Reciprocating air flow for Li-ion battery thermal management to improve temperature uniformity

The thermal management of traction battery systems for electrical-drive vehicles directly affects vehicle dynamic performance, long-term durability and cost of the battery systems. In this paper, a new battery thermal management method using a reciprocating air flow for cylindrical Li-ion (LiMn₂O₄/C) cells was numerically analyzed using (i) a two-dimensional computational fluid dynamics (CFD) model and (ii) a lumped-capacitance thermal model for battery cells and a flow network model. The battery heat generation was approximated by uniform volumetric joule and reversible (entropic) losses. The results of the CFD model were validated with the experimental results of in-line tube-bank systems which approximates the battery cell arrangement considered for this study. The numerical results showed that the reciprocating flow can reduce the cell temperature difference of the battery system by about 4 °C (72% reduction) and the maximum cell temperature by 1.5 °C for a reciprocation period of τ = 120 s as compared with the uni-directional flow case (τ = ∞). Such temperature improvement attributes to the heat redistribution and disturbance of the boundary layers on the formed on the cells due to the periodic flow reversal.     

Preparation and characterization of 18650 Li(Ni1/3Co1/3Mn1/3)O2/graphite high power batteries

The commercial 18650 Li(Ni_1/3Co_1/3Mn_1/3)O₂/graphite high power batteries were prepared and their electrochemical performance at temperatures of 25 and 50 °C was extensively investigated. The results showed that the charge-transfer resistance (R_ct) and solid electrolyte interface resistance (R_sei) of the high power batteries at 25 °C decreased as states of charge (SOC) increased from 0 to 60%, whereas R_ct and R_sei increased as SOC increased from 60 to 100%. The discharge plateau voltage of batteries reduced greatly with the increase in discharge rate at both 25 and 50 °C. The high power batteries could be discharged at a very wide current range to deliver most of their capacity and also showed excellent power cycling performance with discharge rate of as high as 10 C at 25 °C. The elevated working temperature did not influence the battery discharge capacity and cycling performance at lower discharge rates (e.g. 0.5, 1, and 5 C), while it resulted in lower discharge capacity at higher discharge rates (e.g. 10 and 15 C) and bad cycling performance at discharge rate of 10 C. The batteries also exhibited excellent cycle performance at charge rate of as high as 8 C and discharge rate of 10 C.     

Solar cell junction temperature measurement of PV module

The present study develops a simple non-destructive method to measure the solar cell junction temperature of PV module. The PV module was put in the environmental chamber with precise temperature control to keep the solar PV module as well as the cell junction in thermal equilibrium with the chamber. The open-circuit voltage of PV module V_oc is then measured using a short pulse of solar irradiation provided by a solar simulator. Repeating the measurements at different environment temperature (40-80 °C) and solar irradiation S (200-1000 W/m²), the correlation between the open-circuit voltage V_oc , the junction temperature T_j , and solar irradiation S is derived.The fundamental correlation of the PV module is utilized for on-site monitoring of solar cell junction temperature using the measured V_oc and S at a short time instant with open circuit. The junction temperature T_j is then determined using the measured S and V_oc through the fundamental correlation. The outdoor test results show that the junction temperature measured using the present method, T_jo, is more accurate. The maximum error using the average surface temperature T_ave as the junction temperature is 4.8 °C underestimation; while the maximum error using the present method is 1.3 °C underestimation.     

