Shidi Xun

Polymers with Tailored Electronic Structure for High Capacity Lithium Battery Electrodes

A conductive polymer is developed for solving the long-standing volume change issue in lithium battery electrodes. A combination of synthesis, spectroscopy and simulation techniques tailors the electronic structure of the polymer to enable in situ lithium doping. Composite anodes based on this polymer and commercial Si particles exhibit 2100 mAh g -1 in Si after 650 cycles without any conductive additive. Copyright

Toward an Ideal Polymer Binder Design for High-Capacity Battery Anodes

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 multifunctionality 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 electronically 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 nonconductive 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.

Li3PO4-coated LiNi0.5Mn1.5O4: a stable high-voltage cathode material for lithium-ion batteries.

LiNi0.5Mn1.5O4 is regarded as a promising cathode material to increase the energy density of lithium-ion batteries due to the high discharge voltage (ca. 4.7 V). However, the interface between the LiNi0.5Mn1.5O4 cathode and the electrolyte is a great concern because of the decomposition of the electrolyte on the cathode surface at high operational potentials. To build a stable and functional protecting layer of Li3PO4 on LiNi0.5Mn1.5O4 to avoid direct contact between the active materials and the electrolyte is the emphasis of this study. Li3PO4-coated LiNi0.5Mn1.5O4 is prepared by a solid-state reaction and noncoated LiNi0.5Mn1.5O4 is prepared by the same method as a control. The materials are fully characterized by XRD, FT-IR, and high-resolution TEM. TEM shows that the Li3PO4 layer (<6 nm) is successfully coated on the LiNi0.5Mn1.5O4 primary particles. XRD and FT-IR reveal that the synthesized Li3PO4-coated LiNi0.5Mn1.5O4 has a cubic spinel structure with a space group of Fd3m, whereas noncoated LiNi0.5Mn1.5O4 shows a cubic spinel structure with a space group of P4(3)32. The electrochemical performance of the prepared materials is characterized in half and full cells. Li3PO4-coated LiNi0.5Mn1.5O4 shows dramatically enhanced cycling performance compared with noncoated LiNi0.5Mn1.5O4.

Improved initial performance of Si nanoparticles by surface oxide reduction for lithium-ion battery application

Author(s): Xun, S; Song, X; Grass, ME; Roseguo, DK; Liu, Z; Battaglia, VS; Liu, G | Abstract: This study characterizes the native oxide layer of Si nanoparticles and evaluates its effect on their performance for Li-ion batteries. x-ray photoelectron spectroscopy and transmission electron microscopy were applied to identify the chemical state and morphology of the native oxide layer. Elemental and thermogravimetric analysis were used to estimate the oxide content for the Si samples. Hydrofluoric acid was used to reduce the oxide layer. A correlation between etching time and oxide content was established. The initial electrochemical performances indicate that the reversible capacity of etched Si nanoparticles was enhanced significantly compared with that of the as-received Si sample.

Li4P2O7 modified high performance Li3V2(PO4)3 cathode material

Li3V2(PO4)3 was prepared from a stoichiometric and a non-stoichiometric set of precursors. The non-stoichiometric preparation led to particles coated with a thin layer (<5 nm) of Li4P2O7 and Li3PO4 (G-LVPO), as verified through high resolution transmission electron microscopy and slow scan X-ray diffraction. The stoichiometric material was bare (B-LVPO), i.e. no film was present, as confirmed by the same techniques. Amorphous and crystalline Li3V2(PO4)3 will co-exist when the synthesis temperature ranges from 700 °C to below 900 °C. The Li3V2(PO4)3 phase will completely crystallize and particles grow bigger than 300 nm when the synthesis temperature reaches to or higher than 900 °C. Cyclic voltammetry plots of B-LVPO and G-LVPO show that they undergo the same phase transitions between 3.0 V and 4.3 V and preserve a good structural stability over cycled in the range from 3.0 V to 4.8 V. G-LVPO has a smaller ohmic/charge transfer resistance compared with B-LVPO, which enables a better rate capability and cycling ability of G-LVPO than B-LVPO. In this report we were able to determine that the non-stoichiometric chemistry leads to a coating of Li4P2O7 and Li3PO4 on the Li3V2(PO4)3 and that the coating appears to improve the rate capability and the cycling ability of the material.

High performance LiNi0.5Mn1.5O4 cathode material with a bi-functional coating for lithium ion batteries

LiPO3, one of the compounds from the Li2O–P2O5 binary phase diagram, is successfully coated on LiNi0.5Mn1.5O4 particles as a bifunctional layer with respect to its good ionic conductivity and chemical passivation properties. The coating layer with a thickness of 1 nm is identified by X-ray diffraction (XRD) and high resolution transition electron microscopy (TEM). Fourier transform-infrared spectrometer (FT-IR) and Raman spectra reveal that LiPO3 coated LiNi0.5Mn1.5O4 (LiPO3/LiNi0.5Mn1.5O4) possesses a cubic spinel structure with a space group of Fdm. The electrochemical properties of synthesized materials are evaluated in both Li ion half cells and full cells. LiPO3/LiNi0.5Mn1.5O4 exhibits significantly enhanced rate performance and superior cyclability compared with non-coated LiNi0.5Mn1.5O4. Impedance analysis indicates that the LiPO3 coating dramatically reduces the LiPO3/LiNi0.5Mn1.5O4 cell impedance, especially the resistances of the lithium ion migration compared with non-coated LiNi0.5Mn1.5O4. In addition, the LiPO3 coating can effectively act as a passivation layer to minimize electrolyte–electrode interface side reactions and thus improve the long-term cyclability.

Biomimetic Nanostructuring of Copper Thin Films Enhances Adhesion to the Negative Electrode Laminate in Lithium‐Ion Batteries

Thin films of copper are widely used as current collectors for the negative electrodes in lithium-ion batteries. However, a major cause of battery failure is delamination between the current collector and the graphite anode. When silicon or tin is used as active material, delamination becomes a key issue owing to the large volume changes of these materials during lithation and delithation processes. Learning from Nature, we developed a new biomimetic approach based on the adhesion properties of the feet of geckos. The biomimetic approach improves adhesion between the laminate and the copper surface by introducing an array of Cu(OH)2 nanorods, which increases the surface area of the current collector. When graphite anode laminate is casted onto regular and a modified copper surfaces, the modified current collector displays superior adhesion to graphite and the PVDF binder-based electrode. The electrochemical performance of the batteries using these electrodes is not compromised by the additional chemistry of the Cu(OH)2 on the copper surface. The technique can lead to enhanced battery lifetimes over long-term cycling.