High-power Lithium-ion Batteries Research Articles

Electrochemical Properties of Composite Electrodes Containing Lithium-Ion Conducting Solid Particles and Liquid Electrolytes in Lithium-Ion Batteries

Lithium-ion batteries for automotive applications have required to enhance power density, low-temperature performance, life, energy density, and safety. All-solid-state batteries using lithium-ion conducting solid electrolytes have been much interest as candidates to respond to these demands. However, for practical applications, all-solid-state batteries have some problems to solve low charge-discharge performance under high rate and low temperature operations because of low ionic conductivities and large resistances of interface between the solid electrolyte and the active electrode material. We have focused on hybrid electrolytes consisting of lithium-ion conducting solid particles (LCSP) and a gel polymer electrolyte leading to a decrease of cell resistance, especially at low temperatures for LTO cells [1,2]. In this study, we have investigated effects of LCSP with liquid electrolytes in composite electrodes on electrochemical properties and electrode performance in order to develop high-power lithium-ion batteries using the solid electrolytes. NASICON-type Li-Al-Ti-P-O (LATP) particles with a particle size of submicron were used as LCSP. The composite electrodes consisted of LiNi0.5Co0.2Mn0.3O2 (NCM523) as cathode active material, carbon filler, polyvinylidene difluoride binder, and LATP particles, which were coated on aluminum foil as current corrector. Electrochemical measurements of the composite electrodes containing LCSP were performed using a three-electrode glass cell with a lithium metal foil counter electrode, a lithium metal chip reference electrode, a glass filter separator, and LiPF6-based liquid electrolytes. Figure 1 shows typical AC-impedance spectra of the composite electrodes with and without LATP particles at -20°C. The impedance spectra of both electrodes exhibited two depressed semicircles in the high- and low-frequency range, which can be interpreted as resulting from the passivating film formed on the NCM523 active material and the charge transfer process of lithium insertion, respectively. The ohmic resistances at 100 kHz such as the ionic resistance of electrolyte and the resistance of passivating film in the spectra showed no difference between the electrodes with and without LATP. On the other hand, it was noted that the charge transfer resistance of electrode with LATP was significantly smaller than that of electrode without one. Furthermore, the activation energy for the charge transfer of the electrodes with LATP is estimated into 55.7 kJ/mol, which is smaller than that of the electrode without LCSP as shown in Fig. 2. These results indicate that LCSP and liquid electrolytes in the electrodes plays an important role of reducing the charge transfer resistance rather than enhancing the lithium ion conductivity in the electrolytes. Therefore, we consider that LCSP in the electrode enhances to provide lithium ions in the liquid electrolyte to the surface of the active materials, leading to maintain high concentration of lithium ions at the surface of active material. The detail of the mechanism for reducing the charge transfer resistance by containing LCSP to the electrode will be discussed in this presentation. [1] K. Yoshima, Y. Harada and N. Takami, J. Power Sources, 302,283-290(2016). [2] N. Takami, K. Yoshima and Y. Harada, J. Electrochem. Soc., 164,A6254(2017). Figure 1

Step Potential Electrochemical Spectroscopy (SPECS) Analysis Using Various Diffusion Model for Comparison of Spinel LiMn2O4 As Cathode Material for Li-Ion Battery (LIBs)

Step potential electrochemical spectroscopy (SPECS) or current transient technique for determining the mechanisms by which lithium ion transport through spinel LiMn2O4 positive electrode material during intercalation/de-intercalation was investigated. In this work, step potential electrochemical spectroscopy (SPECS) in three electrode systems have been conducted on spinel prepared by solid state and sol-gel methods. Based on the data obtained from the SPECS experiment the data has been fitted with planar, double planar and a spherical diffusional model, to better understand the diffusional mechanism and to obtain an accurate diffusional parameter for these materials. Theoretical models clearly illustrate that both spherical and double plane diffusion models are in excellent agreement with experimental data from beginning short time of the potential step till the end for long time 3600s. This work aims to develop a more comprehensive analysis technique for future work. By using SPECS technique, the various curves for Cottrellian type behaviour were also investigated, such as I(t)*sqrt(t) vs decimal logarithm as Li-ion insertion/de-insertion into the spinel. The crystal structure, materials morphology and elemental composition were characterized by x-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive x-ray spectroscopy (EDS), and high-resolution transmission electron microscopy (HR-TEM). These experiments reveal the potential benefits of understanding Li-ion diffusion of spinel LiMn2O4 for high-power lithium-ion batteries (LIBs) storage performance.

