Lithium-Ion Battery Condition Monitoring: A Frontier in Acoustic Sensing Technology

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. For the Keywords, 'lithium-ion battery', 'safety and lifespan', and 'non-destructive' should be added to attract a broader readership.  

2. Page 1, 'LIB is widely used in consumer electronics, new energy vehicles, and grid energy storage due to its advantages of high energy density, long cycle life, and low self-discharge [1], and has made significant progress in the past few decades.'     I consider the disadvantages of LIBs to be introduced, such as thermal runaway risk. In terms of the potential danger and large-scale application with renewable energy sources, redox flow batteries are also very promising and the lifespan can be as long as 20 years (10.1002/wene.541). Similarly, lead-acid batteries can also be a good selection. I consider a brief comparison of these three kinds of batteries should be made to enrich the contents.

  3. For the 'Ultrasonic testing technology', I consider the literature in recent two years should be reported more. Especially, thermal runaway is a big safety concern for lithium batteries, hence state of charge and temperature joint estimation based on ultrasonic reflection waves for lithium-ion battery applications should be introduced as well.   

4. Battery nondestructive monitoring technology is mainly based on acoustic and optical battery nondestructive testing technology. So why does this manuscript focus on acoustics rather than optics? I think the two should be properly compared. At the same time, is it better if acoustics and optics are combined for nondestructive testing? Are the two highly complementary?  

5. Besides SOH and SOC, the micro-health parameters are also critical to evaluate the health state of the batteries. Micro-health parameters stand for the performance of active material and electrolytes inside the battery, and the changes in the micro-health parameters can present the battery's internal health state. Can acoustic sensing technology also determine the micro-health parameters?

Author Response

Comment 1: For the Keywords, 'lithium-ion battery', 'safety and lifespan', and 'non-destructive' should be added to attract a broader readership.

Reply 1: Thank you for pointing this out. We agree with this comment and have made revisions. The revisions have been highlighted in red. 

Keywords: Lithium-ion battery; Safety and lifespan; Acoustic perception; Ultrasonic testing; Acoustic emission; State of Charge；State of Health; Overcharging; Non-destructive;

Comment 2: Page 1, 'LIB is widely used in consumer electronics, new energy vehicles, and grid energy storage due to its advantages of high energy density, long cycle life, and low self-discharge [1], and has made significant progress in the past few decades.'    I consider the disadvantages of LIBs to be introduced, such as thermal runaway risk. In terms of the potential danger and large-scale application with renewable energy sources, redox flow batteries are also very promising and the lifespan can be as long as 20 years (10.1002/wene.541). Similarly, lead-acid batteries can also be a good selection. I consider a brief comparison of these three kinds of batteries should be made to enrich the contents.

Reply 2: Thank you for pointing this out. We agree with this comment and have made revisions. We introduced the drawbacks of LIBs and briefly compared three types of batteries. The revisions have been highlighted in red.

    The internal structure of LIB is complex, including multiple layers of electrodes and porous membranes, which directly affect its electrochemical performance and thermal management behavior. The actual operating conditions of LIB are often complex and variable, which may lead to serious safety issues such as rapid capacity decay and even thermal runaway in extreme environments [14]. In the context of large-scale application of renewable energy, alternative battery technologies such as redox flow batteries and lead-acid batteries have also received attention. The lifespan of redox flow batteries can reach 20 years, providing a promising solution for large-scale energy storage. Similarly, lead-acid batteries remain a viable option due to their cost-effectiveness and reliability. Table 1 provides a brief comparison of these battery technologies.

Table 1. Comparison of Battery Technologies

Battery Type	Energy Density	Cycle Life	Safety	Cost	Applications
Lithium-ion	High	Long	Moderate Risk	Moderate	Consumer electronics, EVs, Grid storage
Redox Flow	Moderate	Very Long	Low Risk	High	Large-scale energy storage
Lead-acid	Low	Moderate	Low Risk	Low	Backup power, grid storage

     Despite the advantages of redox flow and lead-acid batteries, LIB remains the primary choice for many applications due to its superior energy density and cycle life. However, the safety and lifespan of LIB are key factors that need to be addressed to ensure its reliable use in various applications. Therefore, researchers are committed to exploring the reaction mechanism, aging mechanism, and safety hazards inside lithium batteries, and achieving efficient characterization through the development of ad-vanced characterization techniques. In 2020, the "Battery 2030+" R&D roadmap re-leased by Europe clearly pointed out that the existing Battery Management Systems (BMS) have insufficient monitoring capabilities at the individual battery level, such as the inability to directly measure the internal temperature of the battery.

