CN114335541A - Positive electrode slurry and preparation method and application thereof - Google Patents
Positive electrode slurry and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a positive electrode slurry and a preparation method and application thereof, wherein the positive electrode slurry comprises lithium iron phosphate, conductive carbon black, carbon nano tubes, a water-based binder and water; the aqueous binder comprises a combination of an ammonium substituent of sodium carboxymethyl cellulose and styrene butadiene rubber. The positive pole slurry provided by the invention can solve the problem of shortage of PVDF resources on one hand, and has high solid content on the other hand, and a further formed positive pole piece has good toughness.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to anode slurry and a preparation method and application thereof.
Background
In recent two years, with the increasing demand of energy vehicles, many cell raw materials are in short supply, wherein polyvinylidene fluoride (PVDF) in the positive electrode slurry is particularly in short supply.
PVDF is a binder in the anode material, and mainly has the functions of bonding a main material to a current collector and preventing the main material from cracking and falling off; however, one major problem with PVDF is that the production scale of upstream materials is limited, resulting in resource shortages of PVDF.
In the initial stage of research and development of power batteries, water system and oil system positive electrode slurry are tried by manufacturers, but the oil system positive electrode process occupies most of power markets since PVDF is low in price and meets processing requirements, and water system positive electrodes are gradually out of the question. However, with the expanding price, shortage and stricter environmental control requirements of PVDF, water-based formulations gradually enter the consideration range of battery cell factories.
CN104282911A discloses a method for manufacturing a positive electrode slurry of a lithium ion battery, a positive electrode plate and a lithium ion battery, wherein the method for manufacturing the positive electrode slurry comprises the following steps: (1) mixing and uniformly stirring an oil-based solvent, a water-based adhesive and a water-based solvent; (2) adding a conductive agent into the slurry prepared in the step (1), mixing and stirring uniformly; (3) adding active substances into the slurry prepared in the step (2) and stirring to obtain lithium ion battery anode slurry; the weight ratio of the aqueous solvent, the oil solvent, the aqueous adhesive, the conductive agent and the active substance is (100) -150: (0.1-2.0): (3-7): (2-6): (85-96). The positive pole slurry prepared by the method for preparing the positive pole slurry of the lithium ion battery has the advantages of good dispersion performance, strong stability, easy dressing, good pole piece uniformity and better flexibility than that of a common oil-based pole piece, can effectively reduce the use cost of the current oil-based positive pole, and can improve the capacity, the multiplying power charge-discharge performance and the cycle performance of the lithium ion battery.
CN101872856A discloses a positive electrode slurry of a lithium iron phosphate battery, the lithium iron phosphate battery using the positive electrode slurry and a preparation method thereof. The anode slurry comprises the following components in parts by weight: lithium iron phosphate: 40-55%; conductive agent: 2-5%; aqueous adhesive: 3-5%; and a solvent: 40-55 percent. The disclosed battery comprises a positive pole piece coated with the positive pole slurry. The disclosed aqueous anode slurry greatly improves the quality of the anode lithium iron phosphate active material; the positive pole piece is relatively friendly to water in the manufacturing process, and the adverse phenomena of water absorption, powder removal, material falling and the like can be avoided; the positive pole piece has good softness and adhesion after being pressed into sheets, and the performance is good in the processes of slitting and sequence conversion; the solvent in the anode slurry is relatively green and environment-friendly, and the safety performance of the water-based adhesive is stable.
Currently, there are two main directions for aqueous positive electrode systems: firstly, PVDF is replaced by polyacrylic binder, but the pole piece produced by the binder has poor flexibility and is easy to break and fall; the other type is the combination adhesive of sodium carboxymethylcellulose (CMCNa) and Styrene Butadiene Rubber (SBR), wherein the CMCNa mainly plays a role in dispersing and thickening, and the SBR mainly plays a role in bonding, but the solid content of the slurry produced by the scheme is too low, the required thickness is higher during coating, and the pole piece is easy to crack.
In summary, it is important to develop a positive electrode slurry with high toughness and high solid content of the formed positive electrode.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide the positive electrode slurry and the preparation method and application thereof, the positive electrode slurry does not need to use PVDF, can solve the problem of resource shortage of PVDF, has high solid content, and further forms a positive electrode plate with good toughness.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a positive electrode slurry comprising lithium iron phosphate (LFP), conductive carbon black (SP), Carbon Nanotubes (CNT), an aqueous binder and water;
the aqueous binder of the present invention comprises an ammonium substituent of sodium carboxymethylcellulose (CMCNH)4) And Styrene Butadiene Rubber (SBR).