Li4Ti5O12/TiO2 dual-phase anode materials synthesized in supercritical water-methanol system and investigations on its superior electrochemical performance for lithium-ion batteries

Li4Ti5O12/TiO2 dual-phase composite compound is prepared through a supercritical fluid process with the mixture of water and methanol as solvothermal reaction media (380 °C and 31.5 MPa). When employed as anode material for lithium-ion batteries, the newly synthesized Li4Ti5O12/TiO2 composite exhibits a high initial discharge capacity of 191 mA h g−1 at a current density of 100 mA g−1, and delivers a capacity retention of 90.7% even after 500 cycles at 1000 mA g−1 with the voltage window of (1.0–2.5)V. The enhanced electrochemical performance is attributed to the oxygen vacancies, the phase grain boundaries and reduced size of the Li4Ti5O12/TiO2 composite particles. In addition, pseudocapacitive effect for the superior electrochemical performance of Li4Ti5O12/TiO2 dual-phase composite is investigated in detail. The carbon-free Li4Ti5O12/TiO2 dual-phase composite with high safety would be a promising candidate for applications in high-power lithium ion batteries.

An analytical approach to test a thermal management system for Li-ion battery under a real driving condition

A hybrid thermal management system (TMS) for high power lithium-ion battery modules of EVs with low energy consumption and high reliability was tested under a real state driving condition. An experimental investigation was performed to compare the hybrid TMS with an active air-cooling and a passive TMSs. We employed all three TMSs in standard weather conditions of 24 °C. For dynamic mode, a study of driving cycle in comparison with US, Europe, and Japan driving cycle data was conducted to perform a dynamic model based on a high traffic city to challenge our TMSs in a real driving state including high and standard discharge rate and a stop mode in which there was no air convection. The results showed that just in the hybrid TMS, the cell surface could reach a steady-state under 60 °C while the active TMS could keep temperature only for three cycles. Furthermore, our test proved that the proposed hybrid TMS maintains outstanding reliability and efficiency in the hot weather condition of 40 °C.

Lithiation-Induced Structural Rearrangement and Stress Change in SiCO-Derived Porous Carbon: A First-Principles Study

Silicon oxycarbide (SiCO)-derived porous carbon is a promising anode material for high-power lithium-ion batteries with large reversible capacity and high rate performance. In this work, porous carbon compounds with various morphologies are successfully reproduced by simulating the etching process of SiCO and then lithiation-induced structural rearrangement and stress change in porous carbon are investigated using first-principles calculations. Upon insertion of lithium, Si–C/O mixed-bond units are destroyed with breaking of Si–O bonds, the lithium atoms prefer to form bonds with oxygen, and the pores are gradually filled with the Li–O complex. The negative stress of the lithiated system indicates local compression of Si–C/O units, which is also demonstrated by the shorter Si–O bonds and enhanced bulk modulus. The local compression is related to constraint of the carbon network that act as a buffering structure to limit volume expansion during lithiation, and the increase and decrease in normal stress are related to the stretching and breaking of the carbon network. Moreover, it is revealed that the lithium content that corresponds to the maximum stress can be used to estimate the specific capacity of the system. Our analysis of the lithiation process provides a conceptual foundation for future design of porous carbon-based anode materials.

Going Nano with Confined Effects to Construct Pomegranate-like Cathode for High-Energy and High-Power Lithium-Ion Batteries.

Pomegranate-like Li3V2(PO4)3@C (LVP@C) cathode materials are fabricated through confined effect helped by the vacuum-assisted capillary action. The performance of LixV2(PO4)3 (x = 0-5) at an extended working voltage of 1.2-4.8 V has been studied by operando X-ray powder diffraction and hybrid functional density functional theory (DFT) calculation. The DFT calculation results suggest that Li3V2(PO4)3 can be intercalated with another two Li+ with a stable crystalline structure, which improves the specific capacity of LVP significantly. The cathode exhibits a specific capacity of 320 mAh g-1 with an energy density of 736 Wh kg-1, which is one of the best performances for intercalation cathode materials for Li-ion batteries to our knowledge. Besides, the cathode showed excellent rate capability. In the working potential of 3.0-4.8 V, it exhibits a high specific capacity of 195 mAh g-1 at 0.2 C, and even at a high rate of 30 C, it still delivers the specific capacity of 145 mAh g-1 with a power density of 15.93 kW kg-1. The good performance is mainly attributed to the unique pomegranate structure, which can provide continuous three-dimensional conductive networks for fast electron and Li-ion transfer. This paper provides a new strategy for synthesizing other cathode or anode materials with high energy and power density.

