Lithium-ion batteries have gained widespread use in consumer electronics due to their high energy density and low weight. However, for electric vehicle applications, further improvements in capacity and safety are highly challenging but necessary for lowering the cost and extending the driving distance. Materials with high lithium storage capacity, such as silicon and tin based alloys, have recently been extensively studied for their potential applications as Lithium battery anodes. But the large-volume change associated with lithiation and delithiation severely hinders the practical employments. [1][2][3][4][5][6][7] Despite the intensive efforts, [6][7][8][9][10][11][12] an effective low-cost solution to the volume-change problem remains elusive.Here, we developed a new conductive polymer through a combination of material synthesis,x-ray spectroscopy, density functional theory, and battery cell testing. Contrasting other polymer binders, the tailored electronic structure of the new polymer enables lithium doping under the battery environment. The polymer thus maintains both electric conductivity and

The dilemma of employing high-capacity battery materials and maintaining the electronic and mechanical integrity of electrodes demands novel designs of binder systems. Here, we developed a binder polymer with multi-functionality to maintain high electronic conductivity, mechanical adhesion, ductility, and electrolyte uptake. These critical properties are achieved by designing polymers with proper functional groups. Through synthesis, spectroscopy and simulation, electronic conductivity is optimized by tailoring the key electronic state, which is not disturbed by further modifications of side chains. This fundamental allows separated optimization of the mechanical and swelling properties without detrimental effect on electronic property. Remaining electrically conductive, the enhanced polarity of the polymer greatly improves the adhesion, ductility, and more importantly, the electrolyte uptake to the levels of those available only in non-conductive binders before. We also demonstrate directly the performance of the developed conductive binder by achieving full-capacity cycling of silicon particles without using any conductive additive.3

Using x-ray absorption and resonant inelastic x-ray scattering, charge dynamics at and near the Fe L edges is investigated in Fe pnictide materials, and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. Best agreement with experiment is obtained using Hubbard parameters U 2eV and J ≈ 0.8eV.

Mn evolution has long been considered critical for understanding the capacity fading of spinel electrodes in batteries. However, the detailed mechanism is still under debate; chemical evolution and distribution of the detrimental Mn is yet to be experimentally clarified. Here we perform a comparative soft X-ray absorption spectroscopic study on two batches of LiNi 0.5 Mn 1.5 O 4 with the same bulk spinel phase, but different electrochemical performance. By virtue of the sensitivity of soft X-ray to the transition-metal 3d states and oxygen 2p states, evolutions of Ni, Mn, and O in LiNi 0.5 Mn 1.5 O 4 are compared between the two batches of electrodes. In the LiNi 0.5 Mn 1.5 O 4 with fast capacity fading, Mn 2+ is evidently observed in the initial charge cycle. Strikingly, the Mn 2+ content is notably high at the fully charged state. This sharply contradicts the conventional wisdom that Mn 2+ evolves from a disproportional reaction favored in the discharged state. Additionally, the shallow probe depth of soft X-ray spectroscopy enables another finding that Mn 2+ manifests itself mostly on the side of the