Ultra-thin lithium-ion battery implantable temperature sensor and preparation method thereof

Abstract

The present invention provides an ultra-thin lithium-ion battery implantable temperature sensor and a preparation method thereof. The preparation method comprises the following steps: applying a laser sensitizer suspension or solution to the surface of a flexible polymer film material, subsequently removing the solvent, irradiating the surface with a laser, forming an electrode activation pattern in the irradiated area, immersing the film in a metal plating solution for chemical plating, and forming a flexible metal electrode pattern at the activation pattern, thereby preparing a flexible substrate metal electrode based on LISM technology; then, using carbon-based temperature-sensitive functional ink, a grid-shaped thermal-sensitive unit precursor is printed on the flexible substrate metal electrode by ink direct writing 3D printing, and finally, undergoing freeze-curing treatment and drying, thereby obtaining an implantable temperature sensor. The present invention achieves the ultra-thin requirement of the sensor and implants it into a lithium-ion soft-pack battery for single-point and multi-point temperature monitoring, which is of great significance to the thermal management and thermal design of lithium-ion batteries.

Description

Technical Field

[0001] The present invention belongs to the field of temperature sensors and relates to an ultra-light and thin lithium-ion battery implantable temperature sensor and a preparation method thereof, and specifically relates to a lithium-ion battery safety monitoring implantable temperature sensor and its application in lithium-ion battery thermal management and safety warning. Background Art

[0002] Lithium-ion batteries, due to their high energy density, long cycle life, and lightweight design, have been widely used in everyday electronics, electric vehicles, mobile communications, and other fields. However, in recent years, safety incidents such as spontaneous combustion and explosions have become a frequent concern. Battery safety is affected by many factors, including internal factors such as material defects and aging, as well as external factors such as overcharging, over-discharging, impact, and puncture. Furthermore, internal heat in the battery cannot dissipate quickly, causing the temperature to continue to rise, ultimately leading to thermal runaway, resulting in serious consequences such as spontaneous combustion and explosion.

[0003] The key to monitoring the safety status of lithium-ion batteries lies in advanced sensors and sensing technologies. The most direct and common method of applying sensors to lithium-ion battery monitoring is to place them on the surface of the lithium-ion battery to directly sense the temperature, pressure and other information on the surface of the lithium-ion battery.

[0004] At present, considerable achievements have been made in the external safety monitoring of lithium-ion batteries. Hu et al. (X.Peng, J.Han, Q.Zhang, Y.Xiang, X.Hu. Real-time mechanical and thermal monitoring of lithium batteries with PVDF-TrFE thin films integrated within the battery. Sensors and Actuators A: Physical, 2022, 388, 113484.) prepared a new array sensor and used it to monitor the surface temperature and pressure of lithium-ion batteries. The sensor array consists of piezoelectric / thermoelectric polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and a thin film transistor array. The sensor array manufactured simultaneously monitors dynamic pressure and temperature, and can locate mechanical damage to lithium-ion soft-pack batteries during service.

[0005] Hayden et al. (Hayden L. Atchison, Zachary R. Bailey, David A. Wetz, Matthew Davis, John M. Heinzel. Fiber Optic Based Thermal and Strain Sensing of Lithium-Ion Batteries at the Individual Cell Level. Journal of The Electrochemical Society, 2021, 168, 040535.) used an optical distributed sensor detector (Optical Distributed Sensor Interrogator, ODiSI) to measure the surface temperature and shell deformation of 18650 batteries under normal and abnormal conditions. After many experiments, it was proved that ODiSI can measure temperature and stress / strain changes respectively, and has very high repeatability, which is a very promising lithium-ion battery monitoring technology.

[0006] Bliss et al. (Y.Hua, A.Cordoba-Arenas, N.Warner, G.Rizzoni, A multi time-scale state-ofcharge and state-of-health estimation framework using nonlinearpredictive filter for lithium-ion battery pack with passive balance control. J.Power Sources, 2015, 280, 293.) proposed a small, low-power, multi-frequency (1-1000Hz) impedance-based battery management system for multi-cell batteries of different capacities. Compared with traditional lithium-ion battery management systems (BMS), this technology tracks and responds to emerging mismatches and other electrical and thermal anomalies in each individual battery and takes action.

[0007] Based on the aforementioned existing technologies, using external sensors on lithium-ion batteries for battery safety management and status tracking is a relatively simple and mature method. Many electric vehicles incorporate external sensors within their battery modules. However, this inevitably increases battery size and changes battery shape. More importantly, externally monitored parameters cannot truly reflect the real-time changes in parameters such as temperature and pressure caused by various chemical reactions within the battery. In particular, external monitoring cannot quickly detect sudden changes in temperature or pressure. When the external temperature also experiences significant changes, the battery is likely to have already entered or is on the verge of thermal runaway. Furthermore, these measurements and associated protocols have not successfully ensured battery safety or improved efficiency. Data from maliciously aged and over-discharged batteries convincingly demonstrates that such BMSs are unable to identify cell mismatches and emerging faults. Therefore, to better monitor battery safety and performance in real time and manage status, the shift from external to implantable sensors is an inevitable trend in the development of high-performance, ultra-safe lithium-ion batteries.

[0008] Monitoring the surface temperature of a battery pack cannot accurately reflect the internal temperature of the battery. Furthermore, external parameter monitoring cannot fully simulate and reflect the electrochemical changes within the battery, making it impossible to effectively assess the potential thermal runaway risk of a battery cell. To address this issue, researchers have developed a variety of implantable thermocouples, thermal resistance sensors, and fiber optic sensors to monitor internal battery temperature, providing a variety of feasible solutions for preventing battery safety.

[0009] Li et al. (Z.Li, JZ, B.Wu, J.Huang, ZN, Y.Sun, F.An, N.Wu. Examining temporaland spatial variations of internal temperature in large-format laminatedbattery with embedded thermocouples. Journal of Power Sources, 2013, 241, 536.) used thermocouples in a 25Ah soft-pack lithium-ion battery to detect the temperature inside the battery in real time. The results showed that the temperature difference between the inside and outside of the battery was 1.1°C, and the internal thermal response time was tens of seconds longer than that of the outside. In addition, the temperature change on the surface of the battery cell during the 1.5C discharge process was greater than 10°C, which was much higher than the temperature change on the surface of the battery pack. Therefore, 12 thermocouples needed to be arranged to reflect the actual temperature of the battery cell surface.

[0010] Wang et al. (C.-Y. Wang, G. Zhang, S. Ge, T. Xu, Y. Ji, X.-G. Yang. Lithium-ion battery structure that self-heats at low temperatures. Nature, 2016, 529, 515.) implanted a platinum (PT1000) thermal resistor into a lithium coin cell to monitor its internal temperature in real time. The results showed that the temperature changes followed the same trend as those measured by a microcalorimeter. Furthermore, the embedded sensor significantly impacted the electrochemical performance, by as much as 50% at a 2C rate.

[0011] Micael et al. (Wenxin Mei, Zhi Liu, Chengdong Wang, Chuang Wu, Yubin Liu, Pengjie Liu, Xudong Xia, Xiaobin Xue, Xile Han, Jinhua Sun, Gaozhi Xiao, Hwa-Yaw Tam, Jacques Albert, Qingsong Wang, Tuan Guo. Operando monitoring of thermal runaway in commercial lithium-ion cells via advanced lab-on-fiber technologies. Nat Commun, 2023, 14, 5251.) proposed a hybrid sensor consisting of a Bragg grating and a Fabry-Perot cavity that can be used to simultaneously monitor strain and temperature. The dual-function sensor is embedded in lithium-ion pouch cells to monitor and distinguish in-situ internal strain and temperature changes in three different regions (top, middle, and bottom) of the battery.

[0012] Mei et al. (Li W, Li L, Sun Q. Direct Fabrication of High-resolution and high-performance flexible electronics via surface-activation-localized electrodeless plating. Chemical Engineering Journal, 2021, 416, 127644.) developed a compact multifunctional fiber optic sensor (12 mm in length and 125 μm in diameter) that can be inserted into commercial 18650 batteries to continuously monitor the internal temperature and pressure effects during battery thermal runaway.

[0013] However, to prevent the electrolyte in the battery from affecting the performance of the temperature sensor, embedded sensors must be packaged before they can be arranged on the surface of the battery cell and then connected to the electrodes to monitor the temperature inside the battery. This assembly process is relatively complex and costly, and the arrangement of multiple sensors will make the interior of the battery uneven, resulting in poor sealing of the battery. In addition, thermocouples are large in size, and when integrated with the battery, they have a significant impact on the battery's mass and volume, seriously affecting the battery's electrochemical performance. Fiber optic sensors, on the other hand, are small and flexible. When implanted inside lithium-ion batteries, they experience minimal loss in battery performance. However, there are still many challenges in the precise analysis of optical signals. Due to the above issues, these built-in sensor solutions are currently stuck in the laboratory stage and cannot be applied in actual production.

