65 research outputs found
From Lithium-Ion to Sodium-Ion Batteries
The research is mainly motivated by the abundance of sodium and the larger amount of sodium compounds in comparison with lithium
Towards low-cost sodium-ion batteries: electrode behavior of graphite electrodes obtained from spheroidization waste fractions and their structure-property relations
Electrode materials for lithium-ion batteries (LIBs) typically show spherical particle shapes. For cathode materials, the spherical shape is obtained through the synthesis method. For graphite, the by far most popular anode material for LIBs, spherical particles are obtained through a spheroidization process. The yield of that process is quite low and limited to about 50%, leaving substantial amounts of by-products. Using such lower quality by-products would be quite attractive for developing low-cost energy stores like sodium-ion batteries (SIBs), for which the requirements for particle sizes and shapes might be less strict as compared to high performing LIBs. Here, we study three different graphite âwaste fractionsâ as anode material for SIBs that are obtained from the spheroidization process and how they compare to LIB battery grade material. Only negligible differences between the fractions are found when analyzing them with x-ray diffraction (XRD), Raman spectroscopy and elemental analysis (EA). More clear differences can be seen from N2 physisorption, scanning electron microscopy (SEM) and particle size analysis. For example, the surface areas of the âwaste fractionsâ can become roughly up to twice as large as compared to the battery grade fraction and the d
50 values shift by up to 11.9 ”m to lower numbers. Electrochemical measurements show that the âwaste fractionsâ can deliver the full electrode capacity and behave similar to the battery grade fraction up to 10 C. However, the higher surface areas lead to more irreversible losses in the first cycle. A surprising finding is that all graphite fractions show almost identical discharge voltages, while the charging voltages differ by as much as 200 mV. This asymmetric behavior only occurs in SIBs and not in LIBs, which indicates a more complex storage behavior in case of sodium.H2020 European Research Councilhttp://dx.doi.org/10.13039/100010663Bundesministerium fĂŒr Bildung und Forschunghttp://dx.doi.org/10.13039/501100002347Deutsche Forschungsgemeinschafthttp://dx.doi.org/10.13039/501100001659EIG Concert JapanPeer Reviewe
In Situ Pore Formation in Graphite Through Solvent Co-Intercalation: A New Model for The Formation of Ternary Graphite Intercalation Compounds Bridging Batteries and Supercapacitors
For Liâion and Naâion batteries, the intercalation behavior of graphite anodes is quite different. While Liâions intercalate, Naâions only coâintercalate with solvent molecules from the electrolyte solution leading to ternary graphite intercalation compound (tâGIC) formation along with an expansion of the graphite interlayer spacing to 1.2Â nm. This large interlayer spacing represents a micropore with parallel slit geometry. Little is known about tâGIC formation, but it is commonly believed that throughout the reaction the ion is accompanied by either a full or partial solvation shell. Here, it is elucidated for the first time, using two independent methods â mass measurements and electrochemical impedance spectroscopy â supplemented by operando microscopy, entropymetry and simulations, that the storage mechanism is far more complex. A new model for the electrochemical solvent coâintercalation process is proposed: As soon as solvated ions enter, the graphite structure is flooded with free solvents, which are subsequently replaced by solvated ions. Close to full sodiation, few free solvents remain and structural rearrangement take place to reach the full storage capacity. Thus, tâGICs represent a unique case of switchable microporous systems and hence appear as a bridge between ion storage in the bulk phase and in micropores, i.e., between batteries and supercapacitors.Peer Reviewe
Copper Thiophosphate (Cu3PS4) as Electrode for Sodium-Ion Batteries with Ether Electrolyte
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Abstract
Lithium and sodium thiophosphates (and related compounds) have recently attracted attention because of their potential use as solid electrolytes in solidâstate batteries. These compounds, however, exhibit only limited stability in practice as they react with the electrodes. The decomposition products partially remain redox active hence leading to excess capacity. The redox activity of thiophosphates is explicitly used to act as electrode for sodiumâion batteries. Copper thiophosphate (Cu3PS4) is used as a model system. The storage behavior between 0.01 and 2.5 V versus Na+/Na is studied in half cells using different electrolytes with 1 m NaPF6 in diglyme showing the best result. Cu3PS4 shows highly reversible charge storage with capacities of about 580 mAh gâ1 for more than 200 cycles @120 mA gâ1 and about 450 mAh gâ1 for 1400 cycles @1 A gâ1. The redox behavior is studied by operando Xâray diffraction and Xâray photoelectron spectroscopy. During initial sodiation, Cu3PS4 undergoes a conversion reaction including the formation of Cu and Na2S. During cycling, the redox activity seems dominated by sulfur. Interestingly, the capacity of Cu3PS4 for lithium storage is smaller, leading to about 170 mAh gâ1 after 200 cycles. The results demonstrate that thiophosphates can lead to reversible charge storage over several hundred cycles without any notable capacity decay.Peer Reviewe
Designing Cathodes and Cathode Active Materials for SolidâState Batteries
Solid-state batteries (SSBs) currently attract great attention as a potentially safe electrochemical high-energy storage concept. However, several issues still prevent SSBs from outperforming today\u27s lithium-ion batteries based on liquid electrolytes. One major challenge is related to the design of cathode active materials (CAMs) that are compatible with the superionic solid electrolytes (SEs) of interest. This perspective, gives a brief overview of the required properties and possible challenges for inorganic CAMs employed in SSBs, and describes state-of-the art solutions. In particular, the issue of tailoring CAMs is structured into challenges arising on the cathode-, particle-, and interface-level, related to microstructural, (chemo-)mechanical, and (electro-)chemical interplay of CAMs with SEs, and finally guidelines for future CAM development for SSBs are proposed
