First, create a sequence for your corresponding model.

eg:

1.

<record id="seq_id_id" model="ir.sequence">
    <field name="name">name</field>
    <field name="code">model.name</field>
    <field name="prefix">- %(y)  </field>
    <field name="padding">3</field>
</record>

2.

override Create function:

from datetime import datetime, date

@api.model
def create(self, vals):
    res = super(batch_payment, self).create(vals)
    next_year = date.today().year - 1
    res.name = str(next_year) + self.env['ir.sequence'].next_by_code('model.name') 
    # or use str(next_year)[2:] for geting last two digits. eg 2018 -> 18, use it for the sequence.
    # do the changes needed. this is the logic
    return res