[0014] In summary, internal temperature monitoring, which can directly monitor the surface temperature of battery cells, is an effective method for ensuring safe battery operation. However, implantable temperature sensors currently face challenges such as complex manufacturing processes, high costs, poor sealing, and tangled wiring, hindering widespread application. Therefore, the development of implantable, flexible, ultra-thin temperature sensors / sensor arrays that can accurately monitor the internal temperature of lithium-ion batteries in real time is crucial for battery thermal management and safety warnings. Summary of the Invention

[0015] In order to solve the problems in the above-mentioned prior art, the present invention provides an ultra-thin lithium-ion battery implantable temperature sensor and a preparation method thereof. The present invention realizes the ultra-thin requirement of the sensor by combining laser activated selective metallization (LISM) technology with ink direct writing 3D printing technology, and implants it into the lithium-ion soft-pack battery for single-point and multi-point temperature monitoring, which is of great significance to the thermal management and thermal design of lithium-ion batteries.

[0016] To achieve the above objectives, the present invention is implemented by adopting a technical solution consisting of the following technical measures.

[0017] In one aspect, the present invention provides a method for preparing an ultra-thin lithium-ion battery implantable temperature sensor, which mainly comprises the following steps:

[0018] (1) Preparation of flexible substrate metal electrodes based on LISM technology

[0019] (1-1) mixing a laser sensitizer with a solvent to obtain a laser sensitizer suspension or solution, then applying the suspension or solution to a surface of a flexible polymer film by blade coating, and then removing the solvent to obtain a flexible polymer film having a sensitizer coating;

[0020] The flexible polymer film material is a polyimide film (PI) or a polyethylene terephthalate film (PET);

[0021] The laser sensitizer is an organic copper sensitizer or an inorganic copper sensitizer;

[0022] (1-2) irradiating the surface of the flexible polymer film having the sensitizer coating obtained in step (1-1) with a laser, forming an activated electrode pattern in the irradiated area, and then washing away excess laser sensitizer to obtain a laser-activated flexible polymer film;

[0023] (1-3) immersing the laser-activated flexible polymer film obtained in step (1-2) in a metal plating solution for chemical plating to form a flexible metal electrode pattern at the activated pattern, thereby preparing a flexible substrate metal electrode based on LISM technology;

[0024] (2) Preparation of implantable temperature sensors

[0025] (2-1) The following raw materials are mixed in parts by weight to prepare a carbon-based temperature-sensitive functional ink:

[0026] 3-5 parts of nanocellulose (CNF),

[0027] Single-walled carbon nanotubes (SWCNT) 1-1.5 parts,

[0028] 93.5 to 96 parts of solvent,

[0029] Among them, nanocellulose, single-walled carbon nanotubes and solvent totaled 100 parts;

[0030] (2-2) loading the carbon-based temperature-sensitive functional ink obtained in step (2-1) into the printing syringe of an ink direct writing 3D printer, and printing 2 to 4 layers of a grid-shaped thermosensitive unit precursor on the flexible substrate metal electrode obtained in step (1-3);

[0031] The printed product is then freeze-cured and dried to obtain an implantable temperature sensor.

[0032] Herein, the laser sensitizer in step (1-1) is an organic copper sensitizer or an inorganic copper sensitizer, both of which are conventional laser sensitizers in the art. Those skilled in the art can select a suitable organic copper sensitizer or inorganic copper sensitizer according to specific needs and process requirements.

[0033] In order to better illustrate the present invention and provide a preferred technical solution for reference, the laser sensitizer in step (1-1) is selected from any one of Cu2(OH)PO4, CuBr, Cu2O, copper (II)-phenanthroline complexes, and copper (II)-phthalocyaninetetrasulfonate.

[0034] In this article, the solvents described in steps (1-1) and (2-1) are conventional solvents in the field of chemical materials. Those skilled in the art can select appropriate solvents according to specific needs and process requirements, and can also optimize them according to their applicable purposes. For example, in step (1-1), the solvent plays a role in uniformly dispersing the laser sensitizer so that it is suitable for scraping on the surface of the flexible polymer film material, and in step (2-1), the solvent is the main ink component in the ink direct writing 3D printing technology. Those skilled in the art can optimize it based on the conventional ink solvents for the ink direct writing 3D printing technology in the prior art.

[0035] To better illustrate the present invention and provide a preferred technical solution for reference, the solvent selected in steps (1-1) and (2-1) includes any one of ethanol, deionized water, ethylene glycol, aqueous ammonia, dimethylformamide, and dimethyl sulfoxide. Theoretically, the solvents in steps (1-1) and (2-1) can be the same solvent or different solvents. In one preferred technical solution, the solvent in step (1-1) is ethanol; and the solvent in step (2-1) is deionized water.

[0036] In this document, in step (1-1), the laser sensitizer is mixed with a solvent to obtain a laser sensitizer suspension or solution. The ratio of the laser sensitizer to the solvent can be directly referenced by conventional laser sensitizer applications in the prior art, such as the ratio recommended in the product manual. To better illustrate the present invention and provide a reference technical solution, the laser sensitizer and solvent in step (1-1) are mixed at a ratio of 1 g: (15-40) ml.

[0037] In one of the technical solutions, in order to enable the irradiated area in step (1-2) to form a better activation pattern, the suspension or solution described in step (1-1) is scraped onto the surface of the flexible polymer film, preferably to form a coating with a thickness of 40 to 60 μm, and then the solvent is removed to obtain a flexible polymer film with a sensitizer coating.

[0038] Herein, the removal of the solvent in step (1-1) is performed by a conventional method of removing the solvent of a coating after coating in the chemical industry. For example, when the solvent is ethanol, the solvent is left to stand at room temperature until the ethanol evaporates.

[0039] One of the inventive points of the present invention is that, based on the prior laser activated selective metallization (LISM) technology of the applicant of the present invention, it was found that the specific process parameters of laser irradiation will significantly affect the quality and peel strength of the activated pattern and the flexible metal electrode pattern. The inventors of the present invention found through a large number of orthogonal experiments that under specific laser parameters and number of laser irradiations, a metal coating with uniform thickness and high peel strength can be formed, while exhibiting excellent continuity and fineness.

[0040] Based on the above invention points, in one of the technical solutions, the surface of the flexible polymer film material having a sensitizer coating obtained in step (1-1) is irradiated with a laser in step (1-2), and an activation pattern of an electrode is formed in the irradiated area. Specifically, the surface of the flexible polymer film material having a sensitizer coating is subjected to a second laser irradiation. The laser frequency of the first laser irradiation is 50 kHz, the laser power is 6 W, and the laser scanning speed is 2000 mm / s. The laser frequency of the second laser irradiation is 50-70 kHz, the laser power is 6-7 W, and the laser scanning speed is 2000 mm / s.

[0041] In this context, the electrode activation pattern formed in the irradiated area in step (1-2) can be a conventional electrode line pattern, such as an interdigitated electrode activation pattern. Furthermore, multiple electrode line array patterns, such as an interdigitated electrode array activation pattern, can also be formed based on existing techniques.

[0042] It should be noted that the size and dimensions of the activated pattern of the formed electrode can be designed according to the relevant public specifications of microelectrodes in the prior art, and its size and dimensions are preferably matched with the grid-shaped thermosensitive unit precursor described below.

[0043] Herein, the excess laser sensitizer is washed away in step (1-2), usually by using the solvent in step (1-1), or other conventional methods in the art.

[0044] In this document, the metal plating solution described in steps (1-3) is a metal plating solution commonly used in the field of electroless metal plating of metal electrodes. Those skilled in the art can directly select an appropriate publicly available metal plating solution formula to configure the corresponding metal plating solution based on existing processes or actual needs. In one technical solution, the metal plating solution selected in steps (1-3) includes a copper metal plating solution, a nickel metal plating solution, a silver metal plating solution, a chromium metal plating solution, or a gold metal plating solution.

[0045] In one technical solution, the metal plating solution in step (1-3) is a copper metal plating solution, and chemical copper plating is performed according to the following reaction formula:

[0046] Cu 2+ +2HCHO+4OH - →Cu+2HCOO - +H2O+H2↑.

[0047] In order to better illustrate the present invention and provide a technical solution for reference, the composition of the metal plating solution in steps (1-3) is: 8g / L CuSO4, 30g / L NaKC4H4O6, 3g / L EDTA, 3g / L C6H5Na3O7, 12ml / L HCHO and 150ml / L CH3OH, and the solvent is deionized water.

[0048] In this article, the chemical plating described in steps (1-3) is a conventional chemical plating method for chemically plating metal electrodes in this technical field. Those skilled in the art can determine the specific chemical plating process conditions based on the chemical reaction conditions of the selected metal plating solution.

