Low-temperature Electrochemical Performance Research Articles

Correlation between lithium-ion accessibility to the electrolyte–active material interface and low-temperature electrochemical performance

With continuous growth in the demand for energy storage, batteries are increasingly required to operate under extreme environmental conditions, including low temperatures. In this study, we systematically investigate the correlation between lithium-ion accessibility to the electrolyte–active material interface and the low-temperature electrochemical properties of electrode materials. Holey graphene with different number densities of in-plane defects on the graphene basal plane is synthesized and employed for the synthesis of Li4Ti5O12/holey graphene composites. The electrochemical performances of the Li4Ti5O12/holey graphene composites are evaluated at operating temperatures of –25 to 50 °C. As the number density of in-plane defects in the holey graphene increased, the polarization decreased and the apparent lithium-ion diffusion coefficient increased at operating temperatures of –25, 0, and 25 °C, resulting in improved low-temperature electrochemical performance. Based on the comparative analysis of the electrochemical properties of the Li4Ti5O12/holey graphene composites, the introduction of in-plane defects in the carbon layer is an effective strategy for improving the low-temperature electrochemical performance of electrode materials. The results suggest that the lithium-ion accessibility to the electrolyte–active material interface becomes more important to the electrochemical properties at low operating temperatures.

Implementing Low Temperature Strategies to Advance “Really Cool” Molten Sodium Batteries

Though batteries for portable electronics and electric vehicles continue to advance at an impressive rate, the needs for safe, low-cost, reliable batteries suitable for large-scale implementation remain unsatisfied. Here, we describe advances toward a promising new class of low temperature molten sodium-halide batteries, capable of safe, reliable operation near 100oC, a dramatic reduction from the ~300oC operating temperatures common to traditional molten sodium batteries. While realizing this low temperature goal promises reduced system costs and improved material lifetimes, it introduces a host of new material performance challenges including molten catholyte phase control and electrochemistry, solid state separator performance, and charge transfer at critical solid-liquid interfaces. The new battery design described here relies on highly conductive NaSICON-based ion-conducting membranes to separate a molten sodium anode and, critically, a molten inorganic sodium iodide (NaI)-based halide salt catholyte. Through engineering of novel molten salt catholyte compositions, we have identified several chemistries capable of producing a high voltage (>3V) while avoiding problems of thermal runaway and electrolyte flammability. Our studies further show that catholyte composition not only impacts low temperature electrochemical performance, but also the accessible capacity and even techno-economic viability of the system. Implementing these catholytes in lab-scale prototypes with charge-transfer interfaces engineered for low-temperature operation, we have demonstrated 5 months of stable electrochemical cycling at 110oC. Continued refinement of these material-enabled strategies promises a new class of grid-scale energy storage technologies based on molten sodium.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Improve the low-temperature electrochemical performance of Li4Ti5O12 anode materials by ion doping

We adopt the strategy of doping ions of Mg2+, Cr3+, and F− into Li4Ti5O12 (LTO) to substitute Li, Ti, and O, respectively (called the corresponding sample Mg-LTO, Cr-LTO, and F-LTO, respectively), and investigated its influences on the low-temperature electrochemical performance of LTO. After doping, the electrical conductivity of Mg-LTO, Cr-LTO, and F-LTO increased from less than < 10− 13 S cm− 1 to 3.07 × 10− 7 S cm− 1, 5.57 × 10− 7 S cm− 1, and 7.04 × 10− 7 S cm− 1, respectively. Structural refinement shows that doping has little effect on the radius of the crystal diffusion sites. Further research shows that the main reason for the improvement of low-temperature electrochemical performance is that doping affects the electrical conductivity, micromorphology, and phase composition of LTO. At −20 °C/10 C (1C corresponding to 175 mAh g− 1), the discharge capacities of Mg-LTO, Cr-LTO and, F-LTO are 113 mAh g− 1, 123 mAh g− 1, and 128 mAh g− 1, respectively. As a contrast, there is no discharge capacity for Pure LTO at the same conditions. After 600 cycles at −20 °C/5C, the discharge capacities of the sample of Pure LTO, Mg-LTO, Cr-LTO, and F-LTO are 69.7 mAh g− 1, 107.5 mAh g− 1, 142.3 mAh g− 1, and 133.2 mAh g− 1, respectively. Mg-LTO, Cr-LTO, and F-LTO exhibit excellent low-temperature rate performance and cycling stability. The related electrochemical factors and materials structure mechanisms involved were discussed in detail.