Theoretical evaluation of high-energy lithium metal phosphate cathode materials in Li-ion batteries

Lithium metal phosphates (olivines) are emerging as long-lived, safe cathode materials in Li-ion batteries. Nano-LiFePO₄ already appears in high-power applications, and LiMnPO₄ development is underway. Current and emerging Fe- and Mn-based intercalants, however, are low-energy producers compared to Ni and Co compounds. LiNiPO₄, a high voltage olivine, has the potential for superior energy output (>10.7 Wh in 18650 batteries), compared with commercial Li(Co,Ni)O₂ derivatives (up to 9.9 Wh). Speculative Co and Ni olivine cathode materials charged to above 4.5 V will require significant advances in electrolyte compositions and nanotechnology before commercialization. The major drivers toward 5 V battery chemistries are the inherent abuse tolerance of phosphates and the economic benefit of LiNiPO₄: it can produce 34% greater energy per dollar of cell material cost than LiAl_0.05Co_0.15Ni_0.8O₂, today's “standard” cathode intercalant in Li-ion batteries.     

2,2-Dimethoxy-propane as electrolyte additive for lithium-ion batteries

2,2-Dimethoxy-propane (DMP) was studied as an additive in 1 mol dm⁻³ LiPF₆ ethylene carbonate and diethyl carbonate (1:1, w/w) for lithium-ion battery, which was characterized by cyclic voltammetry and half cell tests. Cyclic voltammetry and half cell data show that the use of DMP as an additive to the organic solutions at very low level (ca. 0.005 wt%) offers the advantage of forming fully developed passive films on the graphite anode surface. The electrochemical performance of the additive-containing electrolytes in combination with LiCoO₂ cathode and graphitic anode was also tested in commercial cells 103448. The results reveal that the cyclic life test and storage performance at high temperature (ca. 60 °C) in electrolyte with DMP additive was better than that in an electrolyte without additive. Therefore, DMP can be considered as a desirable additive in electrolyte for lithium-ion batteries operating at high temperature, ca. 60 °C.     

Effect of oxygen non-stoichiometry and temperature on cation ordering in LiMn2−xNixO4 (0.50 ≥ x ≥ 0.36) spinels

The effect of oxygen stoichiometry on the transition metal ordering and electrochemical activity of LiMn_2−xNi_xO₄ solid solutions was investigated. Temperature–oxygen-partial-pressure–composition (pO₂–T–x) diagrams of ordered and disordered phases of LiMn_2−xNi_xO₄ (0.50 ≥ x ≥ 0.36) in the vicinity of order–disorder transition temperature (T_c) was constructed by means of infrared spectroscopy, thermogravimetric analysis and galvanostatic measurements. Despite their simplicity and limitations over traditional diffraction techniques, all three techniques offered near excellent capability to distinguish ordered and disordered phases. The effect of oxygen-partial-pressure (pO₂) in the annealing atmosphere and nickel content of the spinel on T_c was studied. The transition temperature increased with pO₂ and nickel content, except in oxygen-rich (pO₂ = 1) atmosphere for the maximum nickel content spinel of LiMn_1.5Ni_0.5O₄. An explanation for the dependence of the transition temperature on the two variables and changes induced by the post-fabrication heat treatments is provided.     

Improved electrochemical performances of 9LiFePO4·Li3V2(PO4)/C composite prepared by a simple solid-state method

9LiFePO₄·Li₃V₂(PO₄)₃/C is synthesized via a carbon thermal reaction using petroleum coke as both reduction agent and carbon source. The as-prepared material is not a simple mixture of LiFePO₄ (LFP) and Li₃V₂(PO₄)₃ (LVP), but a composite possessing two phases: one is V-doped LFP and the other is Fe-doped LVP. The typical structure enhances the electrical conductivity of the composite and improves the electrochemical performances. The first discharge capacity of 9LFP·LVP/C in 18650 type cells is 168 mAh g⁻¹ at 1 C (1 C_9LFP·LVP/C = 166 mA g⁻¹), and exhibits high reversible discharge capacity of 125 mAh g⁻¹ at 10 C even after 150 cycles. At the temperature of −20 °C, the reversible capacity of 9LFP·LVP/C can maintain 75% of that at room temperature.     

