CN115133029A

CN115133029A - Transformation method of lithium battery pole piece and lithium battery

Info

Publication number: CN115133029A
Application number: CN202110312701.9A
Authority: CN
Inventors: 冼剑光
Original assignee: Zhan Biwei
Current assignee: Jitong Technology (Guangzhou) Co.,Ltd.
Priority date: 2021-03-24
Filing date: 2021-03-24
Publication date: 2022-09-30

Abstract

The invention relates to a lithium battery pole piece transformation method and a lithium battery, and is based on an innovative discovery that the existing lithium battery positive pole piece structure mainly comprises an active material, a conductive material and a PVDF (polyvinylidene fluoride) adhesive of a high molecular polymer, so that the positive pole piece structure actually comprises a PPTC (positive temperature coefficient of the high molecular polymer) core structure, and therefore, a PTC (positive temperature coefficient) effect exists, and the battery cannot be sufficiently protected only because the effect is weak. Based on the discovery, the invention strengthens the PPTC structure of the positive plate structure of the lithium battery, transforms the positive plate structure of the lithium battery into the strong enough PPTC, forms the lithium battery, imagines that the whole battery positive electrode is filled with the PPTC unit, and all positive active materials are surrounded by the PPTC unit, thereby providing better thermal runaway protection for the battery.

Description

Transformation method of lithium battery pole piece and lithium battery

Technical Field

The invention relates to a lithium battery pole piece transformation method and a lithium battery, and belongs to the field of batteries and electrical equipment.

Background

In recent years, the ignition of the electric car occurs from time to time, the ignition is mainly caused by a battery loaded on the electric car, wherein the lithium ion battery accounts for a large proportion, and the important reason of the ignition of the lithium ion battery is thermal runaway caused by overheating inside the battery, and the overheating is most likely to occur in the charging and discharging processes of the battery. Because the lithium ion battery has certain internal resistance, certain heat can be generated during charging and discharging, the temperature of the lithium ion battery is increased, and after the temperature is continuously increased and exceeds a safety threshold value, thermal runaway is caused, and finally spontaneous combustion and explosion of the battery are caused.

The ignition and explosion of the battery directly threatens the safety of users, and an effective prevention and coping scheme is urgently needed to be found.

Disclosure of Invention

The invention shows a technical scheme for preventing thermal runaway of a battery.

The polymer matrix is filled with conductive materials such as Carbon Black (CB) and metal powder to obtain a composite conductive material, which generally has a PTC effect (Positive Temperature Coefficient), and thus, the manufactured element is a pptc (polymeric Positive Temperature Coefficient), i.e., a polymer Positive Temperature Coefficient element. When the temperature reaches a specific temperature turning point, the resistance is increased by several orders of magnitude, so that the passing current is reduced sharply, and therefore, the PPTC can provide effective overheat protection and is widely applied to many fields.

The invention is based on an innovative discovery: the existing positive plate structure of the lithium battery mainly comprises an active material, a conductive material and a PVDF (polyvinylidene fluoride) adhesive of a high polymer, which actually comprises a PPTC core structure, so that a PTC effect is generated, and the battery cannot be sufficiently protected due to the weak effect.

The invention is based on the discovery that the positive plate structure of the lithium battery is reinforced by the PPTC structure, and the reinforcing measures are any part combination or all of the following:

1. and carrying out crosslinking treatment on the high molecular polymer of the positive plate.

2. More than two high molecular polymers with different melting points are used as the positive plate adhesive to form a high molecular matrix of the positive electrode, wherein when the polymer with the lowest melting point reaches the melting point of the polymer, the matrix generates double-permeation behavior because of the existence of a composition with a higher melting point, and the whole matrix cannot be melted.

3. Conductive particles with low resistivity are added, including nano-scale carbon nanotubes, metal powder, metal carbide powder and the like.

