Open Access
ARTICLE
Abnormal State Detection in Lithium-ion Battery Using Dynamic Frequency Memory and Correlation Attention LSTM Autoencoder
Department of Computer Engineering, Chonnam National University, Yeosu, 59626, South Korea
* Corresponding Author: Chang Gyoon Lim. Email:
(This article belongs to the Special Issue: Emerging Artificial Intelligence Technologies and Applications)
Computer Modeling in Engineering & Sciences 2024, 140(2), 1757-1781. https://doi.org/10.32604/cmes.2024.049208
Received 30 December 2023; Accepted 27 February 2024; Issue published 20 May 2024
Abstract
This paper addresses the challenge of identifying abnormal states in Lithium-ion Battery (LiB) time series data. As the energy sector increasingly focuses on integrating distributed energy resources, Virtual Power Plants (VPP) have become a vital new framework for energy management. LiBs are key in this context, owing to their high-efficiency energy storage capabilities essential for VPP operations. However, LiBs are prone to various abnormal states like overcharging, over-discharging, and internal short circuits, which impede power transmission efficiency. Traditional methods for detecting such abnormalities in LiB are too broad and lack precision for the dynamic and irregular nature of LiB data. In response, we introduce an innovative method: a Long Short-Term Memory (LSTM) autoencoder based on Dynamic Frequency Memory and Correlation Attention (DFMCA-LSTM-AE). This unsupervised, end-to-end approach is specifically designed for dynamically monitoring abnormal states in LiB data. The method starts with a Dynamic Frequency Fourier Transform module, which dynamically captures the frequency characteristics of time series data across three scales, incorporating a memory mechanism to reduce overgeneralization of abnormal frequencies. This is followed by integrating LSTM into both the encoder and decoder, enabling the model to effectively encode and decode the temporal relationships in the time series. Empirical tests on a real-world LiB dataset demonstrate that DFMCA-LSTM-AE outperforms existing models, achieving an average Area Under the Curve (AUC) of 90.73% and an F1 score of 83.83%. These results mark significant improvements over existing models, ranging from 2.4%–45.3% for AUC and 1.6%–28.9% for F1 score, showcasing the model’s enhanced accuracy and reliability in detecting abnormal states in LiB data.Keywords
Nomenclature
Set of real numbers | |
All Data | |
Single data point | |
Number of dataset cycles | |
Feature number | |
Time series length | |
Exponents | |
Input data for single cycle | |
Number of heads of attention mechanisms | |
Weight | |
Number of input channels | |
Number of output channels | |
Number of convolution kernels | |
Sequence length at a specific step size and padding | |
Memory module | |
Number of memory items | |
Number of moves | |
Head averaging output | |
Q | Query matrix |
K | Key matrix |
V | Value matrix |
Forget gate | |
Input gate | |
Candidate valzue | |
Cell state | |
Output gate | |
Hidden state | |
b | Bias |
Encoder | |
Decoder | |
Potential representation | |
Loss function | |
First branch road of DFTM | |
Second branch road of DFTM | |
Third branch road of DFTM | |
Dimension of the hidden state | |
The i-th maximal time index | |
Hadamard product |
As the electrical systems become increasingly intricate and distributed energy sees broader implementation, Virtual Power Plants (VPP) have been developed. These plants consolidate multiple energy resources, including wind and solar, facilitating centralized control and management. In this context, Lithium-ion batteries (LiBs), with their superior efficiency and energy density, have become an essential component within VPPs. These batteries provide important energy buffering and modulation capabilities for VPPs. For instance, V2G (Vehicle-to-Grid) technology enables electric vehicles (EVs) to act as distributed energy storage devices, selling electricity back to the grid during peak usage times, thereby ensuring the stable operation of the power system. Compared to traditional fossil fuel power generation, EVs cause less pollution in terms of emissions. In addition, Battery Replacement Stations can provide quick battery replacement for EVs. These stations allow EV owners to replace a depleted battery with a fully charged one in minutes, significantly reducing the time spent waiting for a recharge. However, during the use of LiBs in EVs, various abnormal states, such as overcharging, over-discharging, and internal short-circuiting, may occur. These abnormal states not only affect battery performance and lifetime, but also reduce the transmission efficiency of EVs when delivering power to the grid, thus posing a threat to the stability of the VPP system. Therefore, it is essential to accurately and timely detect the abnormal state of LiB [1,2].
