Silicon suboxide (SiOx) is one of the promising anode materials for the next-generation lithium-ion batteries. However, SiOx has a severe capacity fading problem during cycling. It is thus desired to investigate the detailed fading mechanisms of SiOx anode materials. In this study, limited capacity cycling was employed to examine the electrochemical behaviors of the SiOx anode, and the lithiation/delithiation cycling was limited within a range of 10% theoretical capacity. This strategy minimizes the volume variation of SiOx materials upon charging/discharging, which helps to reveal their decay factors other than volume fluctuation. It is demonstrated that the instability of the SiOx surface during cycling was likely a parallel factor of active material fading, which seems to cause unfavored electrode interface rearrangements with lowered electric conductivity.

The doping mechanism of poly (1-pyrenemethyl methacrylate) (PPy) is investigated through electrochemical analytical and spectroscopic method. The performance of PPy as a Si materials binder is studied and compared with that of a commercial available lithium polyacrylate (PAALi) binder. The pyrene moiety consumes lithium ions according to the cyclic voltammogram (CV) measurement, as a doping to the PPy binder. Based on the lithium consumption, PPy based Si/graphite electrode doping is quantified at 1.1 electron/pyrene moiety. The PPy binder based electrodes surface are uniform and crack free during lithiation/delithiation, which is revealed through Scanning electron microscope (SEM) imaging.

We report the effects of component ratios and mixing time on electrode slurry viscosity. Three component quantities were varied: active material (graphite), conductive material (carbon black), and polymer binder (carboxymethyl cellulose, CMC). The slurries demonstrated shear-thinning behavior, and suspension properties stabilized after a relatively short mixing duration. However, micrographs of the slurries suggested their internal structures did not stabilize after the same mixing time. Increasing the content of polymer binder CMC caused the greatest viscosity increase compared to that of carbon black and graphite.

Polysulfide shuttling has been the primary cause of failure in lithium-sulfur (Li-S) battery cycling. Here, we demonstrate an nucleophilic substitution reaction between polysulfides and binder functional groups can unexpectedly immobilizes the polysulfides. The substitution reaction is verified by UV–visible spectra and X-ray photoelectron spectra. The immobilization of polysulfide is in situ monitored by synchrotron based sulfur K-edge X-ray absorption spectra. The resulting electrodes exhibit initial capacity up to 20.4 mAh/cm2, corresponding to 1199.1 mAh/g based on a micron-sulfur mass loading of 17.0 mg/cm2. The micron size sulfur transformed into nano layer coating on the cathode binder during cycling. Directly usage of nano-size sulfur promotes higher capacity of 33.7 mAh/cm2, which is the highest areal capacity reported in Li-S battery. This enhance performance is due to the reduced shuttle effect by covalently binding of the polysulfide with the polymer binder.

Flexible butyl interconnection segments are synthetically incorporated into an electronically conductive poly(pyrene methacrylate) homopolymer and its copolymer. The insertion of butyl segment makes the pyrene polymer more flexible, and can better accommodate deformation. This new class of flexible and conductive polymers can be used as a polymer binder and adhesive to facilitate the electrochemical performance of a silicon/graphene composite anode material for lithium ion battery application. They act like a "spring" to maintain the electrode mechanical and electrical integrity. High mass loading and high areal capacity, which are critical design requirements of high energy batteries, have been achieved in the electrodes composed of the novel binders and silicon/graphene composite material. A remarkable area capacity of over 5 mAh/cm² and volumetric capacity of over 1700 Ah/L have been reached at a high current rate of 333 mA/g.

A highly graphitized carbon on a silicon monoxide (SiO) surface coating at low temperature, based on polymer precursor π⁻π stacking, was developed. A novel conductive and electrochemically stable carbon coating was rationally designed to modify the SiO anode materials by controlling the sintering of a conductive polymer, a pyrene-based homopolymer poly (1-pyrenemethyl methacrylate; PPy), which achieved high graphitization of the carbon layers at a low temperature and avoided silicon carbide formation and possible SiO material transformation. When evaluated as the anode of a lithium-ion battery (LIB), the carbon-coated SiO composite delivered a high discharge capacity of 2058.6 mAh/g at 0.05 C of the first formation cycle with an initial Coulombic efficiency (ICE) of 62.2%. After 50 cycles at 0.1 C, this electrode capacity was 1090.2 mAh/g (~82% capacity retention, relative to the capacity of the second cycle at 0.1 °C rate), and a specific capacity of 514.7 mAh/g was attained at 0.3 C after 500 cycles. Furthermore, the coin-type full cell composed of the carbon coated SiO composite anode and the Li[Ni_0.5Co_0.2Mn_0.3O₂] cathode attained excellent cycling performance. The results show the potential applications for using a π⁻π stacking polymer precursor to generate a highly graphitize coating for next-generation high-energy-density LIBs.