TinâContaining Graphite for SodiumâIon Batteries and Hybrid Capacitors
The limited Na-storage capacity of graphite anodes for sodium-ion batteries (âŒ110â
mAhâgâ1) is significantly enhanced by the incorporation of nanosized Sn (17â
wt%). The composite (SntGraphite), prepared by simple annealing of graphite with SnCl2, shows a specific capacity of 223â
mAhâgâ1 (at 50â
mAâgâ1) combined with excellent cycle life (i.âe., 96â% of capacity retention after 2,200 cycles at 1â
Aâgâ1) and initial Coulomb efficiency (90â%). The combined storage of sodium in graphite (by solvent co-intercalation) and Sn (by alloy formation) is followed by inâ
situ X-ray diffraction and inâ
situ electrochemical dilatometry (ECD). While the additional tin almost doubles the electrode capacity, its contribution to the electrode expansion (âŒ3â%) is surprisingly small. The use of SntGraphite as anode for sodium-ion hybrid capacitors with activated carbon as cathode provides a maximum energy and power density of âŒ93â
Whâkgâ1 and 7.8â
kWâkgâ1, with a capacity retention of âŒ80â% after 8,000 cycles.Peer Reviewe
Tin-Containing Graphite for Sodium-Ion Batteries and Hybrid Capacitors
The limited Na-storage capacity of graphite anodes for sodium-ion batteries (âŒ110â
mAhâgâ1) is significantly enhanced by the incorporation of nanosized Sn (17â
wt%). The composite (SntGraphite), prepared by simple annealing of graphite with SnCl2, shows a specific capacity of 223â
mAhâgâ1 (at 50â
mAâgâ1) combined with excellent cycle life (i.âe., 96â% of capacity retention after 2,200 cycles at 1â
Aâgâ1) and initial Coulomb efficiency (90â%). The combined storage of sodium in graphite (by solvent co-intercalation) and Sn (by alloy formation) is followed by inâ
situ X-ray diffraction and inâ
situ electrochemical dilatometry (ECD). While the additional tin almost doubles the electrode capacity, its contribution to the electrode expansion (âŒ3â%) is surprisingly small. The use of SntGraphite as anode for sodium-ion hybrid capacitors with activated carbon as cathode provides a maximum energy and power density of âŒ93â
Whâkgâ1 and 7.8â
kWâkgâ1, with a capacity retention of âŒ80â% after 8,000 cycles.Peer Reviewe
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Structural Aspects of P2-Type Na0.67Mn0.6Ni0.2Li0.2O2 (MNL) Stabilization by Lithium Defects as a Cathode Material for Sodium-Ion Batteries
A known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-Ύ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH Gmb
Origin of Aging of a P2-NaMnNiO Cathode Active Material for Sodium-Ion Batteries
Sodium-ion batteries (SIB) are currently being developed and commercialized as a promising new technology for cost-effective and powerful electrical energy storage. In this study, we investigate the origin of capacity fading in P2-type layered sodium cathode materials for SIBs using a micron-sized single-crystalline P2-NaMnNiO model cathode active material. Using various electrochemical techniques, we identify the following aging effects upon cycling: (i) a state of charge (SOC)-independent increase in polarization, (ii) a SOC-dependent increase in polarization at high voltage, and (iii) a loss of active material due to electronic disconnection after prolonged cycling. With high-resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray (EDX) spectroscopy, we identify surface densification, resulting in 5â10 nm thick surface layers on cycled cathode active materials as the origin for SOC-independent increase of polarization. The corresponding oxygen loss is in accordance with gas evolution in differential electrochemical mass spectrometry (DEMS) measurements. Furthermore, with scanning electron microscopy (SEM) electrode cross sections, we identify (partly) reversible cracking at a high SOC as the cause for increased polarization depending on SOC. Operando X-ray diffraction (XRD) identifies significant anisotropic volume change, which suggests mechanical stress as the cause for cracking at a high SOC and loss of active material after prolonged cycling. We believe that the herein provided understanding on the aging of this highly attractive class of cathode active materials for SIBs will enable the development of future powerful and stable layered oxide cathode materials for SIBs
Unravelling the Mechanism of Pulse Current Charging for Enhancing the Stability of Commercial LiNi0.5Mn0.3Co0.2O2/Graphite LithiumâIon Batteries
The key to advancing lithium-ion battery (LIB) technology, particularly with respect to the optimization of cycling protocols, is to obtain comprehensive and in-depth understanding of the dynamic electrochemical processes during battery operation. This work shows that pulse current (PC) charging substantially enhances the cycle stability of commercial LiNi0.5Mn0.3Co0.2O2 (NMC532)/graphite LIBs. Electrochemical diagnosis unveils that pulsed current effectively mitigates the rise of battery impedance and minimizes the loss of electrode materials. Operando and ex situ Raman and X-ray absorption spectroscopy reveal the chemical and structural changes of the negative and positive electrode materials during PC and constant current (CC) charging. Specifically, Li-ions are more uniformly intercalated into graphite and the Ni element of NMC532 achieves a higher energy state with less NiâO bond length variation under PC charging. Besides, PC charging suppresses the electrolyte decomposition and continuous thickening of the solid-electrolyte-interphase (SEI) layer on graphite anode. These findings offer mechanistic insights into Li-ion storage in graphite and NMC532 and, more importantly, the role of PC charging in enhancing the battery cycling stability, which will be beneficial for advancing the cycling protocols for future LIBs and beyond.Otto MĂžnsteds Fond http://dx.doi.org/10.13039/501100004209China Sponsorship Council http://dx.doi.org/10.13039/501100002860Peer Reviewe
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