The parameters in the charging and discharging process of LiBs are primarily obtained by measuring the battery’s voltage, current, and temperature. LiBs used in EVs come in various structures, including cylindrical, prismatic, and pouch types. The diversity in LiB structures demands greater adaptability in traditional fault detection methods, as performance characteristics and management requirements vary significantly across different applications [3]. In addition, one of the critical challenges in LiB management is to address inhomogeneities within individual cells and variations between cells. These inconsistencies may originate from the manufacturing process and charging and discharging cycles. For example, during the manufacturing process, a cell with a slightly thicker cathode coating may have a higher capacity but also a higher internal resistance, affecting its performance and heat generation during charging and discharging. As the number of charging and discharging cycles increases, the electrolyte and active materials continually degrade, ultimately decreasing the battery’s capacity and efficiency [4].
Conventional Battery Management Systems (BMS) and statistical approaches such as Autoregressive Integrated Moving Average (ARIMA) provide fundamental monitoring capabilities [5], such as tracking parameters like voltage, current, and temperature. These often only reveal the superficial state of the battery and might fail to detect more complex internal abnormal states. For example, internal pressurization of the battery leads to delamination and thus failure of the battery [6–8]. LiB fault diagnosis algorithms that utilize battery models, faults are detected by generating and analyzing residuals based on the models. This includes state estimation, parameter estimation, parity checks, and structural analysis. These methods focus on the physical characteristics and working principles of batteries. For different battery types or operating conditions, continuous adjustments and optimizations of the models may be necessary [9]. As shown in Fig. 1, the parameters of LiBs during charging are complex and inconsistent, with certain abnormal samples closely resembling normal ones, making it challenging to identify irregular states through basic features alone. To achieve more accurate and timely detection of abnormal states, as well as to overcome the challenges of acquiring abnormal samples and the high cost of data labeling, researchers have begun to explore unsupervised machine learning methods. Traditional unsupervised machine learning methods for time series abnormal state detection include One-Class Support Vector Machine (OC-SVM) [10], Isolation Forest (IF) [11], and Principal Component Analysis (PCA) [12], which typically do not require stringent assumptions about the data distribution and can handle complex data patterns. Despite the numerous successes of conventional machine learning approaches in abnormal state detection, they are typically sensitive to the choice of parameters, incur high computational costs, and might struggle with handling exceedingly complex, high-dimensional, or non-linear data structures.
Recently, unsupervised deep learning abnormal state detection algorithms based on autoencoders (AE) have garnered widespread attention [13,14]. AE can automatically learn high-level features from normal data and capture complex and nonlinear patterns in the data. Generating significant reconstruction errors when encountering abnormal samples, thus detecting abnormal states [15]. However, the behavior of batteries is highly time-correlated, changing according to the current state of the battery (such as charging status, temperature, or electrochemical state), meaning that the same absolute measurements can indicate different things under different states. For instance, a rapid increase in current may be normal during the early stages of charging, but such an increase nearing full charge could be indicative of an abnormal state [16]. Such temporal correlations are easily neglected by AE. Furthermore, battery behavior is also frequency-dependent. These dependencies are conspicuous in new batteries but may start to diverge subtly with battery aging. For example, aged batteries may exhibit irregular frequency characteristics in thermal cycles at the same working temperature due to decreased thermal management capabilities [17]. AE is also not very sensitive to frequency correlations. Lastly, given the high complexity of LiB data, AE typically requires the setting of numerous parameters, which results in an overly strong generalization capability, effectively reconstructing some abnormal samples too well [18].