In the present invention, CMCNH is used4And SBR as aqueous binder, mixing with LFP, SP, CNT, and water to form aqueous positive electrode slurry, homogenizing with CMCNH4The contained ammonium ions can be attached to the LFP main material, and through the electrostatic repulsion and volume steric hindrance generated by the ammonium ions, van der Waals force among particles of the positive electrode material is resisted, so that the slurry agglomeration is avoided, and the solid content of the slurry is improved.
Preferably, the positive electrode slurry comprises the following components in parts by weight based on 100 parts by weight of the total solute in the positive electrode slurry:
in the invention, the positive electrode slurry formed by the ammonium substituent of the sodium carboxymethylcellulose in the weight portion of 0.4-2 parts is better in performance because the additive amount is higher, the solid content of the slurry is lower, and the pole piece is easy to crack during coating or rolling, based on 100 parts of the total mass of the solute in the positive electrode slurry; the addition amount is low, so that slurry sedimentation is easy to cause; further preferably 0.5 to 2 parts.
The positive slurry formed by the styrene butadiene rubber in the weight portion range of 1-2 parts has better performance because the addition amount is higher and the dynamic performance of the battery cell is poor; the addition amount is low, and the pole piece is easy to crack when being coated.
In the invention, the weight parts of the lithium iron phosphate are 93-98.5 parts, such as 94 parts, 95 parts, 96 parts, 97 parts, 98 parts and the like.
The conductive carbon black is 0.5-2 parts by weight, such as 0.6 part, 0.8 part, 1.0 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts and the like.
The carbon nano tube is 0.5 to 2 parts by weight, such as 0.6 part, 0.8 part, 1.0 part, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts and the like.
The weight portion of the ammonium substituent of the sodium carboxymethyl cellulose is 0.4-2 portions, such as 0.6 portion, 0.8 portion, 1.0 portion, 1.2 portions, 1.4 portions, 1.6 portions, 1.8 portions and the like.
The styrene butadiene rubber is 1-2 parts by weight, such as 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts and the like.
Preferably, the solid content of the positive electrode slurry is 60% or more, such as 62%, 64%, 66%, 68%, 70%, and the like, and further preferably 62% to 66%.
Preferably, in the ammonium group substituent of the sodium carboxymethyl cellulose, the substitution degree of the ammonium group is 0.6 to 1.1, such as 0.7, 0.8, 0.9, 1.0, and the like.
In the present invention, the degree of substitution is defined as: the amount of substance in which the active hydroxyl groups on each D-glucose unit on the cellulose molecular chain are substituted.
In a second aspect, the present invention provides a method for preparing the positive electrode slurry according to the first aspect, the method comprising the steps of:
mixing lithium iron phosphate, conductive carbon black, a carbon nano tube, an ammonium substituent of sodium carboxymethyl cellulose, styrene butadiene rubber and water to obtain the anode slurry.
Preferably, the preparation method specifically comprises:
(1) mixing an ammonium substituent of sodium carboxymethylcellulose with water to obtain a first premix solution;
(2) mixing the first premixed liquid, the conductive carbon black and the carbon nano tube, and then mixing the mixture with the lithium iron phosphate to obtain a second premixed liquid;
(3) and mixing the third premixed solution with styrene butadiene rubber to obtain the anode slurry.
Preferably, in the step (1), the mass percentage of the ammonium substituent of the sodium carboxymethyl cellulose in the first premixed liquid is 0.6% to 2%, such as 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, etc
Preferably, the means of mixing comprises stirring.
Preferably, the linear velocity of the agitation is from 4 to 8m/s, such as 4.5m/s, 5m/s, 5.5m/s, 6m/s, 6.5m/s, 7m/s, 7.5m/s, and the like.
Preferably, the stirring time is 3-5h, such as 3.2h, 3.4h, 3.6h, 3.8h, 4.0h, 4.2h, 4.4h, 4.6h, 4.8h, and the like.
Preferably, in the step (2), the mixing of the first premix, the conductive carbon black and the carbon nanotubes comprises stirring;
preferably, the linear velocity of the agitation is from 6m/s to 14m/s, such as 7m/s, 8m/s, 9m/s, 10m/s, 11m/s, 12m/s, 13m/s, and the like.
Preferably, the stirring time is 0.5-2h, such as 0.6h, 0.8h, 1.0h, 1.2h, 1.4h, 1.6h, 1.8h, and the like.
Preferably, the mixing with the lithium iron phosphate in the step (2) further includes stirring.
Preferably, the linear velocity of the agitation is from 6m/s to 14m/s, such as 7m/s, 8m/s, 9m/s, 10m/s, 11m/s, 12m/s, 13m/s, and the like.
