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All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

New Hayabusa2 and OSIRIS REx Curation Facilities at Nasa Johnson Space Center

Asteroids are made up of rocky material that is left over from the formation of our solar system [1]. This material holds the key to unlocking information about the history of the planets and our sun. Hayabusa2 and OSIRIS-REx are two sample return missions that have collected rocky material from carbonaceous asteroids which are rich in water, carbon, and organic compounds [1]. Hayabusa2 is a spacecraft that collected samples from asteroid Ryugu launched by the Japan Aerospace Exploration Agency (JAXA). Samples were returned to Earth in December 2020 and 10 percent of the collected material is currently housed in a state-of-the-art laboratory at NASA Johnson Space Center (JSC) dedicated to Ryugu material [1]. OSIRIS-REx is a spacecraft launched by NASA that collected samples from asteroid Bennu. The samples are on their journey to Earth and will arrive in September 2023. They will be stored in a separate cleanroom dedicated to Bennu material. From these two missions, scientists will examine dust particles and rocky material to research clues on how the early solar system formed and how life began [2]. Because these samples are so precious and rare, it is important to keep them free from Earth contamination. In September of 2020, a massive construction project began to provide curation facilities to meet the needs of two incoming asteroid collections, Hayabusa2 and OSIRIS-REx. Despite numerous setbacks caused by the coronavirus pandemic, these facilities have been completed in the fall of 2021. Some of these setbacks included strict PPE requirements, keeping safe working distances as well as access to the facilities as NASA was operating under a Stage 3 condition in response to the pandemic. These facilities will provide curation laboratories to safely house the precious asteroid samples as well as facilities to manipulate samples, do sample preparation and process samples into and out of the labs for future studies by the scientific community. The lab suite consists of several different rooms including an initial anteroom (ISO 7), a staging area (ISO 7), two gowning areas (one for OSIRIS-REx and one for Hayabusa2; both ISO 6)), the Haybusa2 Curation Laboratory (ISO 5), the OSIRIS-REx Curation Laboratory (ISO 5), an ultramicrotomy laboratory (ISO 7) and a thin section laboratory (not a cleanroom). To maintain cleanliness levels necessary for these lab spaces quarterly to monthly Balazs organic and inorganic sampling has been conducted on a regular basis before, during and after the construction project to monitor the cleanliness levels in the new labs that will house the asteroid samples. These new facilities feature a Ruuvi (Grafana) monitoring system that measures temperature, humidity, and pressure of the lab suite. This is a small puck shaped sensor that sends signals to the Grafana cloud where the data can be plotted and set up on dashboards within the lab suite. These sensors are easy to set up and install and they run off a cell battery that is good for 3-5 years before needing replacement. This system can deliver text messages and emails to the appropriate personnel when values fall outside of set limits. In addition to the monitoring system, this new lab suite features viewing windows from several different locations and sliding motion censored doors. We have obtained some state-of-the-art equipment to outfit the lab spaces (desiccators, microscopes, ultramicrotome) and are in the process of outfitting the suite with additional items such as: nitrogen gloveboxes, additional desiccators, micromanipulators, etc. The Hayabusa2 samples provided to NASA by JAXA included 23 millimeter sized grains and 4 containers with finer material. OSIRIS-REx is expected to return as much as 400 grams of asteroid Bennu. Samples will be stored in a nitrogen glove box and separated into nitrogen sealed transfer containers. Small Bennu and Ryugu particles will be handled and prepared (e.g., ultra-thin sections for scanning electron microscopy (SEM) or transmission electron microscopy (TEM)) using an Axis Pro micromanipulator and Leica EM UC7 ultramicrotome. Analyzing samples at the atomic scale will provide greater insight to the origins of the solar system and life formation on Earth. All the curation preparation for these sample collections is essential to ongoing research and efforts to understand our solar system, both nowand for future generations.

