NCA Cathode Research Articles

External Short-Circuit Scenarios under Different Mechanical Pressures Applied to Lithium-Ion Cells with Silicon-Dominant Anodes

Abstract The safety behavior of lithium-ion cells using high contents of silicon as new anode active material was barely investigated. This work investigates the short-circuit behavior of self-manufactured single-layered pouch cells using 70%wt microscale silicon and NCA cathodes in a novel dual reference cell setup consisting of a gold wire and a lithium metal reference electrode. Six cells were externally shortened at three different compression levels using a novel developed quasi-isothermal calorimetric shortcircuit test bench. The same current plateaus and transition zones were observed for all pressure settings, as reported in the literature for graphite-containing anodes. In addition, a direct dependency of the short-circuit intensity and the heat generation is measured for the differently compressed cells. This higher short-circuit intensity was quantitatively explained by the decreasing impedance at increased pressure levels. The built-in reference electrodes allow for monitoring of the negative terminal voltage, revealing potentials of up to 3:508 V versus Li+/Li and thus explaining the measured over-discharge in the range of ≈25% SoC. The post-mortem analysis reveals copper deposition on both electrodes and the separator, confirming the electrochemically measured over-discharge. Linear scans and potential trajectories reveal 3.379 V versus Li+/Li as oxidation potential for copper dissolution using copper||lithium-metal coin cells.

Characterization of identical lithium-ion battery electrodes before and after charge/discharge cycles via in-plane large-area polishing

As an effective method to fabricate a large-area cross-sectional sample for lithium-ion battery electrodes, we perform in-plane polishing of LiNi0.8Co0.15Al0.05O2(NCA) cathode samples and obtain a large cross-sectional area with a diameter of 1.5 mm. The polished cross-sections of NCA cathode particles are sufficiently flat to perform the atomic force microscopy (AFM) measurements on each cathode particle. Following AFM-based Kelvin probe force microscopy and scanning spreading resistance microscopy measurements, an identical in-plane polished NCA sample is assembled into a coin cell for the charge and discharge processes. After 90 charge/discharge cycles, the in-plane-polished sample is successfully disassembled from the coin cell without causing critical damage. In addition, a microcrack structure, which is a typical degradation feature of the cycles of NCA particles, is observed for the identical in-plane polished NCA sample. This indicates that the in-plane polishing method is effective for investigating identical NCA electrode samples before and after the charge/discharge process. Furthermore, the in-plane polishing method can be successfully applied to the large-area polishing of a Si-based anode which is a mixture of Si carbon complexes and graphite particles. This study presents a novel methodology for analyzing the degradation of lithium-ion battery electrode materials.

Cycling Aging in Different State of Charge Windows in Lithium-Ion Batteries with Silicon-Dominant Anodes

Reducing the capacity utilization of silicon-containing anodes and choosing the optimal full-cell voltage window improve the lifetime significantly. In this study, we investigate how different voltage windows affect the aging modes with a common 50% cycling depth. First, the cyclic stability, the anode potentials, and the polarization increase are analyzed for the different voltage windows using 70 wt% microscale silicon anodes and NCA cathodes with a lithium metal reference electrode to investigate the electrode-specific characteristics. Further, the underlying aging modes are quantified in the post-mortem analysis. Finally, the anode thickness increase is quantified using a dilatometer setup for different anode lithiations. In contrast to the literature, the highest voltage window is most beneficial for the lifetime since high anode delithiation potentials and high surface increases are avoided. The anode potential at the end-of-discharge, the charge-averaged full-cell potentials, and the resistance increase are a function of the state of health (SoH). The common underlying main aging mechanism is the loss of lithium inventory, followed by the loss of anode active material. In contrast, the loss of cathode active materials only plays a minor role.

In-situ cladding PEDOT:PSS on V-doped NCA cathodes for optimized interface and high electrochemical performance of Li-ion battery

The LiNi0.8Co0.15Al0.05O2 (NCA) nickel-rich layered cathode material is widely used for Li-ion batteries because of its excellent structural stability and high specific capacity. However, the Li/Ni mixing effect and the generation of interfacial secondary reactions in NCA cathode materials reduce the electrochemical properties of Li-ion batteries. Herein, we report a series of vanadium (V)-doped NCA cathode (VNCA) materials with different amounts of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) polymers in-situ coated on the surface using a liquid-phase method. The introduction of PEDOT:PSS coating not only improves the conductivity of NCA cathode materials but also protects the surface of cathode materials from cracking during the cycle. Electrochemical results show that the PEDOT:PSS (2 wt%) coating possesses high capacity retention rate (83.58%) after 200 cycles at 1 C, which is better than that of the sample without coating (66.7%). The PEDOT:PSS (2 wt%) coated cathode materials also display superior rate performance to VNCA at high magnification. This work provides new methods and theoretical guidance for the development of efficient ternary cathode materials for Li-ion batteries.

