Performance Of Lithium-ion Cells Research Articles

Residual NMP and Its Impacts on Performance of Lithium-Ion Cells

Abstract N-methyl-2-pyrrolidone (NMP) is the most common solvent used in coating positive electrode materials on aluminum foil during the manufacturing of lithium-ion batteries. NMP is a strongly polar aprotic solvent that effectively dissolves the polyvinylidene difluoride binder. While the majority of NMP typically evaporates during the electrode baking process, trace amounts may persist, particularly in positive electrodes containing nano-sized and highly-porous active materials. We noted residual NMP in the positive electrodes of Li-ion pouch cells containing LiMn0.8Fe0.2PO4 due to the extremely high surface area of the material and we wanted to determine the impact of this residual NMP. Therefore, a control electrolyte was purposely spiked with varying amounts of NMP and used in NMC532/graphite pouch cells to investigate the impact of residual NMP on lithium-ion battery performance. Experimental results indicate that NMP has the potential not only to neutralize the electrolyte additive ethylene sulfate but also to independently increase cathode impedance, leading to a higher rate of capacity loss during charge-discharge cycling. It is crucial to establish the appropriate procedure for baking electrodes containing NMP, both in laboratory and industrial settings, to mitigate these effects.

Degradation and safety performance of lithium-ion cells under high-rate charging/discharging scenarios

Given the increasing popularity of high-rate charging and discharging for lithium-ion cells, this research aims to investigate the degradation and safety performance of these cells under high-rate scenarios. The study considers high rates including 4 C, 6 C, 8 C, and 10 C. The results show that high-rate charging and discharging leads to significant degradation of the cells, with the degradation rate linearly declining with the charging/discharging rate. Furthermore, cells that undergo long-term high-rate charging and discharging exhibit worsened safety performance at elevated temperatures, and this severity increases with the charging/discharging rate. It is also found that charging and discharging have different effects on the thermal runaway behaviour of cells when subjected to over-heating. Charging causes thermal runaway to occur much earlier than discharging, likely due to the difference in stored energy. Additionally, the intensity of thermal runaway is more severe during charging. Compared to the reference, high-rate charging deteriorates the safety features of cells, while high-rate discharging suppresses thermal runaway. Discharging has a more noticeable impact on thermal runaway. Eventually, cell’s state of charge is proved to be an especially vital factor determining the thermal runaway characteristics of cells.

(Keynote) Thermal Performance Optimisation at Cell Level, to Achieve Better, Longer Lasting Battery Packs

Temperature is a major issue in the operation of lithium-ion batteries, with both high and low temperatures causing problems. Cold batteries are inefficient, while hot batteries are at risk of thermal runaway and fire, making it crucial to maintain a safe and optimal temperature range. Temperature gradients can negatively impact battery performance, reducing accessible energy and increasing the degradation rate. This is a critical issue for electric vehicles (EVs), which can experience reduced driving range and deteriorating performance over time.Despite these challenges, current lithium-ion cell designs prioritize maximizing specific energy, which can negatively impact thermal performance. Thermal management systems are used to extract heat from poorly designed cells, but they are a significant parasitic load, demanding on average 8 kW in typical operation. Further, they can introduce uneven distribution of current throughout the battery pack, leading to diminished performance and accelerated degradation. The limited performance of these systems contributes towards range anxiety, which is a major barrier to the widespread adoption of electric vehicles in the UK, Europe, and the USA.To address these challenges, the authors propose the use of a new metric, the cell cooling coefficient (CCC). The CCC is a constant for a given cell and thermal management method (e.g. surface cooling or tab cooling), and is measured in W.K-1 (the reciprocal of thermal resistance). The CCC define a cell's ability to reject heat energy. The CCC is defined as the temperature gradient across a cell in idealized operating conditions, normalized against the heat generation rate in the same conditions. This allows for the comparison of geometrically dissimilar cells and can be used to optimize the thermal performance of lithium-ion cells.Experimental results presented in the paper demonstrate that increasing the thickness of the tabs in a typical lithium-ion pouch cell by 34% can yield a tab cooling performance enhancement of 20%, with a specific energy reduction of just 0.7%. Numerical methods predict that for a large format automotive pouch cell, increasing the tab thickness from 0.2 mm (negative) and 0.45 mm (positive) to 2 mm will lead to a 90% increase in the CCC for tab cooling (see in the attached figure). This yields a 51% reduction in temperature gradient across the cell in any instance of operation. As with all geometric optimisation, our models highlight a law of diminishing returns and we discuss the optimal tab thickness for various operations and applications.The authors also consider the use of the CCC metric for edge cooling in pouch cells and cylindrical cells. They find that tabs used to connect jelly rolls to the external can of cylindrical cells create a considerable thermal bottleneck. Redesign of this tab is well documented through Tesla’s proposed tab-less 4680.The use of thermal models at cell-level alongside existing battery models is critical for the development of future lithium-ion cells. The authors demonstrate that optimisation of thermal performance is entirely achievable within the numerical domain, reducing the requirement for expensive and timely prototyping phases during any product development process.By designing cells to have better thermal performance, it is possible to reduce the temperature gradient required between the hottest and coolest points in the thermal management system. This, in turn, reduces the power required by the thermal management system, allowing for more power to be directed towards extending the driving range of electric vehicles. Reduced temperature gradients at the battery pack level will also extend battery pack lifetime, reducing the lifetime cost to end-users and lessening the strain on raw material supply chains and battery recycling technology.The use of the CCC metric offers a promising approach to optimizing the thermal performance of lithium-ion cells. By addressing thermal management challenges, it is possible to reduce the parasitic load of thermal management systems, improve the lifetime and cost-effectiveness of battery packs, and lessen range anxiety for EV users. Figure 1

