月份：2019年11月

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• The coupled model is then rearranged in the state-space form, and the states SOC, Rc, Ts, and Ti are estimated in real-time using an extended Kalman filter .
• Although this does not include an estimation algorithm, it directly calculates the temperature based on online EIS and surface temperature measurements with a maximum error of 0.9°C.

The estimation errors for the internal temperature of cells have a maximum value of 0.6 K at a 3 m/s air velocity, and 0.8 K at a 0.1 m/s air velocity (Ma et al., 2020). However, as the CFD simulation results are considered as the measurements for the estimator, the generated noise may not represent the real conditions, which could increase the estimation error compared to the reported values for real measurements. Where Cp3 is the heat capacity of the air, ṁa is the mass flow rate of air between the cells, Cpa is the specific heat capacity of air, and i is the cell number in a row. Ti, Ts and Ta were taken as the states, the resistive heat and the air temperature of the previous cell (Ta, i-1) were inputs in the linear system, while the Ts was the measurement. From the tests on a single cell, a second order polynomial was fitted for the internal resistance of the cell, using the average temperature of Ts and Ti. For the rest of the parameters, off-line parameterization with recursive least squares was conducted for a single cell.

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Generally, hard sensors are the most accurate; however, proper sealing methods are needed for embedding, and good insulation and protective layers are needed for the durability and reliability of the sensor. Typical soft sensors are non-destructive, flexible, low-cost, and low-power; however, proper parameterization and accurate additional measurements such as surface temperature, current, voltage are needed for the accuracy of the sensor. Both types of sensors need rapid advancements to cater to the future BMS requirements as well as future smart battery requirements. Typical contactless sensors that are used in LIBs are electrochemical impedance spectroscopy , Johnson noise thermometry , thermal imaging and liquid crystal thermography. EIS and JNT are used for internal temperature measurements, while thermal imaging and liquid crystal thermography are mostly used for surface temperature distribution measurement or hot spot detection (Khan et al., 2017; Raijmakers et al., 2019). Another main benefit is that additional information on various parameters that are useful for SOC estimation, can be obtained from the estimators apart from the temperatures.

• This again leads to further problems like combustion of the organic electrolyte if oxygen is available from the delithiated positive electrode.
• The estimation results follow the actual values in general, except with the HEV-III test results where the temperature was considerably underestimated.
• The absolute measuring error of JNT temperature and the reference measurements for two different tests were within the range of −1.42 and 1.76°C and −1.37 and 1.83°C.
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• Ti, Ts and Ta were taken as the states, the resistive heat and the air temperature of the previous cell (Ta, i-1) were inputs in the linear system, while the Ts was the measurement.

A common estimation algorithm can be represented for state x as shown in Eq. Here, xkm, ykm and yk represent the model value of the state, the model value of measurements and the actual measurements, respectively at time k. Estimators that use physics-based mathematical models are discussed here which are mainly categorized in to local bulk temperature estimation and distributed temperature estimation. Sealing configurations of a cylindrical cell with an embedded thermo-electrochemical sensor (McTurk et al., 2018; Panel 2, p. 311).

Future Trends in Thermal Sensing in Batteries

Similarly, Parekh et al. have developed internal sensors using RTD sensors and placed them inside an LCO CR2032 coin cell. A Pt-1000 sensor of 4 × 5 mm was placed in a 3D-printed spacer composed of polylactic acid and the assembly was placed behind the current collector of the anode. The temperature measurements ranged between 24 and 38°C, while the maximum temperature difference between internal and surface temperatures was 8.8°C.

The soft sensors include estimators/observers that use surface measurements and various models to estimate the internal temperature. More focus is given to the soft sensors due to the lack of an existing, in-depth review of these. These methods are analyzed in detail with their accuracy, implementation, measurement frequency, and the common challenges and benefits are discussed.

2 Hybrid Model-Based Estimators

This adds an advantage towards models using the entropy change over the cell as the maximum temperature as well as internal temperature gradients are underestimated. The estimation results, temperatures, internal resistance against the actual values. Internal temperature is denoted as Tcell, surface temperature is denoted as Tsens and the casing temperature is denoted as Tcas. vpn for iphone and android devices EIS is commonly used in kinetic and transport property extraction in electrode materials, in aging, modeling and SOC/SOH estimation studies (Waag et al., 2013; Xie et al., 2014; Westerhoff et al., 2016; Zhou and Huang, 2020; Babaeiyazdi et al., 2021). Further, EIS is also used as an internal temperature inference method by relating impedance parameters to the temperature.

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher. Ep 3 – In one scene, several of the privateer crew are situated in the lower left of the shot and up a staircase positioned along the left and upper centre part of the shot. In the lower center and right part of the shot is the MZ “blaster”, the one covered with foil. Watch this lower area for a mike on a boom, intruding a long way into the picture, trying to catch the voices of people on the staircase. Ep 1,3 – On several occasions, dirt is visible on the floor of the white void set .