Intergranular Shielding of Ultrafine-Grained Ni-Rich Layered Cathode for Advanced Lithium-Ion Batteries

To achieve carbon neutrality on a global scale, fuel-powered vehicles are being steadily phased out over environmentally recommended electrified vehicles (EVs) with low greenhouse gas emissions. In a battery, the cathode is among the foremost components, as it predominantly determines the LIB’s performance and price. However, since current fleet of layered oxide NCM and NCA cathodes have a relatively lower Ni content, they can extract only a limited amount of reversible capacity (210 mAh∙g-1), restricting the driving range of EVs. To achieve higher energy densities, many studies have focused on increasing the average fraction of Ni in NCM or NCA cathodes to more than 90%. However, the extraction of large amounts of lithium ions is seriously compromised by the rapid deterioration of both cycle life and thermal safety. Recent studies on X-doped cathodes (X = B, Nb, Ta, Sb, W, and Mo) have offered promising results by engineering their geometric microstructural configurations to suppress intergranular cracking.1,2 This approach has proven its potential to improve the electrochemical cycling performance of Ni-rich NCA, NCM(A), and NM cathodes. However, prolonged exposure of the Ni-enriched (Ni ≥ 95%) cathode to the electrolyte generally results in continuous oxidative decomposition of electrolytes and subsequent cathode structural transformation, rendering the cathode unsuitable for applications requiring long battery life.3 Herein, we propose a highly stabilized Ni-enriched (Ni ≥ 95%) layered cathode by adopting a multi-stage engineering strategy, i.e., the construction of an ultrafine-scaled microstructure and subsequent intergranular shielding of the refined grains. The formation of an F induced protective layer at the intergranular boundaries of the ultrafine grains in Li[Ni0.95Co0.04Mo0.01]O2 (denoted as Mo1-NC96) noticeably improved both the structural and chemical stability of the cathode, with a limited degree of structural degradation and gas evolution. Reference s : [1] U.-H. Kim, G.-T. Park, B.-K. Son, G.W. Nam, J. Liu, L.-Y. Kuo, P. Kaghazchi, C.S. Yoon, Y.-K. Sun, Nat. Energy, 5 (2020) 860-869.[2] G.-T. Park, B. Namkoong, S.-B. Kim, J. Liu, C.S. Yoon, Y.-K. Sun, Nat. Energy, 7 (2022) 946-954.[3] F. Kong, C. Liang, L. Wang, Y. Zheng, S. Perananthan, R.C. Longo, J.P. Ferraris, M. Kim, K. Cho, Adv. Energy Mater., 9 (2019) 1802586.

Influence of Cycling in Different State-of Charge Windows on Lifetime and Electrode Expansion of Microscale Silicon-Dominant Lithium-Ion Batteries