Curation↗
NASA NTRS2012

Rugged, Portable, Real-Time Optical Gaseous Analyzer for Hydrogen Fluoride

Hydrogen fluoride (HF) is a primary evolved combustion product of fluorinated and perfluorinated hydrocarbons. HF is produced during combustion by the presence of impurities and hydrogen- containing polymers including polyimides. This effect is especially dangerous in closed occupied volumes like spacecraft and submarines. In these systems, combinations of perfluorinated hydrocarbons and polyimides are used for insulating wiring. HF is both highly toxic and short-lived in closed environments due to its reactivity. The high reactivity also makes HF sampling problematic. An infrared optical sensor can detect promptly evolving HF with minimal sampling requirements, while providing both high sensitivity and high specificity. A rugged optical path length enhancement architecture enables both high HF sensitivity and rapid environmental sampling with minimal gaseous contact with the low-reactivity sensor surfaces. The inert optical sample cell, combined with infrared semiconductor lasers, is joined with an analog and digital electronic control architecture that allows for ruggedness and compactness. The combination provides both portability and battery operation on a simple camcorder battery for up to eight hours. Optical detection of gaseous HF is confounded by the need for rapid sampling with minimal contact between the sensor and the environmental sample. A sensor is required that must simultaneously provide the required sub-parts-permillion detection limits, but with the high specificity and selectivity expected of optical absorption techniques. It should also be rugged and compact for compatibility with operation onboard spacecraft and submarines. A new optical cell has been developed for which environmental sampling is accomplished by simply traversing the few mm-thick cell walls into an open volume where the measurement is made. A small, low-power fan or vacuum pump may be used to push or pull the gaseous sample into the sample volume for a response time of a few seconds. The optical cell simultaneously provides for an enhanced optical interaction path length between the environmental sample and the infrared laser. Further, the optical cell itself is comprised of inert materials that render it immune to attack by HF. In some cases, the sensor may be configured so that the optoelectronic devices themselves are protected and isolated from HF by the optical cell. The optical sample cell is combined with custom-developed analog and digital control electronics that provide rugged, compact operation on a platform that can run on a camcorder battery. The sensor is inert with respect to acidic gases like HF, while providing the required sensitivity, selectivity, and response time. Certain types of combustion events evolve copious amounts of HF, very little of other gases typically associated with combustion (e.g., carbon monoxide), and very low levels of aerosols and particulates (which confound traditional smoke detectors). The new sensor platform could warn occupants early enough to take the necessary countermeasures.

Pilgrim, Jeffrey↗
DOE OSTI2025

Controlled phosphate doping into nanoscopic SiO 2 proton conducting membranes

This article describes a method to introduce phosphate (PO 4 ) into SiO 2 atomic layer deposition (ALD) films in a self-limiting fashion. The method involves the use of a less common phosphate precursor, trimethyl phosphite [P(OMe) 3 ], to introduce PO 4 as a low-level dopant, <1 at. %, into a SiO 2 ALD process using bis(ethylmethylamino)silane and a modified O 3 conversion. P(OMe) 3 does not deposit a film with typical oxygen sources but incorporates as PO 4 in an ABC-type ALD scheme at deposition temperatures ranging from 100 to 300 °C. Addition of up to ∼1 at. % of PO 4 does not significantly impact the film density or concentrations of carbon and nitrogen impurities, which are both <0.4 at. %. Despite the relatively low dopant concentrations, PO 4 incorporation is shown to have a large impact on transport properties of the film. When explored as proton (H + )-conducting membranes, undoped SiO 2 ALD films showed H + conductivities (3 × 10 −6 –8 × 10 −5 S cm −1 ) and low H 2 permeabilities (<10 −9 cm 2 s −1 ) when measured at room temperature. The addition of PO 4 is shown to increase H + conductivity to 2 × 10 −4 S cm −1 , while maintaining low H 2 permeability of <10 −9 cm 2 s −1 . The ratio of H + conductivity to H 2 permeability, a key performance metric for H + -conducting membranes used in water electrolyzers, exceeds that of commercial Nafion-117 membranes. Here, the moderate H + conductivity and very low H 2 permeability of PO 4 -doped SiO 2 films make them promising candidates as fluorine-free replacements for Nafion in applications such as water electrolysis, hydrogen fuel cells, and redox flow batteries.

