Mechanical Pulverization of Co-Free Nickel-Rich Cathodes for Improved High-Voltage Cycling of Lithium-Ion Batteries
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25 ENERGY STORAGE↗
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Enabling High-Temperature and High-Voltage Lithium-Ion Battery Performance through a Novel Cathode Surface-Targeted Additive
We report lithium-ion batteries (LIBs) are being used in locations and applications never imagined when they were first conceived. To enable this broad range of applications, it has become necessary for LIBs to be stable to an ever broader range of conditions, including temperature and energy. Unfortunately, while negative electrodes have received a great deal of focus in electrolyte development, stabilization of positive electrodes remains an elusive target. Here, we report a novel additive that shows the ability to protect positive electrodes against elevated temperatures and voltages. This additive can be used in small quantities, and its targeted behavior allows it to remain functional in complex electrolyte packages. This can prove an effective approach to targeting specific aspects of cell performance.
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Asymmetric Lithium Extraction and Insertion in High Voltage Spinel at Fast Rate
Spinel-structured ordered-LiNi 0.5 Mn 1.5 O 4 (o-LNMO) has experienced a resurgence of interest in the context of reducing scarce elements such as cobalt from lithium-ion battery. O-LNMO undergoes two two-phase reaction at slow rates. However, it is not known if such phenomenon also applies at fast rates. Herein, we investigate the rate-dependent phase transition behavior of o-LNMO through in operando time-resolved X-ray diffraction. The results indicate that a narrow region of solid solution reaction exists for charge and discharge at both slow and fast rate. The overall phase transition is highly asymmetric at fast rates. During fast charge, it is a particle-by-particle mechanism resulting from asynchronized reaction among the particles. Finally, during fast discharge, it is likely a core-shell mechanism involving transition from Li 0+x Ni 0.5 Mn 1.5 O 4 to Li 1+x Ni 0.5 Mn 1.5 O 4 in the outer layer of particles. The Li 0.5 Ni 0.5 Mn 1.5 O 4 phase is suppressed during fast discharge and only appears through Li redistribution upon relaxation.
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Molecular engineering of ethereal electrolyte for ultrastable Si-based high voltage full cells
The successful application of Si-based high-energy Li-ion batteries (LIBs) depends on our ability to tailor electrolyte properties to achieve long-term stability and reliable performance. In this work, we demonstrate our rationale for the molecular design of ethereal solvents to address low anodic stability issues and produce a highly electrochemically stable electrolyte for Si‖LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) high-energy full cells. Unlike the trimethylsilyl group, the trifluoromethyl (–CF 3 ) group exerts a very strong electron-withdrawing effect on the glycol ether backbone, reducing the highest occupied molecular orbital (HOMO) energy level of the fluorinated glycol ether (FGE) and significantly enhancing its oxidation potential. The FGE-based electrolyte enables stable cycling of Si‖NMC811 full cells, delivering high specific capacity (900 mA h g −1 ) and coulombic efficiency (>99.78%) over extended (500) cycles. The improved electrochemical performance originates from the terminal fluorination of the diglyme backbone, which strengthens anion coordination in the solvation structure, leading to the preferential reduction of the FSI anion and the formation of robust solid electrolyte interphases (SEIs) on the Si surface. Through molecular engineering of ethereal solvents, we have discovered a promising candidate for a next-generation stable electrolyte, paving the way for the design of practical and commercially viable Si batteries.
Silicon anode↗
Research advances on cobalt-free cathodes for Li-ion batteries - The high voltage LiMn 1.5 Ni 0.5 O 4 as an example
LiMn 1.5 Ni 0.5 O 4 is one of the most promising cathode materials for use in either next generation lithium-ion batteries or all solid-state batteries. However, despite the significant Research and Development (R&D) carried out throughout the last two decades the material has not made serious inroads into market. One of the major reasons is the lack of consistency in the reported intrinsic properties and electrochemical performance owing to major controversies in synthesis, crystal structure and bulk and interfacial properties of LiMn 1.5 Ni 0.5 O 4 , notably in contact with electrolytes. This paper is a compelling review providing an assessment on the mainstream R&D dealing with the various crystal structures of LiMn 1.5 Ni 0.5 O 4 and their evolutions observed during synthesis and cycling in correlation with their electrochemical performance. Influence of electrolytes and additives along with modifications through doping and surface treatments are interrelated, and the electronic and ionic transport properties of the ordered and disordered LiMn 1.5 Ni 0.5 O 4 phases are discussed. Overall, this review provides a detailed assessment on LiMn1.5Ni0.5O4 and the underlying mechanisms governing its electrochemical performance broadly providing a focused framework for further advancement towards commercialization.