Comment 3: For the 'Ultrasonic testing technology', I consider the literature in recent two years should be reported more. Especially, thermal runaway is a big safety concern for lithium batteries, hence state of charge and temperature joint estimation based on ultrasonic reflection waves for lithium-ion battery applications should be introduced as well.   

Reply 3: Thank you for pointing this out. We agree with this comment and have made revisions. We have added relevant content in section 3.1.1 and highlighted it in red.

     In addition, Zhang et al. [47] proposed a joint estimation method for SOC and temperature of lithium iron phosphate batteries based on ultrasonic reflection waves. The method utilizes piezoelectric transducers attached to the surface of the battery to generate and receive ultrasonic signals. By analyzing the characteristic parameters of the ultrasonic signals, such as time-domain peak value, time-domain envelope peak value, energy integration, waveform index, kurtosis coefficient, and shape coefficient, high-precision estimation of SOC and temperature of lithium-ion batteries is achieved. The root mean square errors (RMSE) of SOC and temperature are 7.42% and 0.40 ° C, respectively. This study highlights the potential of ultrasound reflection waves in non-destructive and real-time monitoring of battery status, which is crucial for pre-venting thermal runaway and improving battery management systems.

Comment 4: Battery nondestructive monitoring technology is mainly based on acoustic and optical battery nondestructive testing technology. So why does this manuscript focus on acoustics rather than optics? I think the two should be properly compared. At the same time, is it better if acoustics and optics are combined for nondestructive testing? Are the two highly complementary?  

Reply 4: The optical and acoustic non-destructive testing technologies you mentioned are indeed important means of battery monitoring. The manuscript focuses on acoustic sensing technology due to its unique advantages in non-destructive monitoring of lithium-ion batteries, such as strong penetration and high sensitivity to internal structural changes. While optical sensing is also an important method for battery non-destructive testing, this manuscript emphasizes acoustic sensing because it provides distinct capabilities for evaluating the State of Charge (SOC), State of Health (SOH), and overcharge behavior of batteries. The combination of acoustic and optical sensing could be a promising direction for future research, as they are highly complementary. Optical sensing can provide information on internal thermodynamic, chemical, and mechanical data, while acoustic sensing excels at monitoring internal structural changes. However, due to the specific focus of this manuscript on acoustic sensing, the optical sensing part is not included.

Comment 5: Besides SOH and SOC, the micro-health parameters are also critical to evaluate the health state of the batteries. Micro-health parameters stand for the performance of active material and electrolytes inside the battery, and the changes in the micro-health parameters can present the battery's internal health state. Can acoustic sensing technology also determine the micro-health parameters?

Reply 5: The micro health parameters you mentioned are indeed crucial for evaluating the health status of batteries. These parameters reflect the performance of the active materials and electrolyte inside the battery, and their changes can reveal the internal health status of the battery. Acoustic sensing technology has shown potential in monitoring battery health, mainly by detecting changes in the internal structural characteristics of the battery. Although acoustic sensing technology is currently mainly used to evaluate the SOC and SOH of batteries, by analyzing the propagation characteristics of ultrasound inside the battery, such as changes in wave velocity and attenuation, the condition of active substances and electrolytes can be inferred, which can be used to detect micro health parameters. However, research in this area is still in the exploratory stage and further work is needed to improve the application of acoustic sensing technology in monitoring micro health parameters.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript is a review article covering the study of acoustic sensing technology for battery characterization applications. This article is timely as more and more researchers are beginning to focus on the application of acoustic sensing technology in batteries. The article is well-structured and well-written. However, I have noticed some problems in the manuscript regarding the specific points. The comments listed below are intended to offer the authors ways to improve their manuscript to make it more accessible to the broad readership.

