CN108400396A - A method of improving the first charge-discharge specific capacity of lithium ion battery and first effect - Google Patents

Abstract

The invention provides a method for improving the first-time charge-discharge specific capacity and first-efficiency of a lithium-ion battery, comprising the following steps: A) discharging the negative electrode material to a voltage platform of _b1 at a current density _{of a1} , standing for 20-40min, and cycling This process is repeated many times, and the cycle of this stage is stopped; B) The process of step A) is carried out with the current density a ₂ , a ₃ ... a _i in turn, until the discharge capacity of a certain step or a certain stage is ≤0.1mAh, and the discharge is stopped; C) Charge the discharged negative electrode material to the B ₁ platform at the current density A ₁ , let it stand for 20-40 minutes, repeat the process several times, and stop the cycle at this stage; D) Use the current density A ₂ , A ₃ ... A in sequence _j Carry out the process of step C) respectively until the charging capacity of a certain step or a certain stage is ≤0.1mAh, and stop charging. The lithium ion battery obtained by the method of the present application has higher first-time Coulombic efficiency and first-time charge-discharge capacity.

Description

A method for improving the first charge-discharge specific capacity and first effect of lithium-ion batteries

technical field

The invention belongs to the technical field of lithium-ion batteries, and in particular relates to a method for improving the first-time charge-discharge specific capacity and first-efficiency of lithium-ion batteries

Background technique

Lithium-ion batteries have the advantages of high capacity, no pollution, no memory effect, etc., and are widely used in today's social life. The negative electrode of traditional lithium-ion batteries is made of graphite, and the theoretical capacity is only 372mAh/g, which is relatively low. Among the negative electrode materials, there are two types of graphite negative electrode materials and silicon negative electrode materials. Graphite negative electrodes have the advantages of high energy density, low voltage, good electrical conductivity, abundant resources and low price, but graphite materials have low charging capacity and easy surface The shortcomings of lithium-ion analysis lead to low effective capacity of lithium-ion batteries and serious safety problems. With the development of social production, people increasingly need lithium-ion batteries with high energy density. For this reason, silicon negative electrodes have begun to enter people's field of vision. Silicon has a very high theoretical capacity (3587mAh/g, 9786mAh/cm ³ ; Li ₁₅ Si ₄ ) which is close to ten times the capacity of graphite negative electrode, has the largest reserves in nature, and has no pollution to the environment. However, the silicon negative electrode has poor conductivity (<10 ^-3 s/cm; 25°C) and exhibits a volume change rate close to 300% when lithium ions are released and intercalated. Huge volume changes lead to easy pulverization of silicon particles, poor contact between active material and conductive agent/binder, repeated growth of solid electrolyte interfacial film consumes electrolyte and lithium source in positive electrode, in order to reduce the side effects caused by volume expansion and improve The conductivity of silicon materials, so silicon carbon materials are formed by adding graphite to silicon materials. But even so, silicon-carbon materials still have disadvantages such as low first-time Coulombic efficiency and low first-time charge-discharge capacity.

The first Coulombic efficiency and the first charge-discharge capacity are important because the voltage platform generated during the first week of charging lays the foundation for subsequent cycles. The first Coulombic efficiency represents the stability of the material structure and the excellent kinetic performance. Low Coulombic efficiency means that there are side reactions, which will directly reduce the discharge capacity of the battery and shorten the cycle life of the battery. At the same time, the charge capacity in the subsequent cycle fluctuates based on the discharge capacity in the first week.

Patent CN105186002A discloses a method for improving the discharge capacity of the positive electrode material of lithium-ion batteries. In this method, the conductive agent is dispersed in an organic solvent and subjected to ultrasonic treatment, and the treated suspension is stirred for 20 hours. At the same time, the positive electrode of the lithium-ion battery is activated. The materials are dry-mixed at 170°C to 200°C, and then the suspension obtained from the conductive agent is slowly added to the active material of Zhengji. After drying, the powder is obtained and ground, and finally calcined under the atmosphere of protective gas. The steps of the method are cumbersome, the cost is high, and the cycle is long.

