Search

Broadening the portfolio of cathode active materials for Li-ion battery applications is now more important than ever. Recent focus on enabling diversity and security in supply chains, as well as concerns over sustainability of a massively growing energy storage market, have put emphasis on enabling more Earth-abundant cathode materials as an attractive strategy. With respect to relatively near-term options, manganese-based cathodes are particularly interesting. Herein we discuss some of the challenges associated with advancing the development of manganese-based oxides and, in particular, those that take advantage of complex local structures and/or over-lithiated compositions. Discussion centers on the representative, lithium- and manganese-rich class of cathodes and considerations to future development are given that range from the atomic-scale to the electrode level. [ABSTRACT FROM AUTHOR]

The work herein reports on studies aimed at exploring the correlation between electrolyte volume and electrochemical performance of full cell, pouch-cells consisting of graphite/Li1.02Ni0.50Mn0.29Co0.19O2 (NMC-532) as the electrodes and 1.2 M LiPF6 in ethylene carbonate:ethylmethyl carbonate (EC:EMC) as the electrolyte. It is demonstrated that a minimum electrolyte volume factor of 1.9 times the total pore volume of cell components (cathode, anode, and separator) is needed for long-term cyclability and low impedance. Less electrolyte results in an increase of the measured ohmic resistances. Increased resistance ratios for charge transfer and passivation layers at cathode, relative to initial values, were 1.5-2.0 after 100 cycles. At the cathode, the resistance from charge transfer was 2-3 times higher than for passivation layers. Differential voltage analysis showed that anodes were less delithiated after discharging as the cells were cycled. [ABSTRACT FROM AUTHOR]

Manganese dissolution from metal-oxide cathodes, and subsequent deposition at graphitic anodes, are considered to be key causes of capacity fade in lithium-ion batteries. The Mn2+ redox state is thought to be the major solvated Mn species, but its coordination environment is not well understood. Herein, we present the effects of Mn2+-containing electrolytes (Mn(PF6)2 and Mn(TFSI)²) on the performance of lithium-iron-phosphate//graphite (LFP//Gr) cells. Clear differences in first-cycle capacities and subsequent cycling efficiencies depending on the associated counter-ion indicate that the Mn coordination environment has a profound effect on the associated electrochemical degradation mechanisms. [ABSTRACT FROM AUTHOR]

Herein we report early results on efforts to optimize the electrochemical performance of a cathode composed of a lithium- and manganese-rich “layered-layered-spinel” (LLS) material for lithium-ion battery applications. Pre-pilot scale synthesis leads to improved particle properties compared with lab-scale efforts, resulting in high capacities (∼200 mAh g −1 ) and good energy densities (>700 Wh kg oxide −1 ) in tests with lithium-ion cells. Subsequent surface modifications give further improvements in rate capabilities and high-voltage stability. These results bode well for advances in the performance of this class of lithium- and manganese-rich cathode materials. [ABSTRACT FROM AUTHOR]

Coin-cells are often the test format of choice for laboratories engaged in battery research and development as they provide a convenient platform for rapid testing of new materials on a small scale. However, reliable, reproducible data via the coin-cell format is inherently difficult, particularly in the full-cell configuration. In addition, statistical evaluation to prove the consistency and reliability of such data is often neglected. Herein we report on several studies aimed at formalizing physical process parameters and coin-cell construction related to full cells. Statistical analysis and performance benchmarking approaches are advocated as a means to more confidently track changes in cell performance. We show that trends in the electrochemical data obtained from coin-cells can be reliable and informative when standardized approaches are implemented in a consistent manner. [ABSTRACT FROM AUTHOR]