1.     “In 2020, the "Battery 2030+" R&D roadmap released in Europe clearly 51 pointed out that the existing battery management system (BMS) has insufficient monitor-52 ing capabilities at the single cell level…” The authors should provide reference source for this information.

2.     When using ultrasound to study battery overcharge behavior, can this technique detect lithium plating behavior? Can the author provide comments on this point?

3.     Compared with ex-situ characterization technology, in-situ technology is more powerful in establishing the relationship between obtained signals and electrochemical behavior. It is highly recommended that the author include more discussion on the development and challenges of in-situ technology in the review paper.

4.     Can the author provide a table listing representative acoustic work in battery research field in recent years?

Author Response

Comment 1: “In 2020, the "Battery 2030+" R&D roadmap released in Europe clearly 51 pointed out that the existing battery management system (BMS) has insufficient monitor-52 ing capabilities at the single cell level…” The authors should provide reference source for this information.

Reply 1: Thank you for pointing this out. We agree with this comment and have made revisions. The revisions have been highlighted in red.

15. DOMINKO R.; FICHTNER M.; OTUSZEWSKI T.: Battery 2030+. In.

Comment 2: When using ultrasound to study battery overcharge behavior, can this technique detect lithium plating behavior? Can the author provide comments on this point?

Reply 2: Thank you for raising this question. In ultrasonic testing, the overcharging behavior of lithium-ion batteries is indeed associated with lithium plating behavior. We have added the relevant content to the paper and highlighted it in red.

    

  The formation of lithium plating is an important sign of battery overcharge behavior. Li et al. [63] found through research that ultrasonic nondestructive testing technology can be used to detect lithium plating during battery charging. When the lithium plating is formed, gas will be generated inside the battery, resulting in significant changes in the ultrasonic signal. Specifically, ultrasound waves undergo reflection and scattering at the interface of different acoustic impedance media during propagation, resulting in significant signal attenuation [64]. The formation of lithium plating will increase the attenuation of ultrasonic wave, so the occurrence time of lithium plating can be diagnosed by ultrasonic detection. In the experiment, Li et al. used a phased array ultrasound probe (Figure 7), placing the probe directly above the battery and placing a coupling layer between the probe and the battery. Ultrasonic waves are emitted by the array elements in the probe and propagate inside the battery. The ex-perimental results showed that batteries without lithium plating exhibited strong re-flection signals in ultrasonic detection images, while batteries treated with lithium plating showed significantly reduced reflection signal intensity. This indicates that the formation of lithium plating leads to more gas generation, which prevents the ultra-sonic wave from propagating to the back of the battery.

Figure 7. The phased array ultrasonic probe for battery testing and the electrode samples. (a) The physical structure of the probe. (b) Ultrasound image of a fresh battery. (c) Negative electrode sample of the fully charged fresh battery. (d) Relationships between the probe and the battery. (e) Ultrasound image of a lithium plating battery. (f) Negative electrode sample of the battery with lithium plating.

Comment 3:  Compared with ex-situ characterization technology, in-situ technology is more powerful in establishing the relationship between obtained signals and electrochemical behavior. It is highly recommended that the author include more discussion on the development and challenges of in-situ technology in the review paper.

Reply 3: Thank you for raising this question. In ultrasonic testing, the overcharging behavior of lithium-ion batteries is indeed associated with lithium plating behavior. We have added the relevant content to the paper and highlighted it in red.

3.1.4. In situ detection

      In situ technology has become a powerful tool in the field of battery research, which can monitor the internal status of batteries in real-time during operation. Compared with non in situ characterization techniques, in situ techniques can better establish the relationship between the obtained signals and electrochemical behavior, thereby gaining a deeper understanding of the dynamic processes occurring inside the battery.

