High-power Lithium-ion Batteries Research Articles

Preparation of 3D micro/mesoporous LiFePO4 composite wrapping with porous graphene oxide for high-power lithium ion battery

A 3D spray-dried micro/mesoporous LiFePO4/porous graphene oxide/C (denoted as SP-LFP/PGO/C) composite material is synthesized via a three-step process, i.e., hydrothermal process, carbon coating, and spray dry method in sequence. The 2D porous graphene oxide (denoted as PGO) material is first prepared through an activation method. The galvanostatic charge-discharge measurements of LFP composites without graphene oxide, with 1 wt% graphene oxide, and 1 wt% PGO are conducted in the potential range of 2–3.8 V at various rates (0.1–10C). It is revealed that the SP-LFP/PGO/C material shows the best performance among three samples. The discharge capacities of the SP-LFP/PGO/C composites are observed to 160, 152, 151, 149, 144, 139, 127 mAh g−1 at 0.1C, 0.2C, 0.5C, 1C, 3C, 5C and 10C rate. In particular, the discharge capacity of the SP-LFP/PGO/C composite with 1 wt% PGO is 107 mAh g−1 after 1000 cycles at a 10C rate, and its capacity retention is ca. 97%. It is due to the unique structural and geometrical feature of SP-LFP/PGO/C composite, there the diamond-like (rhombus) LFP nanoparticles are embedded in porous GO matrix which forming a porous three-dimensional network for fast electronic and ionic transport channels.

Adaptive State of Health Evaluation Method Study for High Power Aerial Lithium-ion Battery Packs

A novel and effective method is proposed to estimate the SOH (State of Health) value of the high power aerial LIB (Lithium-Ion Battery) packs. The comprehensive SOH evaluation is realized by using the improved CI-EKF (Credibility Inference - Extended Kalman Filter) algorithm together with the discharging and charging maintenance experimental process, implying the accurate and adaptive SOH effect. The proposed method is used in the SOH evaluation process of the aerial LIB pack, with minimal time demand of self-learning treatment. The results indicate that the SOH values can be estimated effectively at different working conditions, in which the evaluation accuracy rate is up to 95.00% for the experimental samples of the aerial LIB pack, providing the technical support for the reliable application of the high power LIB pack and playing a core role in its power supply promotion.

Nanostructured Networks for Energy Storage: Vertically Aligned Carbon Nanotubes (VACNT) as Current Collectors for High-Power Li4Ti5O12(LTO)//LiMn2O4(LMO) Lithium-Ion Batteries

As a concept for electrode architecture in high power lithium ion batteries, self-supported nanoarrays enable ultra-high power densities as a result of their open pore geometry, which results in short and direct Li+-ion and electron pathways. Vertically aligned carbon nanotubes (VACNT) on metallic current collectors with low interface resistance are used as current collectors for the chemical solution infiltration of electroactive oxides to produce vertically aligned carbon nanotubes decorated with in situ grown LiMn2O4 (LMO) and Li4Ti5O12 (LTO) nanoparticles. The production processes steps (catalyst coating, VACNT chemical vapor deposition (CVD), infiltration, and thermal transformation) are all scalable, continuous, and suitable for niche market production to achieve high oxide loadings up to 70 wt %. Due to their unique transport structure, as-prepared nanoarrays achieve remarkably high power densities up to 2.58 kW kg−1, which is based on the total electrode mass at 80 C for LiMn2O4//Li4Ti5O12 full cells. The tailoring of LTO and LMO nanoparticle size (~20–100 nm) and VACNT length (array height: 60–200 µm) gives insights into the rate-limiting steps at high current for these kinds of nanoarray electrodes at very high C-rates of up to 200 C. The results reveal the critical structural parameters for achieving high power densities in VACNT nanoarray full cells.

Tri-functional coating to enhance the capacity retention of LiNi0.5Mn1.5O4 for high power lithium ion battery

LiNi0.5Mn1.5O4 is a promising cathode material for high power lithium ion batteries (LIBs) for electric vehicles (EVs) and hybrid electric vehicles (HEVs). For the first time we design a tri-functional coating to improve the cycling performance of LiNi0.5Mn1.5O4. With the designed BiPO4 coating, the capacity retentions of LiNi0.5Mn1.5O4 are largely improved from 84.3% to 93.6% at 0.5 C after 50 cycles and from 80.6% to 96.2% at 10 C after 100 cycles. The tri-functional coating reduces the charge transfer resistance of LiNi0.5Mn1.5O4 cathode and plays a critical role in enhancing the electrochemical performance and lifetime. This strategy provides a new way to modify electrode materials to elevate the performance of LIBs.