Three-dimensional spherical graphene coated nano-lithium iron phosphate cathode material for high power lithium ion batteries

Lithium iron phosphate LiFePO4 (LFP) nanoplatelets with crystals growth along the desired orientations were successfully coated onto the three-dimensional (3D) spherical graphene, through the electrostatic attraction, which can form the structure of 3D spherical graphene and the coating of nano-LFP particles at the same time. Various characterization techniques, including SEM, TEM, EDX, XRD, BET, galvanostatic charge-discharge, CV and EIS were applied to investigate the morphological structure, phase composition, carbon content, pore structure and electrochemical performance of the synthesized samples. Under optimized synthetic conditions the LFP nanoplatelets were tightly surrounded by 3D spherical graphene, which promises a good electronic contact between LFP and the 3D spherical graphene and effectively suppress the aggregation of the LFP crystals. Combined with the investigation results it can be concluded that the increase of introduced negatively charged graphene sheets and positively charged polystyrene spheres are responsible for both the improvement of conductivity and the formation of spherical porous structure of resultant samples. The good rate capability as well as the cycling stability of fabricated cathode material were ascribed to the well-crystallized nature and the desired crystal orientation of LFP as well as the bifunctional pathways for both Li+ and electron constructed by the 3D porous spherical graphene.

Electrochemical impedance analysis of Li[Li0.1Al0.1Mn1.8]O4 used as lithium-insertion electrodes by the diluted electrode method

Electrochemical impedance analysis was performed for Li[Li0.1Al0.1Mn1.8]O4 (LAMO) used as a lithium-insertion electrode by the diluted electrode method to identify the origin of resistance. Utilization of diluted electrodes, in which some portion of active material, LAMO, was systematically replaced with the same amounts of spectator Al2O3 material to maintain the original structure of the LAMO electrode, is a promising method to discriminate between the resistance attributed to the lithium-insertion reaction in LAMO (charge-transfer resistance) and that accompanied by conduction of electron and/or ion in the porous electrodes. Electrochemical impedance spectra of the diluted electrodes consisted of two semicircles. The radius of a semicircle in the lower frequency region depends on the LAMO content in a diluted electrode, indicating that the semicircle is associated with charge-transfer resistance. On the other hand, the radius of the other semicircle in the higher frequency region is independent of the LAMO contents, suggesting that the semicircle is mainly related to the resistance accompanied by the porous structure of electrodes. Thus, the structure of lithium-insertion electrode should be carefully considered in designing high-energy and high-power lithium-ion batteries that employ thick electrodes.

One-Step Synthesis of a Nanosized Cubic Li2TiO3-Coated Br, C, and N Co-Doped Li4Ti5O12 Anode Material for Stable High-Rate Lithium-Ion Batteries.

Nanosized Li4Ti5O12 with both a Li2TiO3 coating and C-N-Br co-doping (CLLTO) was successfully synthesized via a facile reverse microemulsion method in one step using hexadecyl trimethyl ammonium bromide as a surface control agent and as a carbon, nitrogen, and bromine source. A uniform Li2TiO3 layer was formed on the surface and strongly adhered to the host material Li4Ti5O12 (LTO), which played an important role in improving the cyclic stability of CLLTO. The thin and stable Li2TiO3 layer has the same cubic structure as LTO, which provides many three-dimensional channels for ion transport. C, N, and Br co-doping in CLLTO promoted the transition of Ti4+ to Ti3+ in Li4Ti5O12, which could improve the capacity and facilitate the Li+ ion and electron transfer at the interface. The conductive behavior induced by co-doping was estimated by UV-vis diffuse reflectance spectra and further supported by theoretical calculations. The electrical conductivity of both p-type and n-type LTO can be well improved by co-doping C, N, and Br. This improvement may be due to the band gap reduction and the increased n-type electronic modification of the entire LTO. Owing to the synergistic effect of coating, co-doping, and nanosizing at one time, the CLLTO exhibits a high discharge capacity of 177.3-153.9 mA h g-1 at the working rate of 0.1C-20C, with a capacity retention of 86%. The stable cycling of CLLTO is also obtained after 500 cycles at 20C, with a capacity retention of 95.5% (approximately 8 times higher than that of pure LTO) and almost 100% Coulombic efficiency. With high capacity, excellent rate performance, and good cycling stability, CLLTO can be applied in high-power lithium-ion batteries.

