Search

The ionic conductivity of electrolytes, fluid or solid, in lithium-ion cells is essential for the high-performance application in the automotive field. In colder temperatures, the literature shows the polymer solid-state approach has a weakness connected to ionic conductivity (Grundish et al., 2021; Kamaya and et al., 2011; Manthiram et al., 2017) [1-3]. At elevated temperatures the ionic conductivity rises and becomes attractive for the automotive usage. In this work, it is investigated how large automotive pouch cells, with polymer electrolyte and lithium-metal anode, can be heated up. Different heating systems and boundary conditions, as ambient temperature and heating power are investigated. Due to the anisotropic thermal conductivity in- and through-plane of the cell, a high variance in the heating time with different heating systems occurs, with up to 13% difference. A reciprocal effect of heating time and temperature spread inside one cell is observed - the shorter the heating time, the higher the temperature spread. Also, a strong influence of the ambient temperature can be seen. With lower surrounding temperature the heating time rises strongly. In comparison between the ambient temperatures -25 °C and 10 °C the heating time can be reduced by 17%. This work shows that the thermal behavior of new cell technologies needs to be investigated more closely.

Zero-excess Li metal batteries (ZELMBs), in which a Li-anode is formed in situ during charging, have received much attention in recent years. ZELMBs bear great potential to increase energy density and facilitate battery produc-tion, thereby reducing cost as well as material and energy consumption. Practical application of ZELMBs has so far been limited by challenges related to the non-uniform deposition behavior of Li, leading to inadequate perfor-mance and safety concerns. To address these issues, promising approaches have been developed in recent years, including modifications of the current collector, electrolyte, and cycling protocols. While these approaches improve the long-term stability of ZELMB, they also reduce the energy density by introducing inactive materials into the cell. Herein, critical design criteria for the various optimization approaches in ZELMB research are established. Nominal volumetric and gravimetric energy densities are determined based on the degree of modification. Thresholds are determined for each of the strategies at which the energy density gain of ZELMB vanishes compared to other cell configurations. These findings are compared to literature results to provide guidance for the further development of ZELMB.

To enable solid-state batteries with Li metal anodes, different classes of electrolytes are being investigated, mainly polymers, oxides, and sulfides. To overcome individual drawbacks of the material classes, so called bilayer hybrid cells combining layers of different electrolyte materials are considered highly promising. However, the introduction of an additional interface between the two solid electrolytes raises the question of the corresponding interfacial resistance. Herein, the properties of the interface between the two promising electrolytes Al-LLZO (Li6.16Al0.28La3Zr2O12) and LPS (Li7P3S11) are investigated by comprehensive impedance analyses. A series of systematic measurements allows to deconvolute the pressure dependence of the resistances related to the LPS material and the LPS/LLZO interface. This analysis reveals a significant pressure dependence of the LPS/LLZO interfacial resistance, mainly attributed to constriction resistance. Optimization of the LPS/LLZO interface is carried out by targeted surface treatment, resulting in a dramatic decrease of the interfacial resistance to virtually zero. These mechanistic studies and optimization approaches are complemented by practically relevant cycling tests using Li-metal electrodes. The cells show excellent cycling stability and negligible degradation. These findings contribute to the fundamental understanding of solid-solid interfaces in bilayer hybrid cells, indicating that solid-state batteries with hybrid LPS/LLZO electrolytes appear highly promising.

Understanding and optimizing the electrolyte wetting of lithium-ion cells provides a high potential to reduce the manufacturing costs of lithium-ion cells. However, established methods to investigate the wetting of porous materials are not easily transferable to lithium-ion cells, since they neglect major paths in the wetting process. In this study, a novel method is proposed to in situ quantify the wetting progress in lithium-ion cells with graphite-based anodes. A constant potential is applied to the cell immediately after the electrolyte wetting process has been initiated and the current response is carefully analyzed as it reflects the progress of the electrolyte wetting process accompanied by SEI film formation. By applying this procedure, the influence of different separators, cell formats and ambient temperatures on the wetting time is investigated. Furthermore, the wetting behavior of laser-structured electrodes is investigated as well as of electrodes with ceramic multilayer coating which can replace the standard separator. The results demonstrate that the interface between the separator and the electrodes plays a dominant role and mainly influences the wetting process of a lithium-ion cell. The findings point out the importance of using in situ methods to analyze the wetting process of lithium-ion cells.

