The high charge-state dopant Zr4+ improves the structural stability and electrochemical behavior of the lithiated transition metal oxide LiNi0.6Co0.2Mn0.2O2.

Secondary lithium ion battery technology has made deliberate, incremental improvements over the past four decades, providing sufficient energy densities to sustain a significant mobile electronic device industry. Because current battery systems provide ∼100-150 km of driving distance per charge, ∼5-fold improvements are required to fully compete with internal combustion engines that provide >500 km range per tank. Despite expected improvements, the authors believe that lithium ion batteries are unlikely to replace combustion engines in fully electric vehicles. However, high fidelity and safe Li ion batteries can be used in full EVs plus range extenders (e.g., metal air batteries, generators with ICE or gas turbines). This perspective article describes advanced materials and directions that can take this technology further in terms of energy density, and aims at delineating realistic horizons for the next generations of Li ion batteries. This article concentrates on Li intercalation and Li alloying electrodes, relevant to the term Li ion batteries.

This paper is dedicated to studies of the electrochemical behavior, the structural and thermal features of the Ni-rich LiNi 0.5 Co 0.2 Mn 0.3 O 2 undoped and Al-doped (∼0.01 at.%) materials for positive electrodes of lithium batteries. We have found that structural characteristics of these materials are quite similar from the crystallographic point of view. It was demonstrated that Al substitution in the doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 is preferred at Ni sites over Co sites, and the thermodynamic preference for Al 3+ substitutions follows the order: Ni>Co>Mn. The lower capacity fading of the Al-doped electrodes upon cycling and aging of the cells in a charged state (4.3 V) at 60 • C, as well as more stable mean voltage behavior, are likely due to the chemical and structural modifications of the electrode/solution interface. The Al-doped LiNi 0.5 Co 0.2 Mn 0.3 O 2 electrodes demonstrate also lower resistances of the surface film and charge-transfer as well as lower activation energies for the discharge process. From XPS studies we conclude that the modified stable and less resistive interface on the Al-doped particles comprises the Li + -ion conducting nano-sized centers like LiAlO 2 , AlF 3 , etc., which promote, to some extent, the Li + ionic transport to the bulk. A partial layered-to-spinel transformation was established upon cycling of LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathodes.One of the major challenges in lithium batteries technology is, undoubtedly, the further improvement of battery components -electrodes, solutions, and separators. 1-7 Among several modern strategies to improve electrochemical performance and structural characteristics of materials for positive electrodes, doping has attracted the attention of scientists over the years. This is due to the effectiveness of dopants in stabilizing the structure of materials (even in minute amounts) and thus to increase the electrochemical cycling activity and to diminish the heat evolution of the electrodes in a charged state. A variety of dopant ions, like Co 2+ , Al 3+ , Ti 4+ , Zr 4+ , Zn 2+ , Fe 3+ , Cu 2+ , and Cr 3+ , has been used to improve the stability, morphology and microstructure of cathode materials, to enhance the electrode cycleability and rate capability, and to reduce capacity fading upon cycling. 8-13 For instance, doping of LiNi 0.5 Mn 0.5 O 2 with Co, Al, Ti resulted in decrease of the irreversible capacity loss and in almost no capacity fading of the doped electrodes. 14,15 In a systematic study of the Al-doped Ni-rich electrodes (LiNi 0.8 Co 0.15 Al 0.05 O 2 ), which are promising materials for use in batteries for electromotive applications, the authors have shown high cycling stability of these electrodes upon accelerated testing. 16 Several other doping metals, such as silver, magnesium, cobalt, gallium, lanthanum, bismuth, 17-19 as well as non-metallic ions (boron, fluorine), 20,21 were also explored in an attempt to increase the electrochemical cycling behavior of cathodes (both of layered and spinel structures) and to reduce their in...

Li-rich electrode materials of the family xLi 2 MnO 3 •(1-x)LiNi a Co b Mn c O 2 (a + b + c = 1) suffer a voltage fade upon cycling that limits their utilization in commercial batteries despite their extremely high discharge capacity, ca. 250 mAhg -1 . We exposed Li-rich, 0.35Li 2 MnO 3 •0.65LiNi 0.35 Mn 0.45 Co 0.20 O 2 , to NH 3 at 400 °C , producing materials with improved characteristics: enhanced electrode capacity and a limited average voltage fade during 100 cycles in half cells vs. Li. We established three main changes caused by NH 3 treatment. First, a general bulk reduction of Co and Mn was observed via XPS and XANES. Next, a structural rearrangement lowered the coordination number of Co-O and Mn-O bonds, as well as formation of a surface spinel-like structure. Additionally, Li + removal from the bulk causes the formation of surface LiOH, Li 2 CO 3 , and Li 2 O. These structural and surface changes can enhance the voltage and capacity stability of the Li-rich material electrodes after moderate NH 3treatment times of 1 -2 hours.

We present the results of our in situ X‐ray diffraction (XRD) and Raman spectroscopy measurements for the first Li‐ion extraction/insertion (charge/discharge) processes of nickel‐rich Li1+x(NiyCozMnz)wO2 (0.005

This research sheds light on the intriguing phenomena of structural transformations that take place in spinel LiMn2O4 (space group Fd3m) when charged to high anodic potentials (4.3 to 5.1 V) in lithium cells. It was established from the XRD and electron diffraction analyses that the orthorhombic o-LiMnO2 (space group Pnma) is formed due to the partial transformation of spinel starting at 4.7 V. The Raman spectroscopy measurements of the LiMn2O4 samples charged to 5.1 V also provided evidence of o-LiMnO2, although its band overlaps with the delithiated spinel species. An additional important finding is that some layered-type LiMnO2 is formed upon cycling of the spinel material to 4.5 V, even upon the first charge. LiMnO2 exists as a stable component of the solid electrolyte interphase developed on these electrodes. We also concluded the formation of the layered LiMnO2 structure via solid-state 7Li NMR. The analysis of those results further indicated that the onset of the creation of the intermediate spinel-layered (“splayered”) phase clearly takes place between 4.5 and 4.7 V.

Lithium manganese rich cathode materials (represented as xLi 2 MnO 3 -(1-x)LiMO 2 , where M = Mn, Ni, Co) for Li-ion batteries have gained considerable research interests as they exhibit higher nominal voltage (∼4.0 V) and specific capacity (>250 mAhg −1 ) as compared to commercially available cathodes. In the present work, we have studied the effect of zirconium ion doping in Li 2 MnO 3 and Li 1.2 Mn 0.55 Ni 0.15 Co 0.1 O 2 (layered notation of 0.5Li 2 MnO 3 -0.5LiMn 0.375 Ni 0.375 Co 0.25 O 2 ) cathode. As compared to its undoped counterpart Li 1.2 Zr 0.008 Mn 0.542 Ni 0.15 Co 0.1 O 2 is found to yield superior cycleability, rate capability and voltage fade characteristics. Thus, capacity retention ∼78% is maintained in Zr doped LMR cathode after 100 charge-discharge cycles whereas for undoped LMR <30% capacity is retained after similar number of charge-discharge cycles. We have performed pre and post cycling X-ray diffraction, Raman spectroscopy, impedance spectroscopy, and dQ/dV analyses to understand the effect of Zr doping on the electrochemical performances of these LMR cathodes. We have demonstrated that the cycling induced layered to spinel phase transformation is substantially suppressed in Zr modified LMR cathodes and leads to their improved electrochemical performances. Also, as analyzed using galvanostatic intermittent titration technique, we have found that Zr doping increases the Li + diffusion coefficient and thereby improves the rate performance of the doped LMR cathode.

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