All-climate Battery Research Articles

An electric conductive wide-temperature flexible phase change material for all-climate battery thermal management

Battery thermal management with phase change materials (PCM) has been limited by leakage, low thermal conductivity and rigidity, and the inability to preheat at low temperatures. To solve these problems, a wide-temperature flexible composite PCM (FCPCM) was prepared with a high-temperature open refining method. Styrene ethylene butylene styrene (SEBS) and expanded graphite (EG) absorb paraffin (PA) onto a three-dimensional network. The FCPCM possesses good flexibility before and after phase transition. It can be bent and stretched arbitrarily at room temperature, and the shape memory function enable it can be restored to its original state after heating. The latent heat of the FCPCM-15 is 159.9 J/g and its thermal conductivity was 7.45 times higher than that of pure paraffin. The FCPCM also possesses a good volume conductivity of 92–2952 S/m and allows for uniform electrical heating. The excellent thermal and electrical performance of the FCPCM allows it to cool batteries at high temperatures and preheat batteries at low temperatures. After ten charge/discharge cycles at 30 °C, the battery pack’s temperature based on FCPCM cooling is still reduced by 3.9 °C. At a low temperature of −20 °C, the preheating rate of the battery pack can reach 12.9 °C/min, and the discharge voltage and capacity of the battery pack were increased by 15 % and 20.8 % after preheating. The FCPCM suggests a promising and practical approach way for the all-climate thermal management of batteries.

All-climate battery thermal management system integrating units-assembled phase change material module with forced air convection

Phase change material (PCM) is widely adopted to construct integrated battery thermal management systems (BTMSs) for all climates. However, integrated BTMSs in cylindrical battery modules remain arduous challenges due to the compact/massive cuboid-shaped PCM module and the curved surface of the cells. Herein, we propose a novel all-climate BTMS integrating units-assembled composite PCM (CPCM) module with force air convection. The CPCM module assembled by sleeve-like CPCM units provides developed airflow channels and enlarged heat transfer surface from 1.17 × 10−3 to 3.63 × 10−3 m2 for enhancing convective heat transfer. Consequently, compared to conventional cuboid-shaped module, the thermal resistance of the units-assembled module is remarkably reduced by 52.0% and 60.1%, and the heat flux is enhanced by 7 times under both cooling and preheating modes. In cooling tests, this BTMS demonstrates superior performance by controlling the temperature and temperature difference below 40.30 and 2.80 °C at 3-C discharge, respectively. In preheating tests, it effectively preheats the battery module from 0 to 10 °C in 302 s with a low temperature difference of 3.82 °C. Furthermore, this units-assembled CPCM module saves 53.8 wt% of the CPCM dosage, and thus the energy density of the battery module is increased from 75.6 to 94.4 Wh·kg−1.

Cointercalation-Free Ether-Based Deep Eutectic Electrolyte for All-Climate Battery

Cointercalation-Free Ether-Based Deep Eutectic Electrolyte for All-Climate Battery

Dual-strategy-encapsulated phase change materials with thermal immune functions for efficient energy storage and all-climate battery thermal management

The utilization of phase-change materials (PCMs) has garnered great interest in purposes of energy storage and thermal management due to its lightweight, high-energy efficiency, and cost-competitiveness. However, the intrinsic limitations of low thermal conductivity and leakage in PCMs impede their usage in high-power-density energy harvesting applications. Here, we designed multifunctional phase-change composites (PCCs) via a dual-encapsulation strategy to realize all-climate thermal managements for lithium-ion batteries. For PCMs, polyethylene glycol was interpenetrated into porous polyurethane network (PEG@PU) to enclose a considerable amount of PEG. Then, the PCMs were infiltrated into the highly oriented graphite frameworks (HOGF). A series of processes enabled to form multi-layered structures as well as alleviate the leakage issue of PEG, and thereby improving the thermal storage ability. The so-obtained PCCs exhibited excellent electrothermal properties (134.9 °C at 1.8 V) and high electromagnetic interference performances (larger than 90 dB). These findings presented that the thermal managements of PCCs can be utilized as active preheating or passive cooling system in a battery thermal management system for the all-climate demands.

