Synthesis, structural and electrochemical properties of V4O9 cathode for lithium batteries

Single-phase three-dimensional vanadium oxide (V4O9) was synthesized by reduction of V2O5 using a gas stream of ammonia/argon (NH3/Ar). The as-synthesized oxide, prepared by this simple gas reduction method was subsequently electrochemically transformed into a disordered rock salt type-“Li3.7V4O9” phase while cycling over the voltage window 3.5 to 1.8 V versus Li. The Li-deficient phase delivers an initial reversible capacity of ∼260 mAhg−1 at an average voltage of 2.5 V vs. Li+/Li0. Further cycling to 50 cycles yields a steady 225 mAhg−1. Ex situ X-ray diffraction studies confirmed that (de) intercalation phenomena follows a solid-solution electrochemical reaction mechanism. As demonstrated, the reversibility and capacity utilization of this V4O9 is found to be superior to battery grade, micron-sized V2O5 cathodes in lithium cells

Consequences of Utilizing a Redox-Active Polymeric Binder in Li-ion Batteries

Development of new polymeric binders can help enable the use of silicon-rich anodes in Li-ion batteries, by providing stronger adhesion to the active material particles. The compositional features that improve interfacial interactions and mechanical properties can often impart electronic conductivity and redox activity to these polymers, which are generally seen as beneficial to cell performance. Alternatively, it is also possible that the addition of charge-transferring centers to the electrode can accelerate cell degradation. Here, we use an aromatic polyimide (~320 mAh/g of reversible capacity) to explore how a redox-active conductive polymer can affect cell performance. We demonstrate that the lithiated polymer is less stable than the traditional binders upon storage, leading to increased rates of calendar aging. Furthermore, we show that the adhesion properties of the polymer deteriorate upon repeated cycling, to an extent that is proportional to the degree of delithiation of the binder. More critically, we show that progressive degradation of the redox behavior of the polymer leads to the release of extra Li+ into the cell, which can give the false perception of good performance even under conditions of poor stability. Our work suggests that redox-active conductive binders can sometimes be detrimental to cell performance, and that works evaluating new polymers must include careful experimental validation under realistic conditions

Direct Observation of Lattice Aluminum Environments in Li Ion Cathodes LiNi_{1–<i>y</i>–<i>z</i>}Co_<i>y</i>Al_<i>z</i>O₂ and Al-Doped LiNi_<i>x</i>Mn_<i>y</i>Co_<i>z</i>O₂ via ²⁷Al MAS NMR Spectroscopy

Direct observations of local lattice aluminum environments have been a major challenge for aluminum-bearing Li ion battery materials, such as LiNi_{1–<i>y</i>–<i>z</i>}Co_<i>y</i>Al_<i>z</i>O₂ (NCA) and aluminum-doped LiNi_<i>x</i>Mn_<i>y</i>Co_<i>z</i>O₂ (NMC). ²⁷Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is the <i>only</i> structural probe currently available that can <i>qualitatively</i> and <i>quantitatively</i> characterize lattice and nonlattice (i.e., surface, coatings, segregation, secondary phase etc.) aluminum coordination and provide information that helps discern its effect in the lattice. In the present study, we use NMR to gain new insights into transition metal (TM)–O–Al coordination and evolution of lattice aluminum sites upon cycling. With the aid of first-principles DFT calculations, we show direct evidence of lattice Al sites, nonpreferential Ni/Co–O–Al ordering in NCA, and the lack of bulk lattice aluminum in aluminum-“doped” NMC. Aluminum coordination of the paramagnetic (lattice) and diamagnetic (nonlattice) nature is investigated for Al-doped NMC and NCA. For the latter, the evolution of the lattice site(s) upon cycling is also studied. A clear reordering of lattice aluminum environments due to nickel migration is observed in NCA upon extended cycling

Composite of LiFePO \u3c inf\u3e 4 with titanium phosphate phases as lithium-ion battery electrode material

We report the synthesis of LiFePO4 (LFP) battery materials where during synthesis the iron has been substituted by up to 10 mol % with titanium. Analysis of the Ti-substituted materials revealed that at the substitution levels investigated, the Ti did not form a solid solution with the LFP, but rather minority phases containing Ti phosphates were formed and segregated at the nanoscopic scale. The minority phases were amorphous or not well-crystallized and accepted Li on first discharge in a lithium half cell, and solid state NMR spectra were consistent with one of the constituents being LiTi2(PO4)3. The Ti substituted materials had increased electrochemical capacities and discharge voltages relative to LFP prepared in an equivalent process, and the ability to accept Li on first discharge may find utility in using previously inaccessible capacity in battery cathode formulations and in balancing excess capacity from high energy cathode materials. © 2013 American Chemical Society