To address the challenges mentioned, we propose a novel unsupervised abnormal state detection model for LiB time series: DFMCA-LSTM-AE (Long Short-Term Memory Autoencoder with Dynamic Frequency Memory and Correlation Attention). We primarily enhance the conventional AE through two components: the Dynamic Frequency Memory and Correlation Attention mechanism (DFMCA) and the Long Short-Term Memory network (LSTM) [19]. DFMCA is a core component of the DFMCA-LSTM-AE model, merging the benefits of dynamic convolution and fast Fourier transform to enhance the model’s ability to capture frequency correlations. Dynamic convolution can adjust its kernel size adaptively, thus more flexibly capturing local and global features in the time series [20]. The model can detect frequency patterns of battery behavior across various time scales by weighting the fast Fourier transform after multi-scale dynamic convolution. Notably, all fast Fourier transforms within the DFMCA are followed by a memory module that can remember the frequency characteristics of normal samples during the training phase and reconstruct the input samples based on the memory items to assist in distinguishing between normal and abnormal states. The LSTM layer follows closely after the DFMCA. Its role is to receive frequency correlation features enhanced by the attention module and further analyze how these features evolve. The internal gate-controlled mechanism of the LSTM proficiently filters and retains important temporal points, ignoring irrelevant data, thus allowing the LSTM layer to detect subtle shifts in battery status. The principal contributions of this paper are as follows:
• We proposed the DFMCA-LSTM-AE abnormal state detection model for the EV LiB time series. This model is end-to-end and unsupervised.
• Dynamic Frequency Memory and Correlation Attention mechanism and LSTM layer are introduced, effectively capturing battery behavior’s frequency and temporal correlations.
• A memory module is incorporated after the fast Fourier transform to remember features of normal samples, reducing the model’s overgeneralization.
• Experiments on a real-world LiB dataset demonstrate the effectiveness of DFMCA-LSTM-AE, with its performance significantly surpassing other representative models and the state of art model.
Time series abnormal state detection is an active research topic that has been extensively studied. The related work involved in this paper includes unsupervised time series abnormal state detection and memory networks.
2.1 Unsupervised Time Series Abnormal State Detection
An abnormal state refers to values that deviate significantly from observations. Methods for detecting abnormal states in time series can be divided into statistical methods, machine learning methods, and deep learning methods. Statistical methods include algorithms such as the standard deviation method (Z-Score) [21], Autoregressive Integrated Moving Average (ARIMA) [22], and Exponential Smoothing [23]. Statistical methods often require specific assumptions like data distribution, which may not always hold in practical applications. Machine learning techniques involve algorithms like k-means [24], OC-SVM [10], IF [11], and PCA [12]. However, most machine learning models cannot learn directly from raw time series data, often necessitating initial feature engineering and meticulous parameter selection and tuning to identify features significant for detecting abnormal states. Deep learning methods include the use of Autoencoders, Variational Autoencoders (VAE) [25], LSTM [19], and Generative Adversarial Network (GAN)-based approaches [26]. In general, deep learning can learn high-level data representations to capture complex patterns and relationships effectively. Additionally, deep learning allows for direct training of models from raw data to outcomes, significantly reducing the need for data preprocessing and feature engineering.
Furthermore, time series abnormal state detection methods based on deep learning can be divided into two types. The first type generates predicted data based on historical data and compares it with the input sample to detect abnormal states. Wu et al. utilized LSTM to predict time series data, followed by applying a naive Bayes model for error evaluation [27]. Meng et al. employed the Transformer for time series forecasting, incorporating an attention mechanism with parallel time step updates and a masking strategy for early abnormal state detection, improving the ability to recognize abnormal states [28]. Nonetheless, these methods are deficient in global observation and can be affected by real-time impacts from other variables, rendering them unsuitable for the dynamically changing data of LiB. The other type is based on models trained on historical data to reconstruct input samples, with the reconstruction results compared with the input samples to detect abnormal states. This method makes better use of global information and is more stable than other methods. Zhang et al. combined Convolutional Neural Networks (CNN) with LSTM to concurrently capture the spatial and temporal characteristics of time series data, embedding this hybrid into the architecture of an autoencoder. By comparing multi-scale data reconstructions, the architecture can effectively identify abnormal patterns [29]. Zhang et al. proposed a Dynamic Autoencoder Model (DyAD) that dynamically encodes LiB data, adding an auxiliary loss to achieve latent space regularization [30].
