Integrated rocksalt–polyanion cathodes with excess lithium and stabilized cycling

Co- and Ni-free disordered rocksalt cathodes utilize oxygen redox to increase the energy density of lithium-ion batteries, but it is challenging to achieve good cycle life at high voltages >4.5 V (versus Li/Li+). Here we report a family of Li-excess Mn-rich cathodes that integrates rocksalt- and polyanion-type structures. Following design rules for cation filling and ordering, we demonstrate the bulk incorporation of polyanion groups into the rocksalt lattice. This integration bridges the two primary families of lithium-ion battery cathodes—layered/spinel and phosphate oxides—dramatically enhancing the cycling stability of disordered rocksalt cathodes with 4.8 V upper cut-off voltage. The cathode exhibits high gravimetric energy densities above 1,100 Wh kg−1 and >70% retention over 100 cycles. This study opens up a broad compositional space for developing battery cathodes using earth-abundant elements such as Mn and Fe

Novel Material Design of Co-/Ni-rich Cathodes for Advanced Lithium-ion Batteries

School of Energy and Chemical Engineering (Battery Science and Technology)In our modern society, the demands on lithium-ion batteries (LIBs) with higher energy density are ever increasing to apply this system currently prevailing in portable electronics to large-scale energy storage systems and electric vehicles. Cathode material, the major components of LIBs, could enable smaller and lighter rechargeable batteries theoretically but accomplishing this mission would be tough because it acts as a bottleneck of total energy density of a battery in practical. The feasible ways to boost the energy density of cathode materials could be achieved by widening the operational voltage range of conventional material. However, at higher voltages where the O 2p orbitals gradually hybridizes with the TM 3d orbitals, the peroxide ion O1??? with high ionic mobility near the surface are especially prone to leaving the cathode particle, disrupting the cathode-electrolyte interface, and the effluent oxygen will react with liquid electrolyte and burn up this scarce resource, leaving voids and reduced transition metals (TM) and resistive cathode-electrolyte interphase behind within cathode electrode. For now, what then happen afterwards inside cathode material are not very clear, but there are theories and practices about mitigating the ill effects, by either (i) suppressing irreversible phase transformations in the bulk by bulk doping or (ii) suppressing surface instabilities, including formation of spinel-phase cathode-electrolyte interphase (CEI) by engineering cathode surface via various coating process. Moreover, the thorough studies on this field is still scarce due to the needs on interdisciplinary research on degradation origin of cathode materials and comprehensive deterioration phenomena in cell system and limitation of evaluation tool. Therefore, in this thesis, fundamental studies on interfacial behavior between cathode and electrolyte have been conducted to contribute to this unattended field. In Chapter 2, we have investigated and unveil the role of dopant within high-voltage LiCoO2. It has turned out bulk doping and surface coating both help, which seems to diverge the degradation mechanism of high-voltage LiCoO2???is it a bulk (otherwise bulk doping should not work) or surface (otherwise surface coating should not work) dominating process or of equal importance from both sides? This is the question we seek to address in the present work, by a systematical study of how a uniform nickel bulk doping helps. The surprising conclusion is this ???thought??? bulk doping has minimal bulk effect but very profound surface effect to increase the stability of 4.45 V LiCoO2, and all the previous studies were ???fooled??? by the apparent suppression of reversible high-voltage phase transitions, which we argued has (almost) nothing to do with the degradation. In this sense, while in the present work we do provide one of best practical solution to stabilize 4.45 V LiCoO2 in a simple cost-effective way, we consider our work more to be a conceptual paper, which calls for better understandings of surface chemistry that may be hidden behind robotic practice of bulk doping in battery industry. In Chapter 3, new method to modify both outer surface and interconnected grain boundaries of Ni-rich with high-voltage cycling stability was suggested. This work applies the materials theory of reactive wetting to innovate the state-of-the-art electrode coating techniques for lithium-ion batteries ??? (LIBs). We report a new ???coating-plus-infusion??? strategy of a refractory boride compound that (i) not only fully covers the surface of the micron-sized secondary particles of Ni-rich layered cathodes (proved by X-ray photoelectron spectroscopy over a large sample area on the order of mm2, offering much better statistics than typical ???proof??? in the literature by transmission electron microscope over a local area on the order of 100 nm2), (ii) but also infuses into the grain boundaries between the nano-sized primary particles with zero wetting angle during room-temperature synthesis without subsequent heat treatment. Such facile kinetics and resultant irrigated surface-grain-boundary network are enabled by the huge chemical driving force from the strongly hybridized interfacial bonding. It not only ensures ultra-uniform conformal coating/infusion, but also de-activates the labile surface oxygen of the cathodes. As a result, our strategy offers superior electrochemical performance of high-loading (10.5 mg cm???2, ~2.05 mAh cm???2) and high-electrode-density (3.20 g cm???3) cathodes under high-rate (up to 1540 mA g???1, ~7 C) and high-temperature (45??C) conditions, by mitigating the correlated microstructural degradation (stress-corrosion cracking, SCC problem) and side reactions of Ni-rich layered cathodes as well as the cross-over effect on lithium metal anodes (all of them are fully supported by extensive, direct experimental evidences). Beyond technical advances, a consistent unified theory is provided by analyzing the electronic structure of local structural motifs using first-principles calculations, which explains the reactive wetting and suppressed oxygen activity observed experimentally, and the scientific approach can be applied to understand other surface/interface problems in energy materials.clos