Enhanced Solar-Driven-Heating and Tough Hydrogel Electrolyte by Photothermal Effect and Hofmeister Effect.

Although plenty of progress and achievements are made on hydrogel electrolyte researches, the inherent inferior low-temperature performance of hydrogel electrolyte is still a severe challenge for wider application on the energy storage devices, due to the high content of water within hydrogel. Herein, an enhanced solar-driven-heating composite hydrogel electrolyte and a solar-driven-heating graphene based micro-supercapacitor are developed utilizing the photothermal conversion ability and self-initiation of MoS2 nanosheets and additional Hofmeister effect. The MoS2 composite hydrogel electrolyte not only improves the reliability of micro-supercapacitor owing to its splendid mechanical properties, but also endows the micro-supercapacitor with superior low-temperature electrochemical performance and broadens its operating environment to a much lower temperature (-56 °C), which should be attributed to the excellent ability in converting endless solar energy into required thermal energy. These efforts would construct a new application platform for solar energy conversion and present an efficient method to structure severe-cold resistant solid state energy storage devices for next-generation.

The optimized LiBF4 based electrolytes for TiO2(B) anode in lithium ion batteries with an excellent low temperature performance

It is a great challenge to improve the low temperature electrochemical performance of lithium ion batteries because of the sluggish kinetics at such temperature. In this work, an optimized LiBF4 based electrolyte formulation for TiO2(B) anode in lithium ion battery is designed to heighten the low temperature electrochemical performance. TiO2(B) anode with optimized ratio electrolyte exhibits a reversible capacity as high as ~ 240 mAhg−1 at 0.1 A g−1 at −20 °C. In such optimized electrolyte, TiO2(B) shows excellent electrochemical performance at a low temperature up to −30 °C. It is found that the separation energy of lithium ion and solvents at the optimized formulation accounts for the improved electrochemical performance based on molecular dynamics simulation.

Influence of Lithium Polysulfide Clustering on the Kinetics of Electrochemical Conversion in Lithium-Sulfur Batteries.

The electrochemistry of lithium-sulfur (Li-S) batteries is heavily reliant on the structure and dynamics of lithium polysulfides, which dissolve into the liquid electrolyte and mediate the electrochemical conversion process during operation. This behavior is considerably distinct from the widely used lithium-ion batteries, necessitating new mechanistic insights to fully understand the electrochemical phenomena. Testing at low-temperature conditions presents a unique opportunity to glean new insights into the chemistry in kinetically constrained environments. Under such conditions, despite the low freezing point and favorable ionic conductivity of the glyme-based electrolyte, Li-S batteries exhibit counterintuitively poor performance. Here, we show that beyond just existing in single-molecule conformations, lithium polysulfides tend to cluster and aggregate in solution, particularly at low-temperature conditions, which subsequently constrains the kinetics of electrochemical conversion. Energetics and coordination implications of this behavior are extended towards a new framework for understanding the solution-coordination dynamics of dissolved lithium species. Based off this framework, a favorable strongly-bound lithium salt is introduced in the Li-S electrolyte to disrupt polysulfide clustered networks, enabling substantially enhanced low-temperature electrochemical performance. More broadly, this mechanistic insight heightens our understanding of polysulfide chemistry irrespective of temperature, confirming the link between the solution conformation of active material and electrochemical behavior.