4. And adjusting the proportion of each substance of the positive plate.

5. The high molecular polymer of the positive plate adopts a low-melting-point copolymer.

6. And carrying out thermal annealing treatment on the positive plate.

After the structure of the positive plate of the lithium battery is modified into the strong enough PPTC to form the lithium battery, the whole battery positive electrode is imagined to be full of PPTC units, and all positive active materials are surrounded by the PPTC units, so that better thermal runaway protection can be provided for the battery.

In the present invention, the core spirit of the present invention is mainly explained based on the existing lithium ion battery, and it can be understood by those skilled in the art that the core spirit of the present invention is applicable to various battery forms such as lithium ion battery, lithium solid state battery, lithium metal battery, fuel battery, etc.

The invention is further illustrated by the following examples in conjunction with the drawings.

Drawings

Fig. 1 is a positive electrode sheet structure in a lithium ion battery.

In fig. 1, 10 is a current collector, 11 is a positive electrode coating layer including 101, 102 and 103, 101 is a positive electrode active material, 102 is conductive particles, and 103 is a polymer binder.

Fig. 2 is a schematic diagram of series-parallel connection of batteries.

Fig. 2 shows a plurality of battery cells in the lithium ion battery, which are connected in series to form a battery string, and are connected in parallel to form a battery pack. In the drawings, 1, 2 and 3 represent a battery string composed of battery cells connected in series, the

battery cells

101, 102 and 103 constitute a battery string 1, the

battery cells

201, 202 and 203 constitute a battery string 2, and the

battery cells

301, 302 and 303 constitute a battery string 3. The battery string 1, the battery string 2, and the battery string 3 are connected in parallel to form a battery pack.

110 is a relay of the battery string 1, and when the current of the battery string 1 is too large, the relay 110 is cut off, so that the whole battery string 1 is disconnected.

210 is a relay of the battery string 2, and when the current of the battery string 2 is too large, the relay 210 is cut off, thereby disconnecting the whole battery string 2.

The relay 310 is a relay of the battery string 3, and when the current of the battery string 3 is too large, the relay 310 is cut off, so that the whole battery string 3 is disconnected.

Detailed Description

The embodiments of the present invention will now be described in detail with reference to the drawings, in which:

interpretation of some nouns:

the PPTC structure: in the invention, pptc (polymeric Positive Temperature coefficient) refers to a high polymer Positive Temperature coefficient structure formed by a Positive electrode, and includes a Positive electrode active material, conductive particles such as Carbon Black (CB), and a pvdf (polyvinylidene fluoride) adhesive of a high polymer.

A battery management system: BMS (Battery Management System) is an important component of the power battery system of the electric automobile. The method comprises the steps of monitoring the single batteries in real time, sending out safety early warning when potential safety hazards are found, and cutting off the single batteries or battery strings (battery packs) with abnormal isolation when the single batteries are abnormal.

PPTC unit: in the positive plate structure, around each active material particle, there will be a microscopic PPTC structure connecting the active material particle and the current collector.

Explanation of the prior art:

lithium battery structure: the main constituent materials of the lithium ion battery comprise electrolyte, an isolating membrane, a positive active material, a positive conductive material, a negative material, a positive current collector, a negative current collector and the like. According to the difference of the positive active materials, the common lithium batteries in the market at present are classified into lithium iron phosphate batteries and ternary lithium batteries. The positive active material of the lithium iron phosphate battery is lithium iron phosphate. The ternary lithium battery is subdivided into an NCM battery and an NCA battery, the NCM means that a positive electrode active material is nickel-cobalt-manganese lithium manganate, the three materials are combined according to a certain proportion, the positive electrode material of the NCA is nickel-cobalt-lithium aluminate, the three materials are combined according to a certain proportion, and each letter corresponds to a chemical initial letter of a related element. The positive electrode conductive material is usually Carbon Black (CB), and the active material generally has a high resistivity, and a conductive material needs to be added to reduce the on-resistance with the current collector. In the common lithium battery in the market at present, the negative electrode material is usually graphite. The current collector of the positive electrode applied to actual production is aluminum foil, the thickness is generally 10 to 20um, the current collector of the negative electrode is copper foil, and the thickness is generally 4.5 to 10 um. The isolating membrane is a microporous and porous membrane, is mainly made of PE (polyethylene, polyethylene for short) and PP (polypropylene for short), is arranged between a positive electrode and a negative electrode, is mainly used for isolating the positive electrode and the negative electrode to prevent the internal short circuit of the battery, and has an important function of enabling electrolyte ions to pass through.