Preferably, the stirring time is 3-4h, such as 3.2h, 3.4h, 3.6h, 3.8h, etc
Preferably, the step (2) further comprises the operation of adding water to adjust the viscosity.
Preferably, in the step (3), the mixing manner includes stirring.
Preferably, the linear velocity of the agitation is 2 to 6 m/s.
Preferably, the stirring time is 0.5-1h, such as 0.6h, 0.7h, 0.8h, 0.9h, etc.
Preferably, the preparation method of the ammonium substituent of the sodium carboxymethyl cellulose comprises the following steps:
sequentially acidifying and aminating the sodium carboxymethylcellulose, centrifuging, filtering and drying to obtain the ammonium substituent of the sodium carboxymethylcellulose.
Preferably, said acidification comprises in particular: washing sodium carboxymethylcellulose in solvent, filtering, oven drying, adding concentrated acid, stirring, filtering to obtain precipitate, and acidifying.
Preferably, the solvent comprises ethanol at a concentration of greater than 70% (e.g., 75%, 80%, 85%, 90%, 95%, etc.) by volume.
Preferably, the number of washing and filtering is 3-4.
Preferably, the concentrated acid comprises any one of concentrated nitric acid, concentrated hydrochloric acid or concentrated sulfuric acid.
Preferably, the stirring time is 1-3h, such as 1.2h, 1.4h, 1.6h, 1.8h, 2.0h, 2.2h, 2.4h, 2.6h, 2.8h, and the like.
Preferably, the acidification also comprises a post-treatment of the precipitate after it has been obtained.
Preferably, the post-treatment specifically comprises: centrifuging and washing the precipitate in a solvent, filtering to obtain a precipitate, and repeating the operation for 3-4 times.
Preferably, the solvent comprises ethanol at a concentration of greater than 70% (e.g., 75%, 80%, 85%, 90%, 95%, etc.) by volume;
preferably, the ammoniated treatment agent comprises ammonia and/or urea.
Preferably, the mass ratio of the treating agent to the sodium carboxymethylcellulose is (1-2):1, wherein 1-2 may be 1.2, 1.4, 1.6, 1.8, etc., and more preferably 1.5: 1.
Preferably, the amination comprises in particular: and dissolving the acidified precipitate in a solvent, and adding a treating agent to complete amination.
Preferably, the solvent comprises ethanol at a concentration of greater than 70% (e.g., 75%, 80%, 85%, 90%, 95%, etc.) by volume.
In a third aspect, the invention provides a positive electrode plate, and the raw material for preparing the positive electrode plate comprises the positive electrode slurry of the first aspect.
The positive electrode slurry further forms CMCNH when a positive electrode piece is coated4Ammonium ions in the positive electrode plate are decomposed, and self-crosslinking reaction is generated between main chains, so that the binding power of the positive electrode plate is enhanced, and the cracking of the positive electrode plate is avoided.
In a fourth aspect, the invention provides a method for preparing the positive electrode plate in the third aspect, which comprises the following steps: and coating the positive electrode slurry on one side or two sides of the aluminum foil or the carbon-coated aluminum foil to obtain the positive electrode piece.
The positive electrode slurry further forms CMCNH when the positive electrode plate is coated and baked4Ammonium ions are decomposed under the high-temperature condition, and self-crosslinking reaction is generated between main chains, so that the bonding force of the pole piece is enhanced, and the drying rate of the positive pole piece is increased while the pole piece is prevented from cracking.
Preferably, the temperature of the coating is 80-105 ℃, e.g., 90 ℃, 100 ℃, etc.
Preferably, the time of coating is 2-5min, such as 3min, 3.5min, 4min, 4.5min, and the like.
In a fifth aspect, the present invention provides a lithium ion battery, which sequentially comprises the positive electrode plate, the isolating membrane and the negative electrode plate of the third aspect, which are stacked;
electrolyte is arranged between the positive pole piece and the isolating membrane and between the isolating membrane and the negative pole piece.
Preferably, the negative electrode plate comprises a negative active material, a conductive agent, a thickening agent and a binder.
Compared with the prior art, the invention has the following beneficial effects:
(1) the anode slurry disclosed by the invention is a water-system anode formula, so that the problem of raw material shortage of an oil-system anode formula can be solved, and the problems of low solid content and brittleness in the existing water-system anode slurry formula can be solved.
(2) The anode slurry disclosed by the invention is environment-friendly, does not need to control the environment humidity, and can greatly reduce the production cost.