Atomic layer deposition↗
DOE OSTI2021

Solid-state batteries and the critical role of interfaces

The Grand Challenge for the next generation of energy storage technologies is no longer the identification of electroactive cathode or anode materials thanks to extensive worldwide synthesis efforts along with theory and modeling like the Materials Project.1 Instead, the critical challenges revolve around assembling materials in the right architecture to achieve maximum performance and cell life at reasonable temperatures and pressures. Nowhere is this more critical than on the next generation of energy storage technologies revolving around all solid-state batteries. These batteries are the ultimate challenge for materials science requiring new ways to assemble multiple dissimilar materials such that: (1) interfaces are optimized to facilitate ion motion across the different compounds while (2) maintaining chemical stability and (3) simultaneously preserving the crystal structures of each phase during (4) large volume changes due to shuttling of lithium, at (5) room temperature and under (6) atmospheric pressure. To address these requirements will require insights and expertise from research fields outside the traditional lithium-ion battery community such as solid oxide fuel cells, synthesis science, barrier layers, interface formers, sintering, and mechanical properties.

25 ENERGY STORAGE↗
DOE OSTI2022

Predictive coarse-grained (CG) modeling of morphologies in polymer nanocomposites with specific and directional intermolecular interactions (Final Report)

The overarching goal of the proposed work was to develop predictive models for investigating structure and dynamics in soft materials with chemistries that have specific and directional molecular interactions. The motivation behind studying materials with specific and directional interactions lies in the many desirable features these interactions provide when designing novel soft materials. Soft materials with specific and direction interactions (such as hydrogen bonds or H-bonds) can have a) thermally reversible phase behavior with different functions with varying temperature, b) precisely tuned nanostructure with desirable geometries that afford unique physical properties (e.g., color response, mechanical properties) and c) well-mixed/blended morphologies that are useful for variety of applications in energy field (e.g., materials for batteries require use of blended polymers where one domain gives superior mechanical properties and one domain promotes electrical conduction). Notably, biology makes extensive use of specific and directional interactions, in many cases based on H-bonds, to construct materials with precisely defined architectures and properties. Engineered soft materials with precisely tuned nanostructures and improved processiblity through thermoresponsive phase behavior are useful in numerous applications that are relevant to the Department of Energy (DOE) including high efficiency electronic devices, light-weight high-strength composite materials for batteries and fuel cells, and polymer membranes for separations, etc. While past computational studies have been tremendously useful in understanding molecular phenomena and guiding synthesis of new macromolecular soft materials for a wide variety of applications, the inability to capture small scale specific and directional interactions alongside macromolecular length and time scales represented a key limitation of most studies to date. Our work in this project addressed this grand challenge in computational materials chemistry, i.e., ability to model the anisotropic, directional, and specific interactions that govern the behavior of many macromolecular soft matter systems of interest, thus, has greatly expanded the predictive potential of simulations. Specifically the key outcomes were: successful development of new coarse-grained (CG) polymer models to study generic and specific polymer chemistries in which hydrogen-bonding interactions are dominant. These CG models were then used in molecular simulations to study structure and thermodynamics in polymer nanocomposites and blends; some studies were conducted in collaboration with experimentalists. We also published a perspective and a viewpoint which included some of the work we completed in this DOE project; we believe these perspective and viewpoint articles guide other researchers in the soft materials community on how to extend the computational approaches and models we have developed for the purposes of their studies.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Nanoscopic Plugs Block Hydrogen Crossover in Submicron Thick Proton-Conducting SiO 2 Membranes for Water Electrolysis

