Li-ion Polymer Batteries Research Articles

Thermomechanical analysis and durability of commercial micro-porous polymer Li-ion battery separators

Static and dynamic thermomechanical analysis was performed with a dynamic mechanical analyzer (DMA) to identify thermal and mechanical transitions for commercially available polymer separators under mechanical loading. Clear transitions in deformation mode were observed at elevated temperatures. These transitions identified the onset of separator “shutdown” which occurred at temperatures below the polymer melting point. Mechanical loading direction was critical to the overall integrity of the separator. Anisotropic separators (Celgard 2320, 2400 and 2500) were mechanically limited when pulled in tensile in the transverse direction. The anisotropy of these separators is a result of the dry technique used to manufacture the micro-porous membranes. Separators prepared using the wet technique (Entek Gold LP) behaved more uniformly, or biaxially, where all mechanical properties were nearly identical within the separator plane. The information provided by the DMA can also be useful for predicting the long-term durability of polymer separators in lithium-ion batteries exposed to electrolyte (solvent and salt), thermal fluctuations and electrochemical cycling. Small losses in mechanical integrity were observed for separators exposed to the various immersion environments over the 4-week immersion time.

Synthesis and Performance of Gel Polymer Li-Ion Batteries

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Electrochemical performance of methyl methacrylate graft-copolymerized composite separator based on radiation polymerization technique

The pre-irradiation method is introduced to prepare methyl methacrylate graft-copolymerized composite separators. The morphologies of the grafted membranes (GMs) were observed under a scanning electron microscope. The cyclic voltammetry and electrochemical impedance spectra results indicated that the obtained polymer electrolytes (PEs) based on GMs could hold the excellent performance of Li+ transportation and possess good affinity with Li metal electrode. The Li/PEs/LiCoO2 cells demonstrated excellent cycling performance with little capacity loss after 80 cycles. These cells also showed a good rate property and could retain 70.2% (25 °C) and 81% (75 °C) of discharge capacity at 2C rate as compared to that at C/5 rate. The results of this paper suggest that the high-quality composite separators can be obtained by pre-irradiation technique, and this also offered a new and convenient way for the large-scale manufacture of Li-ion polymer battery.

Frequency and Temporal Identification of a Li-ion Polymer Battery Model Using Fractional Impedance

The modelling of high power Lithium batteries may work as a powerful tool in the sizing of batteries pack in hybrid vehicles. Moreover, this tool can be used to evaluate accurately the battery characteristics at each level of its lifetime. Until now, the model structure differs according to its end-use due to simulation limitation. Indeed, impedance measurements obtained by electrochemical impedance spectroscopy needs non-integer order impedance in order to correctly model diffusive phenomenon. However, this impedance cannot be simulated easily in software dedicated to hybrid vehicles and needs approximations. Furthermore, impedance measurements are realised with low currents comparing to currents that are forecast in normal uses of high power batteries and can induce errors if the impedance is varying with the current. This paper deals with non linear dynamic models that use band-limited frequency impedance with non-integer order. The parameters are identified partly by impedance measurements for high frequencies and partly by chronopotentiometry measurements for low frequencies. Validation tests are made with staircase of high intensity and current profile simulated on a hybrid vehicle software. The hypothesis of non-linearity is verified.

Design of a Solar Power Management System for an Experimental UAV

The design of a solar power management system (SPMS) for an experimental unmanned aerial vehicle (UAV) is summarized. The system will provide power required for the on-board electronic systems on the UAV. The power management system mainly consists of the maximum power point tracking (MPPT), the battery management, and the power conversion stages. The MPPT stage attempts to obtain the maximum power available from the solar cell panels. The battery management stage monitors and controls the charge and discharge processes of the Li-ion polymer battery modules. The last stage is for power conversion that consists of dc/dc synchronous buck converters to generate +5 V and +12 V powers for the on-board computers and other electronic circuitries.