Detailed Approach to Calculate the Heat Generation of Lithium-Ion Cells during Heat-Wait-Seek Tests in Accelerating Rate Calorimetry

By means of the Heat-Wait-Seek test in Accelerating Rate Calorimeters (ARC) the safety performance of Lithium-ion cells can be estimated. The most interesting measured parameters that can be extracted from these tests are the critical temperatures, such as the onset of self-heating, the venting or thermal runaway temperature. Another essential safety factor is the generated heat during cell failure. In general, the generated heat is calculated by an average heat capacity of the cell and the temperature difference in the experiment, which is not accurate enough especially when facing the challenges in specific volumetric energy density and safety of battery packs.In this study a more accurate way to calculate the generated heat is proposed, which consists of using temperature dependent heat capacity of the cell, based on its individual components. This leads to a significant difference in the calculated generated heat, for instance the specific heat capacity of NMC as a cathode material increases in the temperature range from 298 K to 398 K from 0.83 to 0.96 J/g·K, which is an increase of about 16 %. This leads to a difference in the calculated generated heat in this small range of 7 J/g (or 8 %), if a static specific heat capacity of 0.83 J/g·K and on the other hand a temperature dependent specific heat capacity is used. Moreover, the influence of additional heating steps, venting of the cell, melting of the separator and the overall accuracy of the measurement will be discussed. The investigation of these effects is in the focus of the project AnaLiBa (Analytics of Lithium-ion-Batteries), funded by the German Federal Ministry of Education and Research (BMBF) in the framework of the competence cluster Analytics/quality assurance (AQua). In this project the approach is applied to commercial type 21700 cells. The 21700 type cells are extensively used in battery packs, for instance in electric cars, due to their 20 % higher energy density with respect to the former used type 18650 cells. The cells were measured in an ES-ARC from Thermal Hazard Technologies, UK, using the Heat-Wait-Seek test. The generated heat was compared for either fresh cells and cells after cyclic aging. The cyclic aging was performed at 0 °C and 20 °C with a charging rate of 0.3C for 0 °C and 0.7C for 20 °C and a discharging rate of 2C for 20 °C and 0.5C for 0 °C until the state of health was at 80 % ±2 %. The two different temperatures studied in the cyclic aging were chosen as 0 °C to cause lithium plating and as 20 °C to cause a higher internal resistance due to a thicker solid-electrolyte-interface, which has a high influence on the measured properties in the Heat-Wait-Seek test and therefore on the generated heat.With this approach the generated heat in abuse tests can be calculated more accurately to simulate the propagation of heat during a single cell failure in a pack or to calculate the necessary thickness of a heat barrier for safer battery packs. This helps manufacturers to improve their battery pack design with respect to the specific volumetric energy density and safety.