High energy densities of lithium-rich transition metal oxides cannot be sufficiently maintained on cycling due to high-voltage first-cycle activation and the subsequent structural changes. These changes can be seen as a continuous decrease of the average voltage with cycling, known as voltage fade. Electrochemical and chemical insertion of protons has been reported suggesting that protons generated in the electrolyte could be involved in electrochemical cycling which could play a similar role in the "Li2MnO3 component" of lithium rich transition metal oxides. Here, electrochemical insertion of structural protons, changes in lithium occupancy at various states of charge, and changes in local structure have been investigated via a combination of local probes including solid state NMR, X-ray absorption spectroscopy and first principle calculations. While significant evidence is found for the deposition of non-structural proton-bearing species on electrodes, which accumulate with extensive cycling, structural proton insertion is not found to be a significant process directly effecting voltage fade. The electrochemical activity of disordered Li2MnO3, synthesized at low temperature, is also investigated and its Li removal/insertion properties measured quantitatively with NMR. Major reordering of Li sites and subsequent local structural transitions are observed by NMR and are found to be synchronous with voltage fade. [ABSTRACT FROM AUTHOR]

The results of a detailed structuralinvestigation on the influenceof cooling rates in the synthesis of lithium- and manganese-rich 0.5Li2MnO3·0.5LiCoO2composite electrodematerials, which are of interest for Li-ion battery applications,are presented. It is shown that a low-temperature, intermediate firingstep, often employed in cathode synthesis, yields a minor secondarycomponent representing a polydisperse distribution of lattice parameters,not found in the absence of low-temperature treatments. However, regardlessof the heating and cooling conditions employed, all samples presenttwo distinctly different local environments as evidenced by X-rayabsorption fine structure spectroscopy (XAFS) and nuclear magneticresonance (NMR) analysis. Transmission electron microscopy (TEM) datashow discrete domain structures that are consistent with the XAFSand NMR findings. Furthermore, high resolution synchrotron X-ray diffraction(HR-XRD), as well as the XAFS and NMR data show no discernible differencesbetween sample sets heated in similar fashion and subsequently cooledat different rates. The results contradict recent reports, using X-raydiffraction, that rapidly quenched samples of the same compositionare true solid solutions. This apparent discrepancy is assigned, inpart, to the inherent nature of conventional diffraction, which firmlyelucidates the average long-range structure but does not capture thelocal domain microstructure of these nanocomposite materials. Thecombined use of HR-XRD, XAFS, NMR, and TEM data indicate that chargeordering, which is initiated at relatively low temperatures, is thedominant force that produces a nanoscale, inhomogeneous compositestructure, irrespective of the cooling rate. [ABSTRACT FROM AUTHOR]

The commercialization of lithium-ion batteries has intimately changed our lives and enabled portable electronic devices, which has revolutionized communications, entertainment, medicine, and more. After three decades of commercial development, researchers around the world are now pursuing major advances that would allow this technology to power the next generation of light-duty, electric, and hybrid-electric vehicles. If this goal is to be met, concerted advances in safety and cost, as well as cycle-life and energy densities, must be realized through advances in the properties of the highly correlated, but separate, components of lithium-ion energy-storage systems. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemical study of structurally-integrated xLi2MnO3•(1−x)LiMn0.5Ni0.5O2 ‘composite’ materials has been undertaken to investigate the stability of electrochemically-activated electrodes at the Li2MnO3-rich end of the Li2MnO3–LiMn0.5Ni0.5O2 tie-line, i.e., for 0.7≤ x ≤0.95. Excellent performance was observed for x =0.7 in lithium half-cells; comparable to activated electrodes that have significantly lower values of x and are traditionally the preferred materials of choice. Electrodes with higher manganese content (x ≥0.8) showed significantly reduced performance. Implications for stabilizing low-cost, manganese-rich, layered lithium-metal-oxide electrode materials are discussed. [Copyright &y& Elsevier]