Highly Densified Fracture-Free Silicon-based Electrode for High Energy Lithium-Ion Batteries

There has recently been an increasing volume of research in silicon-based anodes for high energy density lithium-ion batteries. Micron-sized composites with high tap density and a number of pores accommodating the massive volume expansion of silicon (Si) exhibit considerable electrochemical performance with high volumetric energy density. However, huge pressure on the particle during the calendering process brings about mechanical failure which causes the formation of additional by-products upon lithiation and electrical contact loss. Here, we discover specific particle size distribution based on the constructive simulation including calculation of the packing density depending on the different particle size distribution and stress evolution of each particle at high pressure. A silicon/graphite hybrid anode in which the silicon nanolayer (similar to 15 nm) is coated on the graphite is selected to validate the simulation. This anode sustains its morphological integrity and secures its void space without crack propagation of the silicon nanolayer in the densely packed electrode. As a result, it demonstrates high initial specific capacity (>500 mAh g(-1)), high initial Coulombic efficiency (95.2 %), low electrode swelling ratio (35 % at first cycle), and excellent capacity retention ratio (99.1 % during 50 cycles) for high energy density lithium-ion batteries

Feasibility of Cathode Surface Coating Technology for High-Energy Lithium-ion and Beyond-Lithium-ion Batteries

Cathode material degradation during cycling is one of the key obstacles to upgrading lithium-ion and beyond-lithium-ion batteries for high-energy and varied-temperature applications. Herein, we highlight recent progress in material surface-coating as the foremost solution to resist the surface phase-transitions and cracking in cathode particles in mono-valent (Li, Na, K) and multi-valent (Mg, Ca, Al) ion batteries under high-voltage and varied-temperature conditions. Importantly, we shed light on the future of materials surface-coating technology with possible research directions. In this regard, we provide our viewpoint on a novel hybrid surface-coating strategy, which has been successfully evaluated in LiCoO2-based-Li-ion cells under adverse conditions with industrial specifications for customer-demanding applications. The proposed coating strategy includes a first surface-coating of the as-prepared cathode powders (by sol-gel) and then an ultra-thin ceramic-oxide coating on their electrodes (by atomic-layer deposition). What makes it appealing for industry applications is that such a coating strategy can effectively maintain the integrity of materials under electro-mechanical stress, at the cathode particle and electrode-levels. Furthermore, it leads to improved energy-density and voltage retention at 4.55 V and 45 degrees C with highly loaded electrodes (approximate to 24 mg.cm(-2)). Finally, the development of this coating technology for beyond-lithium-ion batteries could be a major research challenge, but one that is viable