Characterization of Ba1.0Sr1.0FeO4+δ cathode on La0.9Sr0.1Ga0.8Mg0.2O3−δ electrolyte for intermediate temperature solid oxide fuel cells

Ba_1.0Sr_1.0FeO_4+δ (BSFO) with A₂BO₄ structure as a cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs) is synthesized through an ethylene diamine tetraacetic acid (EDTA)-citrate process, and characterized by X-ray diffraction. Field emission scanning electron microscopy shows that BSFO cathode is well attached to the La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte. The electrical conductivity measured by DC four-probe method increases as the temperature increases. A linear relationship between ln(σT) and 1000/T indicates that the conducting behavior obeys the small polaron conductivity mechanism. Electrochemical performance of BSFO cathode on LSGM electrolyte is investigated in the temperature range from 500 °C to 800 °C. The results indicate that oxygen adsorption/dissociation process dominates cathodic reaction. Furthermore, the polarization resistance of BSFO cathode decreases with increasing temperature, and declines to 1.42 Ω cm² at 800 °C. These results show that BSFO can be a promising cathode material used on LSGM electrolyte for IT-SOFCs.     

Fabrication of all-solid-state lithium battery with lithium metal anode using Al2O3-added Li7La3Zr2O12 solid electrolyte

Li₇La₃Zr₂O₁₂ (LLZ) solid electrolyte is one of the promising electrolytes for all-solid-state battery due to its high Li ion conductivity and stability against Li metal anode. However, high calcination temperature for LLZ preparation promotes formation of La₂Zr₂O₇ impurity phase. In this paper, an effect of Al₂O₃ addition as sintering additive on LLZ solid electrolyte preparation and electrochemical properties of Al₂O₃-added LLZ were examined. By the Al₂O₃ addition, sintered LLZ pellet could be obtained after 1000 °C calcination, which is 230 °C lower than that without Al₂O₃ addition. Chemical and electrochemical properties of the Al₂O₃-added LLZ, such as stability against Li metal and ion conductivity, were comparable with the LLZ without Al₂O₃ addition, i.e. σ_bulk and σ_total were 2.4 × 10⁻⁴ and 1.4 × 10⁻⁴ S cm⁻¹ at 30 °C, respectively. All-solid-state battery with Li/Al₂O₃-added LLZ/LiCoO₂ configuration was fabricated and its electrochemical properties were tested. In cyclic voltammogram, clear redox peaks were observed, indicating that the all-solid-state battery with Li metal anode was successfully operated. The redox peaks were still observed even after one year storage of the all-solid-state battery in the Ar-filled globe-box. It can be inferred that the Al₂O₃-added LLZ electrolyte would be a promising candidate for all-solid-state battery because of facile preparation by the Al₂O₃ addition, relatively high Li ion conductivity, and good stability against Li metal and LiCoO₂ cathode.     

A comprehensive investigation on thermal management of large‐capacity pouch cell using micro heat pipe array

A proper and effective battery thermal management system (BTMS) is critical for large‐capacity pouch cells to guarantee a suitable operating temperature and temperature difference. Hence, in this paper, a micro heat pipe array (MHPA) is utilized to build the thermal management system for large‐capacity pouch cells. In order to study the property of BTMS in depth, experimental and numerical investigation are carried out by considering the C‐rate, working medium, air velocity and duty. The experimental results present that the T_max can be maintained below 43.7°C and the ΔT is below 4.9°C at the discharge rate of 3C in the battery module with MHPA‐liquid. Moreover, the T_max of the battery module with MHPA‐liquid falls as the air velocity increases. The simulation results show that the variation and distribution of temperature matched well with experimental results. It demonstrates that the MHPA‐based BTMS is viable and effective for large‐capacity pouch cell battery, even at high C‐rate and cycle duty.     

