► A method for investigating electrodes of lithium-ion batteries inside a scanning electron microscope is introduced. ► Using this method, electrode materials can be investigated during electrode ...operation with high spatial resolution. ► Morphological in situ observations on SnO2 show the formation of interface layers, large volume expansions, growth of extrusions as well as mechanical damage in the electrodes. ► The electrochemical behavior of SnO2 was found to be particle size dependent.
We present an experimental platform that can be used for investigating lithium-ion batteries with very high spatial resolution. This in situ experiment runs inside a scanning electron microscope (SEM) and is able to track the morphology of an electrode including active and passive materials in real time. In this work it has been used to observe SnO2 during lithium uptake and release inside a working battery electrode. The experiment strongly relies on an ionic liquid which has very low vapor pressure and can therefore be used as an electrolyte inside the vacuum chamber of the SEM. In contrast to common electrochemical characterization tools, this method allows for the observation of microscopic mechanisms in electrodes. Depending on the SEM, resolutions down to 1nm can be achieved. As a result, the experimental platform can be used to investigate chemical reaction pathways, to monitor phase changes in electrodes or to investigate degradation effects in batteries. SnO2 is a potential anode material for future high capacity lithium-ion batteries. Our observations reveal the formation of interface layers, large volume expansions, growth of extrusions, as well as mechanically induced cracks in the electrode particles during cycling.
Layered alkali-containing 3d transition-metal oxides are of the utmost importance in the use of electrode materials for advanced energy storage applications such as Li-, Na-, or K-ion batteries. A ...significant challenge in the field of materials chemistry is understanding the dynamics of the chemical reactions between alkali-free precursors and alkali species during the synthesis of these compounds. In this study, in situ high-resolution synchrotron-based X-ray diffraction was applied to reveal the Li/Na/K-ion insertion-induced structural transformation mechanism during high-temperature solid-state reaction. The in situ diffraction results demonstrate that the chemical reaction pathway strongly depends on the alkali-free precursor type, which is a structural matrix enabling phase transitions. Quantitative phase analysis identifies for the first time the decomposition of lithium sources as the most critical factor for the formation of metastable intermediates or impurities during the entire process of Li-rich layered LiLi0.2Ni0.2Mn0.6O2 formation. Since the alkali ions have different ionic radii, Na/K ions tend to be located on prismatic sites in the defective layered structure (Na2/3-xNi0.25Mn0.75O2 or K2/3-xNi0.25Mn0.75O2) during calcination, whereas the Li ions prefer to be localized on the tetrahedral and/or octahedral sites, forming O-type structures.
Structure changes of a mixture of alkali-free precursor and alkali species during the synthesis of layered Li-, Na-, or K-containing 3d transition-metal oxides (ATMOs) were monitored by in situ high-resolution synchrotron-based X-ray diffraction. The intermediate phases, contributing to the ATMO formation pathway, were directly observed, which provide valuable information for the rational design and synthesis of advanced layered oxides with desirable structural and chemical properties. Display omitted
•In situ high-resolution HT-sXRD techniques was used to unveil the Li/Na/K-ion insertion induced structural evolution during heating.•The dynamics of chemical reaction between alkali-free precursor and alkali species upon calcination were systematically investigated.•High-temperature lithiation reaction pathway strongly depends on the alkali-free precursor type.•Site preferences of Li/Na/K-ion leads to the formation of various types of layered structures.
In view of the requirements for high-energy lithium ion batteries (LIBs), hierarchically layered LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode materials have been prepared using a hydroxide coprecipitation ...method and subsequent high-temperature solid-state reaction. The diffraction results show that the synthesized NCM111 has a well-defined layered hexagonal structure. The initial specific discharge capacity of a Li/NCM111 cell is 204.5 mAh g−1 at a current density of 28 mA g−1 between 2.7 and 4.8 V. However, the cell suffers from poor capacity retention over extended charge-discharge cycles. The structural evolution of NCM111 electrode during electrochemical cycling is carefully investigated by in situ high-resolution synchrotron radiation diffraction. It is found that the nanodomain formation of a layered hexagonal phase H3 and a cubic spinel phase after charging to voltages above 4.6 V is the main source for the structural collapse in c direction and the poor cycling performance. This process is accompanied by the removal of oxygen, the transition metal (TM) migration and the crack generation in the nanodomains of the primary particles. These results may help to better understand the structural degradation of layered cathodes in order to develop high energy density LIBs.