Patent CN104795600A discloses a method for improving the first coulombic efficiency of lithium-ion batteries, which mainly includes the following two steps, material modification and soaking treatment, the steps are cumbersome, the cost is high, and the cycle is long.

Contents of the invention

The object of the present invention is to provide a method for improving the first charge-discharge specific capacity and first effect of lithium-ion batteries. The method of the present invention can effectively improve the first-time Coulombic efficiency and first-time charge-discharge capacity of lithium-ion batteries, and the steps are simple and the cost is low. ,Short cycle.

The present invention provides a kind of method that improves the specific capacity of charging and discharging for the first time and the first effect of lithium-ion battery, comprising the following steps:

A) Discharge the negative electrode material at a current density of a ₁ to a voltage platform of b ₁ , let it stand for 20-40 minutes, cycle this process several times, and stop the cycle at this stage;

B) Carry out the process of step A) with current densities a ₂ , a ₃ ... a _i respectively, until a certain step or a certain stage discharge specific capacity ≤ 0.1mAh/g, stop discharging;

C) Charge the discharged negative electrode material to the _B1 platform with a current density of _A1 , let it stand for 20-40min, cycle this process several times, and stop the cycle at this stage;

D) Carry out the process of step C) with current densities A ₂ , A ₃ ... A _j in turn, until the charging capacity of a certain step or a certain stage is ≤0.1mAh/g, then stop charging;

Wherein, 0.05C≤a _i ≤1C; 0.001V≤b ₁ ≤0.01V; 0.05C≤A _j ≤1C; 1.5V≤B ₁ ≤2V; i≥3; j≥3.

Preferably, in each independent stage, each stage charges or discharges the battery to a predetermined voltage value in a constant current manner and then ends.

Preferably, said a ₁ ≥ _{a 2} ≥ a ₃ , ... ≥ a _i .

Preferably, said A ₁ ≥ _{A 2} ≥ A ₃ , ... ≥ A _j .

Preferably, 0.005V≤b ₁ ≤0.006V.

Preferably, the negative electrode material is discharged to a voltage plateau of _b1 at a current density of _a1 , left standing for 20 to 40 minutes, and repeated 2 to 5 times;

Discharge at current density a ₂ to b ₂ voltage platform, let stand for 20-40min, repeat 2-5 times;

Discharge at current density a ₃ to b ₃ voltage platform, let stand for 20-40min, repeat 2-5 times;

Discharge at a current density of a ₄ to a voltage platform of b ₄ , stand still for 20-40 minutes, repeat until a certain step or a certain stage discharge specific capacity ≤ 0.1mAh/g;

_{0.8C≤a1≤1C} ; _{0.5C≤a2≤0.7C} ; _{0.1C≤a3≤0.4C} ; _{0.05C≤a4≤0.08C} . Wherein C is the theoretical specific capacity of the negative electrode material.

Preferably, the negative electrode material is charged to a voltage platform of _B1 at a current density of _A1 , left standing for 20 to 40 minutes, and repeated 2 to 5 times;

Charge at current density A ₂ to B ₂ voltage platform, let stand for 20-40min, repeat 2-5 times;

Charge at current density _A3 to _B3 voltage platform, let stand for 20-40min, repeat 2-10 times;

Charge at current density A ₄ to voltage platform B ₄ , let stand for 20-40 minutes, repeat until a certain step or a certain stage discharge specific capacity ≤ 0.1mAh/g;

_{0.8C≤A1≤1C} ; _{0.5C≤A2≤0.7C} ; _{0.1C≤A3≤0.4C} ; _{0.05C≤A4≤0.08C} . Wherein, C is the theoretical specific capacity of the negative electrode material.

