Dynamic control and performance assessment / optimization of secondary battery cell finishing (formation / aging / sorting / grading) utilizing simultaneous inline electrochemical methods and closed-loop process control

Abstract

To provide a system for dynamic control and optimization of a secondary battery finishing process to improve quality, throughput, and safety of cells produced and to facilitate a finishing (formation / aging / sorting / grading) process.SOLUTION: A system includes a closed-loop process control module that is configured to process real-time in-line manufacturing data derived from at least one of electrochemical impedance spectroscopy (EIS), self-discharge analysis (SDA), amperometric, or potentiometric battery measurements. The control module provides real-time feedback to predecessor operations / materials for confirmations, refinements, corrections, and / or recognition or isolation of better / worse performance characteristics. It also provides feedforward information of aspects recognized that may indicate performance deviations from the norm.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates generally to electrochemical battery manufacturing, and more particularly to control, evaluation, and optimization techniques to improve the quality, throughput, and safety of secondary batteries, such as lithium-ion cells, during finishing processes. [Background technology]

[0002] A lithium-ion cell is a type of secondary battery and includes four main parts: a positive electrode (cathode), a negative electrode (anode), a separator placed between the electrodes to prevent contact and short circuiting, and an electrolyte. Examples of cathode active materials can include, but are not limited to, mixed metal oxides, metal phosphates, or related materials. Examples of anode materials can include, but are not limited to, graphite, silicon, or composites thereof. The electrolyte provides the transport of ions and may be a liquid, solid, or liquefied gas. Battery manufacturing begins with the fabrication of large sheets of double-sided coated anode copper substrate and double-sided coated cathode aluminum substrate. The electrodes are manufactured in a continuous roll-to-roll process in which premixed anode or cathode materials are coated onto sheets of metal substrates that act as current collectors. The electrode sheets are cut into appropriately sized double-sided coated metal substrates.

[0003] There are two main methods for constructing individual cells. Winding the cells into a "jelly roll" of electrodes and separators is one, combining separate electrode sheets and separator film with a z-fold or stack between each electrode is another. Cylindrical cells and some prismatic cells are wound on a rotating machine that is fed with rolls of anode and cathode electrodes and two rolls of separator film. Pouch cells and some prismatic cells utilize a robotic arm to alternate anode and cathode stacks as the separator film unfolds from overhead to interlace the stack, which is completed with a rotation of the separator film.

[0004] Lithium-ion cells are assembled in an uncharged state. The initial charging or formation of the cell is critical for the expected cycle life and energy capacity. It involves multiple stages where the rate and duration and current / voltage limits of each step are designed to form a metastable passivation layer called solid electrolyte interface (SEI) layer on the anode. The formation of the SEI layer consumes some of the lithium from the available lithium in the cell and is a product of electrolyte decomposition. Similarly, a cathode electrolyte interface (CEI) is also developed, which brings uniform passivation to the positive electrode. This CEI layer allows to maintain ion transport pathways while suppressing undesirable side reactions between the positive electrode particles and the electrolyte. However, for the anode SEI, forming too thin and / or inhomogeneous SEI layer allows electrolyte ions to flow to the anode material, increasing the risk of lithium plating and / or lithium dendritic growth, decreasing the life cycle of the cell. Producing the proper SEI layer thickness is one of the key process parameters in the cell production process, more specifically, in the cell finishing area. Cell finishing operations also include outgassing which is a result of the formation process, and cell aging to screen out cells which have unacceptable levels of self-discharge.

[0005] The formation and finishing processes are separated from the rest of the production process because a failed cell can catch fire when it is first charged, resulting in rapid failure known as "thermal runaway." Because of the long periods of time required to perform the formation and aging processes (often three weeks or more), this process typically occupies the largest area in the factory, represents a significant operation in inventory, and consumes approximately 40% of the capital expenditure required for a major factory project. Currently, the formation and aging of lithium-ion cells are performed according to static recipes that are not adjusted during any process based on real-time observations.