An Electrical Circuit for Modeling the Dynamic Response of Li-Ion Polymer Batteries

An equivalent electrical circuit model based on parameters taken from ac impedance measurements obtained from a Li-ion polymer battery is simulated in a Matlab/Simulink environment. The model representation contains relevant parameters, including ohmic resistance, slow migration of Li-ions through the surface layers, faradaic charge transfer process, solid-state diffusion of Li-ions, and charge accumulation (intercalation capacitance) within the host material. The model also takes into account the non-homogeneous distribution properties (e.g, particle size, pore geometry) of the electrode which account for deviation from the ideal finite space Warburg behavior. The simulated and experimental results are compared and demonstrate that the impedance model can accurately predict the discharge power performance and transient and dynamic behavior of the Li-ion polymer batteries.

Enhanced ionic conductivities in composite polymer electrolytes by using succinonitrile as a plasticizer

Four different kinds of Li salts were complexed with poly(ethylene oxide) membranes plasticized by succinonitrile (SN). Plasticizing effects were reflected by ionic conductivities enhancement. The high ionic conductivities can be attributed to the high free carrier concentration because of the high polarity and diffusivity of SN, decreased crystallinity of polymer and dissociable Li salt. Moreover, the membranes still preserved high mechanical strength. The combination of enhanced mechanical and electrical properties renders the electrolyte a potential candidate in Li–ion polymer batteries.

Development of gel-polymer electrolytes and nano-structured electrodes for Li-ion polymer batteries

A novel methacrylic gel-polymer membrane was synthesized by free radical photo polymerisation (UV-curing technique). The polymerisation was very easy, fast and reliable and the membrane shows good behaviour in terms of both conductivity and cyclability in Li cells. The anode materials were prepared by high energy ball milling obtaining nanocrystalline Ni–Sn alloys, while the hydrothermal processing in presence of a template was used to prepare nanostructured LiFePO4/C as cathode material. Every component has been characterised separately from the structural and electrochemical point of view. The first experimental data on the performance of a complete Li-ion polymer cell assembled with the components studied are also presented. The results obtained demonstrate the overall satisfying, and some superior performances of the various single components and their feasibility as a complete system.

PVDF-HFP composite polymer electrolyte with excellent electrochemical properties for Li-ion batteries

Poly (vinylidene fluoride-co-hexafluoropropylene)-based composite polymer electrolyte (CPE) was prepared by phase inversion technique. In this work, we first applied a novel surface-modified sub-micro-sized alumina, PC-401, as ceramic filler. Various electrochemical methods were applied to investigate the electrochemical properties of the polymer electrolytes. We found that the CPE with 10 wt.% PC-401 has excellent electrochemical properties, including the ionic conductivity as high as 0.89 mS cm−1 and the Li-ion transference number of 0.46. Polymer Li-ion batteries using LiFePO4 as cathode active material exhibited excellent cycling and high-temperature performances. PC-401 shows a promising applicability in the preparation of polymer electrolyte with high electrochemical properties.

Effect of nanoscale CeO2 on PVDF-HFP-based nanocomposite porous polymer electrolytes for Li-ion batteries

New poly (vinylidenefluoride-co-hexafluoro propylene) (PVDF-HFP)/CeO2-based microcomposite porous polymer membranes (MCPPM) and nanocomposite porous polymer membranes (NCPPM) were prepared by phase inversion technique using N-methyl 2-pyrrolidone (NMP) as a solvent and deionized water as a nonsolvent. Phase inversion occurred on the MCPPM/NCPPM when it is treated by deionized water (nonsolvent). Microcomposite porous polymer electrolytes (MCPPE) and nanocomposite porous polymer electrolytes (NCPPE) were obtained from their composite porous polymer membranes when immersed in 1.0 M LiClO4 in a mixture of ethylene carbonate/dimethyl carbonate (EC/DMC) (v/v = 1:1) electrolyte solution. The structure and porous morphology of both composite porous polymer membranes was examined by scanning electron microscope (SEM) analysis. Thermal behavior of both MCPPM/NCPPM was investigated from DSC analysis. Optimized filler (8 wt% CeO2) added to the NCPPM increases the porosity (72%) than MCPPM (59%). The results showed that the NCPPE has high electrolyte solution uptake (150%) and maximum ionic conductivity value of 2.47 × 10−3 S cm−1 at room temperature. The NCPPE (8 wt% CeO2) between the lithium metal electrodes were found to have low interfacial resistance (760 Ω cm2) and wide electrochemical stability up to 4.7 V (vs Li/Li+) investigated by impedance spectra and linear sweep voltammetry (LSV), respectively. A prototype battery, which consists of NCPPE between the graphite anode and LiCoO2 cathode, proves good cycling performance at a discharge rate of C/2 for Li-ion polymer batteries.

