CN115621560A

CN115621560A - Thin film sensor and preparation method thereof

Info

Publication number: CN115621560A
Application number: CN202210810533.0A
Authority: CN
Inventors: 孙启皓; 胡潇然; 黎雨桐; 张语芯; 慎戈斐; 司致远; 李旭; 李辰骏; 向勇; 张晓琨
Original assignee: University of Electronic Science and Technology of China
Current assignee: University of Electronic Science and Technology of China
Priority date: 2022-07-11
Filing date: 2022-07-11
Publication date: 2023-01-17

Abstract

The invention provides a lithium ion battery pressure and temperature monitoring thin film sensor based on a flexible printed circuit anode current collector, which relates to the field of battery sensors and comprises an electrode material, a current collector, a sensing layer and a high polymer coating from bottom to top.

Description

Thin film sensor and preparation method thereof

Technical Field

The invention belongs to the technical field of battery sensors, and particularly relates to a thin film sensor and a preparation method thereof.

Background

Compared with disposable energy sources such as petroleum and natural gas, the lithium battery has received considerable attention due to its high power density, long service life and relatively low influence on the environment, and thus has been widely used in mobile devices, electric vehicles and biomedical devices.

Lithium Ion Batteries (LIBs) are complex electrochemical systems whose health, safety and lifetime during operation are directly or indirectly influenced by factors during operation, such as manufacturing processes, electrode materials, working environment, etc. The deterioration of the battery material during use seriously affects the safety of the battery, and may cause local overheating or sudden increase in pressure of the battery. External influences, such as overcharge and overdischarge, impacts, drops, punctures, crushing, etc., may also cause problems, including internal short circuits and swelling of the battery, resulting in a sudden increase in the internal temperature and pressure of the battery. Both of these conditions can cause irreparable damage to the structure of the cell and create safety issues. Furthermore, as the size and capacity of batteries increase, they are subject to considerable non-uniformity in temperature distribution, with the accompanying phenomenon of internal swelling. The sudden increase in the temperature of the battery and the swelling phenomenon may even cause serious safety accidents, and accidents caused by spontaneous combustion or explosion of the battery have been increasing in recent years.

Lithium batteries generally employ a sealed structure. Throughout the life cycle of such batteries, electrical/chemical/force/thermal multi-field coupling interactions occur when in use. In-situ characterization of the internal mechanical and temperature parameters of a battery is therefore crucial to managing the safety of the battery.

As a sealing system, a large sensor device cannot be embedded in a battery to monitor its safety performance, and a sensor is generally placed on the outer surface of the battery to directly monitor changes in the internal environment of the battery. Previous studies have also used electrochemical models and algorithms to analyze electrical performance characteristic parameters detected during cell operation, but they typically require extensive support data.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a thin film sensor and a preparation method thereof, aiming at realizing direct and real-time monitoring on mechanical and thermal damages in a battery under the condition of not interfering the normal work of the battery, so as to more accurately provide early warning for battery faults, prevent the battery faults from causing large-scale accidents and catastrophic faults and obviously improve the safety performance of the battery.

In order to realize the purpose, the invention adopts the following technical scheme:

the utility model provides a lithium ion battery pressure and temperature monitoring film sensor based on flexible printed circuit positive pole mass flow body, its includes by bottom to last electrode material layer, current collector layer, sensing layer and the high molecular polymer coating that sets gradually, wherein, the material of electrode material layer is flexible graphite, the current collector layer is made with the copper electroplating complex by the polyimide as the base plate, the sensing layer is integrated on the current collector layer, the sensing layer is made by piezoelectricity and the polyvinylidene fluoride-trifluoroethylene material of pyroelectricity, the high molecular polymer coating with be used for monitoring pressure, temperature the sensing layer all forms on the copper electroplating layer of current collector layer through the mode of sculpture and/or coating.

Preferably, the current collector layer is formed by composite plating of a light interface-modified polyimide as a support and ultra-thin copper plating layers on both surfaces thereof.

Preferably, two sensor electrode pads which are not connected with each other and have different sizes are formed in the central area of the ultra-thin electroplated copper layer on one side of the current collector layer by etching, and the two sensor electrode pads are respectively connected with two copper signal leads.

Further preferably, the side on which the sensor electrode pad is formed is located on the side away from the electrode material layer.

Preferably, the polyvinylidene fluoride-trifluoroethylene material covers the sensor electrode pads with larger size in a form of a film, and the polyvinylidene fluoride-trifluoroethylene film is connected with the electrode pad with smaller size in the two sensor electrode pads by using a conductive copper foil belt; and wherein the polyvinylidene fluoride-trifluoroethylene film is slightly larger than the pad in both the length and width directions.