[0006] Specifically, finishing encompasses the functions of formation for charge / discharge to "form" the solid electrode / electrolyte interface SEI for the anode and CEI cathode. This is a long and critical process that greatly impacts the length of cell life. It can take at least 24-48 hours and requires significant space in racking, power electronics, energy, and in-process inventory. The process of aging the battery cells is even more time consuming, taking 2-3 weeks. This also requires significant floor space to stage and store the cells. Determining ΔOCV or voltage drop is a common test to determine cell quality and final cell grading. The main drawback of this approach is that delays can result in the production of substandard batteries in significant numbers without timely quality feedback to correct, which results in the accumulation of scrap and / or degraded suboptimal product. As is evident, this conventional methodology impedes cell throughput and in operandi impedes optimization of Li-ion cell performance. Summary of the Invention

[0007] The present invention is based in part on the development of a method for dynamic performance assessment and control of secondary battery cell finishing, which encompasses the formation, aging, sorting, and grading steps in battery production. The method utilizes simultaneous, in-line, multi-frequency fast response electrochemical impedance spectroscopy (EIS) and closed-loop process control, along with real-time data analysis, for the battery cell finishing process. The method reduces time, capital expenditures, operational expenditures, and increases battery cell throughput and quality. In addition, the present invention allows for fast performance feedback to prior actions for confirmation, improvement, and / or correction. The present invention is applicable to any secondary battery type that undergoes a formation / aging process. Although the present invention is described in the production of lithium-ion battery cells, it is understood that the present invention is also applicable to, for example, sodium-ion batteries and solid-state batteries.

[0008] The present invention addresses the high throughput, superior quality requirements of large-scale mass production facilities. The use of electrochemical techniques such as EIS in the formation and / or aging process provides capabilities that are novel in the Li-ion battery production industry. This capability checks the battery cell's ohmic resistance, surface film (SEI / CEI), and charge transfer resistance to ensure the highest quality "start of life" levels. Dynamic closed-loop control allows fast recognition of quality defects for upstream adjustment and correction to minimize downtime and scrap waste. For example, "bad cells" can be recognized early during the formation process to prevent aging. Advanced charge / discharge algorithms are used to optimize the batteries in the formation process, smartly charge / discharge, and ensure plant and personnel safety.

[0009] The present invention reduces forming / aging floor space requirements and equipment and capital and operating costs compared to conventional systems. Specifically, the present invention allows for dramatic reductions in forming times. For example, forming can be reduced to less than 24 hours compared to several days with current technology, and aging can be reduced to less than one hour compared to two to three weeks with current technology.

[0010] In one aspect, the present invention is directed to a system for dynamic control and optimization of a secondary battery cell finishing process that includes a closed-loop process control module configured to manage or process real-time in-line manufacturing data, determine charging and discharging protocols for lithium-ion batteries during formation, and determine cell performance classifications for lithium-ion batteries during aging. The in-line data is derived from electrochemical impedance spectroscopy (EIS), self-discharge analysis (SDA), amperometric measurements, and / or potentiometric measurements. Process parameters monitored by the module include, for example, ohmic resistance R Ω , charge transfer resistance R ct , leakage current I leak, open circuit voltage (OCV), and / or voltage drop (ΔV).

[0011] In one embodiment, the closed loop functionality of the control module allows for the comparison of in-line real-time process parameters to a set of preselected values ​​and / or a computerized supervisory control system. Based on deviations of the in-line values ​​from the set values, the control module instructs the EIS measurement system and / or the SDA measurement system to execute a set of preconfigured charge / discharge protocols to move the measurements closer to the selected target values. Based on deviations derived from the feedback data, the control module can execute, terminate, or implement alternating charge / discharge procedures. This feature of closed loop feedback control allows for optimization of the time spent in the formation and / or aging process that is not possible with conventional offline formation and aging stations.

[0012] In another aspect, the present invention is directed to a system for feedback alert and / or control of a secondary battery cell finishing process including a closed loop process control module configured to manage or process real-time in-line production data from charge / discharge functions, EIS measurements, SDA measurements, current measurement systems, and / or potentiometric measurement systems to identify and quantify performance deviations from a standard and identify previous operating deviations to their potential contribution from the standard. Representative examples of monitored process parameters include, for example, current (I), voltage (V), ohmic resistance R, and the like. Ω、 Charge transfer resistance R ct , leakage current I leak , open circuit voltage (OCV), and voltage drop (ΔV).

