An insight into the errors and uncertainty of the lithium-ion battery characterisation experiments

Errors and uncertainty within the experimental results have long-term implications in lithium-ion battery research. Experimental directly feed into the development of different battery models, thus having a direct impact on the accuracy of the models, which are commonly employed to forecast short to long term battery performance. The estimations made by such models underpin the design of key functions within the BMS, such as state of charge and state of health estimation. Therefore, erroneous experimental results could evolve into a much larger issue such as the early retirement of a battery pack from the end-use application. For original equipment manufacturers (OEM), such as automotive OEMs this may have a significant impact, e.g. high warranty returns and damage to the brand. Although occasionally reported in published results, currently, little research exists within the literature to systematically define the error and uncertainty of battery experimental results. This article focuses on the fundamental sources of error and uncertainty from experimental setup and procedure and suggests control measures to remove or minimize the contributions from the sources identified. Our research shows that by implementing the control measures proposed, the error and uncertainty can be reduced to around 0.6%, from the figure of around 4.0%

Micro Gas Turbine Range Extender Performance Analysis Using Varying Intake Temperature

A micro gas turbine (MGT) can potentially be an alternative power source to the conventional internal combustion engine as a range extender in hybrid electric vehicles. The integration of the MGT into a hybrid vehicle needs a new approach for technical validation requirements compared to the testing of an internal combustion engine. Several attributes of the MGT are predicted to cause concerns for vehicle sub-system requirements such as high ambient temperature and start-stop behaviour. This paper describes the results from specially developed experimental techniques for testing the MGT in a typical automotive environment. A black box MGT was used in this study for performance investigation during hot and cold starts. The MGT was instrumented and fitted with automotive standard components to replicate typical vehicle operational conditions. The intake air temperature was varied between 10 and 24 °C. A significant reduction in the power output of the MGT was observed as the intake temperature was increased. The proposed case scenario caused a reduction in nitrogen oxide emissions in the range of 0.02−0.04 g/km because of the lower combustion temperature at high intake temperature. However, hydrocarbon and carbon monoxide emissions have not shown a noticeable reduction during the power output degradation. The experimental results have highlighted the potential issues of using the MGT at higher intake temperatures and suggest design change to take the effect of higher engine bay temperature into account

Characterisation of micro turbine generator as a range extender using an automotive drive cycle for series hybrid electric vehicle application

This study investigated a micro turbine generator (MTG) as a range extender for a series hybrid electric vehicle application for a range of constant and dynamic power demand strategies. The power demands were calculated through a mathematical model based on a specific vehicle platform using the New European Drive Cycle (NEDC). The power demands were then used to characterize the MTG in a controlled test environment. Each of the strategies produced interesting results in terms of fuel consumption, specific emissions, net efficiency, and power responses. The experimental results revealed the lowest specific emissions, and fuel consumption while the MTG operated at constant power demand. One of the dynamic power demand strategies also produced low fuel consumption, but with higher specific emissions. Although exhaust emissions in each strategy were well below the Euro 6c limits. These results indicate the potential of MTG as a range extender in a series hybrid vehicle. Even, the MTG can be operated dynamically with relatively low fuel consumption and very low specific emissions, compared to the traditional approach of a constant power demand

Looking Deeper into the Galaxy (Note 7)

Li-ion cell designs, component integrity, and manufacturing processes all have critical influence on the safety of Li-ion batteries. Any internal defective features that induce a short circuit, can trigger a thermal runaway: a cascade of reactions, leading to a device fire. As consumer device manufacturers push aggressively for increased battery energy, instances of field failure are increasingly reported. Notably, Samsung made a press release in 2017 following a total product recall of their Galaxy Note 7 mobile phone, confirming speculation that the events were attributable to the battery and its mode of manufacture. Recent incidences of battery swelling on the new iPhone 8 have been reported in the media, and the techniques and lessons reported herein may have future relevance. Here we look deeper into the key components of one of these cells and confirm evidence of cracking of electrode material in tightly folded areas, combined with a delamination of surface coating on the separator, which itself is an unusually thin monolayer. We report microstructural information about the electrodes, battery welding attributes, and thermal mapping of the battery whilst operational. The findings present a deeper insight into the battery’s component microstructures than previously disseminated. This points to the most probable combination of events and highlights the impact of design features, whilst providing structural considerations most likely to have led to the reported incidences relating to this phone