The invention provides a method for improving the first-time charge-discharge specific capacity and first-efficiency of a lithium-ion battery, comprising the following steps: A) discharging the negative electrode material to a voltage platform of _b1 at a current density _{of a1} , standing for 20-40min, and cycling This process is repeated many times, and the cycle of this stage is stopped; B) The process of step A) is carried out with the current density a ₂ , a ₃ ... a _i in turn, until the discharge capacity of a certain step or a certain stage is ≤0.1mAh, and the discharge is stopped; C) Charge the discharged negative electrode material to the B ₁ platform at the current density A ₁ , let it stand for 20-40 minutes, repeat the process several times, and stop the cycle at this stage; D) Use the current density A ₂ , A ₃ ... A in sequence _j Carry out the process of step C) respectively until a certain step or a certain stage charging capacity ≤0.1mAh, stop charging; among them, 0.05C≤a _i ≤1C; 0.001V≤b ₁ ≤0.01V; 0.05C≤A _j ≤1C; 1.5V≤B ₁ ≤2V; i≥3; j≥3.

When a lithium-ion battery is discharged at a certain constant current density, it will be found that the voltage is higher than the preset voltage value after standing for a certain period of time. The value should be low, indicating that the polarization phenomenon inside the battery is more serious (the electrode potential deviates from the equilibrium electrode potential due to the polarization effect during the charging and discharging process of the battery, and after shelving, the polarization effect is gradually eliminated, so the electrode potential changes , resulting in a change in battery voltage).

Compared with the one-time charge and discharge process, the pulsed charge and discharge process adopted by the present invention can weaken the polarization inside the battery, so that the lithium ions can be inserted and extracted more thoroughly during the charge and discharge process of the battery. It can eliminate the ohmic polarization inside the lithium-ion battery, reduce the internal resistance, effectively slow down the voltage rise in the battery, and enable the battery to accept more power in the next charging process. In addition, it can prolong the service life of the battery, reduce the charging time, improve the utilization rate of active materials, and form a better SEI film.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Fig. 1 is the concrete process parameter of pulse charging in the embodiment 1 of the present invention;

Fig. 2 is the concrete process parameter of pulse discharge in the embodiment of the present invention 1;

Fig. 3 is the voltage change curve in the pulse discharge process of embodiment 1 of the present invention;

Fig. 4 is the voltage change curve in the pulse charging process of embodiment 1 of the present invention;

Fig. 5 is the specific process parameter of constant current charging and discharging of comparative example 1 of the present invention;

Fig. 6 is the voltage change curve in the constant current discharge process of comparative example 1 of the present invention;

FIG. 7 is a voltage variation curve during constant current charging in Comparative Example 1 of the present invention.

Detailed ways

The invention provides a method for improving the first charge-discharge specific capacity and the first effect of a lithium-ion battery, comprising the following steps:

A) Let the negative electrode material stand still for 20-40 minutes, discharge it to the voltage platform of b ₁ at the current density of a ₁ , cycle this process several times, and stop the cycle at this stage;

B) Carry out the process of step A) with current densities a ₂ , a ₃ ... a _i in turn until the discharge capacity of a certain step or stage is ≤0.1mAh, and the discharge is stopped;

C) Leave the discharged negative electrode material to stand for 20-40 minutes, charge it to the B ₁ platform at a current density of A ₁ , cycle this process several times, and stop the cycle at this stage;

D) Carry out _the process of step C) with current densities A ₂ , A ₃ .

Wherein, 0.05C≤a _i ≤1C; 0.001V≤b ₁ ≤0.01V; 0.05C≤A _j ≤1C; 1.5V≤B ₁ ≤2V; i≥3; j≥3.

The lithium-ion battery in the present invention charges and discharges the negative electrode material in a pulsed manner, and starts with high current density charging and discharging, and ends with low current density discharging, which helps to further develop its charge and discharge capacity, At the same time, repeating the process of single-stage constant current charge and discharge multiple times can reduce its voltage drop and achieve further charge and discharge depth. The macroscopic performance of charge and discharge capacity is improved. In addition, its repeated process can form a better SEI film.