PTC effect of polymer: filling a high molecular polymer matrix with a conductive filler such as Carbon Black (CB) or metal powder results in a composite conductive material, which generally has a PTC effect. The cause of the PTC effect has been much explored. One reasonable explanation is that at normal temperature, the conductive particles form conductive chains in the high molecular polymer matrix, the resistivity is low, and as the temperature rises, because the thermal expansion coefficient of the conductive particles is far lower than that of the high molecular polymer matrix, the distance between the conductive particles is increased due to the difference of the expansion degrees, so that the current path formed by the conductive particles is broken, and the resistivity is increased. In the vicinity of the melting point of the high-molecular polymer matrix, the volume expansion of the composite conductive material sharply increases, and the resistivity sharply increases. The volume expansion curve of the composite conductive material is very similar to the shape of the resistivity change curve, and the transition temperatures of the resistivity change curve and the volume expansion curve are basically consistent, which shows that the PTC characteristic and the volume expansion do have an internal relation.

PPTC (polymeric Positive Temperature coefficient) i.e. a high molecular polymer Positive coefficient Temperature element. Also known as Resettable fuses (Resettable fuses) or polymer fuses (Poly fuses), are commonly referred to as self-restoring fuses or overcurrent protection plates in China. It is often called a polymer Switch (Poly Switch) abroad. The published data shows that PPTC, a trade name of Raychem (which has been incorporated into Tyco Electronics), was invented in 1981 and is mainly applied to overcurrent protection of various electronic products in the industries of batteries, computers, motors, communications and the like. PPTC is a mature and reliable application, currently on the order of $ 4 billion per year worldwide. The PPTC currently on the market is mainly applied as a single element. The published data show that the PPTC application using PVDF as the high molecular polymer is also common and the PTC effect is significant, which means that the PPTC structural reinforcement of the existing lithium battery positive electrode sheet structure is economically feasible.

PTC trip temperature: when the temperature reaches the trip temperature, the resistance of the PTC increases sharply, the current becomes sharply small, and the safety of the battery is protected. The main determinants of the trip temperature include the melting point of the high molecular polymer and the doping concentration of the conductive particles. As the doping concentration of the conductive particles decreases, the trip temperature gradually moves toward a low temperature, below the melting point of the polymer.

Magnitude of resistance jump of PPTC cell: after the temperature crosses the PTC trip temperature, the maximum resistance achieved by the PPTC unit is often several orders of magnitude greater than the resistance at 25 ℃ room temperature. The resistance jump order of magnitude is 7, which represents that the highest resistance is 10 of the resistance value at the room temperature of 25 DEG C ⁷ Times, i.e., the 7 th power of 10.

NTC effect of PPTC cells: the resistivity of the PPTC unit increases along with the increase of temperature, and when the temperature rises to be near the melting point of the high molecular polymer, the resistivity sharply increases, and the obvious PTC effect is presented. After the resistance reaches the peak value, it starts to drop sharply again with further increase of the Temperature, and exhibits NTC (Negative Temperature Coefficient) resistance effect. The NTC effect is caused by that after the high molecular polymer reaches the melting point, the high molecular polymer becomes soft and even can flow, the conductive filler moves and aggregates, and the stability and reliability of the PPTC are reduced by the NTC effect. The method for eliminating the NTC effect comprises the following steps: 1. limiting the movement and agglomeration of the conductive particles by crosslinking; 2. more than two polymers with different melting points are used as a matrix to replace a single polymer, wherein the polymer with the lowest melting point has PTC effect when reaching the melting point, but the matrix has a composition with a higher melting point, so that double-permeation behavior occurs, and the whole matrix can not be melted; 3. surface treatment of the conductive particles, such as carbon black oxidation, high temperature treatment, etc., improves surface properties of the conductive particles, thereby improving compatibility of the conductive particles with the polymer.