Rationally fabricating nitrogen-doped carbon coated nanocrystalline Li2FeSiO4@N-C with excellent Li-ion battery performances

Nitrogen-doped carbon coated nanocrystalline Li2FeSiO4@N-C cathode materials are rationally synthesized via tartaric acid assisted sol-gel method by using urea as the nitrogen source. The addition of urea not only successfully dopes N into the carbon coating but also decreases the average particle size by heat induced ammonium molecular releasing that affects the agglomeration process of the precursor sol. The optimized sample of Li2FeSiO4@N-C1 is composed of uniformly distributed Li2FeSiO4 nanocrystals with a diameter of ∼10 nm coating by N-doped carbon layer (about 1 nm). N-doping on the carbon layer significantly increases the electronic conductivity of Li2FeSiO4, and results in ultrahigh rate performance and excellent cycling stability for lithium storage. Li2FeSiO4@N-C1 delivers a high capacity of 246.1 mAhg−1 at 0.1 C that corresponds to reversible 1.48 Li+ storage capacity. Charge/discharge cycling at 0.5 C shows a steady capacity of 220 mAhg−1 without obvious capacity fading within 100 cycles. Thus, we believe that the nirogen-doped carbon coated nanocrystalline-Li2FeSiO4@N-C composites, possessing high-capacity and excellent cyclic performance, is a promising next-generation cathode material for high-power lithium-ion batteries.

Aramid nanofibers/polyphenylene sulfide nonwoven composite separator fabricated through a facile papermaking method for lithium ion battery

Separator is a vital component in lithium ion battery (LIB) and its property is directly related to cell performance and safety. However, the current widely used polyolefin separator suffers from lower heat resistant and inferior electrolyte wettability. Therefore, more attention has been attracted in the development of high performance separator. In this study, aramid nanofibers (ANFs), poly(p-phenylene terephthalamide), and heat-resistant polyphenylene sulfide (PPS) nonwoven were used to fabricate LIB composite separator by a facile papermaking process, which was abbreviated as ANFs/PPS. It was found that the introduced polar aramid nanofibers in this composite separator significantly regulated the porosity and improved electrolyte wettability, thus being helpful for lithium ion transfer between electrodes, increasing the ionic conductivity and exhibiting better interfacial compatible. These behaviors finally endowed battery with superior rate capability and excellent cycling performance. Moreover, the incorporation of aramid nanofibers in PPS membrane was confirmed to own higher Young's modulus to supply enough anti-deformation ability. In addition, we found the composite separator displayed outstanding thermal stability, flame retardant ability and broader electrochemical window, which would guarantee higher safety during battery operation. Accordingly, ANFs/PPS composite separator will provide a promising potential for application in high power LIB.

A Facile Way to Synthesize Carbon-Coated LiMn0.7Fe0.3PO4/Reduced Graphene Oxide Sandwich-Structured Composite for Lithium Ion Batteries

