In Situ Monitoring of Temperature inside Lithium-Ion Batteries by Flexible Micro Temperature Sensors

Lithium-ion secondary batteries are commonly used in electric vehicles, smart phones, personal digital assistants (PDA), notebooks and electric cars. These lithium-ion secondary batteries must charge and discharge rapidly, causing the interior temperature to rise quickly, raising a safety issue. Over-charging results in an unstable voltage and current, causing potential safety problems, such as thermal runaways and explosions. Thus, a micro flexible temperature sensor for the in in-situ monitoring of temperature inside a lithium-ion secondary battery must be developed. In this work, flexible micro temperature sensors were integrated into a lithium-ion secondary battery using the micro-electro-mechanical systems (MEMS) process for monitoring temperature in situ

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Department of Energy Engineering (Battery Science and Technology)Aprotic electrolyte based lithium-oxygen batteries are of considerable interest due to its ultrahigh theoretical specific energy density (1675 mAh per gram of oxygen) against the present lithium-ion battery. In spite of the attractiveness of its high theoretical capacity, there is a number of drawbacks such as instability of electrochemical reaction of electrode and electrolytes. In order to overcome these parasitic reactions, significant efforts have been devoted to developing the key materials such as carbon-free air cathodes and high concentrated electrolytes. However, the CO2 evolution during the charging process and low ionic conductivity limit the ideal electrochemical reaction in aprotic electrolytes. In this thesis, we applied the molten electrolyte based on nitrate-based electrolyte (Li/Na/K/Cs/Ca-NO3). The molten electrolyte, which has a eutectic point of 65???, has the advantages of high stability and high-temperature operation, thereby preventing detrimental solvent byproducts in lithium-oxygen batteries. We examined the Oxygen Evolution Reaction (OER) and Oxygen Reduction Reaction (ORR) on operating temperature using in situ pressure drop and gas analyses, Differential Electrochemical Mass Spectrometry (DEMS). Our results demonstrated that the Li2O2, a discharge product, formed a stable hexagonal morphology in the lithium-oxygen battery upon discharge process by scanning electron microscopy and X-ray diffraction techniques. Also, it leads to improved oxygen mobility at high temperature since a molten salt was used as the electrolyte in lithium-oxygen batteries. In addition, we found that kinetics are improved with increasing operating temperature in molten salt electrolyte cells.ope

On-board monitoring of 2-D spatially-resolved temperatures in cylindrical lithium-ion batteries: Part II. State estimation via impedance-based temperature sensing

Impedance-based temperature detection (ITD) is a promising approach for rapid estimation of internal cell temperature based on the correlation between temperature and electrochemical impedance. Previously, ITD was used as part of an Extended Kalman Filter (EKF) state-estimator in conjunction with a thermal model to enable estimation of the 1-D temperature distribution of a cylindrical lithium-ion battery. Here, we extend this method to enable estimation of the 2-D temperature field of a battery with temperature gradients in both the radial and axial directions. An EKF using a parameterised 2-D spectral-Galerkin model with ITD measurement input (the imaginary part of the impedance at 215 Hz) is shown to accurately predict the core temperature and multiple surface temperatures of a 32113 LiFePO$_4$ cell, using current excitation profiles based on an Artemis HEV drive cycle. The method is validated experimentally on a cell fitted with a heat sink and asymmetrically cooled via forced air convection. A novel approach to impedance-temperature calibration is also presented, which uses data from a single drive cycle, rather than measurements at multiple uniform cell temperatures as in previous studies. This greatly reduces the time required for calibration, since it overcomes the need for repeated cell thermal equalization.Comment: 11 pages, 8 figures, submitted to the Journal of Power Source

Surface-to-Bulk Redox Coupling through Thermally Driven Li Redistribution in Li- and Mn-Rich Layered Cathode Materials.

Li- and Mn-rich (LMR) layered cathode materials have demonstrated impressive capacity and specific energy density thanks to their intertwined redox centers including transition metal cations and oxygen anions. Although tremendous efforts have been devoted to the investigation of the electrochemically driven redox evolution in LMR cathode at ambient temperature, their behavior under a mildly elevated temperature (up to ∼100 °C), with or without electrochemical driving force, remains largely unexplored. Here we show a systematic study of the thermally driven surface-to-bulk redox coupling effect in charged Li1.2Ni0.15Co0.1Mn0.55O2. We for the first time observed a charge transfer between the bulk oxygen anions and the surface transition metal cations under ∼100 °C, which is attributed to the thermally driven redistribution of Li ions. This finding highlights the nonequilibrium state and dynamic nature of the LMR material at deeply delithiated state upon a mild temperature perturbation

Gaussian Process Regression for In-situ Capacity Estimation of Lithium-ion Batteries