In 2014, Weston et al. first introduced a model called Memory Networks [31], which is a memory structure for external information, applicable to many tasks such as question answering and language modeling. Subsequently, Sukhbaatar et al. proposed its end-to-end version, optimizing the training process [32]. Kumar et al. then released an improved version of the memory network known as the Dynamic Memory Network (DMN). This DMN model combines a Recurrent Neural Network (RNN) with an external memory component, first processing the input through the RNN, and then saving the processed results in the memory component [33]. Chang et al. utilized a memory module as a dynamic knowledge base to capture its long-term patterns. Moreover, it is easy to know which parts of the historical data are most frequently referenced by the attributes of the memory module, making the model highly interpretable [34]. Gao et al. proposed a memory-augmented time series autoencoder (TSMAE). A memory module is added between the encoder and the decoder, and each memory item is encoded and recombined based on the similarity of latent representations, encouraging the memory module to extract typical normal patterns of the time series, thus suppressing the model’s generalization ability [35].
Integrating EVs into smart grid ecosystems brings about complex data streams and interactions, requiring advanced techniques for monitoring and management. To unlock the full potential of this integration, advanced models must be utilized to interpret and act upon the substantial data produced by EVs. The proposed DFMCA-LSTM-AE model’s application context, depicted in Fig. 2, demonstrates how EVs are capable of producing diagnostic data through the Battery Management Systems (BMS) at charging facilities during the charge and discharge cycles. This encompasses a sequence of fluctuating parameters that develop over the course of LiB charge-discharge cycles. Subsequently, this diagnostic information is transmitted to a cloud-based server for further analysis and processing. The trained DFMCA-LSTM-AE is deployed on the cloud server to perform real-time abnormal state detection on the monitoring data, and report to the user if abnormal states are generated when EVs are charging. On the other hand, when EVs discharge to the grid, if too many abnormal states are detected, additional planning is done to utilize other energy sources in the virtual power plant. By situating the DFMCA-LSTM-AE model within the cloud server, we benefit from the computational power and scalability needed to process large datasets in real time. This high-level functionality is crucial for rapidly identifying potential issues and implementing corrective measures within the VPP ecosystem.
The proposed DFMCA-LSTM-AE model consists of a Dynamic Frequency Memory and Correlation Attention Mechanism (DFMCA), LSTM layers, and the corresponding encoders and decoders. Fig. 3 shows the input being mapped onto queries (Q), keys (K), and values (V). Q and K are then fed into the Dynamic Fourier Transform Memory Module (DFTM), depicted in Fig. 4. Within the DFTM, inputs pass through one fast Fourier transform (FFT) branch without dynamic convolution. Additionally, they go through two FFT branches that include dynamic convolutions of different sizes. This process allows for the dynamic capture of multi-scale frequency features. The output of each branch is then processed by the memory module, which retrieves the most relevant items in memory based on attention-based addressing weights and outputs them. The six frequency features output by the DFTM are multiplied accordingly to obtain three sets of frequency relevance features, which are then subjected to inverse FFT projection into the time domain. Weighted summation via the attention mechanism. Finally, the largest
3.2 Time-Series Data Preprocessing
Larger numerical values can expand the range of scales, rendering the model insensitive to minor variations in smaller numerical values, which could result in neglecting their crucial properties. Hence, considering the sensor context information under the same timestamp, it is necessary to standardize the raw data for all temporal dimensions.
