The integration of proton exchange membrane fuel cells (PEMFCs) in heavy-duty vehicles and other demanding applications, such as aviation, would be simplified if the stacks could operate above 100 °C instead of the traditional low temperature (LT, up to 80 °C), thereby allowing a reduction in cooling system in size and power. This review offers a comprehensive compilation of experimental studies reported in the literature on PEMFCs operated in the intermediate temperature (IT)-range, here defined as above 80 °C and up to 120 °C, which represented the targeted upper temperature for PEMFCs. Membranes, electrodes and gas diffusion layers for IT-PEMFCs are discussed. Particular attention is paid to polymers in membranes and catalyst layer ionomers. Results from current state-of-the-art perfluorosulfonic acids and alternatives, including hydrocarbon polymers, are evaluated considering their properties and limitations. Further, system benefits and drawbacks of IT- compared to the traditional LT-operation are discussed, such as the interplay between vapour and oxygen pressure, hydrogen crossover and water management. We report on the lack of consistency between ex-situ and in-situ studies and underline the importance of in-situ tests, proposing guidelines to evaluate novel materials. For IT-operation, the development of stable polymers, which are the weakest components of the PEMFCs, is the most urgent challenge. As degradation happens faster at higher temperatures, further long-term tests are needed above 80 °C and accelerated stress tests should be specifically designed for IT-operation according to the polymer chemistries. We conclude that, compared to LT-, IT-operation requires improved materials and additional research.

Conditions such as the temperature and pressure experienced by lithium-ion battery components are dependent oncell geometry and can vary widely within a large cell. The resulting uneven degradation is challenging to study at thefull cell level but can be revealed upon disassembly and post mortem analysis. In this work, we report localizedlithium plating in automotive-grade, prismatic lithium-ion cells, also under cycling conditions generally consideredto be mild (e.g., 5–65 %SOC, 23 ◦C, 0.5C cycle rate). Dead lithium content is quantified using 7Li nuclear magneticresonance spectroscopy in both electrode and separator samples, corresponding to substantial capacity fade(26–46%) of the full cells. Severe lithium plating is typically initiated in regions near the positive tab, in which boththe separators and negative electrodes are ultimately deactivated. High pressure arises during cycling, and wepropose a deactivation mechanism based on high local stress due to electrode expansion and external constraint.Further, we develop a model to demonstrate that component deactivation can result in lithium plating even undermild cycling conditions. Notably, components harvested from regions with no detected lithium plating maintainedadequate electrochemical performance.

During the last decade, the market interest for electrified vehicles has increased considerably alongside global climate initiatives. This has coincided with vast improvements in automotive-grade, lithium-ion battery performance. This has increased the range of battery electric vehicles and plug-in hybrids, but lifetime remains a challenge. Aging during fast charging is especially difficult to understand due to its nonlinear dependence on charge rate, state-of-charge, and temperature. We present results from fast charging of several energy-optimized, prismatic lithium-ion battery cell generations with a nickel manganese cobalt (NMC)/graphite chemistry through comparison of capacity retention, resistance, and dQ/dV analysis. Changes in cell design have increased energy density by almost 50% over six years of cell development and acceptable cycle life can be expected, even under fast charging, when restricting the usage of the available capacity. Even though this approach reduces the useable energy density of a battery system, this tradeoff could still be acceptable for vehicle applications where conventional overnight charging is not possible. The tested cell format has been used for a decade in electrified vehicles. The ongoing development and improvement of this cell format by several cell manufacturers suggests that it will continue to be a good choice for future vehicles.

An important step toward safer and more reliable lithium-ion battery systems is the improvement of methods for detection and characterization of battery degradation. In this work, we develop and track aging indicators over the life of 18650-format lithium-ion batteries with a blended NMC532-LMO positive electrode and graphite negative electrode. Cells are cycled until reaching 80% of their original capacity under combinations of four cycling conditions: ambient and sub-ambient temperatures (29 degrees C and 10 degrees C) and fast and mild rates (2.7 and 1.0C). Loss of lithium inventory dominates aging for all cases, with additional loss of NMC capacity under the combination of sub-ambient temperature and mild rate. A novel, easily acquired polarization factor complements capacity fade analysis; it correlates well with impedance and galvanostatic cycle life and indicates changes in active aging processes. These processes are further revealed by differential voltage analysis (DVA) and incremental capacity analysis (ICA). New indicators and aging scenarios are evaluated for these techniques and supported by post mortem analysis. From in operando cycling data and a single, slow discharge curve, these four methods (capacity fade, polarization factor, DVA, and ICA) comprise a simple, explanatory, and non-invasive toolbox for evaluating aging in lithium-ion battery systems.