Ionic conductivities of Li-ion conducting ceramic electrolytes, mostly evaluated by means of impedance spectroscopy, are a key parameter decisive for their application. Nevertheless, significant deviations in the ionic conductivity of nominally identical samples are reported in literature, which are attributed to material and sample preparation as well as measurement related differences. The goal of this study is a detailed assessment of impedance measurement deviations of 10 identically prepared samples of each Li6.45La3Zr1.6Ta0.4Al0.05O12 (LLZO:Ta:Al) and Li1.3Al0.3Ti1.7(PO4)3 (LATP), respectively. By introducing a harmonized testing procedure for impedance measurement and data analysis, deviations among the participating labs were reduced to differences

Filling of cells with liquid electrolytes is the time-determining step in the production of lithium-ion batteries (LIBs). The influencing factors are not completely understood and need furt...

The application of lithium-ion batteries is widely spread nowadays. They can be found especially in consumer electronics such as mobile phones and notebooks, as well as in the rapidly growing field of electric cars. Highly available power and energy density of a lithium-ion battery over its lifetime are crucial for their effective operation. A replacement of the battery is recommended if the capacity is reduced by aging to below 80% of the initial capacity. For the estimation of the remaining cell-life, a precise estimation of the state of charge (SoC) and state of health (SoH) is necessary. This cannot be assured by common battery management systems, which only rely on current counting and cell voltage measurements. This work presents the potential to determine the SoC and SoH of lithium-ion cells with elastic guided waves. As the propagation of guided waves is dependent on the density and elastic modulus of a media, a correlation between the state of charge and the measured amplitude and phase of the wave can be shown, as the porosity of the anode will change during charge and discharge. Experimental studies in a pitch-catch arrangement of piezoelectric transducers were conducted on a representative pouch cell. The attached transducer network allows the examination of multiple travel paths through the battery.

All solid-state batteries (ASSB) employing solid Li-ion conductors instead of liquid electrolytes are considered promising candidates for future energy storage solutions with increased energy density and improved safety properties. For oxidic electrolytes, this is enabled by proper densification of the mixed powder compacts made of oxidic solid electrolyte and active material, e. g. by sintering at high temperatures. For this purpose, oxide glasses with lower softening temperatures (< 1000 °C) are discussed as Li-conductive electrolyte. Herein, the synthesis of Li-ion conductive glasses in the system Li2O-Nb2O5-P2O5-LiCl by means of melting and quenching, powder preparation by milling and sintering of powder compacts in air are investigated. The highest Li-ion conductivity of 5.5 × 10−6 S/cm was obtained for the optimized composition of 40Li2O-10Nb2O5-30P2O5-20LiCl in glassy state as well as for glass ceramics obtained after sintering at 700 °C. The high Li-ion conductivity of the glasses is retained in the glass-ceramic microstructure after sintering, although crystallization, grain size and porosity significantly influence the resulting overall properties.

A simple semi-empirical master curve concept, describing the rate capability of porous insertion electrodes for lithium-ion batteries, is proposed. The model is based on the evaluation of the time constants of lithium diffusion in the liquid electrolyte and the solid active material. This theoretical approach is successfully verified by comprehensive experimental investigations of the rate capability of a large number of porous insertion electrodes with various active materials and design parameters. It turns out, that the rate capability of all investigated electrodes follows a simple master curve governed by the time constant of the rate limiting process. We demonstrate that the master curve concept can be used to determine optimum design criteria meeting specific requirements in terms of maximum gravimetric capacity for a desired rate capability. The model further reveals practical limits of the electrode design, attesting the empirically well-known and inevitable tradeoff between energy and power density.

To increase the user acceptance and to push electric mobility towards mass suitability, the energy and power density of Li-ion batteries for electric vehicles are among the most crucial features to be improved. The two major approaches to increase the energy density are the development of improved active materials and favorable cell designs. However, the identification of an optimal cell design is a sophisticated challenge due to the large number of interdependent factors influencing the different performance parameters. In the present study, a straightforward model based on the concept of diffusion-limited C-rate is proposed to optimize the energy density of Li-ion battery cells with specified rate performance. The model is introduced and the underlying assumptions are verified by comprehensive experimental investigations. The model is used to identify optimal design parameters of anode and cathode regarding maximum volumetric and gravimetric energy for specified rate performance. A sensitivity analysis is carried out to quantify optimization potentials of cell components and their properties. The results are discussed regarding promising improvement strategies and the practical limits of Li-ion batteries.

