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Summer 2013 Blog - Elise Lim

Elise Lim is spending twelve weeks in the Bay Area working at Imprint Energy.

August 2, 2013


Elise preparing samples for imaging.

My internship at Imprint Energy is coming to a close, but Emil and I are still just as busy with testing battery cells and working on our projects. Most recently I finished compiling results related to a “master baseline” data set. A baseline is the standard in terms of battery architecture and results, and it is updated as the battery technology is improved. It allows us to compare results of new experiments to an existing standard. In fact, Imprint Energy is planning on updating their baseline soon, the result of many weeks of research and development. In addition, I started on a project that required several different inks to be made, and I really enjoyed getting to suit up in a lab coat (the powders we use get everywhere) and mix with Dirk, a chemist who joined the team not too long before Emil and I did.

Imprint Energy is also planning on revamping how they plan their experiments. With so many people working on their own projects, it’s sometimes difficult to compile data and new findings related to a central problem. In order to focus on different problems, Imprint is going to have weekly research “sprints.” Each week will focus on one issue, and experiments that address that issue will be planned a week in advance. The first research sprint will focus on improving cycle fade, or the decrease in capacity of the battery cells. Just the other day the company had a big meeting where we went over cycle fade, how it can be improved, and generally bounced ideas and hypotheses off each other.


Elise and the rest of Imprint Energy at their summer BBQ.

We also recently had our summer BBQ, which was really awesome! Someone even brought home-made sausages made from wild boar, and we spent the afternoon relaxing, barbequing various meats and vegetables, and enjoying some tunes with planes taking off from Oakland Airport to the left and a fantastic view of the San Francisco skyline to the right. While my last week at Imprint Energy is coming up, I am glad to have had the chance to be a part of their team, and I can definitely say I’ll be taking away a lot from my experience here.

July 16, 2013


Elise and her coworkers at a Vietnamese restaurant in Alameda.

One of my favorite aspects of start-up culture is how dynamic each work week is! Just last week I worked on a project that aimed to prototype a fixture that would connect a sheet of printed batteries in parallel and in series. Emil and I will hopefully be finishing those up this week along with a way to present the prototype (i.e. have it power up an LED light). Along with that project, we’ll soon begin working on testing for the diffusion coefficients of different electrolytes, a key test that will gather important data for Imprint Energy. While we’re still very involved with the general process of printing batteries, including measuring the thickness of each battery component after they’re printed, packaging the battery, and running “Day 0” tests, I’ve definitely felt that I’ve contributed to Imprint Energy by designing my own experiments, helping others run a variety of tests throughout the lab, and collecting and interpreting data.

Another aspect of Imprint Energy that I’ve really enjoyed is that a lot of the materials/equipment we use in the lab are “home-made.” Darren, a Cal alumni, has built a number of fixtures in the lab such as controlled environment boxes (to test batteries at high and low humidity) and a flex tester (this was actually for an upper division ME class at Cal!). Most recently I helped him by soldering new fixtures for a machine that allows us to run multiple tests on battery cells.

Something also pretty awesome happened last week! In preparation for company meetings with outside partners, customers, and investors, Darren and Karthik, another engineer, prototyped the world’s thinnest watch. It was basically a thin strip of metal with a display and batteries that made the watch as a whole barely thicker than the metal band by itself. Working prototypes like these are always helpful to demonstrate to the outside world how the batteries can be used. We also celebrated with delicious cupcakes, and it was entertaining to search for who had the most model-esque arm for a prototype photoshoot.

Just as a fun side remark: today we noticed that data being collected from one of the computers indicated strangely “pretty,” repetitive, and almost sinusoidal data patterns. Someone then explained to us that it was practically too good to be true, and it was. The watch being tested was sending signals faster than the computer was collecting data; in effect, the recorded signal aliased down to what looked like a sinusoidal wave because the test violated the Nyquist frequency rule. This was especially cool for me because having recently taken the intro electronics class, I got more of an appreciation and understanding for a concept I learned last semester.