Effect of Ti doping on LiFePO4/C cathode material with enhanced low-temperature electrochemical performance

A series of LiFePO4/C composites with Ti in-situ doped has been synthesized by a combination of wet ball-milling, spray drying, and carbothermal reduction. The test result shows that the composite ion doping can significantly improve the electrochemical performance of the material. The discharge specific capacity of the button cell at 0.2C is 160.2 mAh g−1. After 500 cycles, the battery capacity remained 96.8% of the initial discharge capacity, which shows an excellent rate discharge performance and cycle performance. The study found that the appropriate amount of Ti doping does not much affect the crystal structure, but the particle size of the primary particles exhibits a trend of nanocrystallization, which could effectively shorten the deintercalation distance of Li+. Especially the low-temperature performance of the Ti doping LiFePO4, there was the highest discharge capacity of 122.3 mAh g−1 at 1C and − 20 °C. But the excessive doping of Ti could cause the deformation and blockage of lithium-ion channels, which reduced the lithium-ion diffusion coefficient. Besides, the 14,500 cylindrical batteries were performed to verify the effectiveness of application, which could reach a 148.8 mAh g−1 at 1C rate.

Effect of Nb5+ Doping on the Structure and Electrochemical Performances of LiFePO4

Nb-doped LixNb0.005FeyPO4/C cathode material for lithium-ion batteries were prepared by two-fluid spray-drying using FePO4·2H2O, LiOH·H2O, C6H12O6(glucose) as raw materials under N2 atmosphere. The effects of doping Nb5+ on the structure, morphology and electrochemical performances of LiFePO4 were investigated. The results show that LixNb0.005FeyPO4/C has Olivine Structure and pure phase. The LixNb0.005FeyPO4/C had an initial discharge specific capacity of 158.5mAh/g at 0.1C and its specific capacities were 109mAh/g at 5C. The initial charge/discharge efficiency reached 93.9%. The discharge specific capacity of the LixNb0.005FeyPO4/C at 253K is 82.2mAh/g. This investigation suggests that the Nb5+ doped material possess high rate capability and excellent low temperature electrochemical performance.

Temperature-Dependent Li Storage Performance in Nanoporous Cu-Ge-Al Alloy.

The performance fading process and safety concerns of lithium ion batteries at low temperature (LT) prohibit their application in cold climates. The alloy-type electrodes demonstrate great potentials in stable and dendrite-free anodes at LT. Herein, we report a temperature-dependent Li storage performance in Al-based nanoporous alloy anode. The nanoporous-structured Cu-Ge-Al ternary alloys (NP-CuGeAl) have been designed and prepared by selectively etching Al out. The high-Al-content NP-CuGeAl (acid etching for 6 h, named CGA-6) is composed of multi-intermetallic compounds (denoted as M xN y, M, N = Cu, Al, Ge) with bimodal porous architectures. Investigated as anode at room temperature, the CGA-6 delivers a capacity as high as 479.7 mAh g-1 at 0.5 A g-1 of over 1020 cycles, and the low-Al-content ones show improved LT electrochemical performance. At -20 °C, the CGA-48 (acid etching for 48 h) shows much better performance as compared with the CGA-6. In Situ transmission electron microscopy and ex situ characterizations confirm that the M xN y/Li zM xN y couples are highly reversible and the porous structure is durable upon battery cycling.

A Practical Li-Ion Full Cell with a High-Capacity Cathode and Electrochemically Exfoliated Graphene Anode: Superior Electrochemical and Low-Temperature Performance

Lithium-ion batteries (LIBs) are widely adopted power sources for portable digital products and electrical vehicles (EV). However, the high cost associated with raw materials and manufacturing and low-temperature performance are primary concerns for large-scale deployment of LIBs, especially for EV and grid-scale storage applications. Herein, a novel lithium-ion full cell assembled by 3 μm-LiNi0.6Co0.2Mn0.2O2 (LNCM-3) cathode and electrochemically exfoliated graphene (EG) anode was fabricated, generating an energy density of ∼278 Wh kg–1, which is calculated on the basis of the design of commercial 18650 LIBs. Besides, it also exhibits outstanding rate capability, superior low-temperature electrochemical performance and ultralong cycle life (no capacity fading within 300 cycles at temperatures from 25 to −30 °C at 180 mA g–1). The proposed novel full cell configuration will enable the next-generation high performance batteries for EV applications.