Layered Li(Co0.5Ni0.5)1−yFeyO2 (0.0 ≤ y ≤ 0.25) oxides were prepared by citric-acid assisted sol–gel method. Elemental and structural properties were investigated by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Raman scattering (RS) and Mossbauer spectroscopy, and magnetometry. EDX images show a homogeneous distribution of Fe ions. XRD and RS spectroscopy reveal that the materials crystallize as a LiNiO2 LiCoO2 LiFeO2 solid solution with the typical rhombohedral α-NaFeO2 structure (R 3 ¯ m S.G.) up to y = 0.2 at which composition a secondary phase was observed. For y > 0.2 the XRD results show the appearance of the α-LiFeO2 phase with the cubic structure (Fm3m S.G.). The degree of cation mixing investigated by XRD analysis and magnetic measurements is z

The key material for all-solid-state batteries is the solid electrolyte. In concepts with high energy density and capacity, this Li+ conductive component has two essential functions: Substituting the liquid electrolyte in the cathode and separating the cathode from the anode. Therefore, the research on Li+ conductive solids is one important step to realize high performing all-solid-state batteries. In this study, two different methods of preparing Li1.3Al0.3Ti1.7(PO4)3 (LATP) powder are compared with regard to particle size, phase purity and sintering properties. As top-down method the melting and as bottom-up route the sol-gel synthesis are applied. Spark Plasma Sintering (SPS) is used to densify the powders at temperatures between 800 and 1000 °C. The densities, the microstructures and the Li+ conductivities are compared in relation to the preparation method. Using sol-gel synthesis, the phase purity of the LATP powder is higher compared to the top-down route. The milling of the synthesized powder increases the homogeneity of the resulting microstructure and enhances the ionic conductivity. Room temperature Li+ conductivity of 1 × 10−3 S cm-1 with a high density of 99.4% was achieved with the milled, sol-gel synthesized powder at a sintering temperature of 1000 °C.

X-ray photoelectron spectroscopy (XPS) is a key method for studying (electro-)chemical changes in metal-ion battery electrode materials. In a recent publication, we pointed out a conflict in binding energy (BE) scale referencing at alkali metal samples, which is manifested in systematic deviations of the BEs up to several eV due to a specific interaction between the highly reactive alkali metal in contact with non-conducting surrounding species. The consequences of this phenomenon for XPS data interpretation are discussed in the present manuscript. Investigations of phenomena at surface-electrolyte interphase regions for a wide range of materials for both lithium and sodium-based applications are explained, ranging from oxide-based cathode materials via alloys and carbon-based anodes including appropriate reference chemicals. Depending on material class and alkaline content, specific solutions are proposed for choosing the correct reference BE to accurately define the BE scale. In conclusion, the different approaches for the use of reference elements, such as aliphatic carbon, implanted noble gas or surface metals, partially lack practicability and can lead to misinterpretation for application in battery materials. Thus, this manuscript provides exemplary alternative solutions.

The degradation of LiNi 0.8 Co 0.15 Al 0.05 O 2 (LNCAO), a cathode material in lithium-ion-batteries, was studied using in situ powder diffraction and in situ Ni K edge X-ray absorption spectroscopy (XAS). The fatigued material was taken from a 7 Ah battery which was cycled for 34 weeks under defined durability conditions. Meanwhile, a cell was stored, as reference, under controlled conditions without electrochemical treatment. The fatigued LNCAO used in this study showed a capacity loss of 26% ± 9% compared to the non-cycled material. During charge and discharge the local and the overall structure of LNCAO was investigated by X-ray near edge structure (XANES) analysis, the extended X-ray absorption fine structure (EXAFS) analysis and by using Rietveld refinement of in situ powder diffraction patterns. Both powder diffraction and XAS revealed additional, rhombohedral phases which do not change with electrochemical cycling. Moreover, a phase with the lattice parameters of fully lithiated LNCAO was still present in the fatigued material at high potentials, while it was absent in the non-fatigued reference material. The coexistence of these phases is described by domains within the LNCAO particles, in correlation with the observed fatigue.

