High Discharge Rates Research Articles

Aqueous Processed Thick-Film Li(Ni0.6Mn0.2Co0.2)O2 Electrodes with 3D Architectures

The development of high areal energy density electrodes with layered metal oxide cathode materials is currently worldwide a main topic in research and industry. Water-based binders were applied in the presented work for the manufacturing of NMC 622 (Li(Ni0.6Mn0.2Co0.2)O2) cathodes in order to achieve environmental friendly and cost-reduced production, replacing the conventional organic PVDF binder and the toxic and volatile NMP solvent. However, the pH value of aqueous processed cathode slurries increases to over 12 due to the reaction between NMC 622 particles and water, which decreases the specific discharge capacity of the cells and on the other side results in the chemical corrosion of the current collector during casting. In order to avoid the damage of the current collector and protect the cathode material, different acids could be applied during mixing process to adjust the slurry pH value. In addition, the energy density at battery level can be increased with increasing electrode film thickness which corresponds to an enhanced areal capacity. However, capacity fading of thick-film electrodes at C-rates above C/2 is mainly due to a limited lithium-ion diffusion kinetics and crack formation in cathode particles. 3D electrode architectures produced by ultrafast laser ablation are proven to improve the capacity retention at high discharge rates and the electrolyte wettability of electrodes as reported in our previous works.In this work, NMC 622 electrodes with a film thickness of 150 µm (5.8 mAh/cm2) were manufactured with aqueous binders TRD 202A and CMC, and were subsequently laser structured. With increasing film thickness from 70 µm to 150 µm, the mass loading of cathodes increased from 17 mg/cm2 to 36 mg/cm2. The slurry pH values were adjusted between 9 - 10 with citric acid (CA), phosphoric acid (PA), and acetic acid (AC). The dried electrodes were characterized using XPS and SEM. The unstructured and structured electrodes with different thicknesses were afterwards assembled versus lithium in coin cells. Rate capability test and cyclic voltammetry (CV) were performed in order to investigate the electrochemical performance of the electrodes. Cells containing 70 µm cathodes with PA and CA+PA showed about 10 mAh/g higher capacity at C/20 to C/5 compared to cells with PA, while at 1C to 3C cells with CA showed the lowest capacities With increasing electrode film thickness, cells with PA and PA+CA retained 5-10 mAh/g more capacity than cells with CA at C/20 to C/5. The cells with PA maintained about 120 mAh/g discharge capacity at C/2, while cells with PA+CA and CA showed about 80 mAh/g and 45 mAh/g, respectively. In comparison to cells with unstructured electrodes, laser structuring increased the discharge capacity of cells with 70 µm electrodes from 1C to 3C, regardless of the type of added acid. As for cells with thick-film electrodes, the discharge capacity of cells containing structured electrodes with CA+PA increased to 120 mAh/g, which is about 40 mAh/g higher compared to cells with unstructured electrodes. Finally, CV proved that the addition of acids had no effect on the redox reaction of NMC 622.

Impact of Electrolyte Volume on the Cycling Performance and Impedance Growth of 18650 Li-Ion Cells

The volume of electrolyte used in commercial cylindrical rechargeable Li-ion batteries needs to be closely controlled to optimize performance. It is widely reported in the open literature that insufficient electrolyte can negatively impact cycling performance. However, there are scant reports showing the impact of excessive amounts of electrolyte on cell performance. Here, we show that adding excessive amounts of electrolyte also negatively impacts the cycling performance, causing cells to show faster capacity fade. The effect can be quite significant, causing a noticeable difference within the first 30 cycles, particularly at higher discharge rates (e.g., 1C to 2C rates, Figure 1). It is important to understand the causes of this “high-volume effect” because it sets an additional constraint on the optimization of the system. We have carried out extensive electrochemical impedance measurements of commercial 3.5 Ah 18650 cylindrical cells with various levels of electrolyte (LiPF6/EC/DMC/EMC; 15/25/56/4 wt%) using PEIS and GEIS protocols at an ambient temperature of 25°C. The collected impedance patterns exhibit typical two loop features reported in the literature 1,2 and were modelled by a series combination of one resistance and two parallel R/C elements to extract the cell ohmic and charge transfer resistance values. The total cell resistance of cells with both nominal and high-volume electrolyte show impedance growth during cycling. However, the high-volume cell shows noticeably higher growth of charge transfer resistance. Details of the experimental work and possible mechanism of this effect will be discussed during the presentation. References N. Ogihara et al., J. Electrochem. Soc., 159, A1034–A1039 (2012).W. Waag, S. Käbitz, and D. U. Sauer, Appl. Energy, 102, 885–897 (2013). Figure 1