[0049] In order to better illustrate the present invention and provide a technical solution for reference, when the metal plating solution is the above-mentioned copper metal plating solution, the chemical plating in step (1-3) is to immerse the flexible polymer film material after laser activation in the metal plating solution, and stir it for 12 to 20 minutes at a temperature of 50 to 60°C to prepare a flexible substrate metal electrode based on LISM technology.

[0050] It should be noted that the preparation of the flexible substrate metal electrode based on LISM technology in steps (1-3) usually also includes conventional operations such as cleaning after chemical plating. These conventional operations are common knowledge to those skilled in the art and will not be repeated here.

[0051] In this article, the preparation of the carbon-based temperature-sensitive functional ink follows common knowledge in the art, and the raw material components are mixed evenly.

[0052] In order to better illustrate the present invention and provide a technical solution for reference, the preparation method of the carbon-based temperature-sensitive functional ink is to mix and stir the raw material components at 20-35°C and 8000-30000 r / min for 20-120 minutes.

[0053] In one technical solution, in order to better adapt to the carbon-based temperature-sensitive functional ink in step (2-1), the parameters of the ink direct writing 3D printer in step (2-2) are set to the air pressure at 15-30 psi and the printing needle movement speed at 5-12 mm s-1 .

[0054] In one of the technical solutions, the printed product is subjected to freeze-solidification treatment and drying in step (2-2), wherein the printed product is frozen using liquid nitrogen for 2 to 10 minutes and then freeze-dried for at least 12 hours.

[0055] In this article, the 2 to 4 layers of grid-shaped thermal-sensitive unit precursor described in step (2-2) are the number of slice layers in ink direct writing 3D printing, for example, each layer is a parallel printing filament formed by straight line filling printing, and the printing filaments of adjacent layers are perpendicular to each other to form a grid structure, so there are at least 2 layers.

[0056] In one of the technical solutions, in order to make the prepared implantable temperature sensor have ultra-light and thin characteristics in terms of size specifications, the single length of the grid-shaped thermal sensitive unit precursor is 7 to 10 mm, the width is 7 to 10 mm, the thickness is 1.5 to 2 mm, and the weight is about 10 to 20 mg.

[0057] In one of the more preferred technical solutions, in order to improve the temperature sensitivity of the prepared implantable temperature sensor, the 2 to 4 layers of grid-shaped thermosensitive unit precursors in step (2-2) are parallel printed wire strips formed by linear filling printing, the printing needle diameter is 0.5 to 0.7 mm, and the spacing between the printed wire strips is 0.4 to 0.6 mm.

[0058] It should be noted that when the flexible substrate metal electrode based on LISM technology obtained in step (1-3) is an electrode array, the grid-shaped thermosensitive unit precursor described in step (2-2) should also form an array corresponding to the electrode array, that is, an array is formed by multiple grid-shaped thermosensitive unit precursors, and finally an implantable temperature sensor array is obtained.

[0059] One of the key innovations of this invention is the development of a SWCNT / CNF system ink for direct-ink 3D printing, and the printing of a thermosensitive cell precursor with a grid structure onto a flexible metal electrode substrate based on LISM technology. This results in an implantable temperature sensor with high sensitivity over a wide temperature range. LISM technology, combined with direct-ink 3D printing, enables ultra-thin sensors to be implanted within lithium-ion soft-pack batteries for single- and multi-point temperature monitoring, which has important implications for lithium-ion battery thermal management and thermal design.

[0060] Specifically, firstly, the thermosensitive unit precursor prepared by the technology of the present invention realizes the regulation of thermistor sensitivity and temperature measurement range, and obtains a sensitivity of -1.7%K -1 , high performance characterization with a temperature sensing range of 30 to 70°C.

[0061] Secondly, the implantable temperature sensor array was implanted into the lithium-ion soft-pack battery for multi-point monitoring. The soft-pack battery showed little loss in cycle performance and rate performance. After 20 cycles of charge and discharge at a rate of 1C, the specific capacity remained above 120mAh / g. After 50 cycles, the specific capacity remained above 118mAh / g, and the coulombic efficiency remained above 99%. The soft-pack battery with the implanted sensor array underwent five charge and discharge cycles at 0.2C, 0.5C, 1C, 2C, and 0.5C, respectively, with specific capacities of 130.1mAh / g, 127.3mAh / g, 113.7mAh / g, 98.1mAh / g, and 128.2mAh / g. Although the specific capacity of the soft-pack battery decayed significantly at a rate of 2C, the specific capacity recovered to 128.2mAh / g after returning to a rate of 0.5C, showing good reversibility.

[0062] Based on the above invention points, the ultra-light and thin lithium-ion battery implantable temperature sensor provided by the present invention can be applied to lithium-ion batteries and can realize thermal management and safety warning of lithium-ion batteries.

[0063] In order to better illustrate the present invention, on the other hand, the present invention also provides a lithium-ion soft-pack battery using the implantable temperature sensor, wherein the implantable temperature sensor is implanted between the negative electrode and the outermost diaphragm of the lithium-ion soft-pack battery, and the implantable temperature sensor is connected to a signal processing module to monitor the internal temperature of the lithium-ion soft-pack battery.

[0064] In this article, the signal processing module includes a single-chip microcomputer and its supporting control system. The analog-to-digital converter on the single-chip microcomputer converts the resistance signal transmitted by the electrode point into a digital signal, and transmits it to the central processing unit on the single-chip microcomputer. The temperature size and change are judged by the resistance size and change.

[0065] When the implantable temperature sensor is an implantable temperature sensor array, or when a plurality of implantable temperature sensors are implanted at different positions inside the lithium-ion soft-pack battery, multi-point temperature monitoring can be performed inside the lithium-ion soft-pack battery.

[0066] The present invention has the following beneficial effects:

[0067] 1. This invention provides an ultra-thin lithium-ion battery implantable temperature sensor and its fabrication method. First, based on laser-activated selective metallization (LISM) and laser-induced carbonization, a highly conductive and highly adhesive metal electrode pattern was successfully fabricated on a flexible polymer film. Further research revealed that secondary laser irradiation and specific laser parameters can produce a uniform metal coating with high peel strength, excellent continuity, and fineness.

[0068] 2. Secondly, by developing a SWCNT / CNF system ink for direct ink 3D printing, they printed a thermosensitive cell precursor with a grid structure onto a flexible metal electrode substrate based on LISM technology, achieving highly sensitive implantable temperature sensors over a wide temperature range. LISM technology, combined with direct ink 3D printing, achieves the ultra-thin sensor required. The sensor can then be implanted inside lithium-ion soft-pack batteries for single- and multi-point temperature monitoring, which has important implications for lithium-ion battery thermal management and thermal design.

[0069] 3. Compared with the existing technology, the implantable temperature sensor array is implanted into the lithium-ion soft-pack battery for multi-point monitoring. The cycle performance and rate performance loss of the soft-pack battery are extremely small, and it shows good reversibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 Schematic diagram of the manufacturing process of the implantable temperature sensor / implantable temperature sensor array prepared in Example 1 and Example 5 of the present invention.

[0071] Figure 2 This is a schematic structural diagram of the implantable temperature sensor / implantable temperature sensor array prepared in Example 1 and Example 5 of the present invention implanted into a lithium-ion soft-pack battery.

[0072] Figure 3 The laser parameter matrix for the first laser irradiation and the photo of the PI film after laser activation in the present invention are shown in Figure 1. (a) is the laser parameter matrix for the first laser irradiation; (b) is the photo of the PI film after laser activation.

[0073] Figure 4 The following are photos of the PI film after the second laser irradiation and after chemical copper plating in the present invention. (a) is a photo of the PI film after the second laser irradiation; (b) is a photo of the PI film after chemical copper plating.

[0074] Figure 5 The following are SEM images of the PI film surface after the first and second laser irradiation in Example 1 of the present invention. (a) and (b) are SEM images of the PI film surface after the first laser irradiation; (c) and (d) are SEM images of the PI film surface after the second laser irradiation.

[0075] Figure 6 The following are photos of the PI film surface after the first and second laser irradiation in Example 1 of the present invention. (a) shows the interdigitated electrode shape on the PI film surface after the first laser irradiation; (b) shows the interdigitated electrode shape on the PI film surface after the second laser irradiation.

[0076] Figure 7Photographs and SEM images of the flexible substrate metal interdigital electrode prepared using LISM technology in Example 1 of the present invention. (a) and (b) are overall and detailed photographs of the flexible substrate metal interdigital electrode, respectively; (c) and (d) are SEM images of the metal interdigital electrodes on the surface of the flexible substrate metal interdigital electrode.

[0077] Figure 8 Photos of the flexible substrate metal interdigital electrode array and the implantable temperature sensor array prepared in Example 5 of the present invention. (a) is a photo of the prepared flexible substrate metal interdigital electrode array; (b) is a photo of the implantable temperature sensor array.