Silicon (Si) is a promising active anode material for next-generation lithium-ion batteries due to its high theoretical electrochemical capacity of 3579 mAh/gSi (Li15Si4) and low costs using microscale Si particles.1,2 However, the wide usage of Si as an active anode material is hindered due to its lower lifetime compared to graphite anodes. The degradation in silicon-containing batteries can be suppressed by partial lithiation strategies,2,3,4 with applications for automotive cells leading to improved lifetime.5 However, the lifetime problem still exists in partially lithiated microscale Si particles with lower volume expansion2,3 with ≈200 cycles for one-third silicon utilization, i.e., 1200 mAh/gSi 2. Moreover, we confirmed in our previous study6 as reported by Wetjen et al.4 and Haufe et al.2 that lower cell discharge cut-off voltages and thus higher silicon delithiation potentials versus Li+/Li led to accerlated aging and should be avoided.Thus, the motivation for this study is to avoid these high anode delithiation potentials by operating the cells in a high full cell state of charge (SoC) and to investigate the influence of different SoC windows on lifetime with laboratory 182.1 ± 0.7 mAh/gNCA Swagelok T-cells comprising a microscale silicon-dominant anode and a NCA cathode. The electrode-specific aging is monitored with the lithium metal reference electrode based on the anode and cathode potentials and pulse tests. To investigate the aging in different SOC regimes, three cycling conditions were chosen in the low (LV), middle (MV) and high voltage (HV) window and compared to cells cycled between 2.8 and 4.2 V as full voltage6. The voltage window of LV, MV and HV were chosen to represent cycling between 0-50%, 25-75%, and 50-100% SOC, respectively. Formation and checkups were the same for all cells with 2.80 V to 4.20 V. After reaching the end-of-life criterion of 55% state of health (SoH), the cells were disassembled and anode and cathodes were re-assembled in half-cells for a post-mortem analysis to reveal loss of lithium inventory (LLI) and loss of active material of the anode LAMAn, and the cathode LAMCat of the respective full-cells. Complementary to the electrochemical aging, dilatometer measurements7 were conducted to quantify the electrode expansion for the different silicon anode SoC windows since particle decoupling is expected to be one of the major aging mechanisms for microscale silicon2, which is expected for high electrode expansions.For the electrochemical results, the lifetime can be drastically increased from ≈230 to ≈560 equivalent full cycles (EFCs) for operating the full cell in the HV compared to the FV window, as shown in Fig. 1a. One EFCs is defined as the total charge throughput for charging and discharging one cycle normalized to the capacity of the initial checkup cycle. Over aging, the full cell degradation correlates very well with the end of discharge potential of the silicon anodes. Moreover, the electrode-specific pulse results show strong anode degradation while the cathode remains intact. The post-mortem results reveal LLI as most dominenat aging mode, which was very similar for all voltage windows. The HV cells showed both the highest LAMNE and LAMPE, whereas LAMNE was more dominant compared to LAMPE. The silicon amorphization was the lowest for the LV anodes and the highest for the HV anodes at the same SoH. The dilatometer results show that the silicon electrode expansion is the lowest for the low lithiation, i.e., LV, and the highest for the highest lithiation, i.e., HV. From the dilatometry results, we conclude that the mechanical electrode stability does not limit lifetime.Our results demonstrate that lifetime can be significantly improved by a factor of ≈2.4 based on the EFCs if operating cells with silicon dominant anodes in high SoCs and that low SoCs should be avoided. Acknowledgments: S. F. gratefully acknowledges the financial support from the BMBF (Federal Ministry of Education and Research, Germany) under the auspices of the ExZellTUM III project (grant number 03XP0255). The authors want to thank our student worker, Maximilian Reichl, for the fabrication of the NCA coatings. We also thank Wacker Chemie AG for kindly providing the microscale silicon material.

Visualizing Reaction Distributions for Materials Validation and Failure Analysis in Li-Ion Batteries

