There are few high-throughput,
in-depth electrochemical tests suitable for manufacturing applications.

INTRODUCTION

batts2.png

Batteries are complex electrochemical devices that undergo extensive testing through materials development, pilot, and scale-up. A wide array of microscopic and spectroscopic techniques are employed to evaluate the materials and chemical processes within the cell. However, these in-depth testing methods require extensive expertise to interpret and are time-intensive, expensive, and often destructive, limiting their use to the laboratory. At manufacturing scale, analysis methods are limited to more basic measurements (e.g., dimensional, voltage, current). While these basic measurements are useful for catching obvious defects, they are only indirect measurements of the key underlying electrochemical phenomena that determine long-term cell performance and reliability.

Basic voltage and current measurements can be used in a more dynamic way to provide greater depth of analysis.

THE CASE FOR IMPEDANCE SPECTROSCOPY

A battery’s impedance is its frequency-dependent voltage magnitude and phase response to a change in sinusoidal current. Measuring the impedance of a battery across many frequencies — often referred to as electrochemical impedance spectroscopy (EIS) — enables a non-destructive test that offers diagnostics information about the internal components of the battery. In fact, it is one of the few non-destructive techniques available for battery analysis. Impedance data can be displayed and interpreted on a Nyquist plot of inverted reactance vs. resistance, where shapes and features can be attributed to various components within the cell. EIS is a well-known laboratory technique for battery characterization and analysis. However, EIS is not a well-used technique due to the high cost of equipment and long time of testing. Additionally, most labs have orders of magnitude more cell cycler channels than EIS channels, making the integration of impedance and lifecycle or state-of-charge testing tedious and inefficient.

 
imp-01.png
 

Introducing a low-cost and scalable cycling platform with embedded real-time impedance spectroscopy.

HIGH THROUGHPUT IMPEDANCE SPECTROSCOPY

Hive Battery Labs is addressing the shortcomings of traditional impedance spectroscopy by introducing a low-cost and scalable cell cycling platform with embedded real-time EIS that enables the continuous monitoring of cell impedance through various charge currents and states of charge. A power module built on efficient switching power electronics enables the platform to be adapted to a wide range of cell formats and capacities. Initial prototypes have been evaluated from single-Ah cylindrical cells to 31 Ah pouch cells and have been shown to offer comparable accuracy to the state-of-the-art potentiostats/galvanostats for the targeted frequency range relevant for full-cell analysis. A proprietary scanning algorithm reduces measurement time from minutes to seconds, enabling the acquisition of high time-resolution spectra for real-time cycling impedance analysis.

 
Hardware prototype for 1A cycling and 100 mA EIS.

Hardware prototype for 1A cycling and 100 mA EIS.

 
 

Impedance spectroscopy can increase the throughput and quality of cell formation, storage, and grading.

FORMATION DIAGNOSTICS

Impedance spectra collected in real-time during the first formation charge.

Impedance spectra collected in real-time during the first formation charge.

Hive applies the unique capabilities of impedance spectroscopy to formation cycling to provide new insight into the complicated formation process. Battery impedance is complex — a three-dimensional measurement significantly influenced by many factors such as chemistry, state of charge, temperature, and charge rate. Thus, successful interpretation of impedance requires effective dimensionality reduction. Hive has developed a battery model to capture important behavior related to phenomena early in formation. This enables Hive to observe the formation process and provides unique information during these critical steps that is much more difficult to detect once formation is complete.

Predictive analytics built from formation impedance will decrease manufacturing time and cost.

PREDICTIVE ANALYTICS

As global production of Li-ion batteries continues to surge, highly-efficient and well-designed industrial processes become increasingly important. Data-driven technologies will continue to improve process efficiency and drive productivity. In contrast to basic testing methods available in manufacturing today that quantify symptoms of manufacturing variation or defects, impedance spectroscopy offers a more direct measurement of the root cause from underlying material and electrochemical defects in the cell. Hive Battery Labs’ unique combination of advanced battery impedance test equipment, physics-based parameter extraction methods, and sophisticated machine learning algorithms enables a new predictive analytics platform that will drive down the cost and improve the efficiency of formation, storage, and test.

Learn more.