Boosting Reaction Homogeneity in High-Energy Lithium-Ion Battery Cathode Materials

Conventional nickel-rich cathode materials suffer from reaction heterogeneity during electrochemical cycling particularly at high temperature, because of their polycrystalline properties and secondary particle morphology. Despite intensive research on the morphological evolution of polycrystalline nickel-rich materials, its practical investigation at the electrode and cell levels is still rarely discussed. Herein, an intrinsic limitation of polycrystalline nickel-rich cathode materials in high-energy full-cells is discovered under industrial electrode-fabrication conditions. Owing to their highly unstable chemo-mechanical properties, even after the first cycle, nickel-rich materials are degraded in the longitudinal direction of the high-energy electrode. This inhomogeneous degradation behavior of nickel-rich materials at the electrode level originates from the overutilization of active materials on the surface side, causing a severe non-uniform potential distribution during long-term cycling. In addition, this phenomenon continuously lowers the reversibility of lithium ions. Consequently, considering the degradation of polycrystalline nickel-rich materials, this study suggests the adoption of a robust single-crystalline LiNi(0.8)Co(0.1)Mn(0.1)O(2)as a feasible alternative, to effectively suppress the localized overutilization of active materials. Such an adoption can stabilize the electrochemical performance of high-energy lithium-ion cells, in which superior capacity retention above approximate to 80% after 1000 cycles at 45 degrees C is demonstrated

Study on Pollution Characteristics of Perfluoroalkyl Substances (PFASs) in Shallow Groundwater

Perfluoroalkyl substances (PFASs) in shallow groundwater are increasingly being studied due to the global occurrence, environment persistence, bioaccumulation, and potential human health risk. In this research, 16 PFAS (11 perfluorinated carboxylic acids and 5 perfluorinated sulfonic acids) concentrations in groundwater were quantified to obtain information on geographical distribution and PFAS detection pattern for 4 years in South Korea. In the results, groundwater PFAS concentration ranged from non-detectable to average 45.2 ng/L (sum of PFASs). The major PFAS compounds were perfluorooctanoic acid (PFOA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluorohexane sulfonate (PFHxS), and perfluorooctane sulfonate (PFOS). The short chain (C 8) PFASs in shallow groundwater. However, the detection patterns of 15 PFASs were different for each aquifer. Subsequently, through a health risk assessment, a non-carcinogenic risk level through ingestion, inhalation, and dermal contact for PFOA and PFOS was determined at 10−1, and it presents the need for PFAS management of groundwater

Reactive boride infusion stabilizes Ni-rich cathodes for lithium-ion batteries

Engineered polycrystalline electrodes are critical to the cycling stability and safety of lithium-ion batteries, yet it is challenging to construct high-quality coatings at both the primary- and secondary-particle levels. Here we present a room-temperature synthesis route to achieve a full surface coverage of secondary particles and facile infusion into grain boundaries, and thus offer a complete 'coating-plus-infusion' strategy. Cobalt boride metallic glass was successfully applied to a Ni-rich layered cathode LiNi0.8Co0.1Mn0.1O2. It dramatically improved the rate capability and cycling stability, including under high-discharge-rate and elevated-temperature conditions and in pouch full-cells. The superior performance originates from a simultaneous suppression of the microstructural degradation of the intergranular cracking and of side reactions with the electrolyte. Atomistic simulations identified the critical role of strong selective interfacial bonding, which offers not only a large chemical driving force to ensure uniform reactive wetting and facile infusion, but also lowers the surface/interface oxygen activity, which contributes to the exceptional mechanical and electrochemical stabilities of the infused electrode. Coating is commonly used to improve electrode performance in batteries, but it is challenging to achieve and maintain complete coverage of electrode particles during cycling. Here the authors present a coating-and-infusion approach on Ni-rich cathodes that effectively retards stress corrosion cracking