A real-time, high-throughput visualization technique for heterogeneity in lithium-ion battery (LIB) electrodes is necessary to understand battery performance on a mechanistic level. Our group, along with others, has seen that battery performance is governed by short range (<20 um) electron transfer between the active material and carbon binder domain (CBD) within electrodes [1]–[3]. Available imaging techniques for visualizing the electronic connectivity of LIB electrodes are limited to nanoscale, single particle resolutions using sophisticated synchrotron X-ray or electron microscopy [4]–[6]. Optical microscopy offers the correct spatial resolution for visualizing the submicron connection of active particles to CBD, but is limited by colorimetry of electrode materials- with graphite being the exception due to its visible color change during lithiation [7]. There is a rapidly growing body of research interested in studying the ionic diffusion pathways of Li-ion using operando optical microscopy, however none currently exist for studying the submicron electronic connectivity through a facile, operando approach- especially under a industrially applicable lens [8]. To the best of our knowledge, this study presents the first spatially- and time- resolved technique for visualizing the electronic connectivity of commercial LIB electrodes using operando electrochemical fluorescent microscopy (EFM). This technique relies on the principle of electrofluorochromism, which we use to our advantage for a simple electrochemical system involving heterogeneous electron transfer. This allows us to use fluorescence as a real-time tracker for electronic heterogeneity, where electronic ‘dead-zones’ present as non-fluorescent regions in 2D images.Using our technique, we visualize commonly used commercial LIB electrodes (carbon content 1-4%, regimented processing), including NMC (LiNixMnyCo1-x-yO2), LFP (LiFePO4), and LCO (LiCoO2) against formulaically similar in-house made LIB electrodes (< 3.5% carbon content) as a proof of concept. We first validate the efficacy of this technique by testing commercial NMC, with a flaked off piece of active material, to show that areas of electronic discontinuities can in fact be represented by non-fluorescence (Fig.1.) We also find that when compared to commercial electrodes, those which are fabricated in house reveal isolated active particles, agglomerated carbon islands, and dead zones, undiscernible by brightfield imaging (Fig. 2.) Global feature extraction is performed on post-processed images to quantify electrode topology and evaluate electronic connectivity of active particles of battery electrodes, as well as heterogeneous mapping to determine the heterogeneity index of electrodes imaged. Testing our technique on low- and high- performing electrodes from an established library of coin-cell data allows for a straightforward way of correlating performance metrics to heterogeneity features. This quick (<1hr), reproducible visualization technique is general enough to be used to study the electronic connectivity of emerging new battery electrodes, as well as verify commercially available ones. Using this approach to verify LIB electrodes prior to assembly could save months to years of battery testing by being used as an alternative to lengthy full cell testing.[1] S. L. Morelly, N. J. Alvarez, and M. H. Tang, “Short-range contacts govern the performance of industry-relevant battery cathodes,” Journal of Power Sources, vol. 387, pp. 49–56, May 2018, doi: 10.1016/j.jpowsour.2018.03.039.[2] R. M. Saraka, S. L. Morelly, M. H. Tang, and N. J. Alvarez, “Correlating Processing Conditions to Short- and Long-Range Order in Coating and Drying Lithium-Ion Batteries,” ACS Appl. Energy Mater., vol. 3, no. 12, pp. 11681–11689, Dec. 2020, doi: 10.1021/acsaem.0c01305.[3] J. Entwistle, R. Ge, K. Pardikar, R. Smith, and D. Cumming, “Carbon binder domain networks and electrical conductivity in lithium-ion battery electrodes: A critical review,” Renewable and Sustainable Energy Reviews, vol. 166, p. 112624, Sep. 2022, doi: 10.1016/j.rser.2022.112624.[4] S. Li et al., “Mutual modulation between surface chemistry and bulk microstructure within secondary particles of nickel-rich layered oxides,” Nat Commun, vol. 11, no. 1, Art. no. 1, Sep. 2020, doi: 10.1038/s41467-020-18278-y.[5] P.-C. Tsai et al., “Single-particle measurements of electrochemical kinetics in NMC and NCA cathodes for Li-ion batteries,” Energy Environ. Sci., vol. 11, no. 4, pp. 860–871, Apr. 2018, doi: 10.1039/C8EE00001H.[6] A. Singer et al., “Nucleation of dislocations and their dynamics in layered oxide cathode materials during battery charging,” Nat Energy, vol. 3, no. 8, Art. no. 8, Aug. 2018, doi: 10.1038/s41560-018-0184-2.[7] Y. Yamagishi, H. Morita, Y. Nomura, and E. Igaki, “Visualizing Lithiation of Graphite Composite Anodes in All-Solid-State Batteries Using Operando Time-of-Flight Secondary Ion Mass Spectrometry,” J. Phys. Chem. Lett., vol. 12, no. 19, pp. 4623–4627, May 2021, doi: 10.1021/acs.jpclett.1c01089.[8] A. J. Merryweather, C. Schnedermann, Q. Jacquet, C. P. Grey, and A. Rao, “Operando optical tracking of single-particle ion dynamics in batteries,” Nature, vol. 594, no. 7864, Art. no. 7864, Jun. 2021, doi: 10.1038/s41586-021-03584-2. Figure 1

Operando Electrochemical Fluorescent Microscopy to Predict Li-Ion Battery Performance