Introduction Olivine-type LiMnPO4 which is a cathode material for lithium ion batteries exhibits a higher operating potential (4.1 V vs. Li+/Li) than LiFePO4 thus has gathered more attention in recent years. However, due to the low electron conductivity of LiMnPO4 and the Jahn-Teller effect of Mn3+, it is difficult to achieve satisfied cycle performance. Fe doping of 10-30 mol% is promising as a solution to this problem [1]. Graphene is a single atomic monolayer of graphite and has been found a variety of applications in energy conversion and storage devices, due to the excellent properties such as high carrier mobility (~10,000 cm2 V−1 s−1 at room temperature), structural flexibility, chemical and thermal stability, mechanical strength and ultrahigh theoretical specific surface area (2630 m2g−1) [2]. Previous studies have reported the improved performance of LiMPO4 (M = Fe, Mn and Co by combining with graphene. In particular, it is attractive that the active material is supported on both sides of graphene to form a sandwich structure. One is that active material particles can be highly loaded and interconnected by the highly conductive matrix formed by graphene. The other one is that the sandwich structure can be beneficial for suppressing the graphene restacking and active material particles agglomeration. It is reported that such a graphene-metal oxide nanoparticle composite material can greatly improve the performances of the anode. However, there is still lack of a facial way to obtain ideally sandwich-structured composite material for cathode [3]. We will introduce a facial and high efficient way to synthesize carbon-coated LiMn0.7Fe0.3PO4 (LMFP)/reduced graphene oxide (rGO) sandwich-structured composite for high power lithium ion batteries [4]. Results and discussion The synthesis of sheet-like carbon-coated LMFP/rGO composite material is shown in Fig. 1. First, 0.3 g of LMFP powder (without carbon coating, average particle size 200 nm), 3 mL of oxidized graphite suspension and 0.04 g of sucrose are dispersed in 100 mL of water. Thereafter, by ultrasonic treatment for 2.5 hours, the oxidized graphite gradually peels off to form graphene oxide, and at the same time, the LMFP nanoparticles are supported on the surface of the GO by interaction with the GO functional group. The dissolved sucrose is coated with GO and LMFP particles to form a polymeric coating. After lyophilization, carbon coated LMFP/rGO composite material (LMFP/rGO@C) having a sandwich structure was obtained by heat treatment at 700 degrees under a reducing atmosphere. LMFP/rGO@C, acetylene black and binder were mixed at a mass ratio of 8:1:1 and coated onto Al foil to obtain a cathode electrode. Electrochemical characteristics were evaluated by preparing a 2032 type coin cell using Li foil as the counter electrode. The electrolyte was 1 mol dm-3 LiPF6/EC-DEC (1: 2). SEM image of the synthesized LMFP/rGO@C composite material is shown in Fig. 2. It is clearly observed that all the LMFP particles are uniformly dispersed on the rGO surface at high density (50 to 100 particles mm-2), forming a sandwich structure. The total content of rGO and carbon coating is estimated to be about 7 wt% from TG. Figure 3 shows the discharge rate performance of LMFP/rGO@C and carbon coated only LMFP (LMFP@C). It was confirmed that the discharge capacity of LMFP/rGO@C is greatly improved compared with LMFP@C. This should be due to the formation of a good three-dimensional conductive network by graphene. Acknowledgement We thank Taiheiyo Cement Co., Ltd for the providing of LiMn0.7Fe0.3PO4 powders and NIMS for the TEM measurement. Reference 1) Gong, et.al., Energy Environ. Sci. 4, 3223 (2011). 2) S. Han, et.al., Small. 9 1173–1187 (2013). 3) Z.-S. Wu, et.al. Nano Energy. 1 (2012). 4) D. Ding, et.al., submitted. Figure 1

Evaluation of High-Rate Pulsed Vs. Continuous Charging in Lithium-Ion Batteries

Many current and future Navy systems require high power lithium-ion batteries (LIB), with recent applications including directed energy weapons and the electromagnetic railgun pushing these requirements to new extremes. LIB with extremely high discharge rate are commercially available, however, high rate charging (or “fast charging”) is significantly more difficult to achieve due to complications occurring at the electrode-electrolyte interfaces as each electrode nears the edge of electrolyte stability. These problems are further exacerbated due to increased Ohmic heating with increasing current density, and can lead to potentially dangerous cell failure events. In this study, pulsed current charging was compared with continuous current charging during extended cycling of commercially available LIB with graphite anode and lithium iron phosphate cathode. Pulsed current charging has been shown in the literature to improve the efficiency and reduce the capacity loss penalties associated with continuous current charging. Charging limits at and above the manufacturers recommended operating limits were implemented. Degradation of cells was evaluated by monitoring cell temperature and impedance and accompanied by cell disassembly to analyze electrode degradation from the macro to the nanoscale using visual inspection, scanning electron microscopy (SEM), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy (XPS). Preliminary results show that in addition to the expected temperature rise associated with high current operation, fast charged cells lose capacity at a faster rate than cells charged at lower rates. Furthermore, signs of an increased solid electrolyte interface (SEI) layer thickness and lithium plating were also observed from cell disassembly.