The raw data
where
3.3 Dynamic Fourier Transform Memory Module
As shown in Fig. 4, when data
where
The
where
After obtaining
The branch where
The frequency features transformed by FFT are represented as
where
The higher the value of
Although backpropagation can reduce the sensitivity of addressing vectors with low relevance to the normal samples based on gradient descent, when the number of addressing vectors reaches a certain scale, even those with low sensitivity can reconstruct abnormal samples through linear combination. To address this issue, we employed the addressing adjustment technique proposed by Gong et al. [38], as shown in Eq. (7), which limits the lower bound of addressing vector
where λ is a threshold allowing
3.4 Dynamic Frequency Memory and Correlation Attention
Dynamic Frequency Memory and Correlation Attention can perform a correlation calculation on the frequency features captured by the DFTM and associate the frequency correlation with multiple similar subsequences through dynamic information synthesis, thereby indirectly linking the frequency correlation with temporal relationships.
As shown in Fig. 3,
where
If conventional feature fusion methods are used to add the three sets of frequency correlation together simply, it is equivalent to assuming that the frequency correlation at each scale is equally significant. Although this increases multi-scale information, it still causes certain information redundancy, making it difficult to allocate attention weights reasonably. Therefore, we have incorporated ECA-Net before feature fusion, allowing the model to dynamically assign weights based on each group’s frequency correlation information content.
3.4.2 Dynamic Information Synthesis
The frequency correlation after weighted feature fusion is compressed to obtain
where
In a time series V of length L, the time points preceding
where
3.5 Long Short-Term Memory Network
To account for the temporal relationships before and after each data item in the time series, DFMCA-LSTM-AE incorporates an LSTM layer. LSTM is a special type of RNN, consisting of multiple sequential cells. Unlike RNN, each cell controls the flow of information through three gates, which determine what information is stored, deleted, or outputted. The forget gate
In the above equation,
The encoder is responsible for extracting the latent representation with attention from the input, while the decoder restores the latent representation to obtain the reconstructed sample. The formulas for the encoder and decoder are seen in Eqs. (17) and (18).
where
In the training phase, the dataset comprises exclusively normal samples. The training aims for the model to acquire the primary characteristics of normal samples, thereby effectively reconstructing them and generating a specific deviation when dealing with abnormal state samples. Mean squared error (MSE) is employed as the loss function, with the computational formula provided in Eq. (19).
where
The design of the loss function is crucial as it guides the model during training by quantifying the difference between the reconstructed time series and the original input. The MSE specifically penalizes larger errors more severely, as the errors are squared, and it averages these overall points in the time series to give a single scalar quantity representing the loss. This function encourages the model to minimize the difference between the normal operational data it has learned and any new data it is reconstructing, thus helping to identify anomalies by the deviation in the reconstruction error.
The computational flow of the DFMCA-LSTM-AE is shown in Algorithm 1. Algorithm 1 commences with the mapping of time series data
This article conducts experiments on the real-world EV lithium-ion battery dataset released in [30]. The dataset contains over 690,000 real charging segments from 347 EVs. The number of abnormal state segments accounts for 18.57% of the total. Each charging segment has 128 time points, with an interval of 10 s between each point, comprising 7 features. The visualization of each feature is shown in Fig. 1.
The Receiver Operating Characteristic (ROC) curve is a common tool for visualizing the classification performance of binary classification models. It works by arranging all possible classification thresholds, calculating a series of False Positive Rate (FPR) and True Positive Rate (TPR) points, and then plotting them on a chart. The Area Under the ROC Curve (AUC) is often used to measure the classification performance of abnormal state detection models. In binary classification problems, TPR and FPR can be calculated as:
where
At different classification thresholds, the values of
In addition to using AUC as an evaluation metric, we have also incorporated the F1 score. The F1 score is the harmonic mean of precision and recall, both of which are critical metrics for understanding the model’s performance in positive class identification. Precision refers to the proportion of positive class predictions, while recall refers to the proportion of positive classes correctly identified by the model out of all actual positive classes. The F1 score can be calculated using the following:
where
The normal data is divided using a five-fold cross-validation method, where in each fold, 80% of the normal samples are used as the training set, and the remaining 20% of the normal samples, along with 100% of the abnormal samples, make up the test set. Incomplete data in the dataset will not be used.