A real-time, high-throughput visualization technique for heterogeneity in lithium-ion battery (LIB) electrodes is necessary to understand battery performance on a mechanistic level. Our group, along with others, has seen that battery performance is governed by short range (<20 um) electron transfer between the active material and carbon binder domain (CBD) in electrodes [1]–[3]. Available imaging techniques for visualizing the electronic connectivity of LIB electrodes are limited to nanoscale, single particle resolutions using sophisticated synchrotron X-ray or electron microscopy [4]–[6]. Optical microscopy offers the correct spatial resolution for visualizing the submicron connections of active particles to CBD, but is limited by the colorimetry of electrode materials- with graphite being the exception due to its visible color change during lithiation [7]. There is a rapidly growing body of research interested in studying the ionic diffusion pathways of Li-ion using operando optical microscopy, however none currently exist for studying the submicron electronic connectivity using an operando approach- especially under a industrially applicable lens [8]. To the best of our knowledge, this study presents the first spatially- and time- resolved technique for visualizing the electronic connectivity of commercial LIB electrodes using operando electrochemical fluorescent microscopy (EFM). This technique relies on the principle of electrofluorochromism, which we use to our advantage for a simple electrochemical system involving heterogeneous electron transfer. This allows us to use fluorescence as a real-time tracker for electronic heterogeneity, where electronic ‘dead-zones’ present as non-fluorescent regions in 2D images.Using this technique, we visualize commonly used commercial LIB electrodes (carbon content 1-4%, regimented processing), including NMC (LiNixMnyCo1-x-yO2), LFP (LiFePO4), and LCO (LiCoO2) against formulaically similar in-house made LIB electrodes (< 3.5% carbon content) as a proof of concept. We first validate the efficacy of this technique by testing commercial NMC, with a flaked off piece of active material, to show that areas of electronic discontinuities can in fact be represented by non-fluorescence (Fig.1.) We also find that when compared to commercial electrodes, those which are fabricated in house reveal isolated active particles, agglomerated carbon islands, and dead zones, undiscernible by brightfield imaging (Fig. 2.) Global feature extraction is performed on post-processed images to quantify electrode topology and evaluate electronic connectivity of active particles of battery electrodes, as well as heterogeneous mapping to determine the heterogeneity index of electrodes imaged. Testing our technique on low- and high- performing electrodes from an established library of coin-cell data allows for a straightforward way of correlating performance metrics to heterogeneity features. This quick (<1hr), reproducible visualization technique is general enough to be used to study the electronic connectivity of emerging new battery electrodes, as well as verify commercially available ones. Using this approach to verify LIB electrodes prior to assembly could save months to years of battery testing by being used as an alternative to lengthy full cell testing.[1] S. L. Morelly, N. J. Alvarez, and M. H. Tang, “Short-range contacts govern the performance of industry-relevant battery cathodes,” Journal of Power Sources, vol. 387, pp. 49–56, May 2018, doi: 10.1016/j.jpowsour.2018.03.039.[2] R. M. Saraka, S. L. Morelly, M. H. Tang, and N. J. Alvarez, “Correlating Processing Conditions to Short- and Long-Range Order in Coating and Drying Lithium-Ion Batteries,” ACS Appl. Energy Mater., vol. 3, no. 12, pp. 11681–11689, Dec. 2020, doi: 10.1021/acsaem.0c01305.[3] J. Entwistle, R. Ge, K. Pardikar, R. Smith, and D. Cumming, “Carbon binder domain networks and electrical conductivity in lithium-ion battery electrodes: A critical review,” Renewable and Sustainable Energy Reviews, vol. 166, p. 112624, Sep. 2022, doi: 10.1016/j.rser.2022.112624.[4] S. Li et al., “Mutual modulation between surface chemistry and bulk microstructure within secondary particles of nickel-rich layered oxides,” Nat Commun, vol. 11, no. 1, Art. no. 1, Sep. 2020, doi: 10.1038/s41467-020-18278-y.[5] P.-C. Tsai et al., “Single-particle measurements of electrochemical kinetics in NMC and NCA cathodes for Li-ion batteries,” Energy Environ. Sci., vol. 11, no. 4, pp. 860–871, Apr. 2018, doi: 10.1039/C8EE00001H.[6] A. Singer et al., “Nucleation of dislocations and their dynamics in layered oxide cathode materials during battery charging,” Nat Energy, vol. 3, no. 8, Art. no. 8, Aug. 2018, doi: 10.1038/s41560-018-0184-2.[7] Y. Yamagishi, H. Morita, Y. Nomura, and E. Igaki, “Visualizing Lithiation of Graphite Composite Anodes in All-Solid-State Batteries Using Operando Time-of-Flight Secondary Ion Mass Spectrometry,” J. Phys. Chem. Lett., vol. 12, no. 19, pp. 4623–4627, May 2021, doi: 10.1021/acs.jpclett.1c01089.[8] A. J. Merryweather, C. Schnedermann, Q. Jacquet, C. P. Grey, and A. Rao, “Operando optical tracking of single-particle ion dynamics in batteries,” Nature, vol. 594, no. 7864, Art. no. 7864, Jun. 2021, doi: 10.1038/s41586-021-03584-2. Figure 1

Direct NCA Cathode Active Materials Recycling from Spent Li-Ion Batteries: Solvent-Free Recovery and Healing by Heat Treatment

Direct NCA Cathode Active Materials Recycling from Spent Li-Ion Batteries: Solvent-Free Recovery and Healing by Heat Treatment

Estimation of overcharge-induced degradation state in lithium-ion cells using differential thermal voltammetry and distribution of relaxation times

Overcharge is recognized as a significant factor contributing to the degradation and potential thermal runaway of Li-ion cells. In this study, a novel approach is proposed to estimate the extent of overcharge-induced degradation in 18,650-type Li-ion cells with NCA cathodes and graphite anodes. Experimental results reveal abnormal heat generation and capacity loss due to overcharge-induced degradation. Using Differential Thermal Voltammetry (DTV) and Distribution of Relaxation Times (DRT) methods, ten degradation factors (DFs) that reflect the extent of degradation are identified. Through Pearson correlation analysis, the height of peak P1 in DTV and S2 in DRT are identified as the most indictive parameters to estimate degradation. Next, a predictive model based on Kriging deep learning method is developed using these parameters, which enables precise estimation. Validation results for the model demonstrate outstanding predictive accuracy, with a mean absolute percentage error (MAPE) of 3.25 % and a root mean square error (RMPE) of 3.62 %. The proposed methodology not only offers a robust approach to estimate overcharge-induced degradation of Li-ion cells, but also provides valuable insights for enhancing the monitoring and management capabilities of battery system.