[0013] In yet another aspect, the present invention is directed to a system for feed-forward alert and / or control of a secondary battery cell finishing process that includes a closed-loop process control module configured to manage or process real-time in-line production data from charge / discharge functions, EIS measurements, SDA measurements, current measurement systems, and / or potentiometric measurement systems to identify and quantify performance deviations from a standard or criteria, and identify post-operation battery materials of similar attributes for potential contributions from that standard or criteria for laboratory analysis or isolation.

[0014] Performance deviations, which can be characterized as better or worse than normal or standard battery acceptable performance, can be evaluated by various techniques such as (i) statistical analysis of process parameters, (ii) rate of change comparison, (iii) application of parameter limits, (iv) data extraction (dQ / dV), (v) machine learning, and (vi) artificial intelligence. Historical data of material components used in the battery and process parameters employed in fabricating the battery are evaluated to determine their contribution to performance deviations. Operating parameters in battery manufacturing lines are constantly upgraded, especially in the formation, aging, sorting, and grading steps.

[0015] The closed-loop process control module may be configured to automatically adjust material and process parameters to establish normal battery performance and to identify material and process parameters that are detrimental and then subject to quality and / or safety review. The control module may also be configured to identify beneficial material and process parameters that improve battery performance. Finally, the control module may be configured to automatically trigger alarms and / or quarantine materials for further evaluation. [Brief description of the drawings]

[0016] [Figure 1] 1 illustrates a system including a manufacturing line and a controller for producing lithium ion batteries. [Diagram 2] 1 is a flow chart of a formation process. [Diagram 3] 1 is a flow chart of an aging process. [Figure 4] FIG. 1 shows a block diagram of a system for optimizing lithium-ion battery top-off. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] FIG. 1 shows a system 2 including a manufacturing line 4 and a controller 6 for making electrochemical cells and batteries. The manufacturing line 4 is configured to perform operations in the fabrication process. At a mixing station 8, individual anode and cathode slurries are typically prepared in batches. The anode slurry is prepared by mixing various anode components, including, for example, graphite, binders, and conductive agents, in a solvent. The source, lot, and amount of each component for each batch, as well as the mixing parameters used, such as temperature and tank agitation speed, are stored in the memory of the controller 6. Similarly, the cathode slurry is prepared by mixing various cathode components, including, for example, lithium oxide, binders, and conductive agents, in a solvent. Examples of lithium oxide include lithium nickel manganese cobalt (NMC), lithium iron phosphate (LFP), lithium cobalt oxide (LCO), and lithium nickel cobalt alumina (NCA). The source, lot, component quantities, and mixing parameters for each batch are stored in the memory of the controller 6. If a solid electrolyte is used, the electrolyte slurry may be prepared by a mixing process. The material start history, genera, component quantities, and mixing parameters for each batch are stored in the memory of the controller 6.

[0018] In the coating and drying station 10, the anode and cathode slurries prepared in the mixing station are coated onto the metal substrate to form the electrodes. The anode or cathode slurries are coated continuously in lanes or intermittently in patches on both sides of the current collector using a slot die coating head or other coating methods. The wet coated foil is fed directly into a long drying oven to evaporate the solvent. The thickness and coating weight applied to the electrode coating are measured by optical, x-ray, and / or beta absorptiometry, and this feedback can be used to control the coating machine. The drying stage is one of the most energy intensive steps of the cell production process. The drying process itself also imparts several important quality aspects to the electrode such as a uniform distribution of pores (porosity), avoidance of hard surfaces and blistering due to solvent evacuation, and the use of just the right amount of energy to achieve the desired drying. After coating, the coated foil undergoes a calendering process in step 12 where it is compressed by a pair of rotating rollers. This process helps to tailor the final physical properties of the electrode (thickness, bonding, conductivity, density, and porosity).

[0019] The operating parameters, conditions and quality aspects of the electrode coating and calendering process are monitored by various in-line sensors and the data is stored in the controller 6. To ensure high quality Li-ion batteries, it is important that the active materials in the anode and cathode slurries are uniformly mixed. In addition, (i) the same coating weight should be on both sides of the electrode, (ii) the top and bottom coatings are aligned, and (iii) the same thickness and density is on both sides of the electrode, which affects porosity and subsequent "wettability" during electrolyte filling. The electrodes must be free of contamination or defects (such as holes and missing coatings) and capable of carrying the required load (mAh / cm) to meet the cell energy storage requirements. 2 ) should be present. The particular materials, process parameters, deviations, etc. are stored in the controller 6.