Preferably, the polyvinylidene fluoride-trifluoroethylene film is formed by carrying out annealing process and in-situ polarization treatment on a polyvinylidene fluoride-trifluoroethylene solution, wherein a system adopted by the in-situ polarization mainly comprises a power supply, a grid and a rotary substrate, and a probe line array of the power supply comprises 12 parallel wires with the interval of 50 millimeters.

Preferably, the two copper signal leads connected to the sensor electrode pads are protected with a high molecular polymer coating, which is a polyimide film.

As a further preferred embodiment, the present invention also provides a method for preparing a thin film sensor for pressure and temperature monitoring of a lithium ion battery based on a flexible printed circuit anode current collector, which comprises the following steps:

step 1, plating ultra-thin electroplated copper layers on two sides of a polyimide substrate, and etching two sensor electrode pads in the central area of the ultra-thin electroplated copper layer on one side; the two electrode pads are not connected and are squares with different sizes;

step 2, connecting two sensor electrode pads by using copper signal leads respectively, and protecting the two sensor electrode pads by using polyimide films respectively so as to capture temperature and pressure signals;

step 3, uniformly coating the polyvinylidene fluoride-trifluoroethylene solution on the electrode pad with the larger size in the two sensor electrode pads drop by drop, and evaporating the electrode pad in a vacuum oven to form a polyvinylidene fluoride-trifluoroethylene film;

step 4, annealing and cooling the polyvinylidene fluoride-trifluoroethylene film, and then carrying out in-situ polarization treatment;

step 5, connecting the polyvinylidene fluoride-trifluoroethylene film and the electrode pad with the smaller size in the two sensor electrode pads by using a conductive copper foil belt to preliminarily obtain a film sensor main body based on piezoelectric and pyroelectric effects, and then coating polyimide glue on the film sensor main body to form a high-molecular polymer coating;

step 6, mixing graphite, carboxymethyl cellulose and styrene butadiene rubber binder according to a certain weight ratio, and then acting on the surface of a copper current collector based on a flexible printed circuit on the lower side of the sensor through a blade coating preparation technology to prepare an anode electrode;

step 7, liCoO ₂ Mixing the powder, the carbon black and the polyvinylidene fluoride binder according to a certain weight ratio, and then coating the mixture on an aluminum foil by a blade coating preparation technology to prepare a cathode electrode;

and packaging the battery by using the prepared anode electrode and cathode electrode, thereby obtaining the lithium ion battery pressure and temperature monitoring thin film sensor based on the flexible printed circuit anode current collector.

Preferably, the weight ratio in step 6 and step 7 is preferably 8.

Compared with the prior art, the invention at least has the following beneficial effects:

1. the PVDF-TrFE material of piezoelectric and pyroelectric has sensitive vertical dynamic force response and pyroelectric characteristics, dynamic mechanical and thermal signals can be jointly converted into electric signals in real time, and the sensor can respond to dynamic mechanical and thermal damage in real time based on the material, so that the early warning speed of the lithium ion battery fault is remarkably improved;

2. the micro thin-film sensor is integrated in the battery, so that mechanical and thermal damages in the battery can be directly monitored, the accuracy of the sensor is obviously improved, sufficient early warning is provided for battery faults, and the safety performance of the battery is obviously improved;

3. the polyimide is adopted as a substrate to electroplate an ultrathin metal layer, and a high-performance novel light composite current collector is prepared, so that the energy density, the weight and the safety performance of the lithium ion battery are obviously optimized;

4. the integration of a multi-parameter micro film sensor is realized on an anode current collector based on a Flexible Printed Circuit (FPC), and the negative effects of an implantable sensor on the speed and the cycle characteristics of a lithium ion battery are greatly reduced by adopting the process technologies of precision coating, printed electronics, weather-resistant packaging and the like;

5. the pressure and temperature rising positions can be positioned through the sensor array, the operation safety of the battery is further improved, and a theoretical basis is laid for a more accurate and efficient battery safety management system.