Interface chemical reconstruction with residual lithium compounds on nickel-rich cathode by nonstoichiometrical MoO3-x coating enables high stability

The layered lithium nickel-rich cathodes have become one of the most promising candidates for next-generation lithium-ion batteries with high energy density, However, the nickel-rich cathode suffers from a rapid decay of capacity due to their intrinsic instability and undesirably residual lithium compounds originated from LiNiO2 structural changes on the surface, hindering large-scale commercial application. Herein, a continuous and uniform oxygen vacancy enriched-MoO3-x coating was successfully synthesized and reacted residual lithium compounds as a functional layer on the cathode. Such chemically reconstructed coating (Li2MoO4) strategy endows the 1 wt% MoO3-x coated NCA cathode with a fast Li+ ions transport and enhanced structural stability, leading to an outstanding discharge capacity of 214.0 mAh g−1 at 0.1C (1C = 270 mA g−1), a better capacity retention of 80.3 % after 120 cycles at 0.5C, and an excellent high rate capability of 120 mAh g−1 at 5C cycled in voltage range of 2.75 V–4.3 V. This work provides an effective strategy to modulate surface structure towards advanced Ni-rich cathodes for high-performance lithium-ion batteries.

Aluminum-distribution-dependent microstructural evolution of NCA cathodes: Is aluminum homogeneity really favorable?

Despite extensive research, the optimal synthesis method and Al concentration for fabricating high-performance Li[NixCoyAl1−x−y]O2 (NCA) cathodes remain to be established. This study provides an in-depth analysis of NCA cathodes prepared using different synthesis methods and Al fractions. Al overdoping (3 mol%) during coprecipitation generates a homogeneous Al distribution in the cathode active material, whereas supplying excess Al during calcination induces a hierarchical spatial arrangement. Interestingly, different Al distributions and concentrations produce strikingly different cathode microstructures, which greatly affect the electrochemical performance of the cathode. Contrary to the common belief that homogeneous Al doping is critical for optimal cycling performance, the electrochemical performance of the cathode is maximized by grain-boundary-segregated Al ions. The proposed Li[Ni0.925Co0.042Al0.033]O2 cathode demonstrates superior cycling performance, retaining 74.1 % of its initial capacity after 1000 cycles in a full cell despite cycling under severe operating conditions (3 C and 45 °C). These findings redefine the fundamental contribution of the elemental distribution to the engineering of cathode microstructures, thereby providing a viable approach for developing high-performance Ni-rich NCA cathodes for advanced Li-ion batteries.

Effects of Ti4+ doping on electrochemical properties of LiNi0.815Co0.15Al0.035O2 cathode materials

The high nickel ternary cathode materials LiNi0.815Co0.15Al0.035O2 (NCA) have been widely used in Li-ion batteries due to their high energy density, low cost, and little environmental pollution. However, it suffers from rapid capacity degradation and poor charging rate. In this work, Ti4+ doping NCA cathode materials are prepared by the high-temperature solid-state method. The results show that 0.5%Ti-NCA has a lower cationic mixing degree and better cycling performance. The capacity retention rate of 100 cycles is 98.91% and 96.59% at current densities of 0.5 C and 1.0 C, respectively. The CV and EIS test results show that 0.5%Ti-NCA has lower polarization and higher lithium ion diffusion coefficient DLi+(8.43×10−14 cm2/S) after 100 cycles, while Pure-NCA only has 6.92×10−15 cm2/S, which effectively enhances the electrochemical properties of NCA cathode materials.

Identifying the origin of inhomogeneous degradation and irreversible swelling inside cylindrical 21700 high-energy lithium-ion cells

Cylindrical cells are gaining market volume in the production of batteries for electric vehicles among others due to high flexibility with regard to space utilization. However, the internal winding structure can be prone for inhomogeneities regarding current distribution, electrode degradation, and mechanical stress. In this study, 27 cylindrical SDI INR21700 50E cells with a nickel-rich NCA cathode and a Si/C composite anode were subjected to five individual aging procedures. Computed tomography scans were conducted at 100%, 90% and 80% capacity retention to investigate internal swelling and deformation of the jelly roll non-destructively. The cells were disassembled at 80% capacity retention for post-mortem analysis on coin half-cells harvested from different locations of the jelly roll to quantify inhomogeneous aging and electrode swelling.Increased cycle depth and discharge current exacerbated inhomogeneous degradation across the electrode length. In comparison to 860 equivalent full cycles (EFC) at 0.5C and 100% cycle depth, limiting the SoC range between 20% to 80% at 25°C increased cycle life to 4150EFC despite a high discharge current of 2C. Minimizing utilization of the silicon content and avoiding lithium plating, the cathode and the anode retained around 4% and 2% increased capacity at the inner winding area in comparison to the outer area, presumably due to increased mechanical pressure at the inner area. At the same time, the inner area displayed reduced swelling, further suggesting increased mechanical pressure at the inner area. Overall, the irreversible swelling measured 6% to 16% and 8% to 20% for the cathodes and the anodes after disassembly, depending on the operating conditions and the location on the electrode. To prevent non-linear capacity fade and deformation of the jelly roll, the results suggest to restrict utilization of the silicon content and to avoid high charging currents at low temperature.