[0078] Figure 9 Comparative line graphs of viscosity / shear rate, storage modulus G', and loss modulus G" of the carbon-based temperature-sensitive functional inks prepared in Examples 2 and 4 of the present invention and Comparative Examples 1 and 2. (a) shows the relationship between viscosity and shear rate of the carbon-based temperature-sensitive functional inks; (b) shows the storage modulus G'; and (c) shows the loss modulus G".

[0079] Figure 10 This is a radar chart comparing the comprehensive performance of the carbon-based temperature-sensitive functional inks prepared in Examples 2 and 4 of the present invention and Comparative Examples 1 and 2.

[0080] Figure 11 The temperature sensitivity comparison curves of the carbon-based temperature-sensitive functional inks prepared in Examples 1 and 2 and Comparative Example 3 of the present invention are shown.

[0081] Figure 12 The following are SEM images, photographs, and weight display diagrams of the grid-shaped thermal-sensitive unit precursor in Example 1 of the present invention. (a) is an SEM image of the grid-shaped thermal-sensitive unit precursor; (b) to (d) are cross-sectional SEM images of the grid-shaped thermal-sensitive unit precursor; (e) is a photograph of unit samples showing different filament spacing; and (f) is a weight display diagram of the grid-shaped thermal-sensitive unit precursor.

[0082] Figure 13 1 is a comparison diagram of the temperature-resistance curves of the grid-shaped thermosensitive unit precursors in Examples 1 and 3 of the present invention and Comparative Examples 4 and 5. DETAILED DESCRIPTION

[0083] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than for limiting the claims of the invention. Those skilled in the art can refer to the contents of this article and appropriately improve the process parameters for implementation. It is particularly important to point out that all similar replacements and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention. Although it is believed that those of ordinary skill in the art fully understand the following terms, the following definitions are still stated to help illustrate the subject matter disclosed by the present invention.

[0084] In one aspect, the present invention provides a method for preparing an ultra-thin lithium-ion battery implantable temperature sensor, which mainly comprises the following steps:

[0085] (1) Preparation of flexible substrate metal electrodes based on LISM technology

[0086] (1-1) mixing a laser sensitizer with a solvent to obtain a laser sensitizer suspension or solution, then applying the suspension or solution to a surface of a flexible polymer film by blade coating, and then removing the solvent to obtain a flexible polymer film having a sensitizer coating;

[0087] The flexible polymer film material is a polyimide film (PI) or a polyethylene terephthalate film (PET);

[0088] The laser sensitizer is an organic copper sensitizer or an inorganic copper sensitizer;

[0089] (1-2) irradiating the surface of the flexible polymer film having the sensitizer coating obtained in step (1-1) with a laser, forming an activated electrode pattern in the irradiated area, and then washing away excess laser sensitizer to obtain a laser-activated flexible polymer film;

[0090] (1-3) immersing the laser-activated flexible polymer film obtained in step (1-2) in a metal plating solution for chemical plating to form a flexible metal electrode pattern at the activated pattern, thereby preparing a flexible substrate metal electrode based on LISM technology;

[0091] (2) Preparation of implantable temperature sensors

[0092] (2-1) The following raw materials are mixed in parts by weight to prepare a carbon-based temperature-sensitive functional ink:

[0093] 3-5 parts of nanocellulose (CNF),

[0094] Single-walled carbon nanotubes (SWCNT) 1-1.5 parts,

[0095] 93.5 to 96 parts of solvent,

[0096] Among them, nanocellulose, single-walled carbon nanotubes and solvent totaled 100 parts;

[0097] (2-2) loading the carbon-based temperature-sensitive functional ink obtained in step (2-1) into the printing syringe of an ink direct writing 3D printer, and printing 2 to 4 layers of a grid-shaped thermosensitive unit precursor on the flexible substrate metal electrode obtained in step (1-3);

[0098] The printed product is then freeze-cured and dried to obtain an implantable temperature sensor.

[0099] Herein, the laser sensitizer in step (1-1) is an organic copper sensitizer or an inorganic copper sensitizer, both of which are conventional laser sensitizers in the art. Those skilled in the art can select a suitable organic copper sensitizer or inorganic copper sensitizer according to specific needs and process requirements.

[0100] In order to better illustrate the present invention and provide a preferred embodiment for reference, the laser sensitizer in step (1-1) is selected from any one of Cu2(OH)PO4, CuBr, Cu2O, copper (II)-phenanthroline complexes, and copper (II)-phthalocyaninetetrasulfonate.

[0101] In this article, the solvents described in steps (1-1) and (2-1) are conventional solvents in the field of chemical materials. Those skilled in the art can select appropriate solvents according to specific needs and process requirements, and can also optimize them according to their applicable purposes. For example, in step (1-1), the solvent plays a role in uniformly dispersing the laser sensitizer so that it is suitable for scraping on the surface of the flexible polymer film material, and in step (2-1), the solvent is the main ink component in the ink direct writing 3D printing technology. Those skilled in the art can optimize it based on the conventional ink solvents for the ink direct writing 3D printing technology in the prior art.

[0102] To better illustrate the present invention and provide a preferred embodiment for reference, the solvent selected in steps (1-1) and (2-1) includes any one of ethanol, deionized water, ethylene glycol, aqueous ammonia, dimethylformamide, and dimethyl sulfoxide. Theoretically, the solvents in steps (1-1) and (2-1) can be the same solvent or different solvents. In one preferred embodiment, the solvent in step (1-1) is ethanol; and the solvent in step (2-1) is deionized water.

[0103] In this document, in step (1-1), the laser sensitizer is mixed with a solvent to obtain a laser sensitizer suspension or solution. The ratio of the laser sensitizer to the solvent can be directly referenced by conventional laser sensitizer applications in the prior art, such as the ratio recommended in the product manual. To better illustrate the present invention and provide a reference embodiment, the laser sensitizer and solvent in step (1-1) are mixed at a ratio of 1 g: (15-40) ml.

[0104] In one embodiment, in order to form a better activation pattern in the irradiated area in step (1-2), the suspension or solution described in step (1-1) is scraped onto the surface of the flexible polymer film, preferably to form a coating of 40 to 60 μm thick, and then the solvent is removed to obtain a flexible polymer film with a sensitizer coating.

[0105] Herein, the removal of the solvent in step (1-1) is performed by a conventional method of removing the solvent of a coating after coating in the chemical industry. For example, when the solvent is ethanol, the solvent is left to stand at room temperature until the ethanol evaporates.

[0106] One of the inventive points of the present invention is that, based on the prior laser activated selective metallization (LISM) technology of the applicant of the present invention, it was found that the specific process parameters of laser irradiation will significantly affect the quality and peel strength of the activated pattern and the flexible metal electrode pattern. The inventors of the present invention found through a large number of orthogonal experiments that under specific laser parameters and number of laser irradiations, a metal coating with uniform thickness and high peel strength can be formed, while exhibiting excellent continuity and fineness.

[0107] Based on the above-mentioned invention, in one embodiment, the surface of the flexible polymer film material having a sensitizer coating obtained in step (1-1) is irradiated with a laser in step (1-2), and an activation pattern of an electrode is formed in the irradiated area. Specifically, the surface of the flexible polymer film material having a sensitizer coating is subjected to a second laser irradiation. The laser frequency of the first laser irradiation is 50 kHz, the laser power is 6 W, and the laser scanning speed is 2000 mm / s. The laser frequency of the second laser irradiation is 50-70 kHz, the laser power is 6-7 W, and the laser scanning speed is 2000 mm / s.

[0108] In this context, the electrode activation pattern formed in the irradiated area in step (1-2) is selected from conventional electrode line patterns, such as, in one embodiment, an interdigitated electrode activation pattern. Furthermore, multiple electrode line array patterns, such as an interdigitated electrode array activation pattern, can also be formed based on existing technologies.

[0109] It should be noted that the size and dimensions of the activated pattern of the formed electrode can be designed according to the relevant public specifications of microelectrodes in the prior art, and its size and dimensions are preferably matched with the grid-shaped thermosensitive unit precursor described below.

[0110] Herein, the excess laser sensitizer is washed away in step (1-2), usually by using the solvent in step (1-1), or other conventional methods in the art.

[0111] In this document, the metal plating solution described in steps (1-3) is a metal plating solution commonly used in the field of electroless metal plating. Those skilled in the art can directly select an appropriate publicly available metal plating solution formula to configure the corresponding metal plating solution based on existing processes or actual needs. In one embodiment, the metal plating solution selected in steps (1-3) includes a copper metal plating solution, a nickel metal plating solution, a silver metal plating solution, a chromium metal plating solution, or a gold metal plating solution.

[0112] In one embodiment, the metal plating solution in step (1-3) is a copper metal plating solution, and chemical copper plating is performed according to the following reaction formula:

[0113] Cu 2+ +2HCHO+4OH - →Cu+2HCOO - +H2O+H2↑.