(Digital Presentation) Synthesis and Properties of Llithium Iron Phosphate Cathode Materials without Carbon Coating with High-Rate Property

Lithium iron (ferrium) phosphate (LFP) use iron as a transition metal, so there is lower resource risk. And because of tolerant to overcharging, they have excellent safety and durability. Lithium-ion secondary batteries using LFP have become widely used as main power sources for EVs and ESSs in recent years. Originally, LFP has higher bulk resistance than other layered rock salt-based positive materials, so that carbon-coating was applied to surface of LFP particles. This idea was extremely effective in putting LFP into practical use. However, the use of the carbon coat has led disadvantage of high cost despite the use of cheaper iron because the manufacturing process increases. We report that we have developed LFP that has extremely high-rate charge and discharge performance even though it does not have carbon coating. Figure 1

(Digital Presentation) Earth-Abundant Copper-Based Electrode Materials for Li-Ion Storage

Lithium-ion batteries (LIBs) find their use in almost all applications starting from electronic gadgets to grid energy storage and hybrid electric vehicles. In this direction, the development of high-capacity anodes is crucial to fulfil the increasing energy demand. To evaluate the Li+ ion storage performance, we have synthesized an earth-abundant copper-based electrode material, Cu3PS4, using the chemical vapor transport (CVT) method from the constituent elements Cu, P, and S in a 3:1:4 ratio. It has an enargite-type structure and has a layered-type morphology (Figure 1a). A high capacity of 970 mAh g-1 is obtained at 0.1 A g-1 current density. The electrode is amenable for high discharge rates up to 5 A g-1, and at a discharge rate of 1 A g-1, the cell can be cycled 5000 times with 90% capacity retention. The high electrochemical performance of the material is related to the conversion reaction as probed by in situ Raman spectroscopy (Figure 1b) and surface-controlled capacitive contribution due to the formation of a polymeric film over the electrode surface. A full cell with LiCoO2 cathode results in a large number of cycles with stable performance. Further improvement is achieved by forming a composite with an organic polymer, polybenzimidazole. The composite electrode delivers almost double the capacity of the pristine electrode. Other studies on the use of the electrode material to multivalent ion storage based on Mg2+, Zn2+, and Al3+ are in progress.Reference D. Tripathy and S. Sampath, J. Power Sources 2020, 478, 229066. Figure 1. (a) Unit cell structure and SEM image of Cu3PS4 and (b) in situ Raman spectra of the electrode after discharge. Figure 1

Calibration of Fiber Bragg Grating - Sensors for Subsequent Temperature and Pressure Measurements in Li-Ion Pouch Cells

The monitoring of temperature during operation of lithium ion batteries is crucial for a stable and safe performance of a battery system. However, a major challenge is to obtain exact internal temperature progression upon charge and discharge processes. Though commonly used resistance temperature sensors can give considerably accurate temperature values, they are limited to the application outside of the cell due to the distortion of their signal through induction effects of the applied cell currents, if installed inside the pouch cell and therefore, they are not suitable for in situ measurements. This poses serious problems especially for big cell stacks, as core temperatures for those cells differ greatly from the outer parts and particularly the surface of the cell encasement. Fiber Bragg Grating (FBG) sensors on the other hand, provide data that are unaffected by induction effects as their operating principle is solely based on the reflection of light of certain wavelengths within a glass fiber. However, a specific difficulty is the distinction between temperature and pressure effects, as the reflected signal is sensitive to both. Often times additional tubing around the sensor is needed to eliminate pressure effects or an additional sensor is placed in close proximity, inside or outside, to the FBG-sensor as a reference. The former, however, can affect the cell stack physically acting as a defect spot with unwanted side effects.In our work, we show that a careful calibration of the FBG-sensor can be accomplished, so that both effects can be separated and the FBG-sensor can then be used to gather information not only about temperature but also about volume changes in an operating cell. Therefore, a temperature calibration took place, with the cell being held at a constant SoC. Subsequently, a calibration of the SoC - dependent pressure-induced mechanical deformation was performed at very low C-rate to minimize thermal effects. The so gathered calibration parameters can then be applied to all performed cycling tests, regardless of the C - rate. A calibration routine and mathematical solution to separate the influences of temperature and pressure to receive exact in situ temperature values for a 10 Ah lithium ion battery cell is presented. The calibration method is applied to cycling and rate tests at various C-rates.The results show, that wavelength shifts upon charging and discharging processes are mainly resulting from volume changes of the active cell components, meaning that the FBG – sensor has a very high sensitivity towards pressure changes. With the before mentioned calibration method the impact of mechanical deformation on the FBG - sensor can be subtracted from the raw data and allow for a direct temperature reading. The temperature data correlates with data gathered from commonly used sensors placed on the outside of the pouch cell. Tests with varying discharge rates confirm these results and show, that the method produces precise temperature data even at different C-rates, even though only slow C-rates were applied during calibration.In detailed comparison, the FBG - sensors show a faster response towards temperature changes compared to conventional external temperature sensors, which can be related to the insulating effect of the pouch foil. In case of high discharge rates, we were able to show that the measured temperatures inside of the pouch cell are higher in comparison to the outside ones. Furthermore, SoC - induced changes in pressure measured by two FBG-sensors, which were located at different positions on the cell stack, are almost identical. This indicates that pressure build-up within a pouch cell occurs evenly through the cell stack.