The citric acid-assisted sol–gel method was used to produce the high-voltage cathodes LiNi 0.5 Mn 1.5 O 4 and LiNi 0.4 Ru 0.05 Mn 1.5 O 4 at 800 °C and 1000 °C final calcination temperatures. High resolution powder diffraction using synchrotron radiation, inductively coupled plasma – optical emission spectroscopy and scanning electron microscopy analyses were carried out to characterize the structure, chemical composition and morphology. X-ray absorption spectroscopy studies were conducted to confirm Ru doping inside the spinel as well as to compare the oxidation states of transition metals. The formation of an impurity Li x Ni 1− x O in LiNi 0.5 Mn 1.5 O 4 powders annealed at high temperatures ( T ≥ 800 °C) can be suppressed by partial substitution of Ni 2+ by Ru 4+ ion. The LiNi 0.4 Ru 0.05 Mn 1.5 O 4 powder synthesized at 1000 °C shows the highest performance regarding the rate capability and cycling stability. It has an initial capacity of ∼139 mAh g −1 and capacity retention of 84% after 300 cycles at C/2 charging–discharging rate between 3.5 and 5.0 V. The achievable discharge capacity at 20 C for a charging rate of C/2 is ∼136 mAh g −1 (∼98% of the capacity delivered at C/2). Since the electrode preparation plays a crucial role on parameters like the rate capability, the influence of the mass loading of active materials in the cathode mixture is discussed.

Finding appropriate positive electrode materials for Li-ion batteries is the next big step for their application in emerging fields like stationary energy storage and electromobility. Among the potential materials 3d-transition metal doped spinels exhibit a high operating voltage and, therefore, are highly promising cathode materials which could meet the requirements regarding energy and power density to make Li-ion batteries the system of choice for the above mentioned applications. The compounds considered here include substituted Mn-based spinels such as Li M 0.5 Mn 1.5 O 4 ( M = Ni, Co, Fe), LiCrMnO 4 and LiCrTiO 4 . In this review, the recent researches conducted on these spinel materials are summarized. These include different routes of synthesis, structural studies, electrode preparation, electrochemical performance and mechanism of Li-extraction/insertion, thermal stability as well as degradation mechanisms. Note that even though the Ni-, Co-, and Fe-doped materials share the same chemical formula, the oxidation state distributions as well as the operating voltages are different among them. Furthermore, apart from the initial structural similarity, the Li-intercalation takes place through different mechanisms in different materials. In addition, this difference in mechanism is found to have considerable influence on the long-term cycling stability of the material. The routes to improve the electrochemical performance of some of the above candidates are discussed. Further emphasis is given to the parameters that limit their application in current technology, and strategies to overcome them are addressed.

Commercial NMC cells of 18650-type based on a Lix(Ni0.5Mn0.3Co0.2)O2 cathode and a graphitic anode were studied in situ using a combination of high-resolution monochromatic neutron powder diffraction and electrochemical analysis. The structural changes of the electrode materials during cell charge/discharge have been determined using Rietveld refinement and single profile decomposition techniques. A transformation of the graphitic anode to LiC12 and LiC6 through the formation of higher ordered lithium intercalated carbons was observed. A different behavior of electrochemically-driven lattice distortion was observed for NMC material in comparison to LixCoO2 and its influence on the overall cell performance has been discussed in brief. Detailed analysis of the structural changes in the Lix(Ni0.5Mn0.3Co0.2)O2 cathode material revealed reversible Li/Ni cation mixing (5.6(8)%), which is state-of-charge independent below 1600 mAh and vanishing above 1800 mAh (∼0.8Qmax).