The improved discharge performance of Li/CFx batteries by using multi-walled carbon nanotubes as conductive additive

The discharge performance of Li/CF_x (x = 1) battery is improved by using multi-walled carbon nanotubes (MWCNTs) as an alternative conductive additive. Compared with the battery using acetylene black as conductive additive at the same amount, the Li/CF_x battery using MWCNTs as conductive additive has higher specific capacity and energy density as well as smoother voltage plateau, especially at higher discharge rate. The specific capacity at discharge rate of 1 C is improved by nearly 26% when MWCNTs are employed as conductive additive. Meanwhile, it is also found that the discharge performance is able to be tuned by the amount of MWCNTs and the battery containing more MWCNTs is favorable to be discharged at higher rates. The specific capacity of Li/CF_x battery with 11.09 wt.% MWCNTs is approximately 712 mAh g⁻¹ at the discharge rate of 1 C. It is proposed that the formed three-dimensional networks of MWCNTs in cathode, which enlarges the contact area of interphase and facilitates electrons delivery, accelerates the rates of lithium ion diffusion into the fluorinated layers and electrons transport in cathode at the same time, which improves the discharge performance of Li/CF_x battery subsequently, especially at higher rates.     

Preparation of Li2S-GeSe2-P2S5 electrolytes by a single step ball milling for all-solid-state lithium secondary batteries

Glass-ceramic and glass Li₂S-GeSe₂-P₂S₅ electrolytes were prepared by a single step ball milling (SSBM) process. Various compositions of Li_4−xGe_1−xP_xS_2(1+x)Se_2(1−x) with/without heat treatment (HT) from x = 0.55 to x = 1.00 were systematically investigated. Structural analysis by X-ray diffraction (XRD) showed gradual increase of the lattice constant followed by significant phase change with increasing GeSe₂. HT also affected the crystallinity. Incorporation of GeSe₂ in Li₂S-P₂S₅ kept high conductivity with a maximum value of 1.4 × 10⁻³ S cm⁻¹ at room temperature for x = 0.95 in Li_4−xGe_1−xP_xS_2(1+x)Se_2(1−x) without HT. All-solid-state LiCoO₂/Li cells using Li₂S-GeSe₂-P₂S₅ as solid-state electrolytes (SE) were tested by constant-current constant-voltage (CCCV) charge-discharge cycling at a current density of 50 μA cm⁻² between 2.5 and 4.3 V (vs. Li/Li⁺). In spite of the extremely high conductivity of the SE, LiCoO₂/Li cells showed a large irreversible reaction especially during the first charging cycle. LiCoO₂ with SEs heat-treated at elevated temperature exhibited a capacity over 100 mAh g⁻¹ at the second cycle and consistently improved cycle retention, which is believed to be due to the better interfacial stability.     

Performance improvement of polyethylene-supported poly(methyl methacrylate-vinyl acetate)-co-poly(ethylene glycol) diacrylate based gel polymer electrolyte by doping nano-Al2O3

Polyethylene (PE)-supported poly(methyl methacrylate-vinyl acetate)-co-poly(ethylene glycol) diacrylate with and without doping nano-Al₂O₃, namely P(MMA-VAc)-co-PEGDA/PE and P(MMA-VAc)-co-PEGDA/Al₂O₃/PE, are prepared and their performances as gel polymer electrolytes (GPEs) for lithium ion battery are studied by mechanical test, scanning electron microscopy, thermogravimetric analyzer, electrochemical impedance spectroscopy, cyclic voltammetry, and charge/discharge test. It is found that the doping of nano-Al₂O₃ in the P(MMA-VAc)-co-PEGDA/PE improves the comprehensive performances of the GPE and thus the rate performance and cyclic stability of the battery. With doping nano-Al₂O₃, the mechanical and thermal stability of the polymer and the ionic conductivity of the corresponding GPE increases slightly, while the battery exhibits better cyclic stability. The mechanical strength and the decomposition temperature of the polymer increase from 15.9 MPa to 16.2 MPa and from 410 °C to 420 °C, respectively. The ionic conductivity of the GPE is from 3.4 × 10⁻³ S cm⁻¹ to 3.8 × 10⁻³ S cm⁻¹. The discharge capacity of the battery using the GPE with doping nano-Al₂O₃ keeps 90.9% of its initial capacity after 100 cycles and shows good C-rate performance.     