Zero-gap electrolyzers based on submicron thick proton-conducting oxide membranes (POMs) represent a promising approach to increasing the efficiency of H 2 production from water electrolysis while moving away from conventional perfluorosulfonic acid (PFSA) membranes. A critical barrier to the commercialization of such electrolyzers is that the ultrathin nature of POMs, which is necessary to achieve low cell resistance, makes them more susceptible to defects that can lead to unacceptably high rates of H 2 crossover. Herein, we demonstrate an approach to mitigate this problem through selective deposition of carbon-containing silicon oxide (SiO x C y ) “nanoplugs” into the defects of submicron thick SiO 2 membranes using a facile electrochemically mediated deposition process. Selective deposition of nanoplugs within the defects was verified by multiple characterization techniques, while scanning electrochemical microscopy (SECM) was used to confirm selective plugging of H 2 -crossover hotspots associated with defects at identical locations. Thanks to the use of nanoplugs, the H 2 permeance of 250 nm thick SiO 2 membranes was reduced by 5 to 6 orders of magnitude compared to the unmodified atomic layer deposition (ALD) SiO 2 membranes while having negligible impact on the ionic resistance of the membrane. These plug-modified membranes also enabled safe and stable operation of a zero-gap full cell electrolysis cell, in contrast to cells lacking nanoplugs that produced anode effluent streams having H 2 concentrations near or exceeding the lower flammability limit (LFL) of H 2 . Furthermore, beyond water electrolysis, this defect-sealing strategy has the potential to be broadly implemented in other applications, such as fuel cells and flow batteries, offering a versatile solution to mitigate crossover-related performance losses.

ALD SiO2↗
DOE OSTI2021

Fast Charging of Li-Ion Cells: Part V. Design and Demonstration of Protocols to Avoid Li-Plating

Fast charging of Li-ion batteries would make “fueling” of electric vehicles comparable in time to fueling of gasoline-powered cars, increasing consumer appeal of the new technology. Taking the US Department of Energy goal of safe 6 C charging to 80% capacity as a guide, we describe approaches that can mitigate Li plating on the graphite anode. To make this possible, a variable-rate anode potential charging protocol has been implemented by using a microprobe reference electrode to continuously monitor and adjust the current, in this way avoiding low anode potentials that favor Li deposition. Various implementations of the anode potential control are considered using electrochemical modeling and compared with the experimental data. For charge to 80% capacity at 30 °C, an average C-rate of 4.97 C was obtained for an NCM523/graphite cell with 70 μ m thick graphite electrode and 7.40 C for a cell with 47 μ m thick graphite electrode. Our electrochemical model accounts for these observations and provides a means to extrapolate the approach to other cell designs and operation regimes, drawing the maximum average fast charging rates that can still avoid Li plating.

25 ENERGY STORAGE↗
DOE OSTI2022

Uniform lithiophilic layers in 3D current collectors enable ultrastable solid electrolyte interphase for high-performance lithium metal batteries

Uniform lithium plating/stripping during charging/discharging in 3D lithiophilic current collectors (3DLCC) is essential to suppress growth of lithium dendrites and to mitigate infinite volume variations of lithium metal for long-lived lithium metal batteries. Additionally, this study reveals the decisive role played by uniformity of the lithiophilic layer of the 3DLCC in achieving uniform lithium plating/stripping. Herein, a series of metal oxide-based 3DLCCs are successfully fabricated with a simple and an ultrafast solution combustion method, from which formation of a uniform and stable lithium dendrite-free solid electrolyte interphase via a uniform lithiophilic layer is demonstrated. Taking Co 3 O 4 as the lithiophilic material deposited on a nickel foam as the 3DLCC (Co@NF) for a proof of concept, the loading amount of Co 3 O 4 , closely correlated with the uniformity of the Co 3 O 4 layer, is modulated to optimize its lithium ion hosting performances. With a uniform Co 3 O 4 layer grown in the 3DLCC, an ultralow nucleation overpotential of 33.4 mV is achieved in half-cell tests at 1 mA cm -2 and 1 mAh cm -2 , and a high Coulombic efficiency of 97.1% is maintained after 210 cycles under a severe cycling condition of 2 mA cm -2 and 1 mAh cm -2 . A small polarization voltage of 13 mV together with an ultralong cycle life of 2400 h at 0.5 mA cm -2 and 1 mAh cm -2 in symmetric Li cells is achieved. Moreover, the composite Li anode delivers sensational rate capability and cyclability in full-cells. This work not only provides new and valuable insights into the interphasial chemistry of solid electrolyte interphase layers, but also sheds light on the development of ultrastable lithium metal batteries.