Mg2+–W6+ co-doped Li2ZnTi3O8 anode with outstanding room, high and low temperature electrochemical performance for lithium-ion batteries

LM6ZTW3O co-doped with Mg2+–W6+ with excellent low temperature electrochemical performance has been synthesized using a simple solid-state method.

Enhanced low temperature electrochemical performances of LiFePO4/C by V3+ and F− co-doping

V3+ and F− co-doped LiFePO4/C cathode materials are prepared via a facile wet milling-spray drying-carbothermal reduction (WSC) process. The obtained products have bowl-like morphologies with the diameters from 5 to 10 μm, which are composed of numerous nanoparticles smaller than 100 nm integrated by carbon network. The effects of ion doping are studied. V3+ and F− co-doped LiFePO4/C shows improved electrochemical performance, which delivers a discharge capacity of 136 mAh·g−1 (10 C) at 20 °C. At 0 °C, a capacity of 86 mAh·g−1 (10 C) can be obtained, which is 20 mAh·g−1 higher than LiFePO4/C. In addition, the V3+ and F− co-doped LiFePO4/C shows excellent cycle performances. The improved performance of V3+ and F− co-doped LiFePO4/C is due to the low charge transfer resistance, enhanced electrical conductivity and the holes on the surface of particles which can provide more ion transport channel.

Improving low-temperature performance of spinel LiNi0.5Mn1.5O4 electrode and LiNi0.5Mn1.5O4/Li4Ti5O12 full-cell by coating solid-state electrolyte Li-Al-Ti-P-O

Octahedral cathode materials LiNi0.5Mn1.5O4 (LNMO), with primary particles size of 300–600 nm are prepared through one-step co-precipitation. Then solid-state electrolyte Li2O-Al2O3-TiO2-P2O5 (LATP) was coated on LNMO to form continuous surface-modification layer. There is no obviously difference of structure, morphology between coated LATP LiNi0.5Mn1.5O4 (LATP-LNMO) and pristine LiNi0.5Mn1.5O4 (P-LNMO). Low-temperature electrochemical performance of P-LNMO and LATP-LNMO electrodes, including charge-discharge capacity, cycle performance, middle discharge voltage and electrochemical impedance spectra (EIS), were measured systematically with three electrode. The results reveal that LATP-LNMO electrode presents superior electrochemical performance at low temperature, compared to P-LNMO electrode. At −20 °C, the capacity retention of LATP-LNMO (61%) is much higher than that of P-LNMO (39%). According to EIS, the enhancement of performance of LATP-LNMO cathode at low temperature can be attribute to LATP coating, which not only promotes lithium-ion diffusion at electrode/electrolyte interface but also decreases the charge transfer resistance. Finally, the electrochemical performances of full cell of LATP-LNMO or P-LNMO cathode vs Li4Ti5O12 anode are investigated. The energy density can be achieved to 270 Wh·Kg−1 at −20 °C if using LATP-LNMO, which is much better than that of P-LNMO.