Li-ion Polymer Battery for Stationary Applications

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4.4 V lithium-ion polymer batteries with a chemical stable gel electrolyte

We tested 4.2 V Li-ion polymer batteries (LIPB) with physical gel electrolyte, poly(vinylidene fluoride) (PVDF), 4.4 V LIPB and 4.4 V Li-ion batteries (LIB) with a liquid electrolyte. The discharge capacity of the 4.4 V LIPB reached 520 Wh l −1 which was 9% higher than that of the 4.2 V LIPB. The 4.4 V LIPB had a high capacity retention ratio of 91.4% at 3 C because of the excellent ion conductivity of the PVDF gel. The capacity retention ratio of the 4.4 V LIPB was 82% after 500 cycles, which is comparable to those of some commercial LIBs. The 4.4 V LIPB retained its original thickness even after many cycles and after being stored at 90 °C, whereas the 4.4 V LIB swelled by over 20%. Peaks in the FT-IR spectrum of the discolored separator in the 4.4 V LIB after storage were assigned to C C double bonds, suggesting that the separator in direct contact with the 4.4 V cathode had been oxidized. The PVDF gel electrolyte not only had a high ionic conductivity but also completely suppressed oxidation. The 4.4 V LIPB with PVDF gel electrolyte has properties suitable for practical cells, namely, high energy density, high permanence and it is safe to use.

Preparation and electrochemical properties of polymer Li-ion battery reinforced by non-woven fabric

A polymer electrolyte based on poly(vinylidene) fluoride-hexafluoropropylene was prepared by evaporating the solvent of dimethyl formamide, and non-woven fabric was used to reinforce the mechanical strength of polymer electrolyte and maintain a good interfacial property between the polymer electrolyte and electrodes. Polymer lithium batteries were assembled by using LiCoO2 as cathode material and lithium foil as anode material. Scanning electron microscopy, alternating current impedance, linear sweep voltammetry and charge-discharge tests were used to study the properties of polymer membrane and polymer Li-ion batteries. The results show that the technics of preparing polymer electrolyte by directly evaporating solvent is simple. The polymer membrane has rich micro-porous structure on both sides and exhibits 280% uptake of electrolyte solution. The electrochemical stability window of this polymer electrolyte is about 5.5 V, and its ionic conductivity at room temperature reaches 0.151 S/m. The polymer lithium battery displays an initial discharge capacity of 138 mA·h/g and discharge plateau of about 3.9 V at 0.2 current rate. After 30 cycles, its loss of discharge capacity is only 2%. When the battery discharges at 0.5 current rate, the voltage plateau is still 3.7 V. The discharge capacities of 0.5 and 1.0 current rates are 96% and 93% of that of 0.1 current rate, respectively.

Accurate electrical battery model capable of predicting runtime and I-V performance

Low power dissipation and maximum battery runtime are crucial in portable electronics. With accurate and efficient circuit and battery models in hand, circuit designers can predict and optimize battery runtime and circuit performance. In this paper, an accurate, intuitive, and comprehensive electrical battery model is proposed and implemented in a Cadence environment. This model accounts for all dynamic characteristics of the battery, from nonlinear open-circuit voltage, current-, temperature-, cycle number-, and storage time-dependent capacity to transient response. A simplified model neglecting the effects of self-discharge, cycle number, and temperature, which are nonconsequential in low-power Li-ion-supplied applications, is validated with experimental data on NiMH and polymer Li-ion batteries. Less than 0.4% runtime error and 30-mV maximum error voltage show that the proposed model predicts both the battery runtime and I-V performance accurately. The model can also be easily extended to other battery and power sourcing technologies.

Ac Impedance and ESEM Analysis of LixC6 Electrode In Li-Ion Polymer Batteries with Continuous Cycling

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Li-Ion Polymer Battery using LiFePO4 as Cathode Material

not Available.