25 ENERGY STORAGE↗
NASA NTRS2018

X-57 Maxwell Battery from Cell Level to System Level Design and Testing

The X-57 Maxwell flight demonstrator aircraft is an experimental aircraft designed to demonstrate radically improved aircraft efficiency with a 3.5 times aero-propulsive efficiency gain at a "high-speed cruise" flight condition for comparable general aviation aircraft. These gains are enabled by integrating the design of a new, optimized wing and a new electric propulsion system. There are 14 propulsors in all: 12 high lift motor that are only active during takeoff and climb, and 2 larger motors positioned on the wingtips that operate over the entire mission. The innovative electric propulsion system will have as its primary power a Li-ion battery system. Integrating a battery system into this innovative design poses unique challenges that require careful design considerations across the system. The presentation will cover a breakout of X-57 battery specifications, battery design and lessons learned when designing a high voltage battery system to power electrified aircrafts.

Hernandez Lugo, Dionne↗
DOE OSTI2023

Bipolar Membranes with an Electrospun 3D Junction

Freestanding bipolar membranes (BPMs) with an entirely new and transformative morphology were fabricated and characterized. The key disruptive design element was a water-splitting/water-generation junction layer of finite thickness composed of interwoven and interlocking electrospun anion-exchange polymer (AEP) fibers and cation-exchange polymer (CEP) fibers. Methods were developed to sandwich the 3D junction layer between two pre-formed dense AEP and CEP films., with the closure of all interfiber voids, where the processing steps are easily incorporated into a commercial roll-to-roll membrane manufacturing scheme. A series of membranes were made using different polymers and junction layers to identify the optimum morphology and composition for water-splitting and water-generation applications. For water splitting, the 3D junction BPMs worked remarkably well with operating current densities at/above 1.0 A/cm2 (10X greater than commercial BPMs) at a transmembrane voltage drop of only 1.1 V. In water generation mode, the 3D junction BPMs operated at 0.5 A/cm2, a world-record current density. The membranes were found to exhibit outstanding durability and can be manufactured at scale for low cost. The high operating current densities and stable long-term operation are due to the 3D junction layer design, where there is a high interfacial area for water splitting or water generation reactions and where the interlocking fibers prevent delamination of the outer films. These new BPMs are ideal candidate materials for both existing water-splitting electrodialysis separations and new electrochemical processes, such as large-scale direct air capture of CO 2 , reactors for CO 2 reduction, self-hydrating fuel cells, and redox flow batteries.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Lithiophilic CoF 2 @C hollow spheres towards spatial lithium deposition for stable lithium metal batteries