In the present invention, the negative electrode material is discharged to the voltage plateau of b ₁ at the current density a ₁ , and left standing for 20-40 min, preferably 30 min; repeat 1-2 times; 0.8C≤a ₁ ≤1C; preferably 1C;

Discharge at current density a ₂ to b ₁ voltage plateau, let stand for 20-40 minutes, preferably 30 minutes; repeat 3-5 times; 0.5C≤a ₂ ≤0.7C; preferably 0.5C;

Discharge at a current density of a ₃ to a voltage plateau of b ₁ , let stand for 20-40 minutes, preferably 30 minutes; repeat 6-12 times; 0.1C≤a ₃ ≤0.4C; preferably 0.1C;

Discharge at a current density of a ₄ to a voltage plateau of b ₁ , let it stand for 20-40 minutes, preferably 30 minutes; repeat until a certain step or a certain stage discharge specific capacity ≤0.1mAh; 0.05C≤a ₄ ≤0.08C; preferably 0.05 c.

Among them, the negative electrode material is preferably silicon carbon negative electrode material; 0.001V≤b ₁ ≤0.01V, preferably 0.005V≤b ₁ ≤0.006V.

The present invention has two criteria for judging the stop of the discharge process. One is to stop the discharge step and carry out the subsequent charging step when the specific capacity of the constant current a _i discharge is less than or equal to 0.1mAh/g; _ai After the end of the discharge, after standing for about 30 minutes, it is found that the difference between the voltage and the voltage after the end of the discharge at this stage is below 0.01V, and the discharge can be stopped.

The above two standards take the first specific capacity as the main judgment basis, and the second standard should be referred to in order to save the corresponding discharge time.

After the discharge is completed, the present invention continues to charge the negative electrode material according to the following steps:

Charge the negative electrode material to the voltage plateau of B ₁ at the current density A ₁ , and let it stand for 20-40 minutes, preferably 30 minutes; repeat 1-2 times; 0.8C≤A ₁ ≤1C; preferably 1C;

Charge at current density A ₂ to B ₁ voltage platform, let stand for 20-40 minutes, preferably 30 minutes; repeat 3-5 times; 0.5C≤A ₂ ≤0.7C; preferably 0.5C;

Charge at current density A ₃ to B ₁ voltage platform, let stand for 20-40 minutes, preferably 30 minutes; repeat 6-12 times; 0.1C≤A ₃ ≤0.4C; preferably 0.1C;

Charge at current density _A4 to _B1 voltage platform, let stand for 20-40min, preferably 30min; repeat until a certain step or stage discharge capacity≤0.1mAh/g; _{0.05C≤A4≤0.08C} , preferably 0.05C.

Among them, 1.5V≤B ₁ ≤2V; preferably 1.8V≤B ₁ ≤2V

The present invention has two criteria for judging the stop of the charging process. One is to stop the charging step when the specific capacity of charging with a constant current a _i is less than or equal to 0.1mAh/g; the second criterion is that after charging with a constant current a _i , After standing for about 30 minutes, it is found that the difference between the voltage and the voltage after charging at this stage is below 0.01V, and the charging can be stopped.

The above two standards take the first specific capacity as the main judgment basis, and the second standard should be referred to in order to save the corresponding charging time.

The invention provides a method for improving the first charge-discharge specific capacity and the first effect of a lithium-ion battery, comprising the following steps: A) placing the negative electrode material for 20-40 minutes, discharging it to a voltage platform of _b1 at _a current density, and cycling This process is repeated many times, and the cycle of this stage is stopped; B) The process of step A) is carried out with the current density a ₂ , a ₃ ... a _i in turn, until the discharge capacity of a certain step or a certain stage is ≤0.1mAh, and the discharge is stopped; C) Let the discharged negative electrode material stand still for 20-40 minutes, charge it to the B ₁ platform at the current density A ₁ , repeat this process for several times, and stop the cycle at this stage; D) Use the current density A ₂ , A ₃ ... A in sequence _j Carry out the process of step C) respectively until a certain step or a certain stage charging capacity ≤0.1mAh, stop charging; among them, 0.05C≤a _i ≤1C; 0.001V≤b ₁ ≤0.01V; 0.05C≤A _j ≤1C; 1.5V≤B ₁ ≤2V; i≥3; j≥3.