And (3) crosslinking: the high molecular polymers are mutually bonded and crosslinked into a three-dimensional network structure, and the reaction converts linear or slightly branched macromolecules into a three-dimensional network structure, so that the performances such as strength, heat resistance, wear resistance, solvent resistance and the like are improved. The irradiation crosslinking refers to the crosslinking reaction of the high molecular polymer by using electron beams generated by an electron accelerator or cobalt 60 gamma rays.

Maximum safe temperature of the battery: in order to ensure the safety of the battery, the internal temperature of the battery needs to be closely controlled and limited below a certain temperature value. Generally, this temperature needs to be controlled below the melting point of the release film, which is about 130 ℃ when the release film is PE, and about 160 ℃ when the release film is PP. After the isolating film is melted, the anode and the cathode lose isolation to cause short circuit. Therefore, when the separator is made of PE, the maximum safe temperature of the battery needs to be 130 ℃. Therefore, when the separator is made of PP material, the maximum safety temperature of the battery is required to be below 160 ℃.

The PTC trip temperature is lower than the battery maximum safe temperature.

The embodiment of the invention comprises the following steps:

the core of the invention is to strengthen the PPTC structure of the positive plate structure of the lithium battery.

The existing positive plate structure of the lithium battery actually comprises a PPTC core structure, so that a PTC effect can be generated, and the reason for the weak PTC effect comprises the following reasons:

1. the NTC effect of the PPTC unit is generated, when the battery is out of control thermally, the temperature rises rapidly, so that the battery rapidly crosses the PTC effect temperature range and enters the NTC effect temperature range, and the PTC protection effect is greatly weakened.

The magnitude of the resistance jump of the PPTC unit is not large enough, and the thermal protection effect is not sufficient.

3. The mass ratio of various materials of the anode does not consider PPTC at present, and various indexes of the PPTC unit are directly influenced.

4. The melting point of PVDF (polyvinylidene fluoride) used as the positive electrode adhesive of the conventional lithium battery is 170 ℃, the melting point of the separator of the conventional lithium battery is usually PE/PP, and when the separator is made of PE, the melting point is about 130 ℃, and when the separator is made of PP, the melting point is about 160 ℃. At 170 ℃, the isolating membrane of the battery is melted to cause short circuit of the anode and the cathode, so that the thermal runaway process is accelerated, and meanwhile, some internal components begin to decompose and generate heat. The melting point of the positive electrode adhesive is preferably 100-130 ℃, is lower than the melting point of the isolating membrane and is lower than the decomposition temperature of substances inside the battery, and the stability of the battery is facilitated.

5. The manufacturing process of the positive electrode does not consider PPTC at present, the high molecular polymer in the PPTC can form a good crystal state through thermal annealing treatment, and the crystal state directly influences various indexes of the PPTC unit.

The manufacturing process of the positive plate of the existing lithium battery comprises the following steps:

1. preparing materials: preparing a positive electrode active material, a positive electrode conductive material and a positive electrode binder, wherein the mass ratio of the positive electrode active material, the positive electrode conductive material and the positive electrode binder is generally (90-98): (0.5-5): 1-5);

2. pulping: the prepared material is mixed with a positive electrode solvent, and the solvent is usually any one of N-methylpyrrolidone NMP, dimethylformamide DMF or dimethylacetamide DMAC or a mixed solvent of at least two of the N-methylpyrrolidone NMP, the dimethylformamide DMF or the dimethylacetamide DMAC. And stirring the mixture by a stirrer to prepare pulp.