Surface engineering of graphite anode material with black TiO2-x for fast chargeable lithium ion battery

One of the most important challenges in the improvement of the lithium ion battery (LIB) for electric vehicle (EV) applications is its fast charging capability. However, currently used graphite anode materials cannot meet this requirement for EVs. Herein, we demonstrate that surface modification of graphite using oxygen-deficient black titanium oxide (TiO2−x) is an efficient way to improve the fast charging capability of graphite anode material for LIB. The proposed surface engineered anode material, 1 wt% TiO2-x coated graphite anode material, at a high rate of 5 C-rate, exhibited 98.2% of the capacity obtained at a rate of 0.2 C without any degradation of other performances. Full cell tests adopting LiCoO2 as a cathode material with TiO2-x coated graphite anode material also confirmed that the TiO2-x coating layer can improve the fast charging capability of graphite anode material. Such an improvement in the fast charging capability has mainly been attributed to the modified interface between the anode and the electrolyte by surface-engineering of the TiO2-x layer on the surface of graphite. These results show that the approach presented in this work, interfacial engineering of graphite using oxygen deficient TiO2-x, deserves to be regarded as one of the most promising ways to develop an anode material with fast charging capability for high power LIB for EV applications.

Phase transitions and related electrochemical performances of Li-Rich layered cathode materials for high-energy lithium ion batteries

The present work systematically probes and tracks the phase transition of Li-rich layered Li[Li0.2Mn0.54Ni0.13Co0.13]O2 (marked as LMNCO) by using an ex-situ chemical activation that is realized through ion-exchange and post-annealing processes, in order to understand related electrochemical performances of Li-rich cathode materials for advanced lithium-ion batteries. Ion exchanges of H+-Li+ and subsequent TBA+-H+ (TBA: tetrabutylammonium) in LMNCO are carried out, resulting in its layered-to-spinel phase transition after optimal heat treatments. The resultant compound shows a Li4Mn5O12-type spinel structure. This converted spinel cathode material can deliver discharge capacities higher than 300 mAh/g at 0.1 C and 200 mAh/g at 1 C (1 C = 250 mA/g), respectively, and also exhibits better cycling stability and rate capability in comparison with pristine layered LMNCO and other derivatives. This work offers a feasible route to study all changes of morphologies, crystal structures, chemical compositions, surface areas and related electrochemical lithium storage behaviors during phase transitions of Li-rich layered cathode materials, and thus provides insights on optimizing electrochemical performances for high-energy and high-power lithium ion batteries.

Engineering 2D Nanofluidic Li‐Ion Transport Channels for Superior Electrochemical Energy Storage

Rational surface engineering of 2D nanoarchitectures-based electrode materials is crucial as it may enable fast ion transport, abundant-surface-controlled energy storage, long-term structural integrity, and high-rate cycling performance. Here we developed the stacked ultrathin Co3 O4 nanosheets with surface functionalization (SUCNs-SF) converted from layered hydroxides with inheritance of included anion groups (OH- , NO3- , CO32- ). Such stacked structure establishes 2D nanofluidic channels offering extra lithium storage sites, accelerated Li-ion transport, and sufficient buffering space for volume change during electrochemical processes. Tested as an anode material, this unique nanoarchitecture delivers high specific capacity (1230 and 1011 mAh g-1 at 0.2 and 1 A g-1 , respectively), excellent rate performance, and long cycle capability (1500 cycles at 5 A g-1 ). The demonstrated advantageous features by constructing 2D nanochannels in nonlayered materials may open up possibilities for designing high-power lithium ion batteries.