However, some of these can be avoided by using them together with physics-based methods as shown from the above examples. 7, the following expression can be obtained for the heat added to the system. Another challenge is when a sensor is inserted into the cell, the sensors can be damaged due to the harsh environment inside the cell. Figure 5B shows a microscopic picture of a damaged thermistor sensor that has been exposed to the electrolyte within the cell, where the damage to the tracks has broken the connectivity and stopped the data collection. Reprinted from (Wang et al., 2016), Copyright with permission from Elsevier.

The tests were carried out at an ambient temperature of 26°C, where the temperature difference of the measured inside and surface temperatures are in the range of 0–0.08°C under various C rates. Richardson and Howey used the same model, estimation, and the method with EIS measurement system and compared with the Ts measurement system. Therefore their model has an additional impedance measurement, which is expressed as a function of the states and the air temperature Ta. Then in the state-space model, both the measurements; the impedance and Ts, are taken as the measurement equation, one at a time.

Online Internal Temperature Sensors in Lithium-Ion Batteries: State-of-the-Art and Future Trends

The results are similar to the results of Kim et al. , where the EKF with impedance measurement overestimated the Ti and underestimated the Ts by approximately 2°C, when the heat transfer coefficient was twice the true value. The DEKF estimation had RMSE values of 0.47 and 0.42°C after the error convergence, for Ti and Ts, respectively. However, the error convergence took a longer time to come to zero from the high mismatch that was introduced initially. Further, the convergence of the DKF is comparatively quicker than with the DEKF. Both the studies show again that the parameter identification is crucial for the estimation, and the parallel estimation of critical parameters together with the maximum temperature provides better estimations even with a simplified lumped thermal model. One major benefit of embedded sensors is that they can give high-fidelity and reliable benchmark values for internal temperatures, especially for thermal model validations and thermal model-based SOC, SOH estimations (Wei et al., 2021).

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• Furthermore, it is stated that the trained model has not considered any battery aging problems.
• This method has been used to measure the surface temperature, and although the measurement error is up to 3°C, it has a good future potential for estimating internal temperature.
• As the estimation accuracy highly depends on the parameters, especially the internal resistance of the cell, parameterization tests need to be done for all possible scenarios to be sufficiently representative.
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Predictions of Ti based on the two cases showed that the auto-regressive process has low prediction error than the white noise model, where the RMSE is ±0.18°C and ±0.3°C, respectively (for ± 3σ level of standard error). This study shows that when the Ts sensor provides inaccurate data, the discharge current measurement with auro-regressive modeling can improve the Ti predictions using this stochastic model. Although this can be used for predictions, it is not practical to use this as an online application for a shorter sampling time , due to the high number of Monte-Carlo simulations that are needed to be run within the sampling time. A similar 2-D model was developed by Hu et al. for a pouch cell for estimation and control. Here, the 2-D transient heat conduction equation was written in Cartesian coordinates for width and length directions of the pouch cell, and then transformed in to unit spectral domain such that the orthogonal functions can be easily approximated.

Furthermore, the soft sensors are easy to add into other estimators in the BMS, such as SOC and SOH estimations. Also, the estimators can be easily re-arranged to work with various BMS control structures, whether it is inbuilt with estimators or not. This is beneficial in smart monitoring and control systems, such as the control of self-heating in cells or control of the cooling system in BMS, where the soft sensor can minimize the time delay due to sensor data transfer by hard sensors. Where ri and ro the radius of the center core, and the outer surface, respectively. This expression is then used with the measured admittance of the cell to get an expression for the maximum temperature of the distribution, which is at the core and interpreted as the internal cell temperature . Although this does not include an estimation algorithm, it directly calculates the temperature based on online EIS and surface temperature measurements with a maximum error of 0.9°C.

The SEI on the carbon anode starts decomposing exothermically when the temperature rises above 85°C. Due to the incomplete SEI, the negative electrode material starts reacting exothermically with the solvent at temperatures near 100–110°C. Some of the released heat might lead to evaporation of the electrolyte and melting of the separator (130–190°C).

Another option is to use a hard sensor to lift this burden by directly measuring the temperature and communicating with the smart sensor. Thin-film thermocouples and thermistors, portable EIS or FBG sensors are good candidates for this. However, the sensors must be well-developed to have frequent real-time measurements, communication, and durability conditions. Another good candidate is the micro-structured optical fibers, also known as photonic crystal fibers. These are optical fibers that obtain total internal reflection by manipulating the waveguide structure, unlike FBGs that rely on the change in refractive index of the bragg gratings.

Once the locations were found, the temperature estimations were carried out. The KF was started with large initial errors (10°C) but quickly converged to zero within about 15 s. The estimation error of the KF is stated as 0.1°C and the time duration for the estimation is mentioned as less than 2 s. A Karhunen-Loeve transformation method is used to approximate the model during the model order reduction to get a set of ODEs. Two different analytical expressions were developed as solutions to these ODEs for known cooling conditions, and unknown cooling conditions, where the h is adapted.