[0114] To better illustrate the present invention and provide an embodiment for reference, the composition of the metal plating solution in steps (1-3) is: 8 g / L CuSO4, 30 g / L NaKC4H4O6, 3 g / L EDTA, 3 g / L C6H5Na3O7, 12 ml / L HCHO and 150 ml / L CH3OH, and the solvent is deionized water.

[0115] In this article, the chemical plating described in steps (1-3) is a conventional chemical plating method for chemically plating metal electrodes in this technical field. Those skilled in the art can determine the specific chemical plating process conditions based on the chemical reaction conditions of the selected metal plating solution.

[0116] In order to better illustrate the present invention and provide an embodiment for reference, when the metal plating solution is selected as the above-mentioned copper metal plating solution, the chemical plating in step (1-3) is to immerse the flexible polymer film material after laser activation in the metal plating solution, and stir it for 12 to 20 minutes at a temperature of 50 to 60°C to prepare a flexible substrate metal electrode based on LISM technology.

[0117] It should be noted that the preparation of the flexible substrate metal electrode based on LISM technology in steps (1-3) usually also includes conventional operations such as cleaning after chemical plating. These conventional operations are common knowledge to those skilled in the art and will not be repeated here.

[0118] In this article, the preparation of the carbon-based temperature-sensitive functional ink follows common knowledge in the art, and the raw material components are mixed evenly.

[0119] In order to better illustrate the present invention and provide an embodiment for reference, the preparation method of the carbon-based temperature-sensitive functional ink is to mix and stir the raw material components at 20-35°C and 8000-30000 r / min for 20-120 minutes.

[0120] In one embodiment, in order to better adapt to the carbon-based temperature-sensitive functional ink in step (2-1), the parameters of the ink direct writing 3D printer in step (2-2) are set to the air pressure at 15-30 psi and the printing needle movement speed at 5-12 mm s -1 .

[0121] In one embodiment, the printed product is freeze-solidified and dried in step (2-2), wherein the printed product is frozen using liquid nitrogen for 2 to 10 minutes and then freeze-dried for at least 12 hours.

[0122] In this article, the 2 to 4 layers of grid-shaped thermal-sensitive unit precursor described in step (2-2) are the number of slice layers in ink direct writing 3D printing, for example, each layer is a parallel printing filament formed by straight line filling printing, and the printing filaments of adjacent layers are perpendicular to each other to form a grid structure, so there are at least 2 layers.

[0123] In one embodiment, in order to make the prepared implantable temperature sensor have ultra-light and thin characteristics in terms of size specifications, the single length of the grid-shaped thermal sensitive unit precursor is 7-10 mm, the width is 7-10 mm, the thickness is 1.5-2 mm, and the weight is about 10-20 mg.

[0124] In one of the more preferred embodiments, in order to improve the temperature sensitivity of the prepared implantable temperature sensor, the 2 to 4 layers of grid-shaped thermosensitive unit precursors in step (2-2) are parallel printed wire strips formed by linear filling printing, the printing needle diameter is 0.5 to 0.7 mm, and the spacing between the printed wire strips is 0.4 to 0.6 mm.

[0125] It should be noted that when the flexible substrate metal electrode based on LISM technology obtained in step (1-3) is an electrode array, the grid-shaped thermosensitive unit precursor described in step (2-2) should also form an array corresponding to the electrode array, that is, an array is formed by multiple grid-shaped thermosensitive unit precursors, and finally an implantable temperature sensor array is obtained.

[0126] One of the key innovations of this invention is the development of a SWCNT / CNF system ink for direct-ink 3D printing, and the printing of a thermosensitive cell precursor with a grid structure onto a flexible metal electrode substrate based on LISM technology. This results in an implantable temperature sensor with high sensitivity over a wide temperature range. LISM technology, combined with direct-ink 3D printing, enables ultra-thin sensors to be implanted within lithium-ion soft-pack batteries for single- and multi-point temperature monitoring, which has important implications for lithium-ion battery thermal management and thermal design.

[0127] Specifically, firstly, the thermosensitive unit precursor prepared by the technology of the present invention realizes the regulation of thermistor sensitivity and temperature measurement range, and obtains a sensitivity of -1.7%K -1 , high performance characterization with a temperature sensing range of 30 to 70°C.

[0128] Secondly, the implantable temperature sensor array was implanted into the lithium-ion soft-pack battery for multi-point monitoring. The soft-pack battery showed little loss in cycle performance and rate performance. After 20 cycles of charge and discharge at a rate of 1C, the specific capacity remained above 120mAh / g. After 50 cycles, the specific capacity remained above 118mAh / g, and the coulombic efficiency remained above 99%. The soft-pack battery with the implanted sensor array underwent five charge and discharge cycles at 0.2C, 0.5C, 1C, 2C, and 0.5C, respectively, with specific capacities of 130.1mAh / g, 127.3mAh / g, 113.7mAh / g, 98.1mAh / g, and 128.2mAh / g. Although the specific capacity of the soft-pack battery decayed significantly at a rate of 2C, the specific capacity recovered to 128.2mAh / g after returning to a rate of 0.5C, showing good reversibility.

[0129] Based on the above invention points, the ultra-light and thin lithium-ion battery implantable temperature sensor provided by the present invention can be applied to lithium-ion batteries and can realize thermal management and safety warning of lithium-ion batteries.

[0130] In order to better illustrate the present invention, on the other hand, the present invention also provides a lithium-ion soft-pack battery using the implantable temperature sensor, wherein the implantable temperature sensor is implanted between the negative electrode and the outermost diaphragm of the lithium-ion soft-pack battery, and the implantable temperature sensor is connected to a signal processing module to monitor the internal temperature of the lithium-ion soft-pack battery.

[0131] In this article, the signal processing module includes a single-chip microcomputer and its supporting control system. The analog-to-digital converter on the single-chip microcomputer converts the resistance signal transmitted by the electrode point into a digital signal, and transmits it to the central processing unit on the single-chip microcomputer. The temperature size and change are judged by the resistance size and change.

[0132] When the implantable temperature sensor is an implantable temperature sensor array, or when a plurality of implantable temperature sensors are implanted at different positions inside the lithium-ion soft-pack battery, multi-point temperature monitoring can be performed inside the lithium-ion soft-pack battery.

[0133] The present invention will be further explained in detail below with reference to the examples. However, it will be appreciated by those skilled in the art that these examples are provided for illustrative purposes only and are not intended to limit the present invention.

[0134] Example

[0135] The embodiments of the present application will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are merely illustrative of the present application and should not be considered as limiting the scope of the present application. In the examples, if no specific conditions are indicated, the conditions are carried out according to normal conditions or manufacturer recommendations. The reagents used or the instruments that are not indicated by the manufacturer are conventional products that can be obtained commercially. The application should not be construed as being limited to the specific examples described.

[0136] 1. Raw materials

[0137]

[0138]

[0139] 2. Preparation method

[0140] (1) Preparation of flexible substrate metal electrodes based on LISM technology

[0141] (1-1) 1 g of the laser sensitizer Cu2(OH)PO4 was mixed with 20 mL of ethanol to obtain a laser sensitizer suspension. The suspension was then applied to a 100 μm thick polyimide (PI) film surface by blade coating to form a 40 μm thick coating. The ethanol was then evaporated to obtain a PI / Cu2(OH)PO4 thin film.

[0142] (1-2) irradiating the surface of the PI / Cu2(OH)PO4 film obtained in step (1-1) with a laser, forming an activated pattern of interdigitated electrodes in the irradiated area, and then washing away excess laser sensitizer to obtain a laser-activated flexible polymer film;

[0143] Specifically, the surface of the PI / Cu2(OH)PO4 film was subjected to laser irradiation twice. The laser frequency of the first laser irradiation was 50kHz, the laser power was 6W, and the laser scanning speed was 2000mm / s. The laser frequency of the second laser irradiation was 60kHz, the laser power was 7W, and the laser scanning speed was 2000mm / s.

[0144] (1-3) immersing the laser-activated flexible polymer film obtained in step (1-2) in a copper metal plating solution for chemical plating to form a flexible metal interdigital electrode pattern at the activated pattern, thereby preparing a flexible substrate metal interdigital electrode based on LISM technology;

[0145] The copper metal plating solution is composed of: 8g / L CuSO4, 30g / L NaKC4H4O6, 3g / L EDTA, 3g / L C6H5Na3O7, 12ml / L HCHO and 150ml / L CH3OH, and the solvent is deionized water. The electroless plating temperature is 52°C and the time is 12 minutes, during which stirring is continuously performed. After the electroless plating is completed, the solution is rinsed once with deionized water and once with ethanol, and finally dried.