[0020] After calendaring, the finished electrode is cleaned and fed to a slitting machine to be cut into thin strips and wound onto "daughter rolls" at slitting station 12. A vision system can be used to ensure proper operation and / or detect non-standard detection and the appropriate specific materials, process parameters, deviations etc. are stored in the controller 6.

[0021] The coil is then sent to a drying station 14 where a vacuum oven removes any residual moisture and solvent.

[0022] At separation station 16, the cell separator material is prepared for winding, or die cut for cell lamination, or prepared for a z-fold method, depending on the cell format process. The separator material may also be calendered to form a separator film, in a continuous moving sheet process, or may be slurry cast, for example, onto a substrate and cured as a discreate. The particular material and process parameters are stored in controller 6.

[0023] At lamination / winding station 18, the battery is constructed. Lamination is used to form pouch cells, and winding is used to form cylindrical and prismatic cells. The specific materials and process parameters are stored in the controller 6.

[0024] At packaging station 20, the batteries are placed into a protective container or shell. The specific materials and process parameters are stored in controller 6.

[0025] At the filling station 22, liquid electrolyte is added to the battery. The electrolyte comprises a lithium solution containing a solvent, additives, and salt. The amount, volume and / or weight of the lithium salt solution added, as well as the specific proportions of the ingredients, source, date, batch, are recorded in the controller 6.

[0026] In the formation station 24, the battery undergoes a series of charge and discharge cycles to build up solid electrolyte interface (SEI) and cathode electrolyte interface (CEI) protective layers on the anode and cathode, respectively. In the present invention, EIS is used to ascertain the electrochemical state of the SEI and / or CEI characteristics, which directly relate to the performance of the battery cell in situ, providing dynamic in-line closed loop process control. In addition to or instead of EIS measurements, amperometric, potentiometric, and / or self-discharge analysis (SDA) measurements can be utilized for parametric analysis of the dynamic response. Representative process parameters monitored include, for example, ohmic resistance R Ω、 Charge transfer resistance R ct , leakage current I leak , open circuit voltage (OCV), and voltage drop (ΔV). These methods are utilized to optimize the throughput, life, quality, and safety of the battery cells.

[0027] Data collected from electrochemical measurements are interpreted by Nyquist plots, Bode plots, or other conventional techniques. Data interpretation provides closed loop optimization of the formation process for fastest throughput. Additionally, trends can be established to identify poor performing cells and out of specification cells, or even higher performing cells. This can also establish grading / sorting. Interpretation provides traceability from preceding processes such as blending, electrode production (drying, calendaring, etc.), cell fabrication (winding, lamination, welding, electrolyte filling), etc., to be identified in a feedback fashion as possible root causes of defects.

[0028] In addition, post-operation materials with similar attributes are identified for potential contributions that can be utilized in feedforward for identifying deviations in performance from the baseline and for material alerts and / or control.

[0029] Fast response from measurement to feedback / feedforward enables recognition of quality defects for upstream adjustment / correction reducing downtime and scrap, thereby reducing forming / aging floor space and equipment. The overall result is an integrated, comprehensive manufacturing solution.

[0030] In the degassing and sealing station 26, the formation reactions generate various mixtures of hydrogen, carbon monoxide, carbon dioxide, hydrocarbons (methane, propane, etc.), and hydrofluorocarbons (HFCs), which are removed from the cell and then sealed.

[0031] In the aging station 28, the sealed cells undergo a coordinated heating regime. In the present invention, self-discharge analysis is used to measure "leakage current", preferably in microamperes, for in-line process control. Specific process parameters are stored in the controller 6.

[0032] At sorting station 30 the batteries are graded. The grading, materials, performance and parameters of a particular battery are stored in controller 6.

[0033] To facilitate movement of batteries and cells between forming stations 24, degassing and sealing stations 26, aging stations 28, and sorting stations 30, manufacturing line 4 (FIG. 1) can include an automated storage and retrieval system (AS / RS) and / or an autonomous mobile robot (AMR) or other automated material movement methods. In this manner, the manufacturing line can accommodate large volumes of batteries with minimal personnel.