July 1, 2013

The past six weeks at Imprint Energy have gone by so fast, and every day I have been learning more and more about batteries and the battery landscape. Emil and I have both grown very comfortable running a variety of tests in the lab as part of the data collection for other experiments as well as running tests for experiments and projects that we designed ourselves.

Our mornings usually start out with routine tests on battery cell batches that include electrochemical impedance spectroscopy (EIS) and current pulse testing.

EIS is a useful technique in which a small amplitude AC signal is applied to the battery cell. A machine records certain current-voltage characteristics, and we are then able to analyze internal impedance changes within the battery cell. By analyzing this data, we can extract information about the battery’s properties including its state of charge and its electrode kinetics. This tool has been especially useful in monitoring how the battery properties change in different environments; we run tests on batteries stored in high and low humidity chambers as well as re-run tests days and weeks after they’re printed to observe how different variables affect how a battery changes with time.

Another routine test we often run is the pulse test in which currents with varying frequencies are pulsed through the battery. By observing battery characteristics during this test, we’re able to further understand how the battery would behave in an application in which lots of current is drawn at once for short periods of time (e.g. cell phone).


Elise at Home Depot shopping for project materials.

Aside from the more routine testing, I have also been able to work on several projects. I recently finished flex testing battery components, a project that collected data needed for a grant proposal. I was able to design the experiment, carry out the tests, and summarize the data. For this project, I observed how the resistance of four battery components (anode, cathode, electrolyte, and current collector) changed over time and while being flexed about different radii of curvature. I then summarized the data in charts and graphs, including images of the experiment procedure as well as images taken with a scanning electron microscope (SEM) of the samples.

Just this week, Emil and I also lent a hand in trying to “pop” lithium-based batteries in a safe environment. As part of the flex testing, lithium-based battery cells were flexed on a machine, which eventually caused them to expand like little pillows. We took a quick trip to Home Depot in order to get wood, brick, and other parts to be used to build a mechanism that would safely allow the cells to rupture.

Most days at Imprint Energy are packed with tests and projects, and it’s been a great learning experience not only designing my own experiments but also being involved with the many other experiments conducted by the team. Next week, I’ll be starting even more projects with Emil, and I’m excited to see how they turn out!

June 3, 2013


Elise working on designing a prototype for connecting batteries.

Two weeks ago, and two days after finals, I packed myself a nice lunch, picked up Emil, the other intern that I would work with, and sped off through rush hour to get to our first day of our internship at Imprint Energy. Founded by two Berkeley graduates, Imprint Energy began as a start-up several years ago whose purpose was to design, test, and market thin, flexible, and high energy density rechargeable batteries. As people develop new, innovative electronic devices, there is a greater demand for batteries to fit certain needs; as a result, Imprint Energy aims to address these needs because it is necessary for battery technology to keep up with the constant development of electronic products.

During my first week at Imprint Energy, I was introduced to the people I would be working with and trained to run some standard tests. I think one of the best things about working at a start-up is that my workday is constantly dynamic; there are always things to do and tests to run, and I meet and work with everyone and on everything. Before long, Emil and I found ourselves juggling electrochemical impedance tests with pulse tests, while at the same time looking at open circuit voltages and prepping more and more batches of cells to test. Having just taken an electrical circuits class and an engineering materials class, it was very interesting and eye-opening to see how class material is applied in industry.  Furthermore, the more tests I ran, the more results I summarized, and the more I understood what exactly the results meant. Just this past week, we’ve started designing our own series of tests that have not been run before.

Outside of the lab, I’ve also enjoyed going out to lunch with my coworkers. Mostly I sit in the sun just outside our lab with the other intern to eat and chat, but every now and then we’ll take a trip to Chipotle or grab In-N-Out with our coworkers. One afternoon, we drove around Alameda to a Moroccan restaurant with a stunning view of the city and a nearby aircraft carrier-turned-museum. I have really enjoyed the first two weeks at Imprint Energy and have learned so much already. I am looking forward to this summer!

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