Synergistic interphase modification with dual electrolyte additives to boost cycle stability of high nickel cathode for all-climate battery

B-containing electrolyte additives are widely used to enhance the cycle performance at low temperature and the rate capability of lithium-ion batteries by constructing an efficient cathode electrolyte interphase (CEI) to facilitate the rapid Li+ migration. Nevertheless, its wide-temperature application has been limited by the instability of B-derived CEI layer at high temperature. Herein, dual electrolyte additives, consisting of lithium tetraborate (Li2TB) and 2, 4-difluorobiphenyl (FBP), are proposed to boost the wide-temperature performances of LiNi0.6Co0.2Mn0.2O2 (NCM) cathode. Theoretical calculation and electrochemical performances analyses indicate that Li2TB and FBP undergo successive decomposition to form a unique dual-layer CEI. FBP acts as a synergistic filming additive to Li2TB, enhancing the high-temperature performance of NCM cathode while preserving the excellent low-temperature cycle stability and the superior rate capability conferred by Li2TB additive. Therefore, the capacity retention of NCM||Li cells using optimal FBP-Li2TB dual electrolyte additives increases to 100% after 200 cycles at −10 °C, 99% after 200 cycles at 25 °C, and 83% after 100 cycles at 55 °C, respectively, much superior to that of base electrolyte (63%/69%/45%). More surprisingly, galvanostatic charge/discharge experiments at different temperatures reveal that NCM||Li cells using FBP-Li2TB additives can operate at temperatures ranging from −40 °C to 60 °C. This synergistic interphase modification utilizing dual electrolyte additives to construct a unique dual-layer CEI adaptive to a wide temperature range, provides valuable insights to the practical applications of NCM cathodes for all-climate batteries.

All-climate thermal management structure for batteries based on expanded graphite/polymer composite phase change material with a high thermal and electrical conductivity

With the large-scale application of lithium battery technology, a thermal management system is required to ensure battery performance and safety in all climates. This study reports an all-climate battery thermal management structure based on an expanded graphite/polymer/paraffin wax ternary composite phase change material with high thermal (19.3 Wm−2/K) and electrical (1590.5 S/m) conductivity. The thermal management structure adopts a double-layer structure, an inter phase change material with high thermal and electrical conductivity, and an outer phase change material with low thermal conductivity as a heat preservation and insulation medium. The thermal management structure innovation uses the phase change material and the battery to form a preheating circuit to generate Joule heat to warm up the battery at low temperatures. This heating method uses the energy of the battery to greatly improve the adaptability of the thermal management system. The preheating speed reaches 20.5 °C/min at –20 °C. The phase change material can continue to generate heat during the discharge process of the battery to ensure normal operation. At a discharge rate of 1C and at –20 °C, the discharge energy increased by 35.5% compared with the case without preheating. In addition to acting as a heating element, phase change materials also act as heat dissipation media in high temperature environments, the structure exhibited a good heat dissipation capacity. At 35 °C, the temperature of the battery was controlled at 42.2 °C after the battery was discharged at a rate of 2C.

Innovative lumped-battery model for state of charge estimation of lithium-ion batteries under various ambient temperatures

Ambient temperature alters properties of lithium-ion batteries and affects the accuracy of estimation of state of charge (SOC), which is an important function to ensure the safety and reliability of electric vehicles. An accurate SOC estimation is critical under various temperatures. The existing methods have two problems: 1) need to perform time-consuming pre-experiments to investigate influence of various temperatures on the battery properties, and 2) use of the Thevenin model which is inaccurate at sub-zero temperatures. This study proposes an innovative lumped-battery model to improve the accuracy of both SOC estimation and battery modeling without pre-experiments. Two main causes of modeling errors by the Thevenin model are analyzed. Proposed model parameters are estimated using the recursive least squares, and the extended Kalman filter is used to estimate SOC in real time. Experiments are conducted under time-invariant and time-varying temperature conditions ranging from −10 °C to 30 °C. The results indicate that relative errors of battery modeling are less than 2.4% and that estimation errors of SOC are at most 0.4% under various temperatures. Therefore, the proposed method can be conveniently and widely applied to all-climate battery management systems to achieve a high accuracy of SOC estimation.