When a lithium-ion battery is discharged at a certain constant current density, it will be found that the voltage is higher than the preset voltage value after standing for a certain period of time. The value should be low, indicating that the polarization phenomenon inside the battery is more serious (the electrode potential deviates from the equilibrium electrode potential due to the polarization effect during the charging and discharging process of the battery, and after shelving, the polarization effect is gradually eliminated, so the electrode potential changes , resulting in a change in battery voltage).

Compared with the one-time charge and discharge process, the pulsed charge and discharge process adopted by the present invention can weaken the polarization inside the battery, so that the lithium ions can be inserted and extracted more thoroughly during the charge and discharge process of the battery. It can eliminate the ohmic polarization inside the lithium-ion battery, reduce the internal resistance, effectively slow down the voltage rise in the battery, and enable the battery to accept more power in the next charging process. In addition, it can prolong the service life of the battery, reduce the charging time, improve the utilization rate of active materials, and form a better SEI film.

In order to further illustrate the present invention, a method for improving the first-time charge-discharge specific capacity and first-efficiency of lithium-ion batteries provided by the present invention will be described in detail below in conjunction with examples, but it should not be understood as limiting the protection scope of the present invention.

Example 1

Taking the button lithium-ion battery as an example, the negative electrode material is silicon carbon negative electrode material; the conductive agent is conductive graphite

The specific discharge process is shown in Figure 1. Figure 1 shows the specific discharge process in Embodiment 1 of the present invention. Since the process is relatively long, the discharge start part and the discharge end part are intercepted, and the processing in the middle is omitted. In Figure 1,

The first to second cycle is charged to 0.005V at a current density of 1C, the third to fifth cycle is discharged to 0.005V at a current density of 0.5C, the sixth to 12th cycle is discharged to 0.005V at a current density of 0.1C, and the remaining cycle is 0.05 C current density discharge to 0.005V; until a certain step or a certain stage discharge specific capacity ≤ 0.1mAh/g;

The specific charging process is as shown in Figure 2, and Figure 2 is the specific process of charging in Embodiment 1 of the present invention, in Figure 2,

Charge to 2V at a current density of 1C in the 1st to 2nd cycle, charge to 2V at a current density of 0.5C in the 3rd to 5th cycle, charge to 2V at a current density of 0.1C in the 6th to 12th cycle, and charge to a current density of 0.05C in the remaining cycles Charge to 2V; until a certain step or a certain stage charging specific capacity ≤0.1mAh/g;

It can be seen from Fig. 1 and Fig. 2 that in this embodiment, the first charge specific capacity is 444.3mAh/g, the first discharge specific capacity is 525.6mAh/g, and the first coulombic efficiency is 84.5%.

Embodiment 2-4

According to the method in Example 1, the button lithium ion battery was charged and discharged for the first cycle. The difference is that the conductive agent in Examples 2-4 is a mixture of conductive graphite and conductive carbon black at a mass ratio of 1:1, graphene, and conductive carbon black.

Comparative example 1-4

The button-type lithium-ion batteries in Examples 1 to 4 were respectively used, discharged to 0.005V at a current density of 0.15C, and charged to 2V at a current density of 0.15C after standing for 2 minutes to complete the first round of charging and discharging.

The coulombic efficiency and discharge capacity for the first time of Examples 1 to 4 and Comparative Examples 1 to 4 are as shown in Table 1,

Table 1 Coulombic efficiency for the first time and discharge capacity for the first time of Examples 1 to 4 of the present invention and Comparative Examples 1 to 4

The charging and discharging voltage curves of embodiment 1 and comparative example 1 are shown in Figures 3 to 7, as can be seen from Figures 3 to 7, Figure 3 is the real-time voltage curve in the pulse discharge process, because the pulse discharge process is when When the battery voltage is placed at a specified voltage at a certain current density, due to a certain polarization phenomenon inside the battery, (due to the polarization effect of the battery during charging and discharging, the electrode potential deviates from the equilibrium electrode potential, and after shelving, the polarization The effect is gradually eliminated, so the electrode potential changes, resulting in a change in battery voltage.)