Simulated discharge overpotential distributions for sintered electrode batteries in rechargeable coin cell form factors

Sintered electrode lithium-ion batteries contain only electroactive material which has undergone a mild thermal treatment to improve particle connectivity and thus electrode mechanical strength. These electrodes can be made very thick, and due to the lack of inactive binders or conductive additives there are ion transport advantages relative to equivalent thickness and porosity composite electrodes. In this study, the discharge of sintered electrode full cells was simulated at the cell level for three different form factors: CR2032, CR2025, and CR2016. Simulations also include relatively high and low rates of discharge and two different electrolytes. Using the simulations, overpotential distributions enable analysis of the contributors to resistance in the cell analyzed for the different regions of the anode, cathode, and separator. Overpotential sources include electronic overpotential, ionic overpotential, interfacial overpotential, and OCV overpotential. As the total thickness increases, the main overpotential contribution shifts from interfacial to ionic, with both originating from the electrodes. In all cases a higher conductivity electrolyte dramatically increases total capacity delivered at higher discharge rates.

Implications of novel cold plate design with hybrid cooling on thermal management of fast discharging lithium-ion battery

Electric cars powered by a green power Lithium-ion battery (LIB) system are realistic options for reducing greenhouse gas emissions and rely on fossil energy supplies. However, the heat dissipation of LIB is critical, especially at high discharge rates. In order to guarantee safety, the present work proposes a novel hybrid cooling approach for the thermal management of fast discharging LIB modules. A dual cooling approach wherein composite phase change material (CPCM) is coupled with forced convection cooling via nanofluid flow through convergent channels is analyzed. Two CPCM configurations viz., CPCM sandwiched between the cold plate (D1) and CPCM wrapped around the width of the cell (D2) are considered. The numerical simulations are performed using the finite element method to study the effects of inlet velocity, nanofluid volume fraction, and the direction of flow on the thermal management of the module. The results show that the module temperature is reduced below the safety limit when hybrid cooling is applied. Further, better cooling performance is observed when CPCM is wrapped around the battery cell as compared to when CPCM is sandwiched in between the cold plates and battery cell both in terms of uniform distribution of temperature and maximum temperature. This is evident from the reduction in maximum temperature (Tmax) by 1.55 K and temperature difference (ΔT) of 2.04 K at Reynolds number (Re) = 150. The effectiveness of the hybrid cooling improves with the increase in Re and becomes thermally stable when Re > 200. The maximum temperature decreases substantially by 8.76 K when the Reynolds number increases from Re = 50 to Re = 200. In addition, the increase in the nanofluid concentration of flowing fluid through the convergent channel in cold plates reduces the maximum temperature of the battery module by 3.05 K at ϕ = 5 % and Re = 200 although does not seem to affect the uniformity in temperature distribution substantially. Further, the temperature distribution is found more uniform when the direction of flow reverses in converging channels in alternate cold plates.