A set membership theory based parameter and state of charge co-estimation method for all-climate batteries

State of charge estimation of the battery is one of the core functions in the battery management system. Accurate and reliable state of charge estimation under wide temperature range is critical for the application of all-climate electric vehicles. The main work of this paper is as follows: (1) To achieve accurate closed-loop state estimation, a temperature dependent battery model is proposed; (2) The common model-based state of charge estimation methods using filters like Kalman filter assume that the state perturbations and measurement noise are white and Gaussian noises, which is not realistic in practical application. To solve this problem, set membership method which holds that the noises are unknown but bounded is used for state of charge estimation. Based on the established temperature dependent battery model and the set membership method, battery parameter and state of charge co-estimation algorithm is proposed for all-climate battery state estimation; (3) The proposed method is fully verified at −10 °C–40 °C and the comparison between the proposed method and extended Kalman filter is conducted to illustrate its superiorities. Furthermore, the validity and real time performance of the co-estimation method are verified in a hardware-in-loop test bench. Results show that the proposed co-estimation method has excellent robustness and the state of charge estimation error is bounded to 5% under wide temperature range.

A model-based state-of-charge estimation method for series-connected lithium-ion battery pack considering fast-varying cell temperature

Accurately estimating the state-of-charge (SOC) of lithium-ion batteries under complicated temperature conditions is crucial in all-climate battery management systems. This paper proposes a model-based SOC estimation method for series-connected battery pack with time-varying cell temperature. Systematic battery experiments are conducted to investigate the influences of changing temperature on both cell characteristics and cell-to-cell inconsistencies. A normalized open-circuit voltage (OCV) model is developed and applied in cell Thevenin model to describe the temperature-dependent OCV-SOC characteristic. The battery pack SOC is analyzed considering the effect of passive balance control. Then, a lumped parameter battery pack model is established by connecting cell models in series. To reduce computational complexity, a dual time-scale parameter identification framework is proposed which is supported by an online filtering process of selecting variable reference cell (VRC). An adaptive co-estimator is presented to update pack parameters in dual time-scale using an optimized recursive least squares algorithm, and to estimate the battery pack SOC using an extended Kalman filter. Experimental verifications are conducted under time-varying environmental temperature ranging from −40 °C to 40 °C. Results indicate the established model can well describe the dynamic behavior of battery pack, and the proposed method can estimate the battery pack SOC with considerably high precision.

Coral-shaped porous LiFePO4/graphene hybrids for high rate and all-climate battery applications

Tailor-designed cathode materials are essential for Li-ion batteries with both high energy density and outstanding capacity retention. Here we have designed and fabricated coral-shaped hierarchical porous LiFePO4/graphene hybrids for lithium-ion batteries. These novel hybrid materials exhibit excellent electrochemical performance over a wide temperature range from −40 ​°C to +60 ​°C. Even at −40 ​°C, the hybrid cathode can deliver a high initial capacity of 120 ​mAhg−1 and still maintain a discharge capacity of 80 mAhg−1 after 500 cycles with a very low capacity loss of 0.066% per cycle. The excellent wide-temperature performance can be ascribed to the porous structure and fast ion/electronic transport kinetics of the high conductive framework.

All-Climate Battery Technology for Electric Vehicles: Inching Closer to the Mainstream Adoption of Automated Driving

The year 2017 was when electric vehicles (EVs) came of age. EV sales, according to Macquarie Bank, climbed from 740,000 vehicles in 2016 to 1.1 million, an increase of 51%. In terms of market shares, EVs accounted for 1.7% of new car sales in 2017, up from 1.1% in 2016. Although still small in the grand scheme of things, the growth rate was exceptional. All market movers are now taking EVs seriously, as evidenced by a flurry of announcements last year about the plans of major automakers for the EV market. Should these plans come to fruition, we are foreseeing roughly 400 models and 25 million sales of EVs by 2025.

Lithium-ion battery structure that self-heats at low temperatures.