Inhibiting Thermal Runaway in Large Format Li-Ion Batteries

NOHMs Technologies is developing novel safe solvent hybrid electrolytes for safe, high energy density, high voltage, and high-power lithium-ion batteries for mobility and consumer applications. Over the past 25 years there has been a proliferation in the use of lithium ion technology and with that ever-increasing market demand for higher energy density cells – demand primarily met by advancements in the cathode and anode. This proliferation has come with the increased rise of safety concerns. There have been high profile incidents of what is known as thermal runaway across a wide variety of applications ranging from consumer electronics to electric vehicles. It is well understood that thermal runaway occurs when the self-heating rate in the cell exceeds the heat dissipation out of the cell. This self-heating is the product of undesired side-reactions in the cell which are onset by abuse conditions such as excess heat, internal short circuits, etc. The key to inhibiting thermal runaway is to modify the cell such that the self-heating rate under abuse conditions is significantly reduced. Reducing the self-heating rate is important when considering battery packs that consist of many cells as is the case in electric vehicles, so that if one cell fails in a pack the thermal runaway does not propagate to adjacent cells. Given that market trends are moving away from low energy electrodes, our approach therefore is to modify the electrolyte system to reduce the overall cell self-heating rate. This is a tunable, drop-in solution to addressing the need for improving battery safety. The incorporation of NOHMs novel safe solvents into the electrolyte formulation is shown to impact the abuse tolerance of cells on both the material level, i.e. the electrolyte-electrode interaction and on the cell level. The presented electrolyte systems demonstrate reduced overall energy and peak heat flow in the exotherm profiles of high-nickel cathode materials as well as lithiated graphite via differential scanning calorimetry (DSC). With this approach, we demonstrate significantly lower self-heating rates in an accelerating rate calorimeter (ARC) heat-wait-seek test on 30 Ah and above high-nickel cathode lithium ion cells. Combined with good rate capability and cycle life NOHMs’ novel safe solvents present an improvement in battery safety without compromising battery performance. This approach carries significance in not just safer individual cells but also in safer overall battery packs.

An adaptive working state iterative calculation method of the power battery by using the improved Kalman filtering algorithm and considering the relaxation effect

The battery modeling and iterative state calculation in the battery management system is very important for the high-power lithium-ion battery packs, the accuracy of which affects its working performance and safety. An adaptive improved unscented Kalman filtering algorithm is developed to realize the iterative calculation process, aiming to overcome the rounding error in the numerical calculation treatment when it is used to estimate the nonlinear state value of the battery pack. As the sigma point is sampled in the unscented transform round from the unscented Kalman filter algorithm, an imaginary number appears that results in the working state estimation failure. In order to solve this problem, the decomposition is combined with the calculation process. Meanwhile, an adaptive noise covariance matching method is implied. Experiments show that the proposed method can guarantee the semi-positive and numerical stability of the state covariance, and the estimation accuracy can reach the third-order precision. The estimation error remains 1.60% under the drastic voltage and current change conditions, which can reduce the estimation error by 1.00% compared with the traditional method. It can provide a theoretical safety protection basis of the energy management for the lithium-ion battery pack.

Mesoporous titania anodes with tunable structural properties and improved electrochemical performance for Li-ion batteries

Abstract Mesoporous titanias (MTs) with controllable structural properties were successfully synthesized following a sol-gel method for improved electrochemical characteristics for lithium-ion batteries (LIBs). Under the experimental conditions studied herein, by carefully considering the synthesis conditions including template type, amount of nitric acid and template, the BET surface area, pore volume and pore size of the resulting MTs could be adjusted in wide ranges of 83 m2g-1 to 170 m2g-1, 0.10 cm3g-1 to 0.46 cm3g-1 and 3.1 nm–12.6 nm, respectively. When used as anode for LIBs, the intrinsic mesoporosity of MTs enabled the large contact interface with electrolyte, thus the substantially reduced resistance of lithium ions, afforded the MTs to possess good cycling performance and rate capability. Herein, a stable specific capacity of 131.2 mA h g−1 even after 1000 cycles at 1C rate was obtained. The capacity fade rate per cycle was only 0.016%, showing an excellent potential for application in high-power LIBs.