Drawings

The invention will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:

FIG. 1 is a flow chart of an LBPTMS manufacturing process;

fig. 2 is a schematic diagram of a battery integrated with LBPTMS;

FIG. 3 is a cross-sectional and top view of LBPTMS based on coating PVDFTrFE thin film on one side of FPC;

FIG. 4 is a schematic view of a pressure test platform;

FIG. 5 is a schematic diagram of the structure and pressure response of LBPTMS;

fig. 6 is a graph of the pressure response signal of LBPTMS integrated within a battery;

fig. 7 is a graph of the relationship between the response signal and force of LBPTMS integrated within a battery;

FIG. 8 is a graph of the pressure response signal of a microsensor that is not packaged in a battery;

FIG. 9 is a graph of the relationship between force and microsensor response signal not encapsulated within a battery;

fig. 10 is an EIS test plot of an integrated LBPTMS cell at 0N and 10N pressures, respectively;

fig. 11 is a graph of LBPTMS swelling damage response signals integrated into a battery;

FIG. 12 is a schematic view of a thermal damage testing platform;

FIG. 13 is a schematic diagram of the structure and response of LBPTMS thermal damage;

FIG. 14 is a thermal imaging before laser heating;

FIG. 15 is a thermal image after laser heating;

FIG. 16 is a graph of the response signal of LBPTMS to low temperature ramping thermal damage;

FIG. 17 is a graph of the response signals of LBPTMS to high temperature heating thermal damage;

fig. 18 is an EIS test plot at elevated temperature for a battery integrated with LBPTMS;

fig. 19 is a discharge capacity plot for different C rates for LBPTMS integrated cells;

FIG. 20 is a graph of cycling performance at 0.5/0.5C for an LBPTMS integrated cell;

fig. 21 is a discharge capacity graph of a normal battery at different C rates;

FIG. 22 is a graph of the cycling performance of a normal cell at 0.5/0.5C;

fig. 23 is a plot of Cyclic Voltammetry (CV) for a cell integrated with LBPTMS versus a normal cell;

fig. 24 is a Nyquist plot for a cell integrated with LBPTMS at OCV and a normal cell;

fig. 25 is a Nyquist plot of the LBPTMS integrated cell and the normal cell after formation;

fig. 26 is a Nyquist plot for LBPTMS integrated cells and normal cells after rate testing;

in the drawings, like parts are provided with like reference numerals. The drawings are not to scale.

Detailed Description

Specific embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. While specific embodiments of the disclosure are shown in the drawings, it should be understood that the disclosure can be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

It should be noted that certain terms are used throughout the description and claims to refer to particular components. As one skilled in the art will appreciate, various names may be used to refer to a component. The description and claims do not intend to distinguish between components that differ in noun but not in function. In the following description and in the claims, the terms "include" and "comprise" are used in an open-ended fashion, and thus should be interpreted to mean "include, but not limited to. The description which follows is a preferred embodiment of the disclosure, but is made for the purpose of illustrating the general principles of the disclosure and not for the purpose of limiting the scope of the disclosure. The scope of the present disclosure is to be determined by the terms of the appended claims.

Specifically, it should be noted that in the description of the present invention, it is to be understood that the terms "upper", "lower", "bottom", "top", "front", "rear", "inner", "outer", "left", "right", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.

To facilitate an understanding of the embodiments of the present disclosure, the following detailed description is to be considered in conjunction with the accompanying drawings, and the drawings are not to be construed as limiting the embodiments of the present disclosure.

As shown in fig. 1 to 5, the present invention provides a Flexible Printed Circuit (FPC) -anode current collector-based lithium ion battery pressure and temperature monitoring thin film sensor (LBPTMS), which comprises an electrode material layer, a current collector layer, a sensing layer and a high polymer coating, which are sequentially arranged from bottom to top, wherein the electrode material layer is made of flexible graphite, the current collector layer is made of polyimide serving as a substrate and electroplated copper in a composite manner, the sensing layer is integrated on the current collector layer, the sensing layer is made of piezoelectric and pyroelectric polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) materials, and the high polymer coating and the sensing layer for monitoring pressure and temperature are formed on an electroplated copper layer of the current collector layer by etching and/or coating. The monitored pressure and temperature are the pressure and temperature inside the lithium ion battery.

Preferably, the current collector layer is formed by composite plating of a very thin copper plating layer on both surfaces thereof using a lightweight interface-modified Polyimide (PI) as a support.

Preferably, the polyvinylidene fluoride-trifluoroethylene material covers the sensor electrode pads with larger size in a form of a film, and the polyvinylidene fluoride-trifluoroethylene film is connected with the electrode pad with smaller size in the two sensor electrode pads by using a conductive copper foil belt; and wherein the polyvinylidene fluoride-trifluoroethylene film is slightly larger than the bonding pad in both the length and width directions.

Preferably, the two copper signal leads connected to the sensor electrode pad are protected by a high molecular polymer coating, which is a polyimide film (a film formed of PI paste).