Electrochemical behavior of lithium ion capacitor under low temperature

Lithium-ion capacitor (LIC) is a novel electrochemical energy storage device that bridges the performance gap between the electrical double-layer capacitor and lithium ion battery. In this work, we fabricated lithium-ion capacitors (LICs) with activated carbon (AC) positive electrode and pre-lithiated hard carbon (HC) negative electrode. The effect of low temperature on the electrochemical performance of LIC is investigated by the galvanostatic charging-discharging, electrochemical impedance tests, rate performance and cycle performance testing. The electrolyte viscosity increases, the ionic conductivity decreases and ionic migration becomes slow in the charge-discharge process with the decrease of temperature, causing the increase of resistance and the electrochemical polarization, which is responsible for the attenuation of LIC electrochemical performance. LIC at the temperature of −20 °C exhibits the optimal low temperature electrochemical performance, high energy density up to 76.6 Wh kg−1 and power density as high as 5.8 kW kg−1 (based on active material mass of two electrodes), excellent capacity retention of 80.1% after 5000 cycles.

Optimized solvothermal synthesis of LiFePO4 cathode material for enhanced high-rate and low temperature electrochemical performances

A series of LiFePO4 nanoparticles were synthesized via solvothermal method for process parameters optimizing. The influences of Li:P:Fe mole ratio, reaction temperature and reaction time were systematically investigated. The obtained LiFePO4 nanoparticles were characterized by X-ray diffraction (XRD), scanning/transmission electron microscope (SEM/TEM), galvanostatic charge-discharge and cyclic voltammetry test. Results show that the mole ratio of Li:P:Fe has significant effects on the morphology and particle size of LiFePO4 material, while reaction temperature and time show little influence on crystal and shape. Prepared with Li:P:Fe = 3:1.5:1 at 180 °C for 4 h, the LiFePO4 shows rectangular nanoplates with well-dispersed, resulting in the best electrochemical performance. After carbon coating, this optimized LiFePO4/C composite exhibits superior high-rate performance with a discharge capacity of 122.5 mAh/g at 50C at 25 °C, as well as excellent low temperature property of 116.7 and 61.4 mAh/g at 0 °C and −20 °C at 5C, respectively. To illustrate the LiFePO4 nanoparticles with different size and shape caused by variations of mole ratio, a possible formation mechanism is demonstrated. This work indicates that the optimized solvothermal process can be a promising guidance used in industrialization to synthesize cathode material with enhanced high-rate and low temperature performance.

Mechanisms of the decrease in low-temperature electrochemical performance of Li4Ti5O12-based anode materials

The electrochemical performances of Li4Ti5O12 (LTO) and Li4Ti5O12-rutile TiO2 (LTO–RTO) composite electrodes at low temperatures were evaluated. The electrochemical performance of both electrodes decreased at low temperatures; regardless, the LTO–RTO electrode performed better than the LTO electrode. First, high viscosity and low ion conductivity of liquid electrolytes at low temperatures significantly reduce electrochemical performance. Second, cycling at low temperatures changes the crystal structure of LTO–based electrodes, impeding lithium ion diffusion and even causing the diffusion path to change from easy to difficult. However, changes in the crystal structure of the LTO–RTO electrode were not sufficient to change this path; thus, diffusion continued along the 8a-16c-8a pathway. Finally, from the perspective of dynamics, aggravation of a side reaction, increase in charge transfer resistance and polarization, and decrease in lithium ion diffusion at low temperatures reduce the electrochemical performance of LTO–based anode materials. However, the activation energy based on lithium ion diffusion is lower in the LTO–RTO electrode than the LTO electrode. The results confirmed that the electrochemical performance of the LTO–RTO electrode was better than that of the LTO electrode at low temperatures.

Hydrogen storage and low-temperature electrochemical performances of A2B7 type La-Mg-Ni-Co-Al-Mo alloys

