A styrene butadiene rubber (SBR)-polyvinylidene difluoride (PVDF) based binder system has been developed for an electrochemical system that is not compatible with the conventional N-methyl pyrrolidinone (NMP) solvent used to cast most Li-ion electrode slurries. This polymer system's binding properties decouple the mechanical and ionic-transport properties. It demonstrates comparable mechanical properties to SBR-based electrodes and cell performance to traditional PVDF-based electrodes. This new binder design however enables the incorporation of stabilized lithium metal powder (SLMP) into a graphite anode to improve its first cycle coulombic efficiency. © The Royal Society of Chemistry 2013.

The lithium garnet solid electrolyte (LLZO) provides an opportunity to consider cathode active materials which are not compatible with the conventional cell architecture based on porous separators and liquid electrolytes. For example, the class of organic materials known as quinones offer high specific capacities (up to 496 mAh/g) but are soluble in liquid electrolytes, leading to rapid capacity degradation. This work demonstrates solid electrolyte/liquid catholyte hybrid battery cells with metallic Li alloy as the anode and lawsone, a biologically derived quinone, as the cathode. LLZO is used as a separator and effectively prevents dissolved cathode material from meeting the anode. Lawsone LLZO hybrid cells reached cathode utilization of up to 67% and had little self-discharge compared to liquid cells. Side reactions at voltages below 2.0 V limited their long-term cycling stability, however. Utilizing a lower cutoff voltage of 2.0 V or higher dramatically reduces capacity fade but prevents complete lithiation of the second lawsone carbonyl group, curtailing capacity to only ca. 120 mAh/g. LLZO cells using 1,4-naphthoquinone, which is structurally identical to lawsone except for the absence of the irreversible hydroxyl lithiation site, were more stable at low voltages. These results suggest that achieving full theoretical capacity in a lawsone LLZO cell will require elimination of the low-voltage side reactions to enable full utilization of both carbonyl groups and mitigation of issues stemming from irreversible lithiation of the hydroxyl group. Nevertheless, use of a solid electrolyte is shown to be a promising approach to enable use of soluble organic cathode active materials.

Polymer-derived silicon carbonitride (SiCN) materials have been synthesized via pyrolyzing from five poly(silylcarbondiimide)s with different contents of carbon (labeled as 1-5#). The morphological and structural measurements show that the SiCN materials are mixtures of nanocrystals of SiC, Si₃N₄, and graphite. The SiCN materials have been used as anodes for lithium-ion batteries. Among the five polymer-derived SiCN materials, 5#SiCN, derived from dichloromethylvinylsilane and di-n-octyldichlorosilane, has the best cycle stability and a high-rate performance at the low cutoff voltage of 0.01-1.0 V. In lithium-ion half-cells, the specific delithiation capacity of 5#SiCN anode still remains at 826.7 mA h g^-1 after 100 charge/discharge cycles; it can even deliver the capacity above 550 mA h g^-1 at high current densities of 1.6 and 2 A g^-1. In lithium-ion full cells, 5#SiCN anode works well with LiNi_0.6Co_0.2Mn_0.2O₂ commercial cathode. The outstanding electrochemical performance of 5#SiCN anode is attributed to two factors: (1) the formation of a stable and compact solid electrolyte interface layer on the anode surface anode, which protects the electrode from cracking during the charge/discharge cycle; and (2) a large amount of carbon component and the less Si₃N₄ phase in the 5#SiCN structure, which provides an electrochemical reactive and conductive environment in the SiCN structure, benefit the lithiation/delithiation process. In addition, we explore the reason for the capacity fading of these SiCN anodes.

To address the significant challenges associated with large volume change of micrometer-sized Si particles as high-capacity anode materials for lithium-ion batteries, we demonstrated a simple but effective strategy: using Si nanoparticles as a structural and conductive additive, with micrometer-sized Si as the main lithium-ion storage material. The Si nanoparticles connected into the network structure in situ during the charge process, to provide electronic connectivity and structure stability for the electrode. The resulting electrode showed a high specific capacity of 2500 mAh/g after 30 cycles with high initial Coulombic efficiency (73%) and good rate performance during electrochemical lithiation and delithiation: between 0.01 and 1 V vs Li/Li(+).