Material and Structural Design of Novel Binder Systems for High-Energy, High-Power Lithium-Ion Batteries

Developing high-performance battery systems requires the optimization of every battery component, from electrodes and electrolyte to binder systems. However, the conventional strategy to fabricate battery electrodes by casting a mixture of active materials, a nonconductive polymer binder, and a conductive additive onto a metal foil current collector usually leads to electronic or ionic bottlenecks and poor contacts due to the randomly distributed conductive phases. When high-capacity electrode materials are employed, the high stress generated during electrochemical reactions disrupts the mechanical integrity of traditional binder systems, resulting in decreased cycle life of batteries. Thus, it is critical to design novel binder systems that can provide robust, low-resistance, and continuous internal pathways to connect all regions of the electrode. In this Account, we review recent progress on material and structural design of novel binder systems. Nonconductive polymers with rich carboxylic groups have been adopted as binders to stabilize ultrahigh-capacity inorganic electrodes that experience large volume or structural change during charge/discharge, due to their strong binding capability to active particles. To enhance the energy density of batteries, different strategies have been adopted to design multifunctional binder systems based on conductive polymers because they can play dual functions of both polymeric binders and conductive additives. We first present that multifunctional binder systems have been designed by tailoring the molecular structures of conductive polymers. Different functional groups are introduced to the polymeric backbone to enable multiple functionalities, allowing separated optimization of the mechanical and swelling properties of the binders without detrimental effect on electronic property. We then describe the design of multifunctional binder systems via rationally controlling their nano- and molecular structures, developing the conductive polymer gel binders with 3D framework nanostructures. These gel binders provide multiple functions owing to their structure derived properties. The gel framework facilitates both electronic and ionic transport owing to the continuous pathways for electrons and hierarchical pores for ion diffusion. The polymer coating formed on every particle acts as surface modification and prevents particle aggregation. The mechanically strong and ductile gel framework also sustains long-term stability of electrodes. In addition, the structures and properties of gel binders can be facilely tuned. We further introduce the development of multifunctional binders by hybridizing conductive polymers with other functional materials. Meanwhile mechanistic understanding on the roles that novel binders play in the electrochemical processes of batteries is also reviewed to reveal general design rules for future binder systems. We conclude with perspectives on their future development with novel multifunctionalities involved. Highly efficient binder systems with well-tailored molecular and nanostructures are critical to reach the entire volume of the battery and maximize energy use for high-energy and high-power lithium batteries. We hope this Account promotes further efforts toward synthetic control, fundamental investigation, and application exploration of multifunctional binder materials.

P.2.f.016 - Pharmacological treatments and risk of re-hospitalisation due to unipolar depression in a nationwide cohort of 123,712 patients

A study of the morphology-controlled growth of olivine LiFePO4 particles by varying the precursor concentration via a facile solvothermal synthesis was carried out. The influences of the solvent product on the structure, morphology and electrochemical performance were systematically investigated by X-ray diffraction, scanning/transmission electron microscopy and charge-discharge tests. It was found that as the precursor concentration increased from 0.15 M to 0.90 M, the morphology of the LiFePO4 particles changed from spindle-shape to plate-type and then to a hierarchical club-shaped structure, and the predominantly exposed facet of all LiFePO4 samples was (100). The shape of LiFePO4 particles remained as nanoplates while synthesized at different reaction temperatures and time with a precursor concentration of 0.30 M. This in turn confirms that the precursor concentration plays an important role in controlling the morphology of LiFePO4 particles. To illustrate the phenomenon caused by variations in the concentration, a possible morphological transformation mechanism was demonstrated. With the optimal precursor concentration of 0.3 M, the obtained LiFePO4 shows square nanoplates with uniform particle size and carbon coating, resulting in excellent electrochemical performance: a discharge capacity of 157.3 mAh/g at 1 C with 95% capacity retention after 1000 cycles and a high-rate capacity of 140.8 mAh/g at 10 C. This facile and precursor concentration-controlled solvothermal method is anticipated to be a guide for large-scale cathode material manufacturing and can fulfil the requirements for its application to high-power lithium-ion batteries.

Improved State of Charge Estimation for High Power Lithium Ion Batteries Considering Current Dependence of Internal Resistance

For high power Li-ion batteries, an important approach to improve the accuracy of modeling and algorithm development is to consider the current dependence of internal resistance, especially for large current applications in mild/median hybrid electric vehicles (MHEV). For the first time, the work has experimentally captured the decrease of internal resistance at an increasing current of up to the C-rate of 25 and developed an equivalent circuit model (ECM) with current dependent parameters. The model is integrated to extended Kalman filter (EKF) to improve SOC estimation, which is validated by experimental data collected in dynamic stress testing (DST). Results show that EKF with current dependent parameters is capable of estimating SOC with a higher accuracy when it is compared to EKF without current dependent parameters.