(3) Compared with an oily formula, the rebound rate of the positive electrode plate further formed by the positive electrode slurry is reduced by about 2%, both normal-temperature and low-temperature HPPC (high pressure propylene carbonate) are reduced, and the cycle number of 3C/1C normal-temperature circulation is equivalent. The positive electrode bounce rate is smaller in response to the rate, and it is presumed that the cycle number application will be advantageous if 1C/1C is cycled at room temperature.
(4) The positive electrode slurry of the invention uses the solute of the positive electrode slurry, namely LFP, SP, CNT and CMCCH4And SBR (styrene butadiene rubber) accounting for 100 parts by mass, namely CMCNH4The addition amount of the SBR is within the range of 0.5-2.0 parts, and the addition amount of the SBR is within the range of 1-2 parts, so that the formed positive pole piece has better performance.
The solid content of the positive electrode slurry is more than 58%, the peel strength is more than 33.2N/m, and the CC _ DCR value is within 12.81m omega and the DC _ DCR value is within 11.09m omega in a 25 ℃ 50% SOC test; -a CC _ DCR value within 389.8m Ω and a DC _ DCR value within 127.4m Ω in a 50% SOC test at 20 ℃; the cycle number at 25 ℃ is 954 or more.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
Example 1
The embodiment provides a positive electrode slurry, wherein a solute of the positive electrode slurry comprises the following components in parts by weight:
the solid content of the positive electrode slurry was 64.37%;
CMCNH4the degree of substitution of (a) is 0.8;
SBR is available from A & L under the trade designation SN 307R.
The positive electrode slurry is prepared by the following method, and the preparation method comprises the following steps:
(1)CMCNH4preparation of
1) Adding CMCNa (with the substitution degree of 0.8) into ethanol while stirring, controlling the stirring linear speed at 5m/s and the volume concentration of the ethanol at 80%, washing and filtering for 4 times, drying a filter, adding concentrated nitric acid with the concentration of 40% which is 8.0 times of the mass of the filter while stirring, stirring for 1H, standing for 2H, and filtering a precipitate, wherein the process is that Na in the CMCNa is replaced by H, so that the CMCNa is acidified.
2) Placing the precipitate in a beaker, adding 80% ethanol with volume concentration 4.0 times the mass of the precipitate while stirring, controlling the stirring linear speed at 2m/s, dissolving sodium salt in CMCH, placing in a centrifuge, centrifuging and washing for 30min, filtering the precipitate, and repeating the process for 4 times.
3) Adding 80% ethanol with concentration of 4.0 times of mass into the washings, adding 20% ammonia water with concentration of 1.5 times of mass while stirring, performing ammonification reaction, stirring at stirring linear speed of 2m/s for 1 hr, standing for 3 hr, centrifuging again, washing for 30min, baking at 75 deg.C for 2 hr in oven, and pulverizing to obtain CMCNH4And (5) finishing.
(2) Preparation of positive electrode slurry
1) Mixing CMCNH4And adding water into a double-planet stirrer, stirring for 4 hours at a linear speed of 3m/s, and controlling the solid content to be 1.5%.
2) Adding the solution 1), SP and CNT in the proportion described in the formula into a double-planet stirrer at the same time, dispersing for 1h at 5m/s, then adding LFP, adding a proper amount of deionized water for 30 parts, dispersing for 3.5h at high speed, adding a proper amount of deionized water for 25 parts in the period, and adjusting the average viscosity of the slurry to 6000 cps.
3) And after the viscosity is adjusted, adding SBR, and dispersing at a linear speed of 2m/s for 0.8h to obtain the anode slurry.
Example 2
The embodiment provides a positive electrode slurry, wherein a solute of the positive electrode slurry comprises the following components in parts by weight:
the solvent of the positive electrode slurry is water, and the solid content of the positive electrode slurry is 63.53%;
CMCNH4the degree of substitution of (a) is 0.8;
SBR is available from A & L under the trade designation SN 307R.
The positive electrode slurry is prepared by the following method, and the preparation method comprises the following steps:
CMCNH from example 1 was used4And the preparation method of the positive electrode slurry is the same as that of example 1.
Example 3
The embodiment provides a positive electrode slurry, wherein a solute of the positive electrode slurry comprises the following components in parts by weight:
the solvent of the positive electrode slurry is water, and the solid content of the positive electrode slurry is 65.32%;
CMCNH4the degree of substitution of (a) is 0.8;
SBR is available from A & L under the trade designation SN 307R.
The positive electrode slurry is prepared by the following method, and the preparation method comprises the following steps:
CMCNH from example 1 was used4And the preparation method of the positive electrode slurry is the same as that of example 1.