The high voltage spinel LiNi0.5Mn1.5O4 (LNMO) is a promising material to increase the energy density of lithium ion batteries. A variety of research was done to investigate the material regarding its properties, synthesis and commercial viability. To investigate in detail the properties of the cathode material during the delithiation and lithiation, in situ measurements are a helpful tool to fully understand changes in the crystal structure, which can give important information how to further improve the electrochemical properties of the cathode material. Especially the ‘ordered’ crystal phase P 4332 and the ‘unordered’ F d¯3 m, which can result from different temperature treatments during the synthesis process, need to be investigated to define the correlation between calcination temperatures, lattice parameters and electrochemical properties. The LNMO investigated was synthesized using a spray drying method. From a solution of acetate and nitrate salts precursors were produced which have been calcined under different conditions to support the crystallization into the ordered and unordered phase, respectively. First, the two powders were characterised by SEM analysis to investigate the crystal morphology. Then slurries (LiNi0.5Mn1.5O4, PVDF binder, carbon, NMP solvent) were prepared and cast on aluminium foil to prepare electrodes. The electrochemical properties of assembled test cells (capacity, cycle life, etc.) were measured. Customized coin cells were used for the in situ measurements. The in situ XRD were measured using the high energy, low-emittance synchrotron radiation source at the Petra III beamline P02.1 at the DESY in Hamburg. 1 In our presentation we will correlate the synthesis temperatures, electrochemical properties and lattice parameters for the synthesized LNMOs. By deeply analysing the in situ measured diffraction patterns for the different state of charge we will fully demonstrate the phase transition for the different samples and correlate the lattice change to properties like the manganese(III) amount and the crystal phase (figure 1). The manganese(III) amount is mostly dependent on the calcination temperature and therefore also on the received crystal phase. Furthermore, we will outline the influence on the degradation for the different samples. The degradation differences between the synthesized samples were investigated by analysing the cumulative charge and discharge capacity. 2 The combination of those results will lead to a deeper understanding of the connection between the different influence factors for the cathode material. References A.-C. Dippel, N. Bindzus, D. Saha, J. T. Delitz, H.-P. Liermann, N. Wahlberg, J. Becker, E. D. Bøjesen and B. Brummerstedt Iversen, Z. Anorg. Allg. Chem., 640(15), 3094–3099 (2014). A. J. Smith, J. C. Burns, D. Xiong and J. R. Dahn, J. Electrochem. Soc., 158(10), A1136 (2011). Figure 1

A brief review ofin situpowder diffraction methods for battery materials is given. Furthermore, it is demonstrated that the new beamline P02.1 at the synchrotron source PETRA III (DESY, Hamburg), equipped with a new electrochemical test cell design and a fast two-dimensional area detector, enables outstanding conditions forin situdiffraction studies on battery materials with complex crystal structures. For instance, the time necessary to measure a pattern can be reduced to the region of milliseconds accompanied by an excellent pattern quality. It is shown that even at medium detector distances the instrumental resolution is suitable for crystallite size refinements. Additional crucial issues like contributions to the background and availableqrange are determined.

LiNi0.33Co0.33Mn0.33O2 which was synthesized by co-precipitation method has been used to investigate the relationships between crystal/interfacial structures and electrochemical performance of the material in the voltage range of 2.5–4.6 V. X-ray diffraction showed that the material maintained high structural stability with charge–discharge cycling. Formation of SEI film was observed by transmission electron microscopy. The chemical compositions of the SEI film were analyzed by X-ray photoelectron spectroscopy, which were mainly composed of some organic compounds such as lithium alkyl carbonate RCH2OCO2Li, as well as some inorganic compounds such as LixPFy and LixPOyFz. Transmission electron microscopy showed that the SEI film gradually grew to a thickness of about 40 nm after 30 cycles. This caused larger and larger interfacial resistance with charge–discharge cycling, which has been attributed to the continuous capacity fading of LiNi0.33Co0.33Mn0.33O2 in the voltage window of 2.5–4.6 V.

Li-excess cathode material, Li1.13Ni0.3Mn0.57O2, was synthesized by the sol–gel method. The material has a reversible discharge capacity of 200 mAh g–1 at a current density of 40 mA g–1. In situ synchrotron X-ray diffraction, electrochemical impedance spectroscopy (EIS), and the galvanostatic intermittent titration technique (GITT) were applied to study the relationships between structural changes and electrochemical kinetics of Li1.13Ni0.3Mn0.57O2 during the first charge. When the charging potential was below 4.4 V, the c/a structural parameter of the material gradually increased, resulting in a higher layered character. The lithium diffusion coefficients during this process were about 10–14 cm2 s–1. When the charging potential was increased to 4.8 V, the bulk of the material was still maintained in a layered structure with space group symmetry R3m. The lithium diffusion coefficient and the charge transfer kinetics rapidly decreased because of the high kinetic barriers associated with concurrent Li+ ext...