Therefore, after standing for a period of time, the voltage will rise. For this reason, we use multi-process discharge until the internal polarization of the battery is weak, so the real-time voltage curve will rise and fall repeatedly. On the contrary, during the charging process, the static After a period of time, the battery voltage will drop.

The above is only a preferred embodiment of the present invention, and it should be pointed out that for those of ordinary skill in the art, some improvements and modifications can also be made without departing from the principles of the present invention. It should be regarded as the protection scope of the present invention.

Claims (7)

1. A method for improving the charge-discharge specific capacity and first effect of lithium-ion battery for the first time, comprising the following steps: A) Discharge the negative electrode material at a current density of a ₁ to a voltage platform of b ₁ , let it stand for 20-40 minutes, cycle this process several times, and stop the cycle at this stage; B) Carry out the process of step A) with current densities a ₂ , a ₃ ... a _i respectively, until a certain step or a certain stage discharge specific capacity ≤ 0.1mAh/g, stop discharging; C) Charge the discharged negative electrode material to the _B1 platform with a current density of _A1 , let it stand for 20-40min, cycle this process several times, and stop the cycle at this stage; D) Carry out the process of step _C ) with current densities A ₂ , A ₃ . Among them, 0.05C≤a _i ≤1C; 0.001V≤b ₁ ≤0.01V; 0.05C≤A _j ≤1C; 1.5V≤B ₁ ≤2V; i≥3; j≥3; among them, C is the negative electrode material theoretical specific capacity. 2. The method according to claim 1, characterized in that, in each independent stage, each stage charges or discharges the battery to a predetermined voltage value in a constant current manner and then ends. 3 . The method according to claim 1 , wherein a ₁ ≥ _{a 2} ≥ a ₃ , . . . ≥ a _i . 4. The method according to claim 1, wherein A ₁ ≥ _{A 2} ≥ A ₃ , ... ≥ A _j . 5. The method of claim 1, wherein _{0.005V≤b1≤0.006V} . 6. The method according to claim 1, characterized in that the negative electrode material is discharged to a voltage plateau of _b1 at a current density of _a1 , left standing for 20-40min, and repeated 2-5 times; Discharge at current density a ₂ to b ₂ voltage platform, let stand for 20-40min, repeat 2-5 times; Discharge at current density a ₃ to b ₃ voltage platform, let stand for 20-40min, repeat 2-5 times; Discharge at a current density of a ₄ to a voltage platform of b ₄ , stand still for 20-40 minutes, repeat until a certain step or a certain stage discharge specific capacity ≤ 0.1mAh/g; 0.8C≤a ₁ ≤1C; 0.5C≤a ₂ ≤0.7C; 0.1C≤a ₃ ≤0.4C; 0.05C≤a ₄ ≤0.08C; wherein, C is the theoretical specific capacity of the negative electrode material. 7. The method according to claim 1, characterized in that, the negative electrode material is charged to a voltage plateau of _B1 at a current density of _A1 , left standing for 20-40min, and repeated 2-5 times; Charge at current density A ₂ to B ₂ voltage platform, let stand for 20-40min, repeat 2-5 times; Charge at current density _A3 to _B3 voltage platform, let stand for 20-40min, repeat 2-10 times; Charge at current density A ₄ to voltage platform B ₄ , let stand for 20-40 minutes, repeat until a certain step or a certain stage discharge specific capacity ≤ 0.1mAh/g; 0.8C≤A ₁ ≤1C; 0.5C≤A ₂ ≤0.7C; 0.1C≤A ₃ ≤0.4C; 0.05C≤A ₄ ≤0.08C; wherein, C is the theoretical specific capacity of the negative electrode material.