As a further preferred embodiment, referring to fig. 1, the present invention also provides a method for preparing a thin film sensor for pressure and temperature monitoring of a lithium ion battery based on a flexible printed circuit anode current collector, which comprises the following steps:

step 1, plating ultrathin copper plating layers (with the thickness of about 5-50 μm, preferably 25 μm) on two sides of a polyimide substrate, and etching two sensor electrode pads in the central area of the ultrathin copper plating layer on one side; the two electrode pads are unconnected squares of different sizes (pad 1=6 × 6mm, pad2=3 × 3mm);

step 2, connecting the two sensor electrode pads by copper signal leads (T1, T2, 27 x 2mm) respectively, protecting by polyimide films (PI films) respectively, and capturing temperature and pressure signals;

step 3, uniformly coating a polyvinylidene fluoride-trifluoroethylene (PVDFTrFE) solution on an electrode pad with a larger size in the two sensor electrode pads drop by drop, and evaporating in a vacuum oven to form a polyvinylidene fluoride-trifluoroethylene film; wherein the PVDFTrFE solution is formed by dispersing PVDF-TrFE powder in butanone at room temperature (25 ℃), the thickness of the formed polyvinylidene fluoride-trifluoroethylene film is about 20 μm (the film thickness can be preferably in the range of 2-40 μm), and the PVDF-TrFE film is larger than that of the electrode pad by at least 1mm in the length and width directions;

step 4, annealing and cooling the polyvinylidene fluoride-trifluoroethylene film, and then carrying out in-situ polarization treatment; specifically, annealing the film at 140 ℃ for 30 minutes, cooling to 25 ℃, and then polarizing in situ;

step 5, connecting the polyvinylidene fluoride-trifluoroethylene film with the electrode pad with the smaller size in the two sensor electrode pads by using a conductive copper foil belt to preliminarily obtain a film sensor (LBPTMS) main body based on piezoelectric and pyroelectric effects, and then coating PI glue (a high polymer coating) on the film sensor main body; the PI glue can protect piezoelectric and pyroelectric signals of LBPTMS, and eliminates the influence of electric signals of a thin film sensor on the performance of the battery from the interference of electrochemical signals inside the battery during charging and discharging;

step 6, mixing graphite, carboxymethyl cellulose and styrene butadiene rubber binder according to a certain weight ratio (preferably 8;

step 7, liCoO ₂ (LCO) powder, carbon black, polyvinylidene fluoride (PVDF) binder are mixed in a certain weight ratio (preferably 8; thus, the pressure and temperature monitoring thin film sensor of the lithium ion battery based on the flexible printed circuit anode current collector is prepared.

The pouch integrated with LBPTMS (LIB) was obtained by lamination, liquid injection, battery packaging and other steps as shown in fig. 2; fig. 3 shows a cross-section, a top view and a sample image of LBPTMS coated with PVDF-TrFE film on one side of FPC and negative electrode material on the other side.

After the lithium ion battery pressure and temperature monitoring film sensor based on the flexible printed circuit anode current collector is obtained, various performances of the lithium ion battery need to be tested, and specific test results are as follows:

and (3) testing the performance of the sensor:

the piezoelectric coefficient d33 of the PVDF film was measured using a WXSHIAO YE2730A quasi-static scanner. The response of LBPTMS to stress (4N/6N/8N/10N) and thermal damage was evaluated using NTI AG HS 01-37X 166 linear motors and lasers with excitation wavelength and power of 808nm and 1W, respectively, and collected using a Keithley 6514 system electrometer and a Stanford Research SR570 low noise current preamplifier, respectively. The speed and cycling performance of the cells were measured using the Land CT 2001A cell test system. The rate test was charged at 0.5C, discharged at 0.2C, 0.5C, 1C, and 2C current densities, respectively. The cycle test was carried out at room temperature for 100 cycles at a constant charge/discharge current density of 0.5C/0.5C with a cut-off potential of 3-4.2V. Cyclic Voltammetry (CV) curves were performed between 2-4.5V at a scan rate of 0.1mV s ^-1 Measured by electrochemical workstation (CHI 660, chenghua, china). Electrochemical Impedance Spectroscopy (EIS) was performed using a potentiostat (VersasTAT 3F, princeton Applied Research) at a frequency range of 105-0.05 Hz.