Solution-Based Synthesis and Characterization of Lithium-Ion Conducting Phosphate Ceramics for Lithium Metal Batteries

High conductivity solid electrolytes are promising solutions for extremely high energy density battery systems including Li/air and Li/sulfur. Lithium aluminum titanium phosphate (LATP) ceramics have among the highest reported ionic conductivities and are promising candidates as solid electrolytes. Li_1.3Al_0.3Ti_1.7(PO₄)₃ powders were synthesized for the first time via a solution-based method at synthesis temperatures as low as 650 °C. The ceramic powders are characterized using X-ray powder diffraction, solid state magic angle spinning (MAS) nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The effect of Li and Al local structure and the presence of amorphous and crystalline impurities on electrolyte morphology and sinterability have been studied in detail

Resolving the different silicon clusters in Li ₁₂Si ₇ by ²⁹Si and ^6,7Li solid-state NMR spectroscopy

Structural signatures: The analysis of Si-Si and Si-Li connectivities by solid-state NMR spectroscopy allows the different types of silicon clusters to be discriminated in the model lithium silicide compound Li 12Si 7 (see picture, Si clusters red and blue, Li ions gray). The results provide new NMR spectroscopic strategies with which to differentiate and study the structures formed in silicon-based electrode materials.</p

Si Oxidation and H₂ Gassing During Aqueous Slurry Preparation for Li-Ion Battery Anodes

Si has the possibility to greatly increase the energy density of Li-ion battery anodes, though it is not without its problems. One issue often overlooked is the decomposition of Si during large scale slurry formulation and battery fabrication. Here, we investigate the mechanism of H₂ production to understand the role of different slurry components and their impact on the Si oxidation and surface chemistry. Mass spectrometry and in situ pressure monitoring identifies that carbon black plays a major role in promoting the oxidation of Si and generation of H₂. Si oxidation also occurs through atmospheric O₂ consumption. Both pathways, along with solvent choice, impact the surface silanol chemistry, as analyzed by ¹H–²⁹Si cross-polarization magic angle spinning nuclear magnetic resonance (MAS NMR) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR FTIR). An understanding of the oxidation of Si, during slurry processing, provides a pathway toward improving the manufacturing of Si based anodes by maximizing its capacity and minimizing safety hazards

Correction to “Si Oxidation and H₂ Gassing during Aqueous Slurry Preparation for Li-Ion Battery Anodes”

Correction to “Si Oxidation and H₂ Gassing during Aqueous Slurry Preparation for Li-Ion Battery Anodes

Operando X‑ray Diffraction Studies of the Mg-Ion Migration Mechanisms in Spinel Cathodes for Rechargeable Mg-Ion Batteries

A promising high-voltage spinel oxide cathode material MgCrMnO4 with 18% Mg/Mn inversion was synthesized successfully. A new custom operando battery device was designed to study the cation migration mechanisms of the MgCrMnO4 cathode using 0.1 M Mg(TPFA)2 electrolyte dissolved in triglyme and activated carbon as the anode. For the first time in multivalent batteries, high-quality operando diffraction data enabled the accurate quantification of cation contents in the host structure. Besides the exceptional reversibility of 12% Mg2+ insertion in Mg1-xCrMnO4 (x ≤ 1), a partially reversible insertion of excess Mg2+ during overdischarging was also observed. Moreover, the insertion/extraction reaction was experimentally shown to be accompanied by a series of cation redistributions in the spinel framework, which were further supported by density functional theory calculations. The inverted Mn is believed to be directly involved in the cation migrations, which would cause voltage hysteresis and irreversible structural evolution after overdischarging. Tuning the Mg/Mn inversion rate could provide a direct path to further optimize spinel oxide cathodes for Mg-ion batteries, and more generally, the operando techniques developed in this work should play a key role in understanding the complex mechanisms involved in multivalent ion insertion systems

Silicon Nanoparticles: Stability in Aqueous Slurries and the Optimization of the Oxide Layer Thickness for Optimal Electrochemical Performance

In this study, silicon nanoparticles are oxidized in a controlled manner to obtain different thicknesses of SiO₂ layers. Their stability in aqueous slurries as well as the effect of oxide layer thickness on the electrochemical performance of the silicon anodes is evaluated. Our results show that slightly increasing the oxide layer of silicon nanoparticles significantly improves the stability of the nanoparticles in aqueous slurries and does not compromise the initial electrochemical performance of the electrodes. A careful comparison of the rate and cycle performance between 400 °C treated Si nanoparticles and pristine Si nanoparticles shows that by treating the silicon nanoparticles in air for slightly increasing the oxide layer, improvement in both rate and cycle performance can be achieved