The effect of Mo-addition on hydrogen storage and low-temperature electrochemical performances of La-Mg-Ni-Co-Al alloys is investigated. The alloys were synthetized via vacuum induction melting followed by annealing treatment at 1123K for 8h. The major phases in the annealed alloys are consisted of (La, Mg)2Ni7, (La, Mg)5Ni19 and LaNi5 phases. Mo-addition facilitates phase transformation of LaNi5 into (La, Mg)2Ni7 and (La, Mg)5Ni19 phases. Hydrogen absorption/desorption PCI curves indicates that the hydrogen storage capacity of the alloy increases remarkably with the addition of Mo. Furthermore, the La0.75Mg0.25Ni3.05Co0.2Al0.05Mo0.2 alloy shows excellent hydriding/dehydriding kinetics with a higher capacity, requiring only 100s to reach its saturated hydrogen capacity of 1.58wt% at low temperature of 303K, and releasing 1.57wt% hydrogen within 400s at 338K. Electrochemical experiments manifest that the Mo-added alloy electrode has perfect activation properties and the maximum discharge capacity. The low-temperature dischargeability shows that the La0.75Mg0.25Ni3.05Co0.2Al0.05Mo0.2 alloy exhibits the excellent low-temperature discharge performance, and the maximum discharge capacity is improved from 231.0 to 334.6mAh/g at 253K. The HRD property of the alloy electrode is enhanced, suggesting that Mo enhances the kinetic ability at low-temperature.

Research progress on the low-temperature electrochemical performance of Li4Ti5O12 anode material

Li4Ti5O12 is regarded as the ideal anode material for its stable structure, high charge/discharge platform, and safety performance. But low ionic and electronic conductivity of the Li4Ti5O12 anode material under the condition of low temperature greatly limit its application in practical production. In this paper, some modified methods for improving the low-temperature electrochemical performance of Li4Ti5O12 anode material were summarized. Meanwhile, we explored its influence mechanisms at low temperature, one is, with the subtle changes of lattice parameters and oxygen atom fraction coordinates of Li4Ti5O12 at low temperature, the changes of the bond length influence the structural stability of Li4Ti5O12 and the diffusion path of lithium ions; the other reason is that the charge transfer resistance increases obviously and the lithium ion diffusion coefficient reduces under low temperature. Finally, the research directions for improving the low-temperature electrochemical performance were proposed.

High Energy Density LiFePO4/C Cathode Material Synthesized by Wet Ball Milling Combined with Spray Drying Method

Lithium iron phosphate with high energy density was synthesized by a combination of wet ball milling, spray drying and carbon thermal reduction technology using inexpensive FePO4 as starting material. The effect of morphology on structure and electrochemical properties of LiFePO4/C cathode material was systematically investigated. The as-obtained LiFePO4/C composite has ordered olivine structure and micro-spherical morphology assembled with nanosized primary particles. The lithium iron phosphate microsphere has a core-shell structure, not only does the surface of nanoparticles have a homogeneous and complete carbon coating but also does the surface of secondary particles form a carbon shell, which results in its uniform particle size distribution and enhanced electronic conductivity. All above-mentioned factors lead to its excellent room-temperature and low-temperature electrochemical performance in LiFePO4/Li half-cell, as well as good processabilty in 14500 cylindrical full-cell. More importantly, its high tap density and pole piece compaction density can effectively improve the volumetric specific energy of the battery.

Synthesis and Electrochemical Performance of LiFePO4/C Composite by Improved Solid-State Method Using a Complex Carbon Source

A high-performance LiFePO4/C composite was synthesized by improved solid-state method using starch and PEG6000 as a complex carbon source. The raw materials were mixed by wet-mixing method using de-ionized water as medium. For comparison, a LiFePO4/C composite was prepared using PEG6000 as single carbon source. XRD results show that the sample prepared by improved solid-state method has ordered olivine structure and high purity due to the perfect mixing of the raw materials by wet-mixing method. Fine particles with an average particle size about 400 nm are examined by scanning electron microscopy (SEM). TEM observation illustrates that the complex carbon source leads to the homogeneous and complete carbon coating on LiFePO4 particle surface, resulting in its uniform particle size distribution and enhanced electronic conductivity. All the above factors lead to the better room-temperature and low-temperature electrochemical performances of LiFePO4/C composite synthesized by improved solid-state method in both LiFePO4/Li half-cell and 18650 cylindrical full-cell.