Analysis of internal temperature variations of lithium-ion batteries during fast charging

One of the major challenges that limits the fast charging of Lithium-ion batteries is Lithium (Li) plating at low temperatures. To reduce Li-plating an increased environmental temperature is commonly used. However, the uncertainties in the measurement of key battery internal states such as temperature, is a limiting factor to find the best fast charging profile that considers battery performance, degradation, and safety of the electric vehicles (EVs). We have used our state-of-the-art instrumented cells equipped with internal data acquisition and microcontroller, forming smart cells, that enable sensor data to be transmitted via a USB to a data logger. We demonstrate here that commercially available 21700 format cells were successfully instrumented and gave direct information on internal temperature for continuous fast charging rates from C/2 to 2.5C. The internal temperature was found to be considerably higher than that of the surface of the cell (between 10 and 14°C at 2.5C charge rate). A gradient of up to 2°C was found between the positive and negative end of each cell that became more prominent for higher charge rates. Li-plating was detected for all C-rates below 25°C even though, the internal temperature rose above 30°C when the cells were charged at 2.5C with an ambient temperature of 0°C. At a higher ambient temperature of 40°C, the cell’s internal temperature rose (to ~62°C) beyond the safe limits defined by the manufacturer’s datasheet whilst the external temperature recorded (~52°C) was within the manufacturer’s defined safe operating limits

Experiences with the Technical Accreditation Scheme (TAS) 'teaching the trainee'

There is a gap in hybrid vehicle, automotive electrical / electronic and embedded systems expertise in the UK. There is a demand for new and different skills than those traditionally associated with the automotive industry. Traditional models of taught undergraduate programmes with relatively narrow disciplines are deficient as the automotive industry’s need is at the boundaries and overlap of traditional disciplines. Recently-qualified engineering graduates need additional specialist training to make a significant input in such areas. Until recently, addressing this gap remained a significant challenge to automotive companies in the UK. The Technical Accreditation Scheme (TAS) launched in 2010 by Jaguar Land Rover (JLR) in partnership with leading UK Universities provides the platform to deliver high impact, relevant, specialised, state-of-the-art solutions to bridge this gap. Success lies in the integration of personal experience and knowledge of Subject Matter Experts (SMEs) with relevant theory ensuring both academic outcomes and real-world needs for usable skills are addressed. This is done with the backdrop of a number of challenges ranging from the experience and background of cohorts, understanding the level of pre-requisite learning required and balancing the teaching versus training paradigm. Nevertheless, there has been universal positive feedback from participants and sponsors for the TAS modules delivered by WMG at the University of Warwick. The success of the scheme has led to it being opened up to the UK manufacturing and engineering supply chain employers through the Advanced Skills Accreditation Scheme (ASAS). In addition, make a significant long term impact means providing access to non-traditional disciplines earlier through schools and colleges. The WMG Academy for Young Engineers at the University of Warwick will achieve this through a new state-of-the-art school providing young people interested in engineering access to realising their ambitions

A framework for health monitoring of automotive electrical and electronic control systems (poster)

The automotive industry has seen enormous growth in the size and complexity of electrical and electronic system architectures. As complexity increases the problem of diagnosing faults in a vehicle's electrical and electronic systems is becoming increasingly difficult. Many faults are as a result of system-level disturbances or interactions that are difficult to interpret and diagnose using existing component-level diagnostics which have been traditionally focused on mechanical system diagnostics. The problem of rising complexity is exacerbated by increasing in-service warranty periods with some automotive OEMs now offering 5 or 7 year, or even life-time warranties. This paper discusses the need for a new system-level approach to the management of faults in a vehicle's networked electronic systems and how this might be achieved by using the data that flows over a vehicle's data networks. This paper compares different industry approaches to system-level health monitoring of complex distributed computing environments and presents a proposal for the application of health monitoring to an automotive electrical and electronic architecture. © 2011 IEEE