Robust optimization of prismatic lithium-ion cells for reducing thermal performance fluctuations and manufacturing costs

The thermal performances of lithium-ion cells are significantly influenced by unavoidable uncertainties during manufacturing. However, there is a lack of uncertainty optimization methods to control the thermal performance fluctuations of lithium-ion cells. This paper proposes a robust optimization approach for prismatic lithium-ion cells, aiming to optimize the manufacturing cost and control the thermal performance fluctuations without removing the uncertainties. The cost objective function and thermal robustness constraints are established considering the uncertainties of the manufacturing parameters, thereby formulating the robust optimization model of the prismatic lithium-ion cell. The robust optimization performs a nested optimization by optimizing the parameter standard deviations for an optimal cost and evaluating the cell thermal robustness at each design point. An analytical expression for the cell expansion behaviour is created based on the elastic shell theory. An electrochemical-thermal-mechanics multidisciplinary analysis method with ordinary differential equations is given to evaluate the cell thermal performances such as temperature, pressure, and expansion under thermal abuse. It addresses the efficiency issue in the nested optimization. The robust optimization approach is applied to design problems for two-type lithium-ion cells packaged in pouch and hard-pack. Numerical and experimental results demonstrate the excellent potential of the approach due to its advantages in applicability, accuracy, and efficiency.

Numerical optimization of lithium-ion cell performance using metaheuristic algorithms

The specific energy and power are key performance characteristics of lithium-ion cells. The active materials of these cells determine the energy storage capacity and control their energy and power. The inactive components, on the other hand, influence the electrical losses, the active material utilization uniformity and the heat dissipation. They also contribute significantly to the cell weight. These components must therefore be properly designed in order to optimize the cells performance and weight. The present paper focuses on the optimization of the design of the inactive components. It concentrates on lithium-ion NMC pouch cells and considers three objectives: maximize the specific energy; maximize the specific power, and a trade-off between the two. The optimization combines three metaheuristics with the simulation tool Battery Design Studio to identify the best combination. Evaluations showed that the Cuckoo search algorithm offers the best response. An analysis of the results led to the following conclusions: (i) Large numbers of electrode pairs are beneficial; (ii) Counter-located tabs provide better performance, but lead to bigger cells than the co-located tab option. Thus, the counter-located tab configuration represents the right design for an optimal specific power, whereas co-located tabs are more appropriate for the specific energy; (iii) Finally, the average aspect ratio (height/width) established considering all optimized configurations is less than 0.47. This indicates that the aspect ratios of commercial cells, which are generally greater than 1.0, are not optimal.

La-doped LiMnPO4/C cathode material for Lithium-ion battery

LiMnPO4 and LiMn1-xLaxPO4 (0.01 ≤ x ≤ 0.1) nanostructures with in-situ carbon coating are synthesized by low temperature solvothermal method using Glycerol: Water (2:1) ratio as solvent. Powder X-ray diffraction (XRD) studies confirmed the orthorhombic crystal structure of LiMnPO4 and LiMn0.99La0.01PO4. X-ray diffraction shows that up to 1% La3+ ion doping into manganese sites does not affect the crystal structure of LiMnPO4. Field emission scanning electron microscopy (FESEM) of LiMnPO4 and LiMn0.99La0.01PO4 depicts the formation of nanosized particles with spherical morphology. Electrochemical properties of LiMnPO4 and LiMn0.99La0.01PO4 are investigated by galvanostatic charge discharge tests. The present studies show that 1% La3+ ion doped LiMnPO4 could be a promising cathode material that can improve the performance of Lithium-ion cell by increasing the electrochemical stability at higher C-rate.

Optimisation of Industrially Relevant Electrode Formulations for LFP Cathodes in Lithium Ion Cells

The electrode formulation has a significant effect on the performance of lithium ion cells. The active material, binder, and conductive carbon all have different roles, and finding the optimum composition can be difficult using an iterative approach. In this study, a design of experiment (DoE) methodology is applied to the optimisation of a cathode based on lithium iron phosphate (LFP). The minimum LFP content in the electrodes is 94 wt%. Seventeen mixes are used to evaluate adhesion, resistivity, and electrochemical performance. The coating adhesion increases with binder content, and the coating conductivity increases with carbon nano-tube content. The best coatings achieve 5C:0.2C capacity ratios above 50%, despite the relatively high coat weight. Models based on just the component mixture do not replicate the discharge capacities at high rates. However, a combined mixture + process model can fit the data, and is used to predict an optimum formulation.

Electrochemically Active Polymer Components in Next-Generation LiFePO4 Cathodes: Can Small Things Make a Big Difference?