The crystal structure of the 18650-type Li-ion cell constituents has been studied at ambient temperature by high-resolution neutron powder diffraction at different states of charge. The structure evolution occurring on the anode (graphite) site as a function of the cell state has been accurately monitored by simultaneous electrochemical measurements and powder diffraction. A set of 128 neutron powder diffraction patterns each over a 2θ angular range of 0.95°–160° has been collected during slow cell discharge/charge in a high-resolution mode. Severe deviations from the previously reported details of Li-intercalation into graphite have been observed, such as: structural evolution of the intercalated carbons depending either on charge or discharge; pronounced dependence of the interatomic spacings for the higher ordered LixC6 (incl. previously unknown ones). Instead of higher stages of Li-intercalation in the region of low Li-contents, which would have been observed by Bragg reflections at low 2θ angles, a modulation within the ab-planes is proposed, which is correlated between neighboured graphene layers and changes in dependence of the Li-content. On the basis of these results the phase diagram for lithium-intercalated carbons has been reconsidered and the alternative ordering model for the LixC6 (x < 0.5) has been proposed.

Anode and cathode materials, graphite and LiCoO2, are studied by neutron diffraction under “in operando” conditions in commercial batteries (ICR 18650-type). The evolution of their crystal structure versus state of charge (SOC) and fatigue (state of health, SOH) has been analyzed using the Rietveld refinement technique. Neutron radiography data and their tomography reconstruction revealed the local neutron absorption density, which reflects mainly the Li-distribution density, but also further details of the battery design. Changes in the neutron absorption contrast have also been evaluated in dependence on SOC and SOH.

In situ high-resolution neutron powder diffraction along with electrochemical analysis was applied to study fatigue processes in commercial LiCoO2 (18650-type, 2600 mAh, 3.0–4.2 V) cells. The Rietveld refinement technique was successfully applied for structural characterization of the cell materials as function of fatigue introduced. The capacity loss determined from the electrochemical investigation has been found proportional to the number of cycles, which the cell underwent, and was 21.9% and 12.8% for the cell cycled for 1000 times at 25◦C and 50◦C, respectively. This capacity fade has a close correlation to the structural changes in cathode and anode materials with the cell fatigue.Achange of the lithium occupation and lattice parameters of the LixCoO2 were observed with proceeding battery fatigue. Transformation of the graphitic anode into LiC6 and LiC12 was identified after the batteries were fully charged. Their weight ratio was found to be dependent on the number of executed cycles. It was concluded that loss of the active lithium in both cathode and anode as well as microstructure changes on the anode side are important factors for the battery degradation. A favorable influence of the elevated cycling temperature on the battery performance was observed.

Rod-shaped α-MnO 2 has been synthesized by a novel and facile wet chemical method using simple sugar and potassium permanganate. Redox reaction between KMnO 4 and sucrose is carried out in an acidic medium. Acidic medium provides a reducing character to sucrose through its decomposition to elemental carbon. Carbon coating process was done using simple sugar also as a source for carbon in an absolute ethanol with heating the mixture of α-MnO 2 and sugar at 350 °C for an hour in an ambient atmosphere. A single phase of cryptomelane-like phase MnO 2 was observed from XRD patterns for bare and carbon coated samples. TGA analysis shows the presence of carbon layer through more weight loss percent of carbon coated sample in comparison with that of carbon free MnO 2 . Both virgin and carbon coated MnO 2 have high thermal stability due to high percent of K inside the tunnel determined from ICP analysis. Transmission Electron Microscope (TEM) showed a rod-shaped crystal for both the parent and carbon coated α-MnO 2 and confirmed the presence of a thin film of carbon around MnO 2 particles. Both XRD and TEM investigations show that the prepared powders are in nano-scale. Initial capacity of about 140 mAh/g was obtained for the parent and carbon coated samples. The results show also that carbon coating process improves the capacity retention and the efficiency of α-MnO 2 in comparison with that carbon free sample.