DFMCA-LSTM-AE model’s DFMCA mechanism includes seven attention heads. There are four parallel convolutional kernels in dynamic convolution, with each kernel on the
In this experiment, we first compared DFMCA-LSTM-AE with nine representative models, including OC-SVM [10], IF [11], PCA [12], AE [15], AM-LSTM [41], ICA-Bi-LSTM [42], LSTM-AE [43], GMM-LSTM-AE [44] and TSMAE [35]. It was then contrasted with the SOTA model DyAD [30]. Table 1 lists the five-fold cross-validation comparison results for AUC, Precision, Recall, and F1 scores of DFMCA-LSTM-AE with the above models, and Fig. 5 displays the average ROC curves of each algorithm. The solid line represents the average of five cross-validation runs, and the shaded area indicates the standard deviation of the experiments. It can be observed that DFMCA-LSTM-AE achieved an average AUC of 90.73% and an average F1 score of 83.83%, with an improvement of 2.4%–45.3% in AUC and 1.6%–28.9% in F1 score.
The reconstruction of normal and abnormal samples by DFMCA-LSTM-AE on the LiB dataset is shown in Fig. 6. The blue curve represents the observed original samples, and the red curve indicates the reconstructed samples. ‘∆’ denotes normal samples, while ‘•’ signifies abnormal state samples. The pink area between the two curves represents the error. It can be seen that DFMCA-LSTM-AE reconstructs the normal samples well, with almost no discernible error compared to the observed values. In contrast, the reconstruction of the abnormal states samples is significantly different from the observed values, resulting in a conspicuous reconstruction error, which allows for a good distinction from the normal samples.
In summary, DFMCA-LSTM-AE significantly improves the detection of abnormal states in LiB time series by dynamically seizing frequency correlation and chronological relationships.
To elucidate the function of each component within DFMCA-LSTM-AE, this section will showcase the ablation results for the modules. ‘DFMCA-LSTM-AE without DFMCA’ indicates that the model is stripped of the Dynamic Frequency Memory and Correlation Attention (DFMCA), with only the LSTM and linear layers remaining in both the encoder and decoder. ‘DFMCA-LSTM-AE without LSTM’ indicates the removal of LSTM layers from both the encoder and decoder, preserving just the DFMCA mechanism and linear layers. ‘DFMCA-LSTM-AE without Dyconv branch’ refers to eliminating the
The ablation results, as shown in Table 2, reveal that removing the DFMCA causes the model to fail to capture sufficient frequency correlation features, resulting in a significant drop in accuracy. Eliminating the LSTM layers leads to the inability to capture the relationships in the time series, which also decreases accuracy. Removing the dynamic convolution branches results in a decreased feature receptive field of the model, leading to a slight reduction in accuracy. Without the memory module, the model more effectively reconstructs abnormal samples’ frequency features and the samples themselves. Not implementing a hard threshold in the memory module causes too many minor memory items to combine, affecting the restoration of abnormal frequency features.