Examples 4 to 8
Examples 4-8 differ from example 1 in the maintenance of LFP, SP, CNT, CMCNH4The total mass of SBR is 100 parts, the weight parts of fixed SP and CNT are respectively 1 part and 0.5 part, and CMCNH is adjusted4And the weight parts of SBR, the weight parts of the main material are changed correspondingly according to the weight parts of the other auxiliary materials, and the amount of the added water is the same as that in the embodiment 1, and the weight parts are as follows:
example 4: CMCNH4The weight portion of the SBR is 0.5 portion, the weight portion of the SBR is 1.5 portions, and the rest is the same as that of the embodiment 1;
example 5: CMCNH4The weight portion of the SBR is 1.0 portion, the weight portion of the SBR is 1.5 portions, and the rest is the same as that of the embodiment 1;
example 6: CMCNH4The weight portion of the SBR is 1.5 portions, and the rest is the same as that of the embodiment 1;
example 7: CMCNH4The weight portion of the SBR is 2.0 portions, the weight portion of the SBR is 1.5 portions, and the rest is the same as that of the embodiment 1;
example 8: CMCNH4The weight portion of the SBR is 2.2 portions, the weight portion of the SBR is 1.5 portions, and the rest is the same as that of the embodiment 1;
examples 9 to 12
Examples 9-12 differ from example 1 in the maintenance of LFP, SP, CNT, CMCNH4The total mass of SBR is 100 parts, the weight parts of fixed SP and CNT are respectively 1 part and 0.5 part, and CMCNH is adjusted4The proportion of SBR and the weight of the main materials are changed correspondingly according to the weight of the other auxiliary materials, and the amount of the added water is the same as that in the embodiment 1, and the proportion is as follows:
example 9: CMCNH4The weight portion of the SBR is 1.5 portions, the weight portion of the SBR is 0.8 portion, and the rest is the same as that of the embodiment 1;
example 10: CMCNH4The weight portion of the SBR is 1.5 portions, the weight portion of the SBR is 1.0 portion, and the rest is the same as that of the embodiment 1;
example 11: CMCNH4The weight portion of the SBR is 1.5 portions, the weight portion of the SBR is 2.0 portions, and the rest is the same as that of the embodiment 1;
examples12：CMCNH4The weight parts of (1) and (2) SBR were 1.5 parts and the rest was the same as in example 1.
Examples 13 to 16
Examples 13-16 differ from example 1 in CMCNH4The degrees of substitution of (A) were 0.6 (example 13), 1.1 (example 14), 0.5 (example 15) and 1.2 (example 16), respectively, and the same as in example 1 except for the above.
Comparative example 1
The comparative example provides a positive electrode slurry, which comprises the following components in parts by weight:
the preparation method of the positive electrode slurry comprises the following steps:
and adding PVDF into NMP, adding an LFP main material into a double-planet stirrer, and stirring for 3 hours at a linear speed of 10m/s to obtain the oil-based anode slurry.
Comparative example 2
This comparative example differs from example 1 in that CMCNH is added4The CMCNa was replaced with equal mass, and the rest was the same as in example 1.
Application example 1
The application example provides a positive electrode plate, which is obtained by coating the positive electrode slurry described in embodiment 1 on one side of an aluminum foil, and baking the coated positive electrode plate for 3min in an oven with the temperature of 90 ℃.
Application example 2
The application example provides a positive electrode plate, which is obtained by coating the positive electrode slurry described in the embodiment 2 on two sides of an aluminum foil, and baking the aluminum foil for 2min by using an oven with the temperature of 105 ℃.
Application example 3
The application example provides a positive electrode plate, which is obtained by coating the positive electrode slurry described in the embodiment 3 on one side of a carbon-coated aluminum foil, and baking the coated positive electrode plate for 5min in an oven with the temperature of 80 ℃.
Application examples 4 to 16 and application comparative examples 1 to 2
Application examples 4 to 16 and application comparative examples 1 to 2 are different from application example 1 in that the positive electrode slurry is the positive electrode slurry described in examples 4 to 16 and comparative examples 1 to 2, respectively, and the rest is the same as application example 1.
Performance testing
1. The positive electrode pastes described in examples 1 to 16 and comparative examples 1 to 2 were subjected to the following tests:
(1) solid content: after the preparation of the slurry was completed, about 2g of the slurry was taken into an aluminum foil and placed in a baking oven at 105 ℃ for 30min, weighed and the ratio of the dry slurry to the original slurry was calculated.