The isothermal section at 473 K of the Mg-Ni-Ga system in the entire composition regime and structural characterizations of the observed ternary phases are reported. The MgNi
1+
x
Ga
1-
x
(
x
= ...0.25), MgNiGa, Mg
2
NiGa
3
, Mg
9-
x
Ni
6
Ga
14-
y
(
x
= 0.32,
y
= 0.84), Mg
3
Ni
2
Ga, and MgNi
2
Ga
5
structures were solved and refined from X-ray single crystal diffraction data. MgNi
1+
x
Ga
1-
x
(
x
= 0.25,
Fd
-3
m
, a = 7.0781(2) Å) and MgNiGa (
P
6
3
/
mmc
,
a
= 5.0781(3) Å,
c
= 8.194(1) Å) crystallize in the Laves phase MgCu
2
and MgZn
2
structure types, respectively. Mg
2
NiGa
3
(
Cmcm
, a = 5.415(1) Å, b = 8.651(1) Å, c = 8.562(2) Å, Mg
2
MnGa
3
-type) represents the orthorhombic derivative of Laves phases. Mg
9-
x
Ni
6
Ga
14-y
(
x
= 0.32, y = 0.84,
Fd
-3
m
, a = 19.8621(6) Å) is isostructural with Mg
35
Cu
24
Ga
53
. MgNi
2
Ga
5
(
Pnnm
, a = 6.2704(1) Å b = 6.6902(1) Å c = 6.0794(1) Å) crystallizes in the MgCo
2
Ga
5
-type structure which is derived from tetragonal CoGa
3
-type. The crystal chemistry of these structures is compared and discussed. The hydrogenation properties of the MgNi
1+
x
Ga
1-
x
(
x
= 0.25), MgNiGa, and Mg
2
NiGa
3
Laves phases were studied. MgNi
1.25
Ga
0.75
absorbs up to 2.20 wt.% H
2
, MgNiGa absorbs up to 1.78 wt.% H
2,
and Mg
2
NiGa
3
absorbs up to 1.66 wt.% H
2
.
We present the structural properties and electrochemical capacitance of mesoporous MCo2O4 (M = Co, Zn, and Ni) rods synthesized by a facile solvothermal route without necessity to use templates. The ...Brunauer–Emmett–Teller specific surface areas of these mesoporous rods are found to be about 24, 54, and 62 m2 g–1 with major pore diameters of about 31, 15, and 9 nm for MCo2O4, M = Co, Zn, and Ni, respectively. X-ray photoelectron spectroscopy and X-ray diffraction studies reveal the phase purity of the samples with a predominant spinel-type crystal structure. The spinel crystal structure with lattice parameters of 8.118, 8.106, and 8.125 Å is obtained for MCo2O4, M = Co, Zn, and Ni, respectively. The transmission electron microscopy study reveals that the mesoporous rods are built by self-assembled aggregates of nanoparticles which are well-interconnected to form stable mesoporous rods. The electrochemical capacitor performance was investigated by means of cyclic voltammetry, galvanostatic charge/discharge cycling, and impedance spectroscopy in a three-electrode configuration. As a result, the spinel-type MCo2O4 rods exhibit high specific capacitances of 1846 F g–1 (CoCo2O4), 1983 F g–1 (ZnCo2O4), and 2118 F g–1 (NiCo2O4) at a scan rate of 2 mV/s. Furthermore, the mesoporous spinel-type metal oxides show desirable stability in alkaline electrolyte during long-term cycling with excellent cycling efficiency.
Lithium- and manganese-rich transition-metal oxide (LMR-NMC) electrodes have been designed either as heterostructures of the primary components (“composite”) or as core–shell structures with improved ...electrochemistry reported for both configurations when compared with their primary components. A detailed electrochemical and structural investigation of the 0.5Li2MnO3–0.5LiNi0.5Mn0.3Co0.2O2 composite and core–shell structured positive electrode materials is reported. The core–shell material shows better overall electrochemical performance compared to its corresponding composite material. While both configurations gave the same initial charge capacity of ∼300 mAh/g when cycled at a rate of 10 mA/g at 25 °C, the core–shell sample gives a discharge capacity of 232 mAh/g compared to 208 mAh/g delivered by the composite sample. Also, the core–shell sample gave better rate capability and a smaller first-cycle irreversible capacity loss than the composite sample. The improved performance of the core–shell material is attributed to its lower surface reactivity and limited structural change since the more stable Li2MnO3 shell screens the more reactive Ni-rich core material from interacting with either air or electrolyte at high potentials, thereby preventing electrode surface modification. In situ X-ray diffraction correlated with electrochemical data revealed that the composite sample shows stronger volumetric changes in the lattice parameters during charging to 4.8 V. In addition, X-ray absorption spectroscopy showed an incomplete Ni reduction process after the first discharge for the composite sample. From these results, it was shown that this leads to a more severe degradation in the composite material that affects Li+ intercalation in the subsequent discharge, thereby resulting in its poorer performance. Furthermore, to confirm these results, another LMR-NMC material with a different composition (having a Ni-poor core)0.5Li2MnO3-0.5LiNi0.33Mn0.33Co0.33O2was investigated. The core–shell structured positive electrode material also gave an improved electrochemical performance compared to the corresponding composite positive electrode material. These results show that the core–shell configuration could effectively be used to improve the performance of the LMR-NMC materials to enable future high-energy applications.