Recovery of discarded sulfated lead-acid batteries

The aim of this research is to recover discarded sulfated lead-acid batteries. In this work, the effect of two methods (inverse charge and chemical charge) on the reactivation of sulfated active materials was investigated. At the inverse charge, the battery is deeply discharged and the electrolyte of battery is replaced with a new sulfuric acid solution of 1.28 g cm⁻³. Then, the battery is inversely charged with constant current method (2 A for the battery with the nominal capacity of 40 Ah) for 24 h. At the final stage, the inversely charged battery is directly charged for 48 h. Through these processes, a discarded battery can recover its capacity to more than 80% of a similar fresh and non-sulfated battery.At the chemical charge method, there are some effective parameters that including ammonium persulfate [(NH₄)₂S₂O₈] concentration, recovery temperature and recovery time. The effect of all parameters was optimized by one at a time method. The sulfated battery is deeply discharged and then, its electrolyte was replaced by a 40% ammonium persulfate solution (as oxidant) at temperature of 50 °C. By adding of oxidant solution, the chemical charging of positive and negative plates was performed for optimum time of 1 h. The chemically charged batteries were charged with constant voltage method (2.66 V for the battery with nominal voltage and nominal capacity of 2 V and 10 Ah, respectively) for 24 h. By performing of these processes, a discarded battery can recovers its capacity to more than 84% of the similar fresh and non-sulfated battery. Discharge and cyclelife behaviors of the recovered batteries were investigated and compared with similar healthy battery. The morphology and structure of plates was studied by scanning electron microscopy (SEM) before and after recovery.     

Structural and thermal stabilities of layered Li(Ni1/3Co1/3Mn1/3)O2 materials in 18650 high power batteries

The structural and thermal stabilities of the layered Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode materials under high rate cycling and abusive conditions are investigated using the commercial 18650 Li(Ni_1/3Co_1/3Mn_1/3)O₂/graphite high power batteries. The Li(Ni_1/3Co_1/3Mn_1/3)O₂ materials maintain their layered structure even when the power batteries are subjected to 200 cycles with 10 C discharge rate at temperatures of 25 and 50 °C, whereas their microstructure undergoes obvious distortion, which leads to the relatively poor cycling performance of power batteries at high charge/discharge rates and working temperature. Under abusive conditions, the increase in the battery temperature during overcharge is attributed to both the reactions of electrolyte solvents with overcharged graphite anode and Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode and the Joule heat that results from the great increase in the total resistance (R_cell) of batteries. The reactions of fully charged Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathodes and graphite anodes with electrolyte cannot be activated during short current test in the fully charged batteries. However, these reactions occur at around 140 °C in the fully charged batteries during oven test, which is much lower than the temperature of about 240 °C required for the reactions outside batteries.     

Three-dimensional thermal finite element modeling of lithium-ion battery in thermal abuse application

In order to better understand the thermal abuse behavior of high capacities and large power lithium-ion batteries for electric vehicle application, a three-dimensional thermal model has been developed for analyzing the temperature distribution under abuse conditions. The model takes into account the effects of heat generation, internal conduction and convection, and external heat dissipation to predict the temperature distribution in a battery. Three-dimensional model also considers the geometrical features to simulate oven test, which are significant in larger cells for electric vehicle application. The model predictions are compared to oven test results for VLP 50/62/100S-Fe (3.2 V/55 Ah) LiFePO₄/graphite cells and shown to be in great agreement.     

