Investigation of the Degradation Mechanism of Ni-rich NMC Cathode Material in Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are state-of-the-art battery systems for electrical vehicles (EVs) and thus a key-technology for an emission-reduced future [1]. Besides anode and electrolyte, the cathode site plays an important role for the performance of a battery. Ni-rich NMC (LixNiyMnzCo1-y-zO2, with x > 0, y > 0.6) is the most promising candidate of cathode materials due to its high capacity, high energy density and low costs [1]. However, structural instability is a drawback of a high nickel content leading e.g., to phase transition under high voltages, washing and heat treatment [1,2]. Although it is clear, that a phase transition from layered structure (space group R-3m) over an intermediate spinel-phase (space group Fd-3m) to rocksalt structure (space group Fm-3m) takes place, it is controversially discussed how fast and thick the rocksalt layer grows and if it has a positive influence on the electrochemical performance up to a certain thickness [3-5].One urgent question is, how fast and heavily Ni-rich NMC degrades if it is held at high voltages for long timespans. To answer this question, battery cells were set to 4.5 V for a varying number of days.The formed rocksalt layers were imaged at the atomic scale using scanning transmission electron microscopy (STEM) to obtain valuable information about the phase transition occurring at the surface of the particles. Figure 1 shows STEM images of a battery cell after 30 days, where a pronounced rocksalt layer of roughly 20 nm is visible, indicating degradation of the cathode.The time-dependent study provides a better understanding of the aging of Ni-rich NMC cathodes caused by cut-off voltages

Off-stoichiometry, Vacancy Trapping and Pseudo-irreversible First-cycle Capacity in LiNiO2

We demonstrate that the ubiquitous off-stoichiometry of LiNiO2 in the form of Li_{1-z}Ni_{1+z}O2 slows the kinetics of the material both by diminishing the number of charge carriers and increasing the length of diffusion paths. Excess Ni in the Li layer, Ni_{Li}, exerts an attractive potential on Li vacancies, lowering their energy with respect to defect-free regions. This attractive field extends over a radius of two lattice sites and also considerably lowers the barrier for a Li vacancy to approach the defect, effectively making Ni_{Li} a sink for lithium vacancies. A similar argument can be made for divacancies, which are split by Ni_{Li} and pinned in the form of single vacancies. In addition to pinning effects, which could vary depending on the state of charge, Ni_{Li} also constitutes an obstacle to Li migration, because it is rather immobile and does not undergo site-exchange with an adjacent Li vacancy

Off-stoichiometry, vacancy trapping, and pseudo-irreversible first-cycle capacity in LiNiO₂

We demonstrate that the ubiquitous off-stoichiometry of LiNiO2 in the form of Li1–zNi1+zO2 slows the kinetics of the material by both diminishing the number of ionic charge carriers and increasing the length of diffusion paths. The positive charge of excess Ni in the Li layer, along with the accompanying local chemomechanical strain, creates an attractive potential for Li vacancies, thereby reducing their energy compared to defect-free regions. This attractive field extends over a radius of two lattice sites and also considerably lowers the migration barrier for a Li vacancy to approach the defect, effectively making excess Ni a sink for lithium vacancies. A similar argument can be made for divacancies, which are split by the extra Ni and pinned in the form of single vacancies. In addition to pinning effects, which could vary depending on the Li concentration, excess Ni also constitutes an obstacle to Li migration because it is rather immobile and does not undergo site exchange with an adjacent Li vacancy

State of Charge-Dependent Impedance Spectroscopy as a Helpful Tool to Identify Reasons for Fast Capacity Fading in All-Solid-State Batteries

Thiophosphate-based all-solid-state batteries (ASSBs) are considered the most promising candidate for the next generation of energy storage systems. However, thiophosphate-based ASSBs suffer from fast capacity fading with nickel-rich cathode materials. In many reports, this capacity fading is attributed to an increase of the charge transfer resistance of the composite cathode caused by interface degradation and/or chemo-mechanical failure. The change in the charge transfer resistance is typically determined using impedance spectroscopy after charging the cells. In this work, we demonstrate that large differences in the long-term cycling performance also arise in cells, which exhibit a comparable charge transfer resistance at the cathode side. Our results confirm that the charge transfer resistance of the cathode is not necessarily responsible for capacity fading. Other processes, such as resistive processes on the anode side, can also play a major role. Since these processes usually depend on the state of charge, they may not appear in the impedance spectra of fully charged cells; i.e., analyzing the impedance spectra of charged cells alone is insufficient for the identification of major resistive processes. Thus, we recommend measuring the impedance at different potentials to get a complete understanding of the reasons for capacity fading in ASSBs

Mapping and predicting mortality from systemic sclerosis

To determine the causes of death and risk factors in systemic sclerosis (SSc).status: publishe