Investigation of the electrochemical performance of polyvinylidene fluoride-derived LiFePO4/C composite nanospheres

The wide application of LiFePO4 (LFP) in high-power lithium-ion batteries is limited due to its two main drawbacks: poor electronic conductivity and low lithium-ion diffusivity, which can be greatly improved through a combination of reducing the LFP crystallites to nanoscale and introducing a conductive carbon coating layer. It is well accepted that the choice of carbon precursors has a significant impact on the ultimate lithium storage property of the LiFePO4/carbon (LFP/C) composite. In this work, LFP/C core–shell composite nanospheres using polyvinylidene fluoride (PVDF) as carbon source (LFP/C-PVDF) were prepared and the electrochemical performances in lithium half cells were investigated. The electrochemical properties of LFP/C composite derived from glucose (LFP/C-GLU) and the bare LFP without carbon coating were also investigated for comparison. It was found that LFP/C-PVDF displayed a higher capacity, better rate capability and smaller polarization than its LFP/C-GLU and LFP counterparts, which could be ascribed to lower surface and charge-transfer impedances, and an enhanced lithium-ion diffusivity, as revealed by electrochemical impedance spectroscopy analysis. Our study demonstrates that PVDF is a facile and potential carbon precursor for LiFePO4 in high-performance lithium-ion battery application.

Experimental investigations of an AC pulse heating method for vehicular high power lithium-ion batteries at subzero temperatures

Effect of the AC (alternating current) pulse heating method on battery SoH (state of health) for large laminated power lithium-ion batteries at low temperature is investigated experimentally. Firstly, excitation current frequencies, amplitudes, and voltage limitations on cell temperature evolution are studied. High current amplitudes facilitate the heat accumulation and temperature rise. Low frequency region serves as a good innovation to heat the battery because of the large impedance. Wide voltage limitations also enjoy better temperature evolution owing to the less current modulation, but the temperature difference originated from various voltage limitations attenuates due to the decrement of impedance resulting from the temperature rise. Experiments with the thermocouple-embedded cell manifest good temperature homogeneity between the battery surface and interior during the AC heating process. Secondly, the cell capacity, Direct Current resistance and Electrochemical Impedance Spectroscopy are all calibrated to assess the battery SoH after the hundreds of AC pulse heating cycles. Also, all cells are disassembled to investigate the battery internal morphology with the employment of Scanning Electron Microscope and Energy-Dispersive x-ray Spectroscopy techniques. The results indicate that the AC heating method does not aggravate the cell degradation even in the low frequency range (0.5 Hz) under the normal voltage protection limitation.

The mediated synthesis of FeF3 nanocrystals through (NH4)3FeF6 precursors as the cathode material for high power lithium ion batteries

The exploration of cathode materials with high electrochemical performances is critical to improve the energy and power densities of lithium ion batteries (LIBs). Iron fluoride (FeF3) has been proposed as an ideal candidate of LIBs cathode material because of the high discharge plateau and theoretical capacity. In this study, a precursor-mediated method was proposed to synthesize FeF3 nanocrystals (NCs) with different microstructures. These FeF3 NCs were obtained through the thermal decomposition of the precipitated ammonium hexafluoroferrate [(NH4)3FeF6] precursor, and the morphology and crystallinity could be adjusted by varying the ethanol/water volume ratio in the procursor precipitation process. Electrochemical studies demonstrated that FeF3 NC, derived from (NH4)3FeF6 precipitated from the solution with the ethanol/water volume ratio of 20, delivered the initial specific capacity of 217.6mAhg−1 at 0.2C, associated with excellent rate capability up to 20C (93.8mAhg−1), and showed the capacity retention of 80.6% after 500 cycles at 20C. These results indicate a tunable and convenient strategy towards nanostructured metals fluorides for high power LIBs.

Cornlike Ordered Mesoporous Silicon Particles Modified by Nitrogen-Doped Carbon Layer for the Application of Li-Ion Battery.