Effect of Mechanical Pressure on Lifetime, Expansion, and Porosity of Silicon-Dominant Anodes in Laboratory Lithium-Ion Cells

The impact of mechanical pressure on electrode stability in full-cells comprising microscale silicon-dominant anodes and NCA cathodes was investigated. We applied different mechanical pressures using spring-compressed T-cells with metallic lithium reference electrodes enabling us to analyze the electrode-specific characteristics. Our investigation covers a wide pressure range from 0.02 MPa (low pressure - LP) to 2.00 MPa (ultra high pressure - UHP) to determine the optimal pressure for cyclic lifetime and energy density. We introduce an experimental methodology considering single-component compression to adjust the cell setup precisely. We characterize the cells using impedance spectroscopy and age them at C/2. In the post-mortem analysis, cross-sections of the aged anodes are measured with scanning electron microscopy. The images are analyzed with regard to electrochemical milling, thickness gain, and porosity decrease by comparing them to the pristine state. The results indicate that cycling at UHP has a detrimental effect on cycle life, being almost two-fold shorter when compared to cycling at normal pressure (NP, 0.20 MPa). Scanning electron microscopy showed a dependency of the thickness and the porosity of the aged silicon anodes on the applied pressure, with coating thickness increasing and porosity decreasing for all pressure settings, and a correlation between thickness and porosity.

Numerical study on thermal runaway in a cell and battery pack at critical heating conditions with variation in heating powers

The thermal stability of lithium-ion cell is still a major concern in electric vehicle and energy storage applications affecting the cell to its chemistry level. The thermal abuse is the most common type of thermal runaway which is triggered either by excess heat accumulation or localized heating in the battery pack. Analysis of thermal runaway in the perspective of various critical heating positions with temperature distribution, heat generation still lacks. Thus, the present work is focused on this issue. A three-dimensional homogeneous Multi-Scale, Multi-Dimensional model with a finite volume method solver ANSYS FLUENT has been utilised to assess the effect of heating positions, and variation in spacings on thermal runaway for a 18650 cell and battery pack in a detailed way. It is observed that the direction of flow is the typical deciding factor of the thermal runaway spreading pattern in the cell. The negative solvent is responsible for the generation of maximum heat in the thermal runaway of a 18650 cell. The results show that cell heated at the bottom end (10 mm width) is fast prone to thermal runaway, vertical (5 mm width) being slower in disturbing the separator stability. The NCA cathode material has a safety hierarchy that goes as follows with regard to positions: vertical 10 mm > bottom end > bottom 5 mm > centre 10 mm > bottom 10 mm. The effect of spacing on thermal runaway is varying non-uniformly with the location of the heating position in the 3 × 3 battery pack. The highest temperature attained by the 7000 W/m2 heating power battery pack is discovered to be greater than the 10,000 W/m2 by 10 K. With a power increase from 7000 W/m2 to 10,000 W/m2, there is a reduction in time delay of 17 %.

An Analysis of Calendaric Aging over 5 Years of Ni‐Rich 18650‐Cells with Si/C Anodes

AbstractCalendaric lifetime testing of lithium‐ion cells is time‐consuming and resource‐intensive. As Dubarry et al.[1] state, testing is often limited to a few aging conditions. This paper presents the results of a long‐term aging study on lithium‐ion cells with a nickel‐rich NCA cathode and a graphite‐silicon anode. 69 cells were stored at 5 different voltages and under 4 different temperatures for 5 years. Regular reference performance tests (RPT) provide insights for State of Health (SoH) calculation and further analysis through differential voltage analysis. The results are verified against post‐mortem analyses. The long aging period enables accurate determination of aging rates. Our results demonstrate that the storage voltage level strongly influences the degradation rate, with temperature playing a minor role. The identified aging effects include loss of active material on the cathode side and loss of lithium inventory. Initial degradation follows a ‐trajectory but is caused by overhang effects. The long‐term aging is rather linear.