[0146] (2) Preparation of implantable temperature sensors

[0147] (2-1) The following raw materials are mixed in parts by weight to prepare a carbon-based temperature-sensitive functional ink:

[0148] 3-5 parts of nanocellulose (CNF),

[0149] Single-walled carbon nanotubes (SWCNT) 1-1.5 parts,

[0150] 93.5-96 parts of deionized water,

[0151] Among them, nanocellulose, single-walled carbon nanotubes and deionized water totaled 100 parts;

[0152] (2-2) The carbon-based temperature-sensitive functional ink obtained in step (2-1) is loaded into the printing syringe of the ink direct writing 3D printer, and two layers of grid-shaped thermal-sensitive unit precursor are printed on the metal interdigitated electrode of the flexible substrate obtained in step (1-3); the parameters of the ink direct writing 3D printer are set as follows: the air pressure is set at 20 psi, the printing needle movement speed is set at 6 mm s -1 , the printing needle diameter is 0.5mm;

[0153] The grid-shaped thermal-sensitive unit precursor has a single length of 7 mm, a width of 7 mm, a thickness of 1.5 mm, a spacing between printed filaments of 0.4 to 0.6 mm, and a weight of approximately 10 mg. The grid-shaped thermal-sensitive unit precursor covers the interdigital portion of the metal interdigital electrode on the flexible substrate.

[0154] The printed product was then frozen in liquid nitrogen for 2 minutes, and the frozen sample was placed in a freeze dryer for freeze drying for 12 hours to obtain an implantable temperature sensor.

[0155] Example 1

[0156] Example 1 is in accordance with the above-mentioned "2. Preparation method" steps, except that in step (2-1), the nanocellulose is 5 parts and the single-walled carbon nanotubes are 1.5 parts; in step (2-2), the spacing between the printed filaments is 0.6 mm; and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a sample.

[0157] Example 2

[0158] Example 2 is according to the above-mentioned "2. Preparation method" steps, except that in step (2-1), the nanocellulose is 5 parts and the single-walled carbon nanotube is 1 part; in step (2-2), the spacing between the printed filaments is 0.6 mm; and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a sample.

[0159] Example 3

[0160] Example 3 is according to the above-mentioned "2. Preparation method" steps, except that in step (2-1), the nanocellulose is 5 parts and the single-walled carbon nanotubes are 1.5 parts; in step (2-2), the spacing between the printed filaments is 0.4 mm; and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a sample.

[0161] Example 4

[0162] Example 4 is prepared according to the steps of "2. Preparation method" above, except that in step (2-1), the nanocellulose is 3.3 parts and the single-walled carbon nanotube is 1 part; in step (2-2), the spacing between the printed filaments is 0.6 mm; and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a sample.

[0163] Comparative Example 1

[0164] Comparative Example 1 follows the steps of "2. Preparation Method" above, except that in step (2-1), the nanocellulose is 2.5 parts, the single-walled carbon nanotube is 1 part, and the deionized water is 96.5 parts; in step (2-2), the spacing between the printed filaments is 0.6 mm; and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a comparative sample.

[0165] Comparative Example 2

[0166] Comparative Example 2 follows the steps of "2. Preparation Method" above, except that in step (2-1), the nanocellulose is 10 parts, the single-walled carbon nanotube is 1 part, and the deionized water is 89 parts; in step (2-2), the spacing between the printed filaments is 0.6 mm; and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a comparative sample.

[0167] Comparative Example 3

[0168] Comparative Example 3 follows the steps of "2. Preparation Method" above, except that in step (2-1), the nanocellulose is 5 parts, the single-walled carbon nanotubes are 2 parts, and the deionized water is 93 parts; in step (2-2), the spacing between the printed filaments is 0.6 mm; and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a comparative sample.

[0169] Comparative Example 4

[0170] Comparative Example 4 follows the steps of "2. Preparation Method" above, except that in step (2-1), the nanocellulose is 5 parts and the single-walled carbon nanotubes are 1.5 parts; in step (2-2), the spacing between the printed filaments is 0 mm (i.e., completely filled printing); and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a comparative sample.

[0171] Comparative Example 5

[0172] Comparative Example 5 follows the steps of "2. Preparation Method" above, except that in step (2-1), the nanocellulose is 5 parts and the single-walled carbon nanotube is 1.5 parts; in step (2-2), the spacing between the printed filaments is 0.2 mm; and finally, an implantable temperature sensor having an interdigitated electrode and a corresponding single grid-shaped thermal sensitive unit precursor is prepared as a comparative sample.

[0173] Example 5

[0174] Example 5 is based on the steps of "2. Preparation Method" above. In step (2-1), the nanocellulose is 5 parts and the single-walled carbon nanotube is 1.5 parts; in step (2-2), the spacing between the printed filaments is 0.6 mm; and finally, an implantable temperature sensor array having five interdigitated electrodes and corresponding five grid-shaped thermosensitive unit precursors is prepared as a sample, as shown in FIG. Figure 8 As shown, its thickness is 0.17 mm and its weight is about 430 mg.

[0175] 3. Test methods

[0176] Scanning electron microscopy: A scanning electron microscope (SEM) was used to observe the morphological evolution of the PI film surface during the laser-induced selective metallization process and to evaluate the quality and fineness of the copper layer.

[0177] Energy Dispersive Spectroscopy Elemental Analysis: Energy Dispersive Spectroscopy (EDS) is used to characterize the element distribution during the metallization process.

[0178] Optical microscope: An optical microscope (OM) is used to observe the shape and details of metal circuits and metal patterns.

[0179] Raman spectroscopy: Raman spectroscopy uses a 532 nm excited diode laser and a 25 μm confocal pinhole to record the Raman spectrum of the laser activated PI film surface.

[0180] X-ray photoelectron spectrometer: X-ray photoelectron spectrometer (XPS) is used to study the generation process of active species on the surface of PI films and the valence state of elements during the metallization process.

[0181] Four-probe conductivity tester: Four-probe conductivity tester is used to test the conductivity of various metal circuits and metallization pattern copper layers in metallization manufacturing.

[0182] Ultraviolet-visible-near-infrared spectroscopy: Ultraviolet-visible-near-infrared spectroscopy (UV-Vis-IR) is used to characterize the absorption degree of laser sensitizers to light of various wavelengths.

[0183] Copper Layer Adhesion Tester: The adhesion strength between the copper-plated layer and the polymer substrate is measured using the ASTM D3359B method. Use a grid knife to create a small square grid of 1mm x 1mm on the copper-plated layer. Next, apply Scotch3M 600-1PK test tape to the gridded area and quickly remove the tape. The adhesion strength level is determined based on the area of ​​copper layer peeling. In the ASTM D3359 grading standard, the higher the grade, the higher the adhesion between the polymer substrate and the copper-plated layer. 0B (peeling area > 65%); 1B (peeling area 35%-65%); 2B (peeling area of ​​the grid 15%-35%); 3B (peeling area of ​​the grid 5%-15%); 4B (peeling area of ​​the grid 5%); 5B (no peeling of the grid).

[0184] Rotational rheology instrument: By measuring rheological data such as shear rate, shear stress, and stress-strain amplitude, parameters such as sample viscosity, storage modulus, and loss modulus are calculated. This article used the AR2000 rotational rheometer from IA, a US company. The rheological properties of the ink were characterized using the parallel plate mode. The ink was placed between two plates with a 1mm gap, and the viscosity of the ink was measured at room temperature as a function of shear rate. The storage modulus and loss modulus of the ink were measured using the oscillation mode at room temperature.

[0185] Scanning electron microscopes (SEMs) use high-energy electron beams to interact with samples to stimulate various physical information, collecting and amplifying this information into images to characterize the microscopic morphology of materials. This article uses a Quanta SEM manufactured by FEI (USA). The sample was attached to the sample stage with conductive tape and, after gold sputtering, was observed under vacuum conditions to measure its surface and cross-sectional morphology.

[0186] Optical Microscopy: Use an optical microscope to observe the details of the printed grid as well as the details of the sensor / sensor array.

[0187] Infrared Camera: Use an infrared camera to evaluate the heat transfer performance of thermal cells.

[0188] Blue Electric Test System: Use the Blue Electric Test System to perform charge and discharge tests on soft-pack batteries at different rates, with a lower voltage limit of 2V and an upper voltage limit of 4V. Record relevant data such as voltage-time, voltage-specific capacity, and coulombic efficiency.

[0189] Thermal sensing performance test:

[0190] (1) Sensor calibration: Place the sensor inside the oven, precisely control the temperature, and monitor the sensor resistance change in real time to obtain a temperature-resistance curve, which is used as the sensor calibration curve;

[0191] (2) Temperature monitoring: attach the sensor to the surface of the object to be measured and use the temperature monitoring program to monitor the surface temperature of the object to be measured in real time;

[0192] (3) Heat source position monitoring: The sensor is attached to the glass plate, and the heating rod is placed at different positions relative to the sensor. The heat source position is monitored in real time using the heat source monitoring program, and the monitoring results are displayed on the LED screen. The heat source is moved through different positions in sequence to evaluate the sensing system's monitoring of the heat source path.