And (3) pressure test results:

dynamic mechanical damage includes external force impact, breakdown, drop damage, which may cause the battery to deform and break. According to the piezoelectric performance test platform developed by the research, the linear motor with the force display screen is utilized to simulate the response of LBPTMS in the battery to suddenly increased external force impact. The piezo response signal leads T1 and T2 are connected to the NI capture card and a small bulb is connected to the battery to verify its status at the same time. All devices were placed on a stainless steel table and grounded to reduce interference with the acquired signals, as shown in fig. 24.

After in-situ polarization treatment, the PVDF-TrFE film is converted from alpha crystals into beta crystals, and then the piezoelectric coefficient of the PVDF-TrFE film is enhanced through the oriented arrangement of dipoles after the polarization treatment; the d33 piezoelectric coefficient of the thin PVDF-TrFE film sensor is improved from 1-2 to 17 +/-2 pC/N, and the thin PVDF-TrFE film sensor can quickly respond to external force stimulation in the z direction. At this time, the crystal lattice is deformed due to stress, the electric dipoles are rotationally aligned, the centers of the positive and negative charges shift, charges are induced at the two ends, and an electric signal is output. Thus, different electrical signals can be collected, as shown in fig. 5.

The piezoelectric response signals of LBPTMS to external force impacts are shown in fig. 6-9. Applying a periodic external force impact to LBPTMS integrated inside the cell, the sensor exhibits a periodic piezoelectric pulse voltage response due to the polar crystal deformation of the PVDF-TrFE thin film sensor. When LBPTMS integrated in the battery is struck by forces of 4, 6, 8 and 10N, the piezoelectric pulse voltages are-1.9, -2.4, -4.8 and-8.2 mV, respectively, and the lamp operates normally, as shown in fig. 6. From the fitting result of fig. 7, it can be seen that the absolute value of the piezoelectric pulse voltage increases with the increase of the applied external force, which shows that the sensor can respond to different external force impact values in real time and has better sensitivity.

The piezoelectric pulse voltages were-2.3, -4.5, -7.9, and-13.2 mV when the non-battery encapsulated microsensor was impacted with 4, 6, 8, and 10N forces, respectively, as shown in fig. 8. Fitting the absolute value of the negative pressure, the piezoelectric signal increases with the increase of the external force, and the relationship is positive correlation, as shown in fig. 9.

The sensor pulse voltage signal which is not encapsulated in the battery exceeds the pulse voltage signal of the sensor integrated in the battery, which is caused by the damping effect of the battery housing on the impact forces. Therefore, when the battery is impacted by external force, the built-in miniature membrane sensor can more accurately reflect the pressure change of the internal components of the battery, and the health state of the battery can be evaluated.

EIS testing of cells integrated with LBPTMS at 10N pressure is shown in fig. 10. The Nyquist diagram of the battery appears semicircular in the high-frequency region, which is attributed to Li ⁺ The resistance of (2) is diffused through a surface film (RSEI), a semicircle of a middle frequency region is assigned to Rct, a low frequency regionThe straight line of (2) is assigned to Zw. Experimental data, which were obtained from equivalent circuits, were simulated using ZView software. The RSEI of the cell was 0.41 Ω at no pressure, and decreased to 0.40 Ω at 10N, 1.71 Ω at no pressure, and 1.52 Ω at 10N. The Rct was 1.23 Ω under no compression and increased slightly to 1.28 Ω under 10N compression. EIS of a battery has a significant relationship with the degree of deterioration of the battery.

Swelling test results:

the cell can also inflate during overcharge, overdischarge, or extreme operating conditions, which can also result in a sudden increase in internal pressure. In the process of simulating bulging, we cannot short-circuit the cell, let it actually bulge, which may lead to thermal runaway or explosion of the cell. Therefore, a small hole is formed in the battery, the battery is inflated periodically by a manual cylinder, and then the battery is naturally deflated for about 0.5 s. Not all of the air is released during the deflation process. Within 5.5s, we underwent 8 cycles of the flatulence-healing process. The piezoelectric response is then collected by LBPTMS integrated in the battery. As the battery is manually charged using the manual cylinder, the battery continues to expand unevenly, resulting in uneven response signals acting on the raised portions. During the periodic gassing, a certain area of the battery sample expands, causing different degrees of compression and deformation of the PVDF-TrFE film along the vertical direction, resulting in non-uniform response signals acting on the bulge, with a maximum value of-3.5 mV. When the bat state recovered from ballooning, the PVDF-TrFE film morphology recovered and the voltage dropped accordingly, producing a small positive voltage spike of about 1mV, as shown in fig. 11. During the periodic inflation-recovery process, the piezoelectric response signal differs in magnitude and direction during inflation and recovery, since the force of inflation is greater than the force of natural recovery, and the force acting on the sensor is in the opposite direction. During recovery, the pressure continued to drop over time, and the response curve showed some small interfering peaks near the 1mV peak.