[0034] 2 shows an exemplary formation process in which electrodes are produced in step 100 and electrochemical cells are assembled into batteries in step 102. The formation process is controlled by an algorithm 118. A plurality of batteries are positioned at a formation station, the batteries are connected to a charging circuit configured to connect the plurality of batteries, and the plurality of batteries undergo DC resistance measurements 104. Those that fail are removed for quality inspection 106. Those that pass undergo formation (108), where the batteries are charged (110), rested (112), and tested by EIS (114) per a protocol from the algorithm 118. (Note that the rest step 112 is optional, since EIS can be performed in situ with the charging function.) EIS and cycle data analysis 116 is applied. Those that fail are rejected, and those that pass continue the formation process according to the formation and optimization algorithm procedure 118. If the battery is not charging, proceed to step 110 and the battery is charged.

[0035] Batteries that pass the analysis step 116 and are charged are then discharged in step 120 according to the protocol from the algorithm 118 and rested for a length of time n before EIS pulses 124 are applied in step 122. (Note that rest step 122 is optional, as EIS can be performed in situ using the discharge function.) Another analysis protocol 126 removes defective batteries that fail. Batteries that initially pass this stage are returned to step 118 for additional formation. Some batteries that pass a second time can be subjected to additional charge / discharge cycles as needed in step 128. If the battery is in an acceptable condition, it proceeds to step 130, where it is finally charged to a 100% state of charge to complete formation 132 and proceeds to a cell aging 134 step.

[0036] FIG. 3 illustrates the aging process for batteries that have completed formation 200. Charged batteries undergo an initial cell measurement where the batteries undergo one or more tests, such as EIS, SDA, amperometric, and potentiometric analysis. Failed batteries are inspected for quality defects 204. Those that pass continue to the formation step 206 and are stored at a prescribed temperature for a specified length of time in step 210. The batteries then undergo a second cell measurement 212, and analysis of the data 216 identifies (i) defective batteries that are examined 204, (ii) batteries that meet certain quality specifications but require additional aging (conditionally passed), and (iii) batteries that pass, which proceed to grading 218. After grading, the completed batteries 220 are shipped to inventory 222. Conditionally passed batteries undergo a formation / optimization algorithm 214 where they are tested to determine whether to continue with another aging step 210 or to start again (reform) 208.

[0037] FIG. 4 illustrates a control module 300 that coordinates the functions of the manufacturing line 4 (FIG. 1). As used herein, the term "module" refers to any means for facilitating communication and / or interaction between elements of the manufacturing line and performing additional processes, tasks, and / or functions to support the operation of the manufacturing line, as described herein. In various embodiments, the control module 300 may be any hardware, software, firmware, electronic control components, processing logic, and / or processor devices, individually or in any combination. Depending on the embodiment, the control module 300 may be implemented or realized using a general-purpose processor (shared, dedicated, or group) controller, microprocessor, or microcontroller, and memory that executes one or more software or firmware programs, designed to perform the functions described herein; associative memory; digital signal processor; application specific integrated circuit (ASIC), field programmable gate array (FPGA); any suitable programmable logic device; combinatorial logic circuits including discrete gate or transistor logic; separate hardware components and memory devices; and / or any combination thereof.

[0038] The control module may comprise a computer system including a processing unit 302, memory 304, removable storage 312, and non-removable storage 314. Although an exemplary computing device is illustrated and described as a computer system, the computing device may take different forms in different embodiments. For example, the computing device may instead be a smartphone, tablet, smartwatch, or other computing device. Devices such as smartphones, tablets, and smartwatches are generally collectively referred to as mobile devices. Additionally, while various data storage elements are illustrated as part of the control module 300, the storage may also or alternatively include cloud-based storage accessible over a network such as the Internet.

[0039] The memory 304 may include volatile memory 308 and non-volatile memory 310. The computer system may include or have access to a computing environment that includes a variety of computer-readable media, such as volatile memory 308 and non-volatile memory 310, removable storage 312 and non-removable storage 3144. Computer storage may include random access memory (RAM), read only memory (ROM), erasable programmable read-only memory (EPROM) and electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disc read-only memory (CD ROM), Digital Versatile Disk (DVD) or other optical disk storage, magnetic cassettes, magnetic tapes, magnetic disk storage, or other magnetic storage devices capable of storing computer-readable instructions for performing the functions described herein.