Lattice-Oxygen-Stabilized Li- and Mn-Rich Cathodes with Sub-Micrometer Particles by Modifying the Excess-Li Distribution

In recent years, Li- and Mn-rich layered oxides (LMRs) have been vigorously explored as promising cathodes for next-generation, Li-ion batteries due to their high specific energy. Nevertheless, their actual implementation is still far from a reality since the trade-off relationship between the particle size and chemical reversibility prevents LMRs from achieving a satisfactory, industrial energy density. To solve this material dilemma, herein, a novel morphological and structural design is introduced to Li1.11Mn0.49Ni0.29Co0.11O2, reporting a sub-micrometer-level LMR with a relatively delocalized, excess-Li system. This system exhibits an ultrahigh energy density of 2880 Wh L-1 and a long-lasting cycle retention of 83.1% after the 100th cycle for 45 degrees C full-cell cycling, despite its practical electrode conditions. This outstanding electrochemical performance is a result of greater lattice-oxygen stability in the delocalized excess-Li system because of the low amount of highly oxidized oxygen ions. Geometric dispersion of the labile oxygen ions effectively suppresses oxygen evolution from the lattice when delithiated, eradicating the rapid energy degradation in a practical cell system

Ni-Ion-Chelating Strategy for Mitigating the Deterioration of Li-Ion Batteries with Nickel-Rich Cathodes

Ni-rich cathodes are the most promising candidates for realizing high-energy-density Li-ion batteries. However, the high-valence Ni4+ ions formed in highly delithiated states are prone to reduction to lower valence states, such as Ni3+ and Ni2+, which may cause lattice oxygen loss, cation mixing, and Ni ion dissolution. Further, LiPF6, a key salt in commercialized electrolytes, undergoes hydrolysis to produce acidic compounds, which accelerate Ni-ion dissolution and the interfacial deterioration of the Ni-rich cathode. Dissolved Ni ions migrate and deposit on the surface of the graphite anode, causing continuous electrolyte decomposition and threatening battery safety by forming Li dendrites on the anode. Herein, 1,2-bis(diphenylphosphino)ethane (DPPE) chelates Ni ions dissolved from the Ni-rich cathode using bidentate phosphine moieties and alleviates LiPF6 hydrolysis via complexation with PF5. Further, DPPE reduces the generation of corrosive HF and HPO2F2 substantially compared to the amounts observed using trimethyl phosphite and tris(trimethylsilyl) phosphite, which are HF-scavenging additives. Li-ion cells with Ni-rich cathodes and graphite anodes containing DPPE exhibit remarkable discharge capacity retentions of 83.4%, with high Coulombic efficiencies of >99.99% after 300 cycles at 45 degrees C. The results of this study will promote the development of electrolyte additives

Eutectic salt-assisted planetary centrifugal deagglomeration for single-crystalline cathode synthesis

Single-crystalline layered cathodes are often desirable for advanced lithium-ion batteries. However, constrained by the accessible temperature range to prevent lithium evaporation, lattice defects and particle agglomerations, the production of single-crystalline cathodes with high phase purity, good electrochemical performance and scalability remains challenging. Here we invent a new mechanochemical activation process that offers a general solution to the conundrum of synthesizing coarse single-crystal cathodes with Li-/Mn-rich or Ni-rich chemistry, which differs from the equipment- and energy-intense and long-duration mechanochemical routes that are difficult to scale up. Our approach is based on interfacial reactive wetting, mediated by transient eutectic salts in situ melted by moderate mechanical agitations, to form a colloidal suspension of nanosized oxides dispersed in liquified lithium salts. It efficiently deagglomerates the polycrystalline precursors, repacks the crystals and homogenizes the lithium-salt distribution, thus enabling facile particle coarsening later into the single-crystalline morphology with improved electrochemical performance. Single-crystalline layered oxides are much sought after as they offer high-performance promises in batteries. Here the authors report a facile and scalable planetary centrifugal mixing technique-aided by eutectic lithium salts-that enables the growth of high-quality single-crystalline cathode materials