Ni-rich layered cathode materials are among the most promising candidates for high-energy-density Li-ion batteries, yet their degradation mechanisms are still poorly understood. We report a ...structure-driven degradation mechanism for NMC811 (LiNi
Mn
Co
O
), in which a proportion of the material exhibits a lowered accessible state of charge at the end of charging after repetitive cycling and becomes fatigued. Operando synchrotron long-duration X-ray diffraction enabled by a laser-thinned coin cell shows the emergence and growth in the concentration of this fatigued phase with cycle number. This degradation is structure driven and is not solely due to kinetic limitations or intergranular cracking: no bulk phase transformations, no increase in Li/Ni antisite mixing and no notable changes in the local structure or Li-ion mobility of the bulk are seen in aged NMCs. Instead, we propose that this degradation stems from the high interfacial lattice strain between the reconstructed surface and the bulk layered structure that develops when the latter is at states of charge above a distinct threshold of approximately 75%. This mechanism is expected to be universal in Ni-rich layered cathodes. Our findings provide fundamental insights into strategies to help mitigate this degradation process.
Nickel-rich layered oxide cathodes such as NMC811 (Li x Ni0.8Mn0.1Co0.1O2) currently have the highest practical capacities of cathodes used commercially, approaching 200 mAh/g. Lithium is removed ...from NMC811 via a solid-solution behavior when delithiated to x Li > 0.10, maintaining the same layered (O3 structure) throughout as observed via operando diffraction measurements. Although it is possible to further delithiate NMC811, it is kinetically challenging, and there are significant side reactions between the electrolyte and cathode surface. Here, small format, NMC811-graphite pouch cells were charged to high voltages at elevated temperatures and held for days to access high states of delithiation. Rietveld refinements on high-resolution diffraction data and indexing of selected area electron diffraction patterns, both acquired ex situ, show that NMC811 undergoes a partial and reversible transition from the O3 to the O1 phase under these conditions. The O1 phase fraction depends not only on the concentration of intercalated lithium but also on the hold temperature and hold time, indicating that the phase transition is kinetically controlled. 1H NMR spectroscopy shows that the proton concentration decreases with O1 phase fraction and is not, therefore, likely to be driving the O3–O1 phase transition.
Lithium‐rich cobalt‐free cathodes, such as Li1.2Mn0.6Ni0.2O2 (LMR), are promising next‐generation cathode materials because of their high energy density, cost efficiency, and sustainability. ...Nevertheless, LMRs suffer from degradation problems such as voltage decay during cycling. Different LMR surface doping and coating strategies are proposed to suppress LMR voltage decay with varying extents of success. Here, the role played by different electrolyte solvents in oxygen loss from the LMR surface is instead investigated. X‐ray absorption spectroscopy (XAS), electron energy loss spectroscopy (EELS), synchrotron XRD, and online electrochemical mass spectrometry (OEMS) results show that ethylene carbonate (EC) leads to accelerated oxygen loss from the LMR surface. As a result, cycling LMR cathodes in EC‐free electrolytes such as pure EMC, improves the capacity retention and reduces voltage decay. This approach provides a new strategy to increase the cycling stability of LMR cathodes, which is important for the development of more sustainable high‐performance batteries.
The focus lies in comprehending the reaction mechanisms that occur between different electrolyte components and LMR cathodes. The commonly used electrolyte LP57 exhibits significant side reactions with LMR cathode materials during cycling, resulting in severe voltage decay and structural degradation for LMR cathode. By employing an EC‐free electrolyte, a remarkable reduction in LMR capacity, and voltage decay is demonstrated, which complements ongoing research on LMR surface modification to prolong its lifespan.
A novel, generic methodology to manufacture hierarchically porous electrode structures directly onto current collectors has been developed based on layer-by-layer spray printing, here exemplified ...using TiO
2
(B) nanotubes for lithium-ion batteries. By optimizing and then exploiting the bi-solvent drying behavior of the spray printed ink to trigger self-assembly of the active TiO
2
(B) into a coral-like structure, controlled through-thickness pore channels were created, which were shown to promote lithium-ion mobility throughout the electrode. Using these optimized structures, the electrode thickness-dependent performance of TiO
2
(B) electrodes at high charge/discharge rates was compared with conventional slurry cast electrodes and revealed the superiority of the self-assembled electrodes, especially at the highest discharge rates. We also show this self-assembly effect in other active materials and over large areas, suggesting the potential for wide use of this approach for electrodes where fast dynamic response is prioritized.