As a cathode material for lithium-ion batteries, lithium iron phosphate (LiFePO4, LFP) successfully transitioned from laboratory bench to commercial product but was outshone by high capacity/high voltage lithium metal oxide chemistries. Recent changes in the global economy combined with advances in the battery pack design brought industry attention back to LFP. However, well-recognized intrinsic drawbacks of LiFePO4 such as relatively low specific capacity and poor electronic and ionic conductivity have not yet been fully mitigated. Integration of electrochemically active electron-conducting polymers (EAECPs) into the cathode structure to replace conventional auxiliary electrode components has been proposed as an effective strategy for further performance improvement of LFP batteries. In this review, we show how various combinations of polymer properties/functions have been utilized in composite LiFePO4 electrodes containing EAECP components. We present recent advances in the cathode design, materials, and methods and highlight the impact of synthetic strategies for the cathode preparation on its electrochemical performance in lithium-ion cells. We discuss advantages and limitations of the proposed approaches as well as challenges of their adoption by the battery manufactures. We conclude with perspectives on future development in this area.

(Digital Presentation) Simulating Coupled Effect of Heat Generation and Capacity Degradation on Performance of Lithium-Ion Cells

Lithium-ion batteries are gaining significant interest as energy storage devices in high power demand applications like power grids and EVs as the world seeks to reduce dependence on fossil fuels. High energy and power densities, high coulombic efficiency and low self-discharge of lithium-ion batteries make them a preferred choice in such applications. When a cell is cycled, various degradation processes occur, leading to a reduction in cell capacity over time. Among the various ageing mechanisms, electrolyte decomposition at the graphite electrode is the most significant contributor to capacity loss due to the consumption of cyclable lithium ions. Another mechanism for capacity loss is lithium plating on the surface of the graphite electrode particles and is observed under harsh cycling conditions or after extended cycling. These reactions lead to the formation of a passive layer, called the solid-electrolyte interface (SEI) layer, on the surface of the anode graphite particles. The ionic resistance offered by the SEI layer to the flow of lithium ions in the electrolyte leads to increased heat generation within the cell, thereby leading to higher cell temperature for the same operating conditions with cell ageing. Moreover, the ageing of the cell due to capacity loss, power reduction and impedance rise, is strongly dependent on the cell’s operating temperature and current. The internal cell temperature can be significantly different from its surface temperature for large-format cells when subjected to high current and different extent of forced cooling leading to a spatially varying degradation effects.Even though highly relevant, the coupled effect of current flow, heat generation and capacity fade have not been adequately examined in the literature. While several works have simulated the temperature distribution in large format cells [1,2] or capacity fade for cells [3] under isothermal conditions, very few have examined their coupled effect. Studies considering the coupled effect of capacity fade with heat generation have incorporated a pseudo-2D electrochemical degradation model [4,5]. The thermal model ranges from one to three-dimensional, with higher dimensional thermal models considering uniform heat generation within the cell. However, in a practical scenario, a large-format cell suffers from a non-uniform temperature distribution, leading to non-uniform electrochemical reactions and degradation.Hence, a detailed coupled thermo-electrochemical, capacity-fade model is required to understand cell degradation and temperature rise during its operational life. In a step towards this goal, a two-dimensional physics-based, coupled thermo-electrochemical model with capacity degradation will be demonstrated for cylindrical lithium-ion cells. The electrochemical model with capacity fade is based on the porous-electrode and concentrated solution theories [6]. The thermal model considers the effect of ohmic heat in various cell components and the reversible and irreversible heat of reactions in the electrodes. The contribution of side reactions in heat generation is incorporated. The effect of changing porosity and thermal and electronic impedance with ageing on the cell is considered in the model. The results will give a better understanding of (a) the safe operation of the cell as the internal temperature of the cell changes with ageing, and of (b) the dependence of cell ageing on temperature. Fig.1 shows the spatial distribution of temperature at the end of discharge for an LMO cell under different convective heat transfer coefficients. The cells were subjected to a 5C current at an ambient temperature of 25°C. While the temperature reached for a convective heat transfer coefficient h=5 W/m2.K is much higher, the temperature gradient developed is more significant for h=50 W/m2.K. This can be attributed to the increased Biot number for the cell under forced cooling. A difference of 8°C for h=50 W/m2.K between the internal and external cell temperature show that the capacity-fade model needs to consider the local temperature distribution within the cell for better prediction of cell degradation with cycling.