Accurate on-board capacity estimation is of critical importance in lithium-ion battery applications. Battery charging/discharging often occurs under a constant current load, and hence voltage vs. time measurements under this condition may be accessible in practice. This paper presents a data-driven diagnostic technique, Gaussian Process regression for In-situ Capacity Estimation (GP-ICE), which estimates battery capacity using voltage measurements over short periods of galvanostatic operation. Unlike previous works, GP-ICE does not rely on interpreting the voltage-time data as Incremental Capacity (IC) or Differential Voltage (DV) curves. This overcomes the need to differentiate the voltage-time data (a process which amplifies measurement noise), and the requirement that the range of voltage measurements encompasses the peaks in the IC/DV curves. GP-ICE is applied to two datasets, consisting of 8 and 20 cells respectively. In each case, within certain voltage ranges, as little as 10 seconds of galvanostatic operation enables capacity estimates with approximately 2-3% RMSE.Comment: 12 pages, 10 figures, submitted to IEEE Transactions on Industrial Informatic

A 3D Framework for Characterizing Microstructure Evolution of Li-Ion Batteries

Lithium-ion batteries are commonly found in many modern consumer devices, ranging from portable computers and mobile phones to hybrid- and fully-electric vehicles. While improving efficiencies and increasing reliabilities are of critical importance for increasing market adoption of the technology, research on these topics is, to date, largely restricted to empirical observations and computational simulations. In the present study, it is proposed to use the modern technique of X-ray microscopy to characterize a sample of commercial 18650 cylindrical Li-ion batteries in both their pristine and aged states. By coupling this approach with 3D and 4D data analysis techniques, the present study aimed to create a research framework for characterizing the microstructure evolution leading to capacity fade in a commercial battery. The results indicated the unique capabilities of the microscopy technique to observe the evolution of these batteries under aging conditions, successfully developing a workflow for future research studies

The lithiation process and Li diffusion in amorphous SiO2 and Si from first-principles

Silicon is considered the next-generation, high-capacity anode for Li-ion energy storage applications, however, despite significant effort, there are still uncertainties regarding the bulk Si and surface SiO2 structural and chemical evolution as it undergoes lithiation and amorphization. In this paper, we present first-principles calculations of the evolution of the amorphous Si anode, including its oxide surface layer, as a function of Li concentration. We benchmark our methodology by comparing the results for the Si bulk to existing experimental evidence of local structure evolution, ionic diffusivity as well as electrochemical activity. Recognizing the important role of the surface Si oxide (either native or artificially grown), we undertake the same calculations for amorphous SiO2, analyzing its potential impact on the activity of Si anode materials. Derived voltage curves for the amorphous phases compare well to experimental results, highlighting that SiO2 lithiates at approximately 0.7 V higher than Si in the low Li concentration regime, which provides an important electrochemical fingerprint. The combined evidence suggests that i) the inherent diffusivity of amorphous Si is high (in the order 10−9cm2s−1 - 10−7cm2s−1), ii) SiO2 is thermodynamically driven to lithiate, such that Li–O local environments are increasingly favored as compared to Si–O bonding, iii) the ionic diffusivity of Li in LiySiO2 is initially two orders of magnitude lower than that of LiySi at low Li concentrations but increases rapidly with increasing Li content and iv) the final lithiation product of SiO2 is Li2O and highly lithiated silicides. Hence, this work suggests that - excluding explicit interactions with the electrolyte - the SiO2 surface layer presents a kinetic impediment for the lithiation of Si and a sink for Li inventory, resulting in non-reversible capacity loss through strong local Li–O bond formation

Flexible Integration of Alternative Energy Sources for Autonomous Sensing

Recent developments in energy harvesting and autonomous sensing mean that it is now possible to power sensors solely from energy harvested from the environment. Clearly this is dependent on sufficient environmental energy being present. The range of feasible environments for operation can be extended by combining multiple energy sources on a sensor node. The effective monitoring of their energy resources is also important to deliver sustained and effective operation. This paper outlines the issues concerned with combining and managing multiple energy sources on sensor nodes. This problem is approached from both a hardware and embedded software viewpoint. A complete system is described in which energy is harvested from both light and vibration, stored in a common energy store, and interrogated and managed by the node

Ultrahigh power and energy density in partially ordered lithium-ion cathode materials

The rapid market growth of rechargeable batteries requires electrode materials that combine high power and energy and are made from earth-abundant elements. Here we show that combining a partial spinel-like cation order and substantial lithium excess enables both dense and fast energy storage. Cation overstoichiometry and the resulting partial order is used to eliminate the phase transitions typical of ordered spinels and enable a larger practical capacity, while lithium excess is synergistically used with fluorine substitution to create a high lithium mobility. With this strategy, we achieved specific energies greater than 1,100 Wh kg–1 and discharge rates up to 20 A g–1. Remarkably, the cathode materials thus obtained from inexpensive manganese present a rare case wherein an excellent rate capability coexists with a reversible oxygen redox activity. Our work shows the potential for designing cathode materials in the vast space between fully ordered and disordered compounds