Mapping and predicting mortality from systemic sclerosis

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Mapping and predicting mortality from systemic sclerosis

OBJECTIVES: To determine the causes of death and risk factors in systemic sclerosis (SSc). METHODS: Between 2000 and 2011, we examined the death certificates of all French patients with SSc to determine causes of death. Then we examined causes of death and developed a score associated with all-cause mortality from the international European Scleroderma Trials and Research (EUSTAR) database. Candidate prognostic factors were tested by Cox proportional hazards regression model by single variable analysis, followed by a multiple variable model stratified by centres. The bootstrapping technique was used for internal validation. RESULTS: We identified 2719 French certificates of deaths related to SSc, mainly from cardiac (31%) and respiratory (18%) causes, and an increase in SSc-specific mortality over time. Over a median follow-up of 2.3 years, 1072 (9.6%) of 11 193 patients from the EUSTAR sample died, from cardiac disease in 27% and respiratory causes in 17%. By multiple variable analysis, a risk score was developed, which accurately predicted the 3-year mortality, with an area under the curve of 0.82. The 3-year survival of patients in the upper quartile was 53%, in contrast with 98% in the first quartile. CONCLUSION: Combining two complementary and detailed databases enabled the collection of an unprecedented 3700 deaths, revealing the major contribution of the cardiopulmonary system to SSc mortality. We also developed a robust score to risk-stratify these patients and estimate their 3-year survival. With the emergence of new therapies, these important observations should help caregivers plan and refine the monitoring and management to prolong these patients' survival

Incidence and predictors of cutaneous manifestations during the early course of systemic sclerosis: a 10-year longitudinal study from the EUSTAR database

Objectives: To longitudinally map the onset and identify risk factors for skin sclerosis and digital ulcers (DUs) in patients with systemic sclerosis (SSc) from an early time point after the onset of Raynaud's phenomenon (RP) in the European Scleroderma Trials and Research (EUSTAR) cohort. Methods: 695 patients with SSc with a baseline visit within 1 year after RP onset were followed in the prospective multinational EUSTAR database. During the 10-year observation period, cumulative probabilities of cutaneous lesions were assessed with the Kaplan–Meier method. Cox proportional hazards regression analysis was used to evaluate risk factors. Results: The median modified Rodnan skin score (mRSS) peaked 1 year after RP onset, and was 15 points. The 1-year probability to develop an mRSS ≥2 in at least one area of the arms and legs was 69% and 25%, respectively. Twenty-five per cent of patients developed diffuse cutaneous involvement in the first year after RP onset. This probability increased to 36% during the subsequent 2 years. Only 6% of patients developed diffuse cutaneous SSc thereafter. The probability to develop DUs increased to a maximum of 70% at the end of the 10-year observation. The main factors associated with diffuse cutaneous SSc were the presence of anti-RNA polymerase III autoantibodies, followed by antitopoisomerase autoantibodies and male sex. The main factor associated with incident DUs was the presence of antitopoisomerase autoantibodies. Conclusion: Early after RP onset, cutaneous manifestations exhibit rapid kinetics in SSc. This should be accounted for in clinical trials aiming to prevent skin worsening

Phenotypes Determined by Cluster Analysis and Their Survival in the Prospective European Scleroderma Trials and Research Cohort of Patients With Systemic Sclerosis

Objective Systemic sclerosis (SSc) is a heterogeneous connective tissue disease that is typically subdivided into limited cutaneous SSc (lcSSc) and diffuse cutaneous SSc (dcSSc) depending on the extent of skin involvement. This subclassification may not capture the entire variability of clinical phenotypes. The European Scleroderma Trials and Research (EUSTAR) database includes data on a prospective cohort of SSc patients from 122 European referral centers. This study was undertaken to perform a cluster analysis of EUSTAR data to distinguish and characterize homogeneous phenotypes without any a priori assumptions, and to examine survival among the clusters obtained. Methods A total of 11,318 patients were registered in the EUSTAR database, and 6,927 were included in the study. Twenty-four clinical and serologic variables were used for clustering. Results Clustering analyses provided a first delineation of 2 clusters showing moderate stability. In an exploratory attempt, we further characterized 6 homogeneous groups that differed with regard to their clinical features, autoantibody profile, and mortality. Some groups resembled usual dcSSc or lcSSc prototypes, but others exhibited unique features, such as a majority of lcSSc patients with a high rate of visceral damage and antitopoisomerase antibodies. Prognosis varied among groups and the presence of organ damage markedly impacted survival regardless of cutaneous involvement. Conclusion Our findings suggest that restricting subsets of SSc patients to only those based on cutaneous involvement may not capture the complete heterogeneity of the disease. Organ damage and antibody profile should be taken into consideration when individuating homogeneous groups of patients with a distinct prognosis