LBPTMS can detect not only mechanical shock but also battery swelling. The output of the electric signals can be detected in real time, which is helpful for more accurately evaluating the health condition of the bat.

Temperature test results:

thermal damage to lithium batteries is typically manifested as a sudden increase in temperature of a region of the battery or the entire battery. If the temperature of the battery continues to rise, accidents such as internal short circuits, rupture of the battery case, leakage of liquid, fire, etc. may be caused. Therefore, monitoring the internal temperature of the battery is crucial in battery health management. The research utilizes the pyroelectric effect of the polarized PVDF-TrFE film to determine the response of the film to the temperature surge of the battery inner polar plate. And (3) directly carrying out a thermal damage test on the LBPTMS, and accurately detecting the temperature change and response inside the battery. Since temperature changes in bats are typically instantaneous, here we use a relatively fast ramp rate 1.3 ℃/s test. In the experiment, the LBPTMS is periodically irradiated by infrared laser. Laser irradiation causes a temperature rise and laser ablation causes a temperature drop, with the voltage signals generated by heating and cooling being in opposite directions, including 4 cycles within about 13 s. Thermal damage was simulated using a laser heater that periodically heated the cell sample from 32.4 ℃ to about 33.7 ℃ at a rate of 1.3 ℃/s as shown in fig. 12-15. The sample was then cooled back to 32.4 ℃ within a few seconds as shown by the thermographic results shown in fig. 14, 15. The pyroelectric voltage impulse response is due to the change of the orientation degree of the dipoles in the PVDF-TrFE film, and the maximum pyroelectric impulse voltage is 125 μ V, as shown in FIG. 16. Therefore, when the internal temperature of the battery suddenly rises (1.3 ℃), the lithium removal pulse voltage signal (125 μ V) can be sensed in real time, and the evaluation of the health performance of the battery is facilitated.

In addition, in order to verify that the sensor can also identify high-temperature change, a high-temperature response experiment is also carried out, and the test temperature is about 15-300 ℃. In this experiment, a burning candle was used to periodically irradiate the LBPTMS, simulating the response of the sensor when the cell suddenly burned. The thermoelectric pulse voltage signal (2.25 mV) was sensed in real time as the burning candle (flame temperature about 300 ℃ C.) was instantaneously approached, as shown in FIG. 17. The sensor can not only identify relatively low temperature rise, but also identify relatively high temperature.

The EIS test at 1.3 ℃ temperature rise for the cell integrated with LBPTMS is shown in fig. 17. The Rs of the battery is 0.42 omega without temperature rise, and is slightly reduced to 1.3 ℃ below 0.4 omega. The RSEI of the cell is 1.13 omega under the condition of no temperature rise, and slightly decreases to 1.11 omega under the temperature rise of 1.3 ℃. Rct without temperature rise was 1.85 Ω, and slightly decreased to 1.42 Ω at 1.3 ℃ temperature rise.

LBPTMS can directly respond to internal pressure and thermal damage of the battery in real time. Piezoelectric and pyroelectric response signals can be screened by an oscilloscope and peak separation software, different signals are separated, and the signals are visually distinguished through the difference of response curves. The piezoelectric signal is a pulse, and the pyroelectric signal has a certain delay in temperature response. The difference between the two response curves can be seen visually from fig. 6, 8 and 16.

Electrochemical performance test results:

the miniature film sensor inside the battery can not only detect mechanical pressure impact, but also respond to battery swelling and internal temperature changes. Since LBPTMS was encapsulated inside the cell, we performed rate tests on both LBPTMS integrated cells and normal cells to verify the effect of the sensor on the electrochemical stability of the cell. As shown in fig. 19 to 22, the discharge capacity retention rates of the LBPTMS-integrated batteries at 0.5, 1, and 2C were 100%, 96.7%, and 90.7% respectively, with respect to the discharge capacity at 0.2C, and the discharge capacity loss rate was 3.36% after the large-current discharge was returned to 0.2C. In addition, the discharge capacity of the normal battery at 0.5, 1 and 2C with respect to 0.2C was 96.7%, 95.4% and 92.6%, respectively. After the large current discharge, the discharge capacity was restored to 0.2C, and the discharge capacity loss rate was 3.39%, as shown in fig. 19. As can be seen from fig. 19, 21, the discharge capacity retention rate of the LBPTMS-integrated battery was very similar to that of the normal battery at 0.2, 0.5, 1, 2c rate discharge.