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Achieving Thermodynamic Stability of Single-Crystal Co-Free Ni-Rich Cathode Material for High Voltage Lithium-Ion Batteries
Ni-rich layered cathode materials are progressively considered as the standard configuration of high-energy electric vehicles by virtues of their high capacity and eliminated “range anxiety.” However, the poor cyclic stability and severe cobalt supply crisis would restrain their wide commercial applicability. Here, a cost-effective single-crystal Co-free Ni-rich cathode material LiNi 0.8 Mn 0.18 Fe 0.02 O 2 (NMF), which outperforms widely commercial polycrystalline LiNi 0.83 Co 0.11 Mn 0.06 O 2 (MNCM) and single-crystal LiNi 0.83 Co 0.11 Mn 0.06 O 2 (SNCM) is reported. Surprisingly, NMF can compensate for the reversible capacity loss under the designed conditions of high-temperature and elevated-voltage, achieving a competitive energy density compared with conventional MNCM or SNCM. Further, combining operando characterizations and density functional theory calculation, it is revealed that NMF cathode with improved dynamic structure evolution largely alleviates the mechanical strain issue commonly found in Ni-rich cathode, which can reduce the formation of intragranular cracks and improve the safety performance. Consequently, this new Co-free NMF cathode can achieve a perfect equilibrium between material cost and electrochemical performance, which not only reduces the production cost by >15%, but also demonstrates excellent thermal stability and cycling performance.
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Electrolytes Polymerization‐Induced Cathode‐Electrolyte‐Interphase for High Voltage Lithium‐Ion Batteries
Abstract Lithium‐ion batteries (LIBs) based on LiNi x Co y Mn 1‐x‐y O 2 (NCM) cathode materials have been widely commercialized, because of their high energy density, favorable rate performance, and relatively low cost. However, with increased Ni content to further increase their energy density, their cycling stability deteriorates dramatically and thus fails to meet the commercial application requirements. The artificial cathode‐electrolyte‐interphase (CEI) is a promising approach to solve this problem. Here, a robust CEI is fabricated through in situ polymerization of ethylene carbonate induced by aluminum isopropoxide (AIP). By adding 1 wt.% AIP in a commercial electrolyte, the capacity retention of LiNi 0.8 Co 0.1 Mn 0.1 O 2 ||Li cell at 1 C rate has been significantly increased from 80.8% to 97.8% with a highly reversible capacity of 176 mA h g −1 after 200 cycles. AIP can be also used as an additive during the slurry‐making process, enabling a reversible capacity of 170 mA h g −1 for LiCoO 2 after 200 cycles even at a high charge cut‐off voltage of 4.6 V. It is confirmed that the in situ formed CEI layer can prevent the cathodes from cracking and reduce the irreversible phase transformation.
Yang, Jixiang↗
GaN MOCVD Growth on Native substrates for High Voltage (15-20 KV) Vertical Power Devices
This project aims to develop metalorganic chemical vapor deposition (MOCVD) homoepitaxy of GaN on native substrates with fast growth rate (15-20 μm/hr), low background doping (low-10 15 cm -3 ) and smooth surface morphology via comprehensive understanding of the crystal growth process including high quality GaN substrate development and surface preparation, impurity and native defects control, and their impacts on the breakdown field. The team successfully developed a new growth process by introducing the laser-assisted MOCVD (LA-MOCVD) process to address the limited growth rates of GaN in the traditional MOCVD process. Specifically, the use of the CO2 laser with lasing wavelength of 9.219 μm, the strong coupling between the laser beam with the ammonia (GaN MOCVD precursor) leads to efficient decomposition of NH3 which significantly increases the effective group V/III molar ratio and thus suppresses C impurity incorporation in MOCVD GaN. The reduction in C incorporation in LA-MOCVD GaN is especially prominent when the GaN growth rate is fast (> 10 μm/hr), which allows to develop thick GaN films with high crystalline quality and low controllable doping needed for vertical high power device applications. The results of this project lead to the demonstration of vertical GaN PN diodes with record breakdown voltage of ~ 8kV with high Baliga’s figure of merit.