Control over porous electrode microstructure is critical for the continued improvement of electrochemical performance of lithium ion batteries. This paper describes a convenient and economical method for controlling electrode porosity, thereby enhancing material loading and stabilizing the cycling performance. Sacrificial NaCl is added to a Si-based electrode, which demonstrates an areal capacity of ∼4 mAh/cm(2) at a C/10 rate (0.51 mA/cm(2)) and an areal capacity of 3 mAh/cm(2) at a C/3 rate (1.7 mA/cm(2)), one of the highest material loadings reported for a Si-based anode at such a high cycling rate. X-ray microtomography confirmed the improved porous architecture of the SiO electrode with NaCl. The method developed here is expected to be compatible with the state-of-the-art lithium ion battery industrial fabrication processes and therefore holds great promise as a practical technique for boosting the electrochemical performance of lithium ion batteries without changing material systems.

Vehicle electrification is a critical application of lithium-ion batteries (LIBs), and it is essential to develop LIBs that can operate at sub-ambient temperatures with satisfying performance. Conventional LIBs have performance deficits at low temperatures which hinder their use in extreme environments. One approach to address this problem is to rationally engineer the electrode/electrolyte interface with electrolyte additives to improve the electrochemical kinetics at sub-ambient temperatures. In this work, silicic acid (SiAc) is incorporated into standard LIB electrolyte as an additive to enhance the capacity and energy density of LIBs at temperatures down to −20 °C. Full-cell impedance analysis and X-ray photoelectron spectroscopy of cycled electrodes point towards an additive-induced change in surface chemistry which alters the charge transfer process. It is proposed that the SiAc additive participated in the formation of solid electrolyte interphase (SEI) and lowered the activation energy of the interface impedance, assisting lithium ion transport across the interface at lower temperatures.

The mechanical failure at the electrode interfaces (laminate/current collector and binder/particle interfaces) leads to particle isolation and delamination, which has been regarded as one of the main reasons for the capacity decay and cell failure of lithium-ion batteries (LIBs). Polymer binder provides the key function for a good interface property and for maintaining the electrode integrity of LIBs. Triethylene glycol monomethyl ether (TEG) moieties were incorporated into polymethacrylic acid (PMAA) to different extents at the molecular level. Microscratch tests of the graphite electrodes based on these binders indicate that the electrode is more flexible with 5 or 10% TEG in the polymer binders. Crack generation is inhibited by the flexible TEG-containing binder, compared to that of the unmodified PMAA-based electrode, leading to the better cycling performance of the flexible electrode. With a 10% TEG moiety in the binder, the graphite half-cell reaches a reversible capacity of >270 mAh/g at the 1C rate, compared to a value of ∼190 mAh/g for the unmodified PMAA binder.

Most previous studies about halide solid-state electrolytes have used pellets prepared by uniaxial pressing, which is a good approach for materials development but is not suitable for commercialization. Thinner electrolyte layers that can be scaled up to large cell areas are required, and tape casting is a promising approach. It is challenging, however, as halide materials are reactive with most of the conventional solvents used in the process. In this study, solvents with low polarity, such as toluene, are found to be compatible with the Li3YBr6 halide material. A wide variety of candidate binders that are soluble in toluene are studied. MSB1-13 binder is preferred, based on the ionic conductivity and mechanical properties of the tape. Electrolyte tapes (<70 μm) are successfully cast on Al substrates, using 2 wt% binder. The resulting room temperature ionic conductivity is 2 × 10−4 S cm−1. Two composite cathodes including active material (LiFePO4 or LiNi0.82Mn0.07Co0.11O2) and 1 to 1.5 wt% MSB1-13 are tape cast as proof-of-concept for a scalable cell fabrication approach. A LiFePO4 cell shows good retention at 25 °C. The performance of NMC cells with tape electrolyte or pellet electrolyte is similar. This study demonstrates the feasibility of tape casting halide-based electrolytes and cathodes.

The recently developed Li-excess cation-disordered rock salts (DRXs) exhibit an excellent chemical diversity for the development of alternative Co/Ni-free high-energy cathodes. Herein, the synthesis of a highly fluorinated DRX cathode, Li1.2Mn0.6Ti0.2O1.8F0.2, based on cost-effective and earth-abundant transition metals, via a solid-state reaction, is reported. The fluorinated DRX cathode using ammonium fluoride precursor exhibits more uniform particle size and delivers a specific discharge capacity of 233 mAh g−1 and specific energy of 754 Wh kg−1, with 206 mAh g−1 retained after 200 cycles. The combined synchrotron X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy analysis reveals that the remarkable cycling performance is attributed to the high fluorination and thus enhanced Mn content, enabling the utilization of more Mn redox than the oxide analog. This study demonstrates a great promise to develop next-generation cost-effective DRX cathodes with enhanced capacity retention for high-energy Li-ion batteries.