Under the constant current density of 0.5/0.5C, the performance of the battery integrating LBPTMS and the common battery cell for 100 cycles is shown in figures 20 and 22, and after being combined with the LBPTMS, the battery still maintains the high capacity of 85.24 percent after 100 cycles, as shown in figure 20.

FIG. 6 shows LBPTMS integrated cells at 0.1mV s ^-1 Velocity of (2) to 4.5V scans. LCO delithiation occurs when the potential is swept from 2 to 4.5V, while LCO delithiation also occurs when the potential is swept from 4.5 to 2V.

During the fade, the LBPTMS integrated cell exhibited an oxidation current peak at 3.85V, while the normal cell exhibited an oxidation current peak at 3.83V. Under the same conditions, the LBPTMS-integrated cell showed two reduction peaks at 3.60 and 4.23V, while the normal cell showed two reduction peaks at 3.63 and 4.25V. The location of the redox peaks of the LBPTMS-integrated cell was very similar to that of the normal cell, further illustrating that the electrical performance of the LBPTMS-integrated LCO cell was very similar to that of the normal LCO cell, while the introduction of LBPTMS did not cause electrochemical side reactions.

Electrochemical impedance spectroscopy analysis and testing was performed on cells integrated with LBPTMS and regular cells in the sweep frequency range of 105-0.05Hz after Open Circuit Voltage (OCV), formation and rate testing. As shown in fig. 24, the nyquist plot of the cell at OCV appears as a semicircle in the high frequency region due to charge transfer electrophoresis-resistance (Rct) and a straight line, a slanted line in the low frequency region due to Li + in vivo diffusion process (Zw) [24,25]. Rct for normal batteries is lower than for batteries with integrated LBPTMS. The Nyquist plots (fig. 25, 26) of the cell after formation and rate testing exhibited a semicircular shape in the high frequency region due to the resistance of Li + diffusion through the surface film (RSEI), a semicircle in the medium frequency region, attributed to Rct, and a straight line in the low frequency region, attributed to Zw. The continuous increase in Rct is believed to be the primary cause of the decline in battery capacity, further explaining the decay mechanism of long-cycle data. The ohmic resistance (Rs) of a normal cell was 0.24, 0.21, and 0.23 Ω at OCV, respectively, after formation, after rate testing. The RSEI value after formation was 0.67 Ω, and the rate slightly increased after rate testing to 0.91 Ω. The Rct for the three phases is 0.70, 0.58 and 1.20 Ω, respectively. The Rs, RSEI and Rct values of the normal cell at three stages are all smaller than the cell with integrated LBPTMS. The impedance difference between the LBPTMS-integrated cell and the conventional cell is small, which means that the influence of the fpc-based anode current collector-based embedded micro-thin film sensor pair is small, and the electrochemical impedance of the cell does not significantly affect the cell characteristics, which is consistent with the rate and cycle characteristics described above.

The invention takes the light polyimide material as a support body, the current collector is prepared by compounding the copper films on the two surfaces of the support body, and the total thickness of the prepared new current collector is reduced by 80 percent compared with the original pure metal current collector under the condition that the total thickness is not increased because the organic matter is greatly lighter than metal. Due to the weight ratio of the current collector is reduced, the energy density of the battery can be improved by 8-26% (specific data are different according to different battery types). Meanwhile, the invention increases the steric hindrance of a molecular chain by introducing the trifluoroethylene monomer into the vinylidene fluoride, is favorable for realizing C-F dipole directional orientation, and improves the residual polarization strength, thereby improving the pyroelectric performance of the polymer. As the pyroelectric performance of the pyroelectric polymer directly influences the performance of the sensor, the sensor is prepared by selecting a PVDFTrFE material. The PVDFTrFE polymer is mainly a beta-phase crystal with a polar crystal structure, shows stronger pyroelectric performance, and has sensitive vertical dynamic force response and pyroelectric characteristics. After in-situ polarization treatment, the PVDFTrFE film is converted into beta crystals from alpha crystals, and then the piezoelectric coefficient of the PVDF-TrFE film is enhanced through the oriented arrangement of dipoles after the polarization treatment; the d33 piezoelectric coefficient of the PVDFTrFE film sensor is improved from 1-2 to 17 +/-2 pC/N, and the PVDFTrFE film sensor can quickly respond to external force stimulation in the z direction. At this time, the crystal lattice is deformed due to stress, the electric dipoles are rotationally aligned, the centers of the positive and negative charges shift, charges are induced at two ends, and an electric signal is output. Therefore, different electric signals can be collected, the invention uses the piezoelectric/thermoelectric poly (vinylidene fluoride-trifluoroethylene) (PVDFTrFE) film to form a lithium ion battery pressure/temperature monitoring micro thin film sensor (LBPTMS), the micro thin film sensor is integrated with an anode current collector based on a Flexible Printed Circuit (FPC), piezoelectric and pyroelectric response signals are screened by an oscilloscope and peak separation software, different signals are separated, and the LBPTMS can directly respond to the internal pressure and thermal damage of the battery in real time through the difference of response curves. The features mentioned above can be combined in various suitable ways or replaced by equivalent features as long as the object of the invention is achieved.