Thickness effect on the mechanical performance of cathodes in lithium-ion batteries

As battery capacity and energy density increase, the safety of batteries deteriorates with a more severe capacity fade. Increasing the electrode thickness is an effective approach to enhance battery capacity and energy density. Currently, research on the influence of electrode thickness on batteries has primarily focused on electrochemical aspects, while there is limited study on the impact of thickness on the mechanical properties of electrodes. In this work, we thoroughly investigated the mechanical behavior of NCA (LiNiaCobAlcO2, a + b + c = 1) cathodes with varying thicknesses through uniaxial tensile tests. Experimental measurements show that as the cathode thickness increases, tensile strength and elastic modulus of the cathode decrease. Cathodes with thin coating exhibit brittle fracture, while cathodes with thick coating display relatively higher toughness prior to fracture. The distribution of cracks and the structure of cathodes varying with thicknesses were studied by scanning electron microscopy. Results show that cathodes with thick coating have wider and deeper cracks. Thinner cathode coatings can withstand larger tensile and shear stresses compared to thicker cathode coatings, thus thicker cathode coatings experience more severe damage. By combining microstructural observation and stress analysis, the mechanism for the degradation of mechanical properties and rapid capacity fade in thick electrodes were revealed. This study provides a reference for the optimal design and safe operation of lithium-ion batteries.

Mechanistic cycle aging model for the open-circuit voltage curve of lithium-ion batteries

Cycling lithium-ion batteries causes capacity fade, but also changes the shape of the open-circuit voltage (OCV) curve, due to loss of active material (LAM) and loss of lithium inventory (LLI). To model this change, we recently proposed a novel empirical calendar aging model that is parameterized on component states of health (SOHs) instead of capacity fade only. In this work, we present a mechanistic aging model for cycle aging, allowing prediction of capacity fade, OCV curve change and component degradation. The model is parameterized on cycling data of 59 commercial lithium-ion batteries with NCA cathode and silicon–graphite anode, which were cycled for 2500 equivalent full cycles under varying conditions. We propose a stepwise approach to identify the most relevant stress parameters causing LLI and LAM, where we also separate between loss of accessible graphite and silicon in the blend anode. Stress parameter dependence is modeled with linear combinations of exponential functions and the model predicts capacity fade with 1.04% mean absolute error (MAE). For all test conditions, LLI is the dominating degradation mode and loss of accessible graphite is negligible. Reconstructed OCV curves reduce the median voltage MAE by a factor of 8, compared to not updating the OCV.

Microstructural Refinement and Surface Modification of Ni-Rich Cathodes for High-Performance Li-Ion Battery

Li[Ni1–x–y–zCoxMnyAlz]O2 (NCMA) cathodes have attracted public attention owing to their improved durability by leveraging the advantages of NCM and NCA cathodes. The combination of Mn and Al in a NCMA cathode effectively stabilizes the host layered structure to increase its resistance to microcracking; consequently, NCMA cathodes outperform both NCM and NCA cathodes with the same Ni contents, in terms of cycle life, without sacrificing energy density. However, as the Ni contents of the cathodes exceed 90%, a simple, compositionally engineered NCMA cathode lacks the chemical and mechanical stability to suppress surface degradation and the development of permanent microcracks due to the high incidence of highly reactive Ni4+ species on its surface.1,2 Considering the limitations of NCMA cathodes, a combination strategy involving microstructural engineering to inhibit microcracking, by enabling the efficient dissipation of local strain,3 and the modification of the exposed cathode surface, to protect it against deleterious electrolyte attack, is expected to afford superior Ni-rich layered cathodes.In this study, we improved the cycling stability of a conventional NCMA cathode with a Ni content of 93% (a NCMA93 cathode) using a combination strategy involving microstructural engineering and surface modification. To this end, we prepared a Sb-doped NCMA93 (denoted as Sb-NCMA93) cathode; Sb was incorporated to refine its microstructure and radially align and elongate its primary particles. Furthermore, we generated a protective F layer on the cathode surface through a chemical reaction between residual lithium compounds and a NH4F coating agent. To comprehensively investigate the synergetic effect of this combination strategy, conventional and Sb-doped NCMA93 cathodes with and without F coatings were synthesized and characterized and their fundamental properties and electrochemical performances compared. Post-mortem analyses were performed to elucidate the origins of the remarkable long-term cycling stability of the optimized cathodes. Reference s : [1] H.-J. Noh, S. Youn, C. S. Yoon, Y.-K. Sun, J. Power Sources, 2013, 233, 121.[2] H.-H. Ryu, K.-J. Park, C. S. Yoon, Y.-K. Sun, Chem. Mater. 2018, 30, 1155.[3] U.-H. Kim, H.-H. Ryu, J.-H. Kim, R. Mücke, P. Kaghazchi, C. S. Yoon, Y.-K. Sun, Adv. Energy Mater. 2019, 9, 1803902.