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Coupling Anionic Oxygen Redox with Selenium for Stable High‐Voltage Sodium Layered Oxide Cathodes
Utilizing anion redox reaction is crucial for developing the next generation of high-energy density, low-cost sodium-ion batteries. However, the irreversible oxygen redox reaction in Na-ion layered cathodes, which leads to voltage fading and reduced overall lifespan, has hindered their practical application. In this study, selenium is incorporated as a synergistic redox active center of oxygen to improve the stability of Na-ion cathodes. The redesigned cathode maintains stable voltage by demonstrating reversible oxygen redox while significantly suppressing the redox activity of manganese. The anionic redox contribution capacity of the selenium-doped Na 0.6 Li 0.2 Mn 0.8 O 2 cathode remains as high as 84% after 50 cycles, while the pristine Na 0.6 Li 0.2 Mn 0.8 O 2 cathode experiences a reduction to 39% of its initial capacity. The X-ray photoelectron spectroscopy data and computational analysis further revealed that selenium doping participates in redox as Se +4/5 which stabilizes the charged state and increases the energy step for O─O dimerization, thus improving the stability and lifespan of Na 0.6 Li 0.2 Mn 0.8 O 2 cathodes. In conclusion, the findings highlight the potential of redox coupling design to address the issue of voltage fade caused by irreversible anionic redox.
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Synergistic Coupling Effect of Electronic Conductivity and Interphase Compatibility on High-Voltage Na 3 V 2 (PO 4 ) 2 F 3 Cathodes
Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) has been considered an up-and-coming cathode material candidate for sodium (Na) ion batteries in light of its high specific capacity and working voltage. However, an erratic cathode/electrolyte interface layer is inevitably formed, accompanied by continuous electrolyte decomposition on the NVPF surface, when the voltage exceeds 4.2 V vs Na + /Na. Herein, the interphase features of NVPF are obviously enhanced owing to the ameliorated electronic conductivity obtained by combining it with carbon nanotubes (CNT). The NVPF with 3 wt % CNT (NVPF@3% CNT) reduces the Na + diffusion kinetic energy barrier and electron transport resistance. Furthermore, the conducting network formed by CNT with sturdy structure strength can promptly accommodate the volumetric changes during sequential Na + extraction/insertion and thus effectively improve the long-term cyclic performance of NVPF/hard carbon full cells. The initial discharge capacity approaches 105 mA h g –1 at 0.5C, and it retains 94% capacity retention after 200 cycles at the temperature of –10 °C. The cathode/electrolyte interphase characterization results further demonstrate that the interphase layer on the NVPF@3% CNT cathode is thinner and more compact compared with pristine samples. Here, this research provides a competitive strategy to facilitate the interfacial compatibility between the NVPF and electrolytes and accelerate the commercialization of high-performance Na-ion batteries.
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A fluorine-substituted pyrrolidinium-based ionic liquid for high-voltage Li-ion batteries
A fluorine-substituted ionic liquid based on a pyrrolidinium cation and a bis(fluorosulfonyl)imide anion was synthesized using a facile one-step reaction. Here, the resulting ionic liquid is highly pure and when dissolved with LiFSI, the IL-based electrolyte showed good compatibility both in Li and graphite anodes, and superior voltage stability is demonstrated in a LiNi 0.5 Mn 0.3 Co 0.2 O 2 cell.