Lithium metal (LM) is a promising anode for next-generation batteries due to its high theoretical capacity and low electrode potential. Nonetheless, side reactions, volume change, and unwanted lithium dendrite growth seriously limit the practical application of LM. Herein, with the aid of a hard template approach, a novel lithiophilic CoF 2 -carbon hollow sphere (CoF 2 @C-HS) composite material is successfully prepared via a facile in-situ fluorination and etching strategy. The lithiophilic CoF 2 acts as nucleation sites to reduce nucleation overpotential as well as induces the spatial Li deposition and the formation of LiF-rich solid electrolyte interphase (SEI), and the hollow carbon matrix can enhance the electrical conductivity and offer free space for LM deposition. Theoretical simulations reveal that the synergistic effect of lithiophilic CoF 2 and hollow carbon matrix homogenizes the electric field distribution and Li + flux. Benefiting from these advantages, the CoF 2 @C-HS-modified copper substrate electrode delivers an enhanced Coulombic efficiency (CE) of 93.7% for 280 cycles at 1 mA cm –2 and 1 mA h cm –2 . The symmetrical cell using CoF 2 @C-HS can stably cycle more than 1800 h with a low voltage hysteresis of 11 mV at a current density of 0.5 mA cm –2 and an areal capacity of 0.5 mA h cm –2 . Moreover, the Li@CoF 2 @C-HS composite anode enables more than 300 stable cycles at 1 C with a capacity retention of 95% in LiFePO 4 -based full cell and 110 stable cycles at 1 C in LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811)-based high-voltage full cell. Finally, this work might shed a new light on designing lithiophilic hosts to spatially confine LM deposition, realizing dendrite-free LM anodes and the practical applications of LM batteries.

25 ENERGY STORAGE↗
DOE OSTI2024

A reversible four-electron Sn metal aqueous battery

Sn is a promising metal anode for aqueous batteries, with up to four-electron redox available per atom (903 mAh g −1 Sn ). However, practically harnessing the four-electron Sn(OH) 6 2− /Sn reversibility remains challenging due to limited mechanistic understanding. Here, in this study, we reveal a kinetically asymmetric redox pathway involving a successive four-electron plating and a stepwise 2 + 2 electron stripping through a Sn(OH) 3 − intermediate. The crossover of Sn(OH) 3 − induces a reversible self-discharge that reduces Coulombic efficiency but does not impact cyclability, demonstrated by four-electron Sn-Ni full cells that sustain >800 h of stable cycling. By tuning the ion selectivity of the separator to suppress Sn(OH) 3 − crossover while allowing OH − transport, we further demonstrate high Sn utilization (67%) and high energy density (143.1 Wh L −1 cell). The results provide key understandings of the tradeoffs in engineering reversible multi-electron metal anodes and define a new benchmark for practical energy density that exceeds any Sn-based aqueous batteries to date.

SN anode↗
DOE OSTI2021

An in situ generated polymer electrolyte via anionic ring-opening polymerization for lithium–sulfur batteries

The use of solid polymer electrolytes has previously proven to be an effective approach to address the lithium polysulfide dissolution and high electrode interfacial impedance of Li–S batteries via an in situ polymerization process. However, the conventional in situ synthesis employs a cationic ring-opening polymerization (CROP) of 1,3-dioxolane (DOL) catalyzed by a strong Lewis acid. New polymerization chemistry that is more compatible with Li–S chemistry needs to be developed to mitigate the disadvantages associated with the CROP process. Herein we report a new approach to in situ polymerize a set of new episulfide monomers in solution with LiTFSI salt via an anionic ring-opening polymerization (AROP). This new polymer system takes advantage of the inherent cell chemistry present in the Li–S cell through the nucleophilic lithium sulfides which are generated during the initial discharge cycle and act as the initiator for the polymerization. Additionally, their presence was shown to initiate the monomer solvents through AROP with no need for additional catalysts, rather than the more commonly utilized cationic systems which require an external Lewis acid catalyst. This work offers an important pathway toward in situ polymer electrolytes for Li–S batteries and offers a new avenue of exploration for polymer electrolyte synthesis.