The 3-phenyl-1,4,2-dioxazol-5-one (PDO) Electrolyte Additive for Li(Ni0.6Mn0.2Co0.2)O2 and Li(Ni0.8Mn0.1Co0.1)O2 Lithium-Ion Cells

Electrolyte additives, as a small proportion of the electrolyte, greatly affect the performance of lithium-ion cells. This work performs a comparative study to reveal the difference between commercial 99.8% pure 3-phenyl-1,4,2-dioxazol-5-one (PDO) additive and lab-made 95% pure PDO in NMC622/graphite cells. In addition, a set of experiments were conducted to evaluate the performance of 99.8% pure PDO and its binary blends with vinylene carbonate (VC), 1,3,2-dioxathiolane-2,2-dioxide (DTD) or lithium difluorophosphate (LFO) in NMC811/graphite cells. 99.8% Pure PDO and 95% pure PDO show little difference in the NMC622 cells, with the latter presenting relatively better performance in the best-performing blends for long-term cycling and high-temperature storage tests. Considering all the tests including ultra high precision coulometry (UHPC) cycling, long-term cycling, and high-temperature storage, the NMC811 cells with 2%PDO+ 1%LFO outperformed the other PDO-containing cells. The PDO-based blends were confirmed to be more promising in cells with higher nickel content; that is, PDO could be a useful additive in high-nickel content cells.

Tuning Fluorination of Linear Carbonate for Lithium-Ion Batteries

Liquid electrolyte engineering plays a critical role in modern lithium-ion batteries. However, the existing electrolytes fall short when used with some trending battery chemistries such as high-voltage and high-energy-density electrodes. Fluorination of electrolyte solvents has been identified as an effective approach for improved cyclability, but few works systematically studied the effects of fluorination extent of carbonate solvents on battery performance. Here we design and synthesize a family of fluorinated ethyl methyl carbonates. Different numbers of F atoms are finely tuned to yield monofluoroethyl methyl carbonate (F1EMC), difluoroethyl methyl carbonate (F2EMC) and trifluoroethyl methyl carbonate (F3EMC). The cycling behavior of several types of lithium-ion pouch cells, including graphite (Gr)/single-crystalline LiNi0.8Mn0.1Co0.1O2 (SC-NMC811), Gr-SiOx/LiNi0.6Mn0.2Co0.2O2 (NMC622), high-voltage Gr/LiNi0.5Mn1.5O4 (LNMO), Gr/layered Li-rich Mn-based oxide (LLMO) and fast-charging Gr/NMC622, were systematically investigated to understand the impact of fluorination degree. Compared to the commercially available F3EMC, we found that the partially-fluorinated F1EMC and F2EMC in some cases showed improved cycling stability, which we attribute to their locally-polar –CH2F and –CHF2 groups and thus fast ion conduction than –CF3. This work suggests that highly or fully fluorinated solvents are not necessarily desirable; instead, fluorination degree needs to be rationally and finely tuned for optimized lithium-ion cell performance.

Modular packaging effect on thermal performance of LiCoO2 lithium-ion cells: An experimental study

Thermal performance of lithium-ion cells plays a crucial role in terms of efficiency, safety, and residual lifetime management of many electrical devices. In this paper, a thermal management strategy for cooling-down 26650 LiCoO2 lithium-ion battery cells based on modular packaging is analyzed. Battery modules with different number of cells were arranged and experimentally discharged under natural convection followed by a cooling-down process by air forced convection until cells reached the ambient temperature. Surface temperature of each cell and ambient temperature were recorded and analyzed using a fractal time thermal model. Results show that modular packaging improves the thermal behavior of cells. As the modules became larger, the thermal time constant of the system significantly increased, i.e., heat transfer coefficient of module decreased and the furthest cells from the fans interchanged less heat to surrounding air. In addition, modular packaging improves the energy efficiency of the cooling system since it is more efficient to cool several small modules than cooling a larger one.