3. Coating: the slurry is coated on one side or two sides of a positive electrode current collector by a coating machine, wherein the positive electrode current collector is an aluminum foil, and the thickness of the positive electrode current collector is generally 15 microns. The coating film of the non-dried slurry obtained by the coating process is also referred to as "wet film".

4. Coating and drying: and (3) placing the wet film obtained by coating in an oven for heating and drying, wherein the drying technology comprises hot air drying, infrared drying, microwave drying and the like.

5. Rolling: the dried positive plate is compacted by a roller press, the thickness of the treated positive plate is more uniform, the surface is smooth, and the combination of the coating material and the current collector is enhanced.

The solution of the invention is as follows:

1. and the anode is subjected to crosslinking treatment, so that the thermal stability of the anode high-molecular polymer is improved, and the NTC effect is eliminated. Preferably, electron beam crosslinking is adopted, the energy of the electron beam is 2-10 Mev, the current of the electron beam is 5-20 mA, and the irradiation dose is 100-300 kGy. After the cross-linking treatment, the high molecular polymer of the positive electrode can form a three-dimensional network structure, so that the strength and the heat resistance are improved, and the NTC effect is eliminated. The crosslinking treatment is preferably performed after the coating of the above-described positive electrode sheet manufacturing process. The method can also be carried out after the rolling of the positive plate manufacturing process, and the high molecular polymer can be crosslinked and then crosslinked after the rolling because the mechanical processing performance is reduced after the high molecular polymer is crosslinked. The person skilled in the art can perform cross-linking treatment in any suitable step after the coating of the positive plate manufacturing process according to actual needs, and adjust parameters of electron beam irradiation according to actual application, wherein the selection principle of the parameters is to completely eliminate NTC effect, but not excessive, so that high-molecular polymer is hardened, and mechanical indexes are affected.

2. Instead of one, 2 or more high molecular polymers having different melting points are mixed, and the intervals between the melting points are preferably 30 ℃ or more, and are preferably both soluble in a solvent, which is usually any one of N-methylpyrrolidone NMP, dimethylformamide DMF or dimethylacetamide DMAC or a mixed solvent of at least two thereof. Preferably PVDF-HFP (Polyvinylidene fluoride-hexafluoropropylene copolymer), preferably having a melting point between 100 ℃ and 130 ℃, mixed with PVDF having a melting point of 170 ℃ in a mass ratio such that a PTC effect is produced at the melting point of PVDF-HFP, but the mixture does not melt and can withstand higher temperatures due to the presence of PVDF having a higher melting point. The present invention illustrates this core spirit, and one skilled in the art can apply it to any suitable polymeric formulation under this direction. The part belongs to the material preparation step of the positive plate manufacturing process, and the high molecular polymer belongs to the positive electrode binder in the process.

3. Adding conductive particles with low resistivity, including but not limited to the following materials, or a combination of the following materials: conductive carbon black or nano-sized carbon nanotubes, metal powder, powder of known metal materials such as nickel, copper, aluminum, tin, zinc, silver, gold, etc., metal carbide powder including titanium carbide, tungsten carbide, titanium silicon carbide, titanium aluminum carbide or titanium tin carbide, etc. Therefore, the room temperature resistance is reduced, and the resistance jump magnitude of the PPTC unit is improved. The stability of the conductive particles in the electrolyte of the positive electrode, which needs to be soaked in the electrolyte, affects the long-term reliability of the battery, and the implementation process needs to be comprehensively considered by those skilled in the art. The part belongs to the material preparation step of the positive plate manufacturing process, and the conductive particles belong to the positive conductive material in the process.