25 ENERGY STORAGE↗
DOE OSTI2020

Controlling Surface Phase Transition and Chemical Reactivity of O3-Layered Metal Oxide Cathodes for High-Performance Na-Ion Batteries

O3-layered metal oxides are promising cathode materials for high-energy Na-ion batteries (SIBs); however, they suffer from fast capacity fade. In this work, we develop a high-performance O3-NaNi 0.68 Mn 0.22 Co 0.10 O 2 cathode for SIBs toward practical applications by suppressing the formation of a rock salt layer at the cathode surface with an advanced electrolyte. The cathode can deliver a high specific capacity of ~196 mAh g –1 and demonstrates >80% capacity retention over 1000 cycles. NaNi 0.68 Mn 0.22 Co 0.10 O 2 –hard carbon full-cells with practical loading (>2.5 mAh cm –2 ) and lean electrolyte (~40 μL) demonstrate ~82% capacity retention after 450 cycles. A 60 mAh single-layer pouch cell has also been fabricated and demonstrated stable performance. This work represents a significant leap in SIB development and brings new insights to the development of advanced layered metal oxide cathodes for alkaline-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2022

Facile Surface Coatings for Performance Improvement of NMC811 Battery Cathode Material

High nickel content layered oxide LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) is a promising cathode material with a high theoretical capacity of 200 mAh g -1 for use in high energy density lithium-ion batteries. However, its surface can easily get passivated by LiOH and Li 2 CO 3 due to its surface residual Li 2 O being reacting with ambient moisture and CO 2 . Herein, NMC811 was treated in a 3.0 M solution of lithium bis(fluorosulfonyl)imide (LiFSI) in dimethyl carbonate (DMC) at 60 °C for 8 h, 16 h and 24 h, respectively, resulting in coating of the NMC811 surface with LiF due to the basic nature of those residual lithium salts that react with LiFSI. The facile treatment of NMC811 in LiFSI/DMC not only improves the cycling stability but also enhances the capacity of the Li/NMC811 cells, mainly because of the thinning of the Li 2 CO 3 layer as suggested by cyclic voltammograms and impedance analyses. This method opens a new avenue for activation of passivated NMC811 particles for practical battery applications.

25 ENERGY STORAGE↗
NASA NTRS2009

Modular Battery Charge Controller

A new approach to masterless, distributed, digital-charge control for batteries requiring charge control has been developed and implemented. This approach is required in battery chemistries that need cell-level charge control for safety and is characterized by the use of one controller per cell, resulting in redundant sensors for critical components, such as voltage, temperature, and current. The charge controllers in a given battery interact in a masterless fashion for the purpose of cell balancing, charge control, and state-of-charge estimation. This makes the battery system invariably fault-tolerant. The solution to the single-fault failure, due to the use of a single charge controller (CC), was solved by implementing one CC per cell and linking them via an isolated communication bus [e.g., controller area network (CAN)] in a masterless fashion so that the failure of one or more CCs will not impact the remaining functional CCs. Each micro-controller-based CC digitizes the cell voltage (V(sub cell)), two cell temperatures, and the voltage across the switch (V); the latter variable is used in conjunction with V(sub cell) to estimate the bypass current for a given bypass resistor. Furthermore, CC1 digitizes the battery current (I1) and battery voltage (V(sub batt) and CC5 digitizes a second battery current (I2). As a result, redundant readings are taken for temperature, battery current, and battery voltage through the summation of the individual cell voltages given that each CC knows the voltage of the other cells. For the purpose of cell balancing, each CC periodically and independently transmits its cell voltage and stores the received cell voltage of the other cells in an array. The position in the array depends on the identifier (ID) of the transmitting CC. After eight cell voltage receptions, the array is checked to see if one or more cells did not transmit. If one or more transmissions are missing, the missing cell(s) is (are) eliminated from cell-balancing calculations. The cell-balancing algorithm is based on the error between the cell s voltage and the other cells and is categorized into four zones of operation. The algorithm is executed every second and, if cell balancing is activated, the error variable is set to a negative low value. The largest error between the cell and the other cells is found and the zone of operation determined. If the error is zero or negative, then the cell is at the lowest voltage and no balancing action is needed. If the error is less than a predetermined negative value, a Cell Bad Flag is set. If the error is positive, then cell balancing is needed, but a hysteretic zone is added to prevent the bypass circuit from triggering repeatedly near zero error. This approach keeps the cells within a predetermined voltage range.

Button, Robert↗