(2) Surface density: after the pole piece is baked, cutting an original piece with the diameter of 12mm from the left, the middle and the right of the pole piece, measuring the weight of the wafer, subtracting the weight of the aluminum foil, dividing by the area of the wafer to obtain the surface density, and taking the average value of the surface densities of the three wafers as the final surface density.
(3) Peel strength: cutting a pole piece with the width of 25mm and the length of more than 10cm, pasting an adhesive tape on the pole piece, fixing one end of the pole piece pasted with the adhesive tape at one end of a universal tensile machine, separating the adhesive tape at the other end of the pole piece from the pole piece, fixing the adhesive tape at the other end of the universal tensile machine, starting the tensile machine at the speed of 150mm/min, wherein the required tensile force is the peeling strength.
(4) Number of light transmission folding times: the pole piece is folded in half for 180 degrees, and the number of times is 1 after the pole piece is folded in half in the front and the back, and whether the pole piece is transparent or not is observed under strong light, and the number of times during the light transmission is the number of times of light transmission folding.
Example 1 and comparative example exemplarily give data on the mean of three tests, and the remaining examples were performed in this manner, representing only the final mean.
The test results are summarized in tables 1-2.
TABLE 1
The data in table 1 are analyzed, and it is seen from the results of the solid content of the slurry and the peel strength that the solid content of the slurry of the aqueous positive electrode slurry of the present invention can be increased by 4-7%, the peel strength can be increased by 35%, and the flexibility of the electrode plate can be better improved compared with the oil-based formulation in comparative example 1.
TABLE 2
Where "/" is no measurable data.
As can be seen from the analysis of the data in tables 1 and 2, the solid content of the positive electrode slurry is more than 58%, the peel strength is more than 33.2N/cm, and the number of times of light transmission and folding is more than 3.
As can be seen from the analysis of comparative example 2 and example 1, comparative example 2 is inferior to example 1 in performance, and the performance of the positive electrode slurry formed by substituting sodium carboxymethyl cellulose with ammonium was confirmed to be better.
Analysis of examples 13-16 reveals that examples 15-16 do not perform as well as examples 13-14, demonstrating CMCNH4The degree of substitution in (2) is in the range of 0.6 to 1.1.
2. The positive electrode pieces described in application examples 1 to 16 and application comparative examples 1 to 2 were subjected to the following tests:
preparing an electric core:
the formula of the negative electrode of the battery core is that a negative electrode active material, a conductive agent acetylene black, a thickening agent CMC and a binder SBR are mixed according to the mass ratio of 96.3:1:1.2:1.5, an electrolyte is LiPF6 organic solvent, an isolation film is a polyethylene film isolation film, and finally the positive electrode plate, the isolation film and the negative electrode plate are sequentially stacked, so that the isolation film is positioned between the positive electrode plate and the negative electrode plate to play the role of isolation, and the bare battery core is obtained after the stacking and winding; and placing the bare cell in an outer packaging shell, drying, injecting electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.
Cell test
(1) And (3) testing the basic electrical property: at 25 ℃, the lithium ion batteries prepared in the examples and the comparative examples are pre-charged for 180min at a low current, fully charged to 3.65V at a constant current of 0.33C and fully charged to 0.05C at a constant voltage, fully discharged to 2.5V at 0.33C, and the ratio of the discharge capacity to the charge capacity is calculated to obtain the first effect; then fully charging to 3.65V at constant current of 1C, constantly pressurizing to 0.05C, fully discharging to 2.5V at 1C; and finally, disassembling the battery and measuring the rebound rate of the positive pole piece.
(2) And (3) testing the dynamic performance: the lithium ion batteries prepared in the examples and comparative examples were measured for charge and discharge DCR at different SOCs using the standard HPPC test method at 25 ℃ and-20 ℃ respectively, and charge and discharge DCR at 50% was mainly evaluated.
(3) And (3) testing the cycle performance: the lithium ion batteries prepared in examples and comparative examples were charged at a rate of 3C and discharged at a rate of 1C at 25C, and full charge discharge cycle tests were performed until the capacity of the lithium ion battery had decayed to 80% of the initial capacity, and the number of cycles was recorded.
The test results are summarized in tables 3-4.
TABLE 3
As can be seen from the data in table 3, when the application example 1 and the application comparative example 1 are used as examples, the first effect of the two is not different from the basic electrical property data, the positive electrode rebound rate of the application example 1 is reduced by about 2% compared with the positive electrode rebound rate of the comparative example 1, the room temperature HPPC and the low temperature HPPC are both reduced, and the cycle number of the 3C/1C room temperature cycle is equivalent. The positive electrode bounce rate is smaller in response to the rate, and it is presumed that the cycle number application will be advantageous if 1C/1C is cycled at room temperature.