4. The main consideration of the mass ratio of various materials of the conventional lithium battery anode is to improve the efficiency of active substances and reduce the resistivity, and the high molecular polymer serving as a binder can be reduced if the high molecular polymer meets the adhesion index. When PPTC is considered, the mass ratio is not necessarily proper, and comprehensive consideration and adjustment are needed. A positive electrode active material, a positive electrode conductive material and a positive electrode binder; in the existing lithium battery technology, the mass ratio of the positive electrode active material, the positive electrode conductive material and the positive electrode binder is preferably (90-98): (0.5-5): 1-5), and when PPTC is considered, the mass ratio can be selected from (80-98): 0.5-5): 1-15. When the mass of the binder is relatively large and does not dissolve well in the solvent, this situation requires even heating to the melting temperature during compounding to achieve better mixing. It is particularly noted that mass ratio is more than the factor to be considered, and those skilled in the art can select it according to actual needs. The method belongs to the material preparation step of the positive plate manufacturing process.

5. The positive electrode adhesive of the lithium battery adopts a high molecular polymer with a lower melting point, preferably PVDF-HFP (Polyvinylidene fluoride-hexafluoropropylene copolymer), and preferably selects a copolymer with a melting point between 100 ℃ and 130 ℃. The part belongs to the material preparation step of the positive plate manufacturing process, and the high molecular polymer belongs to the positive binder in the process.

6. The thermal annealing treatment can eliminate internal stress, so that the crystal of the high molecular polymer tends to be perfect continuously. The PVDF is preferably annealed at 120 ℃. In the existing lithium battery positive plate manufacturing process, after the positive plate is coated, a coated wet film needs to be coated and dried, and the drying temperature can reach 200 ℃. Roll pressing also tends to heat to high temperatures. The thermal annealing treatment is preferably performed after the coating and drying or the rolling of the positive electrode sheet manufacturing process.

Example 1: by applying the solution 1, the PPTC structure of the lithium battery positive plate is strengthened.

Example 2: by applying the solution 2, the positive plate structure of the lithium battery is reinforced by a PPTC structure.

Example 3: the solutions 1 and 4 are applied to strengthen the PPTC structure of the lithium battery positive plate structure.

Example 4: the solutions 1 and 3 are applied to strengthen the PPTC structure of the lithium battery positive plate structure.

Example 5: the solutions 1, 3 and 4 are applied to strengthen the PPTC structure of the lithium battery positive plate structure.

Example 6: the solutions 1, 3, 4 and 5 are applied to strengthen the PPTC structure of the lithium battery positive plate structure.

Example 7: the solutions 1, 3, 4, 5 and 6 are applied to strengthen the PPTC structure of the positive plate structure of the lithium battery.

Any combination of the above solutions can be selected as an embodiment by a person skilled in the art according to the actual needs.

In the description of the present invention, PVDF is used as the positive adhesive, and those skilled in the art will understand that the core spirit of the present invention can be applied to any other adhesive and any new adhesive, because the present invention describes the general rule for any high molecular polymer, and those skilled in the art can easily implement various changes, modifications and modified versions within the scope of patent protection under the guidance of this rule.

After the positive plate subjected to the PPTC structure strengthening treatment forms a lithium battery: it is envisioned that the entire cell anode, filled with PPTC units, has all of the anode active material surrounded by PPTC units. When local temperature runaway occurs in the battery, the temperature of the PPTC unit at the position rises, and when the temperature rises, the resistance of the PPTC unit rises, so that the rise of current is reversely restrained, the heat generation of the current is reduced, and the continuous rise of the temperature is restrained.

When a short circuit occurs inside or outside the battery, the current can sharply rise, so that the temperature of a plurality of PPTC units in the positive pole structure sharply rises, when the temperature rises to the PTC tripping temperature, the resistance of the PPTC units can sharply rise by several orders of magnitude, and under the feedback control, the current of the PPTC units can be quickly controlled within a rated range finally. When the short-circuit fault point is inside the battery, the following problems need to be properly dealt with:

1. in the battery cell with the internal short circuit, even if the current of the PPTC unit is controlled within a rated range, the current of the whole battery cell is converged to the internal short circuit, and the internal short circuit is ensured not to generate thermal runaway.