Electrochemical properties and cycle performance of electrospun poly(vinylidene fluoride)-based fibrous membrane electrolytes for Li-ion polymer battery

Prototype cells were prepared by hot pressing of the cathode and the anode coated with poly(vinylidenefluoride-hexafluoropropylene) P(VdF-HFP) and poly(vinylidene fluoride) PVdF-based fibrous membranes, respectively. Electrochemical properties and cycle performance of them before and after hot pressing were investigated. Pressing of the fibrous membrane resulted in decrease of the apparent porosity and electrolyte uptake. The prototype cell using hot-pressed membrane electrolyte showed continuous fading of the capacity while that using non-pressing fibrous membrane almost retained the initial capacity after 100 cycles at room temperature (0.5 C rate). In the case of cycle test at 80 °C, however, the capacity was slightly decreased after the initial capacity fading of about 6.5% during the first 10 cycles due to the evaporation of liquid electrolytes. Rate performance exhibited about 97% and 72% of the full capacity at the 1 C rate and 2 C rate, respectively. The capacities at 5 C rate and 10 C rate were about 27–28% of the full capacity similarly because of the reduction of the entrapped liquid phase due to the swell of the fibrous structure.

Synthesis of nano-crystalline LiSr xMn 2 − xO 4 powder by a novel sol–gel thermolysis process for Li-ion polymer battery

Cubic spinel nano-crystalline LiSr x Mn 2 − x O 4 ( x = 0.10, 0.15, 0.20, 0.25) powders are prepared at low temperature by means of a facile gel-polymer thermolysis process by calcining the prepared precursor samples at 340 °C to obtain the products. X-ray diffraction and scanning electron microscopic analyses confirm that the products consists of nano-crystalline particles with uniform distribution. The effect of calcinations on the crystallinity of the cubic spinel LiSr x Mn 2 − x O 4 powder is examined by differential scanning colorimetric analysis. In order to asses the electrochemical reversibility of the cathode material, cyclic voltametry studies are performed by fabricating button cells with the configuration of carbon/MPPE/LiSr x Mn 2 − x O 4.

LiFePO 4 safe Li-ion polymer batteries for clean environment

The performance of natural graphite-fibers/PEO-based gel electrolyte/LiFePO 4 cells (7 mAh, 4 cm 2) is reported. The gel polymer electrolytes were produced by electron-beam irradiation and then soaked in a liquid electrolyte. The natural graphite-fiber composite anode in gel electrolyte containing 1.5 M LiFSI-EC/GBL (1:3) exhibited high reversible capacity (361 mAh g −1) and high Coulombic efficiency (92%). The LiFePO 4 cathode in the same gel polymer exhibited a reversible capacity of 161 mAh g −1 and 93% Coulombic efficiency. A 1.5 M solution of LiFSI in ethylene carbonate (EC)/γ-butyrolactone (GBL) (1:3, v/v) mixed solvent is advantageous for use as the electrolyte in the laminated film bag because of its high flame point (135 °C), high boiling point (219 °C), low vapor pressure and high conductivity (10.2 mS cm −1 at 20 °C). The Li-ion gel polymer battery shows a very low capacity fade of 5% after 500 cycles and also has high-rate capability. The Li-ion gel polymer cell using LiFePO 4 cathodes is suitable for HEV applications.

Preparation and performance characterization of polymer Li-ion batteries using gel poly(diacrylate) electrolyte prepared by in situ thermal polymerization

A gel polymer electrolyte (GPE) was prepared by in-situ thermal polymerization of 1,3-butanediol diacrylate (BDDA) in a EC/EMC/DMC electrolyte solution at 100 °C. The GPE with 15 wt.% polymer content appears as apparently “dry” polymer with sufficient mechanical strength and shows a high ionic conductivity of 3.2×10−3 S cm−1 at 20 °C. The MCMB–LiCoO2 type polymer Li-ion batteries (PLIB) prepared using this in-situ internal polymerization method exhibit a very high initial charge–discharge efficiency of 92.1%, and can deliver 94.4% of its nominal capacity at 1.0 C rate and 70.7% of its room temperature capacity at −20 °C. Also, the PLIB cells show very good cycling ability with >85% capacity retention after 300 cycles. The excellent charge–discharge properties of the PLIB cells are attributed to the integrated structure in which the polymer matrix spreads over entire region of the cell acting as a strong binder and electrolyte carrier to produce a stabilized electrode–electrolyte interface. In addition, the fabricating process of the polymer cell is quite simple and convenient for practical applications.