[0040] The computer system includes or can access a computing environment including an input 318, an output 320, and a communication interface 316. The output 320 can include a display device such as a touch screen that can also function as an input device. The input 318 can include one or more of a touch screen, a touch pad, a mouse, a keyboard, a camera, one or more device-specific buttons, one or more sensors integrated within the control module 300 or coupled via a wired or wireless data connection, and other input devices 318. The computer system can operate in a networked environment using communication connections to connect to one or more remote computers, such as database servers including cloud-based servers and storage. The remote computers can include personal computers (PCs), servers, routers, network PCs, peer devices or other common network nodes, and the like. The communication connections may include a Local Area Network (LAN), a Wide Area Network (WAN), cellular, WiFi, Bluetooth, or other networks.

[0041] Computer readable instructions stored on a computer readable storage device are executable by the processing unit 302. Hard drives, CD-ROMs, and RAM are some examples of articles that include non-transitory computer readable media, such as storage devices. The terms computer readable media and storage devices do not include carrier waves. For example, the computer program 306 can be used to cause the processing unit 302 to perform one or more of the methods described herein.

[0042] It is understood that while a single control module can control the entire manufacturing line 4 (FIG. 1), individual stations in the manufacturing line can be equipped with control modules to specifically monitor and adjust devices associated with the particular station. For example, a data analysis module 322 is used to receive and process in-line data for analysis and visualization. A communication module 324 is used to send performance evaluation metrics to a manufacturing execution system (MES) 326 or a distributed control system (DCS) 328, which may be located in a remote server, to adjust process parameters. The MES or DCS can then instruct an automated storage and retrieval system and / or an autonomous mobile robot to operate the batteries in the forming, aging, and sorting stations. The MES or DCS can be incorporated into a computer system such as a "centralized operations console" or "integrated operations center," or equivalent, and the data can be displayed on a human-machine interface (HMI). The communications module 324 can transmit in-line process information obtained from the formation and aging stations to a safety control system 330 that can provide early battery damage detection mechanisms, such as early smoke or gas and / or heat detection from the battery, thermal imaging, electrolyte vapor detection, and related safety measures to prevent thermal runaway.

[0043] The foregoing has described the principles, preferred embodiments, and modes of operation of the present invention. However, the invention should not be construed as limited to the particular embodiments discussed. Instead, the above-described embodiments should be considered as illustrative rather than limiting, and it is to be understood that modifications may be made therein by those skilled in the art without departing from the scope of the invention as defined by the following claims.

Claims

1. A system for dynamic control and optimization of a secondary battery cell finishing process comprising a closed-loop process control module configured to process real-time in-line manufacturing data derived from at least one of electrochemical impedance spectroscopy (EIS), self-discharge analysis (SDA), amperometric, or potentiometric battery measurements.

2. The battery measurement is based on the ohmic resistance R Ω , charge transfer resistance R ｃｔ , leakage current I ｌｅａｋ 13. The system of claim 1, comprising a process parameter selected from the group consisting of: open circuit voltage (OCV), voltage drop (ΔV), and combinations thereof.

3. 1. A system for feedback alert and / or control of a secondary battery cell finishing process, comprising: a closed loop process control module, the closed loop process control module comprising: (i) processing real-time in-line production data from charge / discharge functions, electrochemical impedance spectroscopy (EIS) measurements, self-discharge analysis measurements (SDA), amperometric measurements, and / or potentiometric measurements; (ii) identifying deviations in battery performance from a standard; (iii) the system is configured to identify historical battery manufacturing operating conditions that potentially contribute to deviations in battery performance from the baseline.

4. 1. A system for feed-forward alert and / or control of a lithium ion battery cell finishing process, comprising: a closed loop process control module, the closed loop process control module comprising: (i) processing real-time in-line production data from charge / discharge functions, electrochemical impedance spectroscopy (EIS) measurements, self-discharge analysis measurements (SDA), amperometric measurements, and / or potentiometric measurements; (ii) identifying deviations in battery performance from a standard; (iii) A system configured to identify post-operation materials of similar attributes for potential contribution from the baseline for laboratory analysis and / or segregation.

Images