Thermal runaway suppression capability of state-of-the-art coolant fluids for lithium-ion battery applications

With the increasing market uptake of hybrid/electric vehicles, along with growing electrification of transportation, battery safety is under worldwide scrutiny. Lithium-ion chemistries have become popular amongst battery manufacturers due to their superior performance and lifetime compared to lead-acid/nickel-metal-hydride based chemistries. However, due to the nature of the materials and their potential exothermic reactions, lithium-ion cells possess a high risk of thermal runaway related hazards. In this study we aim to investigate how aftermath of a thermal runway can be suppressed by employing coolant fluid. Experiments were conducted to investigate the viability of various coolant fluids as thermal runaway suppressants under external heating abuse conditions; on lithium-ion cells. The test apparatus (see attached image file – figure 1) was half filled with a coolant fluid and a 21700-type cylindrical cell at 100% state of charge (SOC), held vertically, such that half the cell was submerged. An external heating setup was employed via nichrome based special heating elements on the non-submerged half of the cell. The cell was heated with a known power value. Two types of cooling fluid were trialled using identical test set-ups, and 9 experiments were conducted in the following categories: 3 control (no fluid), 3 boiling fluid (having low boiling point in range of 70 to 80 °C) and 3 dielectric oil. There were 3 thermocouples attached to the surface of the cell (1 closer to the positive tab, 1 near the geometric centre, 1 closer to the negative tab). Another 3 K-type thermocouples with range till 1300 °C and accuracy of ±2 °C were employed to measure cell surrounding temperature, i.e. on the pressure cap present on the positive side of the cell, in the coolant fluid and another thermocouple in the air on the likely cell venting path. In the control experiments, the cells initially became internally short-circuited, then, their current interrupt devices (CIDs) were triggered and the cells eventually went into thermal runaway (see attached image file – figure 2). Temperatures in the order of 1100 °C were recorded. In the boiling fluid experiments, there was an order of magnitude increase in the duration to internal short-circuiting compared to no fluid (order of 1000 seconds compared to 100 seconds for control test cases) and the CID of every cell was partially triggered (see attached image file – figure 3). Some of the cells did not undergo thermal runaway. In those cases, temperatures up to 187.7 °C was observed. However, 1 cell went into full thermal runaway with the CID being fully triggered (temperatures up to 394.3 °C was observed). Throughout all the boiling fluid tests, the volume of fluid reduced continually. This might be detrimental to the usability of the fluid as a thermal runaway suppressant in case of longer duration experiments. In the dielectric oil experiments, the time to internal short-circuiting was similar to the boiling fluid and the CID was not triggered on any of the cells. No cells underwent thermal runaway and maximum cell surface temperatures were in the region of 160 °C. Throughout all the dielectric oil experiments, the volume of fluid remained constant. It was observed that both the boiling fluid and dielectric oil have strong potential as thermal runaway suppressants, with the dielectric oil completely preventing thermal runaway in any of the tested cells. This is despite the cell only being half submerged in fluid. A cooling/safety system centred on these types of fluids could manifest, perhaps as permanently submerged battery packs, for hybrid/EV automotive, aerospace and rail applications. One potential drawback for the deployment of fully submerged systems is the additional weight required. This could be mitigated in a number of ways, one being the integration of suppressant fluids into current cooling systems. It should be also noted that the time taken to internal short circuit was longer for the cases where boiling fluid was employed compared to where dielectric oil. However, in one of the cases, where boiling fluid was employed, the cell went into full thermal runaway. This could be due to the low boiling point and high volatility of the boiling fluid which makes it unreliable in an open system. In further work, cells connected in serial strings will be considered under further thermal safety scenarios. Along with Fourier-Transform Infrared Spectroscopy (FTIR) based gas analysis to investigate the effect of various failure modes such as nail penetration, overcharge, external heating on the gas generation at different SOCs and heating rates in submerged environment