The dimension of the memory module
4.2.4 Convolution Kernel Size and Step Size
Fig. 4 demonstrates the configuration of dynamic convolutions in two branches,
4.3 Model Interpretability Analysis
In this study, we specifically focus on the DFTM module in DFMCA-LSTM-AE, as it plays a crucial role in dynamically capturing multi-scale frequency relevancy and suppressing abnormal states. As shown in Fig. 9, the memory modules on the three branches of the Dynamic Memory Fourier Transform module (Fig. 4) were visualized. Fig. 9a corresponds to the memory module without dynamic convolution. Figs. 9b and 9c correspond to memory modules with dynamic convolution. It is apparent that the attention weights of the memory module without dynamic convolution are distributed relatively evenly throughout the entire chart. However, as the value of
This is because the features without dynamic convolution contain richer frequency information, requiring the memory module to maintain a more uniform distribution of attention to capture and utilize this information. When dynamic convolution is introduced as a filter, the model adjusts and reshapes the input features through a series of optimized filters. These filters act as learned weight matrices, selectively amplifying or attenuating different frequency components of the input data. It is similar to the way human vision searches for key information in complex scenes.
Furthermore, we conducted an interpretability analysis of the model’s inputs and outputs. As shown in Fig. 10, after the test set data was visualized using t-distributed stochastic neighbor embedding (T-SNE) and reduced to two dimensions, the abnormal samples were marked with red dots and the normal samples with grey dots. Fig. 10a shows the T-SNE result of the input data, where the red and grey dots are randomly mixed, with no discernible distance between clusters. Fig. 10b shows the T-SNE result of the output data from DFMCA-LSTM-AE, which reveals a clear inter-cluster distance between red and grey dots, indicating distinct clustering behavior. This clustering effect suggests that DFMCA-LSTM-AE has successfully learned the features necessary to differentiate between normal and abnormal patterns, demonstrating an understanding of the intrinsic structure of the data. Moreover, this clear spatial separation also suggests that the model has a good ability to distinguish unseen data, thereby proving its superior performance in abnormal state detection.
This paper addresses the challenge of accurately detecting abnormal states in lithium-ion battery (LiB) data, which is characterized by dynamic irregularities. Our important findings indicate that the DFMCA-LSTM-AE we proposed model not only overcomes the limitations of traditional methods but also demonstrates superior performance in detecting these abnormalities. Through the novel integration of a Dynamic Frequency Memory and Correlation Attention mechanism, our model dynamically recognizes frequency correlations and effectively suppresses the frequencies associated with abnormal samples. The incorporation of Long Short-Term Memory (LSTM) networks into the encoder and decoder components efficiently extracts temporal patterns within the time series data, further enhancing detection accuracy.
In extensive tests conducted on a dataset for abnormal state detection in lithium-ion batteries, DFMCA-LSTM-AE achieved impressive results. It recorded an average Area Under the Curve (AUC) of 90.73% and an average F1 score of 83.83%. These metrics indicate a substantial improvement over other models, with an increase in AUC ranging from 2.4% to 45.3% and an enhancement in F1 score from 1.6% to 28.9%.
Our study still has certain limitations, including the need for further validation of the model across various battery types and operational environments to ensure robustness and real-time performance. Our future work will focus on addressing these limitations. Training it with a small variety of LiB data to achieve good accuracy on a large variety of LiB data. Additionally, we plan to explore the use of shorter LiB time series to detect abnormal states, aiming to improve the model’s real-time performance.
Acknowledgement: The authors would like to thank the editor and anonymous reviewers for their valuable suggestions and comments.
Funding Statement: This research was partly supported by “Regional Innovation Strategy (RIS)” through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (MOE) (2021RIS-002) and the Technology Development Program (RS-2023-00278623) funded by the Ministry of SMEs and Startups (MSS, Korea).
Author Contributions: The authors confirm contribution to the paper as follows: study conception and design: Haoyi Zhong, Chang Gyoon Lim; data collection: Yongjiang Zhao; analysis and interpretation of results: Haoyi Zhong, Yongjiang Zhao; draft manuscript preparation: Haoyi Zhong, Chang Gyoon Lim. All authors reviewed the results and approved the final version of the manuscript.
Availability of Data and Materials: The datasets are available at the links below: https://1drv.ms/u/s!AiSrJIRVqlQAgcjKGKV0fZmw5ifDd8Y?e=CnzELH237.
Conflicts of Interest: The authors declare that they have no conflicts of interest to report regarding the present study.
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