The cornlike ordered mesoporous silicon (OM-Si) particles modified by the nitrogen-doped carbon layer (OM-Si@NC) are successfully fabricated and used as the anode of lithium-ion battery (LIBs). The influences of the N-doped carbon layer on the structure and electrochemical properties of the OM-Si@NC composite are detailedly investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectrum, X-ray photoelectron spectroscopy (XPS), and charge/discharge tests. The results reveal that the amorphous N-doped carbon layer can offer the abundant conductive pathways for fast lithium ion transportation and electron transfer, which not only leads to a high specific capacity under high ampere density but also serves as a structural barrier maintaining the whole integrity and settling the mechanical breaking due to the huge volume changes of Si host. Therefore, the as-synthesized OM-Si@NC composite exhibits a high original discharge capacity of 2548 mA h g-1 under 0.2 A g-1 as well as a large reversible capacity of 1336 mA h g-1 under 1 A g-1 after 200 circles. The OM-Si@NC composite prepared by a relatively simple and feasible synthesis method shows excellent electrochemical performances and turns out to be promising for the application of high power LIBs.

Facile synthesis of LiMn2O4 microsheets with porous micro-nanostructure as high-rate cathode materials for Li-ion batteries

Porous LiMn2O4 microsheets with micro-nanostructure have been successfully prepared through a simple carbon gel-combustion process with a microporous membrane as hard template. The crystal structure, morphology, chemical composition, and surface analysis of the as-obtained LiMn2O4 microsheets are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscope (XPS). It can be found that the as-prepared LiMn2O4 sample presents the two-dimensional (2-D) sheet structure with porous structure comprised with nano-scaled particles. As cathode materials for lithium-ion batteries, the obtained LiMn2O4 microsheets show superior rate capacities and cycling performance at various charge/discharge rates. The LiMn2O4 microsheets exhibit a higher charge and discharge capacity of 137.0 and 134.7 mAh g−1 in the first cycle at 0.5 C, and it remains 127.6 mAh g−1 after 50 cycles, which accounts for 94.7% discharge capacity retention. Even at 10 C rate, the electrode also delivers the discharge capacity of 91.0 mAh g−1 after 300 cycles (93.5% capacity retention). The superior electrochemical properties of the LiMn2O4 microsheets could be attributed to the unique microsheets with porous micro-nanostructure, more active sites of the Li-ions insertion/deinsertion for the higher contact area between the LiMn2O4 nano-scaled particles and the electrolyte, and better kinetic properties, suggesting the applications of the sample in high-power lithium-ion batteries.

Importance of synergistic role of cobalt and aluminum on a greatly improved electrochemical performance of Li-rich oxyfluoride spinel at elevated-temperature

Spinel LiMn2O4 cathode material has been successfully commercialized for various lithium ion batteries (LIBs) and is a very promising candidate for emerging large-scale applications in pure electric vehicles (EVs). Despite its advantages, LiMn2O4 suffers from fast capacity fading at elevated temperature stemming from Mn dissolution and structural distortion. Herein, an investigation on the structure and electrochemical performance of single/double/triple-ion substituted Li1.05Mn1.95O4, which was synthesized by a Sol-gel method combined with heat treatment at 750 °C, was firstly carried out. Enhancements of the tap density, rate capability, and cycling performance at high temperature were achieved without sacrificing its specific capacity via unique morphology control and triple-substitution (Al3+, Co3+, and F− ions) strategy. The as-prepared Li1.05Al0.05Mn1.85Co0.05O3.9F0.1 (LAMCOF) sample exhibits a high specific capacity, a superior rate capability, and an excellent long-term cyclability at the high temperature (55 °C), with the specific discharge capacities of 115 and 110 mAh g−1 and the corresponding capacity retention of 72.3% and 73.0% for up to 800 cycles at 2 and 5 C rates, respectively. The high specific capacity, an excellent cyclability, and a superior rate performance are believed to be caused by the three main reasons: (1) improvement of the specific capacity by the substitution of O2− by F−, (2) stabilization of the crystal structure derived from the synergistic roles of triple substitution by Al3+, Co3+, and F− ions, which decreases the Jahn-Teller distortions and Mn dissolution; and (3) formation of a stable interface of the active material/electrolyte resulting from the high content of Mn4+ at the surface and its unique morphology, which reduces the charge transfer resistances and favors fast Li+ intercalation/deintercalation kinetics. The as-prepared LAMCOF sample may offer a promising cathode material for the high-power LIBs with extended cycle life and superior rate capability at elevated temperature.