Operating commercial LiNi_xCo_yMn_{1–x –y}O₂(NMCs)/ graphite cells at a higher voltage cut-off would deliver a higher energy density. This protocol has been broadly investigated in the literature, and connected with the occurrence of a rapid and severe degradation. In particular, these studies point to a de-coupling between capacity fade (mostly located on graphite) and impedance rise (mostly located on NMC). However, in the present work we unveil a non-negligible contribution of NMC111 to the total capacity fade, not reported in other studies. This unexpected feature is addressed by means of an experimental and modelling approach apt to unveil the causes behind it, and to quantify the relative impact of different, concurrent ageing mechanisms. For this purpose, a physics-based model including different ageing modes is proposed, and cross-validated on Direct and Alternate Current measurements. The fitting reveals that the capacity loss on NMC111 is in fact coupled to its characteristic impedance rise, and the parameters thus extracted are further validated by means of surface and bulk analytical techniques. In this way, the physical validity of these parameters is confirmed, and they can thus be used for lifetime prediction of NMC/graphite cells operated at high voltage. In addition, we investigate how the occurrence of a non-negligible capacity loss on NMC111 impacts the uneven stoichiometric drift occurring in the jelly roll of commercial cells, while demonstrating how lab-scale cells can still be used for representing the behaviour of commercial devices. It is revealed how high temperatures and localized Li plating can potentially push NMC111 above the chosen upper voltage cut-off, with a consequent increase in the degradation rate at cell-level.

With the vehicle industry poised to take the step into the era of electric vehicles, concerns have been raised that AC harmonics arising from switching of power electronics and harmonics in electric machinery may damage the battery. In light of this, we have studied the effect of several different frequencies on the aging of 28 Ah commercial NMC/graphite prismatic lithium-ion battery cells. The tested frequencies are 1 Hz, 100 Hz, and 1 kHz, all with a peak amplitude of 21 A. Both the effect on cycled cells and calendar aged cells is tested. The cycled cells are cycled at a rate of 1C:1C, i.e., 28 A during both charging and discharging, with the exception of a period of constant voltage at the end of every charge. After running for one year, the cycled cells have completed approximately 2000 cycles. The cells are characterized periodically to follow how their capacities and power capabilities evolve. After completion of the test about 80% of the initial capacity remained and no increase in resistance was observed. No negative effect on either capacity fade or power fade is observed in this study, and no difference in aging mechanism is detected when using non-invasive electrochemical methods of post mortem investigation.

The reactions in energy-optimized 25 Ah prismatic NMC/graphite lithium-ion cell, as a function of fast charging (1C-4C), are more complex than earlier described. There are no clear charging rate dependent trends but rather different mechanisms dominating at the different charging rates. Ageing processes are faster at 3 and 4C charging. Cycling with 3C-charging results in accelerated lithium plating but the 4C-charging results in extensive gas evolution that contribute significantly to the large cell impedance rise. Graphite exfoliation and accelerated lithium inventory loss point to the graphite electrode as the source of the gas evolution. The results are based on careful post-mortem analyses of electrodes using: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). SEM results show particle cracking independent of the charging rate used for the cycling. XPS and EIS generally indicate thicker surface film and larger impedance, respectively, towards the edge of the jellyrolls. For the intended application of a battery electric inner-city bus using this type of cell, charging rates of 3C and above are not feasible, considering battery lifetime. However, charging rates of 2C and below are too slow from the point of view of practical charging time.

In the majority of applications using lithium-ion batteries, batteries are exposed to some harmonic content apart from the main charging/discharging current. The understanding of the effects that alternating currents have on batteries requires specific characterization methods and accurate measurement equipment. The lack of commercial battery testers with high alternating current capability simultaneously to the ability of operating at frequencies above 200 Hz, led to the design of the presented experimental setup. Additionally, the experimental setup expands the state-of-the-art of lithium-ion batteries testers by incorporating relevant lithium-ion battery cell characterization routines, namely hybrid pulse power current, incremental capacity analysis and galvanic intermittent titration technique. In this paper the hardware and the measurement capabilities of the experimental setup are presented. Moreover, the measurements errors due to the setup’s instruments were analysed to ensure lithium-ion batteries cell characterization quality. Finally, this paper presents preliminary results of capacity fade tests where 28 Ah cells were cycled with and without the injection of 21 A alternating at 1 kHz. Up to 300 cycles, no significant fade in cell capacity may be measured, meaning that alternating currents may not be as harmful for lithium-ion batteries as considered so far.

Sinusoidal ripple-current charging has previously been reported to increase both charging efficiency and energy efficiency and decrease charging time when used to charge lithium-ion battery cells. In this paper, we show that no such effect exists in lithium-ion battery cells, based on an experimental study of large-size prismatic cells. Additionally, we use a physics-based model to show that no such effect should exist, based on the underlying electrochemical principles.

This paper describes an experimental setup for investigating the effects of current ripple on lithium-ion battery cells. The experimental setup is designed so that twelve li-ion cells can be simultaneously tested in a controlled environment. The experimental setup allows for a wide range of current ripple in terms of frequency and amplitude. Additionally, the quantification of the current ripple effects such as the aging of li-ion cells implies that a precise measurement system has to be designed which also are discussed in the paper.