A new approach to synthesizing high capacity lithium-metal-oxide cathodes for lithium-ion batteries from a Li2MnO3 precursor is described. The technique, which is simple and versatile, can be used to prepare a variety of integrated `composite' electrode structures, such as 'layered-layered' xLi2MnO3•(1-x)LiMO2, `layered-spinel' xLi2MnO3•(1-x)LiM2O4, `layered-rocksalt' xLi2MnO3• (1-x)MO and more complex arrangements, in which M is typically Mn, Ni, and/or Co. Early indications are that electrodes prepared by this method are effective in 1) countering the voltage decay that occurs on cycling `layered-layered' xLi2MnO3•(1-x)LiMO2 electrodes without compromising capacity, and 2) reducing the extent of electrochemical activation required above 4.5 V on the initial charge. In particular, a 0.5Li2MnO3•0.5LiMn0.5Ni0.5O2 electrode, after activation at 4.6 V, delivers a steady capacity of 245 mAh/g between 4.4 and 2.5 V at 15 mA/g (~C/15 rate) with little change to the voltage profile; a first cycle capacity loss of 12%, which is significantly less than usually observed for `layered-layered' electrodes, has been achieved with a manganese-rich 0.1Li2MnO3•0.9LiMn0.50Ni0.37Co0.13O2 electrode. These results have implications for enhancing the performance of the next generation of high-energy lithium-ion batteries. The flexibility of the method and the variation in electrochemical properties of various composite electrode structures and compositions are demonstrated. [ABSTRACT FROM AUTHOR]

The necessity of developing low-cobalt cathode oxides for lithium-ion batteries is increasingly apparent. The most popular strategy followed thus far in addressing this issue has been the development of LiNiO 2 -like, Ni-rich, layered LiMO 2 (M = Ni, Mn, Co; NMC) oxides with low Mn and Co contents, e.g., NMC-811. However, safety, cycle-life, and even cost could remain critical barriers to the success of such cathode materials. Herein an alternative to LiNiO 2 -based, low-cobalt cathodes is suggested based on modifications to the prototypical cobalt-free, layered oxide, LiNi 0.5 Mn 0.5 O 2. • Low cobalt oxides show promise for next generation, lithium-ion cathodes. • Nickel is limited to ~60% allowing increased contents of cheaper, abundant manganese. • Lithium/nickel exchange is limited even in the presence of substantial manganese. [ABSTRACT FROM AUTHOR]

Direct observations of structure-electrochemical activity relationships continue to be a key challenge in secondary battery research. 6Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is the only structural probe currently available that can quantitatively characterize local lithium environments on the subnanometer scale that dominates the free energy for site occupation in lithium-ion (Li-ion) intercalation materials. In the present study, we use this local probe to gain new insights into the complex electrochemical behavior of activated 0.56Li2MnO3- 0.56LiMn0.5Ni0.5C>2, lithium- and manganese-rich transitionmetal (TM) oxide intercalation electrodes. We show direct evidence of path-dependent lithium site occupation, correlated to structural reorganization of the metal oxide and the electrochemical hysteresis, during lithium insertion and extraction. We report new 0.5Li resonances centered at ∼1600 ppm that are assigned to LiMn6-TMtet sites, specifically, a hyperfine shift related to a small fraction of re-entrant tetrahedral TMs (Mntet), located above or below lithium layers, coordinated to LiMn6 units. The intensity of the TM layer lithium sites correlated with tetrahedral TMs loses intensity after cycling, indicating limited reversibility of TM migrations upon cycling. These findings reveal that defect sites, even in dilute concentrations, can have a profound effect on the overall electrochemical behavior. [ABSTRACT FROM AUTHOR]

• Average particle size of transition metal carbonates quadrupled in a small pH range. • Sphericity of particles was highly dependent on ammonia concentration. • Higher reaction temperatures produced larger, more spherical precursor particles. • High sphericity was achieved above a lower boundary RPM. • Longer reaction times improved particle sphericity at lower reaction temperatures. The synthesis of precursors for lithium- and manganese-rich xLi 2 MnO 3 •(1-x)LiMO 2 (M = Ni, Mn, Co) (LMR-NMC) materials is generally carried out via co-precipitation using a continuously stirred tank reactor (CSTR) under steady-state conditions. But during the early stages of research (e.g., when screening compositional spaces of interest), using a CSTR in steady-state mode can be time consuming and wasteful. An alternative is to operate the reactor in semi-batch mode, which shortens reaction times and reduces the amount of waste. However, the effect of this mode on the product is not well documented. The present work investigates how several process variables affect the physical properties of Mn-rich NMC carbonate precursors prepared under semi-batch operation of a CSTR. The process variables examined are pH, ammonia concentration of feed solution, process temperature, stirring speed, and reaction time. The results can help guide research-scale production to support efficient development of Mn-rich carbonates for cathode oxides. [ABSTRACT FROM AUTHOR]