2. In a battery cell with an internal short circuit, even though the current of the PPTC unit is controlled within a rated range, in practical applications, a plurality of battery cells are often connected in series and in parallel, and the currents of other battery cells are gathered at the internal short circuit, so as to ensure that thermal runaway does not occur at the internal short circuit.

The solution is as follows:

1. the capacity of a single battery cell does not exceed a certain safety threshold, so that in the battery cell with an internal short circuit, the current of a plurality of PPTC units can be controlled within a rated range finally and the current of the whole battery cell can be converged to the internal short circuit position, but because the capacity of the single battery cell is within the safety threshold, the heat generated by current convergence is within the safety range, and the internal short circuit position cannot generate thermal runaway.

2. This requires coordinated management of the battery management system to address this issue. At present, an electric vehicle has thousands of battery cells, which are combined in series-parallel connection, and fig. 2 is a schematic diagram of a series-parallel connection of the battery cells. In fig. 2, the

battery cells

101, 102, and 103 belong to the battery string 1, when an internal short circuit occurs in the battery cell 101, batteries of other strings converge to the battery string 1, the battery management system monitors the current of each battery string in real time, and when the current flowing through the battery string 1 exceeds a safety threshold, the battery management system immediately turns off the relay 110, thereby isolating the battery string 1 from other circuits, and records in the system to remind that the short circuit occurs. Another situation is that the relay 110 is not switched off when the battery cell 101 is internally short-circuited and the current flowing through the battery string 1 has not exceeded the safety threshold, but the total voltage between the battery string 1 and the other strings is unbalanced due to the internal short-circuit of the battery cell 101, which is disadvantageous for the operation of the entire battery pack. The battery management system monitors the voltage of each battery cell in real time, the voltage of the battery cell 101 will decrease all the time along with the short-circuit discharge, when the discharge is completed, the voltage will decrease to almost 0, the battery management system can monitor the situation in real time, and the relay 110 will be turned off, so that the battery string 1 is isolated from other circuits, and the short-circuit is recorded in the system to remind the occurrence of the short circuit. In fig. 2, the battery cell 101 has no battery cell directly connected in parallel with it, so it is not necessary to consider monitoring and turning off the battery cell connected in parallel with it, which is relatively simple. In fig. 2, after the battery cell 101 is connected in series with the

battery cells

102 and 103 to form the battery string 1, the battery string is connected in parallel with other battery strings, and the series circuit is characterized in that the currents of the battery cell 101 and the

battery cells

102 and 103 are the same, so that when the battery cell 101 is internally short-circuited, as long as the

battery cells

102 and 103 are not short-circuited, the PPTC units in the

battery cells

102 and 103 limit the currents, and the current of the current string 1 is finally and rapidly controlled within a rated range, so that the series-parallel structure has good stability. Fig. 2 is merely an exemplary illustration of the core spirit of the present invention, and is not intended to limit the present invention, and any suitable combination of cells may be used in the practice.

After the cell is manufactured, regular maintenance is required to ensure that it will continue to function reliably.

The maintenance method comprises the following steps: for each battery cell, a load with a very low resistance value is switched on in a very short time, which is to reduce consumption and impact on the battery, and then the voltage and current values of the load are monitored in real time. Whether the PPTC structure function of the battery cell is normal or not can be judged by analyzing the voltage and current values of the load. This is equivalent to doing physical examination for the battery, and unusual battery monomer (even whole battery cluster) just can be changed, can also examine once more this battery monomer (even whole battery cluster that belongs to) after the change, and is just so more reliable, and all results are all normal. The battery needs to carry out the physical examination regularly, and to the electric motor car, the car also needs regular maintenance, once every year usually, when the car maintains, just can carry out the physical examination to the battery of electric motor car simultaneously. The battery management system can be communicated with the whole vehicle management system of the electric vehicle, the battery management system manages physical examination, and when the physical examination is over time and not done, a prompt is sent out, and the longer the delay time is, the higher the prompt level can be, so as to draw attention of electric vehicle users.