[0193] Finite element simulation: This paper uses COMSOL, a multi-physics direct-coupling analysis software, and, relying on appropriate 3D meshing to achieve high accuracy, introduces the finite element method to monitor internal battery temperature. Using the multi-physics fields of solid heat transfer and convection heat transfer, steady-state or transient studies are added, the thermodynamic properties of each battery material are set, initial and boundary conditions are specified, and the mesh is optimized and refined to achieve the final simulation results.

[0194] 4. Test results

[0195] The manufacturing process of the implantable sensor / implantable temperature sensor array provided by the present invention is as follows: Figure 1 shown.

[0196] like Figure 2As shown, the temperature sensor and the implantable temperature sensor array are respectively implanted into the lithium-ion soft pack battery, and the soft pack battery is assembled in the order of diaphragm-positive electrode tab-positive electrode-diaphragm-negative electrode-negative electrode tab-diaphragm, and the sensor / sensor array is implanted between the negative electrode and the outermost diaphragm. The battery cell equipped with the sensor / sensor array is placed in an aluminum plastic film, and 1M LiPF6 in EC:DMC=1:1Vol% electrolyte is injected in the glove box, and it is packaged into a soft pack battery using a vacuum heat sealer. The capacity of the soft pack battery is calculated in order to set the subsequent battery test conditions. The active material content of the lithium iron phosphate positive electrode sheet is 90%, and the area content is 13mg / cm 2 , theoretical capacity 135mAh / g.

[0197] like Figure 3 As shown in the figure, a laser irradiation parameter matrix was designed to correspond to different laser powers and laser frequencies, and the effects of laser frequency and laser power on laser-activated selective metallization were studied. Figure 3 As shown in (a), the parameter matrix contains 90 squares, corresponding to laser frequencies of 10kHz to 100kHz and laser powers of 1W (10%) to 10W (100%). Laser activation is performed according to the parameters corresponding to each small square, and the results are shown in Figure 1. Figure 3 (b) When the laser power is less than 3W, no matter whether the laser frequency is changed or not, the copper layer cannot be plated. This is because the laser energy is too low and cannot reach the minimum energy required to activate Cu2(OH)PO4. Similarly, when the laser frequency is too low, it is also very difficult to activate Cu2(OH)PO4. Figure 2 The results show that when the frequency is less than 20kHz, a higher laser power is required to effectively activate Cu2(OH)PO4. However, excessive power and frequency are accompanied by severe thermal effects when fully activating Cu2(OH)PO4, which can damage the surface structure of the PI film and cause carbonization. When the PI film is carbonized, the coating effect deteriorates.

[0198] The results show that when the laser frequency is 50kHz and the laser power is 6W, the quality of the electroless copper layer is significantly better than that of other areas. Therefore, these parameters are selected as the optimal laser parameters for the first laser irradiation.

[0199] Although the absorption of near-infrared laser by pure PI film is not obvious, micro-carbonization appears on its surface after the first laser irradiation. These carbonization points will enhance the absorption of near-infrared light by PI film. So the laser activated PI film was subjected to a second laser irradiation and chemical plating. The results are as follows: Figure 4As shown. After the second laser irradiation, the minimum laser power for chemical plating of the PI film is 3W. The overall laser processing window is significantly widened compared to the first laser processing, and copper plating can also be performed in high power and high frequency areas. It is worth noting that the laser sensitizer has a strong selectivity for laser parameters in addition to the minimum activation energy. Figure 4 As shown in the figure, after the second laser irradiation, the morphology of the PI film changed significantly within the laser frequency range of 60kHz and the power range of 6W to 10W. According to the results after chemical copper plating, the second laser irradiation effect is best when the laser frequency is between 50kHz and 70kHz and the power range of 6W to 7W.

[0200] In order to explore the changes in the morphology of PI film induced by laser-induced selective metallization, the morphology of PI before and after laser activation was characterized. Figure 5 (a) and (b) are SEM images of the PI film sample surface after the first laser irradiation. Clear boundaries can be seen between the laser-activated and unactivated areas. The unactivated area has a smooth surface, while the laser-activated area exhibits bubbles and holes. The electroless copper plating reaction preferentially occurs in the roughened areas. The bubbles and holes are caused by the heat released by the laser and Cu2(OH)PO4. These rough microstructures significantly enhance the adhesion of the electroless metallized circuits to the PI film surface. The PI film after the second laser irradiation exhibits even rougher surface microstructures, with a more pronounced boundary between the processed and unprocessed areas. These rough structures are approximately tens of micrometers in size, slightly larger than the preset laser spot size. Due to the thermal effects of the near-infrared laser, the spot size is smaller than the minimum processing point. Adjacent processing points also interact with each other, resulting in uneven size and morphology of the resulting rough microstructures. Furthermore, it is noteworthy that rough surfaces are more susceptible to metallization than smooth surfaces. This is because, during electroless plating on smooth surfaces, the copper layer grows only on the surface, leaving a very smooth interface between the copper layer and the polymer, lacking numerous rivet points. When electroless plating is performed on a rough surface, the presence of holes and depressions on the rough surface allows the electroless plating solution to penetrate these holes and plate inside them. As the electroless plating progresses, when copper fills these rough structures, it diffuses and grows, interconnecting to eventually form a complete copper layer. Because part of the copper layer is embedded in the rough microstructures, the adhesion of the copper layer is greatly improved, and thicker copper layers can be plated without falling off. Compared to smooth surfaces, when the copper layer exceeds 10μm, its adhesion is greatly reduced. These rough microstructures are the key to plating thicker copper layers.

[0201] The pattern of the interdigital electrode was designed using a computer, and the laser was used to perform the first and second laser irradiations, and the surface of the processed PI film was observed. The results are as follows: Figure 6 As shown. Figure 6 As shown in (a), after the first laser irradiation, the PI film produces a rough morphology and carbonization within the preset shape, but the carbonization is not uniform. The carbonization degree of the interdigitated electrode contour is higher, while the carbonization degree of the internal shape of the contour is lower. This is related to the routing method during laser processing. The laser adopts a line scanning processing method for processing. At the end of each scanning line and the beginning of the next scanning line, the processing time interval is short, resulting in a greater accumulation of thermal effects at the contour position, and ultimately producing a greater degree of carbonization at the contour. Figure 6 (b) shows the surface of the PI film after the second laser irradiation. The overall degree of carbonization is higher than that after the first laser irradiation. Similarly, the degree of carbonization at the contour is higher than that within the contour, but the carbonization within the contour is more uniform than that after the first laser irradiation, which can make the subsequent electroless copper layer more uniform and dense.

[0202] The carbonization produced by laser processing was characterized in detail. The interaction between the near-infrared laser and the PI film produces carbonization. Raman spectroscopy results show that the carbonization produced by the second laser irradiation is more uniform, while the carbonization on the surface of the PI film after the first laser irradiation is not uniform. This is because the micro-carbonized areas produced by the first laser irradiation can absorb more heat during the second laser irradiation, resulting in more complete and uniform carbonization. Comparing the Raman spectra corresponding to the red, yellow, green, and blue regions in the Raman imaging, it can be clearly seen that the intensity of amorphous carbon produced by the second laser irradiation increases.

[0203] The PI film after secondary laser irradiation according to the shape of the interdigital electrode was selected for chemical copper plating, and the copper layer on the upper plated layer was observed. The results are as follows: Figure 7 As shown in (a) and (b), chemical copper plating occurs in the laser-processed area, forming a very dense and continuous copper layer.

[0204] Figure 7 (c) and (d) are SEM images of the PI film surface after electroless copper plating. The copper layer appears smooth. Further inspection of the metal traces reveals that the interdigital electrode has a line width of 536.4 μm and a spacing of 140.6 μm. The actual line width is larger than the intended line width of 500 μm. This is due to the unavoidable thermal effect during the laser activation process. Calculations show that the actual line width exceeds the intended line width by 7.2%.

[0205] In summary, the changes in the morphology of the PI film by laser-activated selective metallization and laser-induced carbonization enhance its surface roughness, provide more deposition sites for chemical copper plating, and thus improve the adhesion and selectivity of the metal circuits on the PI film.

[0206] In order to obtain the sample with the best comprehensive performance, we systematically studied the effect of ink formulation on rheological properties, sensitivity, temperature range and microstructure. While keeping the SWCNT content unchanged (1wt.%), we studied the effect of CNF content (2.5, 3.3, 5, 10wt.%) on the rheological properties of the composite ink. Figure 9 As shown in (a), the apparent viscosity of the ink shows a typical shear-thinning property, which makes the ink change from a high viscosity state to a fluid state, thus making pneumatic continuous printing possible. The storage modulus G' and loss modulus G" are respectively Figure 9 (b) and (c) show that the higher storage modulus indicates that the viscoelastic ink has solid material properties, which can ensure stable shape retention and thus maintain the intended printed structure, while the solid-liquid transition causes the ink to flow and deposit after the critical shear stress.