TABLE 4
Analyzing the data in the table 4, the mass ratio of SBR in the anode slurry is ensured to be unchanged, and the CMCNH is adjusted4The results show that the solute of the positive electrode slurry, i.e., LFP, SP, CNT, CMCCH4And SBR accounts for 100 parts in total by mass, and the CMCCH4The addition amount of (A) is between 0.5 and 2 parts (including 0.5 and 2.0), no processing risk exists, and the cell performance is not greatly different. When the amount is less than 0.5 part, the positive slurry has sedimentation risk, and data cannot be measured, which are not listed here; when the amount is more than 2.0 parts (application example 8), the coating of the positive electrode plate cracks, so that CMCCH4The parts by weight are most preferably 0.5 to 2.0 parts.
TABLE 5
Analyzing the data in Table 5, the CMCNH is guaranteed4The mass ratio in the positive electrode slurry was constant, and the ratio of SBR was adjusted, and the results showed that the solutes of the positive electrode slurry, i.e., LFP, SP, CNT, CMCCH4And the total mass of the SBR is 100 parts, the addition amount of the SBR is between 1 and 2 parts (including 1 and 2.0), the processing risk is avoided, the peel strength is increased along with the increase of the proportion of the SBR, the difference between the normal-temperature HPPC and the low-temperature HPPC is not great, the coating is coated at the risk of cracking when the difference is less than 1.0 part (application example 9), the cycle performance is greatly reduced when the difference is more than 2.0 parts (application example 12), and the SBR is not recommended to be used.
TABLE 6
As is clear from the analysis of the data in Table 6, in the application examples 13 to 16, the performance of the application examples 15 to 16 is inferior to that of the application examples 13 to 14, and the CMCNH4The positive electrode slurry with the degree of substitution of 0.6-1.1 has better performance, and the degree of substitution is less than 0.6 (application example 15)) The glue solution has more fibers, the viscosity is reduced when the viscosity is more than 1.1 (application example 16), and the glue solution is not suitable for use.
As can be seen from the analysis of application comparative example 2 and application example 1, application comparative example 2 is inferior in performance to application example 1, and is proved to be CMCNH4And SBR is used as an aqueous binder to form the cathode slurry with better performance.
In summary, as can be seen from the analysis tables 1 to 6, the positive electrode slurry of the present invention is a water-based positive electrode formulation, which can solve the problem of raw material shortage of the oil-based positive electrode formulation, and can also solve the problems of low solid content and brittleness in the current water-based positive electrode slurry formulation. The anode slurry disclosed by the invention is environment-friendly, does not need to control the environment humidity, and can greatly reduce the production cost.
The method comprises the following specific steps:
(1) except for the undetectable data, the solid content of the anode slurry is above 58%, and the peel strength is above 33.2N/m.
(2) Compared with an oily formula, the rebound rate of the positive electrode plate further formed by the positive electrode slurry is reduced by about 2%, both normal-temperature and low-temperature HPPC (high pressure propylene carbonate) are reduced, and the cycle number of 3C/1C normal-temperature circulation is equivalent. The positive electrode bounce rate is smaller in response to the rate, and it is presumed that the cycle number application will be advantageous if 1C/1C is cycled at room temperature.
(3) The positive electrode slurry of the invention uses the solute of the positive electrode slurry, namely LFP, SP, CNT and CMCCH4And SBR (styrene butadiene rubber) accounting for 100 parts by mass, namely CMCNH4The addition amount of the SBR is within the range of 0.5-2.0 parts, and the addition amount of the SBR is within the range of 1-2 parts, so that the formed positive pole piece has better performance.
The solid content of the positive electrode slurry is more than 58%, the peel strength is more than 33.2N/m, and the CC _ DCR value is within 12.81m omega and the DC _ DCR value is within 11.09m omega in a 25 ℃ 50% SOC test; -a CC _ DCR value within 389.8m Ω and a DC _ DCR value within 127.4m Ω in a 50% SOC test at 20 ℃; the cycle number at 25 ℃ is 954 or more.
The present invention is described in detail by the above application examples, but the present invention is not limited to the above detailed methods, that is, the present invention is not meant to be applied only by relying on the above detailed methods. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (10)
1. The positive electrode slurry is characterized by comprising lithium iron phosphate, conductive carbon black, carbon nanotubes, a water-based binder and water;
the aqueous binder comprises a combination of an ammonium substituent of sodium carboxymethyl cellulose and styrene butadiene rubber.