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High-Voltage, Intermediate-Temperature, Fe- and Al-Mixed Metal Halide Molten Salt for Molten Sodium Battery Energy Storage
An inorganic Fe and Al halide-based, low-temperature molten salt catholyte is described, which, when paired with a molten sodium anode, has high operating potentials rivaling those of Li ion batteries. The newly developed catholyte consists of metal halides FeCl 3 /FeCl 2 –AlCl 3 –NaCl and is intended to cycle between Fe 3+ /Fe 2+ redox couples in the molten salt. The multicomponent molten salt was initially evaluated for phase behavior and basic electrochemical behavior before full battery testing. The assembled battery, utilizing a 20:35:45 (FeCl 3 :AlCl 3 :NaCl) composition, with a 50.83 Ah/kg theoretical gravimetric capacity and a specific energy of 176.95 Wh/kg, was cycled at variable depths of discharge (DoD) and current densities to determine its cycling efficiencies and limitations. In conclusion, preliminary cycling tests showed two operational potential regimes, with higher potential, 3.91 V (vs Na/Na + ), at low DoD and lower potential, 3.39 V (vs Na/Na + ), at high DoD with excellent energy efficiencies and cycling behavior under both regimes.
Aluminum↗
Advanced Low‐Flammable Electrolytes for Stable Operation of High‐Voltage Lithium‐Ion Batteries
Abstract Despite being an effective flame retardant, trimethyl phosphate (TMP a ) is generally considered as an unqualified solvent for fabricating electrolytes used in graphite (Gr)‐based lithium‐ion batteries as it readily leads to Gr exfoliation and cell failure. In this work, by adopting the unique solvation structure of localized high‐concentration electrolyte (LHCE) to TMP a and tuning the composition of the solvation sheaths via electrolyte additives, excellent electrochemical performance can be achieved with TMP a ‐based electrolytes in Gr∥LiNi 0.8 Mn 0.1 Co 0.1 O 2 cells. After 500 charge/discharge cycles within the voltage range of 2.5–4.4 V, the batteries containing the TMP a ‐based LHCE with a proper additive can achieve a capacity retention of 85.4 %, being significantly higher than cells using a LiPF 6 ‐organocarbonates baseline electrolyte (75.2 %). Meanwhile, due to the flame retarding effect of TMP a , TMP a ‐based LHCEs exhibit significantly reduced flammability compared with the conventional LiPF 6 ‐organocarbonates electrolyte.
Jia, Hao↗
Advanced Low-Flammable Electrolytes for Stable Operation of High-Voltage Lithium-Ion Batteries
Despite being an effective flame retardant, trimethyl phosphate (TMP a ) is generally considered as an unqualified solvent for fabricating electrolytes used in graphite (Gr) based lithium ion batteries as it readily leads to Gr exfoliation and cell failure. In this work, by adopting the unique solvation structure of localized high-concentration electrolyte (LHCE) to TMP a and tuning the composition of the solvation sheath via electrolyte additive, excellent electrochemical performance can be achieved with TMPa based electrolytes in Gr||LiNi 0.8 Mn 0.1 Co 0.1 O 2 cells. After 500 charge/discharge cycles within the voltage range of 2.5-4.4 V, the batteries containing TMPa based LHCEs with proper additive can achieve a capacity retention of 85.4%, being significantly higher than cells using a LiPF 6 -organocarbonates baseline electrolyte (75.2%). Meanwhile, due to the flame retarding effect of TMP a , TMP a based LHCEs exhibit significantly reduced flammability compared with the conventional LiPF 6 -organocarbonates electrolyte.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Theoretical Design of Lithium Chloride Superionic Conductors for All-Solid-State High-Voltage Lithium-Ion Batteries
The development of solid electrolytes (SEs) is a promising pathway to improve the energy density and safety of conventional Li ion batteries. Several lithium chloride SEs, Li 3 MCl 6 (M = Y, Er, In, and Sc), have gained popularity due to their high ionic conductivity, wide electrochemical window, and good chemical stability. This study systematically investigated 17 Li 3 MCl 6 SEs to identify novel and promising lithium chloride SEs. Calculation results revealed that 12 Li 3 MCl 6 (M = Bi, Dy, Er, Ho, In, Lu, Sc, Sm, Tb, TI, Tm, and Y) were stable phase with a wide electrochemical stability window and excellent chemical stability against cathode materials and moisture. Li-ion transport properties were examined using bond valence site energy (BVSE) and ab initio molecular dynamics (AIMD) calculation. Li 3 MCl 6 showed the lower migration energy barrier in monoclinic structures, while orthorhombic and trigonal structures exhibited higher energy barriers due to the sluggish diffusion along the two-dimensional path based on the BVSE model. AIMD results confirmed the slower ion migration along the 2D path, exhibiting lower ionic diffusivity and higher activation energy in orthorhombic and trigonal structures. For the further increase of ionic conductivity in monoclinic structures, Li-ion vacancy was formed by the substitution of M 3+ with Zr 4+ . Zr-substituted phase (Li 2.5 M 0.5 Zr 0.5 Cl 6 , M = In, Sc) exhibited up to a fourfold increase in ionic conductivity. This finding suggested that the optimization of Li vacancy in the Li 3 MCl 6 SEs could lead to superionic Li 3 MCl 6 SEs.