A Comparison of Lithium-Ion Cell Performance across Three Different Cell Formats

To investigate the influence of cell formats during a cell development programme, lithium-ion cells have been prepared in three different formats. Coin cells, single layer pouch cells, and stacked pouch cells gave a range of scales of almost three orders of magnitude. The cells used the same electrode coatings, electrolyte and separator. The performance of the different formats was compared in long term cycling tests and in measurements of resistance and discharge capacities at different rates. Some test results were common to all three formats. However, the stacked pouch cells had higher discharge capacities at higher rates. During cycling tests, there were indications of differences in the predominant degradation mechanism between the stacked cells and the other two cell formats. The stacked cells showed faster resistance increases, whereas the coin cells showed faster capacity loss. The difference in degradation mechanism can be linked to the different thermal and mechanical environments in the three cell formats. The correlation in the electrochemical performance between coin cells, single layer pouch cells, and stacked pouch cells shows that developments within a single cell format are likely to lead to improvements across all cell formats.

Electron Microscopy Investigation of Graphite Electrodes from Fast-Charged Lithium-Ion Cells

Lithium-ion batteries (LIBs) capable of safe and reliable cycling at a fast-charge rate (i.e., >2C or <30 minutes to full charge) will have a direct impact on today’s consumer technology by improving the utility of portable electronics and reducing the barrier for widespread adoption of electric vehicles. However, at high charge rates, the long-term battery performance suffers because of heterogeneous reactivity across both electrodes (e.g., lithium metal plating on the anode surface, fracture of the cathode particles, etc.) [1]–[3]. A fundamental study of the processes responsible for battery degradation is a necessary step toward designing next-generation LIBs and is a critical research priority for the U.S. Department of Energy. Here, we demonstrate that high charging currents lead to chemical, structural, and morphological changes in the graphite anode that spans the atomic-scale to the bulk-scale. As the integrity of the graphite host is critical to lithium-ion cell performance, our findings regarding the degradation mechanism provide the essential knowledge to enable the development of viable fast-charging LIBs.Our strategies to study the graphite anode degradation are based on advanced analytical electron microscopy and diffraction. We focus on the modifications that occur in the material when subjected to charging rates up to 6C (i.e., 10 minutes to full charge). The characterization is performed post-mortem across different length-scales on as-prepared electrodes and electrodes harvested from cycled cells (represented in Figure 1). At the bulk-scale, we use scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to probe the morphological and chemical changes in cross-sections of the graphite anode samples. At the nano- and atomic-scale, we use advanced transmission electron microscopy (TEM) and diffraction techniques to reveal changes in both the nano-scale chemistry and the graphite microstructure. Key findings from this investigation include the morphological changes to the graphite particles at the micron-scale and the partial-filling of the inter- and intra-particle gaps with solid electrolyte interphase (SEI) compounds at the meso-scale. Further, at the nano- to atomic-scale, we observe greater disorder and amorphous character in the graphite near the internal pore surfaces when compared to that of the bulk graphite regions. The nature of the lattice disorder, and the characterization methods employed to examine this disorder, will be discussed. Additional supporting evidences of graphite disorder and phase change from Raman spectroscopy and X-ray diffraction studies will also be presented. Acknowledgements: SP acknowledges support from the U.S. Department of Energy Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the U. S. Department of Energy under contract number DE‐SC0014664. This work was carried out in part in the Materials Research Laboratory Central Research Facilities, University of Illinois. DA and MTFR acknowledge support from DOE’s Vehicle Technologies Office. This document has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. References : [1] C. Heubner, K. Nikolowski, S. Reuber, M. Schneider, M. Wolter, and A. Michaelis, “Recent Insights into Rate Performance Limitations of Li-ion Batteries,” Batter. Supercaps, Nov. 2020.[2] M.-T. Fonseca Rodrigues et al., “Lithium Acetylide: A Spectroscopic Marker for Lithium Deposition During Fast Charging of Li-Ion Cells,” ACS Appl. Energy Mater., vol. 2, no. 1, pp. 873–881, Jan. 2019.[3] Y. Yang et al., “Quantification of Heterogeneous Degradation in Li-Ion Batteries,” Adv. Energy Mater., vol. 9, no. 25, p. 1900674, Jul. 2019. Figure 1

3D-Printed Testing Plate for the Optimization of High C-Rates Cycling Performance of Lithium-Ion Cells