Surface Chemistry Evolution in Blended Lithium-Ion Battery Cathode Materials

For energy storage applications in which power and safety are paramount, lithium ion batteries (LIB) containing a lithium-iron phosphate (LFP) positive electrode are a common choice. However, due to the relatively low operating potential of LFP and the high proportion of inactive materials in high-power LIB, the energy density of these devices can be well below 100 Wh/kg. Meanwhile, advanced cathode chemistries such as nickel-rich layered compounds and high-voltage spinels could offer improved energy densities, but it’s unclear whether these will ever offer the same power density and safety as LFP cells. Part of the limitation of alternative cathode chemistries is the same avenue by which energy density is increased: significantly higher cathode potentials relative to LFP. One example are spinel-structured manganese oxide compounds with the general formula LiMn2-xMxO4-yNy (LMO) where M are various transition metal oxide cationic dopants and N are typically halogen anionic dopants. Heavily doped spinels have acceptable power, safety, and capacity retention relative to LFP but relatively low specific capacities. Meanwhile, layered nickel-manganese-cobalt compounds with the general formula LiNixCoyMnzO2(NCM) can demonstrate greater than 200 mAh/g when charged to high upper cut-off voltages (4.5 V vs. Li/Li+ and above), but suffer rapid capacity fade as a result. Blends of spinel and layered cathode compounds have been reported as one avenue to achieve a composite electrode with improved power capability, safety, and capacity retention (1) (2) (3). For layered NCM compounds differing explanations for capacity loss when charged above 4.5 V vs. Li/Li+ have been presented. Kang et. Al. and others suggested that capacity loss in NCM materials cycled to high upper cut-off voltages is due to a structural rearrangement at the near-surface of the layered oxide. This structural degradation leads to a dramatic increase in electrochemical polarization, and is in contrast to the formation of a resistive surface film formed by electrolyte decomposition (4) (5) (6). Still, electrolyte additives have been found to suppress structural re-arrangement of NCM compounds, indicating that the electrode-electrolyte interface, rather than a purely structural phenomenon, is involved in NCM capacity loss (5) (6). Thus, from these studies it’s not clear how a simple mechanical mixture of spinel and layered compounds could influence the interfacial degradation of NCM. Our work has found that there are indeed significant changes to LiNi0.5Co0.2Mn0.3O2 surface chemistry as observed by x-ray photoelectron spectroscopy (XPS) after a few electrochemical cycles indicating newly formed C-O and C-F bonds, shown in Figure 1A. Meanwhile, when comparing the potentiodynamic behavior of the layered LiNi0.5Co0.2Mn0.3O2 to high voltage spinel-structured LiNi0.5Mn1.5O4, an apparent irreversible oxidation peak is observed in the layered compound near 4.8 V vs. Li/Li+, which is coincident with the split reversible oxidation peaks observed for the spinel compound. This overlap in apparent reversible and irreversible behaviors may play a key role in determining the surface chemistry of blended cathode materials and will be discussed further during our presentation.

Fundamental Electrochemical Study of Manganese Redox States in Nonaqueous Battery Solvents