Since the battery management system itself monitors each battery cell in real time, the above-described maintenance facility may be added to the battery management system. In order to reduce the cost, an independent maintenance facility can be set, so that when a user goes to do maintenance, a maintenance shop provides the independent maintenance facility, and the battery management system can provide corresponding hardware and software interfaces, thereby facilitating the physical examination of the independent maintenance facility.

Cloud database: each battery, each battery string, and each cell may have a unique identification code, and each battery, each battery string, and each cell are stored in detail in a networked database: 1. date of delivery. 2. And when the product leaves the factory, parameters such as identification codes, models, voltage, current, capacity and the like are marked. 3. And (4) maintenance records, which maintenance master has performed maintenance operation at which time, and specific records. 4. The physical examination records, which maintenance master has done maintenance operation at which time, and the specific records.

With the detailed quality tracing management and control record, the battery can be subjected to lifetime tracking management.

The invention discovers a hidden PPTC structure in the prior anode structure, and develops and strengthens the hidden PPTC structure. With the popularization of electric cars, users pay more and more attention to the problem of spontaneous combustion of batteries of the electric cars, and expect that the batteries of the electric cars can realize zero spontaneous combustion risk.

While the method of the invention and specific examples have been described in connection with the accompanying drawings and examples, it will be understood by those skilled in the art that the invention is capable of many different embodiments. It is therefore to be understood that the invention is not limited to the preferred embodiments described, but embraces various alterations, modifications and variations within the scope of the appended claims.

Claims

1. A method for improving a lithium battery pole piece is characterized in that a PPTC (polymeric Positive Temperature coefficient) structure strengthening measure is carried out on a battery positive pole piece structure.

2. The measure of claim 1, the enhancement measure being any partial combination or all of the following:

a) and carrying out cross-linking treatment on the high-molecular polymer of the positive plate.

b) More than two high molecular polymers with different melting points are used as the positive plate adhesive instead of a single high molecular polymer.

c) Conductive particles with low resistivity are added.

d) And adjusting the proportion of each substance of the positive plate.

e) The high molecular polymer of the positive plate adopts a low-melting-point copolymer.

f) And carrying out thermal annealing treatment on the positive plate.

3. According to claim 2, a) the high molecular polymer of the positive electrode plate is cross-linked, preferably by electron beam cross-linking.

4. The method of claim 2, wherein b) two or more kinds of high molecular polymers with different melting points are used as the positive electrode sheet adhesive instead of a single high molecular polymer, and preferably PVDF-HFP (Polyvinylidene fluoride-hexafluoropropylene copolymer) and PVDF (Polyvinylidene fluoride) are used.

5. The c) addition of low resistivity conductive particles as claimed in claim 2 including but not limited to the following materials, or a combination between the following materials: conductive carbon black or nano-sized carbon nanotubes, metal powder, powder of known metal materials such as nickel, copper, aluminum, tin, zinc, silver, gold, etc., metal carbide powder including titanium carbide, tungsten carbide, titanium silicon carbide, titanium aluminum carbide or titanium tin carbide, etc.

6. The e) positive electrode sheet according to claim 2, wherein the high molecular polymer is a low melting point copolymer, preferably a copolymer of PVDF-HFP (Polyvinylidene fluoride-hexafluoropropylene copolymer), preferably a copolymer having a melting point between 100 ℃ and 130 ℃.

7. The positive plate of the battery according to claim 1, wherein the battery type includes, but is not limited to, lithium ion batteries, lithium solid state batteries, lithium metal batteries, fuel cells and other various battery forms.

8. A battery, characterized in that, the battery pole piece is prepared by any part combination or all methods of claims 1-7.