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Regulating Cation Interactions for Zero–Strain and High–Voltage P2–type Na 2/3 Li 1/6 Co 1/6 Mn 2/3 O 2 Layered Oxide Cathodes of Sodium–Ion Batteries
Deep sodium extraction/insertion of sodium cathodes usually causes undesired Jahn–Teller distortion and phase transition, both of which will reduce structural stability and lead to poor long-cycle reliability. Here we report a zero-strain P2- Na 2/3 Li1/6Co 1/6 Mn 2/3 O 2 cathode, in which the lithium/cobalt substitution contributes to reinforcing the host structure by reducing the Mn 3+ /Mn 4+ redox, mitigating the Jahn–Teller distortion, and minimizing the lattice change. 94.5 % of Na + in the unit structure can be reversibly cycled with a charge cut-off voltage of 4.5 V (vs. Na + /Na). Impressively, a solid-solution reaction without phase transitions is realized upon deep sodium (de)intercalation, which poses a minimal volume deviation of 0.53 %. Finally, it attains a high discharge capacity of 178 mAh g –1 , a high energy density of 534 Wh kg –1 , and excellent capacity retention of 95.8 % at 1 C after 250 cycles.
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Importance of High Valence Element Nb in Ni-Rich Layered Cathodes for High-Voltage Lithium-Metal Batteries
Ni-rich layered cathode materials have attracted extensive attention due to their higher energy density and technological maturity in commercialization. As the nickel content is raised, especially surpassing 80%, the increased energy density comes with the tradeoff of diminished thermal stability and increased electrochemical structural instability of the cathode. Compared with Co, Al, B, and Ta, the introduction of high valence element Nb significantly improved the electrochemical cycling, delivering a capacity of 202 mAh/g, corresponding to a capacity retention of 92% after 200 cycles tested at 45 °C. Further, the ex situ differential scanning calorimetry and in situ isothermal microcalorimetry demonstrate that the Nb-modified cathode has the potential to enhance the safety of ultrahigh nickel (Ni) NMCs and displays remarkable resilience to extensive cycling by inhibiting high-temperature decomposition reactions and exhibiting a lower heat flow during electrochemical cycling.
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High-voltage water-scarce hydrogel electrolytes enable mechanically safe stretchable Li-ion batteries
Soft Li-ion batteries, based on conventional organic electrolytes, face performance degradation challenges due to moisture penetration and safety concerns due to possible leakage of toxic fluorine compounds and flammable solvents under mechanical damage. We design a water-scarce hydrogel electrolyte with fluorine-free lithium salt to achieve wide electrochemical stability window (up to 3.11 volts) in ambient air without hermetic packaging while balancing high stretchability (1348%), ion conductivity (41 millisiemens per centimeter), and self-healing capabilities for mechanically and chemically safe stretchable Li-ion batteries. Molecular synergy between hydrophilicity and lithiophilicity of zwitterionic polymer backbone is revealed by molecular dynamics simulations. The battery exhibits capacity retention under harsh mechanical stresses—enduring stretching, twisting, folding, and multiple through-punctures by a needle—while self-healing from repeated through cuts by a razor blade. Stable ambient operation for 1 month over 500 charge-discharge cycles (average coulomb efficiency, 95%) is achieved. A prototype self-healing electronic system with embedded soft batteries demonstrates practical application as a durable embodied energy source.
Science & Technology - Other Topics↗