO2 nanoparticle based anodes, the TiO2-support-SnO2 nanocomposite anodes exhibit better cyclability and higher Coulombic efficiency. During the first lithiation process, Li+ conducting LixTiO2 is formed in the SnO2/TiO2 composite, which structurally/mechanically supports the electrode. The anode made of amorphous TiO2-cassiterite SnO2 retained a reversible capacity of ∼500 mAh g−1 (based on the weight of SnO2) or ∼320 mAh g−1 (based on the weight of SnO2/TiO2) at 0.2 C after 100 cycles and at a rate as fast as 5 C retained a stable reversible capacity of ∼340 mAh g−1 (based on the weight of SnO2) or ∼220 mAh g−1 (based on the weight of SnO2/TiO2).

Li- and Na-reduction products of meso-Co3O4 form high-rate, stably cycling battery anode materials

High surface area (367 m2 g−1) meso-porous Co3O4 was investigated as the precursor of the anode material for lithium and also sodium ion batteries. Co3O4 is considered a potential anode material due to its theoretical capacity of 890 mA h g−1, over twice that of graphite. This comparatively higher capacity can be safely charged at rapid rates owing to a relatively high Li-insertion potentials, but, consequently, the discharged energy is yielded at an average potential near 2 V vs. Li/Li+, with full Li-extraction achieved over a continuum of potentials up to 3 V. The products of the lithium reduction of Co3O4 cycle stably from 0.01–3.0 V vs. Li/Li+ with 600–900 mA h g−1 capacity retention at C rates from 1–5; the products of its sodium reduction cycle stably from 0.01–3.0 V vs. Na/Na+ at C-rates up to 1 C with a lower 150–400 mA h g−1 capacity retention owing to greater ionic impedance. TEM, SAED and XRD were used to examine the cycled material and the stable performance is attributed to finding that the mesoporous structure is retained. Evaluation of five electrolyte formulations testing EC, FEC and Cl-EC showed that the stable meso-porous structure was best cycled with 5% FEC in EC:DEC at high charge/discharge rates, retaining 77% of its initial capacity at 5 C in a rate test. Comparison of the AC impedance spectra and of the XPS of the SEIs formed in the presence and in the absence of 5 vol% FEC shows that the SEI formed in the presence of FEC contains lithium fluoride and its carbonate layer is thinner than that formed in its absence, resulting in lesser impedance to Li migration through the SEI and facile ion de-solvation, improving the cycling performance. In cycling stability tests with EC:DEC, irregular cycling behaviour attributable to abrupt rises in cell resistance was regularly observed after testing over a few hundred cycles. Long-term cycling irregularities are inhibited by halogenated solvents and completely eliminated by adding fluoroethylene carbonate (FEC).

High tap density microparticles of selenium-doped germanium as a high efficiency, stable cycling lithium-ion battery anode material

Slurry cast electrodes with μm-sized Ge0.9Se0.1 particles cycle stably at ∼800 mA h g−1 with ∼99.9% efficiency for 900 1C-rate cycles while electrodes with μm-size pure Ge particles lose 1/3rd of their capacity after five C/5 cycles. The difference is attributed to an inactive glassy Li–Se–Ge phase forming in the Ge active material of the Ge0.9Se0.1 particle.

Tin microparticles for a lithium ion battery anode with enhanced cycling stability and efficiency derived from Se-doping

In a 100 cycle test at 0.5 C-rate a negative electrode formed of micro-sized Sn0.9Se0.1 particles retains a specific capacity of 500 mA h g−1 with a coulombic efficiency of 99.6%. In contrast, a control electrode made with pure Sn retains only a 200 mA h g−1 capacity with a 98.7% efficiency. The improvement in electrochemical performance of the Sn/Se alloy is attributed to the reduced inactive Se-phase preventing agglomeration of Sn to a size susceptible to particle fracture. The Sn/Se alloy particles are manufacturable, being made by melting the 9:1 atomic ratio mixture of Sn and Se, quenching and jet-milling.

Sub-stoichiometric germanium sulfide thin-films as a high-rate lithium storage material

Nanocolumnar, sub-stoichiometric germanium sulfide thin-films with compositions of Ge0.9S0.1 and Ge0.95S0.05, deposited by glancing angle deposition, were investigated as lithium storage materials. The materials are amorphous and homogeneous as deposited, but lithiation induces phase separation leading to the formation of poorly-crystallized lithium sulfide inclusions during the first cycle. The presence of these inclusions raises the lithium diffusion coefficient above that of pure germanium and provides superior capacity retention at high rates. While the lithium sulfide is non-cycling, the low weight percentage of sulfur necessary for enhanced lithiation/de-lithiation does not significantly reduce the specific lithium storage capacity of the films relative to that of germanium. In addition to high capacity and superior lithium transport, the sub-stoichiometric germanium sulfide thin-films show excellent cycling stability at high rates, retaining 88% of their initial capacity after 500 cycles at a rate of 20 C.