The experimental and numerical investigation on thermal responses of passive thermal protected batteries in different packs from low to high discharge rates

The experimental and numerical investigation on thermal responses of passive thermal protected batteries in different packs from low to high discharge rates

Synergistic and capacitance effects in nanocarbon based capacitor batteries designed for superior rate capability and long-cycle stability

Existing lithium-ion batteries struggle to achieve high-rate discharge stability. To address this problem, this study combines resin-based carbon nanospheres with a double electric layer effect and cathode materials with lithium-ion intercalation/delithiation behavior to form a LiNi0.6Co0.2Mn0.2O2/resin-based carbon-sphere hybrid electrode. For further improvement in electron contact and tap density, the size of the carbon nanospheres was controlled by changing the synthetic parameters, and a size-matched spatial structure model of each component within the hybrid electrode was constructed. Considering the excellent rate capability of small-sized hard carbon, hard-carbon nanospheres derived from glucose were employed as the anode active material to assemble a capacitor battery. With the integration of characteristics of both lithium-ion batteries and supercapacitors, the as-prepared new capacitor battery exhibited a specific capacity of 146.1 mAh/g at 0.1C and an energy density of 474.5 Wh/kg on the cathode active material mass, a reversible capacity of 113.2 mAh/g at 1C after 200 cycles with retention of 85.3%, and the capacity remained at 82 mAh/g even at a high current rate of 10C. These results offer insights into the design of energy storage devices with excellent cycling stability and rate capability.

Revisits After Emergency Department Discharge for Conditions with High Disposition-Decision Variability at Hospitals with High and Low Discharge Rates.

IntroductionThe first proposed emergency care alternative payment model seeks to reduce avoidable admissions from the emergency department (ED), but this initiative may increase risk of adverse events after discharge. Our study objective was to describe variation in ED discharge rates and determine whether higher discharge rates were associated with more ED revisits.MethodsUsing all-payer inpatient and ED administrative data from the California Office of Statewide Health Planning and Development (OSHPD) 2017 database, we performed a retrospective cohort study of hospital-level ED discharge rates and ED revisits using conditions that have been previously described as having variability in discharge rates: abdominal pain; altered mental status; chest pain; chronic obstructive pulmonary disease exacerbation; skin and soft tissue infection; syncope; and urinary tract infection. We categorized hospitals into quartiles for each condition based on a covariate-adjusted discharge rate and compared the rate of ED revisits between hospitals in the highest and lowest quartiles.ResultsWe found a greater than 10% difference in the between-quartile median adjusted discharge rate for each condition except for abdominal pain. There was no significant association between adjusted discharge rates and ED revisits. Altered mental status had the highest revisit rate, at 34% for hospitals in the quartile with the lowest and 30% in hospitals with the highest adjusted discharge rate, although this was not statistically significant. Syncope had the lowest rate of revisits at 16% for hospitals in both the lowest and highest adjusted discharge rate quartiles.ConclusionOur findings suggest that there may be opportunity to increase ED discharges for certain conditions without resulting in higher rates of ED revisits, which may be a surrogate for adverse events after discharge.

Study on the evolution of phase and properties for ternary La-Y-Ni-based hydrogen storage alloys with different stoichiometric ratios

In recent years, some progress has been made in the development and application of the highly anticipated La-Y-Ni hydrogen storage alloy system. However, the relationship between the structure and properties of materials has not been studied systematically and thoroughly. In this paper, the evolution law of AB3-, A2B7- and A5B19-type phases for La-Y-Ni-based hydrogen storage alloys was proposed. The single-phase LaY2Ni9 (AB3), La2Y4Ni21 (A2B7) and La5Y10Ni57 (A5B19) alloys were synthesized by powder sintering method at 1173, 1353 and 1423 K, respectively. The XRD and SEM results of the alloys show that LaY2Ni9 alloy has a single PuNi3 phase (3 R), La2Y4Ni21 alloy is composed of Ce2Ni7 phase (2 H) and Gd2CO7 phase (3 R), and La5Y10Ni57 alloy contains Pr5Co19 phase (2 H) and Ce5Co19 phase (3 R). Among the three alloys, the La2Y4Ni21 alloy has the largest hydrogen storage capacity (1.59 wt%) in solid /H2 reaction at 313 K. The target alloys all exhibit excellent electrochemical activation ability. The maximum discharge capacity of LaY2Ni9, La2Y4Ni21 and La5Y10Ni57 alloys decreases gradually, but their cycle stability increases in turn. The high-rate discharge performance of La2Y4Ni21 alloy is the best, because its exchange current density (I0 = 75.55 mA/g) and hydrogen diffusion coefficient (D0 = 2.51 ×10−10 cm2/s) cooperate well. It is hoped that these findings can offer theoretical guidance and technical assistance for the development of La-Y-Ni-based hydrogen storage alloys.