2. The positive electrode slurry according to claim 1, wherein the positive electrode slurry comprises the following components in parts by weight, based on 100 parts by weight of the total solute in the positive electrode slurry:
preferably, the solid content of the positive electrode slurry is 60% or more.
3. The positive electrode slurry according to claim 1 or 2, wherein the substitution degree of an ammonium group in the ammonium group-substituted substance of the sodium carboxymethylcellulose is 0.6 to 1.1.
4. A method for producing the positive electrode slurry according to any one of claims 1 to 3, characterized by comprising the steps of:
mixing lithium iron phosphate, conductive carbon black, a carbon nano tube, an ammonium substituent of sodium carboxymethyl cellulose, styrene butadiene rubber and water to obtain the anode slurry.
5. The preparation method according to claim 4, wherein the preparation method specifically comprises:
(1) mixing an ammonium substituent of sodium carboxymethylcellulose with water to obtain a first premix solution;
(2) mixing the first premixed liquid, the conductive carbon black and the carbon nano tube, and then mixing the mixture with the lithium iron phosphate to obtain a second premixed liquid;
(3) and mixing the third premixed solution with styrene butadiene rubber to obtain the anode slurry.
6. The preparation method according to claim 5, wherein in the step (1), the mass percentage of the ammonium substituent of the sodium carboxymethyl cellulose in the first premixed liquid is 0.6% -2%;
preferably, the means of mixing comprises stirring;
preferably, the linear velocity of the stirring is 4 to 8 m/s;
preferably, the stirring time is 3-5 h;
preferably, in the step (2), the mixing of the first premix, the conductive carbon black and the carbon nanotubes comprises stirring;
preferably, the linear velocity of the stirring is 6m to 14 m/s;
preferably, the stirring time is 0.5-2 h;
preferably, in the step (2), the mixing with the lithium iron phosphate comprises stirring;
preferably, the linear velocity of the stirring is 6m to 14 m/s;
preferably, the stirring time is 3-4 h;
preferably, the step (2) further comprises the operation of adding water to adjust the viscosity;
preferably, in the step (3), the mixing manner includes stirring;
preferably, the linear velocity of the stirring is 2 to 6 m/s;
preferably, the stirring time is 0.5-1 h.
7. The method according to any one of claims 4 to 6, characterized by comprising the steps of:
the preparation method of the ammonium substituent of the sodium carboxymethyl cellulose comprises the following steps:
sequentially acidifying and aminating sodium carboxymethylcellulose, centrifuging, filtering and drying to obtain an ammonium group substituent of the sodium carboxymethylcellulose;
preferably, said acidification comprises in particular: washing sodium carboxymethylcellulose in a solvent, filtering, drying, adding concentrated acid, stirring, filtering to obtain a precipitate, and completing acidification;
preferably, the solvent comprises ethanol at a concentration of 70% by volume or more;
preferably, the number of washing and filtering is 3-4;
preferably, the concentrated acid comprises any one of concentrated nitric acid, concentrated hydrochloric acid or concentrated sulfuric acid;
preferably, the stirring time is 1-3 h;
preferably, the acidification also comprises a post-treatment of the precipitate after it has been obtained;
preferably, the post-treatment specifically comprises: centrifuging and washing the precipitate in a solvent, filtering to obtain a precipitate, and repeating the operation for 3-4 times;
preferably, the solvent comprises ethanol at a concentration of 70% by volume or more;
preferably, the ammonium treatment agent comprises ammonia and/or urea (with a concentration of 10-25% by mass);
preferably, the mass ratio of the treating agent to the sodium carboxymethyl cellulose is (1-2) to 1;
preferably, the amination comprises in particular: dissolving the acidified precipitate in a solvent, and adding a treating agent to complete amination;
preferably, the solvent comprises ethanol at a concentration of above 70% by volume.
8. A positive electrode plate, characterized in that the raw material for preparing the positive electrode plate comprises the positive electrode slurry of any one of claims 1 to 3.
9. The preparation method of the positive pole piece of claim 8, characterized by comprising the following steps: coating the positive electrode slurry on one side or two sides of an aluminum foil or a carbon-coated aluminum foil to obtain the positive electrode piece;
preferably, the temperature of the coating is 80-105 ℃;
preferably, the coating time is 2-5 min.
10. A lithium ion battery, characterized in that, the lithium ion battery comprises the positive pole piece, the isolating membrane and the negative pole piece of claim 8 which are arranged in a stacking way;
electrolyte is arranged between the positive pole piece and the isolating film and between the isolating film and the negative pole piece;
preferably, the negative electrode plate comprises a negative active material, a conductive agent, a thickening agent and a binder.
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