Synthesis and evaluation of polythiocyanogen (SCN)x as a rechargeable lithium-ion battery electrode material

Polythiocyanogen, (SCN)_x, is a promising lithium-ion battery electrode material due to its high theoretical capacity (462 mAh g⁻¹), safe operation, inexpensive raw materials, and a simple and less energy-intensive manufacturing process. The (SCN)_x was prepared from the solution of trithiocyanate (SCN)₃⁻ in methylene dichloride (MDC), which was prepared by electrochemical oxidation of ammonium thiocyanate (NH₄SCN) in a two-phase electrolysis medium of 1.0 M NH₄SCN in 0.50 M H₂SO₄ + MDC. The (SCN)₃⁻ underwent auto catalytic polymerization to (SCN)_x during MDC removal. Battery electrodes with (SCN)_x as the active material were prepared, and tested in Swagelok cells using lithium foil as the counter and reference electrode. The cells delivered capacities in the range of 200-275 mAh g⁻¹ at the discharge-charge rate of 0.2 C. The cells were tested up to 20 cycles and showed repeatable performance with a coulombic efficiency of 97% at the 20th cycle. The results presented here indicate that (SCN)_x is a promising lithium-ion battery electrode-material candidate for further studies.     

Solvent-free,PYR1ATFSI ionic liquid-based ternary polymer electrolyte systems: I. Electrochemical characterization

The electrical properties of solvent-free, PEO–LiTFSI solid polymer electrolytes (SPEs), incorporating different N-alkyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, PYR_1ATFSI, ionic liquids (ILs), are reported. For this purpose, PYR_1ATFSI materials containing side alkyl groups with different chain-length and branching, i.e., n-propyl, sec-propyl, n-butyl, iso-butyl, sec-butyl and n-pentyl, were properly synthesized and homogeneously incorporated into the SPE samples without phase separation. The addition of ILs to PEO–LiTFSI electrolytes results in a large increase of the conductivity and in a decrease of the interfacial resistance with the lithium metal anode. Most of the PEO–LiTFSI–PYR_1ATFSI samples showed similar ionic conductivities (>10⁻⁴ S cm⁻¹ at 20 °C) and stable interfacial resistance values (400 Ω cm² at 40 °C and 3000 Ω cm² at 20 °C) upon several months of storage. Preliminary battery tests have shown that Li/P(EO)₁₀LiTFSI + 0.96 PYR_1ATFSI/LiFePO₄ solid-state cells are capable to deliver a capacity of 125 mAh g⁻¹ and 100 mAh g⁻¹ at 30 °C and 25 °C, respectively.     

Magnetism and lithium diffusion in LixCoO2 by a muon-spin rotation and relaxation (μSR) technique

Microscopic magnetism of the electrochemically Li-deintercaleted Li_xCoO₂ powders has been investigated by muon-spin rotation and relaxation (μ⁺SR) spectroscopy in the temperature (T) range between 10 and 300 K. Weak transverse-field μ⁺SR measurements indicate that localized moments appear in LiCoO₂ below 60 K, while both Li_0.53CoO₂ and Li_0.04CoO₂ are paramagnetic even at 10 K. Zero-field μ⁺SR measurements for the samples with x = 0.53 and 0.04 show that the field distribution width (Δ) due to randomly oriented nuclear magnetic moments of ⁷Li and ⁵⁹Co decreases monotonically with increasing T up to 250 K, and then it decreases steeper (increasing slope (dΔ/dT)) above 250 K. Because the muon hopping rate (ν) is almost T independent for Li_0.53CoO₂ below 300 K, the decrease in Δ suggests that the time scale of Li⁺ diffusion in Li_xCoO₂ is within a microsecond scale.     

X-ray absorption near-edge structure study on positive electrodes of degraded lithium-ion battery

18650-type cylindrical cells using LiNi_1/3Mn_1/3Co_1/3O₂ (NMC) and hard carbon as positive and negative electrode material, respectively, were fabricated and degraded by cycle tests. The capacity of the cells remained more than 95% and 85% after cycle tests at 25 and 50 °C, respectively. After the cycle tests, Li-deficient cubic phase was observed on the surface of NMC. This phenomenon should be related to the degradation mechanism of this type of cell.