Nowadays, long charging times have become one of the main limitations to a greater worldwide spread of electric vehicles (EV). Enabling high C-rates charging is a promising approach to eliminate this problem and alleviate range anxiety. When a battery is charged at high currents, several factors have to be taken into account. Temperature is certainly a key parameter because when it is too high this can lead to degradation of components (binder, electrolyte, active material, etc), however, when it is too low intercalation kinetics becomes sluggish. Using 3D-printed testing plates (PP3D plates) with Li-reference electrode, we developed a tool for electrochemical investigations of pouch cells. These plates enabled to build a new well-designed 3-electrode pouch cell. This setup allows the identification of the best high C-rate cycling procedure to improve the performance and cycling life of the lithium ion cells. We explored the electrochemical behavior of NMC811 cathodes and graphite anodes, during high discharge C-rates test up to 7 C and charge C-rates up to 2 C. Moreover, the temperature influence on charging performance and longtime cycling stability is investigated. The cells cycled at 25 °C using optimized procedures reached an 80% state of health after more than 1000 cycles.

Improvement of High Voltage Cycling Performance of Lithium-Ion Cells By Employing a Functional Additive

Lithium-ion batteries (LIBs) are being widely used in many applications such as mobile electronic devices, electric vehicles and energy storage systems because of their high energy density and excellent cycle life. As there is always need for increasing the battery capacity, high voltage operating is essential. However, there are several issues in high voltage operation of LIBs; dissolution of transition metal from the active cathode material and oxidative decomposition of liquid electrolyte. Among the strategies for improving the high-voltage cycling performance, an addition of functional additive is one of the most promising methods. Functional additives can form cathode electrolyte interphase (CEI) on the cathode surface during cycling, which suppress the oxidative electrolyte decomposition and the dissolution of transition metal from cathode. In our study, we investigated effective additives for forming the uniform CEI layer and applied them to the LIB composed of graphite anode and NCM cathode. Electrochemical characterization and performance evaluation were performed to examine how these additives could improve the high-voltage cycling performance of LIBs.

The role of the pH value in water-based pastes on the processing and performance of Ni-rich LiNi0.5Mn0.3Co0.2O2 based positive electrodes

The influence of the preset pH value of the binder solution on aqueous processing of LiNi0.5Mn0.3Co0.2O2 positive electrodes is studied. The processed electrodes are investigated by means of electrochemical charge/discharge cycling, potentiostatic electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy. The results show major impact of the pH value of the binder solution on the cycling performance of lithium ion cells. Low binder solution pH values (here 7.6) lead to faster capacity fading within the first 100 cycles. In comparison, higher binder solution pH values (here 12.5) show similar fading compared to the reference electrodes based on poly(vinylidene difluoride) and N-methyl pyrrolidone as solvent. Positive electrode materials undergo a lithium-proton exchange, when in contact with water or other proton sources. Post-mortem analysis revealed that lower pH values of the binder solution potentially lead to more pronounced lithium-proton exchange. The previously inserted protons are extracted from the active material during electrochemical cycling, potentially initiate decomposition of the conductive salt LiPF6 and hence degrade the cell performance.In combination with LiPF6, inter alia HF might be formed, which then reacts with lithium from LiNi0.5Mn0.3Co0.2O2 or other active and inactive components and precipitate as M-F or other resistive interphases on the LiNi0.5Mn0.3Co0.2O2 surface.

A Review on Temperature-Dependent Electrochemical Properties, Aging, and Performance of Lithium-Ion Cells

Temperature heavily affects the behavior of any energy storage chemistries. In particular, lithium-ion batteries (LIBs) play a significant role in almost all storage application fields, including Electric Vehicles (EVs). Therefore, a full comprehension of the influence of the temperature on the key cell components and their governing equations is mandatory for the effective integration of LIBs into the application. If the battery is exposed to extreme thermal environments or the desired temperature cannot be maintained, the rates of chemical reactions and/or the mobility of the active species may change drastically. The alteration of properties of LIBs with temperature may create at best a performance problem and at worst a safety problem. Despite the presence of many reports on LIBs in the literature, their industrial realization has still been difficult, as the technologies developed in different labs have not been standardized yet. Thus, the field requires a systematic analysis of the effect of temperature on the critical properties of LIBs. In this paper, we report a comprehensive review of the effect of temperature on the properties of LIBs such as performance, cycle life, and safety. In addition, we focus on the alterations in resistances, energy losses, physicochemical properties, and aging mechanism when the temperature of LIBs are not under control.

Investigation of the thermal performance in lithium-ion cells during polyformaldehyde nail penetration

Investigation of the thermal performance in lithium-ion cells during polyformaldehyde nail penetration