[0207] In addition, we also conducted a comprehensive comparison of the processability, sensitivity, and temperature monitoring range of printed thermistors with different CNF contents, e.g. Figure 10 Finally, the ink with a CNF content of 5 wt% was selected as the best ink.

[0208] Another important factor affecting the sensing performance of the sample is the content of conductive filler. Figure 11 The sensing performance of samples with different SWCNT contents (1, 1.5, 2 wt.%) is shown. As the SWCNT content increases, the sensitivity of the sample increases (-1.3% K -1 、-1.7%K -1 、-2.1%K -1 ), but the initial resistance of the sample is reduced (39.7kΩ, 18.3kΩ, 9.1kΩ). Although the sensitivity is high and the temperature change can be monitored more sensitively, the initial resistance is small. During the heating process, the sample with low resistance will quickly enter the conductive state from the semi-conductive state. At this time, the SWCNT conductive network in the sample has been constructed very well. It is difficult to significantly reduce the resistance value by heating again, so the thermistor can no longer effectively sense temperature changes. Therefore, we selected an ink with a SWCNT content of 1.5wt.% as the best ink, and the printed sample has excellent sensitivity (-1.7% K -1 ) and a suitable initial resistance (18.3kΩ).

[0209] The grid-shaped thermal-sensitive unit precursor is designed with a grid structure, which is composed of two layers of printing filaments that are perpendicular to each other, ensuring the temperature sensing in the horizontal and vertical directions. Figure 12 (a) to (d) are SEM images of the surface and cross-section of the grid-shaped thermosensitive unit precursor. It can be seen that a porous structure is formed inside it, which is the key to sensing temperature. Figure 12(e) shows the grid-like thermosensitive unit precursor with different filament spacing, and the printed thermosensitive unit has a very small mass due to its porous structure, e.g. Figure 12 (f) shown.

[0210] Due to the advantages of 3D printing in shape and structure design, samples with different wire spacing were designed and their temperature-resistance behavior was tested. The results are as follows: Figure 13 shown.

[0211] The results show that when the spacing between the printed wire strips is small, the temperature-resistance curve fluctuates greatly, and the temperature and resistance cannot correspond one-to-one. Only when the spacing between the wire strips increases to 0.6mm, the temperature-resistance curve of the two-layer grid-shaped thermal sensitive unit precursor becomes relatively smooth, and the resistance and temperature can correspond one-to-one, realizing temperature monitoring.

[0212] For the implantable temperature sensor array prepared in Example 5, considering its large size, implanting it into the soft-pack battery may affect the battery performance. Therefore, the performance of the soft-pack battery with the sensor array implanted was evaluated. First, the battery was charged and discharged 20 times at a rate of 1C. The theoretical specific capacity of the soft-pack battery is 135mAh / g, and the specific capacity of the soft pack in the first cycle test is 126.9mAh / g, which is close to the theoretical specific capacity. The specific capacity of the soft-pack battery implanted with the sensor array after 5, 10, 15 and 20 cycles was 126.1, 124.9, 123.4, and 120.3mAh / g, respectively, and the specific capacity decay was small.

[0213] Furthermore, the coulombic efficiency of the sensor array-embedded soft-pack battery was calculated over 50 charge-discharge cycles at a 1C rate. Over these 50 cycles, the charge and discharge specific capacities remained above 118 mAh / g, and the coulombic efficiency remained above 99%. This is due to irreversible side reactions within the battery. These results demonstrate that the sensor array-embedded soft-pack battery exhibits minimal cycling performance loss and can still undergo normal 1C charge-discharge testing.

[0214] Since the battery will also undergo low-rate (trickle charge and discharge, etc.) and high-rate (fast charge and discharge, pulse charge and discharge, etc.) charge and discharge during service. The soft-pack battery implanted with the sensor array was subjected to charge and discharge tests at 0.2C, 0.5C, 1C and 2C, and the cycle test was 5 times at each rate. After the 2C rate test, 5 charge and discharge cycles of 0.5C were performed. The results show that the charge capacity of 130.1mAh / g at a rate of 0.2C is very close to its theoretical capacity. At a rate of 0.5C, its charge capacity is 127.3mAh / g, and at a rate of 1C it is 117.7mAh / g. At a rate of 2C, the charge capacity is 98.1mAh / g, and the capacity has a large attenuation. However, when the test rate is restored to 0.5C, the charge capacity of the soft-pack battery is restored to 128.2mAh / g, indicating that the soft-pack battery has good reversibility. And the charge and discharge rates at different rates are maintained above 98.8%.

Claims

1. A method for preparing an ultra-thin lithium-ion battery implantable temperature sensor, characterized in that The main steps include: (1) Preparation of flexible substrate metal electrodes based on LISM technology (1-1) mixing a laser sensitizer with a solvent to obtain a laser sensitizer suspension or solution, then applying the suspension or solution to a surface of a flexible polymer film by blade coating, and then removing the solvent to obtain a flexible polymer film having a sensitizer coating; The flexible polymer film material is a polyimide film or a polyethylene terephthalate film; The laser sensitizer is an organic copper sensitizer or an inorganic copper sensitizer; (1-2) irradiating the surface of the flexible polymer film having the sensitizer coating obtained in step (1-1) with a laser, forming an activated electrode pattern in the irradiated area, and then washing away excess laser sensitizer to obtain a laser-activated flexible polymer film; (1-3) immersing the laser-activated flexible polymer film obtained in step (1-2) in a metal plating solution for chemical plating to form a flexible metal electrode pattern at the activated pattern, thereby preparing a flexible substrate metal electrode based on LISM technology; (2) Preparation of implantable temperature sensors (2-1) The following raw materials are mixed in parts by weight to prepare a carbon-based temperature-sensitive functional ink: 3-5 parts of nanocellulose, 1-1.5 parts of single-walled carbon nanotubes, 93.5 to 96 parts of solvent, Among them, nanocellulose, single-walled carbon nanotubes and solvent totaled 100 parts; (2-2) loading the carbon-based temperature-sensitive functional ink obtained in step (2-1) into the printing syringe of an ink direct writing 3D printer, and printing 2 to 4 layers of a grid-shaped thermosensitive unit precursor on the flexible substrate metal electrode obtained in step (1-3); The printed product is then freeze-cured and dried to obtain an implantable temperature sensor.

2. The preparation method according to claim 1, wherein: The laser sensitizer in step (1-1) includes any one of Cu2(OH)PO4, CuBr, Cu2O, copper (II)-o-phenanthroline complex, and copper (II)-phthalocyanine sulfonate.

3. The preparation method according to claim 1, wherein: The solvent in steps (1-1) and (2-1) includes any one of ethanol, deionized water, ethylene glycol, ammonia water, dimethylformamide, and dimethyl sulfoxide.

4. The preparation method according to claim 1, wherein: In step (1-1), the laser sensitizer and the solvent are mixed in a ratio of 1 g: (15-40) ml.

5. The preparation method according to claim 1, wherein: The step (1-2) is to irradiate the surface of the flexible polymer film material having a sensitizer coating obtained in the step (1-1) with a laser, and to form an activation pattern of an electrode in the irradiated area. Specifically, the surface of the flexible polymer film material having a sensitizer coating is subjected to a second laser irradiation. The laser frequency of the first laser irradiation is 50 kHz, the laser power is 6 W, and the laser scanning speed is 2000 mm / s. The laser frequency of the second laser irradiation is 50-70 kHz, the laser power is 6-7 W, and the laser scanning speed is 2000 mm / s.

6. The preparation method according to claim 1, characterized in that: The metal plating solution in step (1-3) is a copper metal plating solution, and chemical copper plating is performed according to the following reaction formula: With 2+ +2HCHO+4OH - →Cu+2HCOO - +H2O+H2↑.

7. The preparation method according to claim 1, characterized in that: The single length of the grid-shaped thermosensitive unit precursor in step (2-2) is 7 to 10 mm, the width is 7 to 10 mm, and the thickness is 1.5 to 2 mm.

8. The preparation method according to claim 1, characterized in that: In the 2 to 4 layers of the grid-shaped thermal-sensitive unit precursor in step (2-2), each layer is a parallel printing filament formed by linear filling printing, the printing needle diameter is 0.5 to 0.7 mm, and the spacing between the printing filaments is 0.4 to 0.6 mm.

9. The implantable temperature sensor prepared by the method for preparing an ultra-thin lithium-ion battery implantable temperature sensor according to claim 1.

10. The implantable temperature sensor according to claim 9 is applied to a lithium-ion battery.

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