The development of new materials for tomorrow's electrochemical energy storage technologies, based on thoroughly designed molecular architectures is at the forefront of materials research. In this ...line, we report herein the development of a new class of organic lithium‐ion battery electrolytes, thermotropic liquid crystalline single‐ion conductors, for which the single‐ion charge transport is decoupled from the molecular dynamics (i. e., obeys Arrhenius‐type conductivity) just like in inorganic (single‐)ion conductors. Focusing on an in‐depth understanding of the structure‐to‐transport interplay and the demonstration of the proof‐of‐concept, we provide also strategies for their further development, as illustrated by the introduction of additional ionic groups to increase the charge carrier density, which results in a substantially enhanced ionic conductivity especially at lower temperatures.
Increasing order: Lithium‐comprising thermotropic organic liquid crystals mimick the lithium‐ion conduction mechanism characteristic for inorganic solid‐state electrolytes, while providing the beneficial mechanical properties of organic electrolyte systems; thus allowing for the complete decoupling of segmental motion and charge transport.
Sulfide-based solid electrolytes (SE) are quite attractive for application in all-solid-state batteries (ASSB) due to their high ionic conductivities and low grain boundary resistance. However, ...limited chemical and electrochemical stability demands for protection on both cathode and anode side. One promising concept to prevent unwanted reactions and simultaneously improve interfacial contacting at the anode side consists in applying a thin polymer film as interlayer between Li metal and the SE. In the present study, we investigated the combination of polyethylene oxide (PEO) based polymer films with the sulfide-based SE Li10SnP2S12 (LSPS). We analyzed their compatibility using both electrochemical and chemical techniques. A steady increase in the cell resistance during calendar aging indicated decomposition reactions at the interfaces. By means of X-ray photoelectron spectroscopy and further analytical methods, the formation of polysulfides, P-Sn-P like bridged PS43− units and sulfite, SO32−, was demonstrated. We critically discuss potential reasons and propose a plausible mechanism for the degradation of LSPS with PEO. The main objective of this paper is to highlight the importance of understanding interfaces in ASSBs not only from an electrochemical perspective, but also from a chemical point of view.
A series of Li(Ni
Mn
Co
)
O
(
= Al, Mg, Zn, and Fe,
= 0.06) was prepared via sol-gel method assisted by ethylene diamine tetra acetic acid as a chelating agent. A typical hexagonal α-NaFeO
structure ...(R-3m space group) was observed for parent and doped samples as revealed by X-ray diffraction patterns. For all samples, hexagonally shaped nanoparticles were observed by scanning electron microscopy and transmission electron microscopy. The local structure was characterized by infrared, Raman, and Mössbauer spectroscopy and
Li nuclear magnetic resonance (Li-NMR). Cyclic voltammetry and galvanostatic charge-discharge tests showed that Mg and Al doping improved the electrochemical performance of LiNi
Mn
Co
O
in terms of specific capacities and cyclability. In addition, while Al doping increases the initial capacity, Mg doping is the best choice as it improves cyclability for reasons discussed in this work.
Doping of cathode materials can considerably improve electrochemical performance and stability. Here, the high-voltage LiNi0.5Mn1.5O4 spinel is used as a candidate material. It is high-voltage ...cycling at a potential of approximately 4.7 V and the ability to host 2 eq. Li, thus leading to a theoretical capacity of 294 mAh g−1, that makes this material interesting. In order to improve stability and electronic conductivity, the spinel is doped with titanium and iron.
Cycling in a voltage range of 2.0–5.0 V leads to a cooperative Jahn-Teller distortion accompanied by a phase transformation from cubic to tetragonal symmetry. This causes a severe capacity fade. To improve capacity retention, the as-prepared spinel is post-doped with fluorine. Influence of different fluorine amounts in LiNi0.5Mn1.4Fe0.1Ti0.027O4−xFx (x = 0–0.3) on the capacity and stability is analyzed. The initial capacities decrease with increasing fluorine content but the low voltage capacity is stabilized. Best electrochemical results are obtained with a fluorine content of x = 0.15. Furthermore, an additional redox couple is found. The intensity of this depends on the fluorine content. It is assumed that manganese, either in the tetrahedral sites or in octahedral sites, bound to fluorine lead to a higher voltage.
•The cycling of 2 Li eq. in doped LiNi0.5Mn1.5O4/Li cells is analyzed.•Postdoping with fluorine is leading to increased stability during cycling.•An additional redox couple is found in the 4–4.5 V region.
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