Fast lithium transport in PbTe for lithium-ion battery anodes

The reversible charging of a lead chalcogenide, PbTe, was studied for use as the anode material in a Li-ion cell and compared to PbO. A similar series of Li–Pb alloys were formed but with Li2Te present instead of Li2O. In the presence of Li2Te, rapid Li–Pb alloying and dealloying were observed in the potential range of 0.01–0.7 V. In the potential range of 0.8–2.5 V, Li2Te formed and decomposed reversibly. Electrodes were cycled stably for 100 cycles at a C/5 rate in both potential domains. The electrodes were also cycled stably at rates up to 10C. The presence of Li2Te reduced the overpotential required at higher charge and discharge rates by acting as a superionic conductor to improve lithium ion diffusion. These results recommend this material for potential use in low-power applications such as cell phones.

Reduced-Graphene Oxide/Poly(acrylic acid) Aerogels as a Three-Dimensional Replacement for Metal-Foil Current Collectors in Lithium-Ion Batteries

We report the synthesis and properties of a low-density (∼5 mg/cm3) and highly porous (99.6% void space) three-dimensional reduced graphene oxide (rGO)/poly(acrylic acid) (PAA) nanocomposite aerogel as the scaffold for cathode materials in lithium-ion batteries (LIBs). The rGO-PAA is both simple and starts from readily available graphite and PAA, thereby providing a scalable fabrication procedure. The scaffold can support as much as a 75 mg/cm2 loading of LiFePO4 (LFP) in a ∼430 μm thick layer, and the porosity of the aerogel is tunable by compression; the flexible aerogel can be compressed 30-fold (i.e., to as little as 3.3% of its initial volume) while retaining its mechanical integrity. Replacement of the Al foil by the rGO-PAA current collector of the slurry-cast LFP (1.45 ± 0.2 g/cm3 tap density) provides for exemplary mass loadings of 9 mgLFP/cm2 at 70 μm thickness and 1.4 g/cm3 density or 16 mgLFP/cm2 at 100 μm thickness and ∼1.6 g/cm3 density. When compared to Al foil, the distribution of LFP throughout the three-dimensional rGO-PAA framework doubles the effective LFP solution-contacted area at 9 mg/cm2 loading and increases it 2.5-fold at 16 mg/cm2 loading. Overall, the rGO-PAA current collector increases the volumetric capacity by increasing the effective electrode area without compromising the electrode density, which was compromised in past research where the effective electrode area has been increased by reducing the particle size.

A free-standing, flexible lithium-ion anode formed from an air-dried slurry cast of high tap density SnO2, CMC polymer binder and Super-P Li

A free-standing electrode film composed of high tap density SnO2 particles and carboxymethyl cellulose binder with Super-P Li (SP-Li) conductive carbon was formed from an aqueous slurry cast by doctor-blading. Upon air-drying, the free-standing film spontaneously evolved via delamination from the substrate as the slurry solvent evaporated. The electrodes cut from the free-standing film were ∼5 μm thick with a SnO2 loading of ∼0.5 mg cm−2. The films were found to be easily handled, flexed and folded. For evaluation of the durability of the free-standing films, the tensile strength and elongation at break were measured: 13 MPa and 1.7%. The robustness of the electrically conductive network was measured with a four-point probe: the initial electrical resistivity of the film (0.6 Ω cm) was observed to increase by 6% after folding, applying pressure to the crease and unfolding. When tested in a coin cell, the electrode cycled stably with near 100% coulombic efficiency at up to 2 C and without capacity fade for 100 cycles at 1 C. To adjust the areal capacity of the cell, multiple free-standing films could be stacked. An electrode formed from several stacked films with an active material mass loading of greater than 4 mg cm−2 was found to cycle stably at 2.6 mA h cm−2 tested at 0.33 mA cm−2 current density. For evaluating cycling performance of the electrode while flexed, an electrode was placed in a once-folded pouch cell for testing at 1 C and cycled stably for 20 cycles before slight capacity fade was observed. For free-standing electrodes, 1D or 2D carbons such as carbon nanotubes (CNT) or graphene are commonly used to provide both mechanical strength and electrical conductivity. Here, CNTs were substituted for the SP-Li and similar free-standing films were made and compared. With CNT, the electrode strength at break as well as the electronic conductivity increased, but, despite this, the cycling performance of the electrodes made using the low-cost SP-Li carbon exceeds that of the electrodes made with orders-of-magnitude more expensive 1D carbon.