Next-generation transition metal oxide cathodes such as lithium nickel manganese oxide (LNMO) are needed to meet the increasing demand for high-voltage, high-power lithium-ion batteries. However, these manganese- and nickel-containing cathode materials accelerate capacity fade due to transition metal dissolution from the electrode. The role of these metals, particularly manganese, in side reactions remains poorly understood. Our work aims to bridge this knowledge gap through fundamental electrochemistry. While the effects of manganese (Mn) dissolution from transition metal oxides have been documented, the fundamental physics of how manganese ions induce capacity fade are not yet determined. Delacourt et al. contend that Mn0 is deposited in the solid-electrolyte interphase (SEI) at the negative electrode creating an electronically conductive SEI, while Vissers et al. show that Mn2+ ion-exchanges with lithium-containing inorganic electrolyte reduction products1,2. Lastly, Wandt et al. demonstrated via operando X-ray absorption spectroscopy that Mn ions are always in the +2 oxidation state on lithiated and delithiated graphite, however Mn metal was detected on lithiated graphite in ex situ analysis3. This disagreement on the redox state of dissolved manganese impedes efforts to prevent SEI contamination by the transition metal ions. Even the standard reduction potential of Mn2+ to Mn0 in nonaqueous electrolyte is not agreed upon. Komaba et al. reported 1.87 V vs. Li/Li+, based on the standard redox potential vs. NHE in an aqueous environment4. Several studies have observed different reduction potentials for Mn2+ ions in both perchlorate- and carbonate-based electrolytes5,6. To better diagnose the redox state of manganese in a nonaqueous battery electrolyte, a fundamental understanding of the potential ranges for various oxidation states of manganese is necessary. In one part of this work, we determine the Mn2+/Mn0 redox potential in nonaqueous electrolyte via three-electrode cell electrochemistry, energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). To our knowledge, this is the first attempt to determine the precise redox potential for the Mn2+/Mn0 reaction in nonaqueous battery electrolytes. It is important to avoid electrolyte and lithium-ion reduction potentials obfuscating the reduction potential of Mn2+; therefore, a stable non-passivating, lithium-free electrolyte is used for this study (namely, 0.1 M tetrabutylammonium perchlorate in tetrahydrofuran). We vary the potential applied at a copper electrode in a manganese-doped electrolyte, correlate the current response to manganese reduction, and then confirm Mn0 deposition via EDS and XPS of the copper electrode. We have demonstrated that Mn0 can be electrochemically deposited on copper foil from a Mn-doped electrolyte and detected via EDS and XPS. In another part of this work, we determine how the presence of manganese affects the formation and characteristics of the SEI using redox mediators, such as the ferrocene-ferrocenium couple. SEI films are formed both in the presence and absence of manganese salts, by applying a constant potential for a specified amount of time. The SEI is probed by adding a redox mediator to the electrolyte, and measuring the current response around the mediator reaction potential. By comparing the cyclic voltammograms for SEIs formed in neat electrolyte versus Mn-contaminated electrolyte, the impact of manganese on through-film mass transport and reaction kinetics has been determined. Results show that the SEI formed in the presence of manganese has an effective through-film ferrocenium diffusivity eight times greater than the SEI formed in neat electrolyte, indicating that manganese may induce higher porosity or cracks. Future work will tune redox mediator size and chemistry to characterize pore or crack sizes in the SEI.

Hierarchical SnO2-Graphite Nanocomposite Anode for Lithium-Ion Batteries through High Energy Mechanical Activation

Development of novel electrode materials with unique architectural designs is necessary to attain high power and energy density lithium-ion batteries (LIBs). SnO2, with high theoretical capacity of 1494mAhg−1, is a promising candidate anode material, which has been explored with various strategies, such as dimensional reduction, morphological modifications and composite formation. Unfortunately, most of the SnO2-based electrodes are prepared by using complex chemical synthesis methods, which are not feasible to scale up for practical applications. In addition, concomitant irrecoverable initial capacity loss and consequently poor initial Coulombic efficiency still persistently plagued these SnO2-based anodes. To overcome hitherto conceived irreversible formation of Li2O by conversion reaction, to fully harness its theoretical capacity, this work demonstrates that a hierarchical structured SnO2-C nanocomposite with 68.5% initial Coulombic efficiency and reversible capacity of 725mAhg−1 can be derived from the mixtures of SnO2 and graphite, by using low cost industrial compatible high energy ball milling activation.

Self nitrogen-doped carbon nanotubes as anode materials for high capacity and cycling stability lithium-ion batteries

The great demand for high-power lithium-ion batteries has spurred extensive research on carbonaceous electrode materials. Herein, we reported a facile way of preparing novel carbon nanotubes with high nitrogen doping. Helical and straight 3-aminophenol formaldehyde resin nanotubes were first prepared based on the self-assembly of the chiral amphiphiles, which were then used as carbon sources to fabricate self nitrogen-doped carbon nanotubes via pyrolysis process. When the resins were carbonized at 600°C, carbon nanotubes with a high nitrogen-content of 9.6wt% were obtained, which maintained the original morphology of the resins. The electrochemical tests disclosed that the carbon nanotubes exhibited excellent Li storage capacity and superior cycling stability. A high reversible specific capacity of 1056mAhg−1 at 0.1Ag−1 was obtained after 300cycles, which is greatly higher than that of graphite and most of polymer derived carbonaceous materials. The research data implied that the nitrogen doping content plays an important role in the electrochemical performance of the carbon nanotubes.