Li-ion batteries have to be improved for high-performance applications especially for automotive application. One aim is the search for new electrode materials with superior properties and their detailed characterization. We used 'quasi in situ' X-ray photoelectron spectroscopy (XPS) to investigate electrode material of the spinel-type LiCrMnO 4 for the cathode during electrochemical cycling. It was found that during charging (de-intercalation of Li from the cathode) chromium is converted from Cr 3+ to Cr 6+ , whereas manganese changes from Mn 4+ to Mn 3+ . Especially when charging to the maximum capacity (at about 5.2 V), this conversion seems to be partially irreversible. The chemical and structural changes connected with this conversion are the possible reason for the irreversible capacity loss at such high charging voltages, which is confirmed by the analysis of the electrode material after 100 charging/discharging cycles.

LiNi0.5Mn0.5O2 powder was synthesized by a coprecipitation method. LiOH.H2O and coprecipitated [(Ni0.5Mn0.5)C2O4] precursors were mixed carefully together and then calcined at 900°C. Surface modified cathode materials were obtained by coating LiNi0.5Mn0.5O2 with a thin layer of amorphous carbon using table sugar and starch as carbon source. Both parent and carbon-coated samples have the characteristic layered structure of LiNi0.5Mn0.5O2 as estimated from X-ray diffractometry measurements. Transmission electron microscope showed the presence of C layer around the prepared particles. TGA analysis emphasized and confirmed the presence of C coating around LiNi0.5Mn0.5O2. It is obvious that the carbon coating appears to be beneficial for the electrochemical performance of the LiNi0.5Mn0.5O2. A capacity of about 150 mAh/g is delivered in the voltage range 2.5–4.5 V at current density C/15 for carbon coated LiNi0.5Mn0.5O2 in comparison with about 165 mAh/g obtained for carbon free LiNi0.5Mn0.5O2 at the same current density and voltage window. About 92% and 82% capacity retention was obtained at 50th cycle for coated LiNi0.5Mn0.5O2 using sucrose and starch, respectively; whereas, 75% was retained after only 30th cycle for carbon free LiNi0.5Mn0.5O2. This improvement is mainly attributed to the presence of thin layer of carbon layer that encapsulate the nanoparticles and improve the conductivity and the electrochemical performance of LiNi0.5Mn0.5O2.

Li[Li0.23Co0.3Mn0.47]O2 cathode material was prepared by a sol–gel method. The material had a primary particle size of about 100 nm, covered by a 30 Å of Li2CO3 layer. The material showed promising electrochemical performance when cycled up to 3C rate. The electrochemical kinetics of the first charge was much slower than that of the second charge, due to the complex electrochemical process which involved not only Li+ diffusion but also release of oxygen. By taking account of this, the material was pre-charged very slowly (∼C/50) in the first cycle. This led to excellent electrochemical performance in the following cycles. For instance, the 1C-rate capacity increased to 168 mA h g−1 after 50 cycles, comparing with the 145 mA h g−1 obtained without pre-charging. Keywords: Lithium ion battery, Cathode material, Nano material, Electrochemical kinetics, Cycling performance

Cr 0.1 V 2 O 5.15 was prepared by an oxalic acid assisted sol–gel method. X-ray diffraction showed that Cr doping induced a slight expansion (ΔV/V ≈ 2.3%) in the crystal lattice of V 2 O 5 . The electrochemical properties of Cr 0.1 V 2 O 5.15 in the potential range of 3.8–2.0 V were studied by cyclic voltammetry, galvanostatic charge–discharge cycling and potentiostatic intermittent titration technique. Cyclic voltammetry showed that the irreversible phase transition of V 2 O 5 during the first cycle was effectively prevented by Cr doping. This caused the good charge–discharge cycling performance of the doped material. The discharge capacities were recorded to be 200, 170 and 120 mAhg − 1 after fifty cycles at the C/10, C/2 and 1C rates, respectively. However, ex-situ X-ray diffraction showed that the crystal structure of the material was destroyed after long-term cycling. The lithium diffusion coefficient of Cr 0.1 V 2 O 5.15 varied between 10 − 11 and 10 − 12 cm 2 s − 1 , which was larger than that of crystalline V 2 O 5 , and was close to those of metal doped V 2 O 5 in previous reports. The improvement in lithium diffusion kinetics was regarded as an important reason for the good electrochemical performance of Cr 0.1 V 2 O 5.15 .