Understanding Interlayer Deprotonation of Hydrogen Titanium Oxide for High-Power Electrochemical Energy Storage

Negative electrode materials that possess fast lithium insertion kinetics are in high demand for high power lithium-ion batteries and hybrid supercapacitor applications. In this work, hydrogen titanium oxides are synthesized by a proton exchange reaction with sodium titanium oxide, resulting in the H2Ti3O7 phase. We show that a gradual water release in four steps yields intermediate phases of hydrogen titanate with different degrees of interlayer protonation. In addition, a synthesis route using zinc nitrate is explored yielding H2Ti3O7 with a high rutile content. This material dehydrates already at a lower temperature, resulting in a lamellar rutile titania phase. The hydrogen titanate materials with partially protonated interlayers are tested as negative electrodes in a lithium-ion battery and hybrid supercapacitor setup, showing an improved performance compared to the fully protonated phases. The performance in half-cells reaches around 168 mAh/g, with high retention of 42 mAh/g at 10 A/g. This transla...

Full-Cell Cycling of a Self-Supporting Aluminum Foil Anode with a Phosphate Conversion Coating.

Aluminum foil is a promising candidate anode material for lithium-ion batteries (LIBs), due to its high theoretical capacity, low lithiation voltage, and abundance. However, as a matter of fact, it has been a great challenge to make Al foil cycle in full cells at industrially acceptable areal capacities of 2-4 mAh/cm2 for commercial 18650 LIBs and some high-power LIBs. In this study, we defined the concepts of electrochemical true contact area (ECA) (areas with perfect electrolyte/electrode contact) and electrochemical noncontact area (ENA) (referred to regions without electrolyte spread on) for the metal foil anode. An initial ECA/ENA partition would cause severe inhomogeneity of the alloying reaction, cause localized electrode pulverization, and exacerbate ECA/ENA inequality even more. Through a phosphate conversion coating on aluminum foil, we killed two birds with one stone: first, the Al foil with a phosphate conversion coating has improved wettability (characterized by the contact angle that decreased from 35.2 to 15.9°) and favors the elimination of ENA, thus guaranteeing uniform electrochemical contact; also, the coating functions as an artificial solid electrolyte interface, which stabilizes the fragile naturally formed solid electrolyte interface and a "steady-state" electrolyte/electrode interface. Therefore, when pairing the phosphated Al foil anode against a commercial LiFePO4 (LFP) cathode (with ∼2.65 mAh/cm2), it can cycle 120 times without Li excess and stabilizes at 1.27 mAh/cm2.

Power capability and cyclic aging of commercial, high power lithium ion battery cells with respect to different cell designs

Commercially available, high power lithium ion batteries with capacities of about 3 Ah, on basis of different cell designs and mainly pouch format (but also one round cell) are cycled under continuous high discharge currents, up to 45C, to test for actual power capability. Using a different batch of cells, in addition low rate cycling tests (1C discharge) are carried out and compared to the respective high power procedures. Impedance measurements are conducted for full cells in their fresh and aged state. In addition, all cells are disassembled in their fresh and end of life states to gain further understanding on correlation of cell design (e.g. cell chemistry, electrode thickness, composition of active coating) and aging mechanisms. Therefore, the cells and electrodes are examined optically and characterized by means of XRD and SEM.It is found that there is a wide spread in quality of commercially available cells in terms of power capability, performance and aging. Aging mechanisms are discussed for all tested cells, and also the effect of high power vs. low power cycling. Aspects like SEI growth, change in particle size, cracking and impedance rise are systematically investigated and discussed.

High electrochemical performance of γ″-FeN thin film electrode for lithium ion batteries

Transition metal nitrides are promising alternative anode materials for the next-generation high-energy and high-power lithium ion batteries because of their large specific capacity and superior electronic and ionic conductivity. In this work, nanocrystalline γ″-FeN thin films are prepared by reactive magnetron sputtering and their lithium-storage performance is investigated. The γ″-FeN electrode retains high specific capacities of 1020.4 mAh/g after 100 discharge/charge cycles at the current density of 0.2 A/g and 667.1 mAh/g after 500 cycles at 2 A/g. Even at 10 A/g, a remarkable specific capacity of 469.0 mAh/g is achieved. Scanning and transmission electron microscopic analyses both prove that the microstructure of γ″-FeN thin film is durable against repeated lithiation and delithiation reactions.