     The latest advances in in-situ ultrasound technology have demonstrated their potential in real-time monitoring of battery behavior. Shen et al. [75] used A-scan and 2D/3D fully focused (TFM) ultrasound technology to monitor lithium-ion batteries under overcharging (Figure 10). They demonstrated that ultrasound signals can detect side reactions with high accuracy (0.4% SOC) at 102% SOC. This study emphasizes the sensitivity of ultrasound signals to physical changes in electrodes, such as density and elastic modulus, and their ability to visualize the internal battery state. This study comprehensively analyzed the ultrasonic behavior of batteries during normal and abnormal operation. During normal charging/discharging processes, it was found that the amplitude of the first echo in A-scan technology is closely related to the acoustic impedance difference between the anode and cathode, which varies with the SOC of the battery. Specifically, the amplitude of the first echo increases with battery charging and decreases with battery discharging, showing an approximately linear relationship with SOC. This relationship is consistent at different current densities (1C, 2C, 3C, and 4C), although the amplitude variation range and certain stages may vary due to concentration polarization.

Figure 10. The schematic diagram and the detecting outcome of ultrasonic detecting techniques. a) the diagram of the ultrasonic detecting in pouch cells. b1) the ultrasonic wave obtained by A-scan techniques. b2) 3D TFM ultrasonic reflection patterns. b3) 2D TFM image throughout the whole cell

     During overcharging, the characteristics of ultrasonic signals undergo significant changes. For example, when the battery is charged to the cut-off voltage of 5.0V, the first echo completely disappears, indicating a large amount of electrolyte decomposition and gas generation. 2D TFM imaging technology can observe the uneven distribution of reflection patterns inside battery bags and accurately locate the location of side reactions. This warning capability allows for timely intervention to prevent further damage and extend battery life.

     Despite the advantages of in-situ ultrasound technology, it faces challenges such as sensor integration into existing systems, data interpretation complexity, and cost. Future research on in-situ ultrasound technology should focus on innovative sensor design and advanced data analysis methods. For example, the development of miniaturized and high-sensitivity ultrasonic sensors can improve the integration of in-situ technology with battery systems. In addition, machine learning algorithms can be used to analyze complex ultrasonic signals and extract meaningful information about the internal state of the battery.

Comment 4: Can the author provide a table listing representative acoustic work in battery research field in recent years?

Reply 4: No problem, I will list the table below.

Year	Authors	Contribution
2020	Huang et al.	Using a focused ultrasound beam for precise scanning of batteries, the inconsistency of ultrasound signal attenuation in solids, liquids, and gases is utilized to detect electrolyte infiltration in square and soft pack batteries. While analyzing the changes in transmittance of different batteries, it is also possible to quickly determine the minimum electrolyte injection amount and wetting time, which can accurately image the electrolyte distribution and gas production of the battery. This has significant implications for process optimization in actual battery production.
2021	Zhao et al.	They found that both TOF and SA decreased with the aging of the battery based on guided wave detection, which may be due to the influence of different ultrasonic excitation frequencies and SOC.
2021	Kai Zhang et al.	A sound emission measurement platform for lithium-ion batteries was established, and stress wave signals during battery cycling were analyzed to obtain continuous AE signals and pulse AE signals that can characterize the state of health (SOH) of lithium-ion batteries.
2023	Gao Jie et al.	An analytical acoustic model was established to study the interaction mechanism between the SOC of LIB and the propagation characteristics of ultrasonic guided waves. The sensitive frequency range of acoustic behavior to SOC changes was determined, and the influence of SOC on the acoustic dispersion behavior of LIB was analyzed in detail, further verifying the reliability of using acoustic detection methods for LIB identification during operation.
2023	Dou et al.	They designed an online ultrasonic ringing counting measurement device to introduce ringing count into the battery overcharge state evaluation to realize real-time detection and early warning of LIB overcharge state.
2023	Shen et al.	Using A-scan and TFM ultrasound technology for in-situ monitoring, the behavior of lithium-ion batteries under overcharge conditions was studied, demonstrating the high sensitivity of ultrasound signals to electrode physical changes such as density and elastic modulus, and the ability to visualize the internal state of the battery.
2023	Wang et al.	A new active AE sensing technology has been proposed for rapidly and simultaneously estimating the state of charge (SOC) and state of health (SOH) of a battery. By exciting the battery with appropriate power ultrasound and triggering AE events, more battery state information can be actively sensed over a wide frequency band.
2024	Li et al.	They found through research that ultrasonic nondestructive testing technology can be used to detect lithium plating during battery charging. When the lithium plating is formed, gas will be generated inside the battery, resulting in significant changes in the ultrasonic signal.

Author Response File: Author Response.docx