Multi-phase Fe90−xZr10Crx alloys with 0 ≤ x ≤ 10 containing cubic C15 and hexagonal C14/C36 Laves phases have been prepared by copper mold casting. The microstructure of the samples consists of micrometer-sized Laves phase particles embedded in an ultrafine eutectic matrix of alternating lamellae of α-Fe and Laves phases. Room temperature compression tests of the binary alloy reveal a high strength of 1900 MPa combined with a plastic strain of about 9%. The addition of Cr improves the plastic strain up to 17% while reducing the strength only by about 70 MPa. The increased plastic deformation is linked to the specific structural features of the Laves phases. For the binary alloy, shearing and crack formation within the C15 phase limits plastic deformation. In contrast, in the samples containing Cr no shearing occurs within the C14/C36 phases and crack formation, which is observed at the particle/ferrite interface, is retarded.

In situ synchrotron diffraction experiments were performed to study the behaviour of the cathode material LiNi0.8Co0.2O2 at high cycle numbers. The battery-cell was cycled 140 times between 4.2 and 2.7 V. The initial cycle and several cycles at proceeded degradation of the cell were investigated. In between the cell was cycled ex situ. The evolution of the lattice parameters during cycling was determined for the different stages of degradation by means of Rietveld refinement. Comparing the initial cycle of the cell with the higher cycle numbers, the mechanism of lithium insertion/extraction does not change significantly. But, the range in which the lattice parameters change during one cycle becomes smaller. This can be attributed to interface layer formation and to slightly less lithium exchange in the same voltage window.

The electrochemical behavior and structural changes of the positive electrode material LiCrMnO4 are studied for different end-of-charge voltages. A potentiostatic intermittent titration technique (PITT) experiment performed up to 5.2 V shows three oxidative peaks. Cells charged to 4.88 V, which corresponds to the minimum between the second and the third oxidative peak, show 89% of capacity retention for the 60th cycle. Compared to that only 23% of capacity are preserved in the 60th cycle when the cell is charged to 5.2 V. The structural analysis by Rietveld refinement shows that for the former case, the amount of structural defects is low and their formation is reversible, while the defect amount is significantly higher for the latter case and the defect formation is only partially reversible.

HT-LiMnO2 was prepared by a solid-state reaction at 900 °C. Electrochemical charge–discharge cycling of HT-LiMnO2 showed an initial charge capacity 113 mA h g− 1, followed by a small first discharge of 25 mA h g− 1. The discharge capacity subsequently increased and reached up to ∼ 120 mA h g− 1 after 30 cycles. In situ synchrotron diffraction showed that HT-LiMnO2 transformed to a new phase (Phase II) during the first charge process, which was metastable and could easily convert to spinel LiMn2O4 in the following cycles. The progressive formation of this spinel phase was responsible for the capacity increase of the battery in the first cycles. The different cycling performance of HT-LiMnO2 and LT-LiMnO2 was attributed to the large stacking faults in LT-LiMnO2, which may facilitate the material to completely convert to spinel LiMn2O4 in the first charge without the medium transition to Phase II.

In situ synchrotron diffraction revealed a stepwise appearance of two new phases upon electrochemical lithium extraction from LiCoPO4. These phases were demonstrated to have the same olivine-like structure as the pristine compound. The lithium-deficient phases were proposed to be Li0.7CoPO4 and CoPO4. The completely delithiated phase appears to be unstable in air and undergoes amorphization. The phase transitions are reversible, but a slow kinetics of the initial delithiation was identified by in situ synchrotron diffraction and the potentiostatic intermittent titration technique. We demonstrated that the electrochemical extraction of lithium is accompanied by significant electrolyte decomposition, contributing to the capacity loss upon cycling. The galvanostatic intermittent titration technique combined with impedance spectroscopy revealed self-discharge of the cell in the charged state. This study argues different mechanisms of lithium extraction from LiCoPO4 in comparison with LiFePO4 and LiMnPO4.

Lithium has been electrochemically extracted and inserted from LixNi0.8Co0.2O2 (0{less than or equal to}xLi{less than or equal to}1) using a dedicated electrochemical cell. The behavior of this cathode material for lithium batteries was studied by in situ-X-ray diffraction using synchrotron radiation and analyzed by Rietveld refinement. Besides the accurate determination of the lattice parameters during cycling, an anisotropic broadening of specific reflections, most pronounced around xLi=0.1, is observed and attributed to reversible microstructural changes at this high degree of lithium extraction.