The foregoing detailed description of the preferred embodiments of the invention has been presented. Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that various dependent claims and the features described herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.

Claims

1. The utility model provides a lithium ion battery pressure and temperature monitoring film sensor based on flexible printed circuit positive pole mass flow body, its characterized in that, it includes by bottom to last electrode material layer, current collector layer, sensing layer and the high molecular polymer coating that sets gradually, wherein, the material on electrode material layer is flexible graphite, the current collector layer is made by polyimide and the copper electroplating complex as the base plate, the sensing layer is integrated on the current collector layer, the sensing layer is made by piezoelectricity and the polyvinylidene fluoride-trifluoroethylene material of pyroelectricity, the high molecular polymer coating with be used for monitoring pressure, temperature the sensing layer all forms on the copper electroplating layer of current collector layer through the mode of sculpture and/or coating.

2. The lithium ion battery pressure and temperature monitoring thin film sensor based on the flexible printed circuit anode current collector is characterized in that the current collector layer takes light polyimide subjected to interface modification as a support body, and an ultrathin electroplated copper layer is formed on two surfaces of the current collector layer through composite electroplating.

3. The lithium ion battery pressure and temperature monitoring thin film sensor based on the flexible printed circuit anode current collector is characterized in that the central area of the ultrathin copper electroplating layer on one side of the current collector layer is etched to form two unconnected sensor electrode pads with different sizes, and the two sensor electrode pads are respectively connected with two copper signal leads.

4. The pressure and temperature monitoring thin film sensor of a lithium ion battery based on a flexible printed circuit anode current collector as claimed in claim 3, wherein the side where the sensor electrode pad is formed is located at the side away from the electrode material layer.

5. The pressure and temperature monitoring thin film sensor of the lithium ion battery based on the flexible printed circuit anode current collector is characterized in that the polyvinylidene fluoride-trifluoroethylene material is covered on the larger one of the two sensor electrode pads in the form of a thin film, and the polyvinylidene fluoride-trifluoroethylene thin film is connected with the smaller one of the two sensor electrode pads by a conductive copper foil tape.

6. The pressure and temperature monitoring thin film sensor of the lithium ion battery based on the flexible printed circuit anode current collector is characterized in that the polyvinylidene fluoride-trifluoroethylene thin film is formed by carrying out annealing process and in-situ polarization treatment on a polyvinylidene fluoride-trifluoroethylene solution, the system adopted by the in-situ polarization mainly comprises a power supply, a grid and a rotating substrate, and a probe line array of the power supply comprises 12 parallel wires with the interval of 50 mm.

7. The lithium ion battery pressure and temperature monitoring thin film sensor based on the flexible printed circuit anode current collector in claim 5, is characterized in that two copper signal leads connected with the sensor electrode pad are protected by a high polymer coating, and the high polymer coating is a polyimide film.

8. The method for preparing the pressure and temperature monitoring thin film sensor of the lithium ion battery based on the flexible printed circuit anode current collector of one of claims 1 to 7, comprising the steps of:

step 1, plating ultrathin copper plating layers on two sides of a polyimide substrate, and etching two sensor electrode pads in the central area of the ultrathin copper plating layer on one side; the two electrode pads are not connected and are squares with different sizes;

step 5, connecting the polyvinylidene fluoride-trifluoroethylene film with the electrode pad with the smaller size in the two sensor electrode pads by using a conductive copper foil belt to preliminarily obtain a film sensor main body based on piezoelectric and pyroelectric effects, and then coating polyimide glue on the film sensor main body to form a high-molecular polymer coating;

9. The production method according to claim 8, wherein the certain weight ratios in step 6 and step 7 are preferably 8.

10. Use of the flexible printed circuit anode current collector based lithium ion battery pressure and temperature monitoring thin film sensor of one of claims 1 to 7 integrated inside a lithium ion battery.