Chronology and Eruption Dynamics of the Historic∼1700 CE Eruption of Tseax Volcano, British Columbia, Canada

Despite having relatively short timespans of eruptions, monogenetic volcanoes can pose significant risks to the nearby population. Here, we describe the ∼1700 CE eruption of Tseax volcano, British Columbia, which killed up to 2,000 people of the Nisga’a First Nation and is ranked as Canada’s worst natural disaster. Within the Nisga’a culture, Adaawak stories preserve an observational account of the Tseax eruption. In this study, we establish the chronology of the eruption by integrating field observations and petrophysical data informed by Nisga’a oral and written histories. The Nisga’a stories corroborate the short duration and exceptional intensity of the eruption as recorded in the volcanic products. The eruption was divided in two main periods: 1) Period A and 2) Period B. 1) The eruption started in a typical Hawaiian style with low levels of lava fountaining that built up a spatter rampart. This pyroclastic edifice was breached by voluminous pāhoehoe lavas erupted at high discharge rates. We estimate that almost half of the emplaced lava volume (0.20 km3) was erupted in Period A and had a flux of 800–1,000 m3/s. The low viscosity lava reached the Nass Valley, 20 km downstream of the volcano, in “swift currents”, and engulfed the former Nisga’a villages in only 1–3 days, thus likely being responsible for the reported fatalities. The discharge rates progressively diminished to 10–200 m3/s until the end of this first eruptive period, which lasted a few weeks to a few hundred days. 2) The Period B eruption produced two ‘a‘ā lavas with discharge rates <50 m3/s. This period was also characterised by an explosive phase of eruption that built a 70 m high tephra cone overlapping with a spatter rampart; Period B lasted approximately 20 days. In total, the eruption produced 0.5 km3 of volcanic materials (mostly in the form of lava flows) on the order of weeks to a few months. The mountainous terrain significantly controlled the emplacement of lava flows that reached long distances in a short amount of time. Our work shows that, under certain conditions, eruptions of small-volume monogenetic volcanoes ca pose risks comparable to flank eruptions on long-lived shield volcanoes.

Enhanced rate performance and specific capacity in Ti-substituted P2-type layered oxide enabled by crystal structure and particle morphology modifications

In recent years, P2-type layered oxides have received considerable attention as potential cathodes for Na-ion batteries owing to their compositional diversity, good specific capacity, and cyclability. However, poor rate performance and low-capacity retention at high discharge rates have limited their use in commercial battery applications. This study aims to mitigate this issue by synthesizing a series of structurally engineered P2-type cathode materials, through Ti substitution, with high cyclability and improved rate performance. P2-type Na0.70Ni0.20Cu0.15Mn(0.65-x)TixO2 were prepared through a sol–gel route and were characterized for their structural, electrical, and electrochemical properties In the Ti-substituted samples, the Rietveld refinement of XRD data revealed an increased size of the bottleneck area of the Na-O6 prism planes, while the SEM images showed a decrease in the aspect ratio of hexagon-type morphology of particles which facilitates faster Na-ion conduction through the material. These changes in the crystal structure and particle morphology induced by Ti substitution have significantly improved electrical and electrochemical performance compared to the parent material. The sample with x = 7.5% exhibited a specific capacity of 126 mAh/g at a discharge rate of 0.1C in the 2.00–4.25 V window, which was about 25% more than that of the undoped material. At a discharge rate of 1C, the specific capacity of Na0.70Ni0.20Cu0.15Mn0.575Ti0.075O2 was 97 mAh/g compared to 74 mAh/g for Na0.70Ni0.20Cu0.15Mn0.65O2 sample. Na0.70Ni0.20Cu0.15Mn(0.65-x)TixO2 samples also exhibited excellent cyclability, with over 95% of original capacity retained after 300 cycles. Complex impedance measurements corroborated the improved Na-ion conductivity in Ti-doped samples and an associated increase in Na-ion transference number from 0.86 for the sample with x = 0 to 0.97 for the sample with x = 0.075.