Lithium-ion batteries suffer severe power loss at temperatures below zero degrees Celsius, limiting their use in applications such as electric cars in cold climates and high-altitude drones. The practical consequences of such power loss are the need for larger, more expensive battery packs to perform engine cold cranking, slow charging in cold weather, restricted regenerative braking, and reduction of vehicle cruise range by as much as 40 per cent. Previous attempts to improve the low-temperature performance of lithium-ion batteries have focused on developing additives to improve the low-temperature behaviour of electrolytes, and on externally heating and insulating the cells. Here we report a lithium-ion battery structure, the 'all-climate battery' cell, that heats itself up from below zero degrees Celsius without requiring external heating devices or electrolyte additives. The self-heating mechanism creates an electrochemical interface that is favourable for high discharge/charge power. We show that the internal warm-up of such a cell to zero degrees Celsius occurs within 20 seconds at minus 20 degrees Celsius and within 30 seconds at minus 30 degrees Celsius, consuming only 3.8 per cent and 5.5 per cent of cell capacity, respectively. The self-heated all-climate battery cell yields a discharge/regeneration power of 1,061/1,425 watts per kilogram at a 50 per cent state of charge and at minus 30 degrees Celsius, delivering 6.4-12.3 times the power of state-of-the-art lithium-ion cells. We expect the all-climate battery to enable engine stop-start technology capable of saving 5-10 per cent of the fuel for 80 million new vehicles manufactured every year. Given that only a small fraction of the battery energy is used for self-heating, we envisage that the all-climate battery cell may also prove useful for plug-in electric vehicles, robotics and space exploration applications.

A Fast Rechargeable Lithium-Ion Battery at Subfreezing Temperatures

Widespread adoption of plug-in electric vehicles hinges upon fast rechargeability of lithium-ion batteries in all climates. To date, Li-ion batteries subject to quick charging in extreme cold grow lithium dendrites which consume cyclable lithium thus severely shortening battery life and compromise safety. Here we experimentally demonstrate 3C fast charging at −30°C for more than 500 cycles using a new cell structure, the all-climate battery (ACB). Addition of a metal foil creates immense internal heating in the ACB cell upon activation by short pulses of discharge and charge current, allowing charge to 80% state-of-charge in 14 min as opposed to 160 min for a conventional Li-ion cell. Moreover, the ACB cell withstands more than 500 fast-charge cycles while the conventional cell incurs 20% capacity loss after only 12 cycles. The experimental pouch cell of 10 Ah consists of a graphite anode and a NCM622 cathode with a nickel foil coated by polyethylene terephthalate as an internal heating element. We believe that the self-heating ACB cell with 11.4× faster charging and 40× better cycle life enables a ubiquitous, weather-independent fast-charging infrastructure required for affordable vehicle electrification free of range anxiety. This fast rechargeable battery at low temperatures is also essential for outdoor robots and drones as well as can substantially reduce battery size and cost for home and grid energy storage.

Fast Charging of Li-Ion Batteries in Extreme Cold

Fast charging is an enabling technology for electric vehicles (EV). Unfortunately lithium-ion batteries are notoriously incapable of fast charging at subzero temperatures,1-3 thereby hindering EVs from dependable and convenient operation under all weather conditions. In this work we describe a novel battery structure, called all-climate battery (ACB), which adds a resistor sheet inside the electrochemical cell to modulate the cell’s internal resistance according to temperature. Based on ACB technology, we have built 12Ah pouch cells using graphite anode, NMC cathode and 1M LiPF6 in EC:EMC (3:7 by wt) + 2% VC and showed that such ACB cells are able to be charged from 20% to 90% state of charge (SOC) in -30oC environment in ~22 minutes, while keeping the cell voltage never exceeding 4.2V (a necessary condition to avoid Li plating). Figure 1 displays the experimental results of fast charging a 12Ah ACB cell from -30oC with a charge protocol of CV (4.2V) and limited by CC (3C or 36A). It is seen that the charge current under 4.2V charge voltage starts only at ~7A; however, it rapidly increases to 36A (3C limit) in around 400 seconds. Simultaneously the cell outer surface temperature increases from the initial temperature of -30oC to above the freezing point. Thereafter, the ACB cell undergoes 3C constant current charging with the cell voltage dips below 4.2V between 400 and 1100 seconds. During this period, the cell SOC rapidly increases from the initial SOC of 20%, eventually reaching 90% in ~22 min. Figure 2 compares two charge experiments under the same charge protocols of a 12Ah ACB cell and its baseline cell without ACB technology. It is clearly shown that ACB technology has dramatically improved the fast charge capability of Li-ion batteries. More efforts are ongoing to accelerate the fast charge process from subzero temperatures and to further reduce the charge time from 22 min to within 15 min. These advanced improvements will be elaborated in this presentation.