Mill scale, which is a waste product from the steel industry, abundantly available and comprising a mixture of iron oxides, has been converted into hollow and porous Fe
2
O
3
micro-rods using a ...facile and scalable chemical treatment. The Fe
2
O
3
morphology and structure was characterised by a range of electron microscopy and other techniques, and then sprayed into large area electrodes that were investigated for electrochemical supercapacitor and lithium ion battery applications. The Fe
2
O
3
supercapacitor electrode delivered a specific capacitance of 346 F g
−1
at 2 mV s
−1
with 88% capacitance retention after 5000 cycles, while the battery electrode delivered an initial reversible specific capacity of 953 mA h g
−1
at 0.1C, reducing to 933 mA h g
−1
after 100 cycles and to 673 mA h g
−1
at 5C. The Fe
2
O
3
electrodes had similar or superior performance to more costly, small batches of laboratory synthesised Fe
2
O
3
in both supercapacitor and battery applications, which was ascribed to the hollow and porous structure that facilitated ion mobility throughout the electrodes, a high surface area and excellent strain accommodation during lithiation and de-lithiation.
We describe a procedure to cheaply manipulate comparatively large amounts of mill scale into Fe
2
O
3
with a porous/hollow morphology with outstanding electrochemical energy storage performance.
Mill scale, which is a waste product from the steel industry, abundantly available and comprising a mixture of iron oxides, has been converted into hollow and porous Fe sub(2)O sub(3) micro-rods ...using a facile and scalable chemical treatment. The Fe sub(2)O sub(3) morphology and structure was characterised by a range of electron microscopy and other techniques, and then sprayed into large area electrodes that were investigated for electrochemical supercapacitor and lithium ion battery applications. The Fe sub(2)O sub(3) supercapacitor electrode delivered a specific capacitance of 346 F g super(-1) at 2 mV s super(-1) with 88% capacitance retention after 5000 cycles, while the battery electrode delivered an initial reversible specific capacity of 953 mA h g super(-1) at 0.1C, reducing to 933 mA h g super(-1) after 100 cycles and to 673 mA h g super(-1) at 5C. The Fe sub(2)O sub(3) electrodes had similar or superior performance to more costly, small batches of laboratory synthesised Fe sub(2)O sub(3) in both supercapacitor and battery applications, which was ascribed to the hollow and porous structure that facilitated ion mobility throughout the electrodes, a high surface area and excellent strain accommodation during lithiation and de-lithiation.
Mill scale, which is a waste product from the steel industry, abundantly available and comprising a mixture of iron oxides, has been converted into hollow and porous Fe
2
O
3
micro-rods using a ...facile and scalable chemical treatment. The Fe
2
O
3
morphology and structure was characterised by a range of electron microscopy and other techniques, and then sprayed into large area electrodes that were investigated for electrochemical supercapacitor and lithium ion battery applications. The Fe
2
O
3
supercapacitor electrode delivered a specific capacitance of 346 F g
−1
at 2 mV s
−1
with 88% capacitance retention after 5000 cycles, while the battery electrode delivered an initial reversible specific capacity of 953 mA h g
−1
at 0.1C, reducing to 933 mA h g
−1
after 100 cycles and to 673 mA h g
−1
at 5C. The Fe
2
O
3
electrodes had similar or superior performance to more costly, small batches of laboratory synthesised Fe
2
O
3
in both supercapacitor and battery applications, which was ascribed to the hollow and porous structure that facilitated ion mobility throughout the electrodes, a high surface area and excellent strain accommodation during lithiation and de-lithiation.
Image contrast is often limited by background autofluorescence in steady‐state bioimaging microscopy. Upconversion bioimaging can overcome this by shifting the emission lifetime and wavelength beyond ...the autofluorescence window. Here we demonstrate the first example of triplet‐triplet annihilation upconversion (TTA‐UC) based lifetime imaging microscopy. A new class of ultra‐small nanoparticle (NP) probes based on TTA‐UC chromophores encapsulated in an organic–inorganic host has been synthesised. The NPs exhibit bright UC emission (400–500 nm) in aerated aqueous media with a UC lifetime of ≈1 μs, excellent colloidal stability and little cytotoxicity. Proof‐of‐concept demonstration of TTA‐UC lifetime imaging using these NPs shows that the long‐lived anti‐Stokes emission is easily discriminable from typical autofluorescence. Moreover, fluctuations in the UC lifetime can be used to map local oxygen diffusion across the subcellular structure. Our TTA‐UC NPs are highly promising stains for lifetime imaging microscopy, affording excellent image contrast and potential for oxygen mapping that is ripe for further exploitation.
A new class of ultra‐small nanoparticle (NP) probes based on triplet‐triplet annihilation upconversion (TTA‐UC) chromophores in an organic–inorganic ureasil host have been prepared and used to stain living cells as a proof‐of‐concept demonstration of TTA‐UC lifetime imaging for the first time. Fluctuations of the UC lifetime in the stained cells indicate the NPs can be used to map local oxygen diffusion across the subcellular structure.
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