A copper nanoparticle enhanced phase change material with high thermal conductivity and latent heat for battery thermal management

In order to maintain the safety temperature of power battery pack within electric vehicle, an anti-leakage composite phase change materials (CPCM) of paraffin (PA)/expanded graphite (EG)/copper nanoparticle (CN) with enhanced thermal conductivity was proposed. Its thermal properties and heat dissipation were verified by thermal property test and discharge experiment respectively. The results show that PA/EG/CN can well control the temperature of the battery pack within a safe range. The CPCM-based battery module shows excellent heat dissipation, the maximum temperature (Tmax) decrease 2.6 °C and 7.2 °C during 1 C and 2 C discharge tests. The temperature difference is 1.0 °C and 0.8 °C. The cooling effect is better under high-rate discharge. During multiple discharge-charge cycle, we find that although the latent heat of the CPCM is limited, the latent heat of the CPCM can be effectively recovered for the abeyance time, which proposes a guiding strategy for the design of CPCM battery thermal management system.

Eruption of ultralow-viscosity basanite magma at Cumbre Vieja, La Palma, Canary Islands

The viscosity of magma exerts control on all aspects of its migration through the crust to eruption. This was particularly true for the 2021 eruption of Cumbre Vieja (La Palma), which produced exceptionally fast and fluid lava at high discharge rates. We have performed concentric cylinder experiments to determine the effective viscosities of the Cumbre Vieja magma, while accounting for its chemistry, crystallinity, and temperature. Here we show that this event produced a nepheline-normative basanite with the lowest viscosity of historical basaltic eruptions, exhibiting values of less than 10 to about 160 Pa s within eruption temperatures of ~1200 to ~1150 °C. The magma’s low viscosity was responsible for many eruptive phenomena that lead to particularly impactful events, including high-Reynolds number turbulent flow and supercritical states. Increases in viscosity due to crystallization-induced melt differentiation were subdued in this eruption, due in part to subtle degrees of silica enrichment in alkaline magma.

Electrochemical behaviors in low-cost and environmentally stable SnS2: An alternative cathode with for high-power primary lithium batteries

Thermal batteries are widely used as the power sources in the field of aerospace and military applications, due to their high-power density and long storage life. Compared to the cubic transition metal disulfides, another hexagonal metal disulfide SnS2, is studied as a new cathode of thermal batteries. SnS2 exhibits good environmental and thermal stability, high electronic conductivity, good wettability, as well as high discharge voltage and rate capability. Its working voltage reaches 2.23 V under discharge current of 100 mA cm−2. During the discharge process, three distinct discharge steps are existed at a cut-off voltage of 1.5 V, as described followed: 1) 2SnS2+2Li++2e−=Sn2S3+Li2S; 2) Sn2S3+2Li++2e−=2SnS+Li2S; 3) SnS+2Li++2e−=Sn+Li2S. In conclusions, SnS2 is proved a most promising cathode material for thermal batteries, and can be widely used.

Fast crystal transformation of nano MnO2 induced by mild interfacial oxidation on hierarchical carbon networks for assembling efficient fibrous MnO2 electrode

The growing demand for wearable electronics boosts researches on flexible fibrous energy storage devices, such as fibrous Zn-MnO2 battery. One bottleneck for the capacity of fibrous MnO2 electrode, especially at high discharge rate, is the inefficient interfacial charge transfer between nano particles within mechanical-mixed MnO2 aggregates. Herein, nano γ-MnO2 has been in-situ grafted on nano carbon branches via a mild interfacial oxidation reaction using KMnO4-doped MnO2 sol precursor, to form nano composites of MnO2@ hierarchical carbon networks. The grafting reaction selectively takes place at defective sites with a mixed bonding state on the surface of the carbon branches, during which a rapid δ-to-γ crystal transformation is largely boosted, instead of traditional slow δ-to-α crystal transformation. An efficient fibrous MnO2 electrode based on the composites of MnO2@ hierarchical carbon networks is successfully applied to fibrous Zn-MnO2 battery, by giving a 2.5 times of capacitance promotion and a better charging-discharging cycling stability.

Thermal management of lithium-ion batteries under high ambient temperature and rapid discharging using composite PCM and liquid cooling

• Composite phase change material (CPCM) is combined with counterflow liquid cooling. • Lithium-ion battery at 5C discharge rate and 40 °C ambient temperature is simulated. • CPCM with 12% expanded graphite is optimal for thermal conductivity and latent heat. • Effects of flow direction, velocity and temperature of coolant are investigated. • Counterflow cooling decreases maximum battery temperature and temperature difference. To improve the thermal performance of the lithium-ion battery at a high ambient temperature of 40 °C and high discharge rate of 5C, a hybrid cooling system composed of composite phase change material (RT44HC/expanded graphite) and counterflow liquid cooling is designed for a battery module with 25 cylindrical batteries. A numerical study is carried out to investigate the influences on the maximum temperature and temperature uniformity of the battery module by different parameters, such as composite phase change material thicknesses, coolant flow directions, expanded graphite mass fractions, coolant velocities and coolant temperatures. The results show that the mass fraction of expanded graphite has an optimal value of 12% in this work, corresponding to the limitations of maximum temperature and temperature difference by 45.25 °C and 3.49 °C, respectively. In addition, compared with the parallel flow direction, the counterflow flow direction scheme possesses better thermal performance. Increasing the coolant velocity can reduce the maximum temperature to a certain extent, but the reduction trend levels off accompanied with a large pressure drop, so a low velocity balancing between the performance and power consumption is preferred. Furthermore, the lower coolant temperature will increase the temperature difference. Therefore, a high inlet temperature should be preferred as close to the ambient temperature. The present hybrid cooling configuration can handle rapid discharging of 5C even under a high ambient environment, which shows outstanding thermal performance and effectively improves the thermal safety of batteries.

Thermal performance revival of composite PCM for hybrid BTMSs by architecture and formula integrated optimization

Composite phase change material (CPCM) cooling is an essential method to ensure better performance of battery thermal management system (BTMS) due to high latent heat. However, long recovery time of CPCM makes it unaffordable especially during continuous high rate discharge–charge cycles. In order to reduce the energy consumption while enhancing the latent heat recovery efficiency, a novel hybrid BTMS architecture coupling with CPCM and liquid cooling is proposed. Liquid cooling is employed to recover the latent heat of PCM. To enhance the heat transfer in BTMS, the structural layout of liquid cooling arrangement is investigated. Meanwhile, mass fraction of expanded graphite (EG) and bulk density of CPCM are considered. Specially, the experiments are conducted to verify the effectiveness of present hybrid BTMS. In solidification, temperature performance especially temperature uniformity is not ideal. Therefore, a novel successive multiple attribute decision making (MADM) algorithm is employed to achieve optimized temperature difference, maximum temperature, solidification rate and mass of CPCM. In MADM algorithm, the order preference by similarity to ideal solution (TOPSIS) is coupled with the analytic hierarchy process (AHP) to solve the multi-objective discrete optimization problem. Results indicate that the optimal solution can make the maximum temperature and temperature difference at the lowest level of 317.51 K and 3.45 K at discharge rate of 4C. Meanwhile, the latent heat of CPCM is improved by about 27.5% at charge rate of 2C. The solution can improve the long-term reliability for the BTMS and the safety and service life for battery module.

Approximate Solutions for Determining Electrolyte Concentrations in Electrochemical Models of Lithium-Ion Batteries

The pseudo two-dimensional (P2D) model and its reduced order models, such as the single particle model (SPM), are widely used in electrochemical modeling and simulating lithium-ion batteries. Although the SPM has a low computational burden, its accuracy is poor under high-rate discharge conditions. Therefore, to balance accuracy and efficiency, the SPM with one-dimensional spatial electrolyte dynamics (SPMe) has been proposed. However, due to the complex diffusion equations for electrolyte dynamics, calculating the lithium-ion concentration in the electrolyte is still difficult. Therefore, we propose the cosine approximation (CA) method to efficiently calculate lithium-ion concentrations. We first use the Laplace transform to analytically solve the diffusion equations, and then, the complete transfer function from the discharge rate to lithium-ion concentration is obtained. In addition, the proposed method is obtained by both truncating the time-domain analytical solution of an infinite series and using error compensation. Moreover, compared to the finite volume method, the new method is verified under the galvanostatic and dynamic profiles, where the higher the order of the method, the higher the accuracy. Finally, the second